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., H$_2$ evolution) and dendrite growth limit the practical applications of ZMBs. Given that HH$_2$ evolution is primarily originated from solvated water, here, a low-cost acetate-based electrolyte constituted by 1 m ZnAcH$_2$ 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 AcH$^-$ enables preferential coordination with Zn$^{2+}$, 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||I$_2$ full cells.