high performance nickel-metal hydride and lithium-ion batteries

JournalofPowerSources105(2002)139±144

Highperformancenickel-metalhydrideandlithium-ionbatteries

Èhler*,J.KuÈmpers,M.UllrichU.Ko

NBTGmbH,AmLeineufer51,D-30419Hannover,Germany

Abstract

Incomparisontopureelectricvehicles(EV)theopportunitiesforhybridelectricvehicles(HEV)aremuchbetter,sincerangerestrictions

nolongerapplyandtheinteractionoftheinternalcombustionengineandelectricaldrivebringincreasedenergyef®ciencyandenvironmentalfriendliness.Thebatteriesusedinsuchapplicationsmustmeetveryhighstandardsintermsofperformanceandservicelife.AlthoughthebatterycapacityissmallerthanforapurelyEV,itneedstobeabletogeneratefarhigherlevelsofpower.Thetechnicalchallengesofhybridapplicationshaveledtothedevelopmentofhigh-performancebatteries.Attheforefrontoftheseisthenickel-metalhydridesystem(NiMH).Withspeci®cpowerandenergydataintherangefrom300to900W/kg,55to37Wh/kg,respectively(basedoncellweight),excellentchargeef®ciencyandenergythroughputlevelsofmorethan10,000timesthenominalenergy,theNiMHsystemcomesveryclosetosatisfyingtheneedsoftheHEV.Paralleldevelopmentswiththelithium-ionsystembasedonmanganesespinelascathodematerialshowthat,withspeci®cpowerandenergylevelsabove1000W/kg,50Wh/kg,respectively,thistechnologywillalsobeabletoplayanimportantroleinthefuture.Servicelife®guresintermsofcalendarlifehavebeenimprovedtremendouslytoaboutthreeyears,butthereisstillaneedforfurtherimprovementinordertomeetthespeci®cationsofcarmanufacturers.Forthisreason,anincreaseoflifespanisthesubjectofintensivedevelopmentwork.#2002ElsevierScienceB.V.Allrightsreserved.

Keywords:Nickel-metalhydride(NiMH);Lithium-ionbatteries;Electricvehicles(EV)

1.Introduction

Electricalroadvehiclescanlookbackonahistoryofmorethanonehundredyears.Theymadeupaconsiderableshareofvehiclesintheearlydaysofroadtraf®c,butthissharewassoonlostinthefaceoftherapidprogressmadebyvehiclesequippedwithinternalcombustionengines.Thefundamen-talweaknessofallelectricvehicles(EV)liesinthebatteryrequiredforenergystorage.Theenergystoragecapacityofbatteriesisunabletoachievetherangesattainedbyvehiclesdrivenbyinternalcombustionengines.Despitealltheprogresswhichhasbeenmade,nottheleastintheresearchanddevelopmentactivitiesconductedsincethestartofthe1990s,therehasbeennofundamentalchangeinthisregard.Signi®canttechnicaladvanceshavebeenmade,butwearestillfarawayfromaproductwhichissatisfactoryineveryrespect[1,3].Thebasiccauseforthelowstoragecapacityofelectrochemicalbatterysystemsliesinthefactthattheirenergydensitiesaremuchsmallerthanthoseofliquidhydrocarbons.Thisshortfallcanonlybecompensatedpar-tiallybythehigheref®ciencyoftheelectricalsystem.Theenergystoragesystemwouldneedtobeatleasttentimes

Correspondingauthor.Tel.: 49-511-9751830;fax: 49-511-9751801.

Èhler).E-mailaddress:uwe.koehler@http://www.wendangwang.com(U.Ko

*largerintermsofvolumeandweight.Thesedrawbacksin

termsofvolumeandweightarecompoundedbyhighcostsandcustomerinconvenience,re¯ectedprimarilyininfra-structureaspectsandchargingtimes.

ThesystemswhichcancurrentlybeusedonthemarketsforEVincludethelead-acidbattery,NiMHtechnology[1,7,9,10,14]andthehigh-temperaturesodium±nickel±chloridesystem.Lithium-ionbatteriesarethesubjectofintensivedevelopmentworkworldwide[16,17].Buteventhismostadvancedsystemintermsofenergydensity,stilllagswellbehindtheenergydensitiespossiblewithconven-tionalpetrol-drivenvehicles.Thebasicadvantageofhydro-carbon-basedenergystoragesystemsisalsothereasonforthenewlyawokeninterestinfuel-celltechnology.Thegeneralweaknessofhydrogen-basedsystemswasthefactthat,inthepast,theystoredenergyintheformofgaseoushydrogen.Storingenergyintheformofmethanolwhichreleaseshydrogenduringsubsequentuseinthereformercomesagooddealnearertoresolvingtheproblemandhasresultedinconsiderableprogressbeingmadeinthisregard[19].

BecauseofthemoresoberviewnowbeingtakenoftheopportunitieswhichexistforpurelyEVinthefuture,hybridvehicleshaveonceagainbecomethefocusofatten-tion[2].Linkinginternalcombustionengineswithelectricdrivesystemsoffersanumberoftechnicalpossibilities

high performance nickel-metal hydride and lithium-ion batteries

high performance nickel-metal hydride and lithium-ion batteries

for

0378-7753/02/$±seefrontmatter#2002ElsevierScienceB.V.Allrightsreserved.PII:S0378-7753(01)00932-6

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