A three-in-one strategy for lithium recovery and upcycling of spent cathode materials

Domain: chemistry
Published: 2026-01-10
Editorial outcome: minor_revision

Abstract
Therecyclingofspentlithium-ionbatteriesisessentialforsustainabledevelopmentofcleanenergyindustry.Traditionalrecyclingmethodsfacechallengessuchashighenergy/chemicalconsumptionandlimitedadaptability.Thisstudyintroducesa‘Three-in-One’strategythatleveragesmechanochemical(MC)treatmenttoenhancelithiumrecovery,transitionmetalupgrading,andCO2sequestration.MCtreatmentinducesmicro-segregationoflithiumandtransitionmetals,resultinginastructurallydisorderedmaterialwithaLi-richsurface,facilitatingselectivelithiumextraction.Subsequently,CO2isusedasthesolereagentandlithiumleachingefficiencyexceeding95%isachievedbyforminglithiumbicarbonate.Conductedunderambientconditionswithoutadditionalgrindingaidsorleachingreagents,thismethodminimizesenvironmentalimpact.Transitionmetalsaresimultaneouslytransformedintohigh-performanceoxygenevolutionreaction(OER)catalysts,demonstratinganoverpotentialof322mVatacurrentdensityof10mAcm-2.Thesecatalystsmaintainstabilityover200hofoperation.Thisapproachnotonlyprovidesanefficientpathwayforlithiumrecoverybutalsoupcyclesspentcathodematerialsintovaluablecatalysts,supportingsustainableenergyconversiontechnologies.Thestrategyisparticularlyeffectiveforhigh-Nicathodesystems,offeringsignificantpracticaladvantages.

Introduction
The rapid application of lithium-ion batteries (LIBs) as essential cleanenergystoragedevicesinelectricvehicles,portableelectronics,andgrid-scalestorageisgeneratingagrowingstreamofspentbatteries1,2.TheglobalvolumeofspentLIBsisprojectedtoreach381millionmetrictonsby20503.Impropermanagementofsuchwastestreamsmaynotonlyresultinsubstantialwasteofstrategicmetalresourcessuchaslithium(Li)4,cobalt(Co),andnickel(Ni)butalso pose major environmental pollution risks, which threaten ecosystems and human health. Consequently, the efficient recovery of critical metals from spent LIBs is crucial for economic, environmental,andsocialsustainability5,6.

Current recycling of critical metals from spent LIBs relies on threeprincipalroutes:pyrometallurgy,hydrometallurgy,anddirectregeneration7. Pyrometallurgy uses high-temperature smelting (typically >1400°C)8torecoverCo, NiandCu,whiletherecoveryratesoflithiumaswellasFeandP(inaLiFePO4battery)arelow.Theprocessisinherentwithstringentrequirementsforinputmaterials andhighenergyconsumption6.Incontrast,hydrometallurgyoffers improved recovery efficiency for different elements through chemicalleachingwithsolventssuchasmineral/organicacidsordeep eutecticsolvents9–11.Nevertheless,conventionalhydrometallurgical processes often encounter challenges, such as high chemical consumption and lengthy purification sequences12. Direct regenerationisapromisingalternativethatemploysshorterprocessingroutestorestoredegradedcathodematerials(e.g.,viasolid-state, sol-gel, or hydrothermal Li replenishment)13–15 or increases cell capacity(e.g.,usingLi-compensatingadditivessuchasLi-Naph)16,17. However, its practical application is limited because it can only process less complex spent LIB streams18. Comparative analysis identifieshydrometallurgyasthemostversatileandwidelyapplicable approach, combining moderate energy requirements, adaptabilitytodiversebatterychemistries,andtuneablemetalseparationprocesses.

Compared with impurity-sensitive conventional hydrometallurgy, selective leaching improves Li recovery and simplifies purification19,20. The mechanisms preferentially induce targeted phasetransformationsinspentcathodes,separatingLifromtransitionmetal(TM)phases,drivenbystrategiessuchasaddingreductants or applying elevated temperature/pressure21. For example, carbothermic reduction converts spent cathodes into lithium carbonate(Li2CO3)andTMelementsortheiroxides20,22,23,andsulfationroastingyieldslithiumsulfate(Li2SO4)andTMoxides24–26.However, these methods often require substantial reagent inputs, produce hazardousemissionsandsecondarypollution,andgenerateleachingresidues.Theseresiduesusuallyrequireacidleachingforconversioninto salt solutions prior to reuse, which severely decreases their value. Consequently, optimizing resource utilization across the selective leaching chain requiresgreener, more efficient processes andsolutionsformanaginglow-valueresidues.FlashJouleheating27 can enable one-step selective Li extraction via second-long, high-temperature reactions. This instantaneous heating offers greener processinganduniquelyinducesstructuraltransformationsinspentcathodes, which could convert residual metals into self-assembled multi-metal hydroxide catalysts28. Electrochemical methods selectivelyleachLiatambienttemperaturebyusinganappliedpotential. The resulting structurally defective, Li-depleted residue can serve directlyasafunctionalmaterial,suchasanoxygenevolutionreaction(OER)catalyst,butelectrodereconstructionrequirementshinder scale-up29–31. Mechanical methods selectively leach Li through induced room-temperature phase transitions32; however, grinding additivesareassociatedwiththeriskofimpuritycontamination33,34.

Insummary,existingtechnologieshaveyettooptimallybalancemild processingconditions,minimalchemicalinput,andtheproduction ofhigh-valueoutputs.

Here,weproposea“Three-in-One”strategythatleverageselemental micro-segregation in spent cathode materials, which is inducedthroughcontrolledmechanochemical(MC)treatment.ThisinnovativeapproachenablesthesimultaneousselectiveextractionofLiandthetransformationofTM-basedleachingproductsintoOERcatalystsusingonlyCO2,asdepictedinFig.1a.Theentireprocedurewasconductedatambienttemperaturewithouttheuseofgrindingaidsorleachingagents.Notably,CO2fixationoccurssimultaneouslyduringthemetalrecoveryprocess.OurstrategyisinspiredbypriorworkonthesynthesisofLi-richdisorderedrocksaltcathodematerials (DRX)35, which showed that ball-milling could alter the initial distributionofLiandTMelementswithinthecathode,creatingLi-rich domains and increasing the charge–discharge capacity. The mechanical forceinourstudyservesasimilarpurposeofdisorderingthearrangementofLiandTMelementstoinducetheirmicro-segregation,whichendowstheseelementswithvaryingleachingactivities.Ultimately, this micro-segregation results in a Li leaching efficiency of >95% only with CO2—which could be prospectively derived entirely from industrial waste streams—thereby enhancing theenvironmentalandeconomicbenefitsoftheprocess.Moreover, thesynergisticeffectsofMCtreatmentandselectiveLiextractionin aweaklyacidicenvironmentresultinthecreationofacatalystwith exceptionalOERperformance.

Results
MechanochemicaltreatmentforselectiveextractionofLi
In the MC process,NCM811, for example, transformsinto an amorphous phase, as evidenced by X-ray Diffraction (XRD) peak broadening36 (Fig. 1b, c). The initial increase followed by a sharp decreaseintheI(003)/I(104)value(Fig.1c)revealstwo-stagestructural evolution:mechanicalenergyfirstinduces(003)-planegrainboundary slipintheR-3mlayeredstructure,enhances(003)planeexposure,and then drives irreversible transformation to the disordered rock-salt phase(Fm-3m)throughprolongedactivation37,38.Rietveldrefinement with internal standardization39 (Fig. 1d and Supplementary Fig. 1) revealeda72.9%amorphouscontentafter2hofactivation(Fig.1e), whichsubsequentlydecreasedto47.9%withextendedMCtreatment, confirming energy-dependent phase dynamics40,41. Amorphization initially dominated42, but the excess energy (activation time >2h) surpassedthedeformationbarrier,inducinglatticereorganization,as evidencedbytheunitcellinformationinSupplementaryFig.1,which reducedtheamorphouscontent43,44.

Systematic leaching experiments validated the correlation betweenmechanochemicallyinducedamorphizationandtheleaching behaviors of Li and TMs. As shown in Fig. 1f, pristine NCM811 (P-NCM811) exhibited a mere 4.68% Li leaching efficiency in aqueous systems. In contrast, after mechanochemical activation (activation time ≥2h), the Li leaching efficiency of mechanochemical activated NCM811(MA-NCM811)exceeded75%underidenticalconditions,with nearly100%Liselectivity,confirmingtheformationofwater-solubleLi phasesduringtheMCprocess.UponintroducingaH+sourceintothe leachingsystem(Fig.1f),H+inducesnonselectivemetalleachinginP-NCM811,whereasinMA-NCM811,itdemonstratessuperiorselectivity forLiextractionwithaLileachingefficiencyof>95%whenthenH⁺/nLi⁺ ratiois1.Experimentsdesignedtoelucidatethisphenomenon(SupplementaryNote2)revealedamorecriticalrolefortheMC-induced amorphizationofthecrystalstructurethanformorphologicalchanges suchasparticlesizereduction.Moreover,aprolongedactivationtime (activationtime>2h)ledtogradualdissolutionoftheTMsinacidic system.IntermsofthepHendpointinacidicsystems(SupplementaryFig. 6a), the final pH first increased (activation time<2h) but then decreased(activationtime>2h),indicatingthatexcessiveactivation diminished the difference in leaching activity between Li and TMs, which could be attributed to recrystallization reducing their differencesinkineticleaching.ThisresultmaintainsthesolutionpHwithina lowervalue,therebyallowingforthedissolutionoflow-valenceTMsin theTM-H2OsystemaccordingtotheE-pHdiagrams(SupplementaryFig. 6b–d). Consequently, 2h was chosen as the optimal activation time to maximize structural disorder while also maximizing the leachingselectivitybetweenLiandTM.Thesamplepreparedunder theseconditionswasthususedasthestartingmaterialforsubsequent leachingexperiments.

This phenomenon facilitates a CO2-assisted leaching system, which relies solely on CO2 as the only H+ source through dissolution–dissociationequilibrium(Eq.1).Underambientpressure, CO2couldserveasaH+source,selectivelyextracting87%ofLifrom MA-NCM811 (Supplementary Fig. 7). However, the H+ concentration generatedundertheseconditionswasinsufficienttocompletelydissolve the water-insoluble residual Li. Enhancing the dissolution-dissociationequilibriumofCO2(e.g.,byincreasingthesystempressure)effectivelypromotedH+release(Fig.1g)45.Asystematicinvestigation of CO2 pressure and leaching time (Supplementary Fig. 7) revealedthatinsufficientpressureoranoverlyshortdurationleadsto inadequate H+ supply, resulting in incomplete Li extraction (<90%). Conversely, excessively high pressure or a prolonged duration disrupts theTM-Oframework,inducingcodissolutionofTMsandthereby reducingselectivity.Nevertheless,theCO32–/HCO3–speciesgenerated insituduringCO2dissociationactasbuffersandcancomplexwithTM ions,thuslimitingtheirdissolutionandhelpingtomaintainselectivity.

Under the optimized conditions of 0.5MPa CO2 pressure and 1h leachingtime,thesystemachievesabalancebetweenH⁺generation andbufferingeffects,ultimatelyenablinghighlyefficientLiextraction whileeffectivelypreservingtheTMframework.Withrespecttoother ternary cathode materials, this method can achieve excellent Li selectiveextractionefficiency.AsshowninFig.1handSupplementaryFig. 8, for NCM811, NCM622, NCM111 and spent layered lithiumtransitionmetaloxide(S-LTMO,whereTMrepresentsNi,Co, andMn),theLileachingefficiencieswere95.43%,91.56%,88.53%and 93.13%,respectively,andtheselectivitiesofLiwere94.63%,97.04%, 99.37%and98.84%,respectively.Incontrast,theweakacidityofCO2 wasinsufficienttodisruptthelatticestructureofpristineLTMOs(P-LTMOs), resulting in a relatively low Li leaching efficiency (<15%). Further exploration of the universality of the raw materials, as discussedinSupplementaryNote3,revealedthatthisprocesswasnot applicable to cathode materials with non-layered structures (e.g., LiFePO4andLiMn2O4)underidenticalconditions.Thisinapplicability underscoresthattheeffectivenessoftheprocessiscontingentupona specificamorphizationpathway.Anotheradvantageofthisprocessis theabsenceofcation(e.g.,Na+,K+)andanion(e.g.,Cl–,SO42–)impurities introduced into the system, as well as the elimination of any gaseousorliquidwastethatwouldrequiresubsequenttreatment.The Li-richleachate(LiHCO3)wasconverteddirectlyintoaLi2CO3product with a purity of >98.5% (Supplementary Fig. 14 and Supplementary Table2)bythermaldecomposition46.

LeachingmechanismsofLiandcharacterizationofleachingproducts
AdditionalcharacterizationwasusedtofurtherelucidatetheleachingpathwayofLiinMA-LTMO.TheXRDpatternsofMA-NCM811anditsleachingproductsindifferentsystemsareshowninFig.2a.The leaching product from the aqueous system (MA-NCM811-WL) exhibited a pattern highly similar to that of MA-NCM811, with no notablenewpeaks.Incontrast,theleachingprocessintheCO2rich aqueous solution (MA-NCM811-CO2L) induced more significant phasechanges,specificallyshowinganotableincreaseintheintensityofthecharacteristicpeakat18.9°,whereastheintensitiesofthe remainingcharacteristicpeaksweremarkedlyreduced.Onthebasis of the earlier leaching results, it is evident that Li was primarily extractedfromtheamorphousregionsintheaqueoussystem,which had minimal impact on the highly disordered residual crystalline regions of MA-NCM811. The CO2 system effectively disrupted the residual crystal structure, thereby releasing additional lattice Li. Depth-profilingX-rayPhotoelectronSpectroscopy(XPS)analysisfor Li1s(SupplementaryFig.15)revealedthatthecharacteristicpeaks relatedtoLicompletelydisappearedonthesurfaceofMA-NCM811-CO2L.Aweakbroadpeak(attributedtoLi-O-Mbonding)gradually emergedatapproximately54eVwithincreasingAr+etchingdepth47. ThisconfirmsthatasmallamountofresiduallatticeLiremainswithin thebulkphaseofMA-NCM811-CO2L.

