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19 oftwoormore.Moredesirably,thissecondsolventshouldbe selectedfromthosehavingadonornumberof16.5orles. Theviscosityofthissecondsolventshouldpreferablybe28 cpsorlesat25°C. 20 NGPswerebetween1and10layers.Thegraphene-water SuspensionwasusedforSubsequentpreparationofaprecur Sormixturecontainingprimaryparticlesofeitherananode activematerialoracathodeactivematerial. Themixingratiooftheaforementionedethylenecarbonate in the mixed solvent should preferably be 10 to 80% by volume.Ifthemixingratiooftheethylenecarbonatefals outsidethisrange,theconductivityofthesolventmaybe loweredorthesolventtendstobemoreeasilydecomposed, therebydeterioratingthecharge/dischargeeficiency.More preferablemixingratiooftheethylenecarbonateis20to75% byvolume.Whenthemixingratioofethylenecarbonateina non-aqueoussolventisincreasedto20%byVolumeormore, thesolvatingefectofethylenecarbonatetolithiumionswil befacilitatedandthesolventdecomposition-inhibitingefect15 thereofcanbeimproved. Examplesofpreferedmixedsolventareacomposition comprising EC and MEC; comprising EC, PC and MEC: comprisingEC,MECandDEC;comprisingEC,MECand DMC;andcomprisingEC,MEC,PCandDEC;withthe volumeratioofMECbeingcontroledwithintherangeof30 to80%.ByselectingthevolumeratioofMECfromtherange of30to80%,morepreferably40to70%,theconductivityof thesolventcanbeimproved.Withthepurposeofsuppressing thedecompositionreactionofthesolvent,anelectrolytehav25 ingcarbondioxidedissolvedthereinmaybeemployed, therebyefectivelyimprovingboththecapacityandcyclelife ofthebatery.Theelectrolyticsaltstobeincorporatedintoa non-aqueouselectrolytemaybeselectedfromalithiumsalt suchaslithiumperchlorate(LiCIO),lithiumhexafluoro30 phosphate(LiPF),lithiumborofluoride(LiBF),lithium hexafluoroarsenide(LiAsF),lithiumtrifluoro-metasul fonate (LiCFSO) and bis-trifluoromethyl sulfonylimide lithiumLiN(CFSO).Amongthem,LiPF LiBFand LiN(CFSO) areprefered.Thecontentofaforementioned electrolyticsaltsinthenon-aqueoussolventispreferably0.5 to2.0mol/l. Thefollowingexamplesservetoilustratethebestmode practiceofthepresentinventionandshouldnotbeconstrued aslimitingthescopeoftheinvention,whichisdefinedinthe40 claims. EXAMPLE1 GrapheneOxidefromSulfuricAcidIntercalation 45 and ExfoliationofMCMBS MCMB2528meso-carbonmicrobeadsweresuppliedby AluminaTrading,whichwastheU.S.distributorfortheSup plier,OsakaGasChemicalCompanyofJapan.Thismaterial50 hasadensityofabout2.24g/cmwithamedianparticlesize ofabout2.5.MCMB2528(10grams)wereintercalated withanacidsolution(sulfuricacid,nitricacid,andpotassium permanganateataratioof4:1:0.05)for48hours.Upon completionofthereaction,themixturewaspouredinto55 deionizedwaterandfiltered.TheintercalatedMCMBs were repeatedlywashedina5%solutionofHCltoremovemostof theSulphateions.Thesamplewasthenwashedrepeatedly withdeionizedwateruntilthepHofthefiltratewasneutral. Theslurywasdriedandstoredinavacuumovenat60°C.for60 24hours.Thedriedpowdersamplewasplacedinaquartz tubeandinsertedintoahorizontaltubefurnacepre-setata desiredtemperature,800°C.for30secondstoobtainSample 1.ASmallquantityofeachsamplewasmixedwithwaterand ultrasonicatedat60-Wpowerfor10minutestoobtaina65 Suspension.Asmallamountwassampledout,dried,and investigatedwithTEM,whichindicatedthatmostofthe EXAMPLE 2 OxidationandExfoliationofNaturalGraphite Graphite oxide was prepared by oxidation of graphite flakeswithSulfuricacid,Sodiumnitrate,andpotassiumper manganateataratioof4:1:0.05at30°C.for48hours, accordingtothemethodofHummersU.S.Pat.No.2,798, 878,Jul.9,1957.Uponcompletionofthereaction,the mixturewaspouredintodeionizedwaterandfiltered.The samplewasthenwashedwith5% HClsolutiontoremove mostofthesulfateionsandresidualsaltandthenrepeatedly rinsedwithdeionizedwateruntilthepHofthefiltratewas approximately7.Theintentwastoremovealsulfuricand nitricacidresidueoutofgraphiteinterstices.Theslurywas driedandstoredinavacuumovenat60°C.for24hours. Thedried,intercalated(oxidized)compoundwasexfoli atedbyplacingthesampleinaquartztubethatwasinserted intoahorizontaltubefurnacepre-setat1,050°C.toobtain highlyexfoliatedgraphite.Theexfoliatedgraphitewasdis persedinwateralongwitha1%surfactantat45°C.ina flat-bottomedflaskandtheresultinggrapheneoxide(GO) Suspensionwassubjectedtoultrasonicationforaperiodof15 minutes.PortionsoftheresultingGO-watersuspensionwere thenspin-coatedontoapolyimidefilmtoformthinfilmsof GOsheetswithvariousdiferentfilmthicknesses,from approximately1nmto30nm. US9,203,084B2 10 35 EXAMPLE 3 PreparationofCathodeActiveMaterial-Coated GrapheneSheetsandSecondaryParticles Continuousgraphenefilmscoatedwithacathodeactive materialwerepreparedfromSputering(e.g.lithiummetal oxide),physicalvapordeposition(e.g.S),andSolutiondepo sition.Thecoatedfilmwasbroken,cutintopieces,andthen airjetmilledtoobtainSmallpiecesofactivematerial-coated grapheneshets. Forthepreparationofgraphene-enhancedparticulates,an amountofaselectedelectrodeactivematerialpowder(con trolsample,nosupportinggrapheneshet)oractivematerial coatedgrapheneshetswasaddedtoadesiredamountofGO SuspensiontoformaprecursormixtureSuspensionwitha solidcontentofapproximately10%byweight.Afterthor oughmixinginanultrasonicationreactor,theSuspensionwas thenspray-driedtoformthegraphene-enhancedsecondary particles(particulates).Thecathodeactivematerialsstudied inthisexampleincludelithiumcobaltoxide,lithiummanga neseoxide,lithiumironphosphate,Vanadiumoxide,and sulfur. EXAMPLE 4 LithiumIronPhosphate-CoatedGrapheneSheets andCathodeElectrodes A LFPtargetforSputeringwaspreparedbycompacting andsinteringLFTpowderstogether.SputteringofLFPwas conductedonagraphenefilmand,separately,carbonnano fiber(CNF)mat.TheLFP-coatedgraphenefilmwasthen brokenandpulverizedtoformLFP-coatedgrapheneshets.PDF Image | CATHODE ACTIVE MATERIAL-COATED DISCRETE GRAPHENE SHEETS FOR LITHIUM
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