9.Expansion and shrinkage of the sulfur composite electrode in rechargeable lithium batteries

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ASME+SEC+II+C+SFA-5.28-2004

SPECIFICATION FOR LOW-ALLOY STEEL ELECTRODES AND RODS FOR GAS SHIELDED ARCWELDINGSFA-5.28(Identical with AWS Speciﬁcation A5.28-96.)1.ScopeThis speciﬁcation prescribes requirements for the clas-siﬁcation of low alloy steel electrodes(solid,composite stranded,and composite metal cored)and rods(solid)for gas metal arc welding(GMAW),gas tungsten arc welding (GTAW),and plasma arc welding(PAW).PART A—GENERAL REQUIREMENTS2.Classiﬁcation2.1The solid electrodes(and rods)covered by this speciﬁcation are classiﬁed according to the chemical com-position of the electrode,as speciﬁed in Table1,and the mechanical properties of the weld metal,as speciﬁed in Tables3and4.The composite metal cored and stranded electrodes covered by this speciﬁcation are classiﬁed according to the chemical composition and mechanical properties of the weld metal,as speciﬁed in Tables2,3, and4,and the shielding gas employed.2.2Electrodes and rods under one classiﬁcation shallnot be classiﬁed under any other classiﬁcation in this speciﬁcation,except that ER80S-D2may also be classi-ﬁed as ER90S-D2,provided that classiﬁcation require-ments for both are met.2.3The welding electrodes and rods classiﬁed under this speciﬁcation are intended for gas shielded arc weld-ing,but that is not to prohibit their use with any other process(or any other shielding gas or combination of shielding gases)for which they are found suitable.6113.AcceptanceAcceptance1of the electrodes and rods shall be in accordance with the provisions of ANSI/AWS A5.01, Filler Metal Procurement Guidelines.24.CertiﬁcationBy afﬁxing the AWS speciﬁcation and classiﬁcation designations to the packaging or the classiﬁcation to the product,the manufacturer certiﬁes that the product meets the requirements of this speciﬁcation.35.Units of Measure and Rounding-OffProcedure5.1U.S.customary units are the standard units of measure in this speciﬁcation.The SI units are given as equivalent values to the U.S.customary units.The stan-dard sizes and dimensions in the two systems are not identical and,for this reason,conversion from a standard size or dimension in one system will not always coincide with a standard size or dimension in the other.Suitable conversions,encompassing standard sizes of both,can be made,however,if appropriate tolerances are applied in each case.5.2For the purpose of determining conformance with this speciﬁcation,an observed or calculated value shall 1See Section A3,Acceptance(in the Annex),for further information concerning acceptance,testing of the material shipped,and ANSI⁄AWS A5.01,Filler Metal Procurement Guidelines.2AWS Standards can be obtained from the American Welding Society, 550N.W.LeJeune Road,Miami,FL33126.3See Section A4,Certiﬁcation,(in the Annex)for further information concerning certiﬁcation and the testing called for to meet this requirement.Copyright ASME InternationalProvided by IHS under license with ASME Licensee=Westinghouse Newington, NH/5945819003Not for Resale, 07/08/2005 01:57:36 MDTNo reproduction or networking permitted without license from IHSSFA-5.282004SECTION IIT A B L E 1C H E M I C A L C O M P O S I T I O N R E Q U I R E M E N T S F O R S O L I D E L E C T R O D E S A N D R O D SW e i g h t P e r c e n t a ,bO t h e r A W S U N S E l e m e n t s C l a s s i ﬁc a t i o n cN u m b e r dCM n S i P S N i C r M o V T i Z r A l C u eT o t a lC a r b o n -M o l y b d e n u m S t e e l E l e c t r o d e s a n d R o d sE R 70S -A 1K 112350.121.300.30–0.700.0250.0250.20—0.40–0.65————0.350.50C h r o m i u m -M o l y b d e n u m S t e e l E l e c t r o d e s a n d R o d sE R 80S -B 2K 209000.07–0.120.40–0.700.40–0.700.0250.0250.201.20–1.500.40–0.65————0.350.50E R 70S -B 2L K 205000.050.40–0.700.40–0.700.0250.0250.201.20–1.500.40–0.65————0.350.50E R 90S -B 3K 309600.07–0.120.40–0.700.40–0.700.0250.0250.202.30–2.700.90–1.20————0.350.50E R 80S -B 3L K 305600.050.40–0.700.40–0.700.0250.0250.202.30–2.700.90–1.20————0.350.50E R 80S -B 6fS 502800.100.40–0.700.500.0250.0250.64.50–6.000.45–0.65————0.350.50E R 80S -B 8gS 504800.100.40–0.700.500.0250.0250.58.00–10.50.8–1.2————0.350.50E R 90S -B 9h ,i S 504820.07–0.131.250.15–0.300.0100.0101.008.00–9.500.80–1.100.15–0.25——0.040.200.50N i c k e l S t e e l E l e c t r o d e s a n d R o d sE R 80S -N i 1K 112600.121.250.40–0.800.0250.0250.80–1.100.150.350.05———0.350.50E R 80S -N i 2K 212400.121.250.40–0.800.0250.0252.00–2.75——————0.350.50E R 80S -N i 3K 312400.121.250.40–0.800.0250.0253.00–3.75——————0.350.50M a n g a n e s e -M o l y b d e n u m S t e e l E l e c t r o d e s a n d R o d sE R 80S -D 2jK 109450.07–0.121.60–2.100.50–0.800.0250.0250.15—0.40–0.60————0.500.50E R 90S -D 2O t h e r L o w -A l l o y S t e e l E l e c t r o d e s a n d R o d sE R 100S -1K 108820.081.25–1.800.20–0.550.0100.0101.40–2.100.300.25–0.550.050.100.100.100.250.50E R 110S -1K 210150.091.40–1.800.20–0.550.0100.0101.90–2.600.500.25–0.550.040.100.100.100.250.50E R 120S -1K 210300.101.40–1.800.25–0.600.0100.0102.00–2.800.600.30–0.650.030.100.100.100.250.50E R X X S -G —N o t S p e c i ﬁe d kN O T E S :a .T h e ﬁl l e r m e t a l s h a l l b e a n a l y z e d f o r t h e e l e m e n t s f o r w h i c h v a l u e s a r e s h o w n i n t h i s t a b l e .I f t h e p r e s e n c e o f o t h e r e l e m e n t s i s i n d i c a t e d i n t h e c o u r s e o f t h i s w o r k ,t h e a m o u n t o f t h o s e e l e m e n t s s h a l l b e d e t e r m i n e d t o e n s u r e t h a t t h e i r t o t a l (e x c l u d i n g i r o n )d o e s n o t e x c e e d t h e l i m i t s s p e c i ﬁe d f o r “O t h e r E l e m e n t s ,T o t a l .”b .S i n g l e v a l u e s a r e m a x i m u m .c .T h e s u f ﬁx e s B 2,N i 1,e t c .,d e s i g n a t e t h e c h e m i c a l c o m p o s i t i o n o f t h e e l e c t r o d e a n d r o d c l a s s i ﬁc a t i o n .d .S A E /A S T M U n i ﬁe d N u m b e r i n g S y s t e m f o r M e t a l s a n d A l l o y s .e .C o p p e r d u e t o a n y c o a t i n g o n t h e e l e c t r o d e o r r o d p l u s t h e c o p p e r c o n t e n t o f t h e ﬁl l e r m e t a l i t s e l f ,s h a l l n o t e x c e e d t h e s t a t e d l i m i t .f .S i m i l a r t o f o r m e r c l a s s E R 502i n A W S S p e c i ﬁc a t i o n A 5.9-81.g .S i m i l a r t o f o r m e r c l a s s E R 505i n A W S S p e c i ﬁc a t i o n A 5.9-81.h .N i o b i u m (C o l u m b i u m )0.02–0.10%i .N i t r o g e n 0.03–0.07%j .T h i s c o m p o s i t i o n w a s f o r m e r l y c l a s s i ﬁe d E 70S -1B i n A W S S p e c i ﬁc a t i o n A 5.18-69.k .I n o r d e r t o m e e t t h e r e q u i r e m e n t s o f t h e “G ”c l a s s i ﬁc a t i o n ,t h e e l e c t r o d e m u s t h a v e a m i n i m u m o f o n e o r m o r e o f t h e f o l l o w i n g :0.50p e r c e n t n i c k e l ,0.30p e r c e n t c h r o m i u m ,o r 0.20p e r c e n t m o l y b d e n u m .C o m p o s i t i o n s h a l l b e r e p o r t e d ;t h e r e q u i r e m e n t s a r e t h o s e a g r e e d t o b y t h e p u r c h a s e r a n d s u p p l i e r .612Copyright ASME InternationalProvided by IHS under license with ASMELicensee=Westinghouse Newington, NH/5945819003 Not for Resale, 07/08/2005 01:57:36 MDTNo reproduction or networking permitted without license from IHS--````,,`,`,,,````,``,,,`,``,-`-`,,`,,`,`,,`---PART C —SPECIFICATIONS FOR WELDING RODS,ELECTRODES,AND FILLER METALSSFA-5.28T A B L E 2C H E M I C A L C O M P O S I T I O N R E Q U I R E M E N T S F O R W E L D M E T A L F R O M C O M P O S I T E E L E C T R O D E S aW e i g h t P e r c e n t b ,cO t h e r A W S U N S E l e m e n t s C l a s s i ﬁc a t i o n dN u m b e r eCM n S i P S N i C r M o V T iZ r A l C uT o t a lM a n g a n e s e -M o l y b d e n u m W e l d M e t a lE 90C -D 2W 192300.121.00–1.900.900.0250.030——0.40–0.60————0.350.50C h r o m i u m -M o l y b d e n u m W e l d M e t a lE 70C -B 2L W 521300.050.40–1.000.25–0.600.0250.0300.201.00–1.500.40–0.65————0.350.50E 80C -B 2W 520300.05–0.120.40–1.000.25–0.600.0250.0300.201.00–1.500.40–0.65————0.350.50E 80C -B 3L W 531300.050.40–1.000.25–0.600.0250.0300.202.00–2.500.90–1.20————0.350.50E 90C -B 3W 530300.05–0.120.40–1.000.25–0.600.0250.0300.202.00–2.500.90–1.20————0.350.50N i c k e l S t e e l W e l d M e t a lE 80C -N i 1W 210300.121.500.900.0250.0300.80–1.10—0.30————0.350.50E 70C -N i 2W 220300.081.250.900.0250.0301.75–2.75——————0.350.50E 80C -N i 2W 220300.121.500.900.0250.0301.75–2.75——————0.350.50E 80C -N i 3W 230300.121.500.900.0250.0302.75–3.75——————0.350.50O t h e r L o w -A l l o y W e l d M e t a lE X X C -GN o t S p e c i ﬁe d fN O T E S :a .C h e m i c a l r e q u i r e m e n t s f o r c o m p o s i t e e l e c t r o d e s a r e b a s e d o n a n a l y s i s o f t h e i r w e l d m e t a l i n t h e a s -w e l d e d c o n d i t i o n a n d u s i n g t h e s h i e l d i n g g a s s p e c i ﬁe d i n T a b l e 3.b .T h e w e l d m e t a l s h a l l b e a n a l y z e d f o r t h e s p e c i ﬁc e l e m e n t s f o r w h i c h v a l u e s a r e s h o w n i n t h i s t a b l e .I f t h e p r e s e n c e o f o t h e r e l e m e n t s i s i n d i c a t e d i n t h e c o u r s e o f t h i s w o r k ,t h e a m o u n t o f t h e s e e l e m e n t s s h a l l b e d e t e r m i n e d t o e n s u r e t h a t t h e i r t o t a l (e x c l u d i n g i r o n )d o e s n o t e x c e e d t h e l i m i t s p e c i ﬁe d f o r “O t h e r E l e m e n t s ,T o t a l .”c .S i n g l e v a l u e s s h o w n a r e m a x i m u m s .d .S o l i d e l e c t r o d e s a r e g e n e r a l l y r e c o m m e n d e d f o r g a s t u n g s t e n a r c w e l d i n g (G T A W )o r p l a s m a a r c w e l d i n g (P A W ).e .S A E /A S T M U n i ﬁe d N u m b e r i n g S y s t e m f o r M e t a l s a n d A l l o y s .f .I n o r d e r t o m e e t t h e r e q u i r e m e n t s o f t h e G c l a s s i ﬁc a t i o n ,t h e e l e c t r o d e m u s t h a v e a s a m i n i m u m o f o n e o r m o r e o f t h e f o l l o w i n g :0.50p e r c e n t n i c k e l ,0.30p e r c e n t c h r o m i u m ,o r 0.20p e r c e n t m o l y b d e n u m .C o m p o s i t i o n s h a l l b e r e p o r t e d ;t h e r e q u i r e m e n t s a r e t h o s e a g r e e d t o b y t h e p u r c h a s e r a n d s u p p l i e r .613Copyright ASME InternationalProvided by IHS under license with ASMELicensee=Westinghouse Newington, NH/5945819003 Not for Resale, 07/08/2005 01:57:36 MDTNo reproduction or networking permitted without license from IHS--````,,`,`,,,````,``,,,`,``,-`-`,,`,,`,`,,`---SFA-5.282004SECTION IITABLE3TENSION TEST REQUIREMENTSNOTES:a.The use of a particular shielding gas for classiﬁcation purposes shall not be construed to restrict the use of shielding gas mixtures.Aﬁllermetal tested with other gas blends,such as Argon/O2or Argon/CO2may result in weld metal having different strength and elongation.Classiﬁcation with other gas blends shall be as agreed upon between the purchaser and supplier.b.Yield strength at0.2%offset and elongation in2in.(51mm)gage length.c.Postweld heat-treated condition in accordance with Table7.d.Shielding gas shall be as agreed to between purchaser and supplier.e.Not speciﬁed(As agreed to between purchaser and supplier).f.These classiﬁcations were previously ER80S-B2,E80C-B2,ER90S-B3L,and E90C-B3L respectively in AWS A5.28–79.The strength levelshave been adjusted downward as shown,in order to accurately reﬂect the capability of the classiﬁcation’s chemical composition ranges.614Copyright ASME InternationalProvided by IHS under license with ASME Licensee=Westinghouse Newington, NH/5945819003No reproduction or networking permitted without license from IHSNot for Resale, 07/08/2005 01:57:36 MDTPART C—SPECIFICATIONS FOR WELDING RODS,ELECTRODES,AND FILLER METALS SFA-5.28TABLE4IMPACT TEST REQUIREMENTSAWS Average Impact Strength a TestingClassiﬁcation(minimum)ConditionER70S-A1ER70S-B2LE70C-B2LER80S-B2E80C-B2ER80S-B3LNot Required—E80C-B3LER90S-B3E90C-B3ER80S-B6ER80S-B8ER90S-B9ER80S-Ni120ft·lbf at−50°F(27J@−46°C)As-WeldedE80C-Ni1ER80S-Ni2E70C-Ni220ft·lbf at−80°F(27J@−62°C)PWHT bE80C-Ni2ER80S-Ni320ft·lbf at−100°F(27J@−73°C)PWHT bE80C-Ni3ER80S-D2ER90S-D220ft·lbf at−20°F(27J@−29°C)As-WeldedE90C-D2ER100S-1ER110S-150ft·lbf at−60°F(68J@−51°C)As-WeldedER120S-1ERXXXS-G As agreed between—EXXC-G purchaser and supplierNOTES:a.Both the highest and lowest of theﬁve test values obtained shallbe disregarded in computing the impact strength.For classiﬁcations requiring20ft-lbf(27J);Two of the remaining three values shall equal or exceed20ft-lbf(27J);one of the three remaining values may be lower than20ft-lbf(27J)but not lower than15ft-lbf(20J).The average of the three shall not be less thanthe20ft-lbf(27J)speciﬁed.For classiﬁcations requiring50ft-lbf(68J):Two of the remaining three values shall equal or exceed50ft-lbf(68J);one of the three remaining values may be lower than50ft-lbf(68J)but not lower than40ft-lbf(54J).The average of the three shall not be less thanthe50ft-lbf(68J)speciﬁed.b.Postweld heat treated in accordance with Table7.be rounded to the nearest1000psi for tensile and yield strength,and to the“nearest unit”in the last right-hand place ofﬁgures used in expressing the limiting valuefor other quantities in accordance with the rounding-off method given in ASTM E29,Recommended Practice615for Using Signiﬁcant Digits in Test Data to Determine Conformance with Speciﬁcations.4PART B—TESTS,PROCEDURES,AND REQUIREMENTS6.Summary of Tests6.1The tests required for each classiﬁcation are speci-ﬁed in Table5.The purpose of these tests is to determine the chemical composition,the mechanical properties,and soundness of the weld metal.The base metal for the weld test assemblies,the welding and testing procedures to be employed,and the results required are given in Sections 8through12.6.2The optional test for diffusible hydrogen in Sec-tion13,Diffusible Hydrogen Test,is not required for classiﬁcation[see note(a)of Table5].7.RetestIf the results of any test fail to meet the requirement, that test shall be repeated twice.The results of both retests shall meet the requirement.Specimens for retest may be taken from the original test assembly or from one or two new test assemblies.For chemical analysis,retest need be only for those speciﬁc elements that failed to meet the test requirement.If the results of one or both retests fail to meet the requirement,the material under test shall be considered as not meeting the requirements of this speciﬁcation for that classiﬁcation.In the event that,during preparation or after completion of any test,it is clearly determined that prescribed or proper