Capacity loss induced by lithium deposition at graphite anode

ElectrochimicaActa111 (2013) 802–808

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Electrochimica

Acta

journalhomepage:www.elsevier.com/locate/electacta

Capacitylossinducedbylithiumdepositionatgraphiteanodefor

LiFePO4/graphitecellcyclingatdifferenttemperatures

LiTana,LiZhanga,QingnaSuna,MingShenb,QuntingQua,∗,HongheZhenga,∗

aSchoolofEnergy,SoochowUniversity,Suzhou,Jiangsu215006,ChinabHuashengChemicalCorporation,Zhangjiagang,Jiangsu215635,China

articleinfo

Articlehistory:Received8July2013Receivedinrevisedform14August2013Accepted14August2013Available online xxx

Keywords:LithiumionbatteriesLiFePO4cathodeCapacityfadeLithiumlossSolidelectrolyteinterphase(SEI)abstract

Capacityfadingofacommercial18650LiFePO4/graphitecellwasinvestigatedatdifferenttemperatures(25,40,50and60◦C)until30%ofitscapacitywaslost.Capacitydecreaseofthecellisinlinearrelationshipwithcyclenumberandtheslopeofthecapacity-fadinglineisincreasedbyelevatingtemperature.Thecapacity-fademechanismswereinvestigatedbyusingacombinationofelectrochemical,structuralandinductivelycoupledplasma(ICP)techniques.Lithiuminventorylosswasfoundtobethemaincauseforthecapacityloss.Attheendofthecyclingtest,theamountoflithiumprecipitatedonthegraphiteanodesurfacewasdetermined.Mostoftheconsumedlithiumisfoundonthegraphiteanode,especiallyathightemperaturecondition,illustratingthatthemajorityoflithiumlosswasascribedtothesidereactionsatthegraphiteanode/electrolyteinterface.Fedepositionatthegraphiteanodesurfacearousedfromitsdissolutionintotheelectrolyteisnotsignificantevenwhenthecelliscycledat50◦Ccondition.© 2013 Elsevier Ltd. All rights reserved.

1.Introduction

Lithiumionbatterieshaveattractedworld-wideattentionsince

thefirstonewasmadebySONYcompany.LiFePO4(LFP)cathode

material,whichwasfirstreportedbyGoodenoughetal.[1],isan

importantcategoryoflithiumionbatterycathodematerialsasit

hastheadvantagesofhighratecapability,highspecificcapacity

(170mAhg−1),goodsafetyattribute,attractivecostcompetitive-

ness,andlowtoxicity.Thiscellchemistryhasbeenextensively

studiedandsuccessivelycommercializedintherecent10years.

Thiscathodematerialexperiencesverysmallchangeinlattice

dimensionsfromfullylithiatedtofullydelithiatedstate,which

endorsestheLFPwithexcellentlong-termcyclingproperty.There-

fore,Li-ionbatteriesbasedonLFPcathodearewidelyacceptedof

greatpromiseforhighenergyPHEVs(plug-inhybridelectricvehi-

cles)andhighpowerHEVs(hybridelectricvehicles)[2,3].However,

capacityfadingofLFP-basedcellsisstillasevereproblemforits

practicalapplicationinPHEVorHEVpurposesastheservicelife

isstillfarfromtheaggressiverequirementsof5000electrochemi-

calcycleswith80%DOD(depthofdischarge)andacalendarlifeof

10–15years.

AsfortheagingmechanismsofLFP-basedcells,fourdiffer-

entcauseshavebeenreported[4–7]:(i)Structuraldamageofthe

∗Correspondingauthors.E-mailaddresses:qtqu@suda.edu.cn(Q.Qu),hhzheng@suda.edu.cn(H.Zheng).activematerial,specifically,phasetransitionand/orstructuraldis-

orderofthecrystalliniteafterlong-termcycles.(ii)Impedancerise

associatedwiththeresistancegrowthattheelectrode/electrolyte

interfaceand/orduetothelossofelectricalcontactbetween

activematerialparticles.(iii)Lossofactivematerialsresulted

fromthedissolutionoftransitioncationsintoelectrolyteand/or

particleisolationfromthebulkelectrode.(iv)Lithiuminven-

torylossresultedfromsidereactionsatelectrode/electrolyte

interfacerelatingtosolidelectrodeinterphase(SEI)growthand

rearrangement.

Inrecentyears,mostoftheresearchstudieshaveshownthatthe

consumptionofcycleableLiduetosidereactionswithinthecellis

themaincauseresponsibleforthecapacityfadeofLFP-basedLi-

ioncells.Striebleetal.[8,9]testedthecycledgraphiteanodeand

LFPcathodeofacycledLFP/graphitecell.Theyfoundthatboththe

electrodeswellmaintainedtheirspecificcapacityexceptthelossof

lithiuminventory.Dubarryetal.[10]attemptedtoidentifythecon-

tributionsofseveralfactorstocapacitylossbyusinganincremental

capacityanalysis.Again,lithiuminventorylossisfoundtobethe

maincauseofthecapacitydegradationoftheLFP-basedcell.Liu

etal.[11,12]investigatedthedischargeprofilesusingadifferential

analysisandtheyconfirmedthatthelossofreversibleLiisresponsi-

bleformostofcapacityfade.Theyalsousedexternallithiumsource

toreplenishthecycledcathodewhichhaslost30%ofitscapacity

after2730cycles.Mostofthelostcapacitywasrecoveredandthe

cellcycledforadditional1500cycles.Weinvestigatedtheelectro-

chemicalcyclingbehaviorofaLFP-basedcellwithdifferentupper

voltagelimitsandtheresultsindicatedthatlithiuminventoryloss

0013-4686/$–seefrontmatter© 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.electacta.2013.08.074