Stable Liquid-Sulfur Generation on Transition-Metal Dichalcogenides toward Low-Temperature Lithium-Sulfur Batteries.

The electrochemical formation of liquid sulfur at room temperature on the basal plane of MoS 2 has attracted much attention due to the high areal capacity and rapid kinetics of lithium-liquid sulfur chemistry. However, the liquid sulfur is converted to the solid phase once it contacts the solid sulfur crystals generated from the edge of MoS 2 . Thus, stable liquid sulfur cannot be formed on the entire MoS 2 surface. Herein, we report entire liquid sulfur generation on hydrogen-annealed MoS 2 (H 2 -MoS 2 ), even under harsh conditions of large overpotentials and low working temperatures. The origins of the solely liquid sulfur formation are revealed to be the weakened interactions between H 2 -MoS 2 and sulfur molecules and the decreased electrical polarization on the edges of the H 2 -MoS 2 . Progressive nucleation and droplet-merging growth behaviors are observed during the sulfur formation on H 2 -MoS 2 , signifying high areal capacities by releasing active H 2 -MoS 2 surfaces. To demonstrate the universality of this strategy, other transition-metal dichalcogenides (TMDs) annealed in hydrogen also exhibit similar sulfur growth behaviors. Furthermore, the H 2 annealing treatment can induce sulfur vacancies on the basal plane and partial oxidation on the edge of TMDs, which facilitates liquid sulfur formation. Finally, liquid sulfur can be generated on H 2 -MoS 2 flakes at an ultralow temperature of -50 °C, which provides a possible development of low-temperature lithium-sulfur batteries. This work demonstrates the potential of a pure liquid sulfur-lithium electrochemical system using functionalized two-dimensional materials.