Self-Assembling Hollow Carbon Nanobeads into Double-Shell Microspheres as a Hierarchical Sulfur Host for Sustainable Room-Temperature Sodium-Sulfur Batteries

Abstract

We report the use of double-carbon-shell passion fruit-like porous carbon microspheres (PCMs) as the sulfur substrate in the room temperature sodium sulfur (RT Na-S) batteries. PCMs are encapsulated with the integrate microsized carbon coating layers on the outside and composed of the interconnected nanosized hollow carbon beads inside, leading to a special multidimensional scaling double-carbon-shell structure with high electronic conductivity and strengthened mechanical properties. Sulfur was filled inside the PCMs (PCMs-S) and protected by the unique double-carbon-shell, which means the following generated intermediate sodium polysulfide species cannot be exposed to the electrolyte directly and well protected inside. In addition, the inside interconnected porous structure provides rooms for the volume expansion of sulfur during discharge processes. It is found that the PCMs-S with a 63.6 % initial coulombic efficiency delivered a reversible discharge capacity of 290 mAh g-1 at the current density of 100 mA g-1 after 350 cycling test. More importantly, PCMs-S exhibited good rate performance with a capacity of 113 and 56 mAh g-1 at the current densities of 1000 and 2000 mA g-1, respectively.