Electrochemical Model for a Three-Electrode Lead Acid Cell: Boundary Conditions for Asymmetric Configurations

A one-dimensional (1D) electrochemical model is developed for a lead-acid demonstration cell comprising two positive electrodes engaging a single negative electrode. Classical 1D models, which analyze a single repeat unit in a full battery, are extended to this non-standard configuration by considering additional porous electrode and electrolyte reservoir domains. The non-standard model necessitates appropriate boundary conditions to couple electrochemical variables in different domains, since symmetry boundary conditions typically employed at the current collector grids are no longer applicable. The modified model, with new boundary conditions, is simulated using standard techniques. Salient modeling and simulation differences compared to a standard lead-acid model are discussed, as are trends in predicted variables. The non-standard model predicts reduced polarization and more uniform utilization of the non-limiting electrodes, in addition to non-zero reaction currents and active material utilization in the terminal electrode faces, which are typically ignored in “unit-cell” analyses. This model is expected to be of substantial utility in guiding evaluations of new lead-acid battery designs through improved prediction of performance of such test configurations. The boundary conditions introduced herein are also useful for 1D modeling of non-standard configurations characterized by multiple, electrochemically interacting porous domains, particularly where spatial current distributions are initially unknown.