Highly crinkled and interconnected N, O and S co-doped carbon nanosheet modified separators for efficient Li-S batteries

Carbon materials with large exposed surfaces and heteroatom doping have great potential in suppressing the shuttle effect in Li-S batteries. In this study, crosslinked triazine frameworks were successfully utilized to synthesize heteroatom-doped carbon nanosheets utilizing g-C₃N₄ nanosheets as the hard template and porogen. Characterization studies show that the nanosheets were highly crinkled and interconnected with a large surface area (1060 m² g⁻¹) and pore volume (2.14 cm³ g⁻¹), and with highly dispersed N, O and S. After coating them on commercial Celgard separators, batteries with the modified separators showed a low self-discharge and an improved rate performance even at 4 C. At 0.5 C, the initial discharge capacity was 1240 mA h g⁻¹ with a capacity decay of 0.059% per cycle for over 1000 cycles. Moreover, excellent cycling performances at 2 C for 500 cycles were also achieved. The excellent performance can be attributed to the large surface area and porous structure of NOS-C, the superior wettability toward the electrolyte, enhanced Li⁺ diffusion, strong interactions between polysulfides and doped atoms, and the accelerated redox kinetics of polysulfides.