procedures were not followed in preparing the weld test assembly or test specimen(s),or in conducting the test,the test shall be considered invalid,without regard to whether the test was actually completed,or whether test results met,or failed to meet,the requirement,that test shall be repeated,following proper prescribed proce-dures.In this case,the requirement for doubling the num-ber of test specimens does not apply.8.Weld Test Assemblies8.1At least one weld test assembly is required,and two may be required(depending on the electrode—solid as opposed to composite—and the manner in which the sample for chemical analysis is taken),as speciﬁed in Table5.They are as follows:4ASTM speciﬁcations may be obtained from the American Society for Testing and Materials(ASTM),100Barr Harbor Drive,Consho-hocken,PA19428-2959.Copyright ASME InternationalProvided by IHS under license with ASME Licensee=Westinghouse Newington, NH/5945819003Not for Resale, 07/08/2005 01:57:36 MDTNo reproduction or networking permitted without license from IHS--````,,`,`,,,````,``,,,`,``,-`-`,,`,,`,`,,`---SFA-5.282004SECTION IITABLE5REQUIRED TESTSChemical AnalysisAWS Diffusible Classiﬁcation Electrode Weld Metal Radiographic Test Tension Test Impact Test Hydrogen TestSolid ElectrodesER70S-A1ER70S-B2LER80S-B2ER80S-B3LRequired Not Required Required Required Not Required aER90S-B3ER80S-B6ER80S-B8ER90S-B9ER80S-Ni1ER80S-Ni2Required Not Required Required Required Required aER80S-Ni3ER80S-D2Required Not Required Required Required Required aER90S-D2ER100S-1ER110S-1Required Not Required Required Required Required aER120S-1ERXXS-G Required b Not Required Required Required Not Required aComposite Metal Cored ElectrodesE70C-B2LE80C-B2Not Required Required Required Required Not Required aE80C-B3LE90C-B3E70C-Ni2E80C-Ni1Not Required Required Required Required Required aE80C-Ni2E80C-Ni3E90C-D2Not Required Required Required Required Required a EXXC-G Not Required Required b Required Required Not Required a NOTES:a.Optional diffusible hydrogen test is required only when speciﬁed by the puchaser and the manufacturer puts the diffusible hydrogen designatoron the label(See A2.2and A8.2in the Annex).b.To be reported.See A7.15in the Annex.(1)The groove weld in Fig.1for mechanical proper-ties and soundness of the weld metal for both composite and solid electrodes(2)The weld pad in Fig.2for chemical analysis ofthe weld metal from composite stranded and composite metal cored electrodesThe sample for chemical analysis of weld metal from composite electrodes may be taken from the reduced section of the fractured all-weld-metal tension test speci-men or from the corresponding location in the groove616weld in Fig.1,thereby avoiding the need to make a weld pad.Alternatively,the sample from the groove weld may be taken from any location in the weld metal above the tension test specimen.In case of dispute,the weld pad in Fig.2shall be the referee method.8.2Preparation of each weld test assembly shall be as prescribed in8.3,8.4,and8.5.The base metal for each assembly shall be as required in Table6,and shall meet the requirements of the ASTM speciﬁcation shownCopyright ASME InternationalProvided by IHS under license with ASME Licensee=Westinghouse Newington, NH/5945819003Not for Resale, 07/08/2005 01:57:36 MDTNo reproduction or networking permitted without license from IHS--````,,`,`,,,````,``,,,`,``,-`-`,,`,,`,`,,`---PART C—SPECIFICATIONS FOR WELDING RODS,ELECTRODES,AND FILLER METALS SFA-5.28FIG.1GROOVE WELD TEST ASSEMBLY FOR MECHANICAL PROPERTIES AND SOUNDNESS617Copyright ASME InternationalProvided by IHS under license with ASME Licensee=Westinghouse Newington, NH/5945819003No reproduction or networking permitted without license from IHSNot for Resale, 07/08/2005 01:57:36 MDTSFA-5.282004SECTIONIIFIG.2PAD FOR CHEMICAL ANALYSIS OF WELD METAL FROM COMPOSITE ELECTRODESthere,or an equivalent speciﬁcation.Testing of the assem-bly shall be as prescribed in 9.2,9.3,and Sections 10through 12.8.3Groove Weld8.3.1For all classiﬁcations,a test assembly shall be prepared and welded as speciﬁed in Fig.1,using base metal of the appropriate type speciﬁed in Table 6,and the preheat and interpass temperature speciﬁed in Table 7.The electrode used shall be 0.045in.(1.1mm)or 1⁄16in.(1.6mm)size (or the size that the manufacturer produces that is closest to one of these,if these sizes are not produced).Welding shall be in the ﬂat position,and the assembly shall be restrained (or preset)during welding to prevent warpage in excess of 5degrees.An assembly that has warped more than 5degrees from plane shall be dis-carded.It shall not be straightened.The test assembly shall be tack welded,and welding shall begin at the preheat temperature speciﬁed in Table 7.This interpass temperature shall be maintained for the remainder of the weld.Should it be necessary to interrupt welding,the assembly shall be allowed to cool in still air to room temperature.The assembly shall be preheated to the temperature shown in Table 7before welding is resumed.When welding has been completed and the assembly has cooled,the assembly shall be prepared and618tested as speciﬁed in Sections 10,11,and 12in the as-welded or postweld heat-treated condition,as speciﬁed in Tables 3and 4.8.3.2When required,the test assembly shall be postweld heat-treated before removal of mechanical test specimens.This postweld heat treatment may be done either before or after the radiographic examination.8.3.2.1The furnace shall be at a temperature not higher than 600°F (320°C)when the test assembly is placed in it.The heating rate,from that point to the speciﬁed holding temperature in Table 7,shall not exceed 400°F per hour (220°C per hour).8.3.2.2The test assembly shall be maintained at the temperature speciﬁed in Table 7for 1hour (−0,+15minutes).8.3.2.3When the one hour holding time has been completed,the assembly shall be allowed to cool in the furnace to a temperature below 600°F (320°C)at a rate not exceeding 350°F (190°C)per hour.The assembly may be removed from the furnace at any temperature below 600°F (320°C)and allowed to cool in still air to room temperature.Testing of the assembly shall be as speciﬁed in Sections 10through 12.8.4Weld Pad.A weld pad shall be prepared using composite stranded and composite metal cored electrodesCopyright ASME InternationalProvided by IHS under license with ASMELicensee=Westinghouse Newington, NH/5945819003 Not for Resale, 07/08/2005 01:57:36 MDTNo reproduction or networking permitted without license from IHS--````,,`,`,,,````,``,,,`,``,-`-`,,`,,`,`,,`---PART C—SPECIFICATIONS FOR WELDING RODS,ELECTRODES,AND FILLER METALS SFA-5.28TABLE6BASE METAL FOR TEST ASSEMBLIESAWS Classiﬁcation Base Metal ASTM Standard a Base Metal UNS Number bER70S-B2LE70C-B2LA387Grade11K11789ER80S-B2E80C-B2ER80S-B3LE80C-B3LA387Grade22K21590ER90S-B3E90C-B3ER80S-B6A387Grade5S50200ER80S-B8A387Grade9S50400ER90S-B9A387Grade91S50460A516Grade60,65,or70K02100,K02403,or K02700 ER80S-Ni1A537Class1or2K12437,K21703,or K22103A203Grade A or B,or HY-80steelJ42015E80C-Ni1in accordance with MIL-S-16216E70C-Ni2A203Grade A or B or HY-80steelER80S-Ni2K22103,K21703,or J42015in accordance with MIL-S-16216E80C-Ni2ER80S-Ni3A203Grade D or E or HY-80steel K31718or K32018E80C-Ni3in accordance with MIL-S-16216J42015ER70S-A1ASTM A36,A285Grade C,K02600,ER80S-D2A515Grade70,or K03101,E90C-D2A516Grade70K02700ER90S-D2ER100S-1ER100S-GE100C-GER110S-1HY-80or HY100steelER110S-G J42015or J42240in accordance with MIL-S-16216E110C-GER120S-1ER120S-GE120C-GERXXS-GSee note aEXXC-GNOTES:a.For any weld metal classiﬁcation in this speciﬁcation,ASTM A36,A285Grade C,A515Grade70,or A516Grade70may be used.Inthat case,the groove faces and the contacting face of the backing shall be buttered,as shown in Figure1,using the electrode being classiﬁedor an electrode of the same weld metal composition as that speciﬁed for the electrode being tested,or using an electrode of the speciﬁedcomposition classiﬁed in another AWS low-alloy steelﬁller metal speciﬁcation.Alternately,for the indicated weld metal classiﬁcation,thecorresponding base metals may be used for weld test assemblies without buttering.In case of dispute,buttered A36steel shall be the refereematerial.b.ASTM/SAE Uniﬁed Numbering System for Metals and Alloys.619--````,,`,`,,,````,``,,,`,``,-`-`,,`,,`,`,,`---Copyright ASME InternationalProvided by IHS under license with ASME Licensee=Westinghouse Newington, NH/5945819003No reproduction or networking permitted without license from IHSNot for Resale, 07/08/2005 01:57:36 MDTSFA-5.282004SECTION IITABLE7PREHEAT,INTERPASS,AND POSTWELD HEAT TREATMENT TEMPERATURESPreheat and InterpassTemperature a PWHT Temperature a AWS Classiﬁcation°F°C°F°CER70S-A1ER80S-B2ER70S-B2L275–325135–1651150±25620±15E80C-B2E70C-B2LER90S-B3ER80S-B3L375–425185–2151275±25690±15 E90C-B3E80C-B3LER80S-B6350–450177–2321375±25745±15ER80S-B8400–500205–2601375±25745±15ER90S-B9300–500150–2601375±25745±15ER80S-Ni2ER80S-Ni3E70C-Ni2275–325135–1651150±25620±15E80C-Ni2E80C-Ni3ER80S-D2ER90S-D2E90C-D2ER80S-Ni1275–325135–165None b None b E80C-Ni1ER100S-1ER110S-1ER120S-1ERXXXS-GConditions as agreed upon between supplier and purchaserEXXC-GNOTES:a.These temperatures are speciﬁed for testing under this speciﬁcation and are not to be considered as recommendations for preheat,interpass,and postweld heat treatment in production welding.The requirements for production welding must be determined by the user.They may ormay not differ from those called for here.b.These classiﬁcations are normally used in the as-welded condition.620Copyright ASME InternationalProvided by IHS under license with ASME Licensee=Westinghouse Newington, NH/5945819003No reproduction or networking permitted without license from IHSNot for Resale, 07/08/2005 01:57:36 MDTas shown in Fig.2,except when,as permitted in8.1,the sample for analysis is taken from the groove weld(Fig.1)or the fractured tension test specimen.Base metal of any convenient size which will satisfy the minimum requirements of Fig.2,and is of a type speciﬁed in Table 6,shall be used as the base for the weld pad.The surface of the base metal on which theﬁller metal is deposited shall be clean.The pad shall be welded in theﬂat position with multiple layers to obtain undiluted weld metal(4 layers minimum thickness).The electrode size shall be 0.045in.(1.1mm)or1⁄16in.(1.6mm),or the size that the manufacturer produces that is closest to one of these, if these sizes are not produced.The preheat temperature shall not be less than60°F(16°C)and the interpass tem-perature shall not exceed that speciﬁed in Table7.Any slag shall be removed after each pass.The pad may be quenched in water between passes(temperature of the water is not speciﬁed).The dimensions of the completed pad shall be as shown in Fig.2.Testing of this assembly shall be as speciﬁed in9.2and9.3.The results shall meet the requirements of9.4.9.Chemical Analysis9.1A sample of the solid electrode or rod shall be prepared for chemical analysis.Solidﬁller metal,when analyzed for elements that are present in a coating(copper ﬂashing,for example),shall be analyzed without remov-ing the coating.When theﬁller metal is analyzed for elements other than those in the coating,the coating shall be removed if its presence affects the results of the analy-sis for the other elements.9.2Composite stranded and metal cored electrodes shall be analyzed in the form of weld metal,notﬁller metal.The sample for analysis shall be taken from weld metal obtained with the electrode and a shielding gas as speciﬁed in Tables2and3.The sample may be taken from the weld pad prepared in accordance with8.4,from an area of the groove weld as speciﬁed in8.1,or from the reduced section of the fractured tension test specimen. In case of dispute,the weld pad is the referee method. The top surface of the pad described in8.4and shown in Fig.2shall be removed and discarded.A sample for analysis shall be obtained from the underlying metal,no closer than3⁄8in.(9.5mm)to the surface of the base metal in Fig.2,by any appropriate mechanical means. The sample shall be free of slag.When the sample is taken from the groove weld or the reduced section of the fractured tension test specimen, that material shall be prepared for analysis by any suitable mechanical means.9.3The sample obtained as speciﬁed in9.1or9.2 shall be analyzed by accepted analytical methods.The referee method shall be ASTM E350,Standard Method for Chemical Analysis of Carbon Steel,Low Alloy Steel, Silicon Electrical Steel,Ingot Iron and Wrought Iron.9.4The results of the analysis shall meet the require-ments of Table1for solid electrode or Table2for com-posite electrodes for the classiﬁcation of electrode under test.10.Radiographic Test10.1The groove weld described in8.3.1and shown in Fig.1shall be radiographed to evaluate the soundness of the weld metal.In preparation for radiography,the backing shall be removed,and both surfaces of the weld shall be machined or ground smooth.Both surfaces of the test assembly,in the area of the weld,shall be smooth enough to avoid difﬁculty in interpreting the radiograph.10.2The weld shall be radiographed in accordance with ASTM E142,Standard Method for Controlling Quality of Radiographic Testing.The quality level of inspection shall be2-2T.10.3The soundness of the weld metal meets the requirements of this speciﬁcation if the radiograph shows no cracks,no incomplete fusion,and no rounded indica-tions in excess of those permitted by the radiographic standards in Fig.3.In evaluating the radiograph,1in. (25mm)of the weld on each end of the test assembly shall be disregarded.10.3.1A rounded indication is an indication(on the radiograph)whose length is no more than3times its width.Rounded indications may be circular,elliptical, conical,or irregular in shape,and they may have tails. The size of a rounded indication is the largest dimension of the indication,including any tail that may be present. The indication may be of porosity or slag.Indications whose largest dimension does not exceed1⁄64in.(0.4 mm)shall be disregarded.Test assemblies with indica-tions larger than the largest indications permitted in the radiographic standards(Fig.3)do not meet the require-ments of this speciﬁcation.11.Tension Test11.1One all-weld-metal tension test specimen shall be machined from the groove weld described in8.3.1and shown in Fig.1as required in Table5.The dimensions of the specimen shall be as shown in Fig.4.11.2Before testing,the specimen may be aged at200 to220°F(93to104°C)for up to48hours,then allowed to cool to room temperature.Refer to A8.3for a discus-sion on the purpose of aging treatments.--````,,`,`,,,````,``,,,`,``,-`-`,,`,,`,`,,`---。

