“Water‐In‐Oil” Electrolyte Enabled by Microphase Separation Regulation for Highly Reversible Zinc Metal Anode

Abstract The sustained hydrogen evolution and zinc (Zn) dendrite growth greatly impede the practical application of low‐cost aqueous Zn metal batteries (ZMBs). Herein, for the first time, a microphase separation strategy is proposed to construct a ″water‐in‐oil (W/O) electrolyte to endow durable ZMBs. As validated by theoretical modeling and experimental characterizations, the unique reverse micelle structure within the electrolyte not only disrupts water hydrogen bonding and efficiently inhibits the water consumption at Zn anode, but also undergoes directed movement and reversible demulsification under electric field, thus enhancing the anode desolvation kinetics and inhibiting the interfacial side reactions. Owing to the simultaneous regulation of water molecules in both electrolyte bulk and anode interface, this W/O electrolyte achieves a high Zn plating/stripping Coulombic efficiency of 99.76% over 6000 cycles, and maintains an extend lifespan in Zn||V 10 O 24 ·12H 2 O (VOH) cells with negligible hydrogen evolution and dendrite formation. These key findings are expected to promote the electrolyte engineering toward reversible ZMBs.