In Situ Observation and Electrochemical Study of Encapsulated Sulfur Nanoparticles by MoS2 Flakes.

Sulfur is an attractive cathode material for next-generation lithium batteries due to its high theoretical capacity and low cost. However, dissolution of its lithiated product (lithium polysulfides) into the electrolyte limits the practical application of lithium sulfur batteries. Here we demonstrate that sulfur particles can be hermetically encapsulated by leveraging on the unique properties of two-dimensional materials such as molybdenum disulfide (MoS2). The high flexibility and strong van der Waals force in MoS2 nanoflakes allows effective encapsulation of the sulfur particles and prevent its sublimation during in situ TEM studies. We observe that the lithium diffusivities in the encapsulated sulfur particles are in the order of 10-17 m2 s-1. Composite electrodes made from the MoS2-encapsulated sulfur spheres show outstanding electrochemical performance, with an initial capacity of 1660 mAh g-1 and long cycle life of more than 1000 cycles.