Self-sulfidation in Oxygen-enriched Vanadium Nitride Enhances Polysulfide Adsorption-Conversion in Lithium-Sulfur Batteries

Abstract

Transition Metal nitrides (TMNs) have been proven to be a class of high-performance host materials capable of effectively suppressing the shuttle effect and enhancing the conversion kinetics in lithium-sulfur (Li-S) batteries due to high chemical affinity for soluble lithium polysulfides (LiPSs) and significant catalytic conversion activity. However, in the current research, there still exists a divergence of opinions regarding the anchoring and catalytic mechanism of polysulfides on TMNs. Herein, we proposed a new mechanism of self-sulfidation and systematically demonstrated its enhanced effect on the anchoring and transformation process of polysulfides via the residual oxygen in the nitride. A series of oxygen-enriched vanadium nitride (VN) with different surface compositions and chemical states were successfully fabricated via tuning nitriding annealing temperatures. The residual oxygen elements in VN can induce LiPSs to spontaneously form stable V-S chemical bonds and activate thiosulfate on the surface of VN. This strengthens the anchoring effect on polysulfides, facilitating rapid charge transfer and redox conversion kinetics, thereby effectively suppressing the shuttling effect of LiPSs. Benefiting from this enhancement mechanism, the oxygen-enriched VN electrode obtained through low-temperature nitriding exhibits an outstanding rate capability (756.8 mAh g^-1 at 5 C) and extremely stable cycling performance (a capacity decay rate of 0.037% per cycle upon 500 cycles at 1 C). Overall, this work elucidates the critical role of self-sulfidation in mitigating the shuttle effect and enhancing sulfur redox kinetics, and provides a targeted design principle for TMNs-based high-energy-density Li-S batteries.