JournalofPowerSources191(2009)127133ContentslistsavailableatScienceDirectJournalofPowerSourcesjournalhomepage:/locate/jpowsourFailuremodesofvalve-regulatedlead-acidapplicationsindeepdischargeYjunaChinabarticleArticleRRAAKCyElectricFSofValedorlightdbycauseratherationatiesthe1Inthelasttwodecades,muchefforthasbeendevotedtothestudyofvalve-regulatedlead-acid(VRLA)batteriesintheapplica-tionsofelectricvehicles(EV)andhybridEVs15.InChina,thereisapopulationofmorethan1.3billion.MostpeoplegotoworkbybicyyelectricapacusethetillVRLofdeandmarofincludingsulfplatecontact,etc.,theyvarywithdifferentdesigns,manufacturingandoperatingconditions715.Inthedeepcycleduty,theinter-faceofthegrid/activemasseasilyaccumulatestheleadsulfatecrystalswithveryhighresistanceandformsabarrierlayerwhenPbSballoysinthepositivegridaresubstitutedbyPbCdSnAl03doi:cleand65.5millionbicycleswereproducedin2007.Inrecentears,however,moreandmorepeopleuseelectricbicyclesorlightscooterstosubstituteforbicycles.Thesenewvehicleshave250or350Welectromotordrivenbya36or48VVRLAbatteryk,respectively5,6.Basedonthepoweroftheelectromotord,thebatterycapacityis12V10,17or20Ah.Theheldamountofelectricbicyclesandlightelectricscootersatleastreaches60Mtheendoflastyear.Itcorrespondstoabout200M12V/10AhAbatteries,oraboutRBM26billion.Thepracticaloperatinglifebatteriesisnormallyintherangeof12years.WiththerapidvelopmentofChineseorAsianeconomy,moreelectricbicyclestheirbatterieswillbeneededandtheyhaveahugepotentialketinthecomingyears,whichalsopromotesthedevelopmentEV.AlthoughtherearemanyfailuremodesofVRLAbatteries,prematurecapacityloss(PCL),gridcorrosion,softening,Correspondingauthor.Tel.:+8659187892893；fax:+8659188073608.E-mailaddress:(Y.Guo).alloys.Itiscalledthe“antimony-freeeffect”andthePCL-1failuremode7,8.AlthoughthebarrierlayercanbeobviouslyimprovedwiththeapplicationofSncontentmorethan1.2wt.%,itissus-ceptibletotheabuseconditionssuchasdeepdischarge.SomostmanufacturersinChinausePbSbCdalloysaspositivegrid.How-ever,Cdispoisonousandmustbeexcluded.Thecorrosionofpositivegridsinthecycledutyisnotheavyascomparedwiththatinthefloatapplications.ThehighcontentsofCaandAlacceleratethecorrosionrateofpositivegridsgreatly,althoughtheyhavegoodmechanicalpropertiesandcastability.Theactivemass(AM)ofpos-itiveplatesundergoesgreatvolumeexpansionandshrinkageinthedeepcycleduty,whichcanleadtopoorcontactbetweenAMpar-ticles8,9.ThisisthePCL-2failuremodeoftentakingplaceintheEVbatteries.Itcanbegreatlyimprovedbycompressingtheplatestack,optimizingthemanufacturetechnologyofpositiveplatesandincreasingtheratioofpositivetonegativeAM.Theserioussulfa-tionofnegativeplatesoftenoccurswhenthebatteryoperatesatthehighratesinapartial-state-of-charge(HRPSoC)orhasahighcurrentofoxygenrecombinationorwhentheadditivesatnega-tiveplatesaredecomposedunderthehightemperaturecondition1,10,11.Itwillbeovercomewiththeuseofhighcontentgraphite78-7753/$seefrontmatter2008ElsevierB.V.Allrightsreserved.10.1016/j.jpowsour.2008.08.059onglangGuoa,ShengqunTanga,GangMengb,ShiCollegeofChemistryandChemicalEngineering,FuzhouUniversity,Fuzhou350108,PRHubeiCamelStorageBatteryCo.Ltd.,Gucheng441705,PRChinainfohistory:eceived26June2008eceivedinrevisedform20August2008ccepted21August2008vailableonline29August2008eywords:clelifebicycleailuremodesteningve-regulatedlead-acidbatteriesabstractThe36or48Vvalve-regulatsourcesofelectricbicyclesbatterieshavebeenstudieItindicatesthatthemainpositiveactivemass(PAM)Whentheelectrolytesaturthedepolarizationofthenegoxygenevolutionaccelerat.IntroductionbatteriesforelectricbicycleYangblead-acid(VRLA)batterypackshavebeenwidelyappliedtothepowerelectricscootersinChina.Thefailuremodesofthe12V/10AhVRLAthecyclelifetestatC2dischargerateand100%depthofdischarge(DOD).ofthebatteryfailureinthiscycledutyisthesofteningandsheddingofthanindividualwaterloss,recombinationefficiencyorsulfation,etc.fallstoacertainextent,thehighoxygenrecombinationcurrentleadstoveplateandtheshiftofthepositiveplatetoahigherpotential.TheviolentsofteningofPAMandtheendofcyclelife.2008ElsevierB.V.Allrightsreserved.ation,dryingout,additivedecompositionandpoorseparator-128Y.Guoetal./JournalofPowerSources191(2009)127133innegativeactivemass(NAM)12.Dryingoutismostlyconnectedwithahighchargevoltageandcurrent,oftenincombinationwithhighbatterytemperature.Intheextremecases,thermalrunawaymaytakeplaceforabatterywithverylowelectrolytesaturation.Waterlossdependsonthegridcompositions,impurities,batterytemperatureandchargevoltage8.Thesuitablechargeregimeincludingfastchargeisveryimportantforprolongingthebatterycyies,andar(2erstrcurrbicyimVRLcy2.poseglasswSn0.0containedensitiesing.HductdiscIn1agagthewhentwiththepo(Ptmicr3.3.batttheir28ththat,60abouting,ttFig.1.Evolutionofdischargecapacityoftwobatteriesinthecyclesat100%DOD.currentandbatteryvoltageatthecurrent-limitedconstantvoltageinthecyclelifetest.Inthefirstconstantcurrentstage(2.5A),theconstantcurrenttimeinFig.2Ashortenswiththecycles.Itisduetothegradualfallingofthebatterycapacity.TherisingofthechargevoltageinFig.2Bindicatestheincreaseofthebatterypolarizationresistanceduetowaterlossandbatterydegeneration,etc.Inthesecondconstantvoltagestage(14.4V),thechargecurrentdropsFig.2.Thechangesof(A)chargecurrentand(B)chargevoltageatthecurrent-limitedconstantvoltageindifferentcycles.clelife13.Forthepracticeoperatingofelectricbicyclebatter-theirdischargecurrentdependsontheelectromotorpowertheacceleratingprocesses.Thecutoffvoltageis10.5V.Theyenormallychargedatacurrent-limitedconstantvoltage(CCCV)A/14.8V)foronenight,twoorthreetimesperweek.Somecharg-alsousethemulti-stepconstantcurrentcharge.Inthestandardest,however,theelectricbicyclebatteriesaredischargedata2hateto70%or100%depthofdischarge(DOD)andchargedattheent-limitedconstantvoltage.AlthoughtheVRLAbatterieshavebeenwidelyusedinelectriccle,theircyclelifeandperformancestillneedtobefurtherproved.Inthiswork,themanufacturetechnologiesof12V/10AhAbatterieswereoptimizedandthefailuremodesinthedeepcledutywereinvestigated.ExperimentalThetestbatterywas12V/10Ah(C2rate)VRLAbatteriescom-dofsevenpositiveandeightnegativeplatesandtheabsorptivemat(AGM)separator.ThepositiveandnegativegridserePb0.065%Ca1.2%Sn0.003%AlandPb0.085%Ca0.35%15%Alalloys,respectively.Thepositiveandnegativepastesd45and42gH2SO4perkgleadpowder.Theirapparentwere4.34.4gcm3.Ittook48hfortheircuringanddry-Thenthebatterieswereassembledandfilledwith1.25gcm32SO4containing1.5%Na2SO4.Thecontainerformationwascon-edbythemulti-stepconstantcurrentchargeregimewithtwohargestepswithin70h.Thebatteryweightwasabout4.25kg.thecycletest,thebatteriesweredischargedat5A(C2rate)to0.5V(100%DOD)andchargedatacurrent