The effect of cathode porosity on the performance of a cylindrical alkaline cell

The effects of varying initial cathode porosity on the discharge performance of an AA-size Zn/MnO2 alkaline cell are studied. An existing model is used to simulate cell behavior. Cell discharge time is chosen as the quantity to maximize for a continuous galvanostatic discharge with a prescribed cutoff voltage. An algorithm is developed that compensates for changes in initial cathode porosity by altering initial anode porosity, with initial separator porosity maintained constant. A constant capacity ratio and fixed external cell geometry are also constraints in this procedure. A different approach is incorporated into the design scheme whereby cathode void volume is obtained by removing graphite from the cathode solid material, without accounting for expected matrix conductivity changes. For each amount of graphite removed, the model predicts an optimum initial porosity for maximizing the discharge time. The longest discharge time occurs when all graphite is removed from the cathode. The influence of effective cathode matrix conductivity is investigated separately. (C) 1999 Elsevier Science S.A. All rights reserved.