A High Energy Density, Non-Flow Zinc Bromine Battery Enabled by a Solubility Product Optimization Strategy

Abstract

Abstract The non-flow zinc-bromine battery (ZBB) is a promising, energy-dense alternative to lead-acid batteries for stationary storage applications. Yet it is plagued by instabilities related to self-discharge and corrosion caused by Br2, which is the product of charging. We report an energy-dense, non-flow ZBB achieved through a systematic screening of tetraalkylammonium halide (QX, where Q = tetraalkylammonium, X=Br–, Cl–) based Br2 trapping agents via solubility product measurements of the respective charged products, i.e. QBr3, simultaneously optimizing for the highest achievable ZnBr2 + QX concentration to maximize cell capacity. Through this strategy, we found that tetraethylammonium chloride (TEACl) provided an optimal bromine trapping ability while enabling high ZnBr2 solubility via the suppression of (TEA)2[ZnX4] formation. These attributes led to enhanced coulombic efficiency, lower charge/discharge hysteresis, and improved capacity retention at high states of charge as compared to other quaternary ammonium salts. Using porous carbon electrodes in a low-cost, stackable cell design that enables refurbishment of all the cell components, we were able to achieve extended cycling stability and a cell level energy density of 154 Wh/kg.