Basic knowledge of lithium battery
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- Time of issue:2020-07-17
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(Summary description)BasicknowledgeoflithiumbatteryInanideallithiumionbattery,apartfromtheinsertionandextractionoflithiumionsbetweenthepositiveandnegativeelectrodes,noothersidereactionsoccur,andnoirreversibleconsumptionoflithiumionsoccurs.Theactuallithium-ionbatteryhassidereactionsandirreversibleconsumptionatalltimes,suchaselectrolytedecomposition,activematerialdissolution,metallithiumdeposition,etc.,butthedegreeisdifferent.Inactualbatterysystems,anysidereactionthatcanproduceorconsumelithiumionsorelectronsineachcyclemaycausechangesinbatterycapacitybalance.Oncethebatterycapacitybalancechanges,thischangeisirreversible,andcanbeaccumulatedthroughmultiplecycles,whichwillhaveaseriousimpactonbatteryperformance.(1)DissolutionofcathodematerialThedissolutionofMninspinelLiMn2O4isthemainreasonforthereversiblecapacitydegradationofLiMn204.TherearegenerallytwoexplanationsforthedissolutionmechanismofMn:redoxmechanismandionexchangemechanism. TheredoxmechanismreferstothehighconcentrationofMn3+attheendofthedischarge.TheMn+onthesurfaceofLiMn2O4willundergoadisproportionationreaction:2Mn3+(solid)Mn4+(solid)+Mn2+(liquid)Thedivalentmanganeseionsgeneratedbythedisproportionationreactiondissolveintheelectrolyte.TheionexchangemechanismreferstotheexchangeofLi+andH+onthesurfaceofthespinel,ThefinalformationofHMn204withnoelectrochemicalactivity.Xiaetal.’sresearchshowedthatthecapacitylosscausedbythedissolutionofmanganeseaccountedforthepercentageofthetotalbatterycapacitylossthatincreasedsignificantlyasthetemperatureincreased(from23%atroomtemperatureto34%at55°C)[14].(2)Phasechangeofcathodematerial[15]Therearetwotypesofphasechangesinlithium-ionbatteries:-isthephasechangeoftheelectrodematerialwhenlithiumionsarenormallyreleased;theotheristhephasechangeoftheelectrodematerialwhenoverchargeoroverdischarge.Forthefirsttypeofphasetransition,itisgenerallybelievedthatthenormaldeintercalationreactionoflithiumionsisalwaysaccompaniedbychangesinthemolarvolumeofthehoststructure,andatthesametime,stressisgeneratedinthematerial,whichcauseschangesinthehostlattice,andthesechangesreducetheparticles.Electrochemicalcontactbetweenparticlesandelectrodes.ThesecondtypeofphasetransitionistheJahn-Tellereffect.TheJahn-Tellereffectreferstotheexpansionandcontractionofthestructurecausedbytherepeatedintercalationanddeintercalationoflithiumions,whichcausestheoxygenoctahedrontodeviatefromthesphericalsymmetryandbecomeadeformedoctahedralconfiguration.TheirreversibletransformationofthespinelstructurecausedbytheJahn-TellereffectisalsooneofthemainreasonsforthecapacitydegradationofLiMn204.Duringdeepdischarge,theaveragevalenceofMnislowerthan3.5V,andthestructureofspinelchangesfromcubicphasetotetragonalphase.Thetetragonalcrystalhaslowrelativesymmetryandstrongdisorder,whichreducesthereversibilityofthedeintercalationoflithiumions,whichismanifestedastheattenuationofthereversiblecapacityofthecathodematerial. (3)Reductionofelectrolyte[15] Electrolytescommonlyusedinlithiumionbatteriesmainlyincludesolventscomposedofamixtureofvariousorganiccarbonates(suchasPC,EC,DMC,DEC,etc.)andelectrolytescomposedoflithiumsalts(suchasLiPF6,LiCIO4,LiAsF6,etc.).Underchargingconditions,theelectrolyteisunstabletothecarbon-containingelectrode,soareductionreactionwilloccur.Electrolytereductionconsumestheelectrolyteanditssolvent,whichhasanegativeimpactonbatterycapacityandcyclelife.Theresultinggaswillincreasetheinternalpressureofthebatteryandthreatenthesafetyofthesystem.