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23 Arbinelectrochemicalworkstationatascanningrateof1 mV/s.Inadition,theelectrochemicalperformancesofvari ouscelswerealsoevaluatedbygalvanostaticcharge/dis chargecyclingatacurentdensityof50mA/g.Forlong-term cyclingtests,multi-channelbaterytestersmanufacturedby LAND wereused. SomerepresentativedataarepresentedinFIG.9,which showstheRagoneplots(celpowerdensityvs.energyden sity)ofthreLi-ScelshavingaS-coatedgraphenebased cathodewithaScoatingthicknessof20nm,65nm,and125 nm,respectively.Clearly,thinestcoatingprovidesthehigh estenergydensityamongthethrecels.Thehighestachiev ablecelenergydensityofthecelcontainingthethinestS coatingSupportedongrapheneshetsisashighas802 Wh/kg,whichis4timesbeterthantheenergydensity(150 200Wh/kg)ofthebestlithium-ionbaterycelscurently availableonthemarket. 5 10 15 24 alexistingmaterials.Highstrengthimpartsgoodstruc turalintegritytotheresultingelectrode. (4)Ahighthermalconductivityimpliesahighheatdissipa tionrate.Thisisanimportantfeaturesincethechargeand dischargeoperationsofabateryproduceagreatamountof heat.Withoutafastheatdisipationrate,thebaterycannot bechargedordischargedatahighrate. (5)Themostcommonlyusedconductiveaditivesarecarbon black(CB)oracetyleneblack(AB),whicharenotvery electricalyconductive.Grapheneshetshaveanelectrical conductivity(upto20,000S/cm)thatisseveralordersof magnitudehigherthanthatofCBorAB(typicaly0.01-10 S/cm). (6)Grapheneshetsintheinteriorandtheexteriorsurfaceof a particulate provide not only a robust 3-D network of electron-conductingpathsandhighconductivity,butalso US9,203,084B2 Thesedatahaveclearlydemonstratedthesuperioradvan tagesofthepresentlyinventedcathodeactivematerial-coated grapheneshets.ThepresentlyinventedLi Sbateryfea turingaS-coatedgrapheneshetcathodecanbecharged/ dischargedfor1,000cycleswithoutsuferinga20%capacity decay.Thehighenergydensityimpliesthatacurentelectric vehiclewitharatingof300milesononebaterycharge(e.g.25 TeslaModel-SalbateryEV)canbeimprovedtoaratingof 1,200milesononecharge,giventhesamebateryweight. Thiswouldreducetheneedtobuildsomanychargingstations andwouldalsoreducedrivers“rangeanxiety',thetwofac torsthathavethusfarpreventedalEVsfrombeenwidely 30 acceptedbyconsumers.With1,200milespercycleandalife expectancy of approximately 1,000 cycles, the presently inventedLi SbaterywouldenableanEVtorunfor1,20, 000milesbeforeneedingabateryreplacement.Thisinven InSummary,thepresentlyinventedgraphene-enhanced particulatesSurprisinglyimpartthefollowinghighlydesir ableatributestoalithiumbateryelectrode:highreversible capacity,lowireversiblecapacity,hightapdensity,electrode fabricationease(shapeofsecondaryparticlestypicalybeing sphericalornearspherical),Smallprimaryparticlesizes(for high-ratecapacity),compatibilitywithcommonlyusedelec trolytes(embracinggrapheneshetshelptoisolateactive materialparticlesfromelectrolyte),andlongcharge-dis chargecyclelife. The invention claimed is: 1.A cathodeelectrodeofalithiumbatery,whereinsaid cathodeelectrodecomprisesacathodeactivematerial-coated grapheneshet,whereinsaidgrapheneshethastwoopposed paralelsurfacesandatleast50%areaofoneofsaidtwo Surfacesiscoatedwithacathodeactivematerialandwherein saidgraphenematerialisinanamountoffrom0.1%to99.5% byweightandsaidcathodeactivematerialisinanamountof atleast0.5%byweight,albasedonthetotalweightofsaid graphenematerialandsaidcathodeactivematerialcombined. (2)Thecathodeactivematerialcoatingcanbeverythin(1 nm-100nm),enablingfastelectronandlithiumiontrans port,yetstilprovidingahighactivematerialcontentand beingconducivetotheformationofelectrodeswitha desiredthicknes(100-250um).Further,eachandevery thinactivematerialcoating(e.g.non-conductingS)hasa60 conductivebacking(grapheneSubstrate).Thesecombined featureshaveneverbeenpossiblewithanypriorartcath 4.Thecathodeelectrodeofclaim1,whereinsaidcoated odeactivematerial. tionrepresentsaverysignificantaccomplishmentthatcan35 haveadramaticimpactontheemergenceofavibrantEV industry. Inconclusion,wehavesucesfulydevelopedanewand novelclasofhigh-capacitycathodeactivematerials(cath odeactivematerial-coatedgrapheneshets)andtherelating40 cathodeelectrodeforlithiumbateries.Suchagraphene enhancedparticulateplatformtechnologyhasthefollowing highlydesirablefeaturesandadvantages: (1)Thecathodeactivematerial-coatedgrapheneshetshave averyhighloading(percentage)oftheactivematerial, typicalyfrom60% to99% (moretypicalyfrom90to 95%)byweightofthecathodeactivematerial.Thecathode activematerialcoatingtypicalycovers60%-100%ofone oftheprimarySurfaceofagrapheneshet.Thelength/ widthofthesecoatedgrapheneshets,typicalyinthe50 rangeof0.5-10um,areamenabletothefabricationof poroussecondaryparticleshavingadiameterof1-10um, themostidealparticlesizesforelectrodefabricationease, lithiumiontransport,andlong-termcyclingstability. 45 55 2.Thecathodeelectrodeofclaim1,whereinatleast80% area of one of said Surfaces is coated with a cathode active material. (3)Grapheneshetsareofhighstrength,highelectricalcon ductivity,andhighthermalconductivity.Singlelayer65 graphenewasrecentlyfoundtoexhibitthehighestintrinsic 5.Thecathodeelectrodeofclaim1,whereinsaidcathode strengthandhighestintrinsicthermalconductivityamong activematerialisselectedfromaninorganicmaterial,an enabletheelectrodematerialstobereadilymadeintoelec trodeswithahightapdensityandlong-termcyclingsta bility. (7)Theembracinggrapheneshetsefectivelyisolatethe anodeactivematerials(e.g.,SiandSnO particles)from theelectrolyte,whichotherwisecouldreactwiththese activematerials,therebyreducingthereversiblecapacity. (8)QuiteSurprisingly,spray-dryingreadilyproduces graphene-enhancedparticulatesofasphericalshapethatis conducivetotheformationofinterconnectedporesinan actualelectrodetoenableeasypenetrationofelectrolyte. Theembracedprimaryparticles(coatedshets)havinga smallthicknes(typicalysmallerthan100nm)providea shortlithiumdifusionpathforlithiumtoenterandleave. Thisisparticularlydesirableforpowertolandelectric vehicleaplicationswherethebaterymustbecapableof beingchargedanddischargedatahighrate. 3.Thecathodeelectrodeofclaim1,whereinsaidcoated grapheneshetcontainsatleast60%byweightorbyvolume ofsaidcathodeactivematerialbasedonthetotalweightof saidcoatedgrapheneshet. grapheneshetcontainsatleast90%byweightorbyvolume ofsaidcathodeactivematerialbasedonthetotalweightof saidcoatedgrapheneshet.PDF Image | CATHODE ACTIVE MATERIAL-COATED DISCRETE GRAPHENE SHEETS FOR LITHIUM
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