Finite element (FE) modelling of current density on the valve regulated lead/acid battery positive grid

During operation of the valve regulated lead/acid (VRLA) battery, a mixed stoichiometry lead oxide corrosion layer is formed on the surface of the positive electrode. The formation of this layer has a number of consequences including increased electrode resistance and decreased strength. Experimental results obtained from cycling 40Ah VRLA batteries revealed an increase in corrosion layer thickness on the sides of the grid bars compared to the top and bottom. It is suggested that the areas of increased corrosion layer thickness corresponded to the areas of high current density on the surface of the grid. In order to investigate this observation the finite element package ANSYS was used to produce qualitative estimates of the values in current density, which would be expected on the tested grid design. Results suggest that corrosion layer thickening is related to current density. The model was then used to predict the expected current distribution around a number of hypothetical electrode designs. These incorporated changes in both grid bar cross-section and positive active material. Results showed that improvements could be made to existing grid designs with respect to lowering current densities.