TG-MS results indicate that the MA-NCM811-CO2L releases H2O andO2gasesat200°C(SupplementaryFig.16).Incombination,the infrared spectroscopy result of MA-NCM811-CO2L (Fig. 2b) shows a broadpeakat3490cm–1,adoubletpeakintherangeof1485-1420cm–1 andasharppeaklocatedatapproximately880cm–1.Thesespectral featurescollectivelydemonstratethepresenceof–OHandCO32–inthe leachingproductsfromCO2system48.Real-timepHmonitoring(SupplementaryFig.17)revealeddistinctevolutionpatternsinwhichthe water leaching process pH increased from 7 to a peak and then decreased to 10.5, whereas the CO2–assisted leaching process pH increasedfrom4.2to6.1andplateauedbelow7.Onthebasisofthe E-pHdiagramsinSupplementaryFig.18,thedissolutionofTM2+and subsequentcomplexationofTM2+withCO32–mayhaveoccurredinthis system. The absence of these phenomena in P-NCM811-CO2L also confirmsthattheyoriginatedsolelyfromthepre-MCprocess(Fig.2b andSupplementaryFig.19).ComparativeanalysisoftheNiK-edgeX-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra of MA-NCM811 and MA-NCM811-WL(SupplementaryFig.20)revealedtracesofHintercalation duringthewaterleachingprocess.Thesefindingsdemonstratethat theleachingmechanismofLi+fromMA-LTMOisnotlimitedtoasingle pathway,evenunderaqueousconditions.J.R.Dahnetal.49.reported thatduringthewashingofhigh-NiLTMO,theionexchangeofLi⁺/H⁺ occursmorefrequentlyinaqueoussolutionswithhigherpH,whereas the dissolution of Li and TMs may occur in solutions with slightly lowerpH.

In brief, the H+ introduced by CO2 may be involved in ion exchangereactionsandacidicdissolutionreactionswithintheresidual insolubleLiinthelattice.ThereleasedLi+fromMA-LTMOintheCO2-assisted leaching may have three pathways: (i) dissolution in the solubleLi-richphase(whichisanalogoustolithiumoxide,Li2O)(Eq.2), (ii)ionexchangeofLi+ and H+ (Eq.3),and(iii)acidicdissolutionoflatticeLi (Eq. 4),asshown in Fig.2c.TMsmayundergodissolution followedbycomplexationundertheweaklyacidicinfluenceofCO2 duringthisprocess(Eq.5).

CO2 +H2O"H2CO3"H++HCO3(cid:1) "2H++CO32(cid:1) (1)

Li2O+H2O!2LiOH (2)

LiTMO2 +xH+ !Li1(cid:1)x H x TMO2 +xLi+ (3)

(1+x)LiTMO2 +4xH+ !2xLi++xTM2++Li1(cid:1)x TMO2 +2xH2O (4)

TM2++CO3(cid:1)!TMCO3 (5)

Accordingtotheprecedinganalysis,theleachingproductispri- marilycomposedoftransitionmetaloxides(TMOswithtraceamounts of residual lattice Li), oxyhydroxides (TMOOH), and complexation productsofTMs.High-resolutionTransmissionElectronMicroscopy (HR-TEM)(Fig.2d)oftheMA-NCM811-CO2LsamplerevealedthatCO2-assistedleachingpreservesthedisorderedstructureofMA-LTMO.A 2nm-thicklayeredphasecoveredtheparticlesurface,withaninterlayerspacingof0.21nm,whichisconsistentwiththe(105)planeof NiOOH50. In contrast, the core consisted of amorphous domains coexisting with spinel, rock-salt and layered phases. This core-shell structureisfurthersupportedbythevariationinthehydroxyloxygen (–OH) content observed by depth-profiling O1s XPS (Fig. 2e). Additionally, the concentration of oxygen vacancies on the surface was significantlygreaterthanthatinthebulkphase,astheyaregenerated tomaintainchargeneutralityduringanionextraction51(Supplementary Note 4). These results suggestthat the leaching products with disordered Li-deficient TMO cores and surfaces were enriched in TMOOHwithoxygenvacancies.TheNi2pXPSspectra(Fig.2f)further revealed a higher proportion of Ni2+ species on the surface, which alignswiththeproposedleachingpathway.Scanningelectronmicroscopy(SEM)results(SupplementaryFig.22)revealedthattheprimary particlesizeoftheleachingproductwasbetween50and100nm.The combinedfeaturesofthenanoscaledimensionsandsurfaceenrichmentofoxygenvacanciesand–OHendowtheleachingproductwitha highcatalyticsurfaceareaandabundantactivesites,whicharecritical forenhancingthecatalyticactivityofTM-basedmaterials52.

Micro-segregationofLi/TMinMA-LTMO
ThereasonsforthesignificantdifferenceinthereactivityofLiandTMs after activation were further explored. Notably, MA-NCM811-2h developedlithiumcarbonate(Li2CO3)phasesduringambientageing (320h),whereasitspristinecounterpartdemonstratedexceptionalair stabilitywithnodetectableLi2CO3formationunderidenticalexposure conditions (Supplementary Fig. 23). This contrast in reactivity confirms that the activation process generates an amorphous Li-containing phase,which ishighly reactive tospontaneous CO2 chemisorption(Li2O+CO2→Li2CO3,ΔGθ=−176kJmol–1,asshowninSupplementaryFig.24).ThehysteresisobservedintheCO2adsorption-desorption isotherms of MA-NCM811 collected at 0°C (Fig. 3a and SupplementaryFig.25)alsoconfirmsirreversibleCO2adsorptionsites. AndMA-NCM811hadapeakspecificsurfacearea(107m2g–1)at2hof activation, which is consistent with the maximum CO2 uptake.

Prolonged MC activation led to a reduction in the CO2 adsorption capacity,whichwasattributedtoparticleagglomeration,asevidenced bytheSEMresultsofMA-NCM811inSupplementaryFig.2(thespecific surface area decreased by ~23.6%), eliminating partial CO2-chemisorption-activesites.Thisfindingalsoindicatesthattheuniquesurface oftheactivatedproducts,whichcanchemicallyadsorbCO2,warrants furtherexploration.

Mechanochemically induced amorphization may promote elemental segregation byperturbingthespatiallyordereddistributionof elements in crystal structures53. Time-of-Flight Secondary Ion Mass Spectrometry(TOF-SIMS)depthprofiling(Fig.3b,c)firstrevealeda pronouncedchemicalgradientinMA-NCM811inwhichtheLi+abundance decreased sharplyfrom the surfaceinward,whereastheTM+ abundance increased, confirming that the Li-rich surface layer was approximately 20nm thick. XPS depth-etching (Fig. 3d–f) further resolvedthechemicalstatesofthesurfaceelements,showingthatthe surfacewasdominatedbyLiOH/Li2CO3,whichmayhavebeenformed by the adsorption of atmospheric H2O and CO2 onto the Li-rich amorphousphase,identifiedbyO1sat531.5eV54andLi1sat55eV54–56. FromtheNi2pspectrumofMA-NCM811(Fig.3fandSupplementary Fig.29),theintensityoftheNi2ppeaksonthesurfacewassignificantly lowerthanthatinthebulkphase,andtheNi2+/Ni3+ratiodecreasedwith depthbutexceeded14%intheouterregions.OnthebasisoftheXPS etchingresultsandtheelementconcentrationinflectionpointsfrom TOF-SIMS,theMCprocessdisruptsthespatiallyordereddistribution ofelementsandtherebydrivesthesegregationofLiandTMs.This mechanism induces the formation of such a reconstruction layer (~20nm)inthenear-surfaceregionofMA-LTMO,whichisessentiallya depth-gradient transition zone dominated by a Li-rich amorphous phase. With increasing depth, the concentration of active Li sites capableofreactingwithatmosphericcomponentsdecreases,whilethe valencestatedistributionofNigraduallychanges,anditsconcentrationshowsanoppositetrendtothatofLi.

CausesfortheMicro-SegregationofLi/TM
The Li-rich domain generated from elemental segregation is water soluble,whichprimarilyleadstotheselectiveextractionofLifromMA-LTMOs.However,theoriginofelementalsegregationcausedbyMC treatmentremainsunresolved.Priorstudiessuggestthathigh-valent Ni ions undergo charge redistribution during electrochemical processes,releasingoxygenandreducingNioxidationstates57,58.Here,the NiK-edgeXANESspectrum(Fig.4a)revealedadownwardsshiftinthe NiK-edgeenergy(~1.5eV)inMA-NCM811,confirmingthereductionin Ni.TheresultsfromtheEXAFSspectra(Fig.4b)revealedanincreasein the interatomic distances of Ni-O and Ni-M after mechanochemical activation,withagradualweakeningoftheNi-Mbondstrength,indicatingthattheshort-rangestructurewassignificantlydisrupted.The RamanspectrashowninFig.4candSupplementaryFig.30demonstrate thatP-NCM811exhibitstypicallayer-like anisotropic vibration modes59.AfterMCtreatment,theA1gpeak60showedbroadeninganda pronounced low-frequency shift (31.3cm–1), along with attenuation andeventualdisappearanceoftheEgpeak.Thisbehaviorissimilarto thatofthedisorderedrocksaltstructure61,indicatingafundamental transformation from an ordered layered structure to a highly disordered configuration, with the lossof distinctin-plane and out-of-plane vibrational modes. Further analysis combining EXAFS spectra and HR-TEM of MA-NCM811 (Fig. 4d) revealed the coexistence of multiplephases(layered,rocksaltandspinelphases)62,reflectingthe basiccompositionofitshighlydisorderedstructure.Thesechangesin thechemicalstateandcoordinationenvironmentofNicanbeattributed to mechanochemically facilitated Li/TM cation migration, as evidenced by the XRD refinement of MA-NCM811 (Supplementary Fig.1).ItshowedsignificantevolutionintheLi/Niantisitemixingratio, whichisakeyparameterforstructuralintegrity63.Themixingratiofirst increasedto45.6%after2h,reflectingstructuralevolutiondrivenby atomicdisplacement.

Collectively, the structural evolution observed in MA-NCM811 fundamentally originates from mechanochemical coupling effects (Fig.4f).High-valentNiionsundergoreductiontoNi2+byaccepting electronsfromlatticeoxygenandpartiallyfromMn4+,asevidencedby XPS-detectedMn7+ (Fig.4e)and Mn-dependentpurpleleachate colouration (Supplementary Fig. 31). Moreover, marked Li/Ni antisite disorderingfurthertriggersphasemicro-segregation,resultinginthe formation of distinctLi-richdomains and TM-concentrated regions. Onthebasisofpreviousanalysisofthephasedistributioncharacteristicsoftheactivatedproduct,wefoundthatMCtreatmentcreatesa highlyamorphousanddefect-richstructure.Withinthisstructure,Li/ TMmicro-segregationoccurs;specifically,Libecomesenrichedinthe amorphoussurfacereconstructionlayer,whereasTMremainsstabilizedwithintheTM-Oframeworkcomposedofalternatingtetrahedral and octahedralcoordination, with only a small amount of lattice Li embeddedintheframework.Thisuniquestructure,resultingfromthe synergistic effect of macroscopicgrainrefinement and microscopic interelement electron transfer and atomic displacement, ultimately convertstheLilockedintheoriginallayeredstructureintoastatethat ishighlyreactivetowardsH2OandCO2.Thismechanismeffectively overcomestheinherentlimitationsencounteredwhenH2OandCO2 areuseddirectlytoleachpristinecathodematerials.

In-situUpcyclingLeachingProductsforOERcatalysts
Theunpairedd-orbitalelectronsofTMsplayapivotalroleinfacilitatingredoxreactions,whiletheirmultivalentcharacteristicsendow themwithhighperformanceincatalyticprocesses64.Theseintrinsic properties render TMs ideal catalysts for diverse electrochemical reactions, with Ni and Co standing out as particularly prominent candidates65,66.Notably,theincreaseincatalyticactivitydependsnot solely on elemental properties but also critically on the rational regulation of microstructural features. Prior studies have demonstratedthatintroducingstructuraldisordercansignificantlyincrease catalytic activity67,68, forming a critical strategy for modifying non-preciousmetalcatalysts.TheMCprocesshasbeenfoundtoimpart favorablestructuraldisorder,whereasthenondestructiveLiextraction process preserved this disorder and concurrently established approximate core–shell heterointerfaces on the surfaces of the leaching products. These interfaces are hypothesized to lower the oxygenvacancyformationenergy65,therebyenhancingthecatalytic performanceoftheOER.

