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Chevrolet Volt Battery: an Introduction

Chevrolet Volt Battery: an Introduction

BATTERY • PAGE 1

Chevrolet Volt Battery: An Introduction Battery: BATTERY 101 Advanced Batteries and the Chevrolet Volt Why -ion is the Right Battery Astheautomotiveindustrytransitionsfromcarsandtruckspowered Whilethemajorityofhybrid-electricvehicles(HEVs)ontheroadtoday primarilybypetroleumtovehiclespoweredbyelectricity,theheartofthis usenickelmetalhydride(NiMH)baerytechnology,theChevroletVolt transformationwillbethe rapidadvancementofbaerytechnology. extended-rangeelectric vehicle(-REV)will bepowered by a16kWh When theChevroletVoltgoesintoproduction, targetedforlate2010, lithium-ionbaerypack manufacturedbyGMandcomprising more itwillbepoweredbyabaerypackthatdeliversupto40milesof than200lithium-ioncells.Lithium-ion baeriesprovide nearlytwo -andemissions-freedriving. tothreetimesthepowerof aNiMHbaery inamuchsmallerpackage. Contrarytopopularthinking,all lithium-ionchemistriesare notalike. Infact,lithium-ionisafamilyof dozensof chemistries withdifferent capabilitiesandperformancecharacteristics.Thecharacteristics requiredforautomotiveapplicationsdiffergreatlyfrom consumer electronics,such aslaptopcomputers. Lithium-ionbaery chemistry isthefastest-growingand most promisingbaerychemistryforseveralreasons,including: •Superior specificenergyandpower •Longlife •Highefficiency •Durability •Lowerinitialmaterialcostandfewerreplacements •Highcell voltagemeansfewercellsareneededto give desired After extensivetestingofdifferentlithium-ion baerysolutions, voltagerange GeneralMotorshasamuchgreaterunderstanding oflithium-ioncells, •Higherenergy-to-weightratio, animportantconsiderationin controlhardwareandthemanufacturabilityofthebaerycomponents automotiveapplicationssinceexcessmassaffectsefficiency neededfor theChevyVolt’ baerypack.Liketoday’s conventional •Configurableintoawidevarietyof shapesandsizesso asto powertrains,GMbelievesthedevelopmentandassemblyofadvanced efficiently fillavailablespacein thedevicesthey baeriesisacorecompetency.GMisrapidlybuildingcapability and resources tosupportthisstrategicdecision,includingassemblyof •Sufferslileornomemory(lazybaery)effect,whichcanoccur theVolt’sbaerypacksatafacilityintheUnitedStates.Thebaery whenbaeriesgraduallylosetheirmaximumenergy capacity if packwillincludecells,majorelectronic componentsandhardware theyarerepeatedlyrechargedafterbeingonlypartiallydischarged suppliedbyLGChem. •Encounterslowlossof charge(alsoknownasself-discharge) whennotin use GM’sexperienceasamanufacturer–combinedwiththebaery integrationskillsandthe technicalexpertiseofits suppliers–will resultinbaerypacksthatmeettheVolt’squality,safety,performance andtimingrequirements. CHEVROLET VOLT BATTERY • PAGE 2

Fast Facts •TheChevroletVoltfeaturesa16kWhlithium-ionbaery pack •Foruptothefirst40milesof driving,theChevroletVolt’sfully thatweighslessthan400pounds(181.4kg). chargedlithium-ionbaerypack powersanelectric motor. •Thebaerypackismadeup ofmultiplelinkedbaerymodules. Additional captured during vehicle braking (theVolt Alltogetherthemodulescontainmorethan200baery cells. isequippedwithRegenerativeBrakes)isconverted into electricityandstoredinthebaery pack. •ThebaerypackisT-shaped,allowing designerstocreate uniquevehicledesignsacrossmultiplebrands.Thebaery’s •Controlsystemswithin thebaery packpreventitfrom floor,or“pan”,isactuallypartofthevehicle’s structure. dischargingbelowitsminimalstateof charge. •Thebaerymodulesandpacks willbeassembledbyGMat •ThevehicleseamlesslyswitchestoExtended-Range modeonce afacilityinMichigan. thebaeryhasreacheditsminimalstateof charge. Inthis secondarymode,asmall flex-fuelpoweredengine-generator operates at one of several optimized speeds, turning the generatorandproducingtheelectricity neededtopowerthe Volt’selectricmotorundermostdrivingconditions. •Thebaerywillcontinuetostoreenergyfromregenerativebraking andany unusedelectricity createdduringextended-range mode operation. Thisenergywillbeusedtosupplementthe - generatortoprovidepeakperformancewhenitis required. •Theenginegeneratordoesnotfullyrechargethe baery because theobjectiveof theVoltistominimizeoreliminatetheuse petroleum. Theonly waytofullyrechargethebaery istoplug thevehicleintoanelectricaloutlet. Thecostof energy from electricityisabout1/6thecostof gasolinesoplugging inthe vehicletochargethebaeryprovidesthelowest operating cost. How the Battery Propels the Volt •TheVolt’slithium-ionbaeryiscontrolledsothatitoperates Recharging the Battery withinastate-of-chargewindow atanygiventime. Controlling •TheChevroletVoltbaeryisrechargedbypluggingthevehicleinto thebaeryinthiswayavoidsfullychargingor dischargingthe ahousehold-typeelectricaloutlet.Rechargingtakesabouteight baerywhichcanshortenthelifeofthebaery. hoursusinga120V outletandlessthanthreehourson240V. CHEVROLET VOLT BATTERY • PAGE 3

