The present invention provides an aqueous electrolyte for use in rechargeable zinc-halide storage batteries that possesses improved stability and durability and improves zinc-halide battery performance (e.g., energy efficiency, Coulombic efficiency, and/or the like). One aspect of the present invention provides an electrolyte for use in a secondary zinc bromine electrochemical cell comprising from about 30 wt % to about 40 wt % of ZnBr