The electrocatalytic performance of MA-LTMO-CO2Ls was evaluated for the OER in 1.0M KOH through electrochemical measurements.CommercialCo3O4wasusedasacontrastsample.Asshownby thelinearsweepvoltammetry(LSV)curvesinFig.5a,comparedwith commercialCo3O4,MA-LTMO-CO2Lspossesssuperiorelectrocatalytic activity,asevidencedbytheirsignificantlyloweroverpotentials,which arerequiredtoachieveacurrentdensityof10mAcm–2.Amongthem, MA-NCM811-CO2Ldemonstratedthebestperformance,withanoverpotentialof322mV,whichisconsiderablylowerthan367mVrequired byCo3O4.ThefittedTafelslopesofMA-NCM811-CO2L(90mvdec–1) and MA-NCM622-CO2L (127mVdec–1) werelower than thatof commercialCo3O4(140mVdec-1),indicatingthatthecatalytickineticsof high-NileachingproductsfortheOERaremorefavorable.Thisfinding isconsistentwiththeresultsoftheelectrochemicalimpedancespectroscopy (EIS) results presented in Fig. 5c, which revealed that the impedance arcs of the high-Ni leaching products weresmaller than those of their counterparts and commercial Co3O4, suggesting that theyhavethelowestchargetransferresistanceandexhibitthefastest OERkinetics.High-Nisystemsexhibitedsuperiorcatalyticsynergies, whichcouldbeattributedtotheirelevatedNi3+content,whichfacilitatestheadsorption–desorptionofOH→Ointermediates66,69.Inaddition, to comprehensively evaluate the OER performance, the electrochemicalsurfacearea(ECSA)wasdeterminedviadouble-layer capacitance (Cdl) measurements from CV scans in the nonfaradaic regionatvariousscanrates(Fig.5dandSupplementaryFig.32).The leaching products, especially MA-NCM811-CO2L, demonstrated a superiorCdl of10.01mFcm–2,markedlyexceedingthatofCo3O4(6.52 mFcm–2),indicatingahigherdensityofOERactivesiteslikelyoriginatingfromthepre-MCMprocess.Critically,theoperationalstability was validated by chronopotentiometry testing (Supplementary Fig.33),whichrevealedaminimalpotentialincreaseoverthecourseof 24h. Notably, the leaching product derived from spent cathode materials (MA-S-LTMO-CO2L) also exhibited excellent stability over 200h ofoperation under identical testing conditions (Fig. 5e).This observationstronglysuggeststhatthestructuralandcompositional defects (e.g., trace impurities) introduced into the cathode waste during long-term electrochemical cycling and insufficient pretreatment did not compromise the catalytic performance of the final leaching product. In fact, the performance continued to improve duringoperation.ItwasfurtherexaminedbyLSV(Fig.5e,inset)andEIS (SupplementaryFig.34),whichrevealedamorefavorablepolarization curveafter200hofoperationthanbeforethestabilitytest.Theoutstanding stability underscores the robustness of the catalytic sites formedinthiswaste-to-catalystprocess.Benchmarkingagainststate-of-the-artTM-basedOERelectrocatalysts(Fig.5fandSupplementary Table3),ourcatalystdemonstratedcompetitiveη10values,withthe performanceadvantagestemmingfromtailoredinterfacialengineering and disordered state modulation. Collectively, these findings establish a sustainable upcycling pathway that transforms battery wasteintohigh-performanceOERcatalysts,bridgingresourcecircularityandenergyconversiontechnology.

Methods
Materials
The cathode materials, including LiNi0.33Co0.33Mn0.33O2 (NCM111), LiNi0.6Co0.2Mn0.2O2 (NCM622), LiNi0.8Co0.1Mn0.1O2 (NCM811), LiCoO2 (LCO), LiMnO2 (LMO)andLiFePO4(LFP)werepurchasedfromMTI Corporation.ThespentcathodematerialswereprovidedbyHuayou Company,andtheircompositionsareshowninSupplementaryTable1 asdeterminedbyInductivelyCoupledPlasma-OpticalEmissionSpectrometry (ICP-OES). Sulfuric acid (H2SO4, analytical pure) was purchasedfromBeijingChemicalPlant.CO2(≥99.99%)usedinthisstudy was provided from a high-purity gas cylinder sourced from Beijing Huan Yu Jing Hui Jing Cheng Gas Technology Co., Ltd. Potassium hydroxide(KOH,analyticalpure)waspurchasedfromShanghaiHushi ChemicalReagentCo.,Ltd.Theaquaregiasolutionwaspreparedby mixing concentrated nitric acid (HNO3, analytical pure) and concentratedhydrochloricacid(HCl,analyticalpure)inavolumeratioof 1:3.HNO3andHClwerepurchasedfromBeijingChemicalPlant.The standardsolutionofLi.Ni,Co,Mn,Al,Fe,Cu,Na,K,Ca,P,ZnandMg usedforICPwerepurchasedfromGuobiao(Beijing)Testing&CertificationCo.,Ltd.Nafion(~5%)waspurchasedfromShanghaiMacklin BiochemicalCo.,Ltd.

Lithiumextractionprocess
TherecyclingofLiisdividedintotwosteps,whicharethemechanochemical (MC) process and the leaching process. The MC is conductedintheballmill(Pulverisette7,FRITSCH,Germany).Ifthereisno additionalmark,therotationconditionsare600rpm,rotation20min and pause 10min, and the ball-to-powder mass ratio is 20:1. The leachingprocessisallowedtooccurinahydrothermalreactionvessel. If there is no additional mark, the solid-liquid ratio is 20gL–1, the leachingtemperatureis25°C,theleachingpressureis0.5MPa,andthe leaching time is 1h. After leaching, the final lixivium was separated from the leaching product(MA-LTMO-CO2L)through filtration. The leachatewaspurifiedbymodulatingpHwith1.0MLiOHsolutionand then prepared for Li2CO3 product through thermal decomposition, andthedecompositionconditionsaretemperatureof95°C,timeof 1.5h,andstirringspeedof300rpm.

Tochooseanappropriaterecyclingroute,theleachingefficiency (R) was determined as shown in Eq. 6, and the selectivity (S) was calculatedaccordingtoEq.7,wheremiL representsthemassofthe element“i”inthelixivium;miR representsthemassoftheelement“i”in theleachingproduct;“i”isLi,Co,Ni,orMn;RAll indicatesthesumof leachingefficiencyofallthemetalelements.

R = miL / (miR + miL) ×100% (6)

S = Ri / RAll ×100% (7)

Materialscharacterization
The compositions of the materials used in this article are analyzed throughanindictivelycoupledplasmaopticalemissionspectrometer (ICP-OES,ICAP6300Radial,ThermoScientific).Thematerialsarefirstly dissolvedbyaquaregiasolution,andthenthecontentsofmetalsinthe solutionandtheleachatearequantifiedbyICP-OES.Thestructuresof thematerialsorleachingproductswerecharacterizedbyanX-raydiffractometer (XRD, SmartLab 9kW, Rigaku) with a Cu Kα radiation source. The proportion of the amorphous phase in MA-LTMO was determined by the XRD internal standard method. The Highscore5.3softwarewasusedtofittheXRDpatterns,andtheRietveld quantitativeanalysiswithoutstandardswasemployedtocalculatethe relativecontentsofLTMOandSi,aspresentinSupplementaryNote1.

ThemicrostructureofMCproductsandleachingproductswascharacterizedusingaJEOLJEM-F200field-emissiontransmissionelectron microscope (TEM) equipped with selected-area electron diffraction, withthespecimenspreparedbydepositinganultrasonicallydispersed suspension onto a TEM grid and drying. The Raman spectra were characterizedbyaRamanspectrometer(inVia,Renishaw).Thevalence statesoftheelementswereanalyzedbyX-rayphotoelectronspectroscopy (XPS, ESCALAB 250Xi, Thermo Scientific). Depth-profiling was performedusinganargonion(Ar+)etchinggun,with4etchingcycles (120s per cycle, corresponding to 8nm per cycle as calibrated on a Ta2O5 standard),totrackthevariationofthevalencestatesfromthe surface to the bulk. Synchrotron radiation X-ray absorption spectroscopy(XAS,attheNiK-edge)wasrecordedinthetransmissionmodeat the XRD station of the beamline 4B9A of the Beijing Synchrotron RadiationFacility.Thespecificsurfaceareaoftheactivatedproductwas determined byCO2adsorption at 0°Cand calculated using the BET model.TheelementaldistributionwascharacterizedbyTime-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS, TOF.SIMS 5, ION-TOF GmbH),andthesputteringdepthiscalibratedbytheSiO2sputtering rate.Thethermaldecompositionbehavioroftheleachingproductwas detectedbyahigh-temperaturethermogravimetricanalyzer(TG-DSC-MS,LABSYSEVOT),withthetestruninanitrogenatmospherefrom 30°Cto800°Cataheatingrateof10°Cmin–1.

Electrocatalyticmeasurements
AlltheelectrocatalyticmeasurementswereconductedusingaCHI760E electrochemicalworkstationunderambientconditions,whichuseda three-electrodecellsystem.TheleachingresiduesobtainedfromCO2-assistedextractionsystem(MA-LTMO-CO2Ls)wereusedastheworking electrode,Hg/HgOandPtservedasreferenceandcounterelectrode, respectively.Thecatalystinkwaspreparedwith2mgactivematerials, 0.5mg acetylene black, 25μL 5wt% Nafion solution, and 375μL isopropanol/H2O(v:v=1:1)mixedsolvent,followedbya30minultrasonic dispersionprocess.23μLcatalystinkwasdroppedontoacarboncloth withthemassloadingof0.38mgcm–2.TheOERwasmeasuredinO2-saturated1.0MKOHsolutionattherotatingspeedof600rpmwiththe scan range of 10mVs–1. All potentials were calibrated versus the reversiblehydrogenelectrode(vs.RHE)usingEq.8:

ERHE = EHg=HgO +0:059×pH+0:098 (8)

AllLSVcurvesweremeasuredatascanrateof10mVs−1,andthen thepotentialwascorrectedby90%IRcompensationtoremovethe solution resistance effect. The overpotential (η) was determined by Eq.9:

η=ERHE (cid:1)1:23 (9)

The LSV curves werefurther used to construct the Tafel plots, which plotoverpotential(η)asafunctionofthecurrentdensitylog(j). The ECSA was measured by scanning the CV in a non-Faradaic region.Then,theECSAwascalculatedusingthefollowingEq.10:

ECSA= Cdl / Cs (10)

WhereCdl isthedouble-layercapacitancederivedfromtheslopeofthe linear regression (R2>0.995)ofthe currentdensityatthe midpoint potentialversustheCVscanrate.;Cs isthespecificcapacitanceofaflat surface(40μF·cm−2).

