Arranged redistribution of sulfur species and synergistic mediation of polysulfide conversion in lithium–sulfur batteries by a cactus structure MnO2/carbon nanofiber interlayer

Abstract

Cactus structure MnO₂/N-rich carbon nanofiber composites were synthesized via an in situ redox reaction to be utilized as the interlayer in lithium–sulfur batteries. The exposed MnO₂ nanosheets vertically aligned on carbon nanofibers provide a large amount of active sites for polysulfide adsorption and conversion. Unlike physical barriers or simple surface interactions, the MnO₂ nanosheets generate an anchor and transfer mediator for polysulfides to dissolve into the electrolyte, and then control the deposition of Li₂S₂ or Li₂S on the designed interlayer. This structure induces an arranged relocation of sulfur species during cycling, resulting in a shortened electron passage and an improved utilization of the active material. With a sulfur loading of 1.65 mg cm⁻² and a sulfur content of 60% at the whole electrode level, the cell with the MnO₂/carbon nanofiber interlayer delivered an initial discharge capacity of 1102 mA h g⁻¹, 965 mA h g⁻¹, and 712 mA h g⁻¹ at 0.1C, 1C and 5C, respectively. It could maintain a reversible capacity of 646 mA h g⁻¹ after 100 cycles at 1C and a specific capacity of 414 mA h g⁻¹ after 1000 cycles at 5C with a fade rate of 0.04% per cycle.