Enhancing lead-acid battery efficiency: A study on separator geometry and electrolyte stratification

Abstract

This study investigates the impact of separator geometry on electrolyte stratification in lead-acid batteries through a comprehensive numerical modeling approach. The simulations include two-dimensional (2D) and three-dimensional (3D) models to accurately capture the spatial distribution of acid concentration during battery discharge. The 3D model, in particular, enables a more realistic analysis of vertical stratification by more accurately accounting for geometric constraints and flow behavior. It also allows the evaluation of various separator geometries, especially those with features along the cell depth, which cannot be adequately represented in a single 2D view. Based on these models, the performance of three separator configurations, simple, vertical rib, and horizontal rib, was evaluated. The 2D simulations showed that the ribbed separator exhibited greater stratification compared to the simple one, with concentration increases of 0.05 M, 0.05 M, and 0.02 M at 4000, 2000, and 1000 mA/cm2, respectively. In the 3D model, under 6000 mA/cm2 and 3200 s, the electrolyte concentration gradient along the cell height was 0.4 M for the vertical rib separator, 0.5 M for the simple separator, and 0.595 M for the horizontal rib separator, demonstrating the superior performance of the vertical rib design in mitigating stratification. The acid flow path over the separator and the geometry through which it moves can have a significant effect on electrolyte stratification. Additionally, increasing the porosity and electrolyte-interfacing surface area of the positive electrode was found to optimize battery performance. The findings suggest that vertical rib separators are more effective in reducing stratification, while horizontal ribs may hinder electrolyte flow and reduce efficiency. The proposed numerical models were validated through one-, two-, and three-dimensional simulations, providing reliable tools for the design and optimization of next-generation lead-acid. © 2025 Elsevier Ltd