Conductive cobalt doped niobium nitride porous spheres as efficient polysulfides convertor for advanced lithium-sulfur batteries

Lithium-sulfur battery has been considered as one of the most potential candidates for energy storage devices owing to its high theoretical specific capacity and superior energy density. However, its practical application still faces challenges such as low sulfur utilization, serious shuttle effect of polysulfides and large volume expansion, especially upon high areal sulfur loading. Herein, conductive cobalt doped niobium nitride (Co-NbN) porous spheres as novel kind of sulfur host material has been fabricated via facile solvothermal and then calcination process under ammonia circumstances. The obtained Co-NbN/rGO/S cathode delivers excellent rate performance of up to ~600 mAh g-1 at 1 C with relative high areal loading of 3.3 mgs cm-2, and excellent long-term cycle stability of 404.5 mAh g-1 after 800 cycles at 1 C (the decay rate is only 0.07 % per cycle) with sulfur loading of 72 %. It is worth to note that the cathode illustrated a superior areal capacity of 3.92 mAh cm-2 at high sulfur loading of 5.6 mgs cm-2 with lean electrolyte (E/S=8 μL mg-1 sulfur). It is considered that the conductive and polar niobium nitride could effectively improve sulfur utilization and polysulfide anchoring of the sulfur cathode, and its unique porous structure could effectively accommodate distribution of the sulfur species and inhibited volume expansion for cathode. In addition, the synergistic effect between cobalt and NbN further facilitated conversion of sulfur species, suppressing shuttle effect and accelerating electrochemistry kinetics.The porous Co-NbN based host material has great potential for practical application of lithium-sulfur batteries.