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "The manuscript presents a short-range clean recycling approach for spent lithium-ion battery cathodes, convincingly demonstrating the efficiency of mechanochemical processes through robust evidence. The mechnochemical treatment enables recycling of spent NCM battery under relatively mild conditions. With carbonation of the as-treated black mass, lithium and transition metals recovery are both achieved. Nevertheless, there are still issues required to be discussed before publication.\nIn extracting valuable metals from spent cathode materials, CO2 as leaching reagent is usually considered as inefficient. The authors should provide detailed discussion on how the mechnochemical treatment enables a high reaction potential. Will the amorphous phase be important during the processing? How was the optimal activation time was determined?\n- Improvement on discussion of state-of-the-art of literature is very necessary and how selective leaching and upcycling of cathode materials are explored should be added in the introduction section.\n- The authors mentioned “Notably, prolonged activation time (activation time >2 h) leads to gradual dissolution of TMs”. What are gradual dissolution and how the dissolution the transition metals reacting with CO2? It is necessary to provide direct evidence on the intermediate products. Additionally, a thermodynamic analysis will be helpful for understanding the process.\n- The research object of the manuscript focuses on ternary materials. Is LCO with a layered structure also feasible? Is LiFePO4 or LiMn2O4 also feasible? Can some experiments or explanations be added to improve the universality of the raw materials?\n- The authors detected oxygen vacancies in the leaching residue, while at which stage the oxygen vacancies appeared is required to be clarified. For example, do oxygen vacancies exist in the mechanically activated products? Or do oxygen vacancies exist in the waste materials used in this study? Additional results is recommended to improve understanding the mechanisms.\n- In Figure 3, the authors claims “a Li-rich surface reconstruction layer have been established on the surface of materials.” However, it is not clear how the layer is defined. Will the surface be easily peeling off if a reconstructed layer is formed?\n- Error bars for the leaching efficiencies in the corresponding figures are required to be added to reflect the repeatability and statistical validity of the data.", "reviewer_2": "In this work, the authors proposed a three-in-one strategy that enables CO2-carbonation with spent cathode materials to achieve selective Li recovery and regeneration of transition metals. The study conducts an in-depth analysis of how mechnochemical (MC) treatment affects the reactivity of different elements in cathode materials and the underlying mechanisms, providing new insights on the role of MC treatment in the recycling process. I think it can be considered for publication if the following concerns are tackled with.\n(1)The introduction can be enriched and a more detailed discussion on selective leaching and direct regeneration is required to be included. The authors only mentioned briefly the pyrometallurgy and hydrometallurgical methods at this version and the statement on “...process requires a large amount of strong acid and alkali...” is not always correct. It is necessary to provide an outline on how this research is correlated and different from a traditional hydrometallurgical process.\n(2)In addition to destroying the crystal structure, the MC process will also reduce the particle size. Together with the size reduction, how it is related to the leaching process, including lithium and other elements?\n(3)A detailed description on how the amorphous content in Figure 1 was determined should be provided. How is the amorphous phase influencing the subsequent recycling process?\n(4)What is the phase of the residual Li in the leaching product? It is required to discuss the carbonation process and how CO2 pressure and leaching time influence the lithium extraction.\n(5)On page 10, the author present the Raman spectrum data of P-NCM811 and MA-NCM811 in Figure 4c. However, this section is unclearly articulated and lacks a robust connection to the contextual discussion. It is advised to revise this part for better coherence.\n(6)Some details in Figures still need to be noted. In Figure 4e, the scale of TEM results is missing; in Figure 5e, the unit of the y-axis should be revised to mA cm-2.", "reviewer_3": "The following are reviewer comments for the article entitled A Three-in-One Strategy: Li/TMs Micro-Segregation to Enable Upcycling of Spent Layered Cathode Materials submitted to Nature Communications by Wang et al.\nThe reviewed article has successfully demonstrated the novel approach of the selective Li recovery from spent Li-ion cathodes and upgrading of transition metals during mechanochemical processes assisted by CO2 sequestration. The Authors performed the broad compositional and structural products analysis and OER catalytic activity. I recommend publishing the article after a major review, and below are the comments and remarks:\n1. Could the Authors describe the XRD results shown in Figure 1b by ascribing the peaks to the proper compounds?\n2. What purity do the recovered Li compounds exhibit?\n3. How does the morphology (e.g., grain size, grain shape) of examined materials change upon mechanochemical processing? Whether SEM analysis was done before and after the MC process?\n4. Were OER experiments performed also for benchmark OER materials e.g. RuO2 or Co3O4 for comparison with recovered catalyst materials?\n5. At which potential were the chronoamperometry measurements performed shown in Fig. 5e?\n6. 6. The description of the Y axis should be “current density” instead of “current”.\n7. The Electrochemical Active Surface Area should be ascertained in order to assess the OER catalytic capabilities."}, "author_response": "Point-by-point response to the reviewers’ comments\nWe thank the reviewers’ efforts on our manuscript. These valuable suggestions\nhave enabled us to revise the manuscript more rigorously, improve our understanding\nof the content, and deepen our analysis. All modifications made in response to the\nreviewers’ comments have been highlighted in blue in this response letter and in red\nwithin the revised manuscript.\nReviewer #1:\nThe manuscript presents a short-range clean recycling approach for spent lithium-ion\nbattery cathodes, convincingly demonstrating the efficiency of mechanochemical\nprocesses through robust evidence. The mechanochemical treatment enables recycling\nof spent NCM battery under relatively mild conditions. With carbonation of the as-\ntreated black mass, lithium and transition metals recovery are both achieved.\nNevertheless, there are still issues required to be discussed before publication.\nIssue 1:\nIn extracting valuable metals from spent cathode materials, CO as leaching reagent is\n2\nusually considered as inefficient. The authors should provide detailed discussion on\nhow the mechanochemical treatment enables a high reaction potential. Will the\namorphous phase be important during the processing? How was the optimal activation\ntime was determined?\nDiscussion:\nThank you for your constructive comment and thoughtful questions.\nGenerally, CO is considered a relatively inefficient leaching agent for extracting\n2\nvaluable metals from spent cathode materials, which is why it is not typically used as\nthe primary reagent. The mechanochemical (MC) process proposed in this study,\nhowever, fundamentally alters the physicochemical properties of the original LTMO\ncathode material. By creating a highly amorphous, defect-rich structure with a large\nspecific surface area, the MC treatment transforms the lattice Li into a state that is\nhighly reactive toward both H O and CO , thereby overcoming the inherent limitation\n2 2\nof directly leaching pristine cathodes with CO . We supplemented the detailed\n2\ndiscussion on how the mechanochemical treatment enables a high reaction potential in\nSection 2.4 of the revised manuscript, as detailed below.\nThe resulting high degree of amorphization in MC process is the key to the success\nof this process. This amorphization transforms the LTMO from the original stable and\nordered R-3m lattice structure into a composite consisting of a Li-rich amorphous phase\nand a crystalline phase that is highly disordered and enriched with TMs. Analysis of the\nleaching behavior of various elements in both aqueous and CO systems, as well as the\n2\nphase composition changes before and after leaching, indicates that the Li within the\namorphous phase exhibits water-soluble characteristics. For example, activated\nNCM811 achieves approximately 75% Li leaching efficiency in aqueous system. The\npresence of this soluble Li contributes significantly to the highly efficient Li extraction\nenabled in CO system.\nevidence, concluding structural evolution of LTMO and leaching performance of Li and\nTMs. First, the XRD patterns in Figure R1 show that the degree of amorphization of\nNCM811 increases markedly with activation time. After 2 h, the activated product\ncontains the highest fraction of amorphous phase and the most disordered residual\ncrystalline components. Second, the leaching results in Figure R2 indicate that the\nactivated product with activation time of 2h achieves a Li extraction yield of 75 % in\naqueous system, with no further significant improvement upon prolonged activation.\nThe effect is even more pronounced in the acidic system, 2 h of MC process gives the\nhighest Li leaching efficiency and selectivity, whereas longer activation times only\nmarginally increase Li recovery while substantially enhancing TMs dissolution. These\nfindings suggest that excessive activation triggers detrimental side reactions and\nreduces Li selectivity. Therefore, 2 h is chosen as the optimal activation time, balancing\nmaximum structural disorder with the best Li recovery while avoiding the loss of\nselectivity. Although this optimal condition was established for NCM811, it also proves\neffective for other layered ternary cathodes such as NCM111 and NCM622.\nNonetheless, given the distinct structural characteristics of low-nickel ternary cathode\nmaterials, further optimization of activation parameters is warranted and will be\nexplored in future work.\nThe related revision in the main text:\nLines 318-328 in Section 2.4: Based on previous analysis of the phase distribution\ncharacteristics of the activated product, we found that MC treatment creates a highly\namorphous and defect-rich structure. Within this structure, Li/TMs micro-segregation\noccurs, specifically, Li becomes enriched in the amorphous surface reconstruction layer,\nwhile TM remains stabilized within the TM-O framework composed of alternating\ntetrahedral and octahedral coordination, with only a small amount of lattice Li\nembedded in the framework. This unique structure, resulting from the synergistic effect\nof macroscopic grain refinement and microscopic inter-element electron transfer and\natomic displacement, ultimately converts the Li locked in the original layered structure\ninto a state that is highly reactive towards H O and CO . This mechanism effectively\n2 2\novercomes the inherent limitation encountered when using H O and CO directly to\n2 2\nleach pristine cathode materials.\nFigure R1 (a) XRD results of P-NCM811 and MA-NCM811 for different activation\ntime. (b) The FMWH of (003) and (104), the value of I / I , and (c) the amorphous\n(003) (104)\nphase ratio in the XRD results of P-NCM811 and MA-NCM811. (Figures 1b-d)\nLi TM\n80 2\n% ) 60\ny\n( 40\nc\nn 20\ne\nci 0\neffi\n100\ng 80\nH+\nn\nhi\n60\nc\na\ne 40\nL\n20\n0\n0 2 4 6 8 10 12 14 16\nActivation time (h)\nFigure R2 The effect of H O and H+ on the leaching efficiency of Li in P-NCM811\n2\nand MA-NCM811. (Figure 1f)\nIssue 2:\nImprovement on discussion of state-of-the-art of literature is very necessary and how\nselective leaching and upcycling of cathode materials are explored should be added in\nthe introduction section.\nDiscussion:\nThank you for your suggestion on strengthening literature discussion and\nsupplementing research progress in the introduction. We have supplemented the\nresearch progress on selective leaching and upcycling in the Section 1 of the revised\nmanuscript, as detailed below.\nThe related revision in the main text:\nLines 61-82 in Section 1: Selective leaching improves Li recovery and simplifies\npurification compared to impurity-sensitive conventional hydrometallurgy 19,20. The\nmechanisms preferentially induce targeted phase transformations in spent cathodes,\nseparating Li from transition metal (TM) phases, driven by strategies like adding\nreductants or applying elevated temperature/pressure21. For example, carbothermic\nreduction converts spent cathodes into lithium carbonate (Li CO ) and transition metal\n2 3\nelements or their oxides 20,22,23, and sulfation roasting yields lithium sulfate (Li SO )\n2 4\nand transition metal oxides 24-26. However, these methods often require substantial\nreagent inputs, risk hazardous emissions and secondary pollution, and generate leaching\nresidues. These residues usually necessitate acid leaching for conversion into salt\nsolutions prior to reuse, which severely diminishes their value. Consequently,\noptimizing resource utilization across the selective leaching chain demands greener,\nmore efficient processes and solutions for managing low-value residues. Flash Joule\nheating 27 is possible to enable one-step selective Li extraction via seconds-long, high-\ntemperature reactions. This instantaneous heating offers greener processing and\nuniquely induces structural transformations in spent cathodes which could convert\nresidual metals into self-assembled multi-metal hydroxide catalysts 28. Electrochemical\nmethods selectively leach Li at ambient temperature using applied potential. The\nresulting structurally-defective, Li-depleted residue can serve directly as functional\nmaterials, such as OER catalysts, but electrode reconstruction requirements hinder\nscale-up 29-31. Mechanical methods selectively leach Li by induced room-temperature\nphase transitions32, yet grinding additives risk impurity contamination 33,34. In summary,\nexisting technologies have yet to optimally balance mild processing conditions,\nminimal chemical input, and the production of high-value outputs.\nReference\nLithium Batteries by Functional Ionic Liquid, ACS Sustainable Chemistry & Engineering, 9, 7022-7029\n(2021).\nand low-carbon strategy for selective lithium recovery from spent lithium-ion batteries: Combining\nmechanochemical activation with biomass reduction roasting, Separation and Purification Technology,\n338, (2024).\nstage extraction for selective recovery of lithium from spent lithium-ion batteries, Separation and\nPurification Technology, 338, (2024).\nSpent Lithium-Ion Batteries Using Carbothermal Shock Method, Angewandte Chemie International\nEdition, 62, e202300074 (2023).\nspent lithium-ion batteries by a carbon conversion control strategy of carbothermic reduction,\nGreen Chemistry, 9734-9744 (2022).