ELECTROCHEMICAL-BEHAVIOR OF SNSO4 IN SULFURIC-ACID-SOLUTION

The effect of SnSO4 on the deep-discharge capacity of lead/acid batter ies is investigated when it is added to the sulfuric acid electrolyte. The electrochemical behaviour of Sn2+ ions in sulfuric acid is studie d by using chemical-analysis and cyclic-voltammetry methods. In the ba ttery system, Sn2+ ions will be reduced to tin on the negative plates or will be oxidized to tin(IV) species on the positive plates. Tin met al formed on the negative plates will improve the charge/discharge pro perties. Tin(IV) species formed on the positive plates may be incorpor ated as SnO2 in the positive active material (PAM) as well as in the a nodic film that is produced at the grid/active-material interface. The effect of SnO2 on the properties of the PAM are explained in terms of the gel-crystal model. The SnO2 is stable during the discharge proces s. The compound increases the electronic conductivity of the gel zones , thereby, enhances the capacity of the PAM. The SnO2 species may also act as nuclei for the formation of beta-PbO2 in the crystal zones. Th e corrosion of positive grids is inhibited by the presence of SnO2. By virtue of these effects, the addition of SnSO4 is beneficial to the o peration of lead/acid batteries.