The electrolyte comprising more robust water and superhalides transforms Zn‐metal anode reversibly and dendrite‐free

A great challenge for all aqueous batteries, including Zn‐metal batteries, is the parasitic hydrogen evolution reaction on the low‐potential anode. Herein, we report the formula of a highly concentrated aqueous electrolyte that mitigates hydrogen evolution by transforming water molecules more inert. The electrolyte comprises primarily ZnCl2 and LiCl as an additive, both of which are inexpensive salts. The O–H covalent bonds in water get strengthened in a chemical environment that has fewer hydrogen bonding interactions and a greater number of Zn–Cl superhalides, as suggested by integrated characterization and simulation. As a result, the average Coulombic efficiency of zinc‐metal anode is raised to an unprecedented >99.7% at 1 mA cm−2. In the new electrolyte, the plating/stripping processes leave the zinc‐metal anode dendrite‐free, and the zinc‐metal anode delivers stable plating/stripping cycles for 4000 hours with an areal capacity of 4 mAh cm−2 at 2 mA cm−2. Furthermore, the high Coulombic efficiency of zinc‐metal anode in the ZnCl2‐LiCl mixture electrolyte is demonstrated in full cells with a limited anode. The V2O5·H2O||Zn full cell with an N/P mass ratio of 1.2 delivers a stable life of more than 2500 cycles, and the LiMn2O4||Zn hybrid cell with an N/P mass ratio of 0.6 exhibits 1500 cycles in its stable life. The mixture water‐in‐bisalt electrolyte of ZnCl2 and LiCl enables Zn anode to show a high Coulombic efficiency and dendrite‐free morphology during the plating/stripping processes with a high areal capacity of 4 mAh cm−2.