\nextraction of lithium from spent lithium-ion batteries by sulfation roasting, ACS Applied Materials &\nInterfaces, 12, 18482-18489 (2020).\nrecovery of valuable metals from spent lithium-ion batteries by using conventional sulfation roasting,\nGreen Chemistry, 21, 5904-5913 (2019).\nrecovery of lithium and transition metals from spent ternary lithium-ion batteries powders, Chemical\nEngineering Journal, 522, 167321 (2025).\nlithium-ion batteries: A rising direct regeneration method, Journal of Energy Chemistry, 105, 501-513\n(2025).\ncathodes by simultaneously extracting lithium and constructing high performance oxygen evolution\ncatalysts, Resources, Conservation and Recycling, 222, 108466 (2025).\nW. Chen, Electrochemical lithium recycling from spent batteries with electricity generation,\nNature Sustainability, 8, 287-296 (2025).\nelectrochemical recycling of spent lithium-ion batteries: Targeting the direct regeneration of de-lithiated\nmaterials, Chemical Engineering Journal, 479, (2024).\nLeaching Method for High-Purity Lithium Recovery from Spent Lithium Batteries, Environmental\nScience & Technology, 57, 4591-4597 (2023).\nChemie International Edition, 63, (2024).\ncathode materials into high-value products via a mechanochemical extraction and thermal reduction route,\nJournal of Hazardous materials, 413, 125222 (2021).\nusing ionic substitution stimulated by mechanochemistry, Journal of Cleaner Production, 279,\n(2021).\nIssue 3:\nThe authors mentioned “Notably, prolonged activation time (activation time >2 h)\nleads to gradual dissolution of TMs”. What are gradual dissolution and how the\ndissolution the transition metals reacting with CO2? It is necessary to provide direct\nevidence on the intermediate products. Additionally, a thermodynamic analysis will be\nhelpful for understanding the process.\nDiscussion:\nThank you very much for your insightful questions.\nRegarding the mechanism of “gradual dissolution” of TM in the acidic system,\nthis study specifies that the phenomenon refers to the dynamic process whereby TM2+\nmigrate from the mechanochemically activated crystal structure into the acidic solution\nphase and remain stable. As shown in Section 2.1, the leaching efficiencies of TMs\nfrom MA-NCM811 initially decreases and then increases with prolonged activation\ntime, which stems from the modulating effect of mechanical activation duration on the\ncrystal structure. At the optimal activation time of 2 h, Li+ is sufficiently released while\nTM ions remain well retained within a relatively intact lattice framework. And further\nextending the activation time, TMs started to migrate into the solution. As for the reason\nof TMs dissolution, we monitored the final pH in both aqueous and acidic systems\n(Figure R3a) revealed no significant change in the aqueous system, indicating that\nwater-soluble Li+ reached saturation at 2 h. In contrast, the pH in the acidic system first\nincreased and then decreased, accompanied by a slight reduction in Li leaching\nefficiency and an increase in TM leaching efficiencies, confirming that the leaching\npathways of Li and TMs evolve with mechanical energy input. Ultimately, excessive\nactivation time diminished the difference in leaching activity between Li and TM,\nmaintaining the solution pH within a range that allows dissolution of low-valence TM\n(e.g., Ni2+). We added the E-pH diagram (Figures R3b-d) obtained from HSC\nChemistry, validating that when the pH is lower than 7, Ni2+ exist primarily as ionic\nspecies in the solution within Ni-H O system. Furthermore, characterization results\n2\nconfirmed the reduction of Ni3+ to Ni2+ (Figure R4), providing a key prerequisite for\nTM dissolution.\nIt is noteworthy that localized TM dissolution also occurs in the CO system. CO₂\n2\ngenerates H⁺ through dissolution-dissociation equilibrium (CO + H O ⇌ H CO ⇌ H+\n2 2 2 3\n+ HCO - ⇌ 2H+ + CO 2-), which attacks M-O bonds and promotes the dissolution of Li\n3 3\nand TM. However, the dissolved TM ions rapidly react with CO 2-/HCO 2- in the system\n3 3\nto form complexes or undergo hydrolytic precipitation. Similarly, according to E-pH\ndiagram in the TM-CO -H O system as shown in Figure R5a-c, low-valence TM ions\n2 2\nare more likely to exist in the form of TMCO in the near-neutral solution. This pathway\n3\nwas verified by the presence of carbonate/hydroxyl species in the Fourier transform\ninfrared (FTIR) spectrum of the leaching product (Figure R5d).\nThe activation process results in the divergent reaction pathways and the\nintermediate products of TMs in the acidic and CO systems, and related\n2\nthermodynamic discussions have been further supplemented in Section 2.1, 2.2 and\nSupplementary Information of the revised manuscript, as detailed below.\nThe related revision in the main text:\nLines 134-141 in Section 2.1: Moreover, prolonged activation time (activation time >2\nh) leads to gradual dissolution of TMs. According to the endpoint of pH in acidic\nsystems (Figure S6a), the final pH first increased (activation time  2h) and then\ndecreased (activation time  2h), indicating excessive activation diminished the\ndifference in leaching activity between Li and TMs, which could be attributed to\nrecrystallization reducing their kinetic leahcing differences. This result maintains the\nsolution pH within a lower value, therby allowing dissolution of low-valence TMs in\nTM-H O system according to the E-pH diagram (Figures S6b-d).\ndissolution of TM2+ and followed complexation of TM2+ with CO 2- may occurs in this\n3\nsystem.\nFigure R3 (a) Endpoint pH value of MA-NCM811 leached in acid system; (b-d) E-PH\ndiagram in TM-H O-system. (Figure S6)\ntime. (Figure 4a)\nFigure R5 (a-c) E-pH diagram in TM-CO -H O-system at 25°C and 0.5 MPa for\n2 2\nsimulating the CO leaching environment. And (d) the FTIR spectra of the MA-\n2 2\nIssue 4:\nThe research object of the manuscript focuses on ternary materials. Is LCO with a\nlayered structure also feasible? Is LiFePO4 or LiMn2O4 also feasible? Can some\nexperiments or explanations be added to improve the universality of the raw materials?\nDiscussion:\nThank you for your practical questions. This study initially focused primarily on\nternary materials with a layered structure. Owing to their unique structural\ncharacteristics and Ni-containing content, the effect of mechanical energy is more\npronounced. However, we did neglect to investigate the impact of the MC process on\nLiCoO (LCO) also with a layered structure, and other common non-layered cathode\n2\nmaterials. In response to your inquiry, we have supplemented the data on the leaching\nefficiency of various elements in LCO, LiFePO (LFP), and LiMn O (LMO) before\n4 2 4\nand after MC treatment in aqueous, acidic (Figure R6) and CO systems, aiming to\n2\nverify the raw material universality of the MC process.\nThe results in Figure R7 and R8 show that LCO exhibits a leaching trend similar\nto that of ternary cathode materials. MC treatment increases the Li leaching efficiency\nof LCO in the aqueous system from 0.52% to 43.51%, and in the acidic system, the Li\nleaching efficiency reaches 91.71% with a Li selectivity of 91.9%, which are\nsignificantly higher than the 21.98% Li leaching efficiency and 67.16% Li selectivity\nof P-LCO. In contrast, LMO with a spinel structure shows a different leaching trend.\nMC treatment does not lead to the formation of a large amount of soluble Li in LMO,\nwith the Li leaching efficiency in the aqueous system being only 14.93%. Although an\nincreasing trend in Li leaching efficiency and a decreasing trend in Mn leaching\nefficiency are observed in the acidic system, the magnitude of the change is limited. P-\nLMO already has a Li selectivity of 81.16% due to the stability of its framework, and\nMC treatment only increases this value to 87.17%. LFP with an olivine structure has\nbetter stability than layered materials; similar to LMO, MC treatment exerts a certain\neffect on LFP but the effect is not significant. As shown in Figure R9, the MC process\ncan alleviate the challenge of weak acid (CO ) in leaching LCO and LMO, though its\n2\neffect is limited, increasing the Li leaching efficiency to slightly above 50%. In contrast,\nfor LFP, the MC treatment does not alter its leaching behavior under the weakly acidic\nconditions provided by CO .\nresults shown in Figure R10. Both LCO and ternary materials exhibit a similar\namorphization trend during the MC process, but the degree of amorphization of MA-\nLCO is lower, which is consistent with the result that less soluble Li is generated after\nMC process. An increase in mechanical energy input might improve the efficiency of\nthe Li extraction process. For LMO, the XRD pattern only shows uniform broadening\nand weakening of the diffraction peaks of all crystal planes, with no obvious structural\ntransformation similar to that of ternary cathode materials observed. Part of Li was\nextracted though the MC-induced reduction of Mn4+ or Mn3+. The diffraction peaks of\nthe MA-LFP product also shows uniform weakening. Combined with earlier studies\n(Green Chem., 2022, 24: 152-162; Mater. Today 2024, 73:130-150), it is known that\nthe selective Li extraction of LFP mostly needs to be achieved in the presence of\noxidants or an oxidizing atmosphere. However, the effect of mechanical energy on\nNCM and LCO is similar to that of a reducing agent. Therefore, the current process\nsystem may not be the optimal choice for Li extraction from LFP. In the future, if an\noxidizing atmosphere or oxidant is introduced during the MC process, more efficient\nselective Li extraction from LFP may be achieved. The above supplementary results\nindicate that the MC process has more significant applicability to layered materials\n(ternary materials and LCO), while its effect on non-layered materials (LMO, LFP) is\nlimited due to structural and compositional differences, which provides a direction for\nsubsequent process optimization.\nThe relevant supplementary content has consolidated in Section 2.1 and\nSupplementary Note 3 (Exploration on the universality of raw materials for the\nMC process) of the revised manuscript. Thank you for your question, which has helped\nto clarify the applicability of this process to various raw materials.\nThe related revision in the main text:\nLines 165-169 in Section 2.1: Further exploration of the universality of the raw\nmaterials, as discussed in Supplementary Note 3, reveals that this process is not\napplicable to cathode materials with non-layered structures (e.g., LiFePO and\n2 4\neffectiveness of the process is contingent upon a specific amorphization pathway.\nFigure R6 Schematic illustration of verification strategy for leaching activities of Li\nand other metal elements in different cathode materials. (Figure S9)\nFigure R7 The leaching efficiency of Li and M from CMs and MA-CMs\n(CM=NCM811, NCM622, NCM111, LCO, LFP and LMO) according to Route Ⅰ.\n(Figure S10)\nFigure R8 The leaching efficiency of Li and M from CMs and MA-CMs\n(CM=NCM811, NCM622, NCM111, LCO, LFP and LMO) according to Route Ⅱ.\n(Figure S11)\n% ) M (Co/Mn/Fe)\n80\n(\ny\nc\nn\ne 60\nci\neffi\n40\n1\n7\n7. 3\n1\n6. 3\n2\n8. 8\n7\nn 8 7 8 7\nhi\nc 20\na\ne\nL\nFigure R9 The leaching efficiency of Li and M from CMs and MA-CMs (CM= LCO,\nLMO and LFP) in CO -assisted leaching process. (Figure S12)\nNCM111-2h and MA-LiCoO2-2h; and the XRD results of MA-LFP-2h and MA-LMO-\n2h. (Figure S13)\nIssue 5:\nThe authors detected oxygen vacancies in the leaching residue, while at which stage\nthe oxygen vacancies appeared is required to be clarified. For example, do oxygen\nvacancies exist in the mechanically activated products? Or do oxygen vacancies exist\nin the waste materials used in this study? Additional results is recommended to improve\nunderstanding the mechanisms.\nDiscussion:\nThank you for your perceptive question. In response to your inquiry, we have\nsupplemented the oxygen vacancy characterization results of products at various stages\nin the research route, as shown in Figure R11. It can be observed that no obvious signals\nat g = 2.003 were detected in all samples except for the leaching residue MA-NCM811-\nCO L obtained in the CO system. This indicates that oxygen vacancies do not appear\n2 2\nduring the MC process but are generated during the leaching process in the CO system.\nmechanical energy input, which theoretically affects the coordination environment of\nelements within the lattice. However, no oxygen vacancies are generated in MA-\nNCM811, and the reasons for this are as follows. MA-NCM811 was prepared under\noptimal activation conditions, where the original crystal structure of NCM811 was\nsignificantly destroyed, and the valence states of local TM were reduced. However,\nEPR results showed no obvious oxygen vacancies at this stage. It is suggested that\nlattice oxygen may have been released in the form of O by losing electrons during the\n2\nactivation process, without forming stable oxygen vacancies. Alternatively, some\ncrystal planes exposed during the MC process might have adsorbed inorganic functional\ngroups from the air, which could occupy oxygen vacancies (J. Power Sources, 2019,\n432: 8-15). However, since MA-NCM811-WL also showed no obvious oxygen\nvacancy signals, this possibility is ruled out.\nIn contrast, oxygen vacancies were generated in MA-NCM811-CO L. This\n2\nsuggests that the extraction of lattice Li or TM remaining in the Li TMO framework\n1-x 2-y\ndisrupts the charge balance and coordination environment of the original lattice. To\nmaintain charge neutrality, O2- are synchronously extracted, leading to the formation of\noxygen vacancies in the lattice (Chem. Eng. J., 2023, 463: 142316; Energy Storage\nMater., 2025, 79: 104307) and ultimately endowing the leaching residue MA-NCM811-\nCO L with oxygen vacancy characteristics.\nInformation of the revised manuscript. Once again, thank you for your inquiry. It has\nbeen invaluable in bringing to our attention the finer details involved in this process.\nThe related revision in the main text:\nLines 230-232 in Section 2.2: Additionally, the concentration of oxygen vacancies (V )\nO\non the surface (Figure 2e) is significantly higher than in the bulk phase, as they are\ngenerated to maintain charge neutrality during anion extraction 50 (Figure S21).\nReference\netching for promoting Ni-rich cathode regeneration, Energy Storage Materials, 79, 104307 (2025).\nFigure R11 EPR results of (a) P-NCM811, (b) MA-NCM811, (c) MA-NCM811-WL\nand (d) MA-NCM811-CO L. (Figure S21)\nIn Figure 3, the authors claims “a Li-rich surface reconstruction layer have been\nestablished on the surface of materials.” However, it is not clear how the layer is\ndefined. Will the surface be easily peeling off if a reconstructed layer is formed?\nDiscussion:\nThank you for your insightful question. The surface reconstruction layer\nmentioned in Section 2.3 of the manuscript was characterized primarily through TOF-\nSIMS and XPS analysis of the activated product (Figure R12). We define the surface\nreconstruction layer as a surface-modified zone, induced by mechanochemical\nactivation, characterized by distinct crystalline phase transitions and continuous depth-\ndependent chemical gradients. Furthermore, this surface reconstruction layer\ndemonstrates significant stability against delamination. Because it forms a continuous\ntransitional structure to the underlying bulk phase, with a blurred boundary rather than\na sharp heterointerface with a fundamentally different composition or crystal structure.