Nickel-hydrogen voltage-efficiency model

A model for providing voltage vs. current relationships and coulombic efficiency has been developed applicable to nickel-hydrogen (Ni-H₂) batteries. The performance relationships can be used directly in dynamic electrical energy storage system models or customized by predicting the particular case of voltage as a function of applied current. The algorithm utilizes electrochemical models for competing cell reactions: a single Butler-Volmer equation for the main Ni-H₂ reaction, and a Tafel relationship for oxygen generation. For the main Ni-H₂ reaction, the dependence on state-of-charge is introduced via a Nerstian term containing concentrations of active materials present. Oxygen recombination and self-discharge are modeled as first order reactions. Model parameters are determined by a modified Marquardt algorithm to provide a best-fit of both voltage and pressure data to the physical model. The data fit is from electrical characterization tests which may include capacity measurements or repeated electrical cycling at specified depths-of-discharge or with particular regimens. It has been found that test performance data covering a wide domain of the independent variables (temperature, current, and state-of-charge) will produce a well-behaved model. The model may be used as a subprogram of a dynamic electrical system performance model operating in the time domain. The using performance model is typified by the model of a spacecraft electrical power system and may include models of other components