N-Doped branched carbon nanofibers@S as a cathode for lithium–sulfur batteries

Abstract

Lithium–sulfur batteries (LSBs) are considered as a new generation of large-scale energy-storage devices. However, LSBs suffer from a lack of desirable cathode materials with excellent specific capacity and cyclic stability. Here, we designed a sulfur-coated nitrogen-doped branched carbon nanofiber (NBCNF@S) hybrid cathode for Li–S batteries, in which the hierarchical structure of the nitrogen-doped branched carbon nanofibers (NBCNFs) with good flexibility and conductivity provides a protective buffer for the volume expansion that occurs during electrochemical processes. The NBCNF@S electrode displayed a reversible specific capacity of 1280 mA h g⁻¹ in the 1st cycle and was able to maintain a stable reversible discharge capacity of 1039 mA h g⁻¹ with the Coulombic efficiency reaching almost 100% for 200 cycles. The electrode was still able to deliver exceptional reversible capacities of 188 and 168 mA h g⁻¹, after 1000 and 2000 cycles, respectively, only decreasing by 0.02%/cycle. The excellent electrochemical performance can be attributed to the confinement of polysulfides, which involves the nitrogen doping effectively preventing the polysulfides from dissolving in the electrolyte during cycling. NBCNF@S synergistically anchors the polysulfides and therefore strongly suppresses the shuttle effect during the charge–discharge process, resulting in less capacity loss and better long-term cycling stability.