High performances of ultrafine and layered LiCoO2 powders for lithium batteries by a novel sol–gel

Journal of Alloys and Compounds 496 (2010) 703–709

Contents lists available at ScienceDirect

Journal of Alloys and

Compounds

j o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /j a l l c o

m

High performances of ultra?ne and layered LiCoO 2powders for lithium batteries by a novel sol–gel process

Chongqiang Zhu a ,Chunhui Yang a ,Wein-Duo Yang b ,?,Ching-Yuan Hsieh c ,Huei-Mei Ysai c ,Yun-Sheng Chen b

a

Department of Applied Chemistry,Harbin Institute of Technology,Harbin 150001,PR China

b

Department of Chemical and Materials Engineering,National Kaohsiung University of Applied Sciences,Kaohsiung 807,Taiwan c

Materials &Electro-Optics Research Division Battery Section,Chung-Shan Institute of Science &Technology,Lung-Tan,Tao-Yuan 325,Taiwan

a r t i c l e i n f o Article history:

Received 2February 2009

Received in revised form 21February 2010Accepted 27February 2010Available online 6 March 2010Keywords:LiCoO 2

Lithium-ion batteries Sol–gel method

Calcination temperature Calcination time

a b s t r a c t

LiCoO 2powders are rapidly becoming important cathode materials in commercial lithium-ion batteries because of their excellent properties.In the present work,LiCoO 2powders were prepared using a novel sol–gel method with citric acid as a chelating agent,hydroxypropyl cellulose as a dispersant agent and LiNO 3,Co(NO 3)2·6H 2O as starting materials.The effects of calcination temperature and the calcination time on the structure and morphology of LiCoO 2powders were characterized by X-ray diffraction,Raman spectroscopy and scanning electron microscopy.According to the analysis,the crystallinity of LiCoO 2powders depends on the calcination temperature and calcination time.The results indicate the layered,pure and ultra?ne HT-LiCoO 2powders can be obtained at 700?C for 4h in air.After 25cycles,the electrode demonstrates the charge/discharge capacities at 175and 154mAh/g,respectively,which will be suitable for high capacity cathode materials in rechargeable lithium-ion batteries.

? 2010 Elsevier B.V. All rights reserved.

1.Introduction

Secondary lithium batteries have been studied since 1970s because they have the highest speci?c energy of the rechargeable batteries [1,2].However,the safety and recharge ability problems associated with using lithium metal as the anode have limited their wide and practical development [3,4].Recently,outstand-ing progress in the development of lithium-ion batteries has been made by overcoming the safety limitations.The mechanism of lithium-ion batteries occurs by lithium-ion insertion or removal from the anode and cathode,which are made of intercalation com-pounds during the recharge process.The repeated process works just like a rocking-chair,so the lithium-ion batteries are also called “rocking-chair lithium”batteries [5].

As far as the lithium-ion batteries are concerned,the capacity of the anode materials is far higher than the cathode materials [6].Thus,to increase the energy density of the lithium-ion batteries,it is important to look for the suitable cathode materials ?rst,and then to promote the capacity of the cathode materials.According to the comparative search,LiCoO 2[7],LiNiO 2[8],and LiMn 2O 4[9]are the most attractive candidates for the high capacity cathode

?Corresponding author.Tel.:+88673814526x5111;fax:+88673830674/3838149.

E-mail address:ywd@https://www.360docs.net/doc/ed2783327.html,.tw (W.-D.Yang).

materials considered for today’s lithium-ion battery https://www.360docs.net/doc/ed2783327.html,pared with other materials,LiCoO 2displays several predom-inant characteristics [10],such as high capacity,good safety,long cycle life,high speci?c energy,low self-discharge,and a wide range of working temperatures.Therefore,LiCoO 2is the most used and promising material for commercial lithium-ion batteries among these compounds [11].

