Fundamental studies to develop the maintenance free lead-acid batteries .6. Plating treatment of positive grid for improvement of rechargeability of sealed lead-acid batteries

As discussed in the previous papers, a high content oi Sn on the positive grid surface is important in lengthening the storage period after overdischarge. Therefore, several methods to increase the Sn content on the positive grid surface were studied, and thermal treatment of Pb-Sn alloy plated positive grid was selected. In addition, the state and behavior of the Sn present in the oxide film layer at the positive grid interface, which greatly influences rechargeability, were analyzed. Microanalytical methods were used to conduct the analysis immediately after overdischarging, storing without recharging after overdischarging, and after recharging. It was found that the formation of oxide films such as PbSO4 and t-PbO at the positive grid interface raised the internal resistance of the battery, and Sn in the positive grid was selectively oxidized to form SnO2, which acted as a protective film and suppressed the formation of oxide films which raised resistance.