An in Situ Prepared Covalent Sulfur–Carbon Composite Electrode for High-Performance Room-Temperature Sodium–Sulfur Batteries

A covalent sulfur–carbon (covalent-SC) composite is successfully prepared in situ by a wet-chemical solvothermal method based on the strong interaction between carbon disulfide (CS2) and red phosphorus. It is demonstrated that sulfur uniformly distributes among the boundary and interior of the carbon skeleton with the formation of S–C bonds. Moreover, the interior sulfur can be electrochemically activated under 0.5 V and then functions as a capacity sponsor, because Na+ can freely transfer into the carbon interlayer (with a stable enlarged distance of ∼0.4 nm after the first cycle) via adsorption-like behavior to be combined with the interior sulfur in the following cycles. Thus, the activated covalent-SC composite delivers ultrahigh reversible capacities of 888.9 and 811.4 mAh g–1 after 600 and 950 deep cycles at 0.8C and 1.6C, respectively. Furthermore, it exhibits outstanding rate performance with the capacity of 700 mAh g–1 at a high rate of 8.1C.