\nTherefore, this continuous gradient inherent to the mechanochemically-induced\ntransformation distinguishes it sharply from discrete, deposited external coatings or\nsurface layers (e.g., via ALD or CVD) (Nanotechnol. Rev., 2017, 6 (6): 527-547; Adv.\nSci., 2016, 3 (10)), eliminating the weak interfaces typically susceptible to detachment.\nRelevant revision has been added to Section 2.3. We appreciate your suggestion,\nwhich helps to deepen the understanding of the relationship between the MC process\nand leaching process.\nThe related revision in the main text:\nLines 280-288 in Section 2.3: Synthesizing the XPS etching results and the elemental\nconcentration inflection points from TOF-SIMS, the MC process disrupts the spatially\nordered distribution of elements and thereby driving the segregation of Li and TMs.\nThis mechanism induces the formation of such a reconstruction layer (~20 nm) in the\nnear-surface region of MA-LTMO, which is essentially a depth-gradient transition zone\ndominated by a Li-rich amorphous phase. With increasing depth, the concentration of\nactive Li sites capable of reacting with atmospheric components decreases, while the\nvalence state distribution of Ni gradually changes, and its concentration shows an\nopposite trend to that of Li.\nFigure R12 (a) TOF-SIMS mass spectrum of the surface in P-NCM811 and MA-\nNCM811. (b) TOF-SIMS depth profile of Li+ in P-NCM811 and (c) MA-NCM811, and\nthe sputter depth is calibrated by the SiO sputtering rate. (d) Li 1s, (e) O 1s and (f) Ni\n2\n2p in in-depth XPS profile of MA-NCM811. (Figures 3b-f)\nIssue 7:\nError bars for the leaching efficiencies in the corresponding figures are required to be\nadded to reflect the repeatability and statistical validity of the data.\nDiscussion:\nThank you for your valuable comment on these details. We agree that error bars\nare essential for demonstrating the reproducibility and statistical significance of the\nexperimental results. We have added error bars to Figures 1f and 1h accordingly as\nfollowed. This revision provides a clearer representation of the data dispersion and\nenhances the reliability of our leaching efficiency data.\nLi TM\n80 2\n% ) 60\ny\n( 40\nc\nn 20\ne\nci 0\neffi\n100\ng 80\nH+\nn\nhi\n60\nc\na\ne 40\nL\n20\n0\n0 2 4 6 8 10 12 14 16\nActivation time (h)\nFigure 1 (f) The effect of H O and H+ on the leaching efficiency of Li and TMs in P-\nP-Li P-TM MA-Li MA-TM\n100\n%)\ny ( 80\nc\nn\nci e 60 % % % % \ng\neffi\n40 4. 1\n7\n7. 3\n1\n6. 3\n2\n8. 8\n7\nn 8 7 8 7\nhi\nc 20\na\ne\nL\nFigure 1 (h) The effect of CO on the Li leaching efficiency of P-LTMO and MA-\nReviewer #2:\nIn this work, the authors proposed a three-in-one strategy that enables CO2-\ncarbonation with spent cathode materials to achieve selective Li recovery and\nregeneration of transition metals. The study conducts an in-depth analysis of how\nmechanochemical (MC) treatment affects the reactivity of different elements in cathode\nmaterials and the underlying mechanisms, providing new insights on the role of MC\ntreatment in the recycling process. I think it can be considered for publication if the\nfollowing concerns are tackled with.\nIssue 1:\nThe introduction can be enriched and a more detailed discussion on selective leaching\nand direct regeneration is required to be included. The authors only mentioned briefly\nthe pyrometallurgy and hydrometallurgical methods at this version and the statement\non “...process requires a large amount of strong acid and alkali...” is not always correct.\nIt is necessary to provide an outline on how this research is correlated and different\nfrom a traditional hydrometallurgical process.\nDiscussion:\nThank you for your comments on enriching the introduction and clarifying the\nresearch positioning. Our research compared to traditional hydrometallurgy achieving\nthree key innovations, involving that integrating “leaching” and “catalysts synthesis”\nto shorten the process, using CO to replace strong acids/alkalis and realizing\n2\n“upcycling” instead of “simple recovery”, which aligns with the sustainable\ndevelopment trend of LIBs recycling. We have supplemented the research progress on\ndirect regeneration, hydrometallurgy and selectrive leaching in the lines 56-61, lines\n25-56 and lines 65-86 of the Section 1 in the revised manuscript, as detailed below. We\nappreciate your suggestion, which helps us better articulate the novelty of this study.\nThe related revision in the main text:\nLines 53-57 in Section 1: Direct regeneration presents a promising alternative by\nemploying shorter processing routes to restore degraded cathode materials (e.g., via\nsolid-state, sol-gel, or hydrothermal Li replenishment) 13-15 or augment cell capacity\n(e.g., using Li-compensating additives like Li-Naph) 16,17. However, its practical\napplication is limited since it can only process less complex spent LIB streams 18.\nLines 49-53 in Section 1: In contrast, hydrometallurgy offers improved recovery\nefficiency of different elements through chemical leaching with solvents such as\nmineral/organic acids or deep eutectic solvents 9-11. Nevertheless, conventional\nhydrometallurgical processes often face challenges including high chemical\nconsumption, and lengthy purification sequences 12.\nLines 61-82 in Section 1: Selective leaching improves Li recovery and simplifies\npurification compared to impurity-sensitive conventional hydrometallurgy 19,20. The\nmechanisms preferentially induce targeted phase transformations in spent cathodes,\nseparating Li from transition metal (TM) phases, driven by strategies like adding\nreductants or applying elevated temperature/pressure 21. For example, carbothermic\nreduction converts spent cathodes into lithium carbonate (Li CO ) and transition metal\n2 3\nelements or their oxides 20,22,23, and sulfation roasting yields lithium sulfate (Li SO )\n2 4\nand transition metal oxides 24-26. However, these methods often require substantial\nreagent inputs, risk hazardous emissions and secondary pollution, and generate leaching\nresidues. These residues usually necessitate acid leaching for conversion into salt\nsolutions prior to reuse, which severely diminishes their value. Consequently,\noptimizing resource utilization across the selective leaching chain demands greener,\nmore efficient processes and solutions for managing low-value residues. Flash Joule\nheating 27 is possible to enable one-step selective Li extraction via seconds-long, high-\ntemperature reactions. This instantaneous heating offers greener processing and\nuniquely induces structural transformations in spent cathodes which could convert\nresidual metals into self-assembled multi-metal hydroxide catalysts 28. Electrochemical\nmethods selectively leach Li at ambient temperature using applied potential. The\nresulting structurally-defective, Li-depleted residue can serve directly as functional\nmaterials, such as OER catalysts, but electrode reconstruction requirements hinder\nscale-up 29-31. Mechanical methods selectively leach Li by induced room-temperature\nphase transitions 32, yet grinding additives risk impurity contamination 33,34. In summary,\nexisting technologies have yet to optimally balance mild processing conditions,\nminimal chemical input, and the production of high-value outputs.\nReferences\nwaste-to-energy storage devices: Recovery of NiMnCoC O as an electrode material for\n2 4\npseudocapacitor from spent LiNiMnCoO batteries, Journal of Hazardous materials, 424, 127481\n2\n(2021).\nOptimization of Synergistic Leaching of Valuable Metals from Spent Lithium-Ion Batteries by the\nSulfuric Acid-Malonic Acid System Using Response Surface Methodology, ACS Applied Materials\n& Interfaces, 14, 11359-11374 (2022).\nthe cathode of Li-ion batteries, Green Chemistry, 22, 4473-4482 (2020).\nfriendly controlled chlorinating technology and mechanism of spent lithium ion batteries recovery,\nJournal of Hazardous materials, 404, 123947 (2020).\nChemistry & Engineering, 8, 17622-17628 (2020).\nIon Batteries: Direct Cathode Regeneration, Advanced Materials, 35, (2023).\n2\nspent batteries and regeneration with solid state synthesis, Green Chemistry, 17, 1276-1280 (2015).\nGong, C. Li, M. Zhu, K. Zhang, Y. Xu, Y. Wang, Z. Hu, P. Chen, B. Wang, K. Zhang, Y. Xia, H.\nPeng, Y. Gao, External Li supply reshapes Li deficiency and lifetime limit of batteries, Nature, 638,\n676-683 (2025).\nKomagata, Y. Aoki, H. Kondo, T. Sasaki, S. Okayama, Direct capacity regeneration for spent Li-ion\nbatteries, Joule, 8, 1364-1379 (2024).\nR.V. Kumar, G. Zhou, S. Ding, K. Xi, Degradation Mechanisms of Electrodes Promotes Direct\nRegeneration of Spent Li-Ion Batteries: A Review, Advanced Materials, 36, 2313273 (2024).\nSpent Lithium Batteries by Functional Ionic Liquid, ACS Sustainable Chemistry & Engineering, 9,\n7022-7029 (2021).\nand low-carbon strategy for selective lithium recovery from spent lithium-ion batteries: Combining\nmechanochemical activation with biomass reduction roasting, Separation and Purification\nTechnology, 338, (2024).\nmulti-stage extraction for selective recovery of lithium from spent lithium-ion batteries, Separation\nand Purification Technology, 338, (2024).\nfrom Spent Lithium-Ion Batteries Using Carbothermal Shock Method, Angewandte Chemie\nInternational Edition, 62, e202300074 (2023).\nfrom spent lithium-ion batteries by a carbon conversion control strategy of carbothermic reduction,\nGreen Chemistry, 9734-9744 (2022).\nselective extraction of lithium from spent lithium-ion batteries by sulfation roasting, ACS Applied\nMaterials & Interfaces, 12, 18482-18489 (2020).\nselective recovery of valuable metals from spent lithium-ion batteries by using conventional\nsulfation roasting, Green Chemistry, 21, 5904-5913 (2019).\nrecovery of lithium and transition metals from spent ternary lithium-ion batteries powders, Chemical\nEngineering Journal, 522, 167321 (2025).\nspent lithium-ion batteries: A rising direct regeneration method, Journal of Energy Chemistry, 105,\n501-513 (2025).\nternary cathodes by simultaneously extracting lithium and constructing high performance oxygen\nevolution catalysts, Resources, Conservation and Recycling, 222, 108466 (2025).\nZhang, W. Chen, Electrochemical lithium recycling from spent batteries with electricity generation,\nNature Sustainability, 8, 287-296 (2025).\nelectrochemical recycling of spent lithium-ion batteries: Targeting the direct regeneration of de-\nlithiated materials, Chemical Engineering Journal, 479, (2024).\nLeaching Method for High-Purity Lithium Recovery from Spent Lithium Batteries, Environmental\nScience & Technology, 57, 4591-4597 (2023).\nChemie International Edition, 63, (2024).\nbattery cathode materials into high-value products via a mechanochemical extraction and thermal\nreduction route, Journal of Hazardous materials, 413, 125222 (2021).\nusing ionic substitution stimulated by mechanochemistry, Journal of Cleaner Production, 279,\n(2021).\nIssue 2:\nIn addition to destroying the crystal structure, the MC process will also reduce the\nparticle size. Together with the size reduction, how it is related to the leaching process,\nincluding lithium and other elements?\nDiscussion：\nThank you for your perceptive question. Our initial manuscript did not thoroughly\nexplore the relationship between these morphological alterations and the leaching\nbehavior. We will address this gap through supplementary experimental investigations.\nFirstly, we explored the effect of the particle size on the leaching process by\nexperimental design. To specifically target our analysis, ethanol was introduced as\nlubricant during MC process. The objective was to preferentially direct mechanical\nenergy towards particle size reduction rather than primary crystal structure destruction.\nAs shown in Figures R13 and R14, the introduction of ethanol cannot suppress\nNCM811 particle fragmentation, while retain the integrity of the phase structure. The\nleaching behaviors of the MC product with the assisting of ethanol (MA-NCM811-WE)\nin aqueous and acidic systems was then evaluated to isolate the effects of mere particle\nsize reduction on Li and TMs leaching efficiencies. As shown in Figure R15, it\ndemonstrates that solely reducing particle size fails to alter the differential leaching\nbehavior between Li and TMs. Consequently, it cannot enable the preferential or\nselective Li extraction under mild conditions.\nIn contrast, the MC route employed in this study was precisely optimized. At the\noptimal activation conditions, it successfully induces targeted amorphization of the\nNCM811 structure accompanied by a surface reconstruction layer forming Li-rich\ndomains as Figure R16. The effect of structural amorphization on the selective leaching\nof Li is more important than the change of particle size.\nThe additional results and corresponding discussions have been incorporated into\nSection 2.1 and Supplementary Note 2 (Determination of the key driving factors in\nthe MC process) of the revised manuscript. We thank the reviewer again for their\ninsightful comments, which have greatly strengthened our analysis of the MC process.\nThe related revision in the main text:\nLines 132-134 in Section 2.1: Experiments designed to elucidate this phenomenon\n(Supplementary Note 2) reveal a more critical role for the MC-induced amorphization\nof the crystal structure than for morphological changes like particle size reduction.\nFigure R13 The SEM results of MA-NCM811-WE with the activation time of 0 h, 1\nh, 2 h, 4 h, 8 h and 16 h. (Figure S3)\nFigure R14 The XRD results of MA-NCM811-WE with the activation time of 0h, 1 h,\n2 h, 4 h, 8 h and 16 h. (Figure S4)\nLi TM\n80 2\n60\n)\n%\n( 40\ny\nc 20\nn\ne\nci 0\neffi\n100\ng\nH+\nn 80\nhi\nc 60\na\ne\nL 40\n20\n0\n0 2 4 6 8 10 12 14 16\nActivation time (h)\nFigure R15 The leaching efficiency of MA-NCM811-WE in aqueous and acidic\nsystems. (Figure S5)\nFigure R16 TOF-SIMS depth profile of Li+ in P-NCM811 and MA-NCM811, and the\nsputter depth is calibrated by the SiO sputtering rate. (Figure 3c)\nA detailed description on how the amorphous content in Figure 1 was determined\nshould be provided. How is the amorphous phase influencing the subsequent recycling\nprocess?\nDiscussion:\nThank you for pointing out the issue. As shown in Figure 1b, the crystal structure\nof LTMO undergoes an amorphization evolution during the MC process. To better\nresolve this disordered structure, a combination of internal standard method and XRD\nRietveld refinement was employed to conduct an in-depth analysis of the amorphous\nphase composition and crystalline structure of MA-NCM811 (J. Appl. Crystallogr.,\n2001, 34 (2):196-202). The specific procedures are as follows. Si powder with 100%\ncrystallinity was used as the internal standard (with a mass proportion of 25%). XRD\ndata were collected using a Rigaku SmartLab 9 kW diffractometer (Cu Kα radiation,\nscanning range 5°~90°, step size 0.01°, scanning speed 3°/min). The XRD patterns were\nrefined using Highscore5.3 software, and the Rietveld quantitative analysis without\nstandards was employed to calculate the relative contents of NCM811 and Si. The\ncontent of Si was corrected to 25% to convert to absolute contents, and the proportion\nof the amorphous phase in the mixture was calculated by 100%-crystalline phase\ncontent-25%. The amorphous content in LTMO was further calculated by dividing the\namorphous content in the mixture by (1-25%). The related revision was supplemented\nin Experimental section and Supplementary Note 1 (Determination of amorphous\nphase fraction) of the revised manuscript.