CATHODE ACTIVE MATERIAL-COATED DISCRETE GRAPHENE SHEETS FOR LITHIUM

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CATHODE ACTIVE MATERIAL-COATED DISCRETE GRAPHENE SHEETS FOR LITHIUM ( cathode-active-material-coated-discrete-graphene-sheets-for- )

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21 Asacontrolsample,theLFPparticle-bondedgrapheneshets werealsoproducedbyfollowingtheprocedureproposedby Ding, et al. Electrochemistry Communications, 12 (2010) pages10-13. ExperimentaldatashowthatNGPs,whenincorporatedto formgraphene-enhancedparticulatesofthepresentinven tion,provideexceptionalelectricalconductivitycharacteris ticstotheelectrodesintermsofamuchlowerpercolation thresholdandhigherelectricalconductivityatagivenweight % ofaditiveascomparedtothecorrespondingCNT-en hancedorcarbonblack-enhancedelectrodes. 10 22 paredfromspincoatingofRGO-waterSuspension.The resultingcoatedfilmwascutandmilledtoproduceCuPc coatedgrapheneshets.TwoCuPecoatingthicknesseswere producedintwoseparatesamples. ThespecificcapacityofthisCuPe-coatedgrapheneshet electrodewasmeasuredbyusingacoincelconfiguration withLimetalastheanodeactivematerialand1MLiClOin propylenecarbonate(PC)solutionastheelectrolyte.Abase linesampleofCuPewith30%byweightofAB(acetylene derivedcarbonblack)astheconductiveaditivewasalso preparedinasimilarmanner.Thecharge/dischargebehaviors ofthiscelwerealsomonitored.FIG.10showsthecycling behaviorsofalithiummetalbateryhavingagraphene-Sup portedCuPeorganiccoating(25nm)cathodeofthepresent invention,thoseofabaterycontainingagraphene-supported CuPCcoating(120nm)basedcathode,andthoseofabatery containingaCuPe-carbonblackcomposite-basedcathode. Thereareseveralsignificantobservationsthatcanbemade fromthesedata.First,giventhesamevolumefractionof CuPC,theCuPe-ABcompositebasedceliscapableofdeliv eringaninitialspecificcapacityofonly345mAh/g,butthe graphene-SupportedCuPecoating(120nm)basedcelhasan initialspecificcapacityof532mAh/g,basedonmeasure mentsconductedat1Crate(1Cratecompletingchargeor dischargein1hour,2Cratecompletingin/2hours,andinC ratecompletingin1/nhours,etc).Thisimpliesthattheuseof carbonblackasaconductivefilerdoesnotenableahigh cathode active material utilization rate. The thinner CuPc coating(25nm)enablesamuchhigheractivematerialutili Zationrate.Second,thedatahavealsoclearlydemonstrated thattheCuPc-ABcompositecathodehasafastcapacity decayratewiththespecificcapacitydroppingtoanunaccept ablylowvalueinlesthan100cycles.Incontrast,thecathode activematerial-coatedgraphenebasedbateries(coating thicknessof25nmand120nm)exhibitminimalcapacity decay(2-5%)evenafter200cycles. EXAMPLE 7 Li SCelsContainingS-CoatedGrapheneSheets S-coatedgrapheneshetscanbeeasilymadebysealinga SuficientamountofSulfurpowderandagraphenefilm(pre paredfromultrasonicspraying)inavacuumchamber(high degreeofvacuumisnotrequired).Sulfurcanbereadily sublimed into vapor by heating the sulfur powder from approximately145°C.to210°C.VariousScoatingthick nessesfromafewnanometerstoafewumcanbeobtained simplybyvaryingthephysicalvapordepositiontimes. S-coatedgrapheneshetsarethenproducedthroughfilm cutingandmiling. Asatypicalprocedureforpreparingelectrochemicaltest ingcels,theworkingelectrodeswerepreparedbymixing85 