Micro-nano structure composite cathode material with high sulfur loading for advanced lithium-sulfur batteries

A micro-nano structure based on polydopamine-grafted hollow carbon nanofiber-sulfur composite (HCNF@PDA-S) is designed as a cathode material for effective trapping of sulfur and polysulfides for lithium-sulfur batteries. Hollow carbon nanofiber@polydopamine (HCNF@PDA) micro-nano structure hybrid is first prepared by an in-situ polymerization dopamine monomer decorating on the surface of HCNFs and then elemental sulfur is infiltrated into the HCNF@PDA hybrid nanostructure by thermal treatment. The obtained HCNF@PDA-S composite shows the micro-nano structure based on the micron-sized hollow carbon nanofiber in length and nano-sized polydopamine grafted on the outer surfaces of the HCNFs with homogeneously distribution of sulfur. Compared with the HCNF-S composite, HCNF@PDA-S composite with a high sulfur content of approximately 80 wt% exhibits better electrochemical performance, which delivers initial discharge capacity of 800 mAh g−1 and maintains 530 mAh g−1 after 200 cycles at 0.5 C rate. The enhancements of electrochemical performances may be attributed to the unique micro-nano hybrid structure based on HCNFs and PDA coating layer, in which the micro-sized HCNFs offer the electronic conductivity and provide a firm porous network of the cathode tolerating the volume expansion of sulfur cathode, and nano-sized PDA layers effectively prevent the dissolution of the polysulfides into the electrolyte.