Reconstructing interfacial electric double layer for efficient sulfur conversion reaction in aqueous zinc sulfur batteries.

Abstract

Aqueous zinc sulfur batteries promise low-cost and safe grid-scale energy storage, but face challenges due to sluggish interfacial Zn²⁺ transfer and H₂O-induced ZnS disproportionation reactions at the interface of sulfur positive electrode. Here, we develop a hybrid electrolyte by introducing ZnI₂ and organic N,N-dimethylformamide cosolvent, in which iodide species contribute to catalytic oxidation of ZnS, while N,N-dimethylformamide cosolvent can effectively facilitate sulfur reduction reaction. By combining operando Raman spectroscopy with non-destructive electrochemical impedance spectroscopy and theoretical calculations/simulations, it demonstrates that N,N-dimethylformamide molecules preferentially adsorb on sulfur electrode surface and strongly interact with Zn²⁺, thereby reconstructing interfacial electric double layer with H₂O-poor inner Helmholtz plane and Zn²⁺-rich outer Helmholtz plane, which not only favors interfacial Zn²⁺ transfer to promote sulfur conversion reaction, but also suppresses H₂O-induced side reactions. Through an additional constant voltage charge procedure to avoid I^-/I₃^- redox shuttle, the assembled Zn||S batteries can exhibit a voltage hysteresis of 0.326 V and a long-term cycling stability with a capacity fading of 0.034% per cycle after 1000 cycles at 2 C (i.e., 3.34 A g^-1), even enabling a high areal capacity of 7.68 mAh cm^-2 and a stable low-temperature performance with a specific capacity of 500 mAh g^-1 at -10 °C.