Hydrophobic Organic‐Electrolyte‐Protected Zinc Anodes for Aqueous Zinc Batteries

Abstract Aqueous Zn batteries are promising energy‐storage devices. However, their lifespan is limited by irreversible Zn anodes owing to water decomposition and Zn dendrite growth. Here, we separate aqueous electrolyte from Zn anode by coating a thin MOF layer on anode and filling the pores of MOF with hydrophobic Zn(TFSI) 2 ‐tris(2,2,2‐trifluoroethyl)phosphate (TFEP) organic electrolyte that is immiscible with aqueous Zn(TFSI) 2 –H 2 O bulk electrolyte. The MOF encapsulated Zn(TFSI) 2 ‐TFEP forms a ZnF 2 ‐Zn 3 (PO 4 ) 2 solid electrolyte interphase (SEI) preventing Zn dendrite and water decomposition. The Zn(TFSI) 2 ‐TFEP@MOF electrolyte protected Zn anode enables a Zn||Ti cell to achieve a high average Coulombic efficiency of 99.1 % for 350 cycles. The highly reversible Zn anode brings a high energy density of 210 Wh kg −1 (of cathode and anode mass) and a low capacity decay rate of 0.0047 % per cycle over 600 cycles in a Zn||MnO 2 full cell with a low capacity ratio of Zn:MnO 2 at 2:1.