Nanostructured Electrode Materials for Lithium-Ion Batteries

Nanostructured Electrode Materials for Lithium -Ion BatteriesA.Manthiram and T.MuraliganthAbstract Electrochemical energy storage systems are becoming increasingly important with respect to their use in portable electronic devices,medical implant devices,hybrid electric and electric vehicles,and storage of solar and wind ener-gies.Lithium-ion batteries are appealing for these needs because of their high energy density,wide range of operating temperatures,and long shelf and cycle life. However,further breakthroughs in electrode materials or improvements in existing electrode materials are critical to realize the full potential of the lithium-ion tech-nology.Nanostructured materials present an attractive opportunity in this regard as they could offer several advantages such as fast reaction kinetics,high power density,good cycling stability with facile strain relaxation compared to their bulk counterparts.In this chapter,we present an overview of the latest progress on the nanostructured anode and cathode materials for lithium-ion batteries. IntroductionEnergy storage and production is one of the greatest challenges facing human kind in the twenty-ﬁrst century.Based on moderate economic and population growth, the global energy consumption is anticipated to triple by the year2010.The rapid depletion of fossil fuel reserves,increasing fuel costs,increasing greenhouse gas emission,and global climate changes are driving the development of sustainable clean energy technologies like fuel cells,solar cells,high energy density batteries, and supercapacitors.While fuel cells and solar cells are energy conversion devices, batteries and supercapacitors are energy storage devices.Nearly one-third of the total energy consumption in the United States is by the transportation sector,and internal combustion engine based automobiles are a sig-niﬁcant contributor of green house gas emission.Hybrid electric vehicles(HEV) and plug-in hybrid electric vehicles(PHEV)are the most viable near-term option A.Manthiram(B)Materials Science and Engineering Program,The University of Texas,Austin,TX78712,USAe-mail:rmanth@211 A.Korkin et al.(eds.),Nanotechnology for Electronics,Photonics,and RenewableEnergy,Nanostructure Science and Technology,DOI10.1007/978-1-4419-7454-9_8,C Springer Science+Business Media,LLC2010212 A.Manthiram and T.Muraliganth Fig.8.1Comparison of theenergy densities of differentbattery systemsfor transportation.Energy storage is also critical for the efﬁcient utilization of the electricity produced from solar and wind energies.Lithium-ion batteries are appeal-ing for automobiles(HEV and PHEV)and the storage of solar and wind energy as they provide higher energy density compared to other rechargeable battery systems such as lead acid,nickel–cadmium,and nickel metal hydride batteries as seen in Fig.8.1[1].However,cost and safety are the major issues with respect to large-scale applications like automobiles and solar and wind energy storage,and they need to be adequately addressed.Lithium-Ion BatteriesRechargeable lithium batteries involve a reversible insertion/extraction of lithium ions into/from a host electrode material during the charge/discharge process.The lithium insertion/extraction process occurring with aﬂow of ions through the elec-trolyte is accompanied by a reduction/oxidation(redox)reaction of the host matrix assisted with aﬂow of electrons through the external circuit(Fig.8.2).The open-circuit voltage V oc of such a lithium cell is given by the difference in the lithium chemical potential between the cathode(μLi(c))and the anode(μLi(a))asV oc=(μLi(c)−μLi(a))/F,(8.1) where F is the Faraday constant.A schematic energy diagram of a cell at open circuit is given in Fig.8.3.The cell voltage is determined by the energies involved in both the electron transfer and Li+transfer.While the energy involved in electron transfer is related to the work functions of the cathode and the anode,the energy involved in Li+transfer is determined by the crystal structure and the coordination geometry of the site into/from which the Li+ions are inserted/extracted[2].Thermodynamic stability considerations require the redox energies of the cathode(E c)and anode8Nanostructured Electrode Materials for Lithium-Ion Batteries213 Fig.8.2Illustration of thecharge–discharge processinvolved in a lithium-ion cellconsisting of graphite as ananode and layered LiCoO2asa cathodeFig.8.3Schematic energydiagram of a lithium cell atopen circuit.HOMO andLUMO refer,respectively,tothe highest occupiedmolecular orbital and lowestunoccupied molecular orbitalin the electrolyte(E a)to lie within the band gap E g of the electrolyte,as shown in Fig.8.3,so that no unwanted reduction or oxidation of the electrolyte occurs during the charge–discharge process.With this strategy,the anode and cathode insertion hosts should have,respectively,the lowest and highest voltages vs.metallic lithium in order to maximize the cell voltage.The concept of rechargeable lithium batteries wasﬁrst illustrated with a transition metal sulﬁde TiS2as the cathode,metallic lithium as the anode,and a nonaque-ous electrolyte[3].Following the initial demonstration,several other sulﬁdes and chalcogenides were pursued during the1970s and1980s as cathodes[4].However, most of them exhibit a low cell voltage of<2.5V vs.lithium anode.This limita-tion in cell voltage is due to an overlap of the higher valent M n+:d band with the top of the nonmetal:p band—for example,with the top of the S:3p band as shown in Fig.8.4.Such an overlap results in an introduction of holes into(or removal of electrons from)the S2−:3p band and the formation of molecular ions such as S2−2,214 A.Manthiram and T.Muraliganth Fig.8.4Relative energies ofmetal:d(for example,Co:3d)and nonmetal:p in(a)asulﬁde and(b)an oxidewhich in turn leads to an inaccessibility of higher oxidation states for M n+in a sul-ﬁde Li x M y S z.The stabilization of higher oxidation state is essential to maximize the cell voltage.Recognizing this difﬁculty with chalcogenides,Goodenough’s group at the University of Oxford focused on oxide cathodes during the1980s[5–7].The location of the top of the O2−:2p band much below the top of the S2−:3p band and a larger raising of the M n+:d energies in an oxide compared to that in a sulﬁde due to a larger Madelung energy(Fig.8.4)make the higher valent states accessible in oxides. For example,while Co3+can be readily stabilized in an oxide,it is difﬁcult to sta-bilize Co3+in a sulﬁde since the Co2+/3+redox couple lies within the S2−:3p band as seen in Fig.8.4.Accordingly,several transition metal oxide hosts crystallizing in a variety of structures(two-dimensional layered and three-dimensional framework structures)have been pursued during the past two decades.Among them LiCoO2, LiNiO2,and LiMn2O4oxides having a high electrode potential of4V vs.metallic lithium have become attractive cathodes for lithium-ion cells.On the other hand, graphite with a low electrode potential of<0.3V vs.metallic lithium has become an attractive anode.Although the initial efforts in rechargeable lithium batteries employed lithium metal as the anode,the strategy failed to attain commercial success due to safety limitations[8,9].The inherent instability of lithium metal and the dendrite for-mation during charge–discharge cycling eventually forced the use of intercalation compounds as anodes.This led to the commercialization of the lithium-ion battery technology by Sony in1990with LiCoO2as the cathode and graphite as the anode. However,the cost and safety issues and the performance limitations associated with the LiCoO2cathode and carbon anode have prompted the search for new electrode materials as well as improvements in existing electrode materials.Nanostructured materials have attracted a lot of interest in the past two decades because of their unusual electrical,mechanical,and optical properties compared to their bulk counterparts[10–15].Recently,nanostructured materials are also gaining increasing popularity for energy storage applications[16–21].This chapter focuses on providing an overview of some of the recent advances in nanostructured anode and cathode materials for lithium-ion batteries.8Nanostructured Electrode Materials for Lithium-Ion Batteries215 Nanostructured Electrode Materials for Lithium-Ion Batteries Nanomaterials offer advantages and disadvantages as electrode materials for lithium-ion batteries.Some of the advantages are given below:•The smaller particle size increases the rate of lithium insertion/extraction because of the short diffusion length for lithium-ion transport within the particle,resulting in enhanced rate capability.•The smaller particle size enhances the electron transport in the electrode, resulting in enhanced rate capability.•The high surface area leads to enhanced utilization of the active materials, resulting in higher capacity.•The smaller particle size aids a better accommodation of the strain during lithium insertion/extraction,resulting in improved cycle life.•The smaller particle size enables reactions that could not otherwise occur with micrometer-sized particles,resulting in new lithium insertion/extraction mechanisms and improved electrochemical properties and performances.Some of the disadvantages are given below:•Complexities involved in the synthesis methods employed could increase the processing cost,resulting in higher manufacturing cost.•The high surface area may lead to enhanced side reactions with the electrolyte, resulting in high irreversible capacity loss and capacity fade during cycling.•The smaller particle size and high surface-to-volume ratio could lead to low packing density,resulting in low volumetric energy density.Nanostructured CathodesNanostructured Layered Oxide CathodesOxides with the general formula LiMO2(M=V,Cr,Co,and Ni)crystallize in a layered structure in which Li+and M3+ions occupy the alternate(111)planes of the rock salt structure to give a layered sequence of-O-Li-O-M-O-along the c axis.The Li+and M3+ions occupy the octahedral interstitial sites of the cubic close-packed oxygen array as shown in Fig.8.5.The structure with strongly(cova-lently)bonded MO2layers allows a reversible extraction/insertion of lithium ions from/into the lithium planes.The lithium-ion movement between MO2layers pro-vides fast two-dimensional lithium-ion diffusion[22],and the edge-shared MO6 octahedral arrangement with a direct M–M interaction provides good electronic conductivity.LiCoO2is the most commonly used transition metal oxide cathode in commercial lithium-ion batteries.It has been used because of its high operating voltage(4V),ease of synthesis,and good cycle life.However,only50%(~140mAh g−1)of the theoretical capacity of LiCoO2can be utilized in practical lithium-ion216 A.Manthiram and T.Muraliganth Fig.8.5Crystal structure oflayered LiCoO2cells due to structural and chemical instabilities at deep charge with(1−x)<0.5in Li1−x CoO2as well as safety concerns[23,24].Moreover the element cobalt is toxic and expensive.In this regard,LiNiO2provides an important advantage compared to LiCoO2since Ni is less expensive and less toxic than Co.However,it suffers from a few problems:(i)difﬁculty to synthesize LiNiO2with all Ni3+and as a perfectly ordered phase without a mixing of Li+and Ni3+ions in the lithium plane[25–27], (ii)Jahn–Teller distortion(tetragonal structural distortion)associated with the low-spin Ni3+:d7(t62g e1g)ion[28,29],and(iii)exothermic release of oxygen at elevated temperatures and safety concerns in the charged state[30,31].As a result,LiNiO2 is not a promising material for lithium-ion cells.However,some of these difﬁculties have been overcome by a partial substitution of Co for Ni forming LiNi1−y Co y O2 [32].For example LiNi0.85Co0.15O2has been found to deliver a high capacity of ~180mAh g−1with good cyclability.In general,LiCoO2and LiNi1−y Co y O2are prepared by solid-state reactions at high temperatures(800–900◦C)[33].The high-temperature method usually results in larger particles and often in irregular morphology and a broad particle size distribution.A number of synthetic routes such as sol–gel,co-precipitation,and emulsion methods have been pursued over the years to synthesize nanostructured layered oxides[34–38].Decreasing the particle size to nanometer range signiﬁ-cantly shortens the lithium-ion diffusion distance and improves the rate performance of the layered oxide cathodes.However,the large surface area of the nanoparticles incurs undesirable side reactions with the electrolyte,especially at higher operating voltages.This effect could be minimized by having nano-sized primary particles agglomerating into micron-sized secondary particles.In this regard,template-assisted methods with the use of porous anodic aluminum oxide have been used to prepare LiCoO2nanotubes with lengths up to several8Nanostructured Electrode Materials for Lithium-Ion Batteries217 Fig.8.6Firstcharge–discharge proﬁles ofsolid solutions betweenlayered Li[Li1/3Mn2/3]O2andLi[Ni1−y−z Mn y Co z]O2micrometers and diameter around200nm[39].Since the rate-determining stepin LiCoO2electrodes is the solid-state lithium-ion diffusion,decreasing the par-ticle size can signiﬁcantly improve the kinetics because of shorter lithium diffusionlength.Accordingly,LiCoO2with a nanotube architecture has been found to exhibitimproved rate performance compared to the conventional LiCoO2[40].Recently,solid solutions between Li[Li1/3Mn2/3]O2(commonly known asLi2MnO3)and LiMO2(M=Mn0.5Ni0.5,Co,Ni,and Cr)have become appeal-ing as they exhibit a high reversible capacity of around250mAh g−1with a lowercost and better safety compared to the LiCoO2cathode[41–45].This capacity isnearly two times higher than that found with the LiCoO2cathode.However,theLi2MnO3−LiMO2solid solutions have a few drawbacks.First,they lose oxygen irreversibly from the lattice duringﬁrst charge as indicated by a voltage plateauat4.5V following an initial sloping region corresponding to the oxidation of thetransition metal ions to4+oxidation state as seen in Fig.8.6.This leads to a largeirreversible capacity loss in theﬁrst cycle.Second,these oxides suffer from poorrate capability,impeding their high-power applications.Decreasing the lithium-ion diffusion distance and having a high surface areananostructure could enhance their rate performance.Especially,one-dimensionalnanowire morphology could be beneﬁcial compared to nanoparticles.Accordingly,Li[Ni0.25Li0.15Mn0.6]O2nanowires with a diameter of around30nm and a highaspect ratio of around100have been synthesized via a template-free hydrother-mal method.Interestingly,the Li[Ni0.25Li0.15Mn0.6]O2sample thus prepared hasbeen found to deliver a stable cycle life and superior rate performance with a highdischarge capacity of around260mAh g−1at7C rate[46].Surface-Modifie(Nanocoating)Layered Oxide CathodesAs pointed out in the earlier section,only50%of the theoretical capacity of layeredLiCoO2cathode could be utilized in practical lithium-ion cells due to the chemi-cal instability in contact with the electrolyte for(1−x)<0.5in Li1−x CoO2[23,24].One way to suppress the chemical reactivity is to coat or modify the surfaceof the cathode with other inert oxides.In fact,surface modiﬁcation of the layered218 A.Manthiram and T.Muraliganth LiCoO2cathode with nanostructured oxides like Al2O3,TiO2,ZrO2,SiO2,MgO, ZnO,and MPO4(M=Al and Fe)has been found to increase the reversible capacity of LiCoO2from~140mAh g−1to about200mAh g−1,which corresponds to a reversible extraction of~0.7lithium per formula of LiCoO2[47–54].The surface modiﬁcation suppresses the reaction of the cathode surface with the electrolyte and thereby decreases the impedance growth of the cathode and improves the capac-ity retention.This clearly demonstrates that the limitation in practical capacity of LiCoO2is primarily due to the chemical instability at deep discharge and not due to the structural(order–disorder)transition at(1−x)=0.5.However,the long-term performance of these nano-oxide-coated cathodes will rely on the robustness of the coating.In addition to the improvement in electrochemical properties,nanocoating of AlPO4on LiCoO2has also been found to improve the thermal stability and safety of LiCoO2cathodes[55].As indicated in the previous section,solid solutions between layered Li2MnO3 and Li[Ni1−y−z Mn y Co z]O2exhibit a huge irreversible loss duringﬁrst cycle.The large irreversible capacity loss is observed to be due to the extraction of lithium as “Li2O”in the plateau region as shown in Fig.8.6and an elimination of the oxygen vacancies formed to give an ideal composition“MO2”at the end of theﬁrst charge, resulting in less number of lithium sites available for lithium insertion/extraction during subsequent cycles[43,56].However,a careful analysis of theﬁrst charge–discharge capacity values in our laboratory with a number of compositions suggests that part of the oxygen vacancies should be retained in the lattice to account for the high discharge capacity values observed in theﬁrst cycle[57].More importantly,it was found that the irreversible capacity loss in theﬁrst cycle can be reduced signiﬁ-cantly by coating these layered oxide solid solutions with nanostructured Al2O3and AlPO4[44,57].Figure8.7shows the TEM images of AlPO4-coated layered oxide, in which the thickness of the AlPO4coating is around5nm.Figure8.8a and b compares theﬁrst charge–discharge proﬁles and the corresponding cyclability data of a series of solid solutions between lay-ered Li[Li1/3Mn2/3]O2and Li[Ni1/3Mn1/3Co1/3]O2before and after surfaceFig.8.7TEM image of4wt.%nano-AIPO4-modiﬁedLi[Li0.2Mn0.54Ni0.13Co0.13]O2cathode8Nanostructured Electrode Materials for Lithium-Ion Batteries219Fig.8.8(a)First charge–discharge proﬁles of the layered(1−x)Li[Li1/3Mn2/3]O2−x Li[Ni1/3Mn1/3Co1/3]O2solid solutions before and after surface modiﬁcation with3wt.% nanostructured Al2O3,followed by heating at400◦C(b)Cyclability of the layered(1−x)Li[Li1/3Mn2/3]O2−x Li[Ni1/3Mn1/3Co1.3]O2solid solutions before and after surface modiﬁ-cation with3wt.%nanostructured Al2O3,followed by heating at400◦Cmodiﬁcation with nanostructured Al2O3[44].The surface-modiﬁed samples exhibit lower irreversible capacity loss and higher discharge capacity values than the pris-tine layered oxide samples.This improvement in surface-modiﬁed samples has been explained on the basis of the retention of more oxygen vacancies in the layered lattice after theﬁrst charge compared to that in the unmodiﬁed samples[57–59]. The bonding of the nano-oxides to the surface of the layered oxide lattice sup-presses the diffusion of oxygen vacancies and their elimination.Remarkably,the surface-modiﬁed(1−x)Li[Li1/3Mn2/3]O2−x Li[Ni1/3Mn1/3Co1/3]O2composition with x=0.4exhibits a high discharge capacity of~280mAh g−1,which is two times higher than that of LiCoO2.Moreover,the surface-modiﬁed cathodes have been found to exhibit higher rate capability than the unmodiﬁed samples despite the electronically insulating nature of the coating materials like Al2O3and AlPO4 [59].This is believed to be due to the suppression of the formation of thick solid-electrolyte interfacial(SEI)layers as the coating material minimizes the direct reaction of the cathode surface with the electrolyte at the high charging voltages.However,these layered oxide solid solutions have to be charged up to about 4.8V,so more stable,compatible electrolytes need to be developed to fully exploit their potential as high energy density cathodes.Moreover,oxygen is lost irreversibly from the lattice duringﬁrst charge,and it may have to be vented appropriately during cell manufacturing.Also,the long-term cyclability of these high-capacity cathodes needs to be fully assessed.220 A.Manthiram and T.Muraliganth Nanostructured Spinel Oxide CathodesOxides with the general formula LiMn2O4(M=Ti,V,and Mn)crystallize in the normal spinel structure(Fig.8.9)in which the Li+and the M3+/4+ions occupy, respectively,the8a tetrahedral and16d octahedral sites of the cubic close-packed oxygen array.A strong edge-shared octahedral[M2]O4array permits reversible extraction of the Li+ions from the tetrahedral sites without collapsing the three-dimensional[M2]O4spinel framework.While an edge-shared MO6octahedral arrangement with direct M–M interaction provides good electrical conductivity,the interconnected interstitial(lithium)sites in the three-dimensional spinel framework provide good lithium-ion conductivity.Fig.8.9Crystal structure ofspinel LiMn2O4As a result,spinel LiMn2O4has become an attractive cathode.Moreover,the element Mn is inexpensive and environmentally benign compared to Co and Ni involved in the layered oxide cathodes.However,LiMn2O4delivers only a limited capacity of around120mAh g−1at an operating voltage of4V.Moreover,LiMn2O4 tends to exhibit capacity fade particularly at elevated temperatures(55◦C).Several factors such as Jahn–Teller distortion occurring on the surface of the particles under conditions of nonequilibrium cycling[60,61],manganese dissolution into the elec-trolyte[62,63],formation of two cubic phases in the4V region,loss of crystallinity [64],and development of micro-strain[65]during cycling have been suggested to be the source of capacity fade.Several strategies have been pursued to overcome the capacity fade of LiMn2O4.The most signiﬁcant of them is cationic substitution to give LiMn2−y M y O4(M=Li,Cr,Co,Ni,and Cu)to suppress the difﬁculties of Jahn–Teller distortion and manganese dissolution[66].Decreasing the particle size to nanometer level can enhance the power perfor-mance of LiMn2O4cathodes further.As a result,a variety of synthetic approaches such as sol–gel[67],solution phase[68],mechanochemical[69],spray pyrolysis [70],and templating methods[71]have been pursued to synthesize nano-sizedLiMn2O4.Recently,single-crystalline LiMn2O4nanorods obtained by usingβ-MnO2nanorods synthesized by hydrothermal reaction have been shown to exhibit high power performance[72].However,the application of nanometer-sized spinel particles for practical lithium-ion batteries is not favorable as the high interfacial contact area between the electrode and the electrolyte will aggravate the dissolution of manganese from the spinel lattice into the electrolyte and increase the capacity fade further. Nano-oxide-Coated Spinel CathodesAs pointed out in the previous section,the major issue with the LiMn2O4spinel cathode is the Mn dissolution from the lattice in contact with the electrolyte. Consequently,coating of the LiMn2O4spinel cathode with nanostructured oxides like Al2O3,TiO2,ZrO2,SiO2,MgO,and ZnO has been found to suppress the Mn dissolution from the spinel lattice in contact with the electrolyte and improve the capacity retention[73–75].Another drawback with the spinel LiMn2O4cathode is the lower energy den-sity compared to the layered oxide cathodes.In this regard,the LiMn1.5Ni0.5O4 spinel cathode is appealing as it offers a discharge capacity of around130mAh g−1at a higher voltage of~4.7V vs.lithium.However,the spinel LiMn1.5Ni0.5O4 encounters the formation of NiO impurity during synthesis and the ordering between Mn4+and Ni2+leads to inferior performance compared to the disordered phase [76].It has been found that the formation of the NiO impurity phase and order-ing can be suppressed by appropriate cation doping as in LiMn1.5Ni0.42Zn0.08O4 and LiMn1.42Ni0.42Co0.16O4[77].One major concern with the spinel LiMn1.5Ni0.5O4cathode is the chemical sta-bility in contact with the electrolyte at the higher operating voltage of4.7V.To overcome this difﬁculty,surface modiﬁcation of LiMn1.42Ni0.42Co0.16O4cathodes with oxides like AlPO4,ZnO,Al2O3,Bi2O3have been carried out(Fig.8.10)[78]. The surface-modiﬁed cathodes exhibit better cyclability and rate capability com-pared to the pristine unmodiﬁed samples as shown in Figs.8.11and8.12.The surface coating not only acts as a protection shell between the active cathode mate-rial surface and the electrolyte,but also offers fast lithium-ion and electron diffusion channels compared to the SEI layer formed by a reaction of the cathode surface with the electrolyte,resulting in enhanced cycle life and rate performance.X-ray photoelectron spectroscopic(XPS)analysis has shown that the surface modiﬁcation indeed suppresses the formation of thick SEI layers and thereby improves the rate capability[78].Moreover,the surface modiﬁcation helps to maintain the high rate capability as the cathodes are cycled compared to the unmodiﬁed cathode,resulting in better rate capability retention during long-term cycling. Nanostructured Polyanion-Containing CathodesA major drawback with cathodes containing highly oxidized redox couples like Co3+/4+and Ni3+/4+is the chemical instability at deep charge and the associatedFig8.10High-resolution TEM images of2wt.%(a)Al2O3-,(b)ZnO-,(c)Bi2O3-,and AlPO4-coated LiMn1.42Ni0.42Co0.16O4Fig.8.11Cycling2wt.%Al2O3-,ZnO-,Bi2O3-,and AlPO4-coatedLiMn1.42Ni0.42Co0.16O4safety problems.Recognizing this,oxides like Fe2(XO4)3that contain the polyanion (XO4)2−(X=S,Mo,and W)and crystallizing in the NASICON-related three-dimensional framework structures were shown in the1980s to exhibitﬂat discharge voltage proﬁles at3.0or3.6V[79,80].In these structures,the FeO6octahedrashare corners with SO4tetrahedra with a Fe-O-S-O-Fe linkage and lithium ionsFig.8.12Comparison of therate capabilities and ratecapability retentions ofLiMn1.42Ni0.42Co0.16O4before and after coating with2wt.%Al2O3,ZnO,Bi2O3,and AlPO4:(a)normalizeddischarge capacity at3rdcycle.(b)normalizeddischarge capacity at50thcyclecould be inserted into the interstitial voids of the framework.Although the lower valent Fe2+/3+couple in a simple oxide like Fe2O3would be expected to offer a lower discharge voltage of<3V,a higher voltage of3.6V is observed with the Fe2+/3+couple in Fe2(SO4)3due to inductive effect caused by the countercation S6+.A stronger S–O covalent bonding weakens the l-bond Fe–O covalence through inductive effect,which results in a lowering of the Fe2+/3+redox couple and an increase in the cell voltage.However,a poor electronic conductivity associated with the Fe-O-X-O-Fe(X=S or P)linkage leads to poor rate capability. Nanostructured Phospho-olivine CathodesFollowing the initial concept of using polyanions[78,79],several phosphates have been investigated in recent years[81–83].Among them,LiFePO4crystallizing inFig.8.13Structure ofolivine LiFePO4the olivine structure(Fig.8.13)with FeO6octahedra and PO4tetrahedra has been shown to be a promising material exhibiting aﬂat discharge voltage of~3.45V, with a theoretical capacity of170mAh g−1.Unlike in the case of layered LiMO2 (M=Co,Ni,or Mn)oxides,the presence of covalently bonded PO4units as well as the operation of Fe2+/3+couple rather than M3+/4+couples leads to good struc-tural and chemical stabilities,resulting in good safety features.Moreover,iron is inexpensive and environmentally benign.However,the initial work was able to extract only<0.7lithium ions from LiFePO4even at very low current densities, which corresponds to a reversible capacity of<120mAh g−1.As the lithium extrac-tion/insertion occurred by a two-phase mechanism with LiFePO4and FePO4as end members without much solid solubility,the limitation in capacity was attributed to the diffusion-limited transfer of lithium across the two-phase interface.Thus, the major drawback with LiFePO4is its poor lithium-ion conductivity resulting from one-dimensional diffusion of Li+ions along the chains(b-axis)formed by edge-shared LiO6octahedra and poor electronic conductivity(~10−9S cm−1).Tremendous efforts have been made in recent years to overcome these prob-lems by cationic doping,decreasing the particle size through various synthesis methods,and coating with electronically conducting agents[84–89].Particularly, nano-sized LiFePO4particles have been shown to exhibit excellent performance with high rate capability due to a shortening of both the electron and lithium-ion diffusion path lengths within the particles.In this regard,dimensionally modulated nanostructures such as nanorods,nanowires,and nanosheets are appealing as they can efﬁciently transport charge carriers while maintaining a large surface-to-volume ratio,enhancing the contact with the electrolyte and the reaction kinetics.Among the various synthesis approaches pursued in the past few years,solution-based methods have been particularly successful for LiFePO4with respect to controlling the chemical composition,tailoring the crystallite size,and particle mor-phologies.However,these methods require either long reaction times(5–24h)or further post-heat treatment processing at temperatures as high as700◦C in reduc-ing atmospheres to achieve phase pure samples and a high degree of crystallinity. In this regard,microwave-assisted synthesis approaches are extremely appealing as they can shorten the reaction time from several hours to a few minutes with enor-mous energy savings and cleanliness.Consequently,our group has demonstrated。