Safety •TheLGChemcellusesamanganese-basedcathodechemistry Differentelectrodematerialshavedifferentcurrent-carryingcapacities, withadditivestoimprovebaerylifeunderhigh-temperature andthisaffectsthestoragecapacitiesof thecells. conditions. Each of theVolt’smorethan200 cellsisa“buildingblock”withinthe •Numerous measures havetakentohelppreventthesafety largerbaerymoduleandpack. An individualcellisabout thesize of issues–namelyshortcircuitingandoverheating–thathave a5-inchby7-inch(12.7-cmby17.7-cm)photoframe,islessthana occurredinlithium-ionbaeriesusedinconsumerelectronics. quarter-inchthickandweighsnearlyapound. LGChem’sexclusiveSafetyReinforcedSeparator consistsof semi-permeablemembranesseparatingtheelectrodesinthe cells,whicharemechanicallyandthermallysuperiortocommonly usedseparators. •Primary,aswellasbackup baerypackcontrols, regulate ,currentstateofchargeandtemperature. •Rigoroustestingoflithium-ionbaerypacksinGM’sbaery labsandon-roadinearlyengineeringdevelopmentcarshasnot revealedanysafetyorperformanceissues.

Durability •Automotivebaeriesoperateinaruggedandhostileenvironment withtheexpectationtheywilllastthelifeofthevehicle:GMis currentlytestingbaerypacksinthelabandengineering developmentvehicles. ThistestingwillhelpGMbeerunderstand howthesepackswilloperateinreal-worlddriving conditions, includingextremehotandcoldweatherclimatesandroad. •TheChevroletVoltbaerycellisencasedina polymer-coated EachVolt’sbaerycellcontainsacarbonanode(thenegativeelectrode), aluminumpackage.This thermallyefficientandsafepackageis a manganese-based cathode (the positive electrode) and a safety- designedtobemoreforgiving underharshconditionsandhelp re inforcedseparator, which providesthemediumforthe transferof reducethecostand complexityofthebaerycooling system. electricalchargeionsbetweentheanodeandthecathode inside the baerycell.

The Battery Cell Theprotectivepolymer-coatedaluminumcoverencasesthe cell, helps Abaerycelldeliverselectriccurrentastheresultofanelectrochemical preventgaspermeation andimprovesbaery coolingefficiency. reaction.Electricalcurrentiscarriedbylithiumions,fromthepositive Tabsatthetopof thecell areusedtolinkthecellswithinthe module. electrode(cathode) tothenegativeelectrode (anode)duringcharging, andfromnegative topositiveduring discharging.Theionsaresmall andresidewithinthecrystalstructureoftheelectrodematerials. CHEVROLET VOLT BATTERY • PAGE 4

The Battery Module Numerous designsarepossibleforassembling cells intoabaery pack •Temperaturesensors foranelectricorhybridvehicle.Amodulardesignisusedinmostcases, allowforinlet/outlet with anumberofcellspackagedtogether intoaunitcalleda“module.” coolantmeasurement Controlsareusedtomonitorthevoltageandcurrentofa cell to •Manifoldsandcoolant determinewhentochargeordischarge.Multiplemodulesarecombined linesallowforheat intoabaerypacksizedto match therequirements ofthevehicle. exchangewiththe Thesamemodulescouldbeusedina varietyofdifferentbaery packs. cell surfaces •Connectorsallowfor singlepointentry/exit of highvoltageloads •Baerycover/enclosure protects andinsulates the pack from the ambientenvironment