wt%activematerial(e.g.,S-coatedgrapheneshets),7wt% acetyleneblack(Super-P),and8wt%polyvinylidenefluo ride(PVDF,5wt%solidcontent)binderdissolvedinN-me thyl-2-pyrolidinoe(NMP).AftercoatingthesluriesonAl foil,theelectrodesweredriedat120°C.invacuumfor2hto removethesolventbeforepresing.Then,theelectrodeswere cutintoadisk(diameter=12mm)anddriedat100°C.for24 hinvacuum.Electrochemicalmeasurementswerecarriedout usingCR2032(3V)coin-typecelswithlithiummetalasthe anodeelectrode,Celgard2400membraneasseparator,and1 M LiPF electrolytesolutiondissolvedinamixtureofethyl enecarbonate(EC)anddiethylcarbonate(DEC)(EC-DEC, RepresentativeelectrochemicaltestingresultsareSumma rized in FIG. 8, which show the cycling behaviors of a lithium-ionbateryhavingaLFP-coatedgraphenesheetcath odeofthepresentinvention,thoseofabaterycontaininga graphene-bondedLFPnanoparticlecathode,andthoseofa15 baterycontainingacarbon-coatedLFPcomposite-based cathode.After140charge/dischargecycles,thebaterycon tainingacarbon-coatedLFPcomposite-basedcathodehas lost26.3%oftheoriginalcapacityandthebaterycontaining asimplemixtureofLFPandgrapheneshetsforthecathode lost16.8%ofthecapacity.Incontrast,thebateryhavinga LFP-coatedgraphenecathodeofthepresentinventionhas exhibiteda4% capacitylos.Thisisahighlysignificant improvementoverthepriorart. EXAMPLE 5 Graphene-EnabledVOs 25 PowderofV2O5particleswascompactedtoformadisc shapetargetforuseinasputeringchamber.Agraphenefilm30 preparedfromspin-castingofgraphene-waterSuspension wasdriedandplacedunderthesputeringtargetforacon troleddurationoftimetoobtainaVOs-coatedfilm.The coatedfilmwasthencutintoSmallpieces(approximately1 cm)andthensubjectedtobal-milingforfurthersizereduc35 tiontoobtainVO-grapheneshets. Forthepreparationofacontrolsample,inatypicalexperi ment,Vanadiumpentoxidegelswereobtainedbymixing V2O5inaLiClaqueoussolution.TheLi'-exchangedgels obtainedbyinteractionwithLiClsolution(theLi:Vmolar 40 ratiowaskeptas1:1)wasmixedwithaGO Suspensionand thenplacedinaTeflon-linedstainlesstel35mlautoclave, sealed,andheatedupto180°C.for12h.Aftersucha hydrothermaltreatment,thegreensolidswerecolected,thor oughlywashed,ultrasonicatedfor2minutes,anddriedat70° C.for12hfollowedbymixingwithanother0.1%GOin45 water,ultrasonicatingtobreakdownnano-beltsizes,andthen spray-dryingat200°C.toobtaingraphene-embracedcom positeparticulates. FIG.7showsthecyclingbehaviorsofthrelithiumbatter ieshavingaVO-coatedgrapheneshetcathode,a50 graphene/VOnanoparticlemixturecathode(co-precipi tatedVOs withGO),andacarbonnanofiber(CNF)-sup portedVOscoatingcathode,respectively.After105cycles, thebaterycelhavingacarbonnanofiber(CNF)-supported VOscoatingcathodehassuferedacapacitydecayof44%55 andthebateryhavingagraphene/V2O5nanoparticlecom positecathodesuferedacapacitydecayof21.5%.Incon trast,thebateryhavingaVO-coatedgraphenesheetcath odehaslostlesthan4%ofitsoriginalcapacityafter105 cycles,representingamajorimprovement. EXAMPLE 6 MetalNaphthalocyanine-ReducedGrapheneOxide (RGO)HybridCathode 60 65 US9,203,084B2 CuPe-coatedgrapheneshetswereobtainedbyvaporizing 1:1V/v).Thecelassembliesweremadeinanargon-filed CuPeinachamberalongwithagraphenefilm(5nm)pre glove-box.TheCVmeasurementswerecariedoutusingan

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