Highly conductive sulfur iodide cathode accelerating sulfur redox kinetics for aqueous Zn–S batteries

Regarding the problems of low electrical conductivity and slow redox kinetics in Zn–S batteries, it is extremely urgent to find a simple and effective construction strategy. Herein, a conversion cathode material (S_xI, x = 9.3 and 1) was prepared by bonding commercial sulfur and iodine. Compared with commercial sulfur, the conductivity of S_xI is increased by 7 orders of magnitude. Density functional theory (DFT) calculated results show that new S–I chemical bonds are formed in S_xI materials, and the band gaps are significantly reduced. Their charge–discharge voltage differences, the differential capacity curves, and the redox peak potential difference of sulfur are significantly reduced. In the voltage window of 1.20–1.40 V, the I⁰/I⁻ reversible redox reaction can provide additional capacity contribution of 38.36 mAh·g⁻¹. At the current density of 1.5 A·g⁻¹, the capacity of S_9.3I could reach up to 370.32 mAh·g⁻¹, and SI could reach up to 220.04 mAh·g⁻¹. S_xI materials have a lower degree of polarization, a smaller Tafel slope, and activation energies. The in-situ ultraviolet–visible spectroscopy results indicate that the dissociation of the Zn–S bond during the charging process is mainly due to the interaction between I⁻ and the ZnS surface, promoting the rapid conversion of I₃⁻ to I⁻. This work presents a paradigm for effectively enhancing the conductivity of sulfur cathode materials, increasing additional capacity and catalyzing sulfur conversion reactions, thereby significantly improving the performance of Zn–S batteries.