工业纯钛在硫酸中的腐蚀行为及其机理研究

Ti 駄叔Vol. 39 No. 2April 2022第39卷第2期2022年 4月工业纯钛在硫酸中的腐蚀行为及其机理研究孔琼匕李丽1,刘正乔1,余世伦1,张孝军1,雷霆3,陈辰4(1.湖南湘投金天钛金属股份有限公司，湖南长沙410025)(2.南方海洋科学与工程广东省实验室(珠海)，广东珠海519080)(3.中南大学粉末冶金研究院，湖南长沙410083)(4.郑州大学材料科学与工程学院，河南郑州450001)摘要：研究了工业纯钛在硫酸溶液中的腐蚀行为及表面形貌演变，利用扫描电镜、粗糙度仪、能谱分析仪和X 射线衍射分析仪对蚀刻前后的表面形貌、粗糙度、成分及物相组成进行分析，利用电子背散射衍射仪及透射电镜对纯钛基体的织构和显微组织进行表征。

结果表明，工业纯钛的表面酸蚀处理可看作微电池腐蚀过程，具体分为3个阶段：钛氧化膜去除、钛基体溶解以及钛表层形成氢化钛吸气层。

钛晶粒的取向差异导致蚀刻后钛表面形成具有取向性的多孔形貌，钛基体内析出的纳米粒子使蚀刻后的钛表面形成丰富的多孔结构。

关键词：工业纯钛；微电池腐蚀；多孔结构；纳米析出；晶粒取向中图分类号：TG146. 23文献标识码：A文章编号：1009-9964(2022)02£18£6Study on Corrosion Behavior and its Mechanism of CommerciallyPure Titanium in Sulfuric AcidKong Bin 1,2 , Li Li 1, Liu Zhengqiao 1, Yu Shilun 1, Zhang Xiaojun 1, Lei Ting 3, Chen Chen 4(1. Hunan Xiangtou Goldsky Titanium Metal Co., Ltd., Changsha 410025 , China)(2. Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai ) , Zhuhai 519080, China)(3. Powder Metallurgy Research Institute , Central South University , Changsha 410083 , China)(4. School of Materials Science and Engineering , Zhengzhou University , Zhengzhou 450001, China)Abstract : The corrosion behaviors and surface morphology evolution of commercially pure titanium in sulfuric acid werestudied , the surface morphology , roughness , elemental content and phase composition before and after etching wereanalyzed by scanning electron microscope , roughness meter , energy dispersive spectroscopy and X-ray diffractometer , and the texture and microstructure of pure titanium matrix were characterized by electron backscattering diflraclomelerand transmission electron microscope. The results show that the etching treatment of pure titanium in sulfuric acid can be regarded as microbattery corrosion , which is divided into three stages. It includes removal of oxide film, dissolution of titanium matrix and formation of titanium hydride getter layer on titanium surface. The orientation of internal grainsleads to directional difference of surface porous morphology after etching , and nano-precipitated particles inside thecrystal lead to rich porous structure.Key words : commercially pure titanium ； microbattery corrosion ； porous structure ； nanoprecipitation ； grain orientation钛是一种阀型金属，具有单相载流体的性能，作阴极是导电的，但用作阳极时不导电，所以作为是重要的离子膜电解槽阳极材料⑴2］。

层状双氢氧化物基复合材料的制备及其电化学性能的研究

层状双氢氧化物基复合材料的制备及其电化学性能的研究The Construction of Layered Double Hydroxides-Based Hybrid Materials for Electrochemical ApplicationAbstractTwo-dimensional (2D) materials have attracted increasing interest in electrochemical energy storage andconversion. As typical 2D materials, layered double hydroxides (LDHs) display large potential in this areadue to the facile adjustableof their composition, structure and morphology. Various preparationstrategies, including in situ growth, electrodeposition and layer-by-layer (LBL) assembly, have beendeveloped to directly modify electrodes by using LDHs materials. Moreover, several composite materialsbased on LDHs and conductive matrices have also been rationally designed and employed in supercapacitors, batteries and electrocatalysis with largely enhanced performances.This paper focus on the construction of LDHs-based composites and its application in electrocatalytic hydrolysis and electrochemical energy storage carried out in a series of trial and research.The controllable synthesis of LDHs-based composites was realized by the method of multi-step hydrothermal process and liquid phase self-assembly. As a result, the electrochemical performance was enhanced.The main contents of this paper are as following:(1) Study on the construction of NiFe LDH@NiCo2O4 compositesHerein, for the first time, we demonstrate NiFe-LDH ultrathin sheets with several atomic layers grown on nickel cobalt oxide (NiCo2O4) nanowire arrays as an efficient bifunctionalcatalyst toward both HER and OER reaction. Nickel (Ni) foam was used as the electrode scaffold support because of its earth abundance and porous three-dimensional structure.NiCo2O4, a typical OER electrocatalyst with high conductivity, was deposited on the Ni foam in the form of rhombus/hexagonal plates interconnected into perpendicular nanowire array morphology, efficientlyfacilitating electron transfer and electrolyte permeation. The electrical conductivity in NiCo2O4 has been believed to originate from the层状双氢氧化物基复合材料的制备及其电化学性能的研究presence of Ni3+ and the electron transfer between Ni2+ and Ni3+. Importantly, the surface of NiCo2O4was a Ni-rich layer, which served as the seed for the following hierarchical growth of NiFe-LDH, ensuring close contact and strong coupling at the interface.(2) Study on the properties of electrocatalytic water splitting of NiFe LDH@NiCo2O4 compositesHerein, the NiFe-LDH sheets were ultrathin of only several atomic layers, combined with its strong coupling with NiCo2O4 and the unique hierarchical structure, enabled the hybrid electrode a remarkable overall water splitting performance of only 1.60 V to achieve 10 mA cm-2 current in single alkaline KOH eletrolyte.Key words: Layered double hydroxides (LDHs)，Electrocatalysis, Overall water splitting, Hydrogen evolution reaction, Oxygen evolution reaction，Heterostructure.Written by: Zhiqiang WangSupervised by: Prof. Fengxia GengProf. Xingwang Wang目录第一章文献综述 (1)1.1 引言 (1)1.2 LDHs及其复合材料的制备 (2)1.2.1 LDHs的基本结构 (2)1.2.2 LDHs的制备方法 (2)1.3 LDHs及其复合材料的应用 (3)1.3.1电催化水解中的应用 (3)1.3.2超级电容器中的应用 (10)1.4论文的选题思路、意义和主要工作 (15)1.4.1选题思路和意义 (15)1.4.2主要工作 (16)参考文献 (16)第二章超薄NiFe LDH纳米片与NiCo2O4纳米线杂化结构的构筑 (16)2.1 引言 (24)2.2 实验部分 (26)2.2.1 实验试剂 (26)2.2.2 仪器 (26)2.2.3 实验步骤 (27)2.3 结果与讨论 (28)2.3.1 SEM分析 (28)2.3.2 XRD和BET分析 (30)2.3.3 TEM分析 (32)2.3.4 EDS和Mapping分析 (33)2.3.5 XPS分析 (35)2.4 小结 (37)参考文献 (37)第三章NiFe LDH@NiCo2O4杂化结构的电催化全解水性能研究 (41)3.1 引言 (41)3.2 实验部分 (41)3.2.1 电化学测试 (41)3.3 结果与讨论 (42)3.3.1析氧反应分析 (42)3.3.2析氢反应分析 (44)3.3.3 全解水分析 (45)3.3.4 CV和EIS分析 (46)3.3.5电催化性能比较 (47)3.3.6 电催化性能的机理探究 (50)3.4 小结 (53)参考文献 (53)第四章结论和展望 (53)4.1 全文总结 (60)4.2 展望 (60)在读期间已发表或录用的论文 (62)致谢 (63)第一章文献综述1.1 引言能源在当今社会的发展中发挥着重要的作用，但近年来由传统能源煤、石油、天然气等资源的日益消耗，以及化石燃料等的大量使用所带来的生活环境的污染，以及温室气体的增加导致的海平面上升、酸雨的形成，使人类面临生存环境的恶化，不可再生能源的枯竭等多重威胁1-4。

