Investigating Multiscale Spatial Distribution of Sulfur in a CNT Scaffold and Its Impact on Li-S Cell Performance

Ever increasing demand on high energy density batteries positions sulfur as a very promising cathode material for next-generation energy storage due to its high theoretical capacity of 1675 mAh/g. Electronically sulfur is highly insulating, and therefore integration of a conducting framework such as a carbon nanotube (CNT) scaffold with sulfur is a key aspect of the cathode design. Despite numerous efforts dedicated to S-CNT cathode development, increasing sulfur loading to above 1 mg/cm²while maintaining the cycling stability of the Li-S cell remains challenging. This could be partly due to the lack of understanding of the spatial distribution of sulfur in the CNT matrix and its location with respect to the morphology of the CNT scaffold. We demonstrate herein that the sulfur has a hierarchical distribution in the CNT cathode at high sulfur loading (>5 mg/cm²) spanning multiple length scales (from nanometer to submillimeter). Sulfur infiltration into the CNT rather than the sulfur loading plays a key role in determining the redox reaction kinetics, Li⁺ion diffusion, and the galvanostatic cycling capacity and stability of Li-S cells. This study provides new insights for the design and fabrication of high loading, binder-free sulfur-carbon-based cathode architectures for next-generation high energy Li-S batteries.