Tuning Sulfur Reduction via Unique Radical-Mediated Solid-Liquid-Solid Pathway for High-Rate Aqueous Zn-S Batteries.

Abstract

The sluggish solid-solid sulfur conversion leads to ultrahigh polarization and poor cycling stability, severely limiting the potential of aqueous Zn-S electrochemistry. Herein, trimethylsulfoxonium iodide (TMSO⁺I^-) as an electrolyte additive is introduced to manipulate the radical-mediated solid-liquid-solid conversion pathway via restructuring electron transport. Specifically, the generated trimethylsulfoxonium radical (TMSO*) enables relayed electron transfer through reversible TMSO⁺/TMSO* redox cycling. Moreover, its orbital coupling with polysulfides (S_<i>n</i>^2-) stabilizes TMSO*-S_<i>n</i>^2- intermediates, lowers their LUMO energy, and facilitates streamlined electron transfer. This restructured electron-transfer pathway guides the stepwise formation of liquid intermediates and tunes the sulfur redox behavior. Consequently, the novel conversion mechanism endows the Zn-S cells with a high capacity of 1728 mAh g^-1, a low overpotential of 0.42 V at 0.1 A g^-1, and stable cycling for over 800 cycles with 80.21% capacity retention at 15 A g^-1. Remarkably, a practical pouch cell delivers a projected cell-level energy density of 95 Wh kg^-1.