-limitedconstantvolt-eof2.5A/14.4Vfor6h,followedbychargingat0.8Afor1hainatambienttemperatureofabout25C.Thespecificenergyofbatteryreaches32.6Whkg1.Thecyclingtestwasterminatedthebatterycapacityfellto7Ah(70%ratecapacity).Inorderomeasurethebatteryinternalresistance,ashortcurrentpulse5Aand1mswasexertedbyArbinBT2000instruments.Aftercyclelifetest,thebatteriesweretorndownandanalyzed.ThewderX-raydiffraction(XRD)ofpositiveandnegativeactivemassAMandNAM)werecarriedoutbyaXPertProMPDDiffractome-er(Philips).Theirappearancewasobservedbyascanningelectronoscope(SEM,Philips,XL30ESEM-TEP).Resultsanddiscussion1.CycletestsFig.1showsthedependenceofthedischargecapacityoftwoeriesoncyclenumberatC2dischargerate.Intheinitialcycles,capacityincreasesandreachesthemaximum,11.55Ah,inthecycle.Thenitdecreasesgraduallybeforethe250thcycle.Afteritbecomesrelativelystable,butitdropsquicklyafteraboutthe0thcycle.ThecyclelifeofbatteryAandBissimilarandreaches680cycles.Sinceinvariousfailuremodes,thegridcorrosion,PAMsoften-dryingout,sulfationorundercharge,etc.arecloselyrelatedothebatterycharge,thechargeregimeaffectsthecyclelifeoftheestbatteriesgreatly1618.Fig.2showsthechangesofthechargeY.Guoetal./JournalofPowerSources191(2009)127133129Fig.3.Evolutionsofchargecurrentat6handchargevoltageat7hinFig.2.quicklyandreachesverysmallvalue.However,thetailcurrentat6hbeginstoincreaseobviouslyafteraboutthe400thcycleanditsdetailevolutionisshowninFig.3.Atthefinalstageofchargeat0.8A,Fig.2Bshowsthatthechargevoltageatfirstincreasesandthendecreasesasthecycletestproceeds.Theturningpointappearsaboutinthe50thcycleandthechargevoltagereaches16.68V.Thenthemaximumchargevoltagedecreasesgraduallywiththeelec-trolyteconsumptionorthedecreaseoftheelectrolytesaturation,whic5meansandconssccizationc0.hascurrandFcFig.5.Thechangesofvoltageandcurrentwhenthethreefailedcellswerechargedbeforeandafteraddingwater.Fig.6.Thevoltagefallingofthreecellsduringtheshelfafteraddingwaterandafewcycles.hleadstothedepolarizationofthenegativeplate.Afterthe70thcycle,themaximumchargevoltageislowerthan14.40V.ItthatsuchlowpolarizationmayresultintheunderchargetheaccumulationofPbSO4atthenegativeplate.Fig.3showsdependenceofthechargecurrentattheendoftantvoltage(6h)inFig.2Aandthevoltageattheendofcon-tantcurrent(7h)inFig.2Bonthecyclenumber.Inpractice,thishargecurrentresponsestotherateofoxygenrecombinationorhargeefficiencyandthechargevoltageresponsestothepolar-oreffectivecharge.ItisfoundfromFig.3thatthebatteryhargevoltageisveryhighandthechargecurrentincreasesfrom12to0.39Aintheinitial50cycles.Itindicatesthatthebatteryhighelectrolytesaturationandverylowoxygenrecombinationentinthisperiod.Thenthechargevoltagedropsveryquicklyisstabilizedintherangeof14.615.0Vtillthe400thcycle,ig.4.Thechangesofthebatteryinternalresistanceattheendofchargeanddis-hargeinthecycles.Fig.7.Thechangesoftheinternalresistanceinthechargeanddischargeofthreecellsbeforeandafteraddingwater.130Y.Guoetal./JournalofPowerSources191(2009)127133Fig.8.ThephotographsoftheplatestackanditspositiveandnegativeplatesoffailedbatteryA.andthechargecurrentliesintherangeof0.2110.388A.Thisisarelativelyidealcycleprocess,inwhichtherelativelyhighvoltagenotonlyensuresthefullchargeandbutalsonomorewaterlossoccurs.Afterthat,especiallythe600thcyclelater,thechargecur-rentatconstantvoltagestageincr