Selection of pre-blended expanders for optimum leadracid battery performance

Expanders are an essential component of leadracid batteries. They prevent performance losses in negative plates that would otherwise be caused by passivation and structural changes in the active material. The functions of the components of modern negative-plate expanders are described and data are presented to show how the capacity and life of the battery are affected by the type and amount of barium sulfate and lignin incorporated in the expander blend. The differences between expanders for automotive, deep-cycle and standby-power batteries are illustrated and typical formulations shown for each application. There are several ways in which expanders can be...
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Selection of pre-blended expanders for optimum leadracid battery performance Journal of Power Sources 73 Ž1998. 89–92 Selection of pre-blended expanders for optimum leadracid battery performance ) D.P. Boden Hammond Lead Products, A DiÕision of Hammond Group, 2323 165th Street, Hammond, IN 46325, USA Received 10 August 1997; accepted 20 December 1997Abstract Expanders are an essential component of leadracid batteries. They prevent performance losses in negative plates that would otherwisebe caused by passivation and structural changes in the active material. The functions of the components of modern negative-plateexpanders are described and data are presented to show how the capacity and life of the battery are affected by the type and amount ofbarium sulfate and lignin incorporated in the expander blend. The differences between expanders for automotive, deep-cycle andstandby-power batteries are illustrated and typical formulations shown for each application. There are several ways in which expanderscan be incorporated into negative plates. These range from adding the individual components to the paste mix to adding a pre-blendedformulation. The benefits of pre-blending are more uniform distribution of expander in the plate, simplification of paste mixing, andimproved quality control. q 1998 Elsevier Science S.A. All rights reserved.Keywords: Leadracid batteries; Expanders; Lignosulfonates; Barium sulfate; Negative plate1. Introduction 2. Functions of expander components 2.1. Barium sulfate Without the use of expanders, the active materialŽsponge lead. in the negative plates of leadracid batteries The function of barium sulfate is to act as a site for thewill lose performance rapidly when cycled. This perfor- precipitation of lead sulfate as the battery is discharged. Itmance loss is due to passivation which results from deposi- is extremely insoluble in sulfuric acid and is electrochemi-tion of an impermeable film of lead sulfate on the lead cally inactive. These properties assure that it remainssubstrate, and to loss of porosity caused by shrinkage of chemically unchanged in the negative plate, even afterthe lead sponge. Studies have shown w1–3x that there is prolonged cycling. The ability of barium sulfate to act as aconsiderable reduction in the surface area of the negative site for lead sulfate precipitation is due to the similarplate after relatively few cycles. structure of the two compounds. Strontium sulfate has also The above behaviour can be reduced significantly by been shown to be an effective expander w4x.the use of certain additives to the negative plate. These Barium, strontium and lead sulfates are isostructural w5x.additives are usually called expanders but, more correctly, All belong to the orthorhombic space group and havethey act as anti-shrinkage agents. Modern expander formu- similar R values and bond lengths, as shown in Table 1.lations are usually a blend of barium sulfate, lignin deriva- The inert barium sulfate provides a large number oftives and carbon black. sites for the precipitation of lead sulfate crystallites and, thereby, prevents its deposition as a thin, impermeable, passivating film. Barium sulfate is used in expanders in two forms: blanc fixe, which is precipitated from solution, and barytes, which is ground and purified mineral ore. Typically, blanc fixe has a median particle size of ; 1 ) Corresponding author. m m, while that of barytes is ; 3.5 m m. Thus, barytes is0378-7753r98r$19.00 q 1998 Elsevier Science S.A. All rights reserved.90 D.P. Boden r Journal of Power Sources 73 (1998) 89–92Table 1 2.3. CarbonStructural characteristics of BASO4 , SrSO4 and PbSO4 BaSO4 SrSO4 PbSO4 Carbon black is added to the expander to improve theR 0.043 0.053 0.067 conductivity of the active material during deep discharges ˚Cation-O bond length ŽA. 2.952 2.831 2.87 where the concentration of highly-resistant lead sulfate is ˚S–O bond length ŽA. 1.478 1.474 1.490 high. It is usually added to the expander formula in an amount equal to the lignosulfonate.much less effective than blanc fixe and can virtually be 3. Expander compositions for various battery applica-regarded as a filler. Whether barytes has the property of tionsslow ...