Porous Molybdenum Carbide Nanorods as Novel Bifunctional Cathode Material for Li-S Batteries

The shuttle effect of polysulfide is the primary obstacle in Li-S batteries. Although some effort has been made to suppress the shuttle process, more highly conductive materials with stronger adsorption ability to polysulfides are still in urgent demand. Another important problem is the deteriorating performance of Li-S batteries with prolonged cycling owing to irreversible deposition of lithium sulfide (Li2S). However, a host material for the effective conversion of insoluble Li2S has been elusive up to now. Herein, porous molybdenum carbide nanorods (Mo2C NRs), with high catalytic activity for Li2S and ultrastrong adsorption for polysulfides, are used as a bifunctional host material and incorporated into sulfur cathodes for the first time. The bifunctional Mo2C NRs have the advantage of immobilizing polysulfides over the conventional host, with adsorption energies from -4.89 to -8.20eV for Li2Sx (x=1, 2, 4, 6, and 8). The electrochemical analysis shows that Mo2C NRs, more than an anchor, can activate Li2S by greatly reducing the charging overpotential. Therefore, the irreversible deposition of polysulfides is effectively restrained and the utilization of Li2S is clearly enhanced. The Mo2C NRs-sulfur composites (Mo(2)CNRs-S) cathodes provide a capacity of 1298mAhg(-1) at 0.1C in the Li-S batteries. More importantly, the battery with Mo(2)CNRs-S cathodes exhibits a much lower capacity decay of 0.062% per cycle at 1C over 500 cycles.