Simultaneous Cobalt and Phosphorous Doping of MoS2 for Improved Catalytic Performance on Polysulfide Conversion in Lithium–Sulfur Batteries

The lithium-sulfur batteries are susceptible to the loss of sulfur as dissolved polysulfides in the electrolyte and their ensuing redox shutting effect. The acceleration of the conversion kinetics of dissolved polysulfides into the insoluble sulfur and lithium sulfide via electrocatalysis has the appeal of being a root-cause solution. MoS2 is the most common electrocatalyst used for this purpose. It is demonstrated that how the effectiveness can be improved by simultaneous cobalt and phosphorus doping of MoS2 nanotubes (P-Mo0.9Co0.1S2-2, containing 1.81 at% of P). Cobalt doping induces the transformation of MoS2 from 2H phase to metallic 1T phase, which improves the electrical conductivity of the MoS2. The Co-P coordinated sites on the catalyst surface are highly active for the polysulfide conversion reactions. Consequently, a sulfur cathode with P-Mo0.9Co0.1S2-2 can decrease the capacity fade rate from 0.28% per cycle before modification (over 150 cycles at 0.5C rate) to 0.046% per cycle after modification (over 600 cycles at 1C rate). P-Mo0.9Co0.1S2-2 also enhances the high rate performance from a capacity of 338 to 931 mAh g(-1) at 6C rate. The results of this study provide the first direct evidence of the beneficial effects of heteroatom codoping of polysulfide conversion catalysts.