Study On The Influence Of Fumed SiO₂ As Electrolyte Additive On The Performance Of The Power Lead Acid Battery

As power lead-acid battery requires high power capability and deep cycling performance, AGM separators with low internal resistance are usually used in the free valve regulated power lead-acid battery. Nevertheless, AGM separators has a limited ability of sulfuric acid adsorption and fixing among the electrolyte,which is caused by the material intrinsic property. Furthermore, the density of sulfuric acid in the AGM separator is layered,which trigger or intensify a nonuniform utilization rate of active material, negative sulfation of upper part, active material softening at the lower part of the positive electrode, even grid corrosion fracture and a series of other failure modes in power lead-acid battery. Fumed Silica is a kind of substance with thixotropic characteristic, which can exist stably in sulfuric acid medium. In this paper, the addition process of fumed SiO₂ as an additive into the electrolyte and the improvement of the performance of the lead-acid battery are studied.The process condition of fumed silica dispersion in the electrolyte is studied by the variation of electrolyte viscosity indicator, including the study of the relationship between electrolyte viscosity and environmental temperature, the amount of fumed SiO₂, and standing time after completely dispersion.According to the previous study,the best process condition under specific sulfuric acid content and the additive amount of fumed SiO₂ is figured out,which decrease electrolyte viscosity to the minimum.That is, filling fumed SiO₂ into the electrolyte under 5¹0 ? as soon as dispersed.The relationship between the additive amount of fumed SiO₂ and ion diffusivity and transmission capability in the electrolyte system is studied through cyclic voltammetry experiments and conductivity measurement. Diffusivity of electrolyte ion enhance with the increasing of the additive amount while the amount percent is under 6%.On the basis of previous results, the influence of maximum aperture parameters of separators and assembling pressure of batteries on the initial capacity and cycling life are studied through orthogonal experiment. The optimizing condition contains2.0% amount of fumed SiO₂, the employment of AGM separator with 19 ± 1?m maximum aperture scope, and 60 ± 5k Pa assembling pressure of dry batteries.Comparing to original batteries manufactured under mature technology with no additive of fumed SiO₂, the optimal batteries obtain 54% increase of cycling performance and 1% decrease of the initial capacity.The testing standard and method for the uniformity of fumed SiO₂ dispersion is established for the sake of quality control during continuous manufacturing. The mechanism of batteries performance improved by fumed SiO₂ addition is discussedby the SEM images of separator and active material with SiO₂ absorption. It can be seen that, fumed SiO₂ could weaken the sulfuric acid stratification phenomenon and decrease the formation of huge Pb SO4 particles when it was adsorbed and fixed on the surface of glass fiber and negative active materials, respectively. Fumed SiO₂ with gel structure could prop up the positive active material, and slow down the softening and shedding of positive active material.