(4)Volumelosscausedbyovercharge[15]Depositionofnegativeelectrodelithium:Whenovercharged,lithiumionsaredepositedonthesurfaceofthenegativeelectrodeactivematerial.Thedepositionoflithiumions-ontheonehand.Thenumberofreversiblelithiumionsisreduced.Ontheotherhand,thedepositedlithiummetalcaneasilyreactwiththesolventorsaltmoleculesintheelectrolytetogenerateLi2CO3,LiForothersubstances,whichcanblocktheelectrodeHole,eventuallyleadingtolossofcapacityandlife.Electrolyteoxidation:Theelectrolytecommonlyusedinlithium-ionbatteriesiseasilydecomposedtoforminsolubleLi2CO3andotherproductswhenovercharged,blockingthepolarporesandgeneratinggas,whichwillalsocausethelossofcapacityandcausesafetyhazards.Oxygendefectinthepositiveelectrode:ThereisatendencytoloseoxygeninthepositiveelectrodeLiMn204inthehigh-voltageregion,whichcausesoxygendefectsandleadstocapacityloss.(5)Self-dischargeMostofthecapacitylosscausedbytheself-dischargeoflithium-ionbatteriesisreversible,andonlyasmallpartisirreversible.Themainreasonsforirreversibleself-dischargeare:thelossoflithiumions(theformationofinfallibleLi2CO3andothersubstances);theelectrolyteoxidationproductblockstheelectrodemicroporesandincreasestheinternalresistance. (6)FormationofinterfacefilmDuetotheirreversiblereactionbetweenlithiumionorelectrolyteandtheelectrode,szwillformasolidelectrolyteinterfacelayer(SEI)attheinterfacebetweenthenegativeelectrodeandtheelectrolyte.Thelossoflithiumionsduetotheformationofthispassivationfilmwillresultinachangeinthecapacitybalancebetweenthetwoelectrodes,andthecapacityofthebatterywilldecreaseinthefirstfewcycles.(7)CurrentcollectorThecur
Basic knowledge of lithium battery
(Summary description)BasicknowledgeoflithiumbatteryInanideallithiumionbattery,apartfromtheinsertionandextractionoflithiumionsbetweenthepositiveandnegativeelectrodes,noothersidereactionsoccur,andnoirreversibleconsumptionoflithiumionsoccurs.Theactuallithium-ionbatteryhassidereactionsandirreversibleconsumptionatalltimes,suchaselectrolytedecomposition,activematerialdissolution,metallithiumdeposition,etc.,butthedegreeisdifferent.Inactualbatterysystems,anysidereactionthatcanproduceorconsumelithiumionsorelectronsineachcyclemaycausechangesinbatterycapacitybalance.Oncethebatterycapacitybalancechanges,thischangeisirreversible,andcanbeaccumulatedthroughmultiplecycles,whichwillhaveaseriousimpactonbatteryperformance.(1)DissolutionofcathodematerialThedissolutionofMninspinelLiMn2O4isthemainreasonforthereversiblecapacitydegradationofLiMn204.TherearegenerallytwoexplanationsforthedissolutionmechanismofMn:redoxmechanismandionexchangemechanism. TheredoxmechanismreferstothehighconcentrationofMn3+attheendofthedischarge.TheMn+onthesurfaceofLiMn2O4willundergoadisproportionationreaction:2Mn3+(solid)Mn4+(solid)+Mn2+(liquid)Thedivalentmanganeseionsgeneratedbythedisproportionationreactiondissolveintheelectrolyte.TheionexchangemechanismreferstotheexchangeofLi+andH+onthesurfaceofthespinel,ThefinalformationofHMn204withnoelectrochemicalactivity.Xiaetal.’sresearchshowedthatthecapacitylosscausedbythedissolutionofmanganeseaccountedforthepercentageofthetotalbatterycapacitylossthatincreasedsignificantlyasthetemperatureincreased(from23%atroomtemperatureto34%at55°C)[14].