Silica Hard Template Extracted from Semicoke Residue Toward the Hierarchical Porous Carbon Skeleton for Lithium–Sulfur Batteries

The nitrogen-doped porous carbon skeleton is considered one of the effective structures to improve the electrical conductivity of sulfur cathode materials and mitigate the shuttling of soluble lithium polysulfides (LiPSs) in Li–S batteries (LSBs) due to its outstanding electrical conductivity, electrochemical stability, and tunable pore size distribution. Here, we report a three-dimensional nitrogen-doped porous carbon skeleton (a-NC) with a high sulfur loading capacity (66.97%) as the sulfur host of LSBs through the combination of SiO₂ microspheres extracted from oil shale semicoke residue as a hard template and urea–formaldehyde resin as a nitrogen-containing carbon precursor. This strategy can not only obtain a hierarchical porous carbon skeleton but also provide a high-value utilization approach for oil shale semicoke residue. The sulfur-loaded a-NC (S@a-NC) electrode obtained comparable performance to S@s-NC electrodes based on SiO₂ templating agents prepared by the Stöber method. Specifically, the initial discharge capacity of 673 mAh g^–1 at a high current density of 1 C, stabilized at 193.9 mAh g^–1 after 400 cycles and an excellent cycling stability of 81.5% over the following 800 cycles, which is attributed to its interconnected and hierarchical pore feature limiting the unfavorable diffusion of LiPSs and the highly defective structure, enhances the adsorption performance for polysulfides.