Due to the different synthesis temperature,LiCoO 2displays two distinct phases,namely,the standard high-temperature phase (HT-LiCoO 2)having a layered structure with a space group of R3m,and a low-temperature phase (LT-LiCoO 2)having a spinel structure with a space group of Fd3m [12].The two structures have the same oxy-gen sublattice and are distinguished by the spatial arrangement of cations.However,because of the well-developed layered structure,HT-LiCoO 2has better electrode characteristics than LT-LiCoO 2[13].Therefore,HT-LiCoO 2is favored in present commercial lithium-ion batteries.

Commercial LiCoO 2powders are usually prepared by the solid-state reaction [14,15],but the method has several disadvantages which could affect the electrode activity [16].The sol–gel process is considered an adapted method for LiCoO 2powder prepa-ration [17,18].The method requires a much lower calcination temperature and shorter calcination time than the solid-state reaction,and most of all,LiCoO 2powders prepared by the method could achieve a higher energy capacity and longer life cycle.

0925-8388/$–see front matter ? 2010 Elsevier B.V. All rights reserved.doi:10.1016/j.jallcom.2010.02.178

704 C.Zhu et al./Journal of Alloys and Compounds496 (2010) 703–709

During the novel sol–gel preparation process,there are several factors in?uencing the structure and morphology of LiCoO2pow-ders.We adopted the sol–gel method to prepare LiCoO2powders in this paper.To obtain the crystalline phase,pure phase,and ultra-?ne LiCoO2powders,the two main factors,calcination temperature and calcination time,in?uencing the structure and morphology of LiCoO2powders were investigated in detail.Also,the electrochem-ical properties of the LiCoO2materials were studied.

2.Experimental

2.1.Preparation of LiCoO2powders

LiCoO2powders were prepared by using the novel sol–gel technique using the following high-purity starting materials:LiNO3(SHOWA,99.5%)and Co(NO3)2·6H2O (Baker,99.8%)as metal ion sources,deionized water as a solvent,citric acid (C6H8O7·H2O,Riedel-de Haen,99.5%)as a chelating agent and hydroxypropyl cellu-lose(ALDRICH,M=105)as a dispersant agent.First,the sol was formed at60?C by mixing LiNO3and Co(NO3)2·6H2O with citric acid,and then a small amount of hydroxypropyl cellulose(Li:Co:C6H8O7·H2O=1:1:2molar ratio,[hydroxypropyl cellulose]=5×10?4mol L?1)was added to the deionized water.Then,the sol was evaporated at120?C in a dry oven until the gel was formed.Finally,LiCoO2powders were obtained by calcining the dried gel precursors in air at various temperatures between300and900?C for a few hours.

2.2.Characterization

The thermal behavior of the gel precursors was examined by thermogravimetric analysis and differential thermal analysis(TGA/DTA,Du Pont,SDT2960)performed at a heating rate of10?C min?1up to1000?C in air.The crystalline phase of LiCoO2 powders was identi?ed by powder X-ray diffraction(XRD,Rigaku,Rint-2000)using Cu K?line at the scanning rate of4?min?1from15?to80?.The particle structure of LiCoO2powders was characterized by Raman spectroscopy(Raman,RENISHAW, inVia).The particle morphology of LiCoO2powders was observed by scanning elec-tron microscopy(SEM,JEOL,TFSEM-6330).

2.3.Electrochemical properties measurement

The mixture containing85wt%LiCoO2powder,10wt%carbon black,and5wt% poly(vinylidene?uoride)(PVDF)were well mixed with appropriate amounts of alco-hol,and then pressed onto aluminum foils calcined at250?C for4h to serve as the cathode.The electrochemical cells were then assembled in an Ar?lled glove box using foils of Li metal as counter electrodes.Further,1M LiPF6(electrolyte)con-taining a solution of ethylene carbonate(EC)and diethylene carbonate(DEC)(1:1in weight)was utilized as an electrolyte.However,the electrochemical measurements were performed in the voltage range3.0–4.2V with a potentiostat or constant cur-rent density using a galvanostatic charge/discharge cycler at a current rate of0.1C (corresponding to27.4mA/g-LiCoO2)for25cycles.Furthermore,a certain sample, after the?rst cycle,was washed several times by deionized water to remove the absorbed lithium ions completely,and then the electrode was dissolved in the2M HCl solution.The contents of Li and Co were characterized by atomic absorption spectroscopy(AA).

