lithium ion batteries

Three-dimension hierarchicalflower-like Ni1.5Co1.5O4nanostructurescomposed of two-dimension ultrathin nanosheets as an anodematerial for lithium ion batteriesYuhong Jin a,Li Wang a,n,Yuming Shang a,Jian Gao a,Jianjun Li a,c,Xiangming He a,b,nna Institute of Nuclear and New Energy Technology,Beijing Key Lab of Fine Ceramics,Tsinghua University,Beijing100084,PR Chinab State Key Laboratory of Automotive Safety and Energy,Tsinghua University,Beijing100084,PR Chinac Huadong Institute of Lithium Ion Battery,Zhangjiagang,Jiangsu215600,PR Chinaa r t i c l e i n f oArticle history:Received11December2014Accepted5February2015Available online17March2015Keywords:Ni1.5Co1.5O4Flower-likeMicrostructureLithium ion batteriesEnergy storage and conversiona b s t r a c tUniform three-dimension hierarchicalflower-like Ni1.5Co1.5O4nanostructures were synthesized on alarge scale by a simple,low-temperature hydrothermal method without any template,catalyst andsurfactant,followed by a calcinating process.The obtained Ni1.5Co1.5O4products were composed of two-dimension ultrathin nanosheets with random attachment.Nitrogen sorption isotherm shows that thisstructure possesses a high specific surface area of118.8m2gÀ1with an average pore diameter of16.67nm.When tested as an anode material,the as-prepared Ni1.5Co1.5O4nanostructures exhibit aninitial discharge capacity of1461.5mAh gÀ1.After30cycles at the current density of100mA gÀ1,thedischarge capacity still keeps980.8mAh gÀ1.The obtained three-dimension hierarchicalflower-likeNi1.5Co1.5O4nanostructures show a promising anode material for lithium ion batteries.&2015Elsevier B.V.All rights reserved.1.IntroductionOver the past decades,extensive research interest on lithiumion batteries(LIBs)has been widely stimulated due to theiradvantages of high energy density,long lifespan,no memoryeffect and environmental benignity,which holds great potentialapplication in the areas of energy storage/conversion devices[1–6].Numerous efforts have been devoted to developing noveland high performance electrode materials with the aim to realizeLIBs with higher energy/power density[7–9].Among the diversematerials that have been studied as potential anode materials forLIBs,Ni x Co3Àx O4mixed oxides have been regarded as potentialelectrodes for the development of next generation LIBs due totheir favorable performance inherited from Co-based metal oxides[10–12].However,the Ni x Co3Àx O4bulk as anode material showsthe large irreversible capacity in thefirst cycle due to the lowelectronic conductivity.In order to solve this problem,synthesis ofNi x Co3Àx O4with distinct nanostructure and morphology is aneffective way to enhance the electrochemical performance for LIBs.Recently,Li and coworkers[10]prepared monodisperse NiCo2O4mesoporous microspheres by a facile solvothermal method fol-lowed by pyrolysis of the Ni0.33Co0.67CO3precursor.The dischargecapacity of the as-prepared sample can reach1198mAh gÀ1after30discharge–charge cycles at a current density of200mA gÀ1.Liand coworkers[11]demonstrated polyvinylpyrrolidone(PVP)-assisted method to prepare3-dimensional(3D)hierarchical por-ousflower-like NiCo2O4.The investigated results show that PVPplays an important role in controlling the formation of thehierarchicalflower-like structure.The as-prepared NiCo2O4exhi-bits an enhanced lithium storage capacity and excellent cyclingstability(939mAh gÀ1at100mA gÀ1after60cycles).Zheng andcoworkers[12]reported a novel and facile route for the large-scalefabrication of2-dimensional porous Ni x Co3Àx O4nanosheets,which exhibited improved lithium storage properties and goodcycle performance.Herein,we successfully developed a facile and scalable methodwithout the help of surfactant to synthesis of three-dimensionhierarchical Ni1.5Co1.5O4material.The high conductivity of Ni1.5Co1.5O4facilitates the electron transfer while three-dimension hierarchicalflower-like structure ensures the large electro-active area and the ionsdiffusion-favored pathway.All these features make the as-fabricatedNi1.5Co1.5O4possess substantially enhanced rate capability and goodcycling stability when used as the anode materials for LIBs.Contents lists available at ScienceDirectjournal homepage:/locate/matletMaterials Letters/10.1016/j.matlet.2015.02.0170167-577X/&2015Elsevier B.V.All rightsreserved.n Corresponding author.nn Corresponding author at:Institute of Nuclear and New Energy Technology,Beijing Key Lab of Fine Ceramics,Tsinghua