Flexible Hierarchical Co-Doped NiS₂@CNF-CNT Electron Deficient Interlayer with Grass-Roots Structure for Li–S Batteries

The key means to improve the performance of lithium–sulfur batteries (LSBs) is to reduce the internal resistance by building an electronic/ionic pathway and to accelerate the conversion kinetics of lithium polysulfides (LiPSs) through modulation of interface functions. Herein, inspired by a grass root system, a flexible hierarchical CNF-CNT (carbon nanofiber-carbon nanotube) membrane decorated with Co-doped NiS₂ nanoparticles (Co-NiS₂@CNF-CNT) is designed as an interlayer for LSBs, in which the in situ grown CNTs (root hairs) are wound on CNF (roots). Density functional theory (DFT) calculations show that Co doping introduces electron-deficient regions at the doping sites in NiS₂, thus improving chemical adsorption and catalytic activities toward LiPSs. The cell pairs with the Co-NiS₂@CNF-CNT interlayer exhibit a high rate performance of 951.4 mAh g⁻¹ at 3 C, a reversible capacity of 944.1 mAh g⁻¹ after 500 cycles at 0.2 C, and a prolonged cycle life of 3000 cycles at 5 C. More importantly, an areal capacity of 7.96 mAh cm⁻² is achieved with a sulfur loading of 9.6 mg cm⁻². This work provides a strategy for enhancing the electrochemical performance of LSBs by combining 3D hierarchical conductive skeletons and electron-deficient functional adsorption and catalysis materials.