BiS3-ppy -main

Contents lists available at ScienceDirectNano Energyjournal homepage:/locate/nanoenFull paperBio-inspired engineering of Bi 2S 3-PPy yolk-shell composite for highly durable lithium and sodium storageHaichen Liang,Jiangfeng Ni ⁎,Liang Li⁎College of Physics,Optoelectronics and Energy,Collaborative Innovation Center of Suzhou Nano Science and Technology,Center for Energy Conversion Materials &Physics (CECMP),Soochow University,Suzhou 215006,PR ChinaA R T I C L E I N F OKeywords:Bismuth sul ﬁde Yolk-shellLithium storage Sodium storageA B S T R A C TBismuth based compounds are uniquely interesting as anode materials in energy storage devices such as rechargeable batteries,owing to their large volumetric capacity and suitable operating potential higher than graphite.How to achieve the high capacity durably and robustly remains an open challenge.To address this issue,here we propose a bio-inspired material engineering of yolk-shell composite that consists of bismuth sul ﬁde (Bi 2S 3)nanowire assembly intimately encapsulated in polypyrrole (PPy)shell.The Bi 2S 3yolk features a large void space and a short di ﬀusion distance,while the PPy shell is highly conductive,ﬂexible and resilient,allowing for the free volume variation upon ion uptake and release.When used as anode,the Bi 2S 3-PPy yolk-shell composite exhibits a superior Li storage cyclability (99%for 500cycles)and a high rate capability (337mAh g –1at 10C),outstripping any previous bismuth based materials.This composite also a ﬀords a high reversible capacity of 591mAh g −1and a favorable durability for Na storage.The discrepancy between Li and Na storage may correlate to the larger volume change of Bi alloying with Na (∼250%)against with Li (~110%).This work o ﬀers a potential creative approach to engineering e ﬃcient electrodes for energy storage applications.1.IntroductionRechargeable battery technologies play a vital role in our everyday life and various ﬁelds of society,for example,electric vehicle propul-sion and stationary energy storage [1,2].The implementation of lithium-ion batteries (LIBs)on a large scale faces increasing concern on the availability and cost of lithium.One most appealing alternative is to use sodium,which exhibits a rich intercalation chemistry and possesses a resource in principle unlimited on the earth [3,4].In addition,room temperature sodium-ion batteries (SIBs)are much cheaper than LIBs and therefore,promising for large-scale energy storage.Currently,one key challenge for both technologies is to ﬁnd suitable anodes with large capacity and notable durability at rational recharge rates [5].While graphite is the dominant Li anode,it does not host a high concentration of Na +ions at room temperature.Some metals (Sn,Sb,Bi,etc.)and their compounds could promise greater capacity and better durability for both lithium and sodium storage,owing to their high volumetric capacity and suitable working potential that eliminates possible metal plating [6–8].Bismuth sul ﬁde (Bi 2S 3),a low bandgap (~1.3eV)semiconductor with a laminar structure and high absorption coe ﬃcient,has emerged as an attractive material for photovoltaics,photodetector,and thermo-electric [9–11].Recently,Bi 2S 3nanomaterials such as nanorods,nanowires,and nanotubes have been shown to be electrochemically active for Li and Na storage [12,13].In particular,their complex assemblies promise enhanced activity for rechargeable batteries due to high surface area and unique architecture [14,15].Theoretically,Bi 2S 3is capable of a ﬀording a speci ﬁc capacity of 625mAh g −1,or volumetric capacity of 4250mAh cm −3,which is much higher than that of graphite.However,such a high capacity is often compromised upon cycling,due to electrode pulverization and loss of electronic connection caused by huge volumetric expansion upon Li or Na insertion.To mitigate this di ﬃculty,our group and others attempted to integrate Bi 2S 3material into nanocarbons such as reduced graphene oxide and carbon nanotube [16–19].Functional groups of the nanocarbons can tightly hold Bi 2S 3nanoparticles on the conductive network,thus largely avoiding the failure of electronic connection [20].Nonetheless,as nanocarbon cannot fully wrap active particles,the dissolution of polysul ﬁde intermediates S x 2−(x ≥2)into electrolyte is inevitable,which is recognized as another major contribution of capacity decay.Consequently,long-term stability of Bi 2S 3materials has not been achieved to date.Further improvement in the cyclability is extremely important and desirable for battery application.Concurrent with the advances of Bi 2S 3nanomaterials,yolk-shell/10.1016/j.nanoen.2017.01.033Received 28October 2016;Received in revised form 12January 2017;Accepted 14January 2017⁎Corresponding authors.E-mail addresses:je ﬀni@ (J.Ni),lli@ (L.Li).Nano Energy 33 (2017) 213–220Available online 15 January 20172211-2855/ © 2017 Elsevier Ltd. All rights reserved.architecture,such as carbon coating on active materials,has been grown by versatile approaches.By employing a second conductive shell,the conductivity of Bi2S3electrodes can be increased while the dissolution of polysulﬁde intermediates will be retarded simultaneously [21,22].Carbon has been frequently employed as a coating shell,owing to its high conductivity and low cost.Most carbon coating relies on thermal decomposition of carbon precursors,and this process often suﬀers from partial structural collapse and grain coarsening at high temperatures[22].Sometimes it causes irreversible reconstruction of bulk and/or yolk-shell interphase such as reduction of active materials. Consequently,a simple yet eﬀective coating shell without thermal treatment would be desired.In this work,we designed a yolk-shell composite that consists of uniformﬂower-like assemblies of Bi2S3nanowires intimately wrapped in a conductive,ﬂexible,and stretchable polypyrrole(PPy)ﬁlm.This material engineering is fully inspired by the cirsium,whose petals are in an ordered assembly and are covered by vegetable wax on the surface (Scheme1a).This architecture can maximize exposure to the sun while minimize the evaporation of water,a natural design.In this design,the nanowire assembly features large surface area,short diﬀusion length, suﬃcient space,and mechanicalﬂexibility,while the resilient PPy shell preserves the structure integrity and prevents polysulﬁdes from dissolution loss.Therefore,the Bi2S3-PPy composite enables superior Li and Na storage capability.It aﬀords a high reversible capacity of 621mAh g–1for Li storage at a rate of0.2C,and a capacity of 337mAh g–1at a rate of10C with an unprecedented retention of 99%over500cycles.It also exhibit a high reversible capacity of 591mAh g–1for Na storage with rational durability,thereby making the Bi2S3-PPy yolk-shell composite a competitive alternative for energy storage devices.2.Experimental section2.1.Synthesis of Bi2S3ﬂower-like assemblyPVP(0.5g)and thiourea(0.3g)were dispersed in60mL of EG under continuous stirring at65°C.Then,to this suspension10mL of 0.1M Bi(NO3)3solution(in ethylene glycol)was added dropwise.After 30min of further stirring,the mixed suspension was transferred to a Teﬂon-lined autoclave and kept at140°C for8h.The resultant black precipitate was collected by centrifugation,washed thoroughly with deionized water and ethanol,and dried in a vacuum at60°C overnight.2.2.Synthesis of Bi2S3-PPy yolk-shell compositeThe resulting Bi2S3powder(0.15g)was immersed in FeCl3 aqueous solution(0.2mL,0.1M)and dried in a vacuum.The dry powder and pyrrole monomer(2mL)were separately placed in two vials,which were then sealed in a bottleﬁlled with argon and kept at 40°C for3h.2.3.Materials characterizationSamples were characterized by scanning electron microscopy(SEM, Hitachi SU-8010)and transmission electron microscopy(TEM,FEI Tecnai G2T20).Structure characteristics were collected using X-ray diﬀraction(XRD,Rigaku D/MAX-2000PC),Fourier transform infrared (FTIR,Bruker Tensor27),Raman spectroscopy(Horiba JY LabRAM HR800),and thermogravimetric analysis(TGA,Seko TG/DTA-7300). Chemical states was probed by X-ray photoelectron spectroscopy(XPS, Thermo Fisher Scientiﬁc Escalab250Xi).2.4.Electrochemical measurementsThe electrochemical evaluation was performed on2032-type coin cells.The working electrode was composed of70%active material,15% acetylene black,5%carbon nanotube,and10%sodium aiginate binder. Slurry of the mixture was cast onto a copper foil using a doctor-blade technique,and vacuum dried at110°C for12h.The loading of active materials is~1.2mg cm−2.For Li half cell,the counter and reference electrode was Li metal foil,the electrolyte1M LiPF6solution in ethylene carbonate and dimethyl carbonate(1:1by volume),and the separator Whatman GF/A glass-ﬁberﬁlters.For Na half cell,the counter and reference electrode was Na metal foil,the electrolyte 1M NaClO4in ethylene carbonate,dimethyl carbonate andﬂuoroethy-lene carbonate(1:1:0.04by volume).Cells were charged and dis-charged on a LAND CT2001A battery test system.An AUTOLAB PGSTAT302N electrochemical workstation was used to collecte cyclic voltammetry(CV)and electrochemical impedance spectroscopy(EIS) at room temperature(~27°C).3.Results and discussionAs illustrated in Scheme1b,the fabrication of yolk-shell composite is based on the polyvinyl pyrrolidone(PVP)assisted self-assembly of Bi2S3nanowires in ethylene glycol(EG),which is followed by an in situ vapor-phase polymerization with pyrrole.Bi(NO3)3and thiourea dis-solved in EG were selected to control the assembly reactions.At high temperature,hydrolysis of thiourea led to the gradual realease of S2−species,which combined with Bi3+species and condensed into Bi2S3 nanowire through a possible oriental attachment mechanism.The Bi2S3nanowires further assembled intoﬂower-like architecture spon-taneously[11].In this process PVP served as proton scavenger by consuming excessive acid and promoted the assembly of Bi2S3nano-wires by adjusting the electrostatic interaction between colloidal nanowires[23,24].After solvothermal condensation at140°C,Bi2S3 microﬂowers2–3µm in diameter comprising numerous ultraﬁne nanowires were readily obtained(Fig.1a).The Bi2S3nanowires are homogeneous in their size,showing a diameter of5–10nm and a length of1–2µm,with a large aspect ratio up to hundreds(Fig.1b). Without PVP,only assemblies of coarse nanorods with a muchlower Scheme1.Schematic diagram illustrating(a)design principle of the architecture inspired by cirsium and(b)synthesis procedure of Bi2S3-PPy yolk-shell architecture.aspect ratio are obtained (Fig.S1,Supporting Information ).The Bi 2S 3assemblies were then coated with a PPy ﬁlm via vapor-phase polymerization,where pyrrole monomer vapor transferred onto the Bi 2S 3assemblies and polymerized in situ [21].A pre-loading of FeCl 3was necessary to facilitate the formation and doping of PPy ﬁlm,which could improve the electronic conductivity of the polymer.After polymer coating,the Bi 2S 3-PPy composite well retains the ﬂower-like morphology of the pristine Bi 2S 3assembly (Fig.1c).The TEM images reveal a thin,uniform,and conformal polymer layer on the surface of each Bi 2S 3assembly (Fig.1d,e).A high-resolution TEM image con ﬁrms that each Bi 2S 3nanowire is wrapped by a 3–5nm thick polymer layer (Fig.1f).The Bi 2S 3nanowire crystallized in an orthor-hombic structure,growing preferentially along (211)direction to one-dimensional structure,with lattice fringe spacing of 0.31nm.Both pristine Bi 2S 3and Bi 2S 3-PPy composite show clear di ﬀraction peaks but in poor resolution,due to a low crystalline temperature (Fig.2a).The patterns can be indexed into an orthorhombic Bi 2S 3phase (PDF#17-0320).The presence of PPy in the product is supported by FTIR spectroscopy (Fig.S2,Supporting Information ),in which several characteristic peaks due to PPy are manifest.The bands at 1551and 1213cm −1can be attributed to the C ˭C and C-N stretching vibrations of pyrrole ring,respectively;whereas the bands at 1045cm −1and 932cm −1may be assigned to the in-plane and out-of-plane vibrations of =C –H,respectively [21].The content of PPy in the composite is ~2.5wt%,as estimated from the TGA curve (Fig.S3,Supporting Information )[14].XPS survey spectrum veri ﬁes the elements of Bi,S,C,N,and O (Fig.S4,Supporting Information ).The core level S 2p reveals a doublet with the 2p 3/2and 2p 1/2peaks at 160.5and 161.6eV (Fig.2b).These peaks along with the S 2s at 225.2eV unambiguously con ﬁrm the presence of sulfur and its oxidation state of −2in Bi 2S 3.The Bi 4f 5/2and 4f 7/2doublet appears at 163.0and 157.8eV,respectively,suggesting that Bi 3+species are dominant in the composite [23].High-resolution scan spectra of C 1s and N 1s are present in Fig.2c and d.The C 1s spectrum reveals C-N peak due to pyrrole besides prominent C-C peak,whereasthe weak carboxyl group signature is possible due to adsorbed CO 2.The N 1s spectrum shows amine peak due to PPy,while amide signatures may be from residual PVP [23].As a comparison,the pristine Bi 2S 3shows N 1s peak at higher energy,which matches well with the amide signatures originating from residual PVP.The Bi 2S 3-PPy composite can be used as anodes for rechargeable LIBs and SIBs,taking advantage of the unique yolk-shell con ﬁguration.The merits for such electrode architecture can be expressed as follows.(1)The internal nanowire assembly exhibits large surface area and open frameworks that allow for e ﬃcient mass transport,contributing a high capacity.(2)The outer polymer layer provides a fast electron transport path,but also e ﬀectively accommodates the stress and strain during the alkaline ion storage through elastic deformation.(3)The PPy networks are directly bonded to Bi 2S 3yolk,possibly through chemical bonding that enables structural stability and good conductiv-ity of nanowires.(4)Last but not least,the robust coating layer e ﬃciently avoids the dissolution loss of polysul ﬁde species,thus ensuring extendable durability.Ideally,the above characteristics work together to result in a ﬂexible structure and improved ion storage properties.We evaluate the Li-storage property of the Bi 2S 3-PPy composite in electrochemical cells using Li metal as both reference and counter electrodes.The Li storage performance is encouraging as indicated by CV and galvanostatic tests (Fig.3).The CV pro ﬁle shows three marked cathodic peaks,suggesting multiple Li-driven evolutions (Fig.3a).The peak at 1.61V (vs.Li for Li storage)re ﬂects the reduction of Bi 2S 3to metallic Bi,which further alloys with Li to form LiBi (0.73V)and Li 3Bi (0.61V)[13,19].The corresponding reverse process exhibits one prominent dealloying peak at 0.97V and overlapped sul ﬁde-generation peaks between 1.8and 2.4V.Most redox peaks come from the Bi 2S 3,as the PPy exhibits a almost featureless CV pro ﬁle (Fig.S5,Supporting Information ).Fig.3b shows that the Bi 2S 3-PPy exhibits initial dis-charge (lithiation)and charge (delithiation)capacities of 824and 621mAh g −1,respectively.The Coulombic e ﬃciency (CE)of ~75%is impressive in bismuth based electrodes [12–14],and soon increasestoFig.1.Morphology of Bi 2S 3and Bi 2S 3-PPy yolk-shell composite.