Rechargeable zinc metal battery

A rechargeable zinc metal battery cell includes a zinc metal anode, a cathode, a porous separator between them, and an electrolyte composition absorbed by the porous separator and in contact with both anode and cathode. The electrolyte composition includes (i) an aqueous solution of zinc chloride at a concentration greater than 15 molal, and (ii) dimethyl carbonate present at a mass ratio between 0.1:1.0 and 1.0:1.0 with respect to water in the aqueous solution. In some examples: the anode includes zinc metal foil stacked on titanium metal foil; the cathode includes vanadium(V) phosphate; the porous separator includes glass fibers and is less than 200 μm thick; or the electrolyte composition includes (i) an aqueous solution of 30 molal zinc chloride, 5 molal lithium chloride, and 10 molal trimethyl ammonium chloride, and (ii) dimethyl carbonate present at a mass ratio of 1.0:1.0 with respect to water in the aqueous solution.