3.Results and discussion

The thermal decomposition behavior of the gel precursors was measured by TGA/DTA.The calcination temperature of the gel pre-cursors could be roughly estimated from the results of TGA/DTA. Fig.1shows the TGA/DTA curves of the gel precursors.There are three discrete weight loss regions in the TGA curve,and the weight loss is terminated at400?C.The initial weight loss region at below 200?C is due to the evaporation of the residual water.The secondary weight loss region at200–320?C,corresponding to the weak peak of the exothermic reaction around260?C in the DTA curve,occurred because of the decomposition of citric acid and nitrates.The last weight loss region occurring at320–400?C,corresponding to the large peak of the exothermic reaction around350?C in the DTA curve,was due to the combustion of the residual organic con-stituents.There is no weight loss above400?C,suggesting that the formation of LiCoO2powders begins at that temperature.

There are two essential factors in?uencing the structure and morphology of LiCoO2powders,the calcination temperature and https://www.360docs.net/doc/ed2783327.html,ing the following techniques to examine the relationship between the calcination temperature and time and the

structure

Fig.1.TGA/DTA curves of the precursors.

and morphology of LiCoO2powders,we could obtain the optimum conditions for preparing ultra?ne LiCoO2powders.

Fig.2shows the XRD patterns of LiCoO2powders calcined at various temperatures for4h in air.When LiCoO2powders are calcined at300–500?C,a signi?cant amount of LT-LiCoO2phase peaks and a small amount of impurity peaks occur in the patterns. For LiCoO2powders calcined at600?C,pure layered phase HT-LiCoO2powders are formed,because the(006)/(012)peaks and the(108)/(110)peaks are clearly appear[19].The crystallinity of HT-LiCoO2powders increases with increasing calcination temper-ature,as indicated by the distinct separation of(006)/(012)peaks and the good symmetry of(108)/(110)peaks.The intensity ratio of the(003)peak to the(104)peak,i.e.,I(003)/I(104),is generally used to examine the crystallinity of LiCoO2powders[20].The higher the I(003)/I(104)value,the better the layered structure of LiCoO2pow-ders.The I(003)/I(104)ratios of LiCoO2powders calcined at600,700, 800,and900?C for4h are1.32,1.39,1.43,and1.25,respectively. Thus,as the calcination temperature is increased,the I(003)/I(104) value is increased.But for900?C,the rule is the antinomy.The cal-cination temperature(900?C)is so high that a small amount of Li is volatilized,resulting in a slightly distorted layered structure.

The vibration modes of layered HT-LiCoO2and spinel LT-LiCoO2 are obtained by factor group analysis[21].The total vibration modes of layered HT-LiCoO2are A1g+E g+2A2u+2E u,where A1g and E g modes are Raman active,and2A2u and2E u modes are IR active.The total vibration modes of spinel LT-LiCoO2

are

Fig.2.X-ray diffraction patterns of LiCoO2powders calcined at various temper-atures:(a)300?C,(b)400?C,(c)500?C,(d)600?C,(e)700?C,(f)800?C,and(g) 900?C.

C.Zhu et al./Journal of Alloys and Compounds496 (2010) 703–709

705

Fig.3.Raman spectra of LiCoO2powders calcined at various temperatures:(a) 300?C,(b)400?C,(c)500?C,(d)600?C,(e)700?C,(f)800?C,and(g)900?C.

A1g+E g+2F2g+5F1u,where A1g,E g and2F2g modes are Raman active,and5F1u mode is IR active.So,two Raman bands for layered HT-LiCoO2and three Raman bands for spinel LT-LiCoO2should be observed in the Raman spectra.Fig.3shows the Raman spectra of LiCoO2powders calcined at various temperatures for4h in air. When LiCoO2powders were calcined at300–500?C,three Raman bands are observed at481,591and678cm?1,suggesting that LiCoO2powders have a spinel structure,i.e.,LT-LiCoO2powders. For LiCoO2powders calcined at600?C,the Raman band located at 678cm?1disappears and only two Raman bands are observed at 481and591cm?1,implying that LiCoO2powders have a layered structure,i.e.,HT-LiCoO2powders.The intensity of the two Raman bands is stronger with an increasing calcination temperature.