(a)SEM and (b)TEM images of ﬂower-like Bi 2S 3assembly.(c)SEM and (d,e)TEM images of Bi 2S 3-PPy yolk-shell composite.(f)High-resolution TEM image of Bi 2S 3-PPy composite.Dash line is used for eye-guide only to separate Bi 2S 3nanowire and PPy ﬁlm.~95%in the subsequent cycles.An unprecedented Li-cycling stability is demonstrated in Fig.3c.After 100cycles at a rate of 0.5C (1C is taken as 625mA g −1),the composite retains a capacity of 643mAh g −1,which is 112%of the initial value.The selected galvanostatic curves at various stages reveal very similar pro ﬁles,suggesting that the additional capacity may stem from increased utilization of Bi 2S 3rather than new species or phases (Fig.S6,Supporting Information ).Capacity increasing upon cycling is a common activation phenomenon for oxide and chalcogenide anodes.The activation of materials is generally attributed to structural evolution,crystalline defects,and/or surface SEI layer [25].EIS probes little variation in the charge transfer resistance (R ct ,Table S1),indicative of stable reaction kinetics (Fig.3d)[19].In contrast,the pristine Bi 2S 3electrode exhibits a rapid capacity decay over cycles,while the PPy displays a much lower capacity level of ~200mAh g −1(Fig.S7,Supporting Information ).This poor cyclability of the pristine Bi 2S 3electrode correlates well with the evolution of SEI ﬁlm,as revealed by EIS (Fig.S8,Supporting Information ).The pristine Bi 2S 3anodes su ﬀers from drastic volume expansion during Li uptake,leading to pulverization of the electrodes and continuous evolution of SEI.When the Bi 2S 3yolk is protected by the PPy shell,pulverization of the electrodes can largely be avoided as the polymer is highly stretchable to accommodate the volume expan-sion.Thus,a relatively stable SEI can be warranted.In addition,the PPy prevents the electrode from direct contact with the electrolyte,which minimizes side reactions and helps to build a stable SEI ﬁlm.At a higher rate of 2C over 500cycles,the capacity of the Bi 2S 3-PPy maintains a high level of 450mAh g −1and the retention is ~99%(Fig.3e).This retention is overwhelmingly superior to pristine Bi 2S 3counterpart and previously reported Bi 2S 3/C [13],Bi 2S 3[14],Bi 2S 3/Bi 2O 3heterostructure [15],Bi 2S 3/RGO [16],Bi 2S 3/CNT [19],and other bismuth based electrodes [26,27](Table S2,Supporting Information ).This durability strongly con ﬁrms the e ﬃcacy of ouryolk-shell engineering that relies on the coating of polymeric ﬁlm.Another important characteristic used to evaluate the performance of an electrode is the robustness at high current rates.Galvanostatic pro ﬁles at various rates ranging from 0.2to 10C are present in Fig.4a.At typical rates of 0.2,1,and 5C,the Bi 2S 3-PPy electrode a ﬀords Li-storage capacity of 608,551,and 391mAh g −1,respectively.At a higher rate of 10C,the composite exhibits a reversible capacity of 337mAh g −1or 2290mAh cm −3.The rather similar charge and discharge pro ﬁles at various rates signal excellent rate performance,regardless of the increased overpotential with rates arising from charge and mass transport limitation [19].When the current rate is switched back and retested again,no appreciable capacity loss is evident (Fig.4b).To further explore the kinetic character,CV curves of the Bi 2S 3-PPy at varied sweep rates are measured (Fig.4c).When the sweep rate increases from 0.2to 1mV s ‒1,the CV curves exhibit subtle distortion,again re ﬂecting a remarkable reversibility.Fig.4d presents the CV peak currents (I p )plotted versus the sweep rates (v )in the logarithmic format.The linear ﬁtting gives the slopes (b )of 0.74and 0.65for the cathodic and anodic processes,respectively,which suggests a pseudocapacitive behavior for Li storage in the yolk-shell composite [28].As SIBs have attracted increasing attention and shown promising perspective in the renewable and energy grids,it is crucial to exploit the Na storage capability in the engineered yolk-shell sul ﬁde composite [29,30].Electrochemical Na storage in the Bi 2S 3-PPy electrodes was investigated by coupling with Na metal reference and counter electro-des [31].Generally,the Na storage characteristic is similar to Li storage,except for a lower redox potential due to thermodynamic origin (Fig.5)[32,33].As shown in the CV curves in Fig.5a,Na storage in the Bi 2S 3-PPy occurs at 0.99V (vs.Na for Na storage),0.58V and 0.22V,which represent the conversion reaction,NaBi alloying,and Na 3Bi alloying,respectively (Fig.S9,Supporting Information ).TheFig.2.Structural characterization of Bi 2S 3and Bi 2S 3-PPy yolk-shell composite.(a)XRD patterns of Bi 2S 3and Bi 2S 3-PPy composite.High-resolution XPS spectra of (b)Bi 4f and S 2p,(c)C 1s for Bi 2S 3-PPy.(d)Comparison of N 1s XPS spectra for Bi 2S 3-PPy and Bi 2S 3.initial sodiation results in a capacity of 765mAh g −1,out of which a capacity of 591mAh g −1(77%)is reversible (Fig.5b).Nonetheless,solid-electrolyte interphase (SEI)on the Na anodes is usually unstable and evolves upon cycling,leading to Na consumption and capacity fading [3].Thus,the Na storage durability is slightly inferior to Li storage,as shown in Fig.5c and Fig.S10Supporting Information .However,it is worth noting that this durability is still comparable to other Bi 2S 3based Na anodes [17,32,33](Table S2,Supporting Information )and much better than the pristine Bi 2S 3sample (Figs.S11and S12,Supporting Information ).The R ct for Na storage shown in Fig.5d is consistently greater than that for Li (Table S1,Supporting Information ),indicating that the uptake and release of larger Na +ion is kinetically more di ﬃcult.Fig.6a and b show that the yolk-shell electrode a ﬀords reversible (desodiation)capacities of 475,422,335,238,and 144mAh g −1,respectively,at rates of 0.5,1,2,5,and 10C.This rate capability issomewhat inferior to Li storage,in particular at higher current rates.Further,the capacity at the second round of rate test is not as stable as Li storage.This discrepancy may stem from more severe di ﬀusive barrier and polarization associated with larger Na +ion.Further exploration on the Na storage kinetics of the Bi 2S 3-PPy by CV is displayed in Fig.6c and d.By analogy,the peak currents (I p )are roughly a linear function of the sweep rates (v )in the logarithmic format.The slope (b )is 0.75for the alloying and 0.5for the dealloying process,again suggesting a pseudocapacitive characteristic for Na storage in the yolk-shell composite.To shed light on the di ﬀerence between Li and Na storage in the Bi 2S 3-PPy yolk-shell composite,SEM images of electrodes before and after 100cycles are compared in Fig.7.While Li cycling electrodes reserve the basic ﬁlm shape,Na storage in electrode ﬁlms introduces many cracks and voids,due to repeated volume expansion and contraction.Based on this observation,we tentatively propose amodelFig.3.Electrochemical Li storage in Bi 2S 3-PPy yolk-shell composite.(a)CV curves at a sweep rate of 0.2mV s −1and (b)galvanostatic pro ﬁles at a rate of 0.2C during initial three cycles.(c)Cycling stability at a rate of 0.5C for 100cycles.(d)Impedance spectra before and after cycles.Inset shows enlarged spectra in the high and middle frequencies.(e)Long-term cycling stability at a rate of 2C for 500cycles.Fig.4.Rate capability and Li storage kinetics in Bi2S3-PPy yolk-shell composite.(a)Galvanostatic curves measured at current rates ranging from0.2to10C.(b)Rate cycling capability at various rates.(c)CV curves measured at sweep rates ranging from0.2to1.0mV s−1.(d)CV peak currents(I p)upon Li alloying and dealloying process logarithmically plotted as a function of the sweep rates(v)to give the slopes(b).Fig.5.Electrochemical Na storage in Bi2S3-PPy yolk-shell composite.(a)CV curves at a sweep rate of0.2mV s−1and(b)galvanostatic proﬁles at a rate of0.2C during initial three cycles.(c)Cycling stability at a rate of0.5C for100cycles.(d)Impedance spectra before and after100cycles.Inset shows enlarged spectra in the high and middle frequencies.to illustrate the structural evolution of the Bi 2S 3-PPy composite in Fig.7d.As for Li storage,Bi alloying with Li results in a volumetric augment of ~110%.The induced stress and strain can be well accommodated by the porous Bi 2S 3core and the stretchable PPy shell and therefore,the whole yolk-shell con ﬁguration sustains hundreds of cycles.Bi alloying with Na,however,results in a much larger volume expansion (~250%)[34].Thus,some yolk-shell architecture may break down upon cycling and polysul ﬁde species leak out into theelectrolyte,Fig.6.Rate capability and Na storage kinetics in Bi 2S 3-PPy yolk-shell composite.(a)Galvanostatic curves measured at current rates ranging from 0.2to 10C.(b)Rate cycling capability at various rates.(c)CV curves measured at sweep rates ranging from 0.2to 1.0mV s −1.(d)CV peak currents (I p )upon Na alloying and dealloying process logarithmically plotted as a function of the sweep rates (v )to give the slopes (b).Fig.7.SEM images of Bi 2S 3-PPy yolk-shell electrode before (a)and after 100cycles for (b)Li storage and (c)Na storage.(d)Scheme showing evolution of Bi 2S 3-PPy yolk-shell architecture upon Li and Na cycling.Polysul ﬁde species will dissolve out when Na-storage yolk-shell particle is cracked.leading to continuous loss of active species and capacity.Our proposal is indeed validated by the post-test analysis on electrolytes after100 cycles(Fig.S13,Supporting Information).The Li electrolyte is transparent and colorless,whereas the Na electrolyte becomes yellow-ish,indicative of the presence of polysulﬁde species[35].4.ConclusionIn conclusion,a bio-inspired yolk-shell architecture comprising uniform Bi2S3assemblies parceled in highly conductive and stretchable network of PPy was designed and synthesized.The Bi2S3assembly can maximize area accessible to electrolyte while minimize the ion diﬀusion length,while the PPy shell prevents polysulﬁdes from dissolution loss. This unique Bi2S3-PPy yolk-shell architecture can be employed as an ideal electrode for electrochemical Li and Na storage.The Bi2S3-PPy composite exhibits a high Li storage capacity of621mAh g−1for Li and an amazing cycling stability,retaining643mAh g−1over100cycles at 0.5C(112%of the initial value)and450mAh g−1over500cycles at a rate of2C(~99%of the initial value).Such durability has yet been realized for bismuth based electrodes previously,fully validating the promise of yolk-shell material engineering.As for Na storage,the reversible capacity reaches591mAh g−1and the retention is fully comparable to previous reports on Bi2S3materials.Moreover,CV measurements of the composite illustrate a pseudocapacitive feature, regardless Li or Na storage.Post-test analysis points out that the Na storage durability may correlate to the large size of Na+ions,which provides an insight to address this issue in future.Owing to ease of operation and greatﬂexibility,the yolk-shell strategy mayﬁnd applica-tion in other high-performance battery electrodes.AcknowledgmentsWe acknowledge theﬁnancial support of the National Natural Science Foundation of China(51672182,51302181,51372159, 51422206),the China Postdoctoral Science Foundation (2015T80580),333High-Level Talents Project in Jiangsu Province, 1000Young Talents Plan,the Jiangsu Natural Science Foundation (BK20151219,BK20140009),Six Talent Peaks Project in Jiangsu Province,and of the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD).Appendix A.Supplementary materialSupplementary material associated with this article can be found in the online version at doi:10.1016/j.nanoen.2017.01.033.References[1] B.Dunn,H.Kamath,J.M.Tarascon,Science334(2011)928–935.[2]J.Lu,L.Li,J.-B.Park,Y.-K.Sun,F.Wu,K.Amine,Chem.Rev.114(2014)5611–5640.[3]M.D.Slater,D.Kim,E.Lee,C.S.Johnson,Adv.Funct.Mater.23(2013)947–958.[4]X.Xiang,K.Zhang,J.Chen,Adv.Mater.27(2015)5343–5364.[5]W.Luo,F.Shen,C.Bommier,H.Zhu,X.Ji,L.Hu,Acc.Chem.Res.49(2016)231–240.[6]Z.Li,J.Ding,D.Mitlin,Acc.Chem.Res.48(2015)1657–1665.[7]J.Liu,Z.Yang,J.Wang,L.Gu,J.Maier,Y.Yu,Nano Energy16(2015)389–398.[8] D.Su,S.Dou,G.Wang,Nano Energy12(2015)88–95.[9]K.Biswas,L.-D.Zhao,M.G.Kanatzidis,Adv.Energy Mater.2(2012)634–638.[10]G.Manna,R.Bose,N.Pradhan,Angew.Chem.Int.Ed.53(2014)6743–6746.[11]X.Zhou,X.Zhao,D.Zhang,S.Chen,X.Guo,W.Ding,Y.Chen,Nanotechnology17(2006)3806–3811.[12]J.Ma,Z.Liu,J.Lian,X.Duan,T.Kim,P.Peng,X.Liu,Q.Chen,G.Yao,W.Zheng,Crystengcomm13(2011)3072–3079.[13]H.Jung,C.-M.Park,H.-J.Sohn,Electrochim.Acta56(2011)2135–2139.[14]Y.Zhao,D.Gao,J.Ni,L.Gao,J.Yang,Y.Li,Nano Res.7(2014)765–773.[15]T.Liu,Y.Zhao,L.Gao,J.Ni,Sci.Rep.5(2015)9307.[16]Z.Zhang,C.Zhou,L.Huang,X.Wang,Y.Qu,i,J.Li,Electrochim.Acta114(2013)88–94.[17]W.J.Li,C.Han,S.L.Chou,J.Z.Wang,Z.Li,Y.M.Kang,H.K.Liu,S.X.Dou,Chem.Eur.J.(2015).[18]Y.Zhao,T.Liu,H.Xia,L.Zhang,J.Jiang,M.Shen,J.Ni,L.Gao,J.Mater.Chem.A2(2014)13854–13858.[19]J.Ni,Y.Zhao,T.Liu,H.Zheng,L.Gao,C.Yan,L.Li,Adv.Energy Mater.4(2014)1400798.[20]J.Ni,Y.Li,Adv.Energy Mater.6(2016)1600278.[21]X.Sun,H.Zhang,L.Zhou,X.Huang,C.Yu,Small12(2016)3732–3737.[22]J.M.Jeong,B.G.Choi,S.C.Lee,K.G.Lee,S.J.Chang,Y.K.Han,Y.B.Lee,H.U.Lee,S.Kwon,G.Lee,C.S.Lee,Y.S.Huh,Adv.Mater.25(2013)6250–6255.[23] A.Purkayastha,Q.Yan,M.S.Raghuveer,D.D.Gandhi,H.Li,Z.W.Liu,R.V.Ramanujan,T.Borca-Tasciuc,G.Ramanath,Adv.Mater.20(2008)2679–2683.[24]L.Li,N.Sun,Y.Huang,Y.Qin,N.Zhao,J.Gao,M.Li,H.Zhou,L.Qi,Adv.Funct.Mater.18(2008)1194–1201.[25]J.Ni,Y.Zhao,L.Li,L.Mai,Nano Energy11(2015)129–135.[26]Y.Li,M.A.Trujillo,E.Fu,B.Patterson,L.Fei,Y.Xu,S.Deng,S.Smirnov,H.Luo,J.Mater.Chem.A1(2013)12123–12127.[27] C.-F.Sun,J.Hu,P.Wang,X.-Y.Cheng,S.B.Lee,Y.Wang,Nano Lett.16(2016)5875–5882.[28]Y.G.Wang,Z.S.Hong,M.D.Wei,Y.Y.Xia,Adv.Funct.Mater.22(2012)5185–5193.[29] C.Wu,Y.Jiang,P.Kopold,P.A.van Aken,J.Maier,Y.Yu,Adv.Mater.28(2016)7276–7283.[30] C.Zhu,X.Mu,P.A.van Aken,Y.Yu,J.Maier,Angew.Chem.Int.Ed.53(2014)2152–2156.[31]J.Ni,S.Fu,C.Wu,J.Maier,Y.Yu,L.Li,Adv.Mater.28(2016)2259–2265.[32]Y.Zhao,A.Manthiram,Chem.Mater.27(2015)6139–6145.[33]W.Sun,X.Rui,D.Zhang,Y.Jiang,Z.Sun,H.Liu,S.Dou,J.Power Sources309(2016)135–140.[34]J.Sottmann,M.Herrmann,P.Vajeeston,Y.Hu,A.Ruud,C.Drathen,H.Emerich,H.Fjellvåg,D.S.Wragg,Chem.Mater.28(2016)2750–2756.[35]H.-J.Peng,W.-T.Xu,L.Zhu,D.-W.Wang,J.-Q.Huang,X.-B.Cheng,Z.Yuan,F.Wei,Q.Zhang,Adv.Funct.Mater.26(2016)6351–6358.。

