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.