Experimental and first-principles study of a metal–organic framework with sulfur embedding cathode for enhanced performance lithium–sulfur battery

Lithium–sulfur (Li–S) batteries, which are well-known and much studied rechargeable batteries, are very promising because of their low cost, environmental friendliness, very high specific capacity and superior energy density. However, applications of Li–S batteries have been obstructed by their fast capacity fading and low coulombic efficiency due to soluble polysulfide migration during charge/discharge cycling. Herein, we present a strategy utilizing cobalt metal–organic framework (CoMOF) with rough porous surface and defective structure as a host material for sulfur accommodation, which implements a CoMOF and S composite (CoMOF–S) as a cathode. Capacity retention of CoMOF–S cathode surpasses that of pure sulfur by 87.18% after 100 cycles at 0.1C, while achieving coulombic efficiency above 98% at a high rate of 2.0C. We reveal structural features by combining X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations, which confirm the covalent bond connection between CoMOF and S. We attribute the excellent cycling performance to covalent bond immobilization of sulfur.