Variance-Based Sensitivity of Localized Sulphation to Microporous Separator Properties Using a Distributed Parameter Model of a Valve-Regulated Lead-Acid Battery

Abstract

Progressive sulphation of the negative electrode in a lead-acid battery under high-rate operation remains a serious problem. This study investigates how healthier end-of-discharge conditions, in a valve-regulated lead-acid battery with an immobilized electrolyte, can be achieved by calculated changes in the separator’s porosity, thickness and tortuosity. The solubility, volume fraction and geometry factor of local PbSO4 crystals are modeled using a distributed parameter model and observed during a high-rate discharge in simulation. A variance-based sensitivity analysis, consisting of a Monte Carlo experiment and Jansen’s formulae for variance decomposition, is performed to quantify the effects of separator design on localized sulphation. The concentration profile across different regions of the cell is also briefly examined by means of a statistical equation for the concentration non-uniformity. The results indicate that the separator thickness has the greatest effect on the PbSO4 crystals at the negative electrode because it severely influences the concentration profile in this region. The simulation results also indicate that separator design with the aim of manipulating the concentration profile, and enabling faster homogenization within a lead-acid cell, can be achieved. We conclude that it is possible to design a microporous separator that improves the dissolution, during recharge, of the PbSO4 crystals on the negative electrode that initially formed during a high-rate discharge. The quantitative approach we have followed can be used to quickly evaluate thousands of different separator designs and determine a suitable starting point for experimental work.