P1-239⚫Chemical species crossover is observed in Li|NCM811.⚫Crossover exacerbates electrode degradation.⚫Transition metals migrate from cathode to anode.⚫F-and S migrate from anode to cathode.ConclusionEffectofchemical crossoverElectrode degradation analysis⚫Inthisstudysolidseparatorisusedtoblockcrossover.⚫Artificial interphase will be used in future.⚫HF scavengers will be used to trap HF.⚫Study will be extended to other cell systems.Future PlanIntroductionLithiummetalbatteriesexperiencedegradationduetothehighreactivityofLiwiththeelectrolyte.Simultaneously,reactionsbetweenthecathodeandtheelectrolytedegradeboththecathodestructureandtheelectrolyteitself.Typically,electrolyteformulationsandoperationalvoltagewindowsareadjustedbasedontherelativestabilitiesoftheindividualelectrodestominimizetheseeffects.However,ourobservationsshowthatevenwhentheindividualelectrodesappearstable,inter-electrodecrossovercanexacerbatedegradation.Theme underDiscussionAutomated Electrochemical Experiments Team, GREEN, Arghya DuttaE-mail：： DUTTA.Arghya@nims.go.jpUnraveling Chemical Crossover Pathways Driving Electrode Degradation inHigh-Voltage Li|NCM811 Pouch CellsKey Words: Rechargeable battery, Chemical crossover, DegradationDevelopinghigh-energylithiumbatteriesiscriticalformeetingthegrowingglobaldemandforcleanandsustainableenergystorage,poweringeverythingfromelectricvehiclestorenewableenergygrids.Achievinghigherenergydensitywhilemaintainingsafetyandlongevityrequiresadeepscientificunderstandingofthefundamentaldegradationmechanismswithinelectrodesandelectrolytes.Whatischemicalcrossover?Electrolytedegradationproductsformedatoneelectrodecanmigratethroughtheelectrolyteandreachtheoppositeelectrode,whichisknownaschemicalcrossover.Whenthesemigratedspeciesarereactive,theycanfurtherattackanddegradetheotherelectrode,exacerbatingthecelldeterioration.CrossoverLiNCMVHF, polysulfidesCrossover is blockedby asolidseparatorNi2+, Mn2+, Co2+,CO2,H+SinglecompartmentcellCrossoverisallowedTwo-compartmentcellCrossoverisblocked020406080100050100150200 Cross-over allowed Cross-over blockedCapacity (mAh g-1)No. of cycles4.5 V cut-off2976020406080100No. of cyclesWhenthecrossoverisblockedbyasolidseparator,thecyclingstabilityimproves.01020304050050100150200Thickness of Li (mmm)No. of cycle Cross-over allowed Cross-over blockedSSNCMNCM200 nmLiLiWithcrossoverNo crossoverEstimation of Li thickness during cycle by using X-ray CTX-ray CT images after 40 cyclesEnhanceddegradationofLielectrodeduetocrossoverisconfirmed3.5 nm11.3 nm5 nm10 nmWithcrossoverNo crossover6.5 nm10.8 nm5 nm2 nmRock-saltLayeredRock-saltLayeredWithcrossoverNo crossoverCEI thickness and NCM811 structure degradation after 50 cyclesCEIthicknessishigherandNCM811isdegradedmoreduetocrossover0.00.10.20.30.40.5Quantity of TMs (a.u.) Ni Co MnWith crossoverNo crossover87%18%13%82%020406080100LiF, C-F/S-F (%) LiF C-F/S-FCrossoverNocrossoverElemental analysis of Li and NCM811 surface after cycleTMs crossover from cathode, and F-and S crossover from anode LisurfaceanalysisNCM811surfaceanalysisWithcrossoverNocrossover
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