Investigation of silica additive for high-rate sealed lead-acid cells

Abstract

This study investigated the effects of silica (SiO 2) additive in the positive electrode on the high-rate discharge performance of sealed lead-acid cells. X-ray diffraction studies reveal that the plate's chemical composition and crystal morphology is independent of the SiO 2 additive in the positive electrodes. Cells with SiO 2 additive in the positive plates decrease the active material, causing a lower initial capacity. However, the plates with SiO 2 additive exhibit a smaller pore size, which has a good mechanical strength and retains the electrolyte in the pore during high-rate discharge causing a lower capacity loss per cycle and a higher average capacity per cycle. Apparently, the SiO 2 additive has the beneficial effect of decreasing the capacity loss during the high-rate discharge cycles. Moreover, the discharge capacity loss rate does not correlate with the amount of SiO 2 additives. Adding more SiO 2 additives to the positive electrode decreases the active material appreciably causing a lower average capacity. The optimal amount of SiO 2 additive is about 3 wt%. The phase composition of the positive electrodes at different locations was determined after the cells completed the high-rate cycle test. The results reveal that the higher utilization of electrode plates at high-rate discharge occurred through the terminal and diagonal areas.