Batteries for Plug-in Hybrid Electric Vehicles (PH

BatteriesforPlug-inHybridElectricVehicles(PHEVs):[e-mail]@[e-mail]tionStudiesUniversityofCaliforniaDavis,CAUCD-ITS-RR-08-14May2008-i-AbstractThisreportdiscussesthedevelopmentofadvancedbatteriesforplug-inhybridelectricvehicle(PHEV)applications.WediscussthebasicdesignconceptsofPHEVs,comparethreesetsofinfluentialtechnicalgoals,andexplaintheinherenttrade-offsinPHEVbatterydesign.Wethendiscussthecurrentstateofseveralbatterychemistries,includingnickel-metalhydride(NiMH)andlithium-ion(Li-Ion),comparingtheirabilitiestomeetPHEVgoals,andpotentialtrajectoriesforfurtherimprovement.Fourimportantconclusionsarehighlighted.First,PHEVbattery“goals”varyaccordingtodifferingassumptionsofPHEVdesign,performance,usepatternsandconsumerdemand.Second,batterydevelopmentisconstrainedbyinherenttradeoffsamongfivemainbatteryattributes:power,energy,longevity,safetyandcost.Third,Li-IonbatterydesignsarebettersuitedtomeetthedemandsofmoreaggressivePHEVgoalsthantheNiMHbatteriescurrentlyusedforHEVs.Fourth,theflexiblenatureofLi-Iontechnology,aswellasconcernsoversafety,haspromptedseveralalternatepathsofcontinuedtechnologicaldevelopment.Duetothedifferencesamongthesedevelopmentpaths,theattributesofonetypeofLi-Ionbatterycannotnecessarilybegeneralizedtoothertypes.Thispaperisnotintendedtobeadefinitiveanalysisoftechnologies;instead,itismoreofaprimerforbatterynon-experts,providingtheperspectiveandtoolstohelpunderstandandcriticallyreviewresearchonPHEVbatteries.-ii-ExecutiveSummaryInthisreportweaddressthestateofbatterydevelopmentforplug-inhybridelectricvehicles(PHEVs).Thisexecutivesummaryhighlightsourfundamentalpoints,avoidingmanyofthetechnologicaldetailsdescribedinourfullreport.However,afullreadingofourreportisrecommendforreadersseekingtobetterunderstandandcriticallyreviewPHEVbatteryresearch.AglossaryofPHEVtermsandacronymsisprovidedonpages24-26.BasicPHEVDesignConcepts:FigureE-1portraysthetwobasicmodesofaPHEV:chargedepleting(CD)andchargesustaining(CS).Foradistance,the“fully”chargedPHEVisdriveninCDmode—energystoredinthebatteryisusedtopowerthevehicle,graduallydepletingthebattery’sstateofcharge(SOC).Oncethebatteryisdepletedtoaminimumlevel,thevehicleswitchestoCSmode,sustainingthebatterySOCbyrelyingprimarilyonthegasolineenginetodrivethevehicle(likeaconventionalhybridelectricvehicle).CDrangeisthedistanceafullychargedPHEVcantravelinCDmodebeforeswitchingtoCSmode(withoutbeingpluggedin).APHEVwithaCDrangeof10milesisreferredtoasaPHEV-10(althoughnotationcandifferamongreports).InCDmode,aPHEVcanbedesignedtousegridelectricityexclusively(all-electric)orelectricityandgasoline(blended).Allelseequal,aPHEVdesignedforall-electricoperationrequiresamorepowerfulbatterythanaPHEVdesignedforblendedoperation.TheCDrangeandoperationcapabilitiesofaPHEVwilldependontheassumeddrivecycle,thatis,howaggressivelyandunderwhatconditionsthevehicleisdriven.FigureE-1:IllustrationofTypicalPHEVDischargeCycleDistanceBatteryStateofCharge(SOC)ChargeSustaining(CSMode)ChargeDepleting(CDMode)GasolineOnlyAllElectricorBlendedSource:AdaptedfromKromerandHeywood(2007,p31).Usedwithpermissionfromauthors.BatteryGoals:TableE-1summarizesPHEVbatterygoalsfromthreedifferentsources:TheU.S.AdvancedBatteryConsortium(USABC),theSloanAutomotiveLaboratoryat-iii-MIT,andtheElectricPowerResearchInstitute(EPRI).Batterygoalsarecontingentonmanyassumptions,includingCDrange,CDoperation(all-electricvs.blended),drivecycle,vehiclemass,batterymass,andotherissues.WefocusonUSABCgoals(Pesarenetal.,2007),whichwecompileinto5maincategories:power,energy,life,safetyandcost.Forpowerdensity,thePHEV-10batterytargetis830W/kg,andthePHEV-40targetis380W/kg.Thecorrespondingenergydensitytargetsare100Wh/kgand140Wh/kg,respectively.NotshowninTableE-1areUSABCsafetygoals,whicharedeterminedthroughabusetesting,andbasedonageneralratingof“acceptability”.Targetedbatterycostsare$200-$300perkWh.Wenotethatthereareinherenttradeoffsamongtheseattributescategories:increasingpowerdensityrequireshighervoltagethatreduceslongevityandsafetyandincreasescost;increasingenergydensitytendstoreducepowerdensity;attemptstosimultaneouslyoptimizepower,energy,longevity,andsafetywillincreasebatterycost.TableE-1:ComparingPHEVAssumptionsandBattery“Goals”UnitsUSABC1MIT2EPRI3VehicleAssumptionsCDRangeMiles1040302060CDOperation-All-electricAll-electricBlendedAll-electricAll-electricBodyType-Cross.SUVMid.CarMid.CarMid.CarMid.CarTotalBatteryMasskg6012060159302TotalVehicleMasskg19501600135016641782Battery“Goals”PeakPowerkW5046445499EnergyCapacitykWh6178618CalendarLifeyears1515151010CDCycleLifecycles5,0005,0002,5002,4001,400CSCycleLifecycles300,000300,000175,000200,000200,000Sources:1Pesarenetal.(2007)2KromerandHeywood(2007)3Grahametal.(2001)BatteryTechnologies:Wediscusstwobroadcategoriesofbatterychemistries:nickel-metalhydride(NiMH)andlithium-ion(Li-Ion).FigureE-2presentsRagoneplotsofthesechemistriesadaptedfromKalhammeretal.(2007).Thelightgreybandspresentthepowerandenerg