Concentration Optimization of Fumed Silica as Gelator in Lead-acid Batteries

The effect of fumed silica (F-SiO2) density on the performance of valve-regulated lead-acid (VRLA) batteries, including the conductivity of H+ ions and the diffusion of HSO4− ions in the gel electrolyte, the redox capacity of lead, and the evolution of hydrogen and oxygen, have been studied over a wide range of F-SiO2 densities. The results show that the influence of F-SiO2 density is not monotonous and always yields a maximum (or inflection) effect at c. 5 to 6 wt% silica, before and after which the effect of F-SiO2 differ. At lower F-SiO2 densities, in general, gel formation favours an improvement of the electrochemical behaviour. However, it may produce an adverse effect on the electrochemical properties if F-SiO2 density further increases. Battery tests at a range between 1 to 3 wt% silica support this observation, in which the discharge capacity, the utilisation of active materials, and the charge efficiency are all enhanced.