Electronic network modeling of rechargeable batteries - II. The NiCd system

Based on the concept of a defined sealed rechargeable NiCd battery, the mathematics of the various electrochemical and physical processes occurring inside the battery are described. Subsequently, these sets of mathematical equations are clustered and converted into an electronic network model. Introducing the relevant electrochemical and physical parameters, the one-dimensional model is shown to be capable of simulating not only the development of the cell voltage during (over)charging and (over)discharging, but also of simultaneously calculating the development of the internal gas pressure. Considering the thermal dependencies of the various electrochemical reactions and those of the battery environment, the temperature development and the mutual interaction with the voltage and gas pressure can also be calculated Since the electronic network approach gives access to all partial currents flowing through the different reaction paths inside the battery it is easy to visualize what processes are occurring during battery operation. This is, for example, illustrated for the two-step overdischarge process, indicating that, respectively, the Cd and 0(2) charge-transfer reactions play a dominant role under these conditions. Electronic network simulations are shown to be not only restricted to direct current applications but are also applicable to processes, like open-circuit voltage relaxation and self-discharge behavior.