A zinc-iodine hybrid flow battery with enhanced energy storage capacity

Zinc-Iodine hybrid flow batteries are promising candidates for grid scale energy storage based on their near neutral electrolyte pH, relatively benign reactants, and an exceptional energy density based on the solubility of zinc iodide (up to 5 M or 167 Wh L-1). However, the formation of zinc dendrites generally leads to relatively low values for the zinc plating capacity, limiting the cycle duration to <2 h even at relatively low current densities. In this study we investigate the effects of various cell configurations as well as complexing Zn2+ with gluconate with the aim of increasing the cycle duration and increasing the current density during charge and discharge. The addition of a non-conductive felt to the negative half-cell provided a significant increase in the plating capacity, while the addition of a nonconductive felt to the positive half-cell was shown to be effective in preventing electrical shorts resulting from dendrite growth at the cost of additional resistive losses. Ultimately, cycles with up to 4.8-h charge/discharge were demonstrated at a current density of 100 mA cm(-2).