石墨稀 锂离子电池.docx

石墨稀 锂离子电池.docx

《石墨稀 锂离子电池.docx》由会员分享，可在线阅读，更多相关《石墨稀 锂离子电池.docx（11页珍藏版）》请在冰点文库上搜索。

石墨稀锂离子电池

GrapheneandGraphene-likeCompositesforanodematerialsinLi-ionbatteryApplications

Seedresearchproposalsubmittedby

SupremRanjanDas†

†TheBirckNanotechnologyCenterandDepartmentofPhysics,PurdueUniversity,WestLafayette,IN

Projectsummary

Singlelayergrapheneandfewlayergraphene,arerecentlyshowntohavenumerousscientificandtechnologicalbreak-throughshavingnovelnanodeviceapplications,themostimportantonesbeingpotentialcandidateforelectronicsandsensorapplications.However,inordertodrivethesecomplexandtinydevicesandcircuitsoneneedsthecompatiblepowersupplysystemsthatmustfitintothesamecircuits.Duetoitsveryhighelectronicconductivity,thismaterialcouldbethoughtofasfabricatingtheanodeelectrodeintheLi-ionbattery.Inthisproposal,wediscussthevariousapproachestomakedifferenttypesofgraphenepowders（bothelementalandcomposite）andlaterusethesematerialstofabricatetheanodeforLi-ionbattery.Priortousingitinsideanelectrochemicalcell,variousstructuraltechniquessuchasIRspectroscopy,X-rayphotoelectronspectroscopyandRamanspectroscopycouldbeusedtoidentifythecorrectphaseofthematerial.PrototypedevicesusingLiMn1.5Ni0.5O4cathodesandbothliquidelectrolyte（EC+DMC（1:

1）withLiPF6salt）andsolidelectrolyte（polyethyleneoxide（PEO）basedsolidelectrolyte）arediscussed.

INTRODUCTIONANDBACKGROUND

Broadlyspeaking,theadvancementsintheLi-iontechnologyarecategorizedinthefollowingcategories:

（a）thereplacementofthecarbonaceousmaterialswithalternativelow-voltage,Li-acceptinganodecompounds,withtheaimofimprovingsafetycharacteristics,（b）thereplacementofcobaltwithnickelormanganeseinthecathodestructure,withtheaimofreducingcostandtheenvironmentaltoxicity,and（c）thereplacementoftheliquid-likeelectrolytewitha（solid）polymerelectrolyte（aplasticlikemembranewhichcanactbothasanelectrolyteandaseparator）withtheaimofimprovingbatterydesign,reliability,andflexibilies.

Thisresearchproposalisintendedtostudythepossibilitiesofusingthegrapheneandgraphene-likecompositesforuseasananodematerialinsecondary（Li-ion）battery.

SincetheinventionoffirstgenerationofLi-ionbatteriesusingso-calledRocking-chairtechnologiesbySonyEnergytecInc.andMoliEnergyLtd.duringlate90’s,numerouscarbonaceousanodematerialsarebeingemployedinLi-ionbatteries[1-3].Evenbeforethat,duetothelimitedrechargeabilityandsafetyhazardconcernsofLi-anodebatteriesattractedtheattentionofcarbonaceousanodes.HOPGwasusedasthepositiveelectrode（cathode）incellshavingpureLianodes[4]andlaterpyrolyticcarbonanodeandmetaloxidecathode（vanadiumoxideandchromiumoxide）wereusedinearlyrechargeablebatteries[5].Thelowcostandlowoperationalvoltagesofcarbonaceousmaterialsinitiallymotivatedgraphiteandcokefortheuseofanodes（calledsoftanodes）intheLi-ionbatteriescoupledwithhighvoltagecathode（likeLiCoO2）,sothatabatteryoperatingin4Vrangelargelycommercialized[6].Thecontinuedefforts,bothbytheresearchersandindustries,sincethenhaveconsistentlyenhancedthecarbonaceousanodeperformance,alongwithitsreliabilitiesandsafety（apartfromissuesonpositiveelectrodeandtheelectrolyte）.However,becauseoflotsofcomplexitiesintheoperationsandstabilitiesofthedeviceinthemicroscopicscale,andvariousemergingnewmaterialsmanyunsolvedissuesaswellasimproveddevicesremainshopefulforresearchinthisarea.Althoughrecentyearsmanyalternativetocarbonaceousanodes（e.g.,Lithiumandmetalalloys）withmuchhighercapacityhavebeenreported,buttheyareprolongedtothesocalledpulverizationeffectswhichlimitsitspracticalusegreatly.So,carbonaceousmaterialsremainintheheartofthefabricationofanodesinLi-ionbatteries.

ThemechanismofLi-intercalationinsoftcarbonanodesisthat,itdevelopsthroughwellidentified,reversiblestagescorrespondingtoprogressiveintercalationwithindiscretegraphenelayers,reachingintotheformationofLiC6.Thetheoreticalvalueofthedischargecapacityoflithiatedcarboniscalculatedtobe372mAh/gmbasedonthecharge/dischargereaction6C+Li↔LiC6[7],extendingtheprocesstotherangeoffewmVvs.Li.However,sincethisiswellbelowthedecompositionlimitofseveralcommonelectrolytes（electrolytedecompositionresultsalwaysasurfaceprotectivefilmthatallowsthecontinuousoperationoftheanode）,theseanodessufferfrompoorspecificcapacityandkinetics,althoughproducesmoresafetyandreversibilities[8].Thisisthemainmotivationforthesearchofothercarbonaceousanodes,withpossiblegreaterspecificcapacity,fasterkinetics,higherreliabilityandretainingthesafetyissues.Severalformsofcarbonwithcapacitieshigherthangraphiteandcokearebeingreportedintheliteraturesincethebeginningofthelastdecade,includinghardcarbons（disorderedcarbons）.Thechargestoragemechanismsinthesecarbonsareneitherwellunderstoodnorisuniqueinalltheformsofcarbonanode[9].Variouskindsofcarbonwithwiderangeofcrystallinity（e.g.1.carbonfibers）aswellas