To observe the particle size and shapes of LiCoO2powders, SEM observations were carried out.Fig.4shows the SEM micro-graphs of LiCoO2powders calcined at various temperatures of4

h Fig.5.X-ray diffraction patterns of LiCoO2powders calcined at600?C for(a)2h, (b)4h,(c)8h,and(d)16h.

in air.LiCoO2powders composed of monodispersed spherical par-ticulates with an average particle size of roughly40–60nm were obtained for600?C calcined LiCoO2powders.As the calcination temperature is sequentially increased,the size of the particulates also increases with more irregular shapes.The growth kinetics are favored at a high temperature,and thus the agglomerated spherical particles change to larger and more irregular particulates.

Summarizing the results of XRD,Raman and SEM,the optimum calcination temperature of4h in air to obtain the ultra?ne HT-LiCoO2powders is600?C.Next,the calcination time was varied to determine the optimum calcination time at600?C to obtain the ultra?ne HT-LiCoO2powders.

The XRD patterns of LiCoO2powders calcined at600?C for2, 4,8and16h in air are shown in Fig.5.The I(003)/I(104)ratios of LiCoO2powders calcined for2,4,8and16h are1.18,1.32,1.30 and1.27,respectively.Thus,as the calcination time is

increased, Fig.4.Scanning electron micrographs of LiCoO2powders calcined at various temperatures:(a)600?C,(b)700?C,(c)800?C,and(d)900?C.

706 C.Zhu et al./Journal of Alloys and Compounds

496 (2010) 703–709

Fig.6.X-ray diffraction patterns between18?and20?for(a)2h,(b)4h,(c)8h,and (d)16h.

the I(003)/I(104)value is decreased.However,except for2h,the layered LiCoO2powders are not completely formed.LiCoO2pow-ders calcined for4h have the largest I(003)/I(104)value.There is a clear distinction between18?and20?in the XRD patterns,as shown in Fig.6.The peak located at18.9?represents the layered LiCoO2phase while the peak located at19.2?represents the spinel LiCoO2phase[22].When LiCoO2powders are calcined for2,8and 16h,the two peaks are observed in the patterns.This means the LiCoO2powders are impure,including both the layered and spinel phases.The Li2[Co2]O4structure is a relatively more stable phase of the lithiated-spinel structure than the layered LiCoO2structure. For LiCoO2powders calcined for4h,the peak located at19.2?dis-appears and only one peak occurs at18.9?.This suggests LiCoO2 powders are pure layered phase.

The Raman spectra of LiCoO2powders calcined at600?C for2,4, 8and16h in air are presented in Fig.7.When LiCoO2powders

are Fig.7.Raman spectra of LiCoO2powders calcined at600?C for(a)2h,(b)4h,(c) 8h,and(d)16h.

calcined for2h,there are four Raman bands in the spectrum.Three Raman bands located at474,587and672cm?1suggest LiCoO2 powders have a spinel structure.The fourth Raman band,located at 508cm?1belongs to Co3O4.When LiCoO2powders are calcined for 8and16h,three Raman bands are noted at474,587and672cm?1, implying the LiCoO2powders have a spinel structure.For LiCoO2 powders calcined for4h,only two Raman bands are noted at474 and587cm?1,indicating the LiCoO2powders have a layered struc-ture.

The SEM micrographs of LiCoO2powders calcined at600?C for 2,4,8and16h in air are given in Fig.8.When LiCoO2powders were calcined for2h,the powders resemble?ocks containing less dispersed irregular particulates.This implies the layered LiCoO2 powders are not completely formed.The LiCoO2powders calcined for4h consist of monodispersed spherical?ne particulates with an average particle size of about60–80nm.As the calcination time is increased to8or16h,the size of the particulates also

increases Fig.8.Scanning electron micrographs of LiCoO2powders calcined at600?C for(a)2h,(b)4h,(c)8h,and(d)16h.

