How does an antisolvent additive affect all interfaces in aqueous Zn–MnO2 batteries?

Abstract

Organic solvents are common additives for aqueous zinc-ion batteries (ZIBs) to improve plating on the zinc metal anode. However, additives are often only studied for anodes, neglecting effects at the cathode as well any evolution of corrosion products over ZIB lifetime. Here, we studied the effect of acetonitrile (ACN) concentration on the overpotentials and efficiencies of Zn anodes and MnO₂ cathodes. Overpotentials for Zn plating and stripping show local minima with low (0.5–2 vol%) ACN concentrations, with all stripping overpotentials lower than plating overpotentials due to the ACN's antisolvent character. The amount of zinc hydroxide sulfate (ZHS), a Zn corrosion byproduct, varies with ACN concentrations and between plating and stripping steps. The energy efficiency and capacity fade of MnO₂ cathodes show different ACN concentration trends but similar degradation products, with optimal performance at 0 vol% ACN. This highlights the importance of analysing additive effects on all battery components and interfaces.