\nThe influence of the amorphous phase on subsequent recycling can be viewed\nfrom two aspects. First, it promotes the highly efficient separation of Li and TMs in a\nweakly acidic environment (provided by H O or CO ). Specifically, in an aqueous\n2 2\nsystem, approximately 75% of the Li can be effectively extracted without damaging the\ncrystalline structure of the activated product. This indicates that the extracted Li\noriginates mainly from the amorphous phase, which also accounts for the near-complete\nLi extraction observed in the CO system. Second, the release of Li is not solely due to\n2\nthe water-soluble nature of the Li-rich amorphous phase. A small portion results from\nan exchange reaction between Li+ and H+. This process not only leaves behind a highly\ndisordered TM-based skeleton in the leaching product, but also introduces surface\nhydroxyl groups, which offer potential advantages for subsequent applications in OER\ncatalysis.\nIssue 4:\nWhat is the phase of the residual Li in the leaching product? It is required to discuss\nthe carbonation process and how CO2 pressure and leaching time influence the lithium\nextraction.\nDiscussion:\nThank you for your penetrating questions.\nRegarding the phase of the residual Li, a comprehensive analysis of the leaching\nefficiencies and products indicates that it is primarily immobilized within the residual\ncrystalline structures. Specifically, the Li is encapsulated in TM-enriched domains.\nAlthough these domains exhibit a highly disordered character overall, they retain a\nhigh-intensity, short-range ordered TM-O bonding network, which renders the\nencapsulated Li particularly resistant to leaching. A detailed analysis about the\ndifference between the residual Li in aqueous system and CO system is as follows.\nobtained in different systems (aqueous system and CO system). It indicates that the Li\n2\nextraction process in the aqueous system did not significantly alter the structure of the\nhighly disordered residual crystalline regions in the MA product. In contrast, the CO\n2\nsystem not only weakened the characteristic peaks of the residual crystalline phase but\nalso generated new ones (18.9°). Combined with their Li leaching efficiencies (~75%\nvs. ~95%), it can be inferred that the leaching process in CO system was sufficient to\n2\ndisrupt the ordered structure of a substantial portion of the residual crystalline domains\nwithin the MA product. However, analysis of XPS results (Figure R17b) for the CO\n2\nleaching residue reveals a critical observation. Although the Li 1s characteristic peak is\nalmost undetectable on the surface, a weak broad peak (attributed to Li-O-M bonding)\ngradually emerges at approximately 54 eV with increasing Ar+ etching depth. This\nconfirms that a small amount of residual Li remains within the bulk phase of the\nleaching residue. Therefore, it could be concluded that residual Li in aqueous system\nprimarily resides within TM-enrich domains retaining the high-intensity short-range\nordered TM-O bonding network. And residual Li in CO system located within deeper\n2\nregions associated with partially destabilized.\nFigure R17 (a) The XRD results of MA-NCM811, MA-NCM811-WL and MA-\nNCM811-CO L. The Li 1s in XPS results of (b) MA-NCM811-CO L. (Figure 2a and\n2 2\nFigure S15)\nThe core mechanism of the CO leaching process (carbonation process), as shown\n2\nin Figure R18, involves dissolved CO reacting with H O to generate H+, HCO -, and\n2 2 3\nCO 2- (CO + H O ⇌ H+ + HCO - ⇌ 2H+ + CO 2-). Resultant protons attack residual\n3 2 2 3 3\nlattice Li through Li-O bond breaking (path Ⅲ) and H+/Li+ cation exchange (path Ⅱ).\nLiberated Li+ immediately combines with HCO -/CO 2- to form soluble species\n3 3\n(LiHCO or Li CO ), ensuring both effective Li dissolution and stabilization in the\n3 2 3\nliquid phase and concurrent H+ consumption that provides pH buffering. This\nstrategically confines protonic attack to Li+, significantly suppressing “TM-O” skeleton\ndissolution while enabling selective Li extraction. Notably, Li accumulates in the\nleachate as soluble carbonate-based species amenable to subsequent recovery. The\nrelevant description has been supplemented in the Section 2.2 of the revised manuscript,\nas detailed below.\nOur systematic investigation of leaching parameters, including leaching pressure\n(0, 0.25, 0.5, 1.0, 1.5 MPa) and leaching time (0.5, 1, 1.5, 2 h), was conducted to\ndetermine how these parameters influence Li extraction. As shown in Figures R19 and\nR20, it revealed dissolved CO has efficacy as a proton donor for selective extraction\n2\nof lattice Li. At suboptimal 0.25 MPa pressure, inadequate CO dissolution yields\n2\ninsufficient proton concentration for effective leaching of limited Li domains. Elevating\npressure to 0.5 MPa substantially enhances CO solubility and H+/HCO -\n2 3\nconcentrations, lowering system pH to achieve >90% Li extraction while restricting\nTM dissolution below 5%. Further pressure elevation beyond 0.5 MPa generates\nexcessive proton. It marginally facilitates lithium dissolution, while initiating TM-O\nskeleton degradation causing pronounced co-dissolution of TMs and selectivity\ndeterioration. The influence of leaching time on the leaching effect parallels that of CO\n2\npressure. During 0.5 h treatments, slow Li leaching kinetics yield incomplete extraction.\nOptimal leaching time (e.g., 1 h) permit sufficient proton-Li interaction for high-yield\nrecovery. Prolonged exposures (>1.5 h) sustain acidic conditions that cumulatively\ncompromise the TM structure, elevating metal dissolution and diminishing Li\nselectivity. Optimum CO leaching conditions therefore balance dual imperatives,\n2\nincluding generating sufficient H+ through controlled pressure and time parameters to\nextract lattice Li, and leveraging CO 2-/ HCO - speciation for pH buffering to restrict\n3 3\nleaching of TMs. The relevant revisions have been supplemented in the Section 2.1 and\nSupplementary Information of the revised manuscript, as detailed below.\nWe are grateful for your comment once again, which has helped us to illustrate the\nleaching process more clearly.\nThe related revision in the main text:\nLines 209-220 in Section 2.2: In brief, the H+ brought by CO have the possibility of\n2\nion exchange reaction and acidic dissolution reaction within the residual insoluble Li\nin the lattice. The released Li+ from MA-LTMO in the CO -rich water system may have\n2\ntriple pathways: (i) the dissolution in the soluble Li-rich phase (Equation 2), (ⅱ) the\nion exchange of Li⁺ and H⁺ (Equation 3), and (ⅲ) the acidic dissolution of Lattice Li\n(Equation 4) as show in Figure 2c. TMs may undergo dissolution followed by\ncomplexation under the weakly acidic influence of CO during this process (Equation\n2\n5).\nCO\n2\n+H\n3\n⇌ H++ HCO 3- ⇌ 2H++ CO\n3\n2- (1)\nLi O + H O → 2LiOH (2)\n2 2\nLiTMO + xH+ → Li H TMO + xLi+ (3)\n2 1-x x 2\n(1+x) LiTMO + 4xH+ → 2xLi+ + xTM2+ + Li TMO + 2xH O (4)\n2 1-x 2 2\nTM2+ + CO 2- → TMCO (5)\n3 3\nLines 148-162 in Section 2.1: Under ambient pressure, CO can serve as an H+ source,\n2\nselectively extracting 87% of Li from MA-NCM811 (Figure S7). However, the H+\nconcentration generated under these conditions is insufficient to completely dissolve\nthe water-insoluble residual Li. Enhancing the dissolution-dissociation equilibrium of\nCO (e.g., by increasing the system pressure) can effectively promote H+ release\n2\n(Figure 1g) 45. A systematic investigation of CO pressure and leaching time (Figure\nsupply, resulting in incomplete Li extraction (<90%). Conversely, excessively high\npressure or prolonged duration disrupts the TM-O framework, inducing co-dissolution\nof TMs and thereby reducing selectivity. Nevertheless, the CO 2-/HCO - species\n3 3\ngenerated in situ during CO dissociation act as buffers and can complex with TM ions,\n2\nthus limiting their dissolution and helping to maintain selectivity. Under the optimized\nconditions of 0.5 MPa CO pressure and 1 h leaching time, the system achieves a\n2\nbalance between H⁺ generation and the buffering effects, ultimately enabling highly\nefficient Li extraction while effectively preserving the TM framework.\nReference\nIntegrated process of CO sequestration and recycling spent LiFePO4 batteries, Energy Storage\nFigure R18 Schematic diagram of Li leaching pathway in a CO -rich water system.\n2\n(Figure 2c)\nFigure R19 The pH-pressure relationship profile (25 ° C) of the CO -H O\n2 2\nequilibrium system. (Figure 1g)\nFigure R20 The effect of CO pressure and leaching time on the leaching efficiencies\n2\nand leaching products from MA-NCM811-2h (Figure S7)\nIssue 5:\nOn page 10, the author presents the Raman spectrum data of P-NCM811 and MA-\nNCM811 in Figure 4c. However, this section is unclearly articulated and lacks a robust\nconnection to the contextual discussion. It is advised to revise this part for better\ncoherence.\nDiscussion:\nThank you for your suggestion. Raman spectroscopy is highly sensitive to short-\nrange atomic coordination environments, chemical bond vibration modes, and changes\nin crystal structure symmetry (Front. Energy Res., 2018, 6), and is particularly suitable\nfor exploring the transition from short-range order to disorder. Based on this, combined\nwith the results from XAFS revealing the reduction in Ni valence states and changes in\nthe coordination environment (Adv. Mater., 2024, 36), we chose Raman characterization\n(Figure R21). The aim was to analyze the evolution of overall structural symmetry,\nthereby complementing the short-range coordination information from XAFS and\nverifying the speculation about changes in the Ni coordination environment. The\nrelevant description and supplementary schematical diagram have been revised in\nSection 2.4 and Supplementary Information of the revised manuscript, as detailed\nbelow. Once again, we are grateful for your constructive comments.\nThe related revision in the main text:\nLines 298-311 in Section 2.4: Here, Ni K-edge XANES spetrum (Figure 4a) reveals\nthe downward shift of Ni K-edge energy (~1.5 eV) in MA-NCM811, confirming the\nreduction of Ni. The results from EXAFS spectra (Figure 4b) showed an increase in\nthe interatomic distances of Ni-O and Ni-M after mechanochemically activation, with\na gradual weakening of the Ni-M bond strength, indicating that the short-range structure\nhas been significantly disrupted. Raman spectra shown in Figure 4c and S31\ndemonstrates that P-NCM811 exhibits typical layer-like anisotropic vibration modes 59.\nAfter MC treatment, the A peak 60 shows broadening and a pronounced low-frequency\n1g\nshift (31.3 cm-1), along with attenuation and eventual disappearance of the E peak. This\ng\nbehavior is similar to that of disordered rock salt structure 61, indicating a fundamental\ntransformation from an ordered layered structure to a highly disordered configuration,\nwith the loss of distinct in-plane and out-of-plane vibrational modes. Further analysis\ncombining EXAFS spectra and HR-TEM of MA-NCM811 (Figure 4d) reveals a\ncoexistence of multiphases (layered, rock salt and spinel phases) 62, reflecting the basic\ncomposition of its highly disordered structure.\nReference\nMetal Oxides for Li-ion Battery Cathodes, Frontiers in Energy Research, 6, (2018).\nAurbach, J. Lampert, A. Volkov, J.-Y. Shin, A. Garsuch, F.F. Chesneau, C. Erk, Li+-Ion\nExtraction/Insertion of Ni-Rich Li (Ni Co Mn ) O (0.005<x<0.03;y:z=8:1,w≈1) Electrodes: In\n1+x y z z w 2\nSitu XRD and Raman Spectroscopy Study, ChemElectroChem, 2, 1479-1486 (2015).\nAdefila, D. Nordlund, S. Zhou, W.H. Kan, T.G. Habteyes, D. Chen, Over-Stoichiometric\nMetastabilization of Cation-Disordered Rock Salts, Advanced Materials, 35, (2023).\nJ. Wang, J. Bae, J. Moon, Y.C. Park, M.H. Hong, M. Kim, Y. Liu, I. Sohn, K. Jung, J. Lim, Solid-\nState Reaction Heterogeneity During Calcination of Lithium-Ion Battery Cathode, Advanced\nMaterials, 35, e2207076 (2022).\nFigure R21 (a) Ni K-edge XANES, (b) EXAFS spectra, (c) Raman results of P-\nNCM811 and MA-NCM811 for different activation time. And (d) the schematic graphic\nof the vibration mode of LTMO. (Figure 4a-c and Figure S31)\nIssue 6:\nSome details in Figures still need to be noted. In Figure 4e, the scale of TEM results is\nmissing; in Figure 5e, the unit of the y-axis should be revised to mA cm-2.\nDiscussion:\nThank you for your correction. Regarding the missing scale of the TEM results in\nFigure 4e, we have now added the appropriate scale bar to this figure. Concerning the\ny-axis unit in Figure 5e, we have revised it to “mA cm-2” as suggested and would be\ncareful in future research and writing. We greatly appreciate the reviewer for catching\nthis error. Additionally, we have conducted a thorough check of all figures in the\nmanuscript to ensure that no similar issues exist.\nFigure 4e HR-TEM images and FFT images of P-NCM811 and MA-NCM811-2h.\n2\n)\n2\n-m\nc\nA\nm\n(\ny\nsit10\nn\ne\nd\nnt\ne\nr\nr\nu\nC\n0\n0 2 4 6 8 10\nTime (h)\nFigure 5e (Original manuscript) Chronoamperometry spectra for MA-NCM811-\nCO L in 1M KOH.\nThe following are reviewer comments for the article entitled A Three-in-One\nStrategy: Li/TMs Micro-Segregation to Enable Upcycling of Spent Layered Cathode\nMaterials submitted to Nature Communications by Wang et al. The reviewed article has\nsuccessfully demonstrated the novel approach of the selective Li recovery from spent\nLi-ion cathodes and upgrading of transition metals during mechanochemical processes\nassisted by CO2 sequestration. The Authors performed the broad compositional and\nstructural products analysis and OER catalytic activity. I recommend publishing the\narticle after a major review, and below are the comments and remarks:\nIssue 1:\nCould the Authors describe the XRD results shown in Figure 1b by ascribing the peaks\nto the proper compounds?\nDiscussion:\nThank you for your thought-provoking question. As mentioned in lines 116-120\nof Section 2.1, the MC process transforms the LTMO material from an R-3m layered\nstructure gradually into a disordered rock-salt phase with an Fm-3m space group.\nHowever, we did not ascribe the XRD pattern of this activated product to any specific\ncompound for the following reasons.\nFirst, the results in Figure 1b were collected from MA-NCM811 obtained by high-\nenergy ball milling of P-NCM811 under different activation time. Compared with the\nP-NCM811, the diffraction peaks of MA-NCM811 exhibit an overall weakening and\nbroadening trend, with significant changes in certain characteristic peaks, particularly\nthe (003) peak, which shows a substantial reduction in intensity and nearly disappears.