Minimizing solvated water via synergistic effect of salt anion and cosolvent enables stable Zn metal anodes in low-cost acetate electrolyte

Aqueous zinc metal batteries (ZMBs) have attracted increasing attention in the past decades owing to their potentially low cost and non-flammability. However, the poor Coulombic efficiency (CE) and short lifespan caused by side reactions (e.g., H2 evolution) and dendrite growth limit the practical applications of ZMBs. Given that H2 evolution is primarily originated from solvated water, here, a low-cost acetate-based electrolyte constituted by 1 m ZnAc2 and 5 m KAc in an 80:20 water:trimethyl phosphate (TMP) (v/v) mixture is proposed to minimize solvated water and boost the electrochemical performance of aqueous ZMBs without compromising intrinsic advantages of the aqueous electrolyte. The relatively high abundance of Ac- enables preferential coordination with Zn2+, meanwhile, the addition of TMP not only further replaces water molecules in the inner solvation shell, but also significantly interrupts the H-bond network of water. Improved electrochemical performance are demonstrated in Zn||Zn and Zn||Cu half-cells and Zn||I2 full cells.