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1、Chem.Mater.2005,17,5085-50925085Atomic-ScaleInvestigationofDefects,Dopants,andLithiumTransportintheLiFePO4Olivine-TypeBatteryMaterialM.SaifulIslam,*DanielJ.Driscoll,CraigA.J.Fisher,andPeterR.SlaterMaterialsChemistryGroup,ChemistryDiVision,SBMS,UniVersityofSurrey,GuildfordGU27XH,Uni
2、tedKingdomReceiVedMay12,2005.ReVisedManuscriptReceiVedJuly15,2005Keyissuesrelatingtointrinsicdefects,dopantincorporation,andlithiumionmigrationintheLiFePO4electrodematerialhavebeeninvestigatedusingwell-establishedatomisticmodelingtechniques.Oursimulationmodelshowsgoodreproductionof
3、theobservedolivine-typestructureofLiFePO4.ThemostfavorableintrinsicdefectistheLi-Feªanti-siteºpairinwhichaLiion(ontheM1site)andanFeion(ontheM2site)areinterchanged.Thistypeofanti-sitedefectorªintersiteexchangeºhasbeenobservedinolivinesilicates.ThelowestLimigrationenergyisfoundforthe
4、pathwayalongthe[010]channel,withanonlinear,curvedtrajectorybetweenadjacentLisites.Trendsindopantsubstitutionenergeticsofarangeofcationswithchargesvaryingfrom+2to+5arealsoexamined.LowfavorableenergiesarefoundonlyfordivalentdopantsontheFesite(suchasMn),whichisinaccordwithexperimental
5、work.Ourresultssuggestthat,onenergeticgrounds,LiFePO4isnottoleranttoaliovalentdoping(e.g.,Al,Ga,Zr,Ti,Nb,Ta)oneitherLi(M1)orFe(M2)sites.1.IntroductionLiFePO4.Thisislargelyduetothehighoperatingvoltage(about3.5VvsLi+/Li)fortheFe3+/Fe2+couple,thelargeThesearchforalternativecathodemate
6、rialstoreplacethetheoreticalcapacitytostorechargeperunitmass(ca.170layeredLiCoO2systemconventionallyusedwithinrecharge--1mAhg)andthegoodstabilityofthephosphatewheninablelithiumbatterieshasgeneratedconsiderableresearchcontactwithcommonorganicelectrolytes.SuchFe-basedactivity.1,2TheC
7、o-basedmaterialsposeproblemsassociatedoxidesarealsorelativelylowincostandenvironmentallywithcostandenvironmentalhazard,particularlyforlarge-benign.scaleapplications(suchashybridelectricvehiclesandback-OneofthekeydrawbackswithusingLiFePO4,however,uppowersystems).Inthiscontext,theoli
8、vinephosphatesisitslowintr
