Defect-Engineered Vertically Aligned Carbon Nanotube Cathodes with High Sulfur Loading for High-Energy Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries hold exceptional promise due to their high gravimetric energy density and affordability, yet their practicality is limited by the poor conductivity of sulfur, polysulfide shuttling between the electrodes, and volume expansion. Conventional sulfur cathodes demand excessive carbon additives, and the fabrication of thick electrodes remains challenging, both of which dilute the active sulfur content and diminish the attainable energy density. To overcome this disadvantage, we introduce a ultrathick three-dimensional (3D) cathode architecture comprising vertically aligned carbon nanotubes (CNTs), directly grown via chemical vapor deposition (CVD), and functionalized by filling the hollow CNTs with sulfur via infusion (S@CNT). The engineered cathode is additionally subjected to reactive ion etching (RIE) to optimize the surface chemistry for robust polysulfide adsorption. This hierarchical design achieved an ultrahigh sulfur content of 72 wt % and a high sulfur loading of 7 mg cm–2, with capacity retention of 87.9% over 100 cycles, thereby significantly surpassing the performance of conventional CNT-based composite sulfur cathodes. The implementation of a 3D Ni foam substrate further enhanced these metrics to realize an even higher sulfur content of 90.2 wt % and sulfur loading of 11.3 mg cm–2. Our work demonstrates a scalable strategy to maximize the utilization of sulfur and energy density in Li–S batteries through rational 3D cathode engineering by offering a pathway to bridge the divide between theoretical promise and practical application.