An amphoteric betaine electrolyte additive enabling a stable Zn metal anode for aqueous batteries

The corrosion and dendritic growth of the Zn anode limit its electrochemical performance in aqueous Zn batteries. Here, we present an amphoteric betaine additive for 5 m ZnCl 2 aqueous electrolyte. The carboxyl group on betaine forms hydrogen bonds with water and reduces the water activity. The molecule also experiences preferential adsorption on the Zn surface and separates the interactions between Zn and water. Side reactions at the Zn electrode are thus inhibited. The regulated interface also ensures uniform Zn deposition. As a result, the electrolyte with betaine additive allows reversible Zn plating/stripping for over 1400 h at 0.5 mA cm −2 . A capacity retention of 94% is obtained after 3000 cycles for a VO 2 cathode. An amphoteric compound of betaine is demonstrated as an electrolyte additive for aqueous zinc batteries. It forms hydrogen bonds with water and preferentially adsorbs on the Zn surface, which inhibits side reactions and ensures uniform Zn deposition.