Lead Acid Battery.docx

Lead Acid Battery.docx

《Lead Acid Battery.docx》由会员分享，可在线阅读，更多相关《Lead Acid Battery.docx（15页珍藏版）》请在冰豆网上搜索。

LeadAcidBattery

阀控式密封铅酸蓄电池（VRLA）的内阻分析

1.概念：

 电池中由于电极的动力学过程，物质转移及欧姆电阻所消耗的能量，通常称之为蓄电池的内部电阻（简称内阻），以Ω或mΩ表示。

电池内阻是监控电池性能的重要参数，电池内阻与其剩余容量之间存在对应关系，因此一些国外大型电信公司也正在用电导检测使用中的阀控密封铅酸蓄电池的剩余容量。

但必须指出，由于影响电池内阻的因素很多，诸如测试频率，荷电状态，搁置时间，电液量，充放电方式及工作环境等。

因此，简单地采用电池内阻代表剩余容量是有疑虑的。

2.内阻的组成：

 铅酸蓄电池具有小的内阻，是碱性蓄电池的1/3～1/5（对同一容量而言），且由于铅酸蓄电池具有其它的一些特点，使得其在过去一百多年里就得到广泛的应用。

  对于一个单元格（单体）蓄电池而言，其内阻主要由五部分组成：

连接部分（含极群总线和端柱），电极活性物质，板栅，隔离板及电解液。

对于正极多孔的PbO2其比电阻类似于半导体物质，可达740mΩ.cm，而负极海绵铅的比电阻为18.3mΩ.cm，可见正极活性物质PbO2引起的欧姆电阻是负极海绵铅的40.4倍。

起动用蓄电池在-18℃起动时，其内阻约为2.05mΩ/单元格，其内阻分布如下图1：

3.内阻的影响因素：

 影响蓄电池内阻的因素是多方面的，主要有下列几点：

3.1电解液浓度（密度）

 硫酸溶液的密度与比电阻的关系见图2。

由图2可见，密度在1.2～1.3g/ml之间比电阻最小，因此各类铅酸蓄电池电解液在完全充足电时，其密度位于其间，以得到较低的内阻。

当电池放电过程中，随着电解液密度的降低，比电阻随之增大；当低于1.10g/ml时，比电阻急增。

3.2电解液温度：

电解液温度对内阻的影响见图3。

由图3可见，内阻随温度的降低而增大，随温度的升高而减小。

以20℃为基准，每降低10℃，则内阻增大12%～15%；温度趋于越低，内阻增大的幅度加大。

这主要是由于硫酸溶液的比电阻与粘度增大的缘故（

3.3荷电状态

 蓄电池荷电状态与放出容量成反比，蓄电池内阻随着放出电量而变化见图4。

当完全充足电时，蓄电池内阻最小；当以20小时率放完电后，其内阻增大到完全充足电时的2.5倍。

这主要因为：

一是由于在放电过程中，在多孔的活性物质与硫酸溶液接触的表面形成了PbSO4层。

这PbSO4层带来了三个不利的影响：

PbSO4层导电性能较差，使活性物质的电阻增大；PbSO4层使极板孔率降低从而降低了电解液在活性物质中的扩散速度，而增大了浓差极化；PbSO4层减少了活性物质的反应面积，增大了电化学极化。

二是放电过程中电解液密度降低而增大了比电阻。

这些因素综合作用结果，使蓄电池的内阻随着放出容量增大而增大。

3.4蓄电池结构

 电池结构主要指极板的类型与板栅结构（若以电池组来说，还包括单元格之间的连接方式）。

合理的极板类型和板栅结构能有效地降低蓄电池的欧姆电阻。

Lead-acidbattery

Lead-acidbattery

leadacidcarbattery

Energy/weight

30-40Wh/kg

Energy/size

60-75Wh/L

Power/weight

180W/kg

Charge/dischargeefficiency

50%-92%[1]

Energy/consumer-price

7（sld）-18（fld）Wh/US$[2]

Self-dischargerate

3%-20%/month[3]

Cycledurability

500-800cycles

NominalCellVoltage

2.105V

Lead-acidbatteries,inventedin1859byFrenchphysicistGastonPlanté,aretheoldesttypeofrechargeablebattery.Despitehavingthesecondlowestenergy-to-weightratio（nexttothenickel-ironbattery）andacorrespondinglylowenergy-to-volumeratio,theirabilitytosupplyhighsurgecurrentsmeansthatthecellsmaintainarelativelylargepower-to-weightratio.Thesefeatures,alongwiththeirlowcost,makethemattractiveforuseinmotorvehiclestoprovidethehighcurrentrequiredbyautomobilestartermotors.

