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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 (SxI, x = 9.3, 1) was prepared by bonding commercial sulfur and iodine. Compared with commercial sulfur, the conductivity of SxI are increased by 7 orders of magnitude. Density functional theory (DFT) calculated results show that new S-I chemical bonds are formed in SxI 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 S9.3I could reach up to 370.32 mAh g-1 and SI could reach up to 220.04 mAh g-1. SxI 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.
Zhang et al. (Tue,) studied this question.