Optimizing C3N5 for advanced lithium‑sulfur batteries: Boron and oxygen modification in porous honeycomb frameworks

Nitrogen-rich C3N5 has promising potential as sulfur host for the cathode of lithium–sulfur batteries (LSBs). Aiming to boost the sulfur hosting performance of C3N5, its active sites and morphology have been manipulated by constructing boron (B) and oxygen (O) atoms modified porous honeycomb–like structure of C3N5 (HB–C3N5–0.8) via a SiO2 nanospheres hard templating strategy. B atoms are incorporated into the skeleton of C3N5 by replacing C atoms and forming BN bonds. The adscititious O atoms tend to form CO/CO groups. The involvement of B and O atoms enhances the electronic conductivity and increases the active sites of C3N5, thereby strengthening the immobilization and transformation of LiPSs intermediates, improving the diffusion kinetics of Li+ ions, and reducing the energy barrier of Li2S nucleation. Porous honeycomb–like structure of C3N5 can guarantee good accessibility of ample sites for hosting S8 reactant, LiPSs intermediates, and Li2S2/Li2S products, facilitate the electrolyte penetration, and buffer the volume expansion. The results indicate that the optimized HB–C3N5–0.8/S cathode demonstrates excellent sulfur reduction capability and stability, with an initial discharge capacity of 1066 mAh g−1 at 0.2C. After 1000 charge-discharge cycles at a high current density of 2.0C, it exhibits a low decay rate of only 0.037 % per cycle. This study offers a convenient and feasible strategy for engineering the morphology and active sites of C3N5 for electrochemical application. [Display omitted] •Porous honeycomb–like structure of C3N5 was prepared.•Boron and additional oxygen atoms were doped into C3N5.•The HB–C3N5 samples unfolded greatly enhanced LiPSs immobilization and conversion.•The optimized HB–C3N5-0.8/S cathode demonstrated excellent sulfur reduction performance.