Design of a Solid Electrolyte Interphase for Aqueous Zn Batteries

Aqueous Zn batteries are challenged by water decomposition and dendrite growth due to the absence of a dense Zn-ion conductive solid electrolyte interphase (SEI) to inhibit the hydrogen evolution reaction (HER). Here, we design a low-concentration aqueous Zn(OTF)(2)-Zn(NO3)(2) electrolyte to in situ form a robust inorganic ZnF2-Zn-5(CO3)(2)(OH)(6)-organic bilayer SEI, where the inorganic inner layer promotes Zn-ion diffusion while the organic outer layer suppresses water penetration. We found that the insulating Zn-5(OH)(8)(NO3)(2).2 H2O layer is first formed on the Zn anode surface by the self-terminated chemical reaction of NO3- with Zn2+ and OH- generated via HER, and then it transforms into Zn-ion conducting Zn-5(CO3)(2)(OH)(6), which in turn promotes the formation of ZnF2 as the inner layer. The organic-dominated outer layer is formed by the reduction of OTF-. The in situ formed SEI enables a high Coulombic efficiency (CE) of 99.8 % for 200 h in Ti parallel to Zn cells, and a high energy density (168 Wh kg(-1)) with 96.5 % retention for 700 cycles in Zn parallel to MnO2 cells with a low Zn/MnO2 capacity ratio of 2:1.

Automated summary

A low-concentration aqueous Zn(OTF)(2)-Zn(NO3)(2) electrolyte was designed to form a robust inorganic ZnF2-Zn-5(CO3)(2)(OH)(6)-organic bilayer SEI, allowing high Coulombic efficiency and energy density. The study achieved a high CE of 99.8% for 200 h in Ti parallel to Zn cells, and a high energy density of 168 Wh kg(-1) with 96.5% retention for 700 cycles in Zn parallel to MnO2 cells with a low Zn/MnO2 capacity ratio of 2:1.