DISCHARGE BEHAVIOR OF TUBULAR PBO2 ELECTRODES .2. MATHEMATICAL-MODEL

A one-dimensional mathematical model has been developed to simulate the discharge behavior of tubular lead dioxide electrodes, with and without a tube envelope at high rates of discharge. The description of the kinetic properties was improved by relating the volumetric exchange current density to the local concentration of sulfuric acid in the electrode. An intrinsic Peukert equation was introduced in order to predict the discharge behavior and to determine the effects of the tube envelope over the actual current range (300 to 1000 Am-2). The model was verified by comparison with experimentally obtained galvanostatic discharge curves, sulfur distributions, and Peukert curves. It was found that there is a maximum degree of discharge in the electrode, near the exterior surface of the electrode. At high current densities the tubular electrodes are working at transport restrictions with respect to sulfuric acid, and the discharge behavior strongly depends on the initial amount of acid in the electrode and the diffusion from the free electrolyte into the electrode. The effects of different design parameters on the discharge capacity and overall degree of discharge are also discussed.