C.Zhu et al./Journal of Alloys and Compounds496 (2010) 703–709

707

Fig.9.Cyclic voltammetry results of the electrodes manufactured from LiCoO2pow-ders obtained at various temperatures.

with more irregular shapes.The results display substantial particu-lates agglomeration due to the increased growth of calcined LiCoO2 powders upon calcination for a long time.These observations show LiCoO2powders calcined for4h have better crystallinity than the powders calcined at other time intervals.

The cyclic voltammetry(CV)results of the electrodes manufac-tured from LiCoO2powders obtained at600,700and800?C were examined in the potential range from4.3to3.0V as shown in Fig.9.It is clear as the LiCoO2calcination temperatures increase, the current intensity of the well de?ned oxidation/reduction peaks decrease as well as the separation of the two peaks,revealing the reversibility decreasing of the material upon deintercalation and intercalation of Li+ions[23].

For the700?C calcined LiCoO2electrode,well de?ned oxidation and reduction peaks are noted at4.05and3.85V,respectively,sep-arated by200mV,and accompanying a highest intensity of current, clearly illustrating the relatively better reversibility for the Li+ions during the C–V analyses.

In contrast,the LiCoO2calcined at800?C revealed a much greater fraction of layered structure(by XRD and Raman stud-ies)despite the particle size increasing signi?cantly.Therefore,the LiCoO2material displays broader oxidation and reduction peaks located at4.15and3.85V with a difference between the peak potentials above300mV.These features show the800?C LiCoO2 is a less oxidizing system than the600and700?C compounds,and is characterized by a lower degree of reversibility.

The?rst run charge/discharge capacity of the electrodes man-ufactured from LiCoO2powders calcined at various temperatures is shown in Fig.10.The particle sizes of LiCoO2powders calcined at various temperatures600,700and800?C were40–60,120–150 and200–350nm,respectively.Clearly,the discharge capacity of the?rst cycle shows the highest value for the LiCoO2obtained at700?C.This highest speci?c capacity could be attributed to the best combination of smaller size and greater fraction of lay-ered structure of HT-LiCoO2,resulting in the fastest rate for the Li+insertion/deinsertion process[24].The maximum value of the charge/discharge capacity at the?rst discharge capacity of the elec-trode prepared by LiCoO2powder calcined at700?C was196and 175mAh/g,respectively.

Fig.11shows the electrode performances examined at0.1C in25 cycles of LiCoO2calcined at700?C for4h.As seen from this?gure,it indicates that the coulombic ef?ciency(discharge-to-charge capac-ity ratio)of the?rst cycle is about89.3%,but the charge–discharge ef?ciency is improved markedly at about94–96%after the sec-ond cycle.Additionally,the coulombic ef?ciency during25

cycles’Fig.10.The?rst run charge/discharge capacity of the electrodes manufactured from LiCoO2powders obtained by various calcination temperatures for4h:(a)600?C,(b) 700?C,and(c)800?C.

charge–discharge of LiCoO2electrode is higher than that of95%, usually.Furthermore,on increasing the cyclic number,the cyclic capacity decay is moderate.At the current of0.1C,the cathode material showed the initial charge and discharge capacity of196 and175mAh/g,and retention of164mAh/g(83%)and154mAh/g (88%)after25cycles,respectively.

Garcia et al.reported that a polymer?lm can be obtained from the reaction of electrolyte with the strong oxidizing agent Co4+, on the surface of the LiCoO2electrode,which would include the slow lithium diffusion through this additional solid phase[25].The oxide?lm affects the resistance component of the impedance at the electrode/electrolyte interface.The electrolyte system showing the higher interface resistance gave the lower discharge capacity after the?rst

cycle.

Fig.11.The electrode performances examined at0.1C in25cycles of LiCoO2calcined at700?C for4h.

708 C.Zhu et al./Journal of Alloys and Compounds496 (2010) 703–709

Table1

Chemical analysis of the LiCoO2powders calcined at the various temperatures for4h in air.

