Enabling uniform zinc deposition by zwitterion additives in aqueous zinc metal anodes

The rechargeable aqueous zinc metal battery is considered one of the most promising next-generation batteries for energy storage systems, owing to its low negative standard reduction potential (−0.76 vs. the standard hydrogen electrode (SHE)), low cost of zinc and water, and no fire-risk. However, the formation of zinc dendrites and hydrogen evolution hinder the commercialization of rechargeable aqueous zinc metal batteries. In this study, we investigate the use of 6-aminohexanoic acid (6-AA), a type of amino acid, as an electrolyte in a 1 M ZnSO₄ solution. The 6-AA molecules become zwitterions, reducing side reactions by adsorbing onto the zinc metal surface and blocking water molecules and other ions, except for zinc ions. Additionally, the adsorbed 6-AA molecules hinder the two-dimensional diffusion of zinc ions on the zinc metal surface and thereby reduce the formation of zinc dendrites. The 6-AA additive enables reduced corrosion, and uniform zinc deposition is observed. Moreover, both the Zn‖Zn symmetric cell and Zn‖Cu cell with the 6-AA added electrolyte exhibit a long cycle life, and the α-MnO₂‖Zn full cell shows improved cycle performance by using the 6-AA additive.