Solvation Structure Design for Aqueous Zn Metal Batteries.

Aqueous Zn batteries are promising energy storage devices for large-scale energy-storage due to low cost and high energy density. However, their lifespan is limited by the water decomposition and Zn dendrite growth. Here, we suppress water reduction and Zn dendrite growth in dilute aqueous electrolyte by adding dimethyl sulfoxide (DMSO) into ZnCl-HO, in which DMSO replaces the HO in Zn solvation sheath due to a higher Gutmann donor number (29.8) of DMSO than that (18) of HO. The preferential solvation of DMSO with Zn and strong HO-DMSO interaction inhibit the decomposition of solvated HO. In addition, the decomposition of solvated DMSO forms Zn(SO)Cl(OH)·5HO, ZnSO, and ZnS enriched-solid electrolyte interphase (SEI) preventing Zn dendrite and further suppressing water decomposition. The ZnCl-HO-DMSO electrolyte enables Zn anodes in Zn||Ti half-cell to achieve a high average Coulombic efficiency of 99.5% for 400 cycles (400 h), and the Zn||MnO full cell with a low capacity ratio of Zn:MnO at 2:1 to deliver a high energy density of 212 Wh/kg (based on both cathode and anode) and maitain 95.3% of the capacity over 500 cycles at 8 C.