Hydrophobic organic electrolyte protected Zn anodes for aqueous Zn batteries.

Aqueous Zn batteries are promising energy-storage device due to low cost and high energy density. However, their lifespan is limited by irreversible Zn anodes due to water decomposition and Zn dendrite growth. Here, we separate aqueous electrolyte from Zn anode by coating a thin metal-organic framework (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-H2O bulk electrolyte. The MOF encapsulated Zn(TFSI)2-TFEP forms a ZnF2-Zn3(PO4)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||MnO2 full cell with a low capacity ratio of Zn:MnO2 at 2:1.