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

Regarding to 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, 1) was prepared by bonding commercial sulfur and iodine. Compared with commercial sulfur, the conductivity of S_xI are 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, 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.