锂离子电池 英文

LiIonBattery(LIB)•Battery:Transducerwhichconvertschemicalenergyintoelectricalenergy.•Chemicalreactions:Oxidationandreduction•Freeenergychangeoftheprocessesappearsaselectricalenergy.•Primarybattery-notrechargeable•Secondarybattery-rechargeableBatteryWhyLi-IonBattery?LeadacidbatteryAppealingtoindustrialapplicationsdueto•Reliable•InexpensiveDisadvantages•Lowlifecycle•Lowenergydensity(30~40Wh/Kg)NimetalhydridebatteryAppealingtohybridelectricvehicleapplicationsdueto•Rechargeable•Nomemoryeffect•Highpowerdensity•Highenergydensity•Currentlyavailablebatterycapacity:1.5kWhDisadvantages•SelfdischargeratesRecharge-ability:Basically,whenthedirectionofelectrondischarge(negativetopositive)isreversed,restoringpower.MemoryEffect:Whenabatteryisrepeatedlyrechargedbeforeithasdischargedmorethanhalfofitspower,itwill“forget”itsoriginalpowercapacity.Cadmiumcrystalshavethememoryeffect(NiCd)J.Mater.Chem.,19(2009)5871SchematicofLiIonBatteryThecathodehalfreaction(withchargingbeingforwards)is:LiCoO2↔Li1-xCoO2+xLi++xe-Theanodehalfreactionis:xLi++xe-+6C↔LixC6•Containsananode,acathode,anelectrolyteandseparator.•Harnessesasetofreversibleoxidation/reductionreactions.•Liiondissolvedbyadischargereactionandreturnstometalliclithiumbyachargingreaction•ElectrolyteprovidesfortheseparationofLiionsandelectrontransport.•InaperfectbatterytheLiiontransportnumberwillbeunity.•Cellpotentialisdeterminedby∆G=-EF•Theelectrodesystemmustbebothagoodionicandanelectronicconductor.•Itisnecessarytoaddanelectronicallyconductivematerialsuchascarbonblack.•Toholdtheelectrodetogether,abinderisalsoneeded.LiIonBatteryAdvantages•Lihasgreatestelectrochemicalpotential•Lighterthanothers•Shapeandsizevariation•Highopencircuitvoltage•Nomemoryeffect•Lowdischargerate5-10%.Disadvantages•Internalresistanceoflithiumionbatteryishighascomparedtootherbatteries.•Duetooverchargingandhightemperaturecapacitywilldiminish.ExistingLi-IonElectrodesGraphite–370mA.h/gLiCoO2–140mA.h/gThedevelopmentofmaterialsforLIBcentresaround“intercalation”andsuitableelectrolytewithappropriate“potentialwindow”.•Intercalationisanequilibriumprocessandgovernedbythefreeenergyconsiderations.•Entropyfactormaypredominateovertheenthalpyfactor.•Thelatticeinwhichintercalationtakesplaceshouldbecapableofinteractingelectronicallywithoutaffectingthetranslational（平动的）entropyoftheintercalant.•Thevalueoftheequilibriumconstantoftheintercalationanddeintercalationreactionshouldbenear1.Intercalation•Shouldbecompletelyreversible.•Shouldbegeometricallyandelectronicallyfittingtotheinterplanarspacing.•Shouldbecapableofelectronexchange.•Othersubstrateslikemesoporouscarbonandotherpillaredmaterialscanalsobeconsidered.Intercalation•Theselectionoftheelectrolytedependsonthepotentialwindow.•Potentialsarebeyondwaterpotentialandhencenonaqueouselectrolyte.•ItshouldnotreactivewithLi+ions,sinceitwilldecidethetransportoftheLi+ionsfortheintercalationreaction.•Theelectrolytesolutioncommonlycomprisesalithiumsaltdissolvedinamixtureoforganicsolvents.•ExamplesincludeLiPF6orLiBOB(theBOBistheanionwiththeboroncoordinatedbytwooxalategroups)inanethylenecarbonate/dimethylcarbonatesolvent.ElectrolyteGraphiteiscommonlyselectedanodematerialinLIBduetoits•Highcoulombicefficiency.•However,thespecificcapacityofgraphiteisrelativelylow(theoreticalvalue:372mA.h/g)sinceeverysixcarbonatomscanhostonlyonelithiumionbyforminganintercalationcompound(LiC6).•Sn:993mA.h/g,Si:4200mA.h/g)thangraphiteviatheformationofalloyswithlithiumorthroughthereversiblereactionswithlithiumions.•Drawbackofthesesubstancesasanodematerialsisthehugevolumevariationduringthecharge/dischargeprocesswhichcausesthepulverizationoftheelectrode,resultinginpoorreversibility.Graphite•Reducingthesizeofthesematerialstonanometerscalecanpartiallysuppresstheexpansionandshrinkageoftheanodematerials.•BydesigningthestructureofthesematerialsashollowsphericalorporousparticlescanimprovethelithiumstoragecapacityandtheirinitialCoulombicefficiencyaswelltoacertaindegree.•However,thecapacitydecayoftheelectrodealongwiththecharge/dischargecyclingstillcannotbecompletelyavoided.BasicbuildingblockforallformsofgraphiticmaterialmadeupofmonolayerCatomstightlypackedinto2Dhoneycomblattice.RemarkablepropertiesYoung’smodulus-1,100GPaFracturestrength-125GPaMobilityofchargecarriers-200,000cm2V-1s-1Thermalconductivity-5,000Wm-1K-1Specificsurfacearea-2630m2g-10D1D3D2DK.S.Novoselov,Nature,438(2005)197.Graphene•Graphene,atwo-dimensionalaromaticmonolayerofcarbonatom,isactuallythebuildingunitofgraphite.•Recently,metaloxidesnanoparticlesencapsulatedbygraphenelayershavebeenreportedtodisplayhighspecificcapacityandexcellentcyclingperformanceasanodematerials.•Thestructure,inwhichthegraphenelayersactedasbotha‘‘bufferzone’’ofvolumevariationofthenanoparticlesandagoodelectrontransfermedium.GrapheneSchematicillustrationsofgraphenebasedcarbonaceousmaterialswithorderedgraphenestructures(A-C)anddisorderedgraphenestructures(D-E),andintercalationofLiionsintheordered(G)anddisordered(H)graphenes.•Lowtheoreticalcapacity(372mA.h/g)(Duetoperfectionofgraphenestructurea