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) -Zn(NO ) electrolyte to in situ form a robust inorganic ZnF -Zn (CO ) (OH) -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 (OH) (NO ) ⋅2 H O layer is first formed on the Zn anode surface by the self-terminated chemical reaction of NO with Zn and OH generated via HER, and then it transforms into Zn-ion conducting Zn (CO ) (OH) , which in turn promotes the formation of ZnF 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∥Zn cells, and a high energy density (168 Wh kg ) with 96.5 % retention for 700 cycles in Zn∥MnO cells with a low Zn/MnO capacity ratio of 2:1.