Flower-Like Interlayer-Expanded MoS2- x Nanosheets Confined in Hollow Carbon Spheres with High-Efficiency Electrocatalysis Sites for Advanced Sodium-Sulfur Battery.

The room-temperature sodium-sulfur (RT-Na/S) battery is one of the most promising technologies for low-cost energy storage. However, application of RT-Na/S batteries is currently impeded by severe shuttle effects and volume expansion that limits both energy density and cycling stability. Herein, first, the first-principal calculation is used to find that the introduction of sulfur vacancies in MoS2 can effectively enhance polysulfide adsorption and catalytic ability as well as both the ion and electron conductivities. Then, unique MoS2- x /C composite spheres are further designed and synthesized with flower-like few-layer and interlayer-enlarged MoS2- x nanosheets space-confined in hollow carbon nanospheres by a "ship-in-a-bottle" strategy. With this novel design, the mass loading of S in the MoS2- x /C composite can be reached to as high as 75 wt%. Owing to the synergetic effect of interlayer-expanded and few-layer MoS2- x nanosheets and hollow carbon spheres matrix with high electronic/Na+ conductivity, the RT-Na/S batteries deliver highly stable cycle durability (capacity retention of 85.2% after 100 cycles at 0.1 A g-1 ) and remarkable rate capability (415.7 mAh g-1 at 2 A g-1 ) along with high energy density. This design strategy of defect- and interlayer-engineering may find wide applications in synthesizing electrode materials for high-performance RT-Na/S batteries.