Rational design of Co3S4-CoN@N-doped carbon hollow spheres with polar S-Co-N bond as bifunctional host materials for lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries have drawn much research attention as a contender for next-generation energy conversion systems because of their high capacity density and abundant raw materials. The large volume expansion and the insulating nature of sulfur and polysulfide shuttling issues limit future Li-S battery development. Herein, MOF-derived CoN nanoparticles embedded in an N-doped carbon layer are successfully constructed on the surface of the Co3S4 hollow sphere to form the Co3S4-CoN@NC heterostructure with strong S-Co-N bonds, which act as bifunctional host materials for Li-S batteries and show excellent adsorption and high-efficiency catalysis for lithium polysulfide (LiPSs). The hollow structure pre-stores a buffer space for the volume change of the electrode, limiting polysulfide dissolution. Furthermore, the carbon layer can improve the material's overall structural strength and electrical conductivity. Co3S4-CoN heterostructure with strong S-Co-N bonds can adsorb and accelerate the catalytic conversion of LiPSs. Co3S4-CoN@NC exhibits a high initial specific capacity of 1542.0 mAh g−1 at 0.1 C and a stable capacity of 872.6 mAh g−1 at 0.5 C after 100 cycles with a high Coulombic efficiency of nearly 100 %.