Development of stack model for tri-electrode rechargeable zinc-air cylindrical flow battery

Abstract

Nowadays, the demand for renewable energy is continuously increasing. Therefore, an efficient energy storage system is essential. Zinc-air batteries have received extensive attention because they use low-cost material but offer great safety benefits. This research, therefore, develops a stack model for a tri-electrode tubular designed rechargeable zinc-air flow battery for using in a large scale system. The connection of battery cells in series and parallel is studied. The connection of battery cell with common flowing electrolyte creates a shunt current. A mathematical model is developed and validated against experimental data, which measured both full cell and half cell potentials. The model agrees well with the experimental results. After that, the model is used to examine the effects of various parameters on the shunt current. Results show that increasing the electrolyte flow rate does not affect the shunt current. It enhances the coulombic efficiency of the charging process and decreases the coulombic efficiency of the discharging process. By increasing the current density, the shunt currents for both charging and discharging processes decrease; the coulombic efficiency of the discharging process increases; the coulombic efficiency of the charging process decreases. The coulombic efficiency of series-connected cells can be improved by increasing the pseudo resistance of the flowing electrolyte. It can be concluded that, by connecting the cells in series, the output potential of the module can be enhanced but the shunt current is also increased. By connecting the cells in parallel, though the shunt current is not observed, the current flow to each cell is not identical but determined by its internal resistivity.