(2)Phasechangeofcathodematerial[15]Therearetwotypesofphasechangesinlithium-ionbatteries:-isthephasechangeoftheelectrodematerialwhenlithiumionsarenormallyreleased;theotheristhephasechangeoftheelectrodematerialwhenoverchargeoroverdischarge.Forthefirsttypeofphasetransition,itisgenerallybelievedthatthenormaldeintercalationreactionoflithiumionsisalwaysaccompaniedbychangesinthemolarvolumeofthehoststructure,andatthesametime,stressisgeneratedinthematerial,whichcauseschangesinthehostlattice,andthesechangesreducetheparticles.Electrochemicalcontactbetweenparticlesandelectrodes.ThesecondtypeofphasetransitionistheJahn-Tellereffect.TheJahn-Tellereffectreferstotheexpansionandcontractionofthestructurecausedbytherepeatedintercalationanddeintercalationoflithiumions,whichcausestheoxygenoctahedrontodeviatefromthesphericalsymmetryandbecomeadeformedoctahedralconfiguration.TheirreversibletransformationofthespinelstructurecausedbytheJahn-TellereffectisalsooneofthemainreasonsforthecapacitydegradationofLiMn204.Duringdeepdischarge,theaveragevalenceofMnislowerthan3.5V,andthestructureofspinelchangesfromcubicphasetotetragonalphase.Thetetragonalcrystalhaslowrelativesymmetryandstrongdisorder,whichreducesthereversibilityofthedeintercalationoflithiumions,whichismanifestedastheattenuationofthereversiblecapacityofthecathodematerial. (3)Reductionofelectrolyte[15] Electrolytescommonlyusedinlithiumionbatteriesmainlyincludesolventscomposedofamixtureofvariousorganiccarbonates(suchasPC,EC,DMC,DEC,etc.)andelectrolytescomposedoflithiumsalts(suchasLiPF6,LiCIO4,LiAsF6,etc.).Underchargingconditions,theelectrolyteisunstabletothecarbon-containingelectrode,soareductionreactionwilloccur.Electrolytereductionconsumestheelectrolyteanditssolvent,whichhasanegativeimpactonbatterycapacityandcyclelife.Theresultinggaswillincreasetheinternalpressureofthebatteryandthreatenthesafetyofthesystem.(4)Volumelosscausedbyovercharge[15]Depositionofnegativeelectrodelithium:Whenovercharged,lithiumionsaredepositedonthesurfaceofthenegativeelectrodeactivematerial.Thedepositionoflithiumions-ontheonehand.Thenumberofreversiblelithiumionsisreduced.Ontheotherhand,thedepositedlithiummetalcaneasilyreactwiththesolventorsaltmoleculesintheelectrolytetogenerateLi2CO3,LiForothersubstances,whichcanblocktheelectrodeHole,eventuallyleadingtolossofcapacityandlife.Electrolyteoxidation:Theelectrolytecommonlyusedinlithium-ionbatteriesiseasilydecomposedtoforminsolubleLi2CO3andotherproductswhenovercharged,blockingthepolarporesandgeneratinggas,whichwillalsocausethelossofcapacityandcausesafetyhazards.Oxygendefectinthepositiveelectrode:ThereisatendencytoloseoxygeninthepositiveelectrodeLiMn204inthehigh-voltageregion,whichcausesoxygendefectsandleadstocapacityloss.(5)Self-dischargeMostofthecapacitylosscausedbytheself-dischargeoflithium-ionbatteriesisreversible,andonlyasmallpartisirreversible.Themainreasonsforirreversibleself-dischargeare:thelossoflithiumions(theformationofinfallibleLi2CO3andothersubstances);theelectrolyteoxidationproductblockstheelectrodemicroporesandincreasestheinternalresistance. (6)FormationofinterfacefilmDuetotheirreversiblereactionbetweenlithiumionorelectrolyteandtheelectrode,szwillformasolidelectrolyteinterfacelayer(SEI)attheinterfacebetweenthenegativeelectrodeandtheelectrolyte.Thelossoflithiumionsduetotheformationofthispassivationfilmwillresultinachangeinthecapacitybalancebetweenthetwoelectrodes,andthecapacityofthebatterywilldecreaseinthefirstfewcycles.(7)CurrentcollectorThecur
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- Time of issue:2020-07-17
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