Contents

[hide]

∙1Electrochemistry

∙2Voltagesforcommonusages

∙3Measuringthechargelevel

∙4Constructionofbattery

o4.1Plates

o4.2Separators

∙5Applications

∙6Cycles

o6.1Startingbatteries

o6.2Deepcyclebatteries

o6.3Fastandslowchargeanddischarge

∙7Valveregulatedleadacidbatteries

∙8Explodingbatteries

∙9Environmentalconcerns

∙10Additives

∙11CorrosionProblems

∙12Maintenanceprecautions

∙13Seealso

∙14References

∙15Externallinks

[edit]Electrochemistry

Inthechargedstate,eachcellcontainselectrodesofelementallead（Pb）andlead（IV）dioxide（PbO2）inanelectrolyteofapproximately33.5%v/v（6Molar）sulfuricacid（H2SO4）.

Inthedischargedstatebothelectrodesturnintolead（II）sulfate（PbSO4）andtheelectrolytelosesitsdissolvedsulfuricacidandbecomesprimarilywater.Duetothefreezing-pointdepressionofwater,asthebatterydischargesandtheconcentrationofsulfuricaciddecreases,theelectrolyteismorelikelytofreezeduringwinterweather.

Thechemicalreactionsare（dischargedtocharged）:

Cathode（reduction）:

Anode（oxidation）:

Becauseoftheopencellswithliquidelectrolyteinmostlead-acidbatteries,overchargingwithhighchargingvoltageswillgenerateoxygenandhydrogengasbyelectrolysisofwater,forminganexplosivemix.Theacidelectrolyteisalsocorrosive.

Practicalcellsareusuallynotmadewithpureleadbuthavesmallamountsofantimony,tin,calciumorseleniumalloyedintheplatematerialtostrengthentheplatesandmakethemeasiertomanufacture.

Voltagesforcommonusages

Thesearegeneralvoltagerangesforsix-celllead-acidbatteries:

∙Open-circuit（quiescent）atfullcharge:

12.6Vto12.8V（2.10-2.13Vpercell）

∙Open-circuitatfulldischarge:

11.8Vto12.0V

∙Loadedatfulldischarge:

10.5V.

∙Continuous-preservation（float）charging:

13.4Vforgelledelectrolyte;13.5VforAGM（absorbedglassmat）and13.8Vforfloodedcells

1.Allvoltagesareat20°C,andmustbeadjusted-0.022V/°Cfortemperaturechanges.

2.Floatvoltagerecommendationsvary,accordingtothemanufacturer'srecommendation.

3.Precise（±0.05V）floatvoltageiscriticaltolongevity;toolow（sulfation）isalmostasbadastoohigh（corrosionandelectrolyteloss）

∙Typical（daily）charging:

14.2Vto14.5V（dependingonmanufacturer'srecommendation）

∙Equalizationcharging（forfloodedleadacids）:

15Vfornomorethan2hours.Batterytemperaturemustbemonitored.

∙Gassingthreshold:

14.4V

∙Afterfullchargetheterminalvoltagewilldropquicklyto13.2Vandthenslowlyto12.6V.

Portablebatteries,suchasforMiners'caplamps（headlamps）typicallyhavetwocells,andsothevoltagesareonethirdofthoseshownhere.[1]

[edit]Measuringthechargelevel

Becausetheelectrolytetakespartinthecharge-dischargereaction,thisbatteryhasonemajoradvantageoverotherchemistries.Itisrelativelysimpletodeterminethestateofchargebymerelymeasuringthespecificgravity（S.G.）oftheelectrolyte,theS.G.fallingasthebatterydischarges.Somebatterydesignshaveasimplehydrometerbuiltinusingcolouredfloatingballsofdifferingdensity.Whenusedindiesel-electricsubmarines,theS.G.wasregularlymeasuredandwrittenonablackboardinthecontrolroomtoapprisethecommanderastohowmuchunderwaterendurancetheboathadremaining.

