Elemental Sulfur Nanoparticles Chemically Boost the Sodium Storage Performance of MoS2/rGO Anodes

The critical role of sulfur nanoparticles in stabilizing MoS2 supported on reduced graphene oxide as anode material for sodium-ion batteries is discovered. The MoS2 supported on reduced graphene oxide decorated with sulfur particles (similar to 50 nm) is in-situ synthesized using an ammonium molybdate/graphene oxide preform and sublimed sulfur through a facile chemical vapor deposition process in a tube furnace with 2 temperature-controlled zones. Although the sulfur particles show no positive effect when the material is tested as anode for Li-ion batteries, they significantly improve the Na storage performance in terms of both, total specific capacity and cycle life. A stable high capacity of 580 mAhg(-1) and an extremely low capacity fade of 94 mAhg(-1) cycle(-1) make the designed assembly one of the best-performing MoS2-based anode materials for sodium-ion batteries so far. The post-cycling analysis reveals that the elemental sulfur nanoparticles play two roles: during the intercalation of Na in-between the layers of MoS2 (above 1.0 V), they function as blockers and inhibit the aggregation of MoS2; in the conversion reaction stage, the sulfur nanoparticles chemically participate in the Na storage process by forming Na2S5-rich compounds, which eventually improve the reversibility of the conversion reaction and thereafter the cycling performance.