\nThese observations indicate that the MC process disrupts the long-range order of the\noriginal crystal and drives its transition toward an amorphous state. Rietveld refinement\nresults further confirm that the amorphous phase has become the dominant component\nof the MA product. Figure R1 clearly illustrates the gradual evolution from a crystalline\nto an amorphous state, in which the residual crystalline regions also exhibit highly\ndisordered characteristics. It should be noted that, while we can deduce the general\namorphization pathway, the specific composition of the amorphous phase and the exact\nnature of the residual crystalline phase remain unclear. Directly attributing the residual\ncharacteristic peaks (their positions are close to those of TM oxides (TMOs) with rock-\nsalt structures, such as NiO) to a specific compound would contradict the mechanistic\nunderstanding that high-energy ball milling in this system primarily induces physical\namorphization rather than the formation of new crystalline phases, and could mislead\nsubsequent research. Therefore, we interpret the residual peaks in Figure R1 as\ndiffraction signals originating from locally ordered regions that have undergone severe\nmechanical damage but still retain the distorted structural features of NCM811. If the\nreviewer has any valuable comments on this point, we look forward to further\ndiscussion and clarification.\nFigure R1 (a) XRD results of P-NCM811 and MA-NCM811 for different activation\ntime. (b) The FMWH of (003) and (104), the value of I / I , and (c) the amorphous\n(003) (104)\nphase ratio in the XRD results of P-NCM811 and MA-NCM811. (Figures 1b-d)\nIssue 2:\nWhat purity do the recovered Li compounds exhibit?\nDiscussion:\nThank you for your question. The purity of recovered Li CO product is a\n2 3\nnecessary indicator for the evaluation of this recycling method. Firstly, as shown in\nFigure R22a, the characteristic peaks in the XRD pattern of the recovered product can\nbe assigned to Li CO (COD#96-900-9642). This assignment is further supported by\n2 3\nthe FTIR spectra of both the recovered and commercial Li CO (Figure R22b), which\n2 3\nexhibit nearly identical characteristic carbonate vibrational modes in the range of 1485-\n1420 cm-1 (J. Power Sources, 2019, 432: 8-15). These results confirm that the recovered\nLi-containing product is Li CO . Since no other anions (with the exception of a\n2 3\nnegligible amount of F⁻ potentially from residual LiPF or the SEI) (Joule, 2025:\n6\n102136) were introduced during the extraction process, the purity of the recovered\nLi CO product was roughly estimated by calculating the ratio of the mass fraction of\n2 3\nLi to the sum of mass fractions of all metallic elements. The ICP analysis results for Li\nand other metallic impurities, with calibration curve R2 values  0.9999, are presented\nin Table R1. The purity of recovered Li CO was 98.62%.\n2 3\nThe relevant data have been supplemented in Section 2.1 and Supplementary\nInformation of the revised manuscript, as detailed below. We thank you again for your\ninquiry, as your comments have helped to enhance this process practical applicability.\nThe related revision in the main text:\nLines 172-173 in Section 2.1: “The Li-rich leachate (LiHCO ) was converted directly\n3\ninto Li CO product with a purity of  98.5% (Figure S14 and Table S2) by thermal\n2 3\ndecomposition 46.”\nReference\ncarbonate, Journal of Materials Research and Technology, 9, 9498-9505 (2020).\nFigure R22 (a) XRD pattern (inset: SEM image) and (b) FTIR spectrum of the\nrecovered Li CO . (Figure S14)\n2 3\nTable R1 The content of recovered Li CO . (Table S2)\n2 3\nElement Li Ni Co Mn Al Fe Cu\n% 18.53 0.04 0.02 0.02 0.02 0.01 0.00\nElement Zn Mg Na K Ca\n% 0.00 0.00 0.05 0.08 0.02\nIssue 3:\nHow does the morphology (e.g., grain size, grain shape) of examined materials change\nupon mechanochemical processing? Whether SEM analysis was done before and after\nthe MC process?\nDiscussion：\nThank you for your question. Regarding the changes in the morphology of\nNCM811 during the MC process, we did not pay sufficient attention to this aspect in\nour initial work. We now supplement the SEM results (Figure R23) before and after\nMC treatment and related explanations. The original particles are regularly spherical\nwith a particle size of approximately 5-10 μm. After MC treatment, the particles\ngradually break into nano-scale irregular fine particles. The specific trend of changes is\nas follows: when activated for 1 h, there are still large particles that are not completely\ndestroyed; as the activation time is prolonged, the large particles disappear, but the\nbroken fine particles begin to aggregate gradually; when activated for 16 h, aggregates\nwith a particle size of 500 nm appear. This phenomenon is mainly attributed to the shear\nforce and extrusion effect generated by the impact of the ball milling medium, which\ncause refinement of the particles. With the continuous input of mechanical energy, the\nrefined particles, due to their high surface energy, then re-aggregate. This result has\nbeen consolidated into the Section 2.1, 2.3 and Supplementary Note 2\n(Determination of the key driving factors in the MC process) of the revised\nmanuscript. We are grateful to the reviewer for the thorough critique, which has greatly\nimproved the integrity of our work.\nThe related revision in the main text:\nLines 132-134 in Section 2.1: Experiments designed to elucidate this phenomenon\n(Supplementary Note 2) reveal a more critical role for the MC-induced amorphization\nof the crystal structure than for morphological changes like particle size reduction.\nLines 259-261 in Section 2.3: Prolonged MC activation leads to a reduction in CO\n2\nadsorption capacity, attributed to particle agglomeration, evidenced by the SEM results\nof MA-NCM811 in Figure S2, (specific surface area decreased by ~23.6%) eliminating\npartial CO -chemisorption-active sites.\nIssue 4:\nWere OER experiments performed also for benchmark OER materials e.g. RuO2 or\nCo3O4 for comparison with recovered catalyst materials?\nDiscussion：\nThank you for your suggestion. We fully agree that benchmarking against well-\nestablished OER catalysts (such as RuO , Co O ) is crucial for evaluating the catalytic\n2 3 4\nperformance of the leaching products obtained in this study. Accordingly, we have\nsupplemented the experimental data with the OER performance of commercial Co O .\n3 4\nAs shown in Figure R24, the commercial Co O benchmark exhibits three key\n3 4\ncharacteristics, including an overpotential of 367 mV at 10 mA cm-2, a Tafel slope of\n140 mV dec-1, and a higher charge transfer resistance (R ) than our leaching products.\nct\nNevertheless, it demonstrated excellent stability in a 24 h chronopotentiometry test,\naffirming its role as a reliable comparator. By comparison, the leaching products exhibit\nsuperior performance across several key metrics to this commercial Co O benchmark.\n3 4\nThe relevant revision has been supplemented in Section 2.5 and Supplementary\nInformation of the revised manuscript, as detailed below. We are grateful to the\nreviewer for this suggestion, which has greatly strengthened the rigor of our research.\nThe related revision in the main text:\nLines 356-368 in Section 2.5: And the commercial Co O was used as contrast sample.\n3 4\nAs shown by the linear sweep voltammetry (LSV) curves in Figure 5a, the MA-LTMO-\nCO Ls possess superior electrocatalytic activity compared to commercial Co O ,\n2 3 4\nas evidenced by their significantly lower overpotentials required to achieve a current\ndensity of 10 mA cm-2. Among them, MA-NCM811-CO L demonstrated the best\n2\nperformance with an overpotential of 322 mV, which is considerably lower than 367\nmV required by Co O . Figure 5b presents the fitted Tafel slope of MA-NCM811-\n3 4\nCO L of 90 mv dec-1 and MA-NCM622-CO L of 127 mV dec-1, which are lower than\n2 2\nthat of commercial Co O (140 mV dec-1), manifesting more favorable catalytic kinetics\n3 4\nof high-Ni leaching products for the OER. It is consistent with the results of\nelectrochemical impedance spectroscopy (EIS) presented in Figure 5c that the\nimpedance arcs of high-Ni leaching products are smaller compared to that of the\ncounterparts and commercial Co O , suggesting they have the lowest charge transfer\n3 4\nresistance and exhibits the quickest OER kinetics.\nFigure R24 The electrocatalytic performance of MA-LTMO-CO Ls and commercial\n3 4\nIssue 5:\nAt which potential were the chronoamperometry measurements performed shown in\nFigure 5e?\nDiscussion：\nThank you for raising this point. The chronoamperometry measurement shown in\nFigure 5e of the original manuscript was conducted at a constant potential of 1.55 V\n(vs. RHE). Since the stability test for the catalyst in the original manuscript was\nconducted for only 10 h, we employed chronopotentiometry to better determine the\ncatalytic stability of the leaching products and to clearly observe the evolution of the\npotential. The potential changes of various component leaching residues (MA-LTMO-\nCO Ls) were monitored under a current density of 10 mA cm-2 for 24 h. Additionally,\n2\nthe potential change of leaching product from the spent cathode materials (MA-S-\nLTMO-CO L) was measured under the same conditions over an extended period of 200\n2\nh. The results, presented in Figures R25 and R26, demonstrate that the catalysts exhibit\nexcellent stability. The related description has been added in Section 2.5 and\nSupplementary Information of the revised manuscript, as detailed below. Thank you\nfor your rigorous feedback, which has significantly helped us improve the quality of\nour manuscript.\nThe related revision in the main text:\nLines 376-387 in Section 2.5: Critically, the operational stability was validated by\nchronopotentiometry (CP) testing (Figure S35), which revealed a minimal potential\nincrease over the course of 24 h. It is noteworthy that the leaching product derived from\nspent cathode materials (MA-S-LTMO-CO L) also exhibited excellent stability over\n2\n200 h of operation under identical testing conditions (Figure 5e). This observation\nstrongly suggests that the structural and compositional defects (e.g., trace impurities)\nintroduced into the cathode waste during long-term electrochemical cycling and\ninsufficient pretreatment did not compromise the catalytic performance of the final\nleaching product. In fact, the performance continued to improve during operation. It\nwas further examined by LSV (Figure 5e inset) and EIS spectrums (Figure S36), which\nrevealed a more favorable polarization curve after 200 h of operation compared to that\nbefore the stability test. The outstanding stability underscores the robustness of the\ncatalytic sites formed in this waste-to-catalyst process.\nFigure R25 Chronopotentiometry curves of MA-LTMO-CO Ls at a constant current\n2\ndensity of 10 mA cm–2. (Figure S35)\n2\n5 100\nE ) -2) \nm 80\nB\nA\ne\nfte\nfo\nr\nre\nal (\nV\nv\ns.\nR\nH\n3\n( m\nu\nA\nr r\nc\nent\ndensity\n2\n4\n6\n0\n0\n0\n0\nnti 2 1.3 1\nP\n.4\noten\n1\nti\n.\n5\na\nl (V v\n1\ns\n.6\n. RHE\n1.\n)\n7 1.8\ne\not\nP1\nElectrolyte replacement (1M KOH)\n0\n0 50 100 150 200\nTime (h)\nFigure R26 Chronopotentiometry curve of MA-S-LTMO-CO L at a constant current\n2\ndensity of 10 mA cm-2 for 200 h without iR compensation (inset: LSV polarization\ncurves of MA-S-LTMO-CO L before and after long-term stability)\nThe description of the Y axis should be “current density” instead of “current”.\nDiscussion：\nThank you for your correction. We would like to express our sincere gratitude to\nthe reviewer for pointing out this mistake. We have corrected this error and will also\npay attention to this issue in future research and writing.\n2\n)\n2\n-m\nc\nA\nm\n(\ny\nsit10\nn\ne\nd\nnt\ne\nr\nr\nu\nC\n0\n0 2 4 6 8 10\nTime (h)\nFigure 5e (Original manuscript) Chronoamperometry spectra for MA-NCM811-CO L\n2\nin 1M KOH.\nIssue 7：\nThe Electrochemical Active Surface Area should be ascertained in order to assess the\nOER catalytic capabilities.\nDiscussion:\nThank you for your valuable suggestion. We agree that determining the\nelectrochemical active surface area (ECSA) is crucial for comprehensively evaluating\nthe OER catalytic performance. In response, we have performed controlled cyclic\nvoltammetry (CV) measurements within the non-faradaic potential window (0.15-0.2\nV vs. Hg/HgO) in 1 M KOH as shown in Figure R27. Linear fitting of the scan-rate-\ndependent current differences at 0.175 V vs. Hg/HgO (Figure R28) yielded the double-\nlayer capacitance (C dl ). ECSA was then calculated via ECSA= Cdl, where the specific\nCs\ncapacitance C = 40 μF·cm−2. As quantified in Figure R29, MA-NCM811-CO L\ns 2\ndelivers an ECSA of 250 cm2, higher than the reference catalyst (163 cm2). This directly\ncorrelates with its superior OER activity, confirming that the increased exposure of\nactive sites is one of the driving factors for the performance enhancement. The relevant\ndata have been supplemented in Section 2.5 and Supplementary Information of the\nrevised manuscript, as detailed below. We appreciate the reviewer’s valuable suggestion,\nwhich has helped us gain a deeper understanding of the leaching products’ superior\nelectrocatalytic performance.\nThe related revision in the main text:\nLines 370-375 in Section 2.5: Besides, to comprehensively evaluate OER performance,\nthe electrochemical surface area (ECSA) was determined via double-layer capacitance\n(C ) measurements from CV scans in the non-Faradaic region at various scan rates\ndl\n(Figure 5d, S33 and S34). The leaching products, especially MA-NCM811-CO L\n2\ndemonstrated a superior C of 10.01 mF cm-2, markedly exceeding that of Co O (6.52\ndl 3 4\nmF cm-2), indicating a higher density of OER active sites likely originating from the\npre-MCM process.\nFigure R27 Cyclic voltammograms of MA-LTMO-CO Ls and Co O in a potential\n2 3 4\nrange where no Faradaic processes are observed. (Figure S33)\n1.5\nMA-NCM811-COL (10.01 mF cm-2)\n2\n)1.0 2\n- 2 m Co 3 O 4 (6.52 mF cm-2)\nc\nA\nm\n(\nj D0.5\n0.0\n20 40 60 80 100\nScan rate (mV s-1)\nFigure R28 Double layer capacitance (C ) of MA-LTMO-CO Ls and Co O . (Figure\ndl 2 3 4\n5d)\n250.25\n250\n200 195.75 199\n)\n2\nm 162.25 163\nc 150\n(\nA\nS\nC 100\nE\n50\nM\n-C\nA\nO\n-N\nL M622\nM\n-C\nA\nO\n-N\nL M111\nM\n-C\nA\nO\n-S\n2\n-\nL LTMO-CO2L Co3O4\nFigure R29 Electrochemical active surface area (ECSA) of MA-LTMO-CO Ls and\n3 4"}, {"round": 2, "reviewer_comments": {"reviewer_1": "(Remarks to the Author)\nAll my concerns have been resolved. It can be published.", "reviewer_2": "(Remarks to the Author)\nAll my questions have been properly answered and resolved. I suggest accepting this manuscript.", "reviewer_3": "(Remarks to the Author)\nThe Authors have thoughtfully and thoroughly responded to the reviewers' comments and remarks. The answers are\nsatisfactory and comprehensive and the revised paper meets the journal's standards for both editing and scientific quality.\nTherefore, I recommend the manuscript for publication."}, "author_response": ""}]

Decision letter