MODELING THE EFFECTS OF ELECTROLYTE DIFFUSION AND PASTE CONDUCTIVITY ON LEAD-ACID-BATTERY PERFORMANCE

Two physical mechanisms normally prevent the positive active material in a lead/acid battery from reacting. One of these mechanisms is the change in plate conductivity that occurs when conductive active material is converted to nonconductive lead sulfate. The other mechanism is electrolyte diffusion. This paper presents a model that combines the effect of both these mechanisms on the discharge capacity of a lead/acid battery for constant current discharge. The model characterizes the electrolyte diffusion in a cell with two equations. A finite difference equation characterizes the diffusion process between the plates, and a McLaurin series approximate the electrolyte diffusion inside the positive plate. The electrolyte stored inside the plate, before the discharge begins, also contributes to the cell's capacity and is included in the model. The critical volume fraction characterizes the conductivity of the positive active material. A sharp decrease in conductivity occurs when the amount of active material, that has reacted in a plate, reaches this fraction. A computer program combines these diffusion and conductivity models into one comprehensive model. The simulated data from this model are compared with experimental data previously reported [1].