Enhancing anchoring and catalytic conversion of polysulfides by nitrogen deficient cobalt nitride for advanced lithium-sulfur batteries

While lithium-sulfur (Li-S) battery has attracted remarkable attention owing to the high theoretical capacity, its practical application is still hindered by the shuttle and sluggish conversion kinetics of intermediate lithium polysulfides (LiPSs). Defect engineering, which can regulate the electronic structure and in turn influence the surface adsorption and catalytic capability, has been regarded as a feasible strategy to deal with the above challenges. However, few studies on nitrogen vacancies and their mechanisms are reported. Herein, cobalt nitride with nitrogen vacancies grown on multi-walled carbon nanotube (CNT-CoN-VN) is designed and applied as the separator modification material to investigate the enhancing mechanism of nitrogen vacancies on Li-S batteries. The experimental evidence and theoretical calculation indicate that the introduction of nitrogen vacancies into cobalt nitride can enhance the chemical affinity to LiPSs and effectively hamper the shuttle effect. Meanwhile the reduced band gap of the d-band center of Co and p-band center of N for CNT-CoN-VN and the promoted diffusion of Li+ can expedite the solid–liquid and liquid–liquid conversions of sulfur species. Due to these superiorities, the cell with CNT-CoN-VN modified separator delivers a favorable initial capacity of 901 mAh g−1 and a capacity of 660 mAh g−1 can be achieved after 250 cycles at 2 C. This work explores the application of metal nitride with nitrogen vacancies and sheds light on the development of functional separators for high-efficient Li-S batteries.