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.