University,Beijing100084,PR China.Tel.:þ861062794226;fax:þ861089796031.E-mail addresses:wang-l@(L.Wang),hexm@(X.He).Materials Letters151(2015)49–522.Experimental sections1mmol of Ni(NO3)2Á6H2O,2mmol of Co(NO3)2Á6H2O and 6mmol of hexamethylenetetramine(HTMA)are dissolved into the mixed solvent(ethanol/water¼20:40,volume ratio)to form a transparent pink solution under stirred for10min at room tem-perature.Then,the homogeneous solution was transferred into a Teflon-lined stainless steel autoclave.The steel autoclave was sealed and kept in an oven at901C for4h.The HTMA is mainly used as the precipitator to produce OHÀin this reaction process.After cooling down to room temperature,the hydroxide precipitate was collected by centrifugation and washed with deionized water and ethanol for several times,the green Ni1.5Co1.5O4precursor was obtained by drying at601C for24h.the Ni1.5Co1.5O4sample was obtained by annealing the precursor at3501C for3h in air with the heating rate of11C minÀ1to obtain black Ni1.5Co1.5O4power.It should be noted that the mole ratio of Co/Ni in the as-prepared product(1:1)is in disagreement with the feeding proportion of the initial reactants (2:1).This is mainly attributed to the fact that Co2þcan coordinate with NH3generated from the decomposition of HTMA more easily than the Ni2þ,and this immobilized the precipitation of the Co ion.Crystal structure of the as-prepared product was characterized by X-ray diffraction(XRD)using D8ADVANCE(3kW).The mor-phology was investigated by thefield emission scanning electron microscope(FESEM,JSM-7001F)with energy dispersive X-ray (EDX)spectroscopy.Nitrogen adsorption and desorption isotherms were performed at77K on a Quantachrome NOVA4200E(USA) volumetric adsorption system.The chemical composition of the products was measured by Inductive Coupled Plasma Atomic Emission Spectrometer(ICP-AES,Varian700).The electrochemical performance of as-prepared Ni1.5Co1.5O4 sample was evaluated using the CR2032-type coin cells.As-prepared Ni1.5Co1.5O4as active material was mixed with acetylene black as conductive agent and polytetrafluoroethylene as binder at a weight ratio of50:30:20to fabricate electrode.The cyclic voltammogram(CV)was performed on an electrochemical work-station(CHI660E).The discharge/charge tests were conducted on LAND batteries test system(Wuhan,China).3.Results and discussionAs observed in Fig.1a,the diffraction peaks are similar to the standard patterns of NiCo2O4(JCPDS No.20-0781),suggesting that the as-prepared Ni1.5Co1.5O4structures also are the spinel structure with similar lattice constants[13].As shown in Fig.1b,according to the results,the specific surface area calculated by the Brunauer–Emmett–Teller(BET)method and the pore volume are118.8m2gÀ1 and0.495cm3g-1.The inset in the Fig.1b shows the Barrett–Joyner–Halenda(BJH)pore size distribution indicates a narrow pore size distribution(10–20nm)centered at around16.67nm.Fig.2a demonstrates the FESEM image for the Ni1.5Co1.5O4.Obviously, uniform three-dimension hierarchicalflower-like Ni1.5Co1.5O4 nanostructures are constructed with two-dimension nanosheets with random attachment.Fig.2b–e shows the corresponding EDX mapping for Co,Ni and O elements,respectively.It is obvious that the distribution of all elements in the as-prepared sample is homogeneous.The representative EDX analysis(Fig.2f)reveals that the content of Ni and Co is3.26and3.19mol%,respectively,close to the stoichimetric molar ratio of1:1in the spinel.The Co/Ni atomic ratio is further confirmed by ICP-AES.Thefirst three CV curves were investigated at the scanning rate of 0.1mV sÀ1in the potential range of0.01–3.00V(vs.Liþ/Li)(Fig.3a). At thefirst cycle,the intense reduction peak at0.81V can be ascribed to the reduction of Ni2þand Co3þto metallic Co and Ni,and the formation of Li2O and solid electrolyte interface(SEI)layer.The following two anodic peaks at$1.7V and$2.2V can be attributed to the oxidation of metallic Ni and Co to nickel and cobalt oxides [7,9].In the second cycle,the main reduction peak shift to$1.0V due to the pulverization of the Ni1.5Co1.5O4[9].However,from the second cycle,the CV curves overlap very well,which indicates the good reversibility of the electrochemical reactions.A high rate capability is investigated as shown in Fig.3b.Even at high rate of 1000mA gÀ1,a capacity of$320mAh gÀ1can still be kept.More-over,when the current density is reduced back to100mA gÀ1,an average discharge capacity