钴酸镍

Engineeringﬁrecracker-like beta-manganese dioxides@spinel nickel cobaltates nanostructures for high-performance supercapacitorsMin Kuang a,Zhong Quan Wen b,Xiao Long Guo a,Sheng Mao Zhang c,Yu Xin Zhang a,b,*a College of Materials Science and Engineering,Chongqing University,Chongqing400044,PR Chinab National Key Laboratory of Fundamental Science of Micro/Nano-Devices and System Technology,Chongqing University,Chongqing400044,PR Chinac Laboratory for Special Functional Materials,Henan University,Kaifeng475004,PR Chinah i g h l i g h t s g r a p h i c a l a b s t r a c tNiCo2O4nanosheets were decorated on b-MnO2nanowires by a facile and large-scale method.Theﬁrecracker core e shell architec-ture exhibited a high capacitance of 343F gÀ1.Excellent cycling stability:95% capacitance retention after3000 cycles.The asymmetric supercapacitor yiel-ded a maximum power density of 2.5kW kgÀ1.a r t i c l e i n f oArticle history:Received1April2014 Received in revised form18June2014Accepted22July2014 Available online30July2014Keywords:Spinel nickel cobaltate SupercapacitorsManganese oxides Electrochemical performance a b s t r a c tAn effective and rational strategy is developed for large-scale growth ofﬁrecracker-like Ni-substituted Co3O4(NiCo2O4)nanosheets on b-MnO2nanowires(NWs)with robust adhesion as high-performance electrode for electrochemical capacitors.The NiCo2O4e MnO2nanostructures display much higher spe-ciﬁc capacitance(343F gÀ1at current density of0.5A gÀ1),better rate capability(75.3%capacitance retention from0.5A gÀ1to8A gÀ1)and excellent cycle stability(5%capacitance loss after3000cycles) than Co3O4e MnO2nanostructures.Moreover,an asymmetric supercapacitor based on NiCo2O4e MnO2 NWs as the positive electrode and activated graphenes(AG)as the negative electrode achieves an energy density of9.4Wh kgÀ1and a maximum power density of2.5kW kgÀ1.These attractiveﬁndings suggest this novel core e shell nanostructure promising for electrochemical applications as an efﬁcient super-capacitive electrode.©2014Elsevier B.V.All rights reserved.1.IntroductionSupercapacitors are one class of energy storage systems that have attracted tremendous attention due to their superior advan-tages including high power/energy density,excellent cycling stability and fast charge/discharge capability[1].Compared with secondary batteries,supercapacitors can provide high power in short-term pulses and be used as peak power sources in hybrid electric vehicles,memory backup devices,and back-up supplies to protect against power disruption[2].On the basis of energy storage mechanism,there are two types of supercapacitors,namely elec-trical double-layer capacitors(EDLCs)and pseudocapacitors[3]. Recent research efforts have been made by exploiting novel elec-trode materials for supercapacitors with both high energy density and power density.Transition metal oxides,such as RuO2[4],MnO2*Corresponding author.College of Materials Science and Engineering,Chongqing University,Chongqing400044,PR China.Tel./fax:þ862365104131.E-mail address:zhangyuxin@(Y.X.Zhang).Contents lists available at ScienceDirect Journal of Power Sourcesjournal ho mep age:www.elsevi /locate/jpowsour/10.1016/j.jpowsour.2014.07.1440378-7753/©2014Elsevier B.V.All rights reserved.Journal of Power Sources270(2014)426e433[5,6,7,8],NiO[9],Co3O4[5,10,11]and TiO2[8,12,13,14],contribute pseudocapacitance,although most of them suffer from low abun-dance,high cost for their raw materials,low electrical conductivity, and poor rate capability and reversibility during the char-ge e discharge process.Recently,a ternary metallic oxide,spinel nickel cobaltite (NiCo2O4),has drawn much research interest[15,16,17,18,19].The higher electrochemical capacitive performances may mainly derive from the superior electrochemical activity of NiCo2O4.More signiﬁcantly,it is reported that NiCo2O4possesses a much better electronic conductivity,at least two orders of magnitude higher, and higher electrochemical activity than nickel oxides and cobalt oxides[20,21,22,23].For example,Wang and co-workers[23]ob-tained nickel cobaltite nanowires on carbon cloth with a speciﬁc capacitance of245F gÀ1at1A gÀ1.Liu et al.[16]reported that NiCo2O4@NiCo2O4core/shell nanoﬂake array showed a speciﬁc capacitance of1.55F cmÀ2at2mA cmÀ2.Jiang et al.[21]synthe-sized the hierarchical porous NiCo2O4nanowires which exhibited a speciﬁc capacitance of743F gÀ1at1A gÀ1.Very recently,rational design of multicomponent combination or mild methods has been applied to improve the speciﬁc capacitance of supercapacitors, which can provide the synergistic effect of all individual constitu-ents,as well as efﬁcient and rapid pathways for ion and electron transport(at their surfaces and throughout the bulk of the chemical distributions)[8,9,16].In addition,manganese oxides(MnO2), characterized by a low-cost material with a large theoretical ca-pacity,abundant and environmentally friendly nature,have attracted signiﬁcant interest as a promising alternative electrode material for supercapacitors[6,7,8].It has been reported that,one-dimensional nanomaterials can facilitate the electrical transport along the axial direction,while maintaining high external surface area and thus high capacitance at fast charging-discharging rates [4,6,9].To the best of our knowledge,there is little work on rational design ofﬁrecrackers-like NiCo2O4e MnO2NWs composite material for supercapacitors.In this work,we develop a cost-effective and simple strategy to design and fabricate novelﬁrecrackers-like NiCo2O4e MnO2NWs as an electrode for high-performance supercapacitors.The morphology,structure and electrochemical properties of the ﬁrecrackers-like NiCo2O4e MnO2NWs were investigated.Remark-ably,due to their1D nanoporous nanosheet microstructure and higher electrical conductivity compared with Co3O4e MnO2NWs, these NiCo2O4e MnO2NWs manifest a high speciﬁc capacity of 343F gÀ1,excellent cycling stability and high rate capability. Furthermore,an asymmetric supercapacitor device based on NiC-o2O4e MnO2//AG is assembled,which shows a maximum energy density of9.4Wh kgÀ1and a maximum power density of 2.5kW kgÀ1.2.Experimental2.1.Material synthesisAll reagents were of analytical purity and used without any further puriﬁcation.MnOOH NWs were prepared by a hydrother-mal method.In a typical procedure,a37mL suspension containing the297mg manganese dioxide,together with2mL ethanol was made.Then the solution was transferred into a50mL stainless-steel autoclave and heated at120 C for24h,and then naturally cooled down to room temperature.The products were collected by ﬁltration,washed with deionized water and ethanol,andﬁnally dried at60 C for12h.The obtained MnOOH NWs were re-dispersed into80mL of ethanol and sonicated for20min to reach good dispersion.Afterward, 1.0mmol nickel nitrate (Ni(NO3)2),2.0mmol cobalt nitrate(Co(NO3)2),2mmol ammonium ﬂuoride(NH4F)and5mmol urea were dissolved in80mL DI water to form a transparent pink solution.The above two solutions were then mixed and heated to90 C in an oil bath for8h.After the solution was cooled down to room temperature naturally,the product was collected through centrifugation and washed with DI water and ethanol for several times.The products were then dried, followed by annealing at300 C for2h with a slow heating rate of 1 C minÀ1in order to get well-deﬁned crystallized NiCo2O4e MnO2 NWs hybrid structure.For comparison,Co3O4e MnO2nano-structures were synthesized through a similar route and subse-quent annealing in air atmosphere.For the direct growth of Co3O4 nanosheets on MnO2NWs,single Co(NO3)2salt was added into the reaction solution instead of the Ni(NO3)2and Co(NO3)2.Except for the above parameters,the rest were the same as that of the syn-thesis of NiCo2O4e MnO2NWs.2.2.Materials characterizationThe crystallographic information of as-prepared products was established by powder X-ray diffraction(XRD,D/max1200,CuK a). The structure and morphology of the products were carried out with focused ion beam scanning electron microscopy(ZEISS AURIGA FIB/SEM)and transmission electron microscopy(TEM, ZEISS LIBRA200).Nitrogen adsorption e desorption isotherms were obtained using a micromeritics ASAP2020sorptometer.2.3.Electrochemical measurementsThe working electrode was prepared by mixing80%active ma-terials,10%carbon black,and10%polyvinylideneﬂuoride(PVDF)in N-methyl-2-pyrrolidone(NMP)and the slurry was spread onto a foam nickel current collector(1Â1cm2).The electrode was heated at120 C for10h to evaporate the solvent and then uniaxially pressed under10MPa.The electrochemical tests of various samples wereﬁrst conducted using a three electrode system in2M KOH using the CHI660E electrochemical workstation.The reference electrode was an Ag/AgCl electrode and counter electrode was a Pt plate.Typically,the loading mass of active material was around 2.8mg.The positive electrodes were investigated by cyclic vol-tammetry(CV)technique with varying the scan rate of 5e100mV sÀ1at potential between0and0.5V.Galvanostatic charge e discharge(GCD)experiments were performed with cur-rent densities ranged from0.5to8A gÀ1at a potential of0e0.43V. The electrochemical impedance spectroscopy(EIS)was conducted in the frequency range between100kHz and0.01Hz with a perturbation amplitude of5mV versus the open-circuit potential.For the tests with a two-electrode conﬁguration,two slices of electrode material with the same size were assembled together withﬁlter paper soaked in2M KOH solution before being con-nected to the potentiostat.In the two-electrode system,NiC-o2O4e MnO2NWs and activated graphenes(AG)were the positive electrode and negative electrode,respectively.CVs were recorded as scan rates of5,10,20,40,60and100mV sÀ1.GCD curves were obtained at constant current densities of0.25,0.5,1,2and4A gÀ1. All the operating current densities were calculated based on the total weight of NiCo2O4e MnO2NWs with AG.3.Results and discussion3.1.Structure and morphologyFig.1shows the composition and crystallite phase purity of the ﬁrecracker-like NiCo2O4e MnO2NWs.Almost all the identiﬁed peaks are indexed with the standard XRD pattern of spinel struc-ture NiCo2O4(JCPDS NO.20-0781,Space group:FÂ3(202),latticeM.Kuang et al./Journal of Power Sources270(2014)426e433427constants:a ¼b ¼c ¼0.811nm)and b -MnO 2(JCPDS NO.24-0735,tetragonal symmetry with P 42/nm space group and lattice con-stants of a ¼4.399nm and c ¼2.874nm).No characteristic im-purity peak is observed,indicating that the high-purity ﬁrecrackers-like NiCo 2O 4e MnO 2NWs are produced by the simple co-precipitation method.Furthermore,the composition and crys-tallite phase of the pure MnOOH NWs are examined by X-ray powder diffraction (See Supplementary information,SI-1).All of the re ﬂections of the XRD pattern can be readily indexed to a monoclinic phase MnOOH (manganite,JCPDS No:41-1379).As illustrated in Fig.2a,the pure MnOOH NWs are prepared by a hydrothermal method.Subsequently,the pure MnOOH NWs are immersed into the reaction solution containing Ni(NO 3)2,Co(NO 3)2,NH 4F and urea.During the following hydrothermal crystallization process,the hydrolysis e precipitation process of NH 4F and urea takes place,which forms the rudiments of ﬁrecracker-like Ni,Co e hydroxide e carbonate (See Supplementary information,SI-2a ).Deriving from the continuously proceeding reaction the rudiments of ﬁrecracker-like Ni,Co e hydroxide e carbonate were formed,andFig.2.(a)Schematic illustration of the synthesis of NiCo 2O 4e MnO 2NWs,(b)SEM image of pure MnOOH nanowires,(c)SEM image of the precursor,(d,e)low-magni ﬁcation and enlarged SEM images of the NiCo 2O 4e MnO 2NWs.Fig.1.XRD pattern of the NiCo 2O 4e MnO 2NWs.M.Kuang et al./Journal of Power Sources 270(2014)426e 433428then fully developed when the reaction time was prolonged(See Supplementary information,SI-2b and c).Moreover,increasing the reaction time to18h,the Ni,Co e hydroxide e carbonate is grown larger and the structure of nanowire is destroyed(See Supplementary information,SI-2d).Afterward,these precursor nanowires are annealed at300 C for2h,and NiCo2O4e MnO2NWs are obtained accordingly.Fig.2b shows SEM image of the pure MnOOH NWs.As shown in Fig2b,it can be seen that the large-scale and uniform features of the pure MnOOH NWs.The average diameter of the MnOOH NWs is range of100e150nm,and the length can reach tens of micrometers.Fig.2c shows that the hy-droxide precursors are uniformly grown on MnOOH NWs.As shown in Fig.2c,the every(Ni,Co)hydroxide precursor nanowires has uniform diameter of approximately1m m,which is much larger than that of pure MnOOH NWs.Moreover,theﬁrecracker-like Ni e Co e hydroxide e carbonate have an average diameter of 200nm and length up to around400nm.After heat treatment,the basic morphology of the sample is perfectly conserved without calcination-induced signiﬁcant alterations(Fig.2d and e).Inter-estingly,theﬁrecracker-like Co3O4e MnO2NWs are also obtained in the absence of Ni(NO3)2salt(See Supplementary information,SI-3 and SI-4).Moreover,we have done the experiment without MnO2 NWs while keeping all the other conditions the same.What we obtained was the pure NiCo2O4nanorods and Co3O4nanosheets, respectively(See Supplementary information,SI-5).The structural characteristics of the NiCo2O4e MnO2and Co3O4e MnO2NWs are further investigated by TEM(Fig.3).Both the NiCo2O4e MnO2NWs(Fig.3a)and Co3O4e MnO2NWs(Fig.3d) consist of numerous interconnected nanoparticles and present a mesoporous structure,which is ascribed to the successive release and lose of CO2and H2O during the thermal decomposition of precursor.It is well known that the mesoporous structures in nanosheets are important to facilitate the mass transport of elec-trolytes within the electrodes for fast redox reactions and double-layer charging/discharging.The porous structure will also greatly increase the electrode/electrolyte contact area,and thus further enhance the electrochemical performance.Fig.3b is an HRTEM image ofﬁrecracker-like NiCo2O4nanosheets.The spacing between adjacent fringes is~0.47nm,close to the theoretical interplane spacing of spinel NiCo2O4(111)planes.The selected area electron diffraction(SAED)pattern(Fig.3c)indicates the polycrystalline nature of the nanosheets,and the diffraction rings can be readily indexed to the(200),(311),(400),and(440)planes of the NiCo2O4 phase,which is consistent with the above XRD result.Fig.3e is an HRTEM image ofﬁrecracker-like Co3O4nanosheets.The lattice fringes show the structural characteristic of the cubic spinel Co3O4 crystal,in which the d-spacings of0.29and0.24nm correspond to the distance of the(220)and(311)planes,respectively.The SAED pattern shows well-deﬁned diffraction rings,suggesting their polycrystalline characteristics.The nitrogen adsorption and desorption isotherms of the NiC-o2O4e MnO2and Co3O4e MnO2NWs are shown in Fig.4.The N2 adsorption e desorption isotherm is characteristic of type IV with a type H3hysteresis loop which mostly corresponds to the presence of aggregated particles with slit shape pores[24,25,26,27].The Brunauer e Emmett e Teller(BET)surface area values of the NiC-o2O4e MnO2and Co3O4e MnO2NWs are calculated to be60.02and 35.24m2gÀ1,respectively.The pore size distribution of the sample calculated by desorption isotherm using Barret e Joyner e Halenda (BJH)method is shown in inset of Fig.4.The average pore diameters of NiCo2O4e MnO2and Co3O4e MnO2NWs are found to be in the mesopore region.However,the pore size distribution maximum of the samples are centered at nearly same pore radii,for NiC-o2O4e MnO2NWs,it is centered at3.67nm,for Co3O4e MnO2NWs at3.29nm.These results show that mesopores of nearly same sizes originate from the nanostructures.The intensities of the pore size distribution in NiCo2O4e MnO2NWs are slightly higher than that of Co3O4e MnO2NWs,suggesting higher pore volumeof Fig.3.TEM images of the NiCo2O4e MnO2NWs(a)and Co3O4e MnO2NWs(d),HRTEM images of the NiCo2O4e MnO2NWs(b)and Co3O4e MnO2NWs(e),SAED patterns of the NiCo2O4e MnO2NWs(c)and Co3O4e MnO2NWs(f).M.Kuang et al./Journal of Power Sources270(2014)426e433429NiCo 2O 4e MnO 2NWs.The pore volume of Co 3O 4e MnO 2NWs is calculated as 0.082cm 3g À1,while the pore volume of NiC-o 2O 4e MnO 2NWs is up to 0.139cm 3g À1.In conclusion,high surface area and large pore volume are achieved for NiCo 2O 4e MnO 2NWs,so it is expected that the NiCo 2O 4e MnO 2NWs may exhibit improved electrochemical performance compared to Co 3O 4e MnO 2NWs,and further electrochemical measurements have been carried out to prove this hypothesis.3.2.Electrochemical performancesIn order to compare the contribution of NiCo 2O 4and Co 3O 4to the electrochemical performance of the electrode materials,cyclic voltammetry (CV),galvanostatic charge e discharge (GCD)and electrochemical impedance spectroscopy (EIS)measurements in a three-electrode system are employed.Representative CV curves for the NiCo 2O 4e MnO 2and Co 3O 4e MnO 2NWs in three electrode con ﬁguration at different scan rates are shown in Fig.5a and b.As compared with CV curves of the NiCo 2O 4e MnO 2NWs,the Co 3O 4e MnO 2NWs has more distinct redox peaks.However,the area under the CV curve of the NiCo 2O 4e MnO 2NWs is clearly much larger than that of the Co 3O 4e MnO 2NWs at the same scan rate.It is well-known that the speci ﬁc capacitance is proportional to the area of the CV curve [10,28].Thus,the NiCo 2O 4e MnO 2NWs has higher capacitances than the Co 3O 4e MnO 2NWs.In order to investigate the capability of the materials,the GCD tests of the NiCo 2O 4e MnO 2and Co 3O 4e MnO 2NWs are carried out at different constant current densities (Fig.5c and d).The curve of NiCo 2O 4e MnO 2NWs is linear and symmetric,indicating an ideal capacitor capable of reversible charging and discharging [29,30].In comparison,the curve of Co 3O 4e MnO 2NWs is distorted to some extent.Low internal resistance is very favorable in energy storage devices,which reduces energy waste during charging/discharging processes [31,32].The increase in the charging time represents the higher capacitance of the NiCo 2O 4e MnO 2NWs.According to the GCD curves,the speci ﬁc capacitances of the electrodes are respectively calculated using the following equation [33]:C m ¼I D t m D Vwhere m ,I ,D t and D V are the weight (g)of the electroactive ma-terials,discharge current (A),the discharging time (s),and the discharging potential range (V),respectively.The speci ﬁc capaci-tances of NiCo 2O 4e MnO 2and Co 3O 4e MnO 2NWs are 343F g À1and 192F g À1at a current density of 0.5A g À1,respectively,which is much higher than the pure MnO 2NWs (14F g À1),NiCo 2O 4nano-rods (102F g À1)and Co 3O 4nanosheets (77F g À1)(See Supplementary information,SI-6).Maximizing the utilization of active materials is always considered as a challenge because only the surface of oxides can be utilized for charge storage.Up to now,the NiCo 2O 4-based electrodes with various substrates and nano-structure have been prepared to improve the utilization of NiCo 2O 4.Thus,the comparison of the speci ﬁc capacitance based on the mass of NiCo 2O 4(the mass of NiCo 2O 4was obtained by chemical anal-ysis)alone between this work and previous reports is summarized (See Supplementary information,Table S1).According to the comparison in Table S1,it can be obtained that the speci ﬁc capac-itance based on the in our work is 798F g À1,indicating that the speci ﬁc capacitance of ﬁrecracker-like NiCo 2O 4e MnO 2NWs nano-structure in this work can actually be higher than many NiCo 2O 4nanostructures-based supercapacitors previously reported.The speci ﬁc capacitance of NiCo 2O 4e MnO 2and Co 3O 4e MnO 2NWs electrodes at various current densities is shown in Fig.5e.We observe that the speci ﬁc capacitance for both electrodes decreases with an increase in the current density from 0.5A g À1to 8A g À1.This is a common phenomenon,caused by the insuf ﬁcient time available for ion diffusion at high current density [34].In addition,the NiCo 2O 4e MnO 2NWs maintains its 75.3%capacitance as the current density is increased from 0.5to 8A g À1,while the Co 3O 4e MnO 2NWs lose 30%of its capacity in the same condition,indicating that the NiCo 2O 4e MnO 2NWs have better rate capability,in good accordance with the CV tests.The EIS analysis has been recognized as one of the principal methods for examining the fundamental behavior of electrode materials,which not only provides useful information on the electrochemical frequency of the system but also allows for the measurement of redox reaction resistance and equivalent series resistance of the electrode [15,35].Typical Nyquist plots of the NiCo 2O 4e MnO 2and Co 3O 4e MnO 2NWs electrode are shown in Fig.5f.The two impedance spectra are composed of a semicircular arc in the high-frequency range and a straight line in the low-frequency range.The intersection of the plot at the x -axis repre-sents the solution resistance (R s ),which includes the following three terms:the resistance of the KOH aqueous solution,the intrinsic resistance of the electroactive materials and the contact resistance at the interface between electroactive materials and current collector [31,36].As can be seen from the inset,the calcu-lated R s values are 0.46and 0.48U for NiCo 2O 4e MnO 2and Co 3O 4e MnO 2NWs electrode,respectively,it's much lowerthanFig.4.Nitrogen adsorption and desorption isotherms for the NiCo 2O 4e MnO 2NWs (a)and Co 3O 4e MnO 2NWs (b).The insets show the corresponding BJH pore size distributions.M.Kuang et al./Journal of Power Sources 270(2014)426e 433430that of pure NiCo 2O 4and Co 3O 4(See Supplementary information,SI-7).At the high frequencies,semicircles can be observed for both with the diameters representing the charge-transfer resis-tance (R ct ).R ct can be directly measured from the Nyquist plots as the semicircular arc diameter.The calculated R ct values for NiC-o 2O 4e MnO 2and Co 3O 4e MnO 2NWs electrode are 0.8U and 1.6U respectively.The NiCo 2O 4e MnO 2NWs electrodes have a low R ct value compared with the Co 3O 4e MnO 2NWs electrode,resulting in an improved charge transfer performance for the electrode.The straight line in the low-frequency range is called the Warburg resistance (W),which is caused by the frequency dependence of ion diffusion/transport from the electrolyte to the electrode surface [37,38].As shown in Fig.5f,NiCo 2O 4e MnO 2NWs electrode has a smaller Warburg region,presenting a minor Warburg resistance.It implies that the highly porous NiCo 2O 4e MnO 2NWs electrode is able to facilitate the penetration of electrolyte,leading to fast diffusion of electrolyte into the pores of NiCo 2O 4[39].It can be seen that the slope of the straight line for NiCo 2O 4e MnO 2NWs electrode are much larger than that of the Co 3O 4e MnO 2NWs electrode.Thisobservation indicates that the NiCo 2O 4e MnO 2NWs electrode has much lower diffusive resistance than that of the Co 3O 4e MnO 2NWs.Long cycle life for the supercapacitors is an important parameter for their practical application.Supercapacitors should work steadily and safely,which requires the speci ﬁc capacitance of electrode ma-terials to change as little as possible.The relationship of the speci ﬁc capacitance and Coulombic ef ﬁciency against cycling number of the NiCo 2O 4e MnO 2NWs electrode is shown in Fig.6a.The speci ﬁc capacitance of NiCo 2O 4e MnO 2NWs electrode decreases gradually with increasing cycle numbers and its capacitance retention is 89.7%after 3000cycles.Such excellent cycling stability is mainly attributed to the following aspects.First,the synergistic contribution from NiCo 2O 4and MnO 2,both the ﬁrecracker-like NiCo 2O 4nanosheets and the MnO 2nanowires can have redox reactions with anions and cations from the electrolyte,respectively,accounting for the elec-trochemical charge storage.Second,the MnO 2nanowires provides a direct pathway for electron transport while the partial connected NiCo 2O 4nanosheets with high speci ﬁc surface area provide more electronic transmission channels (as schematically illustratedinFig.5.Electrochemical evaluations of the NiCo 2O 4e MnO 2and Co 3O 4e MnO 2NWs:(a,b)CV curves,(c,d)charge e discharge curves,(e)capacitances versus current densities,and (f)Nyquist plots (Insert show the enlarged part of Nyquist plots and equivalent circuit for the electrochemical impedance spectrum).M.Kuang et al./Journal of Power Sources 270(2014)426e 433431Fig.6b).Third,the ﬁrecracker-like NiCo 2O 4e MnO 2possess higher pore volume,which is probably more bene ﬁcial to double-layer capacitor.Furthermore,the more porous of ﬁrecracker-like NiC-o 2O 4e MnO 2also provides more channel for electrolyte.So the cycle performance can be enhanced by the fast ion diffusion in the one-dimensional nanoporous architecture.After long-term cycling,the ﬁrecracker-like NiCo 2O 4e MnO 2NWs are overall preserved with little structure deformation,as shown in Fig.6c and d.On the other hand,it is noted that the Coulombic ef-ﬁciency of the NiCo 2O 4e MnO 2NWs can maintain almost 93%after long-term cycling.These results demonstrate the as-prepared NiC-o 2O 4e MnO 2NWs are very stable as an active electrode material.By contrast,Co 3O 4e MnO 2NWs electrode lose 26.2%of its capacitance after 3000cycles with the same current density (See Supplementary Information,SI-8)and the structure of ﬁrecracker-like Co 3O 4e MnO 2NWs is slight destroyed after 3000cycles.The as-assembled NiCo 2O 4e MnO 2//AG asymmetric cell is measured at different potential windows in a 2M KOH aqueous electrolyte at a scan rate of 40mV s À1,and the resulted CV curves are exhibited in Fig.7a.The CV curves show a quasi-rectangular shape from 1.0V to 1.4V.At a potential window of 1.6V,the CV curve shows a distortion and a slight hump around 1.6V.This in-dicates that some irreversible reactions happen when the potential window is higher than 1.4V.Thus,the optimum working potential window for this asymmetric supercapacitor is from 0to 1.4V Fig.7b shows the typical CV curves of the asymmetric cell in the voltage window from 0to 1.4V at the scan rates of 5,10,20,50and 100mV s À1.The CV pro ﬁle of the asymmetric cell remains relatively quasi-rectangular at a high scan rate of 100mV s À1,demonstrating good charge/discharge properties and rate capability of the asym-metric supercapacitor [7,40].To further evaluate the electro-chemical performance of the asymmetric cell,galvanostaticFig.6.(a)Variation of capacitance with cycle number at 5A g À1,(b)schematic of the charge storage advantage of the NiCo 2O 4e MnO 2NWs,(c)and (d)SEM images of the NiCo 2O 4e MnO 2NWs before and after 3000cycles.Fig.7.(a)CV curves of the NiCo 2O 4e MnO 2//AG asymmetric supercapacitor cell measured at different potential windows in 2M KOH electrolyte,(b)CV curves of the NiC-o 2O 4e MnO 2//AG asymmetric supercapacitor cell measured at different scan rates,(c)charge e discharge curves of the NiCo 2O 4e MnO 2//AG asymmetric supercapacitor,(d)a Ragone plot of the NiCo 2O 4e MnO 2//AG asymmetric supercapacitor.M.Kuang et al./Journal of Power Sources 270(2014)426e 433432charge e discharge tests are performed.As shown in Fig.7c,these typical triangular-shape charge/discharge curves exhibit good symmetry and fairly linear slopes at different current densities, again demonstrating the ideal capacitive characteristic.The speciﬁc capacitance of the NiCo2O4e MnO2//AG asymmetric cell is calcu-lated to be31.3F gÀ1based on the total weight of the electrodes at a current density of0.25A gÀ1,and still maintains at24F gÀ1when the current density increases by as much as16times(4A gÀ1).To further illustrate the energy and power property of this asymmetric supercapacitor,a Ragone plot is shown in Fig.7.This device shows a high energy density of9.4Wh kgÀ1at a power density of 175W kgÀ1,while maintaining a high energy density of 5.8Wh kgÀ1at a power density of2500W kgÀ1.This result shows a much improved energy density at high power density compared with a Ni e Co oxide//AC asymmetric device(12Wh kgÀ1at 95W kgÀ1)[41],a MnO2-modiﬁed diatomites//MnO2-modiﬁed diatomites symmetric device(3.75Wh kgÀ1at250W kgÀ1)[42],a CNT//CNT symmetric device(6.1Wh kgÀ1at195W kgÀ1)[43],a NiO//carbon asymmetric device(~10Wh kgÀ1at30W kgÀ1)[44],a TiO2-CNT//CNT asymmetric device(4.47Wh kgÀ1at50W kgÀ1) [45],and a LiMn2O4//MnFe2O4asymmetric device(5.5Wh kgÀ1at 1080W kgÀ1)[46].4.ConclusionIn summary,to bypass the lower electrical conductivity by Co3O4e MnO2NWs electrode,we have successfully fabricated ﬁrecrackers-like NiCo2O4e MnO2NWs via the simple co-precipitation method followed by annealing in atmosphere.Elec-trochemical measurements reveal that the NiCo2O4e MnO2NWs electrode exhibits much higher speciﬁc capacitance and better rate capability compared with Co3O4e MnO2NWs electrode.Specif-ically,the NiCo2O4e MnO2NWs electrode displays a high speciﬁc capacitance of343F gÀ1at current density of0.5A gÀ1,excellent cycle stability with capacitance retention of89.7%at5A gÀ1after 3000cycles.Furthermore,the NiCo2O4e MnO2//AG asymmetric cell delivers an energy density of9.4Wh kgÀ1and a maximum power density of2.5kW kgÀ1,indicating a promising potential application as an effective candidate for supercapacitors.The superior capaci-tive performance of NiCo2O4e MnO2NWs electrode is attributed to the high electrical conductivity,short electron transporting path, with Ni-substitution and good contact.AcknowledgmentsThe authors gratefully acknowledge theﬁnancial supports provided by National Natural Science Foundation of China(Grant no.51104194),Doctoral Fund of Ministry of Education of China (20110191120014),No.43Scientiﬁc Research Foundation for the Returned Overseas Chinese Scholars,National Key laboratory of Fundamental Science of Micro/Nano-device and System Technol-ogy(2013MS06,Chongqing University),State Education Ministry and Fundamental Research Funds for the Central Universities (Project no.CDJZR12248801,CDJZR12135501,and CDJZR13130035, Chongqing University,PR China).Appendix A.Supplementary dataSupplementary data related to this article can be found at http:// /10.1016/j.jpowsour.2014.07.144.References[1]M.Huang,Y.Zhang,F.Li,L.Zhang,R.S.Ruoff,Z.Wen,Q.Liu,Sci.Rep.4(2014)3878,1e7.[2]Y.Liu,D.Yan,R.Zhuo,S.Li,Z.Wu,J.Wang,P.Ren,P.Yan,Z.Geng,J.PowerSources242(2013)78e85.[3] C.Liu,Z.Yu,D.Neff,A.Zhamu,B.Z.Jang,Nano Lett.10(2010)4863e4868.[4]M.-G.Jeong,K.Zhuo,S.Cherevko,W.-J.Kim,C.-H.Chung,J.Power Sources244(2013)806e811.[5]M.Huang,Y.Zhang,F.Li,L.Zhang,Z.Wen,Q.Liu,J.Power 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锰酸锂_碳纳米管复合电极的电化学特性_刘素琴

