Mechanism of Lithium Storage in MoS2 and the Feasibility of Using Li2S/Mo Nanocomposites as Cathode Materials for Lithium-Sulfur Batteries

The most‐popular strategy to improve the cycling stability and rate performance of the sulfur electrode in lithium–sulfur (Li–S) batteries is to astrict the sulfur in a conducting medium by using complicated chemical/physical processing. Lithium sulfide (Li2S) has been proposed as an alternative electrode material to sulfur. However, for its application, it must meet challenges such as high instability in air together with all of the drawbacks of a sulfur–containing electrode. Herein, we report the feasibility of using Li2S, which was obtained by electrochemical conversion of commercial molybdenum disulfide (MoS2) into Li2S and metallic molybdenium (Mo) at low voltages, as a high‐performance active material in Li–S batteries. Metallic Mo prevented the dissolution of lithium polysulfides into the electrolyte and enhanced the conductivity of the sulfide electrode. Therefore, the in situ electrochemically prepared Li2S/Mo composite exhibited both high cycling stability and high sulfur utilization. Batteries not included: The recharge products of deeply discharged MoS2 were found to be metallic Mo and S. As Mo could not be oxidized below 3.0 V, Li2S and S were thought to be the sole redox couple in the cell, S+2 Li↔Li2S. The high cycling stability of the Li2S/Mo nanocomposite demonstrated the feasibility of using Li2S as an alternative to sulfur for lithium–sulfur batteries.