Catalytic V5S8 anchored on PCMFs boosting polysulfides conversion for lithium-sulfur batteries

Abstract

Lithium-sulfur batteries have an ultra-high theoretical specific capacity of 1675 mAh g⁻¹ and a specific energy density of 2600 Wh kg⁻¹, but the low conductivity of sulfur and its discharge products, volume change of sulfur species during charge and discharge as well as the intrinsic lithium polysulfide shuttle characteristics hinder the full potential of the batteries. In this study, porous carbon micron fibers (PCMFs) were prepared by carbonization of cotton at 900 °C, and V₅S₈/PCMF composites were prepared by chemical vapor deposition of V₅S₈ nanoparticles on PCMFs. It is shown that the electrochemical performance of the battery with V₅S₈/PCMF cathode host is significantly improved compared with that of the battery using only PCMF host, thanks to the catalytic conversion of V₅S₈ towards sulfur species. Lithium-sulfur battery with V₅S₈/PCMF/S cathode has an initial discharge specific capacity of 1034 mAh g⁻¹, a capacity of 762.9 mAh g⁻¹ after 100 cycles and a capacity decay rate of 0.28% per cycle at 0.2 C, much improved than the battery with PCMF/S cathode; when cycling at 1 C for 400 cycles, the capacity decay rate is only 0.11% per cycle, showing superior cycle stability. With sulfur areal loading of 4.62 mg cm⁻², there is still a first discharge capacity of 852.2 mAh g⁻¹ at 0.2 C. This CVD method might offer a feasible route for preparing transition metal sulfide for improving the performance of lithium-sulfur batteries.