Antimony lead calcium grids

Some decades ago, when lead-acid batteries with positive lead-calcium grids without antimony were first placed on the market, there was a major disaster in terms of very poor cycle-life. Investigation of the phenomenon revealed that the cause of the failure was the formation of a barrier layer of lead sulfate between the... 

Table 4.2 presents a summary of the lead alloys most widely used for the production of various types of lead—acid batteries [5]. Lead—antimony and lead—calcium grid alloys have dominating positions in the battery industry. The basic characteristics of these two types of alloys and their effects on battery performance will be discussed further in this chapter. 

At the end of the twentieth century, maintenance-free VRLA batteries were invented. The first VRLA batteries employed lead—calcium grids. The antimony-free effect exhibited fully, which forced metallurgists to switch back to Pb—Sb alloys for the positive grids, minimising... 

A semiconductor mechanism was proposed for the electrocatalytic action of tin on the oxidation of PbO to PbO and Pb02. Tin has substituted antimony as an additive to the alloys for lead—acid battery grids. It is added in considerably lower concentrations than Sb and in combination with calcium which improves the mechanical properties of the alloys. Thus the interface problem of lead—calcium grids was resolved and the way was open for the manufacture of maintenance-free wet-charged batteries. 

The use of antimony in grid alloys has become associated with operating problems such as battery water loss and self-discharge, which lowers battery life and raises maintenance requirements. The commercial Introduction of lead-calcium grids in the... 

Rea.ctivity ofLea.d—Ca.lcium Alloys. Precise control of the calcium content is required to control the grain stmcture, corrosion resistance, and mechanical properties of lead—calcium alloys. Calcium reacts readily with air and other elements such as antimony, arsenic, and sulfur to produce oxides or intermetaUic compounds (see Calciumand calciumalloys). In these reactions, calcium is lost and suspended soHds reduce fluidity and castibiUty. The very thin grids that are required for automotive batteries are difficult to cast from lead—calcium alloys. 

Wrought lead—calcium—tin alloys contain more tin, have higher mechanical strength, exhibit greater stabiUty, and are more creep resistant than the cast alloys. RoUed lead—calcium—tin alloy strip is used to produce automotive battery grids in a continuous process (13). Table 5 Hsts the mechanical properties of roUed lead—calcium—tin alloys, compared with lead—copper and roUed lead—antimony (6 wt %) alloys. 

FMl. Replacement of lead antimony alloys with lead-calcium alternatives, as a means to discourage hydrogen evolution, reduces the creep strength of grids so that expansion in the plane of the plate may again become a concern. Use of a separator with insufficient rigidity (i.e., too much compressibility ) may allow expansion normal to the plane of the plate. 

The basis for the performance of the alloy in VRLA batteries is corrosion of the lead-cadmium-antimony alloy to produce antimony in the corrosion layer of the positive grid, which thus eliminates the antimony-free eifect of pure lead or lead-calcium alloys. During corrosion, small amounts of antimony and cadmium present in the lead matrix are introduced into the corrosion product and thereby dope it with antimony and cadmium oxides. The antimony and cadmium give excellent conductivity through the corrosion product. The major component of the alloy, the CdSb intermetallic alloy, is not significantly oxidized upon float service, but may become oxidized in cycling service. 

Highly corrosion-resistant, antimony-free, lead alloys have been used successfully in the positive electrode grids of both single-plate and spiral-wound cells. Spiral-wound cells almost exclusively feature binary lead-tin alloys [36,41] whereas flat-plate electrodes use either lead-calcium alloys, with or without silver additive [26], or lead-tin alloys [48]. Binary lead-tin is known to be highly corrosion-resistant, but rather soft, which is a handicap for plate stacking in prismatic cells. 

The first grid alloys used were lead alloys with 11% antimony content called hard lead . These alloys were replaced with low-antimony lead alloys with additions of Sn, As and Ag. Later, battery grid manufacturers switched to lead—calcium and lead—calcium—tin alloys. 

In 1935, Haring and Thomas from Bell Laboratory replaced the lead—antimony grids with lead—calcium for their stationary batteries. The need for battery maintenance was reduced... 

It seems that only alloys with particular properties are suitable for casting grids for lead—acid batteries. Lead—calcium alloys, similar to lead—antimony alloys, belong to the age-hardening or precipitation-hardening group of alloys. With decrease of temperature, the solubility of calcium in the a-Pb solid—solution decreases and it precipitates in the form of small Pb3Ca particles. A similar picture was described earlier for the Pb—Sb alloys. 

The above lead—calcium—tin alloys are suitable for rolling into thin strips. The strip is then expanded or punched into grids. Industrial production of such grids can be realised at a high rate and their properties yield battery life comparable to that of batteries with lead—high-antimony grids. 

When the lead—antimony alloy commonly used for the positive grids of lead—acid batteries was substituted for lead—calcium alloy, the cycle life of the batteries decreased dramatically. Obviously, antimony influenced the electrochemical behaviour of Pb02- One of the hypotheses was that it affected the hydration of Pb02 PbO(OH)2 particles. This hypothesis was verified through oxidation of Pb—Sb alloys with different content of antimony and determining the water content in the anodic Pb02 layer formed. The obtained results of these investigations are presented in Fig. 10.27 [34]. 

Capacity of batteries with lead—calcium or high-antimony lead grids on cycling a demonstration of the early capacity decline of batteries PCL = premature capacity loss. 

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