Antimony-free Grid Alloys

Important for the maintenance-free properties of these batteries was the possibility to use antimony-free grid alloys instead of the conventional lead-antimony alloys, which were used only at this time. Because antimony in the grid alloys provides a high cycle life for the battery, it was necessary to develop more sophisticated methods in battery manufacturing in order to achieve the required product properties. 

First, by increasing the overvoltage of H2 and O2 evolution by choosing an antimony-free grid alloy. 

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 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. 

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... 

The properties of the corrosion layer, and of its interfaces, depend strongly on the additives to the grid alloy (in this case, antimony). Antimony affects the corrosion layer in such a way that it does not limit the discharge of the active mass, so the latter exhibits its full capacity. This phenomenon is known as antimony-free effect . 

Silver reduces the oxygen evolution potential at the anode, which reduces the rate of corrosion and decreases lead contamination of the cathode. Lead—antimony—silver alloy anodes are used for the production of thin copper foil for use in electronics. Lead—silver (2 wt %), lead—silver (1 wt %)—tin (1 wt %), and lead—antimony (6 wt %)—silver (1—2 wt %) alloys ate used as anodes in cathodic protection of steel pipes and stmctures in fresh, brackish, or seawater. The lead dioxide layer is not only conductive, but also resists decomposition in chloride environments. Silver-free alloys rapidly become passivated and scale badly in seawater. Silver is also added to the positive grids of lead—acid batteries in small amounts (0.005—0.05 wt %) to reduce the rate of corrosion. 

Selenium acts as a grain refiner in lead antimony alloys (114,115). The addition of 0.02% Se to a 2.5% antimonial lead alloy yields a sound casting having a fine-grain stmcture. Battery grids produced from this alloy permit the manufacture of low maintenance and maintenance-free lead—acid batteries with an insignificant loss of electrolyte and good performance stability. 

In general, VRLA batteries use lead alloys that are virtually free of antimony. This is because antimony is released from the positive grid by corrosion and migrates to the... 

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. 

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