Design of a Solid Electrolyte Interphase for Aqueous Zn Batteries
Dan Li, Longsheng Cao, Tao Deng, Sufu Liu, Chunsheng Wang
Abstract
Abstract 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(NO 3 ) 2 electrolyte to in situ form a robust inorganic ZnF 2 ‐Zn 5 (CO 3 ) 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 (NO 3 ) 2 ⋅2 H 2 O layer is first formed on the Zn anode surface by the self‐terminated chemical reaction of NO 3 − with Zn 2+ and OH − generated via HER, and then it transforms into Zn‐ion conducting Zn 5 (CO 3 ) 2 (OH) 6 , which in turn promotes the formation of ZnF 2 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 −1 ) with 96.5 % retention for 700 cycles in Zn∥MnO 2 cells with a low Zn/MnO 2 capacity ratio of 2:1.