Hierarchical Co-CNT@NG Composite with Enhanced Polysulfide Kinetics in High-Performance Li–S Batteries

Abstract

Lithium–sulfur (Li–S) batteries are considered promising candidates for next-generation energy storage systems due to their high theoretical energy density. However, their practical application is severely hindered by the polysulfide shuttle effect and the sluggish redox kinetics of lithium polysulfides (LiPSs). To address these challenges, a polypropylene (pp) separator was modified with Co-CNT@NG, a composite prepared by integrating cobalt-embedded carbon nanotubes (Co-CNTs) onto nitrogen-doped expanded graphite (NG). This three-dimensional hierarchical composite enables the simultaneous physical confinement and strong chemical adsorption of LiPSs, effectively suppressing the shuttle effect. The embedded cobalt nanoparticles and doped nitrogen atoms synergistically promote the conversion of LiPS. The conductive 3D framework ensures fast electron transfer and reduces interfacial resistance. As a result, Li–S batteries with the Co-CNT@NG/pp separator deliver superior electrochemical performance, including a high initial discharge capacity of 1346 mAh g^–1 at 0.1 C, outstanding rate capability with 771 mAh g^–1 at 6 C, and long-term cycling stability over 500 cycles at 0.5 C with nearly 100% Coulombic efficiency under a high sulfur loading of 8.0 mg cm^–2. This work provides an effective strategy for enhancing the kinetic conversion of LiPSs in Li–S batteries through the rational design of a 3D hierarchical catalytic structure.