Multistep C/VN frameworks as highly-efficient sulfur host for high-performance lithium–sulfur batteries

Abstract

Lithium-sulfur (Li–S) batteries are considered as next-generation electrochemical energy storage system because of ultra-high theoretical energy density (2600 Wh kg−1). Although the carbonaceous hosts can effectively address the problems of poor conductivity and low sulfur loading of sulfur cathode, the commercial application of Li–S batteries is seriously hindered by the low volume energy density and catalytic conversion efficiency. This is primarily due to the low tap density and non-polar nature of carbonaceous materials. Here, multistep carbon/vanadium nitride (C/VN) frameworks with high aspect ratio were synthesized by impregnation-annealing-nitriding strategy. The metal-organic framework (MOF)-derived carbon possesses high specific surface area and rich porous structure, providing sufficient space for the uniform distribution of sulfur active material and VN catalysts. Meantime, the uniform loading VN nanoparticles in the derived carbon offer abundant active sites for the catalytic conversion of polysulfides. VN's outstanding catalytic activity and robust chemical polarity significantly promote the redox kinetics and effectively inhibit the excessive dissolution of polysulfides. The S@C/VN cathode reaches the discharge specific capacity of 622.9 mAh g−1 after 100 cycles at 0.5 C. Even at a large current density of 3 C, it can still deliver a discharge specific capacity of 370.3 mAh g−1 after 500 cycles.