of$988mAh gÀ1can be recovered. Representative discharge–charge curves of the as-prepared Ni1.5Co1.5O4microflower electrode at a current density of100mA gÀ1 as shown in Fig.3c.The initial discharge and charge capacities are 1461.5and1098.5mAh gÀ1,respectively.The initial capacity loss during thefirst cycle can be attributed to the formation of a SEIfilm and some undecomposed Li2O phase[9,14].Fig.3d shows the corresponding discharge–charge cycling performance of Ni1.5Co1.5O4/ Li cell.It has a high initial discharge capacity followed with fast decay.However,it keeps a stable capacity of980.8mAh gÀ1from second to30th cycle.Based on the above results,Ni1.5Co1.5O4electrode possesses a large initial discharge capacity and good cycle stability,which can be attributed to unique three-dimension hierarchicalflower-like structure.This structure can increase the Ni1.5Co1.5O4/electrolyte Fig.1.(a)XRD pattern and(b)N2adoption and desorption isotherms(inset:BJH pore size distributions)of the as-prepared Ni1.5Co1.5O4sample.Y.Jin et al./Materials Letters151(2015)49–5250Fig.2.FESEM image (a,b)and corresponding EDX mapping for Co (c),Ni (d),O (e)and the corresponding EDX spectrum (f).Y.Jin et al./Materials Letters 151(2015)49–5251contact area,facilitate the transportation of Li þions and reduce volume change during discharge/charge processes.4.ConclusionsIn summary,the Ni 1.5Co 1.5O 4micro flower has been prepared by the hydrothermal method.The initial discharge and charge capa-cities are 1461.5and 1098.5mAh g À1at 100mA g À1,and then the reversible capacity still keeps 980.8mAh g À1after 30cycles,suggesting that Ni 1.5Co 1.5O 4micro flower structure is a promising anode material for LIBs.AcknowledgmentsThis work is supported by the MOST (Grant nos.2013CB934000,2011CB935902,2014DFG71590,2010DFA72760,2011CB711202,2013AA050903,2011AA11A257and 2011AA11A254)and State Key Laboratory of Automotive Safety and Energy (No.ZZ2012-011).References[1]Poizot P,Laruelle S,Grugeon S,Dupont L,Tarascon JM.Nano-sized transition-metal oxides as negative-electrode materials for lithium-ion batteries.Nature 2000;407:496–9.[2]Ji L,Lin Z,Alcoutlabi M,Zhang X.Recent developments in nanostructuredanode materials for rechargeable lithium-ion batteries.Energy Environ Sci 2011;4:2682–99.[3]Wu HB,Chen JS,Hng HH,Lou XW.Nanostructured metal oxide-basedmaterials as advanced anodes for lithium-ion batteries.Nanoscale 2012;4:2526–42.[4]Armand M,Tarascon JM.Building better batteries.Nature 2008;451:652–7.[5]Zhu B,Fan L,He Y,Zhao Y,Wang H.A commercial lithium battery LiMn-oxidefor fuel cell applications.Mater Lett 2014;126:85–8.[6]Zhou X,Huang B,Zou Y,Xie J,Yang J.Cotton-templated fabrication ofhierarchical SnO 2mesoporous microtubes as the anode material of lithium ion battery.Mater Lett 2014;120:279–82.[7]Yang L,Gao Q,Zhang Y,Tang Y,Wu Y.Tremella-like molybdenum dioxideconsisting of nanosheets as an anode material for lithium ion battery.Electrochem Commun 2008;10:118–22.[8]Wang B,Cheng J,Wu Y,Wang D,He D.Porous NiO fibers prepared byelectrospinning as high performance anode materials for lithium ion batteries.Electrochem Commun 2012;23:5–8.[9]Jin Y,Wang L,Shang Y,Gao J,Li J,He X.Facile synthesis of monodisperse Co 3O 4mesoporous microdisks as an anode material for lithium ion batteries.Electrochim Acta 2015;151:109–17.[10]Li J,Xiong S,Liu Y,Ju Z,Qian Y.High electrochemical performance ofmonodisperse NiCo 2O 4mesoporous microspheres as an anode material for Li-ion batteries.ACS Appl Mater Interfaces 2013;5:981–8.[11]Li L,Cheah Y,Ko Y,Teh P,Wee G,Wong C,et al.The facile synthesis ofhierarchical porous flower-like NiCo 2O 4with superior lithium storage proper-ties.J Mater Chem A 2013;1:10935–41.[12]Zheng F,Zhu D,Chen Q.Facile Fabrication of porous Ni x Co 3Àx O 4nanosheetswith enhanced electrochemical performance as anode materials for Li-ion batteries.ACS Appl Mater Interfaces 2014;6:9256–64.[13]He G,Wang L,Chen H,Sun X,Wang X.Preparation and performance ofNiCo 2O 4nanowires-loaded graphene as supercapacitor material.Mater Lett 2013;98:164–7.[14]Munichandraiah N,Scanlon LG,Marsh RA.Surface films of lithium:anoverview of electrochemical studies.J Power Sources 1998;72:203–10.Fig.3.(a)the first three consecutive CV curves;(b)the rate performance,(c)the discharge –charge curves for the different cycles;(d)speci fic capacity at a current density of 100mA g À1and the coulombic ef ficiency versus the cycle number.Y.Jin et al./Materials Letters 151(2015)49–5252。