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

Abstract

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.