第36卷第9期2008年9月硅酸盐学报JOURNAL OF THE CHINESE CERAMIC SOCIETYVol. 36，No. 9September，2008锰酸锂/碳纳米管复合电极的电化学特性刘素琴，张建峰，黄可龙，于金刚，赵薇(中南大学化学化工学院，长沙 410083)摘要：以多壁碳纳米管(multi-walled carbon nanotubes，MWCNTs)作为正极材料导电剂制备了LiMn2O4/MWCNTs复合电极。

扫描电镜照片显示：MWCNTs形成三维网状结构并且均匀的分散在LiMn2O4活性颗粒之间。

以1C倍率进行充放电测试，质量分数分别为2%，5%和8% MWCNTs的正极材料首次放电容量为分别为96.0，105.5mAh/g和114.8mAh/g。

质量比为5%的乙炔黑(acetylene black，AB)电极放电容量为98.0mAh/g，说明MWCNTs能有效提高电极材料的电子电导率以及活性物质的利用率。

交流阻抗测试结果表明：电极过程中电荷传递电阻随MWCNTs含量的增加而减小，并由此计算得出相同导电剂含量的LiMn2O4/MWCNTs和LiMn2O4/AB复合电极的电荷传递活化能为27.5kJ/mol和32.3kJ/mol。

关键词：锂离子电池；复合电极；电化学性质；交流阻抗中图分类号：TM912.9 文献标识码：A 文章编号：0454–5648(2008)09–1319–06ELECTROCHEMICAL CHARACTERISTIC OF LiMn2O4/MULTI-WALLED CARBONNANOTUBES COMPOSITE ELECTRODELIU Suqin，ZHANG Jianfeng，HUANG Kelong，YU Jinggang，ZHAO Wei(College of Chemistry & Chemical Engineering, Central South University, Changsha 410083, China)Abstract: Composite anodes of LiMn2O4/multi-walled carbon nanotubes (MWCNTs) were prepared by mixing LiMn2O4 particles with MWCNTs as electric agent. The morphology was analyzed by scanning electron microscope, and LiMn2O4 particles were con-nected by MWCNTs to form a three-dimensional network wiring. Electron transport and electrochemical activity were improved ef-fectively by the web wiring structure. Galvanostatic charge/discharge tests at a rate of 1 C show that the initial discharge capacities are 96.0, 105.5mAh/g and 114.8mAh/g, respectively when the contents of MWCNTs are 2%, 5% and 8% compared to 98.0mAh/g with 5% acetylene black(AB). The electrochemical alternating current (AC) impedance spectroscopy results show that during the electro-chemical reaction process the charge transfer resistance decrease obviously with the increase of the content of MWCNTs. The activa-tion energy values of LiMn2O4/MWCNTs and LiMn2O4/AB composite cathodes with the same content of MWCNTs or acetylene black are calculated to be 27.5kJ/mol and 32.3kJ/mol, respectively according to electrochemical impedance spectra measurement at different temperatures.Key words: lithium ion battery; composite electrode; electrochemical character; alternating current impedance锂离子电池正极通常是半导体材料，其电子电导率(κ)在10–3～10–6 S/cm。

基于复合固体聚合物电解质的固态钠电池

第48卷第7期2020年7月硅酸盐学报Vol. 48，No. 7July，2020 JOURNAL OF THE CHINESE CERAMIC SOCIETY DOI：10.14062/j.issn.0454-5648.20200066 基于复合固体聚合物电解质的固态钠电池张强强1,2，苏醒1,2，陆雅翔1,2，胡勇胜1,2(1. 中国科学院物理研究所，北京 100190；2. 中国科学院大学，北京 100049)摘要：将钠离子导体Na-β’’-Al2O3作为活性填料引入聚氧化乙烯(PEO)/双(三氟甲基磺酰)亚胺钠(NaTFSI)固体聚合物电解质(SPE)中，得到有机–无机复合固体聚合物电解质(CPE)。

对SPE及CPE的相结构、相转变、离子电导率、离子迁移数及电化学稳定性等基础理化性质进行了表征分析，对两者在固态钠电池Na3V2(PO4)3@C||Na中的电化学性能进行了测试。

结果表明：Na-β’’-Al2O3的引入，有效提升了钠离子迁移数(SPE为0.19 ，CPE为0.71)和钠离子电导率(80℃时，SPE为1.65×10–4 S/cm，CPE为8.19×10–4 S/cm)。

基于CPE的固态钠电池表现出更加优异的循环稳定性，0.5C循环100周后容量保持率为93.9%，2.0C循环500周后容量保持率为74.0%。

关键词：聚氧化乙烯；双(三氟甲基磺酰)亚胺钠；固体聚合物电解质；复合固体聚合物电解质；钠电池中图分类号：TQ175 文献标志码：A 文章编号：0454–5648(2020)07–0939–08网络出版时间：2020–04–14A Composite Solid-state Polymer Electrolyte for Solid-state Sodium BatteriesZHANG Qiangqiang1,2, SU Xing1,2, LU Yaxiang1,2, HU Yongsheng1,2(1. Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;2. University of Chinese Academy of Sciences, Beijing 100049, China)Abstract: An organic-inorganic composite polymer electrolyte (CPE) was constructed via introducing an active filler of Na-β’’-Al2O3 into a solid-state polymer electrolyte (SPE) composed of poly(ethylene oxide) (PEO) and sodium bis(trifluoromethanesulfonyl)-imide (NaTFSI). The phase composition, ionic conductivity, Na+ transference number, and electrochemical stability were investigated. The electrochemical properties of SPE and CPE in Na||Na3V2(PO4)3@C solid-state sodium batteries were obtained. The results show that the CPE has a greater Na+ transference number of 0.71 than SPE (i.e., 0.19) and a higher Na+ conductivity of 8.19×10–4 S/cm than SPE (i.e., 1.65×10–4 S/cm) at 80℃. The CPE exhibits a superior cycling stability with capacity retentions of 93.9% after 100 cycles at 0.5C and 74.0% after 500 cycles at 2.0C in Na|CPE|Na3V2(PO4)3@C solid-state batteries.Keywords: poly(ethylene oxide); sodium bis(trifluoromethanesulfonyl)imide; solid-state polymer electrolyte; composite polymer electrolyte; sodium batteries随着社会的发展和对能源的巨大需求，人类对能源材料的开发不断增长。

电解浸出废旧锂电池中钴的热力学和动力学

电解浸出废旧锂电池中钴的热力学和动力学张建;满瑞林;徐筱群;贺凤;吴奇;尹晓莹【摘要】Cobalt in spent lithium-ion battery was leached out in sulfuric acid using the cathode bar as cathode and lead plate as anode. And the process was studied in thermodynamics and dynamics two aspects. The results show that LiCoO 2 is reductive leached Co2+by Co(OH)3through compared experiments and thermodynamic data. Through theoretical analysis and experimental research, the process is controlled by chemical reaction process of shrinking core model in the early 5-30 min, leaching rateα and timet satisfy inner diffusion the unreacted core shrinking model equation 1-(1-α)1/3=Kt, apparent activation energy is 7.32 kJ/mol. The middle stage is hybrid control. And the last conforms with the internal diffusion mod el, whereα andt suit to 1-2α/3-(1-α)2/3=Kt, and the apparent activation energy is 17.05 kJ/mol. Al3+ in leach solutions comes from aluminium oxide dissolved in liquid without protection. The cathode material peeled from aluminum foil is related to the dissolution of aluminium oxide, which affects the leaching rate of cobalt.%以废旧锂电池正极条为阴极，以铅板作阳极，在稀硫酸溶液中，电解浸出正极材料中的钴，从热力学和动力学两方面对钴的电解浸出过程进行研究。

溶剂热法合成硫化铜及其电化学性能

溶剂热法合成硫化铜及其电化学性能杜奉娟;张颖;刘军【摘要】以乙醇为溶剂,二水氯化铜为铜源,硫代乙酰胺为硫源,采用超声辅助溶剂热法制备了花状形貌的硫化铜微球.利用X射线衍射光谱(XRD)、扫描电子显微镜(SEM)对其结构和形貌进行了表征,利用循环伏安法(CV)、恒倍率充放电测试研究了其电化学性能,并分别讨论了反应温度和反应时间对材料结构、形貌及电化学性能的影响.研究表明:140℃、20 h条件下制备的花状微球结构硫化铜的首次放电比容量为662 mAh/g,充电比容量为499 mAh/g,库仑效率为75％.【期刊名称】《电源技术》【年(卷),期】2015(039)006【总页数】3页(P1263-1265)【关键词】硫化铜;溶剂热法;花状微球;电化学性能【作者】杜奉娟;张颖;刘军【作者单位】河北工业大学化工学院,天津300130;河北工业大学化工学院,天津300130;河北工业大学化工学院,天津300130【正文语种】中文【中图分类】TM912.9硫化铜因其较高的理论比容量(560 mAh/g)和良好的电导率(10－3S/cm)，是最具发展潜力的锂离子电池负极材料之一[1]，也是锂硫二次电池所用硫系电极材料的研究热点之一。

近年来，利用模板法[2]、微波辐射法[3]、原位法[4]等方法成功制备了多种形貌的硫化铜微纳米材料。

在这些制备方法中，溶剂热法因对设备要求低、工艺简单，制备的材料纯度高，材料的形貌和颗粒大小可控等优点而备受研究者的青睐。

本文以氯化铜和硫代乙酰胺为原料，采用超声辅助的溶剂热法，以较低的能耗、简单的工艺直接制备得到了形貌新颖的纳米花状硫化铜，利用X射线衍射光谱(XRD)、扫描电子显微镜(SEM)对产物的组成结构和物理形貌进行了表征，并考察了不同反应温度、反应时间对产物的结构、形貌和电化学性能的影响。

1 实验1.1 材料的制备将5 mmol CuCl2·2 H2O(99.9%)加入到70 mL乙醇(分析纯)中，超声10 min以使CuCl2·2 H2O完全溶解。

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JournalofPowerSources190(2009)154–156ContentslistsavailableatScienceDirectJournalofPowerSources

journalhomepage:www.elsevier.com/locate/jpowsourShortcommunicationExpansionandshrinkageofthesulfurcompositeelectrodeinrechargeablelithiumbatteries

XiangmingHe∗,JianguoRen,LiWang,WeihuaPu,ChangyinJiang,ChunrongWanInstituteofNuclear&NewEnergyTechnology,TsinghuaUniversity,Beijing100084,PRChina

articleinfoArticlehistory:Received20May2008Receivedinrevisedform10July2008Accepted16July2008Availableonline25July2008Keywords:SulfurcompositecathodeRechargeablelithiumbatteriesElectrodeexpansionandshrinkageabstractTheexpansionandshrinkagecharacteristicsofsulfurcompositecathodeelectrodeinrechargeablelithiumbatterieshavebeeninvestigated.Itwasfoundthatthesulfurcompositeselectrodesexpandedwhendischargingandshrankwhenchargingagain.Thethicknesschangeoftheelectrodewasmeasuredtobeabout22%.Thethicknessoflithiummetalanodeswasalsochangedwhenlithiumdepositionanddissolution,whilethesulfurcompositeselectrodesexpandedandshrankconversely.Theinvestigationshowedthatthethicknesschangesoflithiumanodeandsulfurcompositecathodecouldbecompensatedwitheachothertokeepthetotalthicknessofthecellnottochangesomuch.©2008ElsevierB.V.Allrightsreserved.

1.IntroductionThesulfur-basedcathodematerialsareattractiveforlithiumbatteriesduetotheirlargespeciﬁccapacity,abundantresourcesandlowcost,showinggreatpotentialforthenextgenerationofhigh-performancelithiumbatteries[1–4].Recently,Wangetal.[5–12]reportedthatthesulfurcomposites,whichwerepreparedbysulfurizationofpolyacrylonitrilewithele-mentalsulfur,showednovelperformancescomparedtoelementalsulfurcathodeandeffectivelyovercametheproblemsoccurringinsulfurelectrodes.Thesulfurcompositepresentedhighspe-ciﬁccapacityover800mAhg−1andexcellentcycleability[5–16],showingthatthesulfurcompositewasanalternativepromisingcandidatecathodematerialforhigh-performancecells.Thepro-totypepolymercellwiththesulfurcompositecathodematerialpresentedtheenergydensityof246Whkg−1and401WhL−1[14].Theratecapabilityofthesulfurcompositesandthecyclecharacter-isticsatdifferenttemperatureswereinvestigatedforrechargeablelithiumcells[13,15],demonstratingthatthelithiumcellswiththesulfurcompositecathodescanbeoperatedabove−20◦Candatahighcurrentdensity.Thedischargecapacityofthesulfurcompositecathodematerialincreasedasthetemperatureincreasefrom−30to60◦C.Itpresentedthedischargecapacityof854and632mAhg−1at60and−20◦C,respectively.Thedischargecapacityofthesul-∗Correspondingauthor.Tel.:+861089796073;fax:+861089796031.E-mailaddresses:hexm@tsinghua.edu.cn,hexiangming@tsinghua.org.cn(X.He).furcompositecathodematerialdecreasesasthecurrentdensityincrease.Itpresentsthedischargecapacityof792and604mAhg−1

atthecurrentdensityof55.6and667mAg−1,respectively.Thenovelchargeanddischargecharacteristicsoflithiumcellswithsulfurcompositecathodeswasrevealed[14],showingthatthesul-furcompositepresentedtwodischargevoltageplateausof2.10and1.88V,andtwochargevoltageplateausof2.22and2.36V,via.Li+/Li.Theoverchargetestsdemonstratedthatthesulfurcom-positehadtheintrinsicsafetyforoverchargeoflithiumcells.Thesulfurcompositehadgoodreversiblecapacityafteritwasdeeplydischargedevento0V.Itshowedstablecycleabilityandhighcyclingcapacityof1000mAhg−1whencyclingbetween0.1and3.0V.Inaddition,thelithiumionbatteriesarefoundtobestruc-turallyanddimensionallydynamic[17].Thebatteriesgenerallyexpandduringchargeandcontractduringdischarge.Thisthick-ness,thusvolume,changeiscausedbylithiumionintercalationintohostmaterials,i.e.graphiteandlithiumtransitionmetaloxideandresultantlatticeexpansionandcontraction[18–22].Expan-sionofcarbonmaterialsisobservedtobemuchmoresigniﬁcantthanlithiumcobaltoxide(LiCoO2)[20].Forcarbons,thedegreeofexpansiongreatlyvariesdependingonthestructure.Forexample,naturalgraphiteshowsalmostthreetimesgreatervolumechangethanMCMB[23–25].Quantitativelyabout10%increase[18].Theexpansioncharacteristicoftheelectrodeisofimportantfactorforthebatteryassembly.However,volumechangeofthesulfurcom-positeduringcyclingisstillunknown.Inthisstudy,theexpansionandshrinkagecharacteristicsofthesulfurcompositeelectrodewasprimarilyinvestigated.