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17420074Vol.17No.4TheChineseJournalofNonferrousMetalsApr.20071004-0609(2007)04-0629-0712111(1.417000;2.410083)DSCXRD1mol·L−1LiPF6EMCH2O1mol·L−1LiPF6(EC\DML1׃1)EMCDECDMCDECDMCLiPF6PF5Li0.5CoO2O2Li0.5CoO2LiC6(SEI)LiC6160DSCO646;TM912AReactionsbetweenelectrolyteandelectrodeoflithiumionbatteriesatelevatedtemperatureHUChuan-yue1,LIXin-hai2,GUOJun1,WANGXing-yan1,YITao1(1.DepartmentofChemistryandMaterialScience,HunanInstituteofHumanities,ScienceandTechnology,Loudi417000,China;2.SchoolofMetallurgyScienceandEngineering,CentralSouthUniversity,Changsha410083,China)Abstract:ReactionsbetweenLi0.5CoO2electrodeand1mol·L−1LiPF6electrolyteatelevatedtemperatureforlithiumionbatterieswerestudiedwithdifferentialscanningcalorimeter(DSC)andX-raydiffraction(XRD).Theresultsshowthatthethermalstabilityof1mol·L−1LiPF6ethylenecarbonate(EC)-dimethylcarbonate(DMC)(1׃1,massratio)electrolytedecreasesbytheimpurityH2Oandethylmethylcarbonate(EMC)solvent.DECandDMCareproducedfromthethermaldecompositionreactionofEMC.AlargeamountofgasesandheatareproducedthroughseriesofchemicalreactionsamongDECandDMCandPF5fromdecompositionofLiPF6.Inthepresenceofsufficientelectrolyte,thedecompositionreactionsofLi0.5CoO2proceedsinaclearstepwisemannerthroughsolidphasesasafunctionoftemperature.ElectrolytecombustionreactionstakeplaceduetotheevolvedoxygenfromthedecompositionofLi0.5CoO2thatreleaseslargeamountsofheat.ThethermalreactionsbetweenelectrolyteandLiC6electrodeoflithiumionbatteriesatelevatedtemperatureincludesthechippingreactionofsolidelectrolyteinterface(SEI)film,thereactionbetweenelectrolyteandLiC6andthereactionbetweenadhesivesandLiC6.However,thecrystalstructureofgraphitedoesnotchangeafterthermalreactionat160.Keywords:electrolytes;lithium-ionbatteries;differentialscanningcalorimeter[1−3]2006-09-262007-01-080738-8325065E-mail:huchuanyue@vip.sina.com.cn20074630[1,4−16]11.1(MDSC2910)BS9300()(DZG-404)(MB150B-GMBRAUN)(PVDF)LiCoO21mol·L−1LiPF6EC-DMC-EMC(m(EL)׃m(DML)׃m(EML)=1׃1׃1)1.2DSCPVDFLiCoO2LiCoO2PVDF0.3mmLi/LiCoO2Li/graphiteCR20251mol·L−1LiPF6EC-DMC-EMCLi/LiCoO21.310−4mA·mm−24.2V4.2~2.75V54.2V0mA·mm−24.2VLiCoO2Li0.5CoO2Li/graphite1.310−4mA·mm−20V0~1.5V5510−4mA·mm−20VLiC6LiCoO2Li0.5CoO2LiC6DSC15min20minDSCLi0.5CoO2DMC48h210036hDSCDMCLi0.5CoO2EC-DMC-EMCDSC15024hDSCDSC5~8mg1mg1.3XRDSEM4.2VLiC6−Li0.5CoO2−XRD14014515022.111.0mol·L−1LiPF6EC-DMC(1׃1)a5.8510−3b810−612230~2855.8510−3257240810−627225511.0mol·L−1LiPF6EC-DMC(1׃1)Fig.1InfluenceofH2Oonthermalstabilityof1.0mol·L−1LiPF6EC-DMC(1׃1,massratio)electrolyte2.2LiPF61mol·L−1LiPF6EC-DMC-EMCDSC22(a)LiPF6100~350DSCDSC1951LiPF62502LiPF6250LiPF6250174:6312LiPF61mol·L−1LiPF6EC-DMC-EMCDSCFig.2DSCcurvesofLiPF6(a)and1mol·L−1LiPF6EC-DMC-EMC(1׃1׃1,massratio)electrolytes(b)2(b)1mol·L−1LiPF6EC-DMC-EMC0~300DSCDSC125~2503122(1)~(3)LiPF6LiFHF3215Edstrom[14]LiPF6(CH3)2CHOCOOCH(CH3)2(CH3)2CHF,CH3CH=CH2(CH3)2CHOH,CO2(CH3)CHO(CHCH3)23LiPF6EMCDMC(4)~(12)LiPF6LiF↓+PF5(1)PF5+H2OPF3O+2HF(2)2C2H5OCOOCH3C2H5OCOOC2H5+CH3OCOOCH3CH3OCOOCH3+PF5CH3OCOOPF4+CH3F(4)CH3OCOOPF4PF3O+CO2+CH4+HF(5)CH3OCOOPF4+HFPF4OH+CO2+CH3F(6)C2H5OCOOC2H5+PF5C2H5OCOOPF4+HF+CH2=CH2C2H5OCOOC2H5+PF5C2H5OCOOPF4+C2H5F(8)C2H5OCOOPF4PF3O+CO2+C2H4+HF(9)C2H5OCOOPF4PF3O+CO2+C2H5F(10)C2H5OCOOPF4+HFPF4OH+CO2+C2H5F(11)C2H5OH+CH2=CH2C2H5OC2H5(12)2(b)DSC11mol·L−1LiPF6EC-DMC(1׃1810−6)DSCEMC1mol·L−1LiPF6EC-DMC2.3Li0.5CoO23Li0.5CoO2DSC3(a)DMCLi0.5CoO2DSCLi0.5CoO2LiPF6Li0.5CoO2PVDFPVDF350PVDF3(a)DSC1651PVDFLi0.5CoO2200279243220.5O61OCo610.5LiCoOCoOLi++→(13)3(b)Li0.5CoO2EC-DMC-EMC(CnHmOx)Li0.5CoO23(b)EC-DMC-EMCLi0.5CoO23(a)Li0.5CoO2Li0.5CoO2DSC212300Li0.5CoO2Co3O4(14)(3)(7)200746323Li0.5CoO2,EC-DMC-EMCLi0.5CoO21mol/LLiPF6EC-DMC-EMCLi0.5CoO2DSCFig.3DSCcurvesofLi0.5CoO2(a),Li0.5CoO2withenoughmixturesolventsofEC-DMC-EMC(b)andLi0.5CoO2with1mol/LLiPF6EC-DMC-EMCelectrolyte(c)(15)2CoOCoOLiCoO2CO2Li2CO3Co2CnHmOx+(2n−x+0.5m)O22nCO2+mH2O(14)Co3O43CoO+0.5O2(15)3(c)Li0.5CoO2ECDMCEMCLiPF63(c)DSC1731121021Co3O4CoOCo3O4LiCoO2CoOLiCoO21mol·L−1LiPF6EC-DMC-EMCLi1−xCoO2(0.5x1)−Li0.5CoO21401454LI0.5CoO2XRDLi0.5CoO21mol·L−1LiPF6EC-DMC-EMC145XRDLiCoO2Co3O4CoOXLi0.5CoO2(13)(15)Li0.5CoO2140XRDLiCoO2XRD140LiCoO25Li0.5CoO2SEMLi0.5CoO2140XRDSEMLiCoO2140DSC130~200Li0.5CoO21904Li0.5CoO2XRDFig.4XRDpatternsofLi0.5CoO2electrodeinpresenceof1mol·L−1LiPF6EC-DMC-EMCelectrolyteafterreactionat145(a),beforereactionat140(b)andafterreactionat140(c)174:633190Li0.5CoO2O2Li0.5CoO2Co5Li0.5CoO2SEMFig.5SEMphotographsofLi0.5CoO2electrodeinpresenceof1mol·L−1LiPF6EC-DMC-EMCelectrolytebeforereactionat140(a)andafterreactionat140(b)2.4LiC66LiC6/DSC6(a)DSCDSC34112562564006(b)LiC6/DSC100~30021(SEI)SEI()2LiC6[17−18]2SEISEI61mol·L−1LiPF6EC-DMC-EMCLiC6/DSCFig.6DSCcurvesofpuregraphite(a)andLiC6/graphiteelectrode(b)inpresenceof1mol·L−1LiPF6EC-DMC-EMCelectrolyte-LiC61601657LiC61mol·L−1LiPF6EC-DMC-EMC160XRD160160XRDHossain[19]200746347LiC6160XRDFig.7XRDpatternsofLiC6electrodeinpresenceof1mol·L−1LiPF6EC-DMC-EMCelectrolytebeforereactionat160(a)andafterreactionat160(b)LiC6SEI31)H2OEMC1mol·L−1LiPF6EC-DMC(ECDML1׃1)2)1mol·L−1LiPF6EC-DMC-EMC(ECDMLEML1׃1׃1)EMC