N-doped carbon-coated halloysite nanotubes as cathode materials for high-performance lithium-sulfur batteries

The practical application and development of lithium-sulfur batteries (LSBs) remains a serious issue as a consequence of the shuttle effect of lithium polysulfides (LiPSs). Halloysite (HNT), a clay mineral with a unique hollow tubular structure, is a potential carrier for sulfur. In this work, we employed a strategic approach to modify both inner and outer surfaces of HNT. We synthesized N-doped carbon-coated thin-wall hollow nanotube HNT composites (A5HNT@NC), which were subsequently utilized as sulfur carriers in the cathode of LSBs. This method alleviates the shuttle effect of LiPSs and controls the volume expansion of sulfur during charge-discharge. Acid heat treatment reduced Al-O octahedron in HNT, expanding the inner diameter to enhance the loading of sulfur. A5HNT@NC, prepared through phase inversion and high-temperature pyrolysis, effectively enhanced the electrical conductivity of thin-walled HNT, facilitating Li+ and electron transfer. Meanwhile, the structure of A5HNT@NC effectively adapted volume expansion of sulfur, realized high sulfur loading, and provided abundant active sites for anchoring of LiPSs. Moreover, the incorporation of N elements on carbon layer enhanced the ability to catalyze and adsorb LiPSs. Consequently, A5HNT@NC/S cathode exhibited high cycle stability and specific capacity. At 0.2 C, it retained high capacity of 619.7 mAh g- 1 after 100 cycles, achieving 84.67 % capacity retention. At a higher current density of 0.5 C, A5HNT@NC/S cathode also retained specific capacity of 515.0 mAh g- 1 after 300 cycles. This work can expand the application of HNT for energy storage, provide inspiring insights into the design of novel sulfur carrier materials for LSBs.