Boosting Polysulfide Conversion in Lithium-Sulfur Batteries by Cobalt-Doped Vanadium Nitride Microflowers

The shuttle effect of polysulfide (Li2Sn, 2 < n <= 8) and the sluggish reaction kinetics seriously hinder the development of lithium-sulfur (Li-S) batteries. Regulating the electronic structure of substrate materials could be an effective strategy to further modulate surface polysulfide adsorption and interface electron transfer for advanced Li-S batteries. Herein, a cobalt-doped vanadium nitride (Co-VN) microflower hierarchical structure with a 5% Co/V ratio was synthesized as a substrate material. Theoretical calculation indicated that the polysulfide adsorption energy of Co-VN (-5.04 eV) was enhanced compared to that of VN (-4.14 eV). Electrochemical experiments verified that the polarization and internal resistance of VN were lowed after Co doping. Electrochemical tests showed that the cyclic stability of the Co-VN/sulfur (Co-VN/S) composite cathode was greatly improved compared to the undoped one, achieving an impressive initial capacity of 706 mAh g(-1) at 2.0 C and that the fading rate of discharge capacity over 500 cycles was only 0.034% per cycle. A discharge capacity of 873 mAh g(-1) under remarkable sulfur loading (4.42 mg cm(-2)) was also achieved with a capacity decay rate of 0.028% per cycle over 100 cycles.