Influence of C–S interactions on the electrochemical performance of –COOH functionalized MWCNT/S composites as lithium-sulfur battery cathode

Abstract

Effective trapping of polysulfides within the carbon cathode host strongly depends on intrinsic C–S interactions. We report herein a systematic study of the influence of S-loading process on C–S interactions in MWCNT/S composites prepared by three commonly used industry-friendly methods, namely, mechanical solid-state mixing, infiltration method from a solution of S in CS $$_{2}$$ , and chemical deposition by disproportionation reaction of sodium sulfide and sodium thiosulfate. FESEM and TEM studies reveal strikingly different morphologies of the resulting MWCNT/S composites. XPS and Raman studies indicate different extents of recovery of $$\pi $$ bonds in MWCNT due to varying degrees of C–S interfacial interactions in the composites. Furthermore, it is found that the C/O atomic ratio in the composites plays a crucial role: the higher the C/O value the better is the S-confinement. These subtle physical changes induced by C–S interactions in the composites can be related to electrochemical performance when tested in Li-S coin cells. It is found that the best results (high initial capacity of 1143 mAh g $$^{-1}$$ and better capacity retention) could be achieved when the solution infiltration method was used for S-loading. This conclusion is further validated by using activated carbon as S-host. SYNOPSIS MWCNT/sulfur composites with different S-loading methods have been investigated by XPS and Raman studies. The electrochemical performance in Li-S battery is correlated with different degrees of recovery of $$\pi $$ bonds in MWCNT and the C/O atomic ratio in the composites due to a varying extent of C–S interactions.