Controllable Chain‐Length for Covalent Sulfur–Carbon Materials Enabling Stable and High‐Capacity Sodium Storage.

Room temperature sodium–sulfur batteries have emerged as promising candidate for application in energy storage. However, the electrodes are usually obtained through infusing elemental sulfur into various carbon sources, and the precipitation of insoluble and irreversible sulfide species on the surface of carbon and sodium readily leads to continuous capacity degradation. Here, a novel strategy is demonstrated to prepare a covalent sulfur–carbon complex (SC‐BDSA) with high covalent‐sulfur concentration (40.1%) that relies on SO3H (Benzenedisulfonic acid, BDSA) and SO42− as the sulfur source rather than elemental sulfur. Most of the sulfur is exists in the form of OS/CS bridge‐bonds (short/long‐chain) whose features ensure sufficient interfacial contact and maintain high ionic/electronic conductivities of the sulfur–carbon cathode. Meanwhile, the carbon mesopores resulting from the thermal‐treated salt bath can confine a certain amount of sulfur and localize the diffluent polysulfides. Furthermore, the CSxC bridges can be electrochemically broken at lower potential (<0.6 V vs Na/Na+) and then function as a capacity sponsor. And the R‐SO units can anchor the initially generated Sx2− to form insoluble surface‐bound intermediates. Thus SC‐BDSA exhibits a specific capacity of 696 mAh g−1 at 2500 mA g−1 and excellent cycling stability for 1000 cycles with 0.035% capacity decay per cycle. The covalent sulfur–carbon complex SC‐BDSA (S, 40.1%) with different chain lengths is prepared. The short‐chain bridges can be electrochemically broken at potential <0.6 V (Na/Na+) and then worked together with the long‐chain units as a capacity sponsor. The R‐SO parts anchor Sx2− to form insoluble surface‐bound intermediates, leading to a special capacity of ≈750 mAh g−1 over 200 cycles. [ABSTRACT FROM AUTHOR]