The Dual Functions of Defect-Rich Carbon Nanotubes as Both Conductive Matrix and Efficient Mediator for Li-S Batteries

Li-S batteries are considered a promising energy storage system owing to the great abundance of sulfur and its high specific capacity. Polysulfide shuttling and sluggish reaction kinetics in sulfur cathodes significantly degrade the cycle life of Li-S batteries. A modified method is employed to create defects in carbon nanotubes (CNTs), anchoring polysulfides, and accelerating electrochemical reactions. The defect-rich CNTs (D-CNT) enable dramatic improvement in both cycling and rate performance. A specific capacity of 600 mAh g−1 with a current density of 0.5 C is achieved after 400 cycles, and even at a very high current density (5.0 C), a specific capacity of 434 mAh g−1 is observed. Cycling stability up to 1000 cycles is also achieved under the conditions of high sulfur loading and lean electrolyte. Theoretical calculations revealed that the improvement is mainly attributable to the electronic structure of defect-rich carbon, which has higher binding energy with polysulfides because of the upshift of the p-band center. Furthermore, rotating disk electrode measurements demonstrate that the defect-rich carbon can accelerate the polysulfide conversion process. It is anticipated that this new design strategy can be the starting point for mediator-like carbon materials with good conductivity and high catalytic activity for Li-S batteries.