（2）highlydisorderedformsofcarbon（poly-p-phenylene（PPP）-basedcarbon）werestudiedasanodematerials.Otherformsofcarbonstudiedare（3）specialtypesoflowtemperatureformsofcarbon,suchasthatderivedfromphenolicresin,（4）mesocarbonmicrobeads（MCMB）–lowtemperatureheat-treatedMCMBsarereportedwithhighcapacities[10],（5）poly-p-phenylene（PPP）–PPPheattreatedat7000CinH2atmospherehascapacity~680mAh/gm[11].Carbonandgraphiticmaterialshavelargevarietyinmicrostructures,texture,morphology,andcrystallinity,dependingontheirpreparationprocessesandprecursormaterials,aswellasofvariousformssuchaspowders,fibers,spherulesetc.Also,recentlyalargenumberofvariousformsofcompositematerialsofcarbonanddifferentothermaterialsarebeingreportedinliterature（Appendix）.However,thebasisonwhichthesematerialschosenareneitherquitewellexplainedintheliteraturenoritisknownwell.However,theideasofusingabovementionedfewformsofcarbonaresummarizedasfollows:

Mostofthecharginganddischargecapacityatanode（chargingmeansLiinsertionintoanodeanddischargingmeansLiremovalformcarbon（oppositeterminologyascomparedtotheterminologyforacathodeorthebattery））areexplainedonthebasisofcavitymodel（Liionnotonlyintercalatedinto/outofthecarbonlayersbutalsodopedinthenanocavities.Forexample,highcapacityMCMBshascavitieswiththesizeof0.5-1.5nm）.

OBJECTIVE

ThisprojectreportfocusestheuseofsinglelayergrapheneandmultilayergraphenesheetsofvarioussizestofabricatetheLi-ionbatteryanode,anduseofthesameinaprototypeLi-ioncellcomprisingofLiMn1.5Ni0.5O4cathodeandbothEC+DMC（1:

1volume）withLiPF6liquidelectrolyteandPEObasedsolidelectrolyte.

Theideaofsuperiorbehaviorofgraphenesheetsforanodematerials（dischargecapacity~560mAh/gm）isratherlooselyreportedbyDahnet.al.[12],thoughtheyhavenotfocusedtheirattentiontheimportanceofhavingpuregraphemeelectrodeandtheirbehaviorforLi-intercalation/deintercalation.Withthepresentandfutureresearchinmajorityofthescientificandengineeringfieldsdriventowardsnanodirection,Li-ionbatteryresearchnomoreremainsanexception.Allthethreevitalcomponentsofanelectrochemicalcell（namelyanode,cathodeandelectrolyte）arepotentiallybecominginterestingmaterialstostudywiththeadventofnanotechnologyandlotsofsuccessachievedoverwidevarietyofexperimentalandtheoreticaltechniques.Thoughtherearesomedisadvantageswhichneedstobestudieddependingontheparticularcases,recentlyitisarguedthatnanomaterials,becauseoftheirreduceddimensions,canprovidefarmorethananorderofmagnitudeimprovementofintercalation/deintercalationrates（andhencehighcharge/dischargeandsohighpower）inLi-ionbatteries[IntrinsicdiffusivityofLiioninthesolidstate（lithiumintercalationhost）is~10-8cm2s-1][13].However,useofnanoparticulategraphiteonotherhand,canformamuchmorereactivesolid-electrolyte-interface（SEI）layer（Li-iondeposition）ongraphitesurface,ratherthanaprotectiveSEIlayer,thiscreatesmajorsafetyproblem.ThoughCNTshavereportedlyproducedtwiceasmuchListoragecapacityasgraphite,butsimilarsafetyissuesaredebated.

Therearefewreportswhichsummarizefewpossiblewaysthatmightbeeffectiveforusingthecarbonastheanodematerialofchoicebutstillwithouttheabovestatedsafetyproblem.Wuetalreviewedtheeffectofmildoxidationofgraphite,formationofcompositeswithmetalsandmetaloxides[14].MicroencapsulatedgraphitewithnanosizedSilverandNickelmetalparticlestoformcompositeanodeswerereportedanditsstudyofsuppressionofcointercalationofsolvatedLiionsintographitecouldbeapotentialareaofstudythefutureanodematerialsforLi-ionbatteries.Moreoverinthisproject,wewanttoinvestigatethreeaspects:

（i）makingpureandbulkquantitiesofgraphenepowdersandgrapheneoxidepowders,（ii）makingcompositesofgraphenepowderswithmetalnanoparticles,and（iii）usinggrapheneoxidesandgraphene-metalparticlecompositestobuildnegativeelectrodes（anodes）forLi-ionbatteries.

Weexpectsuperiorbehavioroftheseintermsofcharge-dischargeperformance,Coulombicefficiency,andcycleabilityinaprototypecellusingLiPF6+EC+DMCliquidelectrolyteandLiMn1.5Ni0.5O4cathode,andlaterfurtherwanttoextendt