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.