In-situ formed porous silicon carbonitride/boron nitride composites to boost cathode performance in lithium sulfur batteries

Carbon-rich polymer-derived SiCN ceramic matrix serves as a stabilizing host for sulfur cathodes due to its robust, stress-accommodating properties and well-conductive carbon network. Herein, novel SiCN-BN composites are synthesized through the annealing of a polymer-derived SiCN ceramic alongside boric acid and urea. The prepared cathodes exhibit significantly improved electrochemical performance after sulfur immobilization within the resulting composites. Of particular note is the material annealed at 950 °C, designated as SiCN-BN-950/S. It exhibits a reversible capacity of 445 mAh/g showcasing 62% capacity retention over 60 cycles, using electrodes with an areal density of 3.5–3.8 mg/cm2 and a sulfur loading of 66 wt%. Its good cycling stability is attributed to the remarkable synergistic interplay between BN on the surface and disordered carbon present within the SiCN ceramic matrix. The presence of BN enables effective polar adsorption of polysulfides, while the in-situ formed porous carbon contributes to enhanced electrical conductivity. This combination significantly elevates the overall electrochemical performance of the sulfur cathode. The successful utilization of these novel SiCN-BN composites, a remarkable advancement in sulfur cathode technology, opens up possibilities for further enhancing the efficiency and stability of energy storage systems.