Boron dopant- and nitrogen defect-decorated C 3 N 5 porous nanostructure as an efficient sulfur host for lithium-sulfur batteries.

Active site implantation and morphology manipulation are efficient protocols for boosting the electrochemical performance of carbon nitrides. As a promising sulfur host for lithium-sulfur batteries (LSBs), in this study, C3 N5 porous nanostructure incorporated with both boron (B) atoms and nitrogen (N) defects was constructed (denoted as ND-B-C3 N5 ) using a two-step strategy, i.e., pyrolysis of the mixture of 3-amino-1,2, 4-triazole and boric acid to obtain B-doped C3 N5 porous nanostructure and then KOH etching under hydrothermal condition to generate N defects. The doped B atoms in the C3 N5 porous nanostructure are in the form of B-N bonds and grafted B-O bonds. N defects are primarily created at the CN-C positions of the triazine unit, leaving behind some N vacancies and cyano groups. Benefiting from the involvement of B dopants and N defects, the optimized ND-B-C3 N5 -12 sample exhibits ameliorative conductivity, mass transport, lithium polysulfides (LiPSs) adsorption ability, diffusion of Li+ ions, Li2 S deposition capacity, sulfur redox polarization, and a reversible solid-solid sulfur redox process. Consequently, the ND-B-C3 N5 -12/S cathode delivers accelerated redox performance of polysulfides for LSBs, revealing capacities of 1091 ± 44 and 753 ± 20 mAh/g at 0.2C for the initial and 300th cycles, respectively. The ND-B-C3 N5 -12/S cathode is also endowed with desired sulfur redox activity and stability at 2C for 1000 cycles, holding an initial discharging capacity of 788 ± 24 mAh/g and a low decay rate of 0.05 % per cycle.