Enhanced rate capability and cycle stability of lithium-sulfur batteries with a bifunctional MCNT@PEG-modified separator

As one of the most promising high-energy lithium batteries, the commercialization of lithium-sulfur (Li-S) batteries remains a huge challenge due to their poor rate performance and low cycle stability, which originate partly from the dissolution of polysulfides and their migration from the S cathode to the Li anode through the separator. Novel sulfur-based composite cathodes have been constantly put forward to restraint the dissolution of polysulfides; however, less attention has been paid to modifying the separator. In this work, a multi-walled carbon nanotube@polyethylene glycol (MCNT@PEG) composite is designed and prepared to modify the commercial Celgard separator. With the bifunctional MCNT@PEG-modified separator, Li-S cells possess a high initial discharge capacity of 1283 mA h g(-1) at 0.5 C and undertake a long charge/discharge process of 500 cycles at 1 C with 0.12% capacity fading per cycle. Moreover, when the rate is increased to 5 C, the cells can also deliver a discharge capacity of 657 mA h g(-1). These encouraging electrochemical results highlight the excellent rate capability and high cycle stability of Li-S cells, which could be attributed to the strong chemical and physical absorption properties and high electron conductivity of the MCNT@PEG layer. This facile approach to restrain the shuttle effect of polysulfides makes further progress in obtaining the enhanced performance of Li-S batteries.