Microstructure engineering in sulfuretted coal tar pitch by varying the Cross-Link state for enhanced sodium storage

Sulfur (S) is an efficient dopant to enhance the sodium storage of carbon, yet the conventional in-situ/post treatments cause unstable S configuration or lower S content, and hence unsatisfied electrochemical performance. Herein, we investigate sulfurization at various cross-link state of coal tar pitch (CTP) (pristine, coke, and carbonized states), and the microstructure of the products (SCTP). Experimental and calculational results reveal that introducing S in the coke state of CTP is essential for achieving abundant and stable C-S_x-C bonds between carbon layers. Moreover, this innovative strategy not only achieves a high S content, but also avoids the liquid carbonization, resulting in a hierarchically porous structure with a small particle size. As a result, the SCTP delivers a sodium storage capacity of 318 mA h g^-1 at 0.1 A g^-1 after 200th cycle, and the capacity maintains 207 mA h g^-1 with capacity retention of 99 % after 1000th cycle at 2.0 A g^-1, in half-cells. Moreover, the sample shows a considerable discharge capacity of 328 mA h g^-1_anode at 0.05 A g^-1 in full-cells. Consequently, this approach offers a novel pathway for large-scale production of thermoplastic-derived carbons in battery industry.