Selection of quaternary ammonium bromides for use in zinc/bromine cells

Various cyclic and aliphatic quaternary ammonium bromides have been tested for use in zinc/bromine battery electrolytes. No single compound can be used over the temperature range 0-50°C due to crystallization of solid materials from either the polybromide or the aqueous phases. Electrolytes containing mixtures of quaternary ammonium bromides can avoid this problem of crystallization, and electrolytes containing 1:1 mixtures of N-methyl-N-ethylpyrrolidinium bromide with either N-methyl-N-ethylmorpholinium bromide or dimethylethylpropylammonium bromide have proved acceptable. The performance of a small zinc/bromine cell using electrolytes prepared from various quaternary ammonium bromides is described.