Synthesis of silicon oxycarbonitride nanosphere as cathode host for lithium–sulfur batteries

Silicon oxycarbonitride (SiOCN) composites with different carbon contents were synthesized by pyrolysis of precursors generated from aldimine condensation of 3-aminopropyltriethoxysilane (APTES) with different aldehydes and simultaneous hydrolysis of APTES. Both SiOCN-1 and SiOCN-5 composites, derived from formaldehyde and glutaraldehyde respectively, display similar bulky structure composed by aggregated nanospheres with a diameter of 70–100 nm. SiOCN-5 has a higher carbon content of 30.4% than 15.9% for SiOCN-1, while a lower specific surface area of 38.2 m 2  g −1 than 76.0 m 2  g −1 for SiOCN-1. SiOCN/S cathodes with sulfur loading of 1.2–1.5 mg cm −2 were fabricated using SiOCN as sulfur host on different current collector of aluminum foil (AL) or carbon paper (CP). When using aluminum foil as current collector, SiOCN-5/S-AL cathode exhibits better electrochemical performance than SiOCN-1/S-AL, primarily due to the higher electrical conductivity of SiOCN-5 comparing with SiOCN-1. When using porous carbon paper as current collector, SiOCN-5/S-CP cathode shows the best cycling performance with a discharge capacity of 648.9 mA h g −1 at 0.2C after 100 cycles. Even at a high rate of 1C, SiOCN-5/S-CP also exhibits an excellent cycling stability, delivering a reversible discharge capacity of 374.5 mA h g −1 after 500 cycles with a capacity retention of 73.0%.