Design •Currentlayoutisintheshapeof aT •Steeltray,plasticcover

Integration •Pack ispartof thevehiclestructure The Battery Pack •Pack isanunderbody-mountedcomponent Abaerypackisthefinalassemblyusedtostoreanddischarge electricalenergyfor ahybridor electricvehicle.TheVoltbaery pack Looking Ahead consistsofmultiplemodules, configuredinseries, retainedwithinan Futuregenerationswillproducebaerieswith: enclosurefor underbodyinstallation.Componentsforthecontroland •Lesscostduetobeeruseof partscommonality(lessparts) monitoringofdischargeorchargeenergyarealsohousedwithinthepack. •Higherenergydensity,moreefficientuseof packaging •Modulesareclampedto abaerytrayandjoinedby •Beercold-weatherperformance flexibleinterconnects •Moreefficientinsulation/energyconservation •Relaysandmechanicalassembliesallowforautomatedor manual controlofsubassemblyoutputvoltage •Lowermass •Increasedpowerperformance CHEVROLET VOLT BATTERY • PAGE 5

Battery 101: Commonly Used Terms (Source: International Energy Agency)

Advanced Technology Partial Zero Emission Vehicle (AT-PZEV): Baery state of charge: Theavailablecapacityinabaeryexpressed AsdefinedbytheCalifornia Air ResourcesBoard(CARB), avehicle asapercentageof ratednominalcapacity. that uses electricdrivecomponents to helptheindustryintroduce : Theratioof thechargeononeof theconductorsofa ZeroEmissionVehicles(ZEVs) suchasElectricVehicles(EV)orFuel tothepotentialdifferencebetweentheconductors. Cell Vehicles(FCVs). Capacitor: Adevicethatconsistsof twoconductorsinsulated from Baery cell: Thesmallest,mostdiscreetrepeatingunitof abaery. each otherbyadielectricandwhichintroducescapacitance intoa Acellcontainsananode, cathodeandelectrolyteto deliverelectric circuit,storeselectricalenergy,blockstheflowof directcurrent, and currentastheresultofan electrochemicalreaction. permitstheflowof alternatingcurrenttoadegreedependentonthe Note: Incommonusagetheterm“baery”is oftenappliedtoasingle capacitor’scapacitanceandthecurrentfrequency. cell.However,itismoreaccurateto usetheterm“baerycell”when Charge: Theconversion of electricalenergy–provided inthe form of referringtoasinglecell. currentfromanexternalsource–intochemicalenergy withinacell Baery module: Agroupofinterconnectedelectrochemicalcellsin a orbaery. seriesand/orparallelarrangement,physicallyconnectedinanenclosure Charge factor: Thefactorbywhichtheamountofelectricitydelivered asasingleunit,constituting a direct-currentvoltage sourceusedto duringdischargeismultipliedtodeterminetheminimum amount storeelectricalenergyaschemicalenergy(charge)andtolaterconvert requiredbythebaerytorecoveritsfullychargedstate. chemicalenergydirectlyinto electricenergy(discharge).Theelectro - Charge rate: Thecurrentatwhichabaery ischarged. chemicalcellsareelectricallyconnectedinaseries/parallelarrangement toprovidethemodule’s requiredoperating voltageandcurrentlevels. Charger: Anenergyconverterfortheelectricalcharging ofabaery consistingof galvanic secondaryelements. Baery pack: Acompletelyfunctionalsystemincluding baery modules, baerysupportsystemsandbaeryspecificcontrols. Charge depletion (CD): Whenarechargeableelectric energy storage Acombinationofoneormorebaerymodules, possiblywithanadded system(RESS)onaPHEV,EVorextendedrangeEVisdischarged. coolingsystem,verylikelywith anaddedcontrolsystem.Abaery Charge depletion (CDB): Whenarechargeableenergystoragesystem packisthefinalassemblyusedtostoreanddischargeelectricalenergy (RESS)isdischarged,butitisnottheonly powersource movingthe in aHEV,PHEVorEV. vehicleforward.Aseparatefuelandenergyconversion system works Baery round trip efficiency: Theratio oftheelectricaloutputof in tandemwiththeRESStoprovidepowerandenergytomove the asecondarycell,baerymoduleor baerypackon dischargetothe vehicleaschargeof theRESSiscompleted. electricalinputrequiredtorestoreittotheinitialstateofcharge underspecifiedconditions. CHEVROLET VOLT BATTERY • PAGE 6

