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

Abstract

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/cm2 while 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.

MnCo2O4 Spiny Microspheres as Polysulfide Anchors and Conversion Catalysts for High-Performance Li–S Batteries

“…Because sulfur has poor conductivity and polysulfide adsorption by the metal oxide catalyst is primarily a surface phenomenon, it is important that the cathode architecture is also suitably designed to increase sulfur utilization especially for higher sulfur loadings. 38 We have varied sulfur loadings and investigated areal capacity at faster C rate (0.2 C). The performance of the S@MCO/CNT cathode at sulfur loading of 2.5, 3.8, and 6.1 mg cm −2 was investigated for 100 cycles at 0.2 C rate, and the observed areal capacities are 2.9, 4.4, and 6.39 mA h cm −2 , respectively (Figure S4).…”

“…Because sulfur has poor conductivity and polysulfide adsorption by the metal oxide catalyst is primarily a surface phenomenon, it is important that the cathode architecture is also suitably designed to increase sulfur utilization especially for higher sulfur loadings . We have varied sulfur loadings and investigated areal capacity at faster C rate (0.2 C).…”

Unravelling the Influence of Surface Modification on the Ultimate Performance of Carbon Fiber/Epoxy Composites

“…This peak only shows up in the epoxy reference (Figure S6). Notably, the s-CF has two bands centered at 1349 and 1593 cm –1 , ascribed to the carbon D and G bands, respectively . These two bands convolute with the Raman peaks from the epoxy in the same region.…”

Mapping Techniques for the Design of Lithium‐Sulfur Batteries

“…The cross section S distribution in carbon nanotubes (CNTs) was characterized by Raman mappings to reveal the structure‐performance relationship. [ 76 ] The peak of symmetric SS bending mode (symδ SS ) at 222 cm −1 referring to unstrained S 8 prefers to concentrate on the surface of CNTs (Figure 8b). The excess undissolved S 8 will suspend on CNT surface even the temperature of infiltration treatment is 165 °C.…”

“…b) Cross section Raman mapping of the S-CNT composite. Reproduced with permission [76]. Copyright 2021, American Chemical Society.…”