Enhanced charge performance in near-neutral zinc-air batteries via organic solvent additives

• Aprotic solvent additives lower charge voltage in near-neutral Zn–air batteries. • Additives stabilize H 2 O 2 via solvent adsorption on carbon black. • Pretreating carbon black with solvents yields a similar effect. Zinc–air batteries with near-neutral electrolytes are promising energy storage systems, but their performance remains insufficient for practical applications. Here we show that the addition of just 1 vol.% of aprotic organic solvents, such as dimethyl sulfoxide (DMSO), tetraethylene glycol dimethyl ether (TEGDME) and N,N-dimethylacetamide (DMA), to the aqueous electrolyte reduces the overall charge overpotential in Zn–air batteries with carbon black cathodes. These additives stabilize hydrogen peroxide in the electrolyte, which oxidation potential is much lower than that of the solid discharge product, without altering the discharge product composition or the H 2 O 2 generation rate during discharge. This effect is achieved due to the adsorption of the aprotic organic solvent on the carbon black surface, forming a layer which slows down H 2 O 2 disproportionation rate. A similar effect can be obtained by pretreating the carbon black cathode with organic solvents, while the phenomenon is absent in carbon nanotubes-based cathodes. These results highlight effective approaches for improving the performance of near-neutral Zn–air batteries by engineering both the electrolyte and electrode interfaces.