Temperature(?C)Analytical value(wt%)Molar ratio(mol.%)Approximate chemical composition Li Co Li Co

600 6.8057.16 1.01 1.00Li1.01CoO2(with Co3O4)

700 6.4658.980.98 1.00Li0.98CoO2(with Co3O4)

800 6.4657.750.95 1.00Li0.95CoO2

900 6.318.930.91 1.00Li0.91CoO2

Lithium and cobalt contents of the LiCoO2powders calcined at various temperatures were measured by AA as listed in Table1.It indicates that the molar ratio of lithium and cobalt in the LiCoO2 powders,calcined at600–700?C,was very close to the original design of starting materials at1:1.As calcined temperature above 800?C,a relatively small amount of lithium was examined,because the evaporation of lithium during calcination at high temperature. It results the molar ratio of Li/Co deviated from the stoichiometric ratio of1in the?nal LiCoO2powders.

With further?ring at900?C,a highly crystallized HT-LiCoO2 without any minor phases was obtained.Nevertheless,the inten-sity ratio of the(003)/(104)peaks is reduced markedly(by XRD).It reveals that the LiCoO2powders obtained at the high temperature contained a less layered structure,and demonstrated that some cations reacting into the LiCoO2structure originate from the loss of lithium content during the calcination.

The as-prepared LiCoO2in size of120–150nm with high fraction of layered structure was obtained at700?C.However,the phase of Co3O4existed in the powder was identi?ed by the Raman spec-trum.It reveals that x value in Li1?x CoO2should be smaller than the calculated value(based on the charge capacity)of0.71,and demon-strating that the structure of Li1?x CoO2,after the?rst cycle of charge and discharge will exhibit a stable structure containing more Li in Li1?x CoO2structure than the calculated value,Li1–0.71CoO2.Never-theless,the precision fraction of Co3O4in the LiCoO2electrode has not been identi?ed in the study.

The ultra?ne size and layered structure of LiCoO2electrode exhibit a high value of charge and discharge capacity during the ?rst cycle.Nevertheless,the ultra?ne sized LiCoO2will be facile to produce a?lm on the electrode surface during the?rst cycle,and resulting in decreasing the capacity after the?rst cycle.

The in?uence of the electrolyte on the electrode process of LiCoO2was investigated by an https://www.360docs.net/doc/ed2783327.html,plex-plane impedance plots,Cole–Cole plots,of the various conditions of electrode/electrolyte are shown in Fig.12.The difference in the electrolyte conductivity of the solution is primarily re?ected in the intersection of the plot at the Z axis[26].In this study,the impedance measured in20min after the cell assembled exhibited a linear relationship(Fig.12(a)),revealing that the electrode sys-tem is signi?cantly controlled by the diffusion processes.Then,as charging to4.2V,the impedance plot shows a semicircle for the LiCoO2cell(Fig.12(b)),which demonstrates that a charge trans-fer step may participate in the charging process of the system.And, the size of the semicircle,i.e.,the charge transfer resistance,became large after discharging to3.5V as shown in Fig.12(c).

The electrode of LiCoO2in organic solutions containing lithium salts is controlled by the diffusion of lithium in the solid phase.However,the charge and discharge characteristics depend signi?cantly on the electrolyte composition and interface of elec-trode/electrolyte.

Fig.12reveals that certain resistive components at the electrode/electrolyte interface and play important roles in the charge and discharge processes.It also indicates that a?lm produced on the oxide surface is responsible for the higher resis-tive components,which may control the rate capability of the oxide electrode,and resulting in a larger intersection of the plot at the Z axis after the discharging process.Fig.12.Cole–Cole plots for a.c.impedance obtained for LiCoO2in EC+DEC based solutions containing1M LiPF6:(a)before the cycle,(b)after the charge to4.2V,and (c)after the discharge to3.5V.