Charge depletion (CDE): Whenan RESS isdischarged, and : Thebasicunitabletoconvertchemicalenergy continuouslyprovidestheonlymeansofmovingthevehicleforward directlyintoelectricalenergy. (all-electricoperation). Energy density: Theratioof energyavailablefromacellorbaery Charging equalizer: Devicethatequalizesthebaerystateof relativetoitsvolume. chargeofall themodules inanEVduring charging.Withthismeasure, Equalizing charge: An extendedchargetoensurecompletecharging thevoltageofallthebaerieswillriseequallyandthebaery with of allcellsinabaery. thesmallestcapacityisnotovercharged. Extended-range : An autonomousroad vehicle Controller: Anelementthatrestrictsflow ofelectricpowertoor primarilyusingelectricdriveprovidedbyaRechargableEnergyStorage from anelectricmotor orbaerypack(module,cell).Thiscontrols System(RESS)(e..baery pack),butwithanauxiliary onboard torqueand/orpoweroutput,aswellashelping tomaintainbaery electricalenergygenerationunitandfuelsupplyusedtoextend the lifeand/ortemperaturecontrol. rangeof thevehicleonceRESSelectricalchargehasbeendepleted. Current: Therateoftransferofelectricity.Theunitofmeasureis TheChevroletVoltisanexampleof anextended-range electric vehicle. theAmpere. Lithium ion: Lithiumionisafamilyofbaerychemistries.Lithium-ion Cut-off voltage: Thecellor baeryvoltageatwhich thedischarge baeriesareatypeof rechargeablebaery in whichthe lithium ion isterminated. movesfrom theanodetothecathodeduringdischarge and from the Cycle: Asequenceofadischargefollowedbya charge, or acharge cathodetotheanodewhencharging.Lithiumioniscurrentlyone of followed byadischargeofabaeryunder specifiedconditions. themostpopulartypesof baery for portableelectronics, withone of thebestenergy-to-weightratios,nomemory effect, and aslow loss Depth of discharge: Thepercentage ofelectricityinAmpere- of chargewhennotinuse.Lithium-ionbaeriesareseen asthe next that hasbeendischargedfromasecondarycellor baeryrelativeto enablingtechnology invehicleapplications. its ratednominalfullychargedcapacity. Nickel (NiCd): Nickelcadmiumwasacommonbaery Direct-current motor: Anelectricmotorenergizedbydirectcurrent chemistryusedinmanyEVsofthe‘90s.Itisnolongercommonlyused. toprovidetorque. Nickel Metal Hydride (NiMH): Nickelmetalhydride wasacommon Discharge: Thedirectconversionofthechemicalenergyof acell or commercialbaerychemistry in thelate1990sHEVsand continues baery intoelectricalenergyandwithdrawloftheelectricalenergy tobeusedtoday.Inconsumerelectronics,thisbaery chemistry has intoaload. beenmostlyreplacedbylithium-ion baery chemistry. Discharge rate: Therate,usuallyexpressedinAmperes, atwhich electricalcurrentistakenfroma baerycell, moduleor pack. CHEVROLET VOLT BATTERY • PAGE 7

Normal charging: Themostcommontypeandlocationforchargingof Regenerative braking: Ameansof rechargingthebaery by using aPHEVorEVbaerypacknecessarytoaain thestateofmaximum energyproducedbybrakingthevehicle.Unlikenormalfrictionbrakes, chargeofelectricenergy. whereenergyislostintheform of heatcreatedbyfrictioninbraking, Peak power: Peakpoweraainablefroma baery, electricmachineor regenerativebrakingreducesenergylossbyreturningit tothe baery, engineinthedrivesystemusedto acceleratea vehicle.Peakpoweris resultinginimprovedrange. expressedinkW. Smart charging: Computerizeddevicesthatmonitorthebaery so Power density: Theratioofthepoweravailablefroma baery toits thatchargingisattheoptimumrateandbaery lifeisprolonged. volumeinliters. Specific energy (or gravimetric energy): Theenergy density ofa Range: Themaximumdistancetraveledbya vehicle, underspecific baeryexpressedinWa-hoursperkilogram. conditions,beforerechargingisnecessary.TheChevroletVoltis Specific energy (or gravimetric power density): The rate at expectedtoachieveanall-electricrangeup to40milesbeforean whichabaerycandispensepowermeasuredin Was perkilogram. onboardenginegeneratesadditionalelectricitytoextendtherange State of charge: Seebaery stateof charge. several hundredadditionalmiles. Useable capacity: Thenumberof -hours(or kWhours) that Rechargeable electric energy storage system (RESS): canbewithdrawnfrom abaery pack.Useablecapacity islessthan Baerypacks,flywheelsandultracapacitorsareexamples ofsystems nominalcapacity. that couldberepeatedlyrecharged fromthegrid, regenerativebraking oran electricgenerator. Thebaerypacksarelaterdischargedin Voltage efficiency: Theradioof theaveragevoltageduringdischarge ordertopoweranelectricmachineor movea vehicle. totheaveragevoltageduringrechargeunderspecified conditionsof chargeanddischarge. Wa-hours per kilometer: Energyconsumptionperkilometerata particularspeedandconditionof driving. •••