[edit]Constructionofbattery

[edit]Plates

Theprincipleoftheleadacidcellcanbedemonstratedwithsimplesheetleadplatesforthetwoelectrodes.Howeversuchaconstructionwouldonlyproducearoundoneampereforroughlypostcardsizedplates,anditwouldnotproducesuchacurrentformorethanafewminutes.

GastonPlantérealizedthataplateconstructionwasrequiredthatgaveamuchlargereffectivesurfacearea.Planté'smethodofproducingtheplateshasremainedlargelyunchangedandisstillusedinstationaryapplications.

TheFaurepasted-plateconstructionistypicalofautomotivebatteries.Eachplateconsistsofarectangularleadgridalloyedwithantimonyorcalciumtoimprovethemechanicalcharacteristics.Theholesofthegridarefilledwithamixtureofredleadand33%dilutesulfuricacid.（Differentmanufacturershavemodifiedthemixture）.Thepasteispressedintotheholesintheplateswhichareslightlytaperedonbothsidestoassistinretentionofthepaste.Thisporouspasteallowstheacidtoreactwiththeleadinsidetheplate,increasingthesurfaceareamanyfold.Atthisstagethepositiveandnegativeplatesaresimilar,howeverexpandersandadditivesvarytheirinternalchemistrytoassistinoperationwheninuse.Oncedry,theplatesarethenstackedtogetherwithsuitableseparatorsandinsertedinthebatterycontainer.Anoddnumberofplatesisusuallyused,withonemorepositiveplatethannegative.Eachalternateplateisconnectedtogether.Aftertheacidhasbeenaddedtothecell,thecellisgivenitsfirstformingcharge.Thepositiveplatesgraduallyturnthechocolatebrowncolourofleaddioxide,andthenegativeturntheslategrayof'spongy'lead.Suchacellisreadytobeused.Modernmanufacturingmethodsinvariablyproducethepositiveandnegativeplatesreadyformed,sothatitisonlynecessarytoaddthesulfuricacidandthebatteryisreadyforuse.

Oneoftheproblemswiththeplatesisthattheplatesincreaseinsizeastheactivematerialabsorbssulfatefromtheacidduringdischarge,anddecreaseastheygiveupthesulfateduringcharging.Thiscausestheplatestograduallyshedthepasteduringtheirlife.Itisimportantthatthereisplentyofroomunderneaththeplatestocatchthisshedmaterial.Ifthismaterialreachestheplatesashortedcellwilloccur.

Thepastematerialusedtomakebatteryplatesalsocontainscarbonblack,blancfixe（bariumsulfate）andlignosulfonate.Theblancfixeactsasaseedcrystalfortheleadtoleadsulfatereaction.Theblancfixemustbefullydispersedinthepasteinorderforittobeeffective.Thelignosulfonatepreventsthenegativeplatefromformingasolidmassofleadsulfateduringthedischargecycle.Itenablestheformationoflongneedlelikecrystals.Thelongcrystalshavemoresurfaceareaandareeasilyconvertedbacktotheoriginalstateoncharging.Carbonblackcounteractstheeffectofinhibitingformationcausedbythelignosulfonates.Ithasbeenfoundthatsulfonatednaphthalenecondensatedispersantisamoreeffectiveexpanderthanlignosulfonateandcanbeusedtospeeduptheformationofthebatteryplate.Thisdispersantisbelievedtofunctiontoimprovedispersionofbariumsulfateinthepaste,reducehydrosettime,produceastrongerplatewhichisresistanttoplatebreakage,toreducefineleadparticlesandtherebyimprovehandlingandpastingcharacteristics.Itextendsthelifeofthebatterybyincreasingtheendofchargevoltage.Thesulfonatednaphthalenecondensatepolymerdispersantcanbeusedinaboutone-halftoone-thirdtheamountoflignosulfonateandisstabletohighertemperaturesthanlignosulfonate[2]

About60%oftheweightofanautomotive-typelead-acidbatteryratedaround60Ah（8.7 kgofa14.5 kgbattery）isleadorinternalpartsmadeoflead;thebalanceiselectrolyte,separators,andthecase.[3]

Separators

Separatorsareusedbetweenthepositiveandnegativeplatesofaleadacidbatterytopreventshortcircuitthroughphysicalcontact,mostlythroughdendrites（‘treeing’）,butalsothroughsheddingoftheactivematerial.Separatorsobstructtheflowofionsbetweentheplatesandincreasetheinternalresistanceofthecell.Variousmaterialshavebeenusedto