4.Conclusions

LiCoO2powders were prepared by the sol–gel method for rechargeable lithium-ion batteries cathode materials.The in?uence of calcination temperature and the calcination time on the struc-ture and morphology of LiCoO2powders were investigated using the XRD,Raman and SEM techniques.From the analysis of crys-talline properties,granular structure and surface morphology of LiCoO2powders,it is found the crystallinity of powders strongly depends on the calcination temperature and the calcination time. The results indicate the layered,pure and ultra?ne LiCoO2powders can be obtained at700?C for4h in air.

After25cycles,the stable HT-LiCoO2electrode demonstrates the charge/discharge capacities at175and154mAh/g,respectively. The favorable structure and morphology point out the LiCoO2pow-ders are suitable as cathode materials for secondary lithium-ion batteries.

Acknowledgement

The authors gratefully acknowledge the?nancial support of the National Science Council of the Republic of China(Taiwan). References

[1]D.W.Murphy,P.A.Christian,Science205(1979)651–656.

[2]J.M.Tarascon,M.Armand,Nature414(2001)359–367.

[3]G.T.K.Fey,K.S.Chen,B.J.Hwang,Journal of Power Sources68(1997)519–523.

[4]T.Nakajima,Journal of Fluorine Chemistry128(2007)277–284.

[5]B.Scrosati,Journal of Electrochemical Society139(1992)2776–2781.

[6]Y.Nishi,Journal of Power Sources100(2001)101–106.

[7]C.Y.Yao,T.H.Kao,C.H.Cheng,J.M.Chen,W.-M.Hurng,Journal of Power Sources

54(1995)491–493.

[8]M.Y.Song,R.Lee,Journal of Power Sources111(2002)97–103.

[9]X.Wang,X.Chen,L.Gao,Journal of Crystal Growth256(2003)123–127.

[10]H.Gabrisch,R.Yazami,B.Fultz,Journal of Power Sources119–121(2003)

674–679.

C.Zhu et al./Journal of Alloys and Compounds496 (2010) 703–709709

[11]L.Predoan?a,A.Bar?a u,M.Zaharescu,H.Vassilchina,N.Velinova,B.Banov,A.

Momchilov,Journal of the European Society27(2007)1137–1142.

[12]M.Antaya,K.Cearns,J.S.Preston,Journal of Applied Physics76(1994)

2799–2806.

[13]S.H.Choi,J.W.Son,Y.S.Yoon,J.Kim,Journal of Power Sources158(2006)

1419–1424.

[14]J.N.Reimers,J.R.Dahn,Journal of Electrochemical Society139(1992)

2091–2097.

[15]R.J.Gummow,D.C.Liles,M.M.Thackeray,Materials Research Bulletin28(1993)

235–246.

[16]I.H.Oh,S.A.Hong,Y.K.Sun,Journal of Materials Science32(1997)3177–3182.

[17]S.G.Kang,S.Y.Kang,K.S.Ryu,S.H.Chang,Solid State Ionics120(1999)155–161.

[18]L.J.Fu,H.Liu,C.Li,Y.P.Wu,E.Rahm,R.Holze,H.Q.Wu,Progress in Materials

Science50(2005)881–928.[19]R.J.Gummow,M.M.Thackeray,W.I.F.David,S.Hull,Materials Research Bulletin

27(1992)327–337.

[20]J.Kim,P.Fulmer, A.Manthiram,Materials Research Bulletin34(1999)

571–579.

[21]C.Julien,Ionics5(1999)351–357.

[22]Y.S.Horn,S.A.Hackney,A.J.Kahaian,M.M.Thackerayw,Journal of Solid State

Chemistry168(2002)60–68.

[23]W.S.Yoon,K.B.Kim,Journal of Power Sources81–82(1999)517–523.

[24]E.I.Santiago,A.V.C.Andrade,C.O.Paiva-Santos,L.O.S.Bulh?es,Solid State Ionics

158(2003)91–102.

[25]X.B.Garcia,J.Farcy,J.P.Pereira-Ramos,J.Perichon,N.Baf?er,Journal of Power

Sources54(1995)373–377.

[26]M.Morita,O.Yamada,M.Ishikawa,Y.Matsuda,Journal of Applied Electrochem-

istry28(1998)209–213.