Double Hierarchical 3D Carbon Nanotube Network with Tailored Structure as a Lithium Sulfur Cathode

In this study, double hierarchical and highly porous 3D carbon nanotube/sulfur (CNTT/S) composites were synthesized. By coating a ceramic template material with a simple and versatile infiltration process of an aqueous carbon nanotube (CNT) dispersion a self-organized CNT layer is formed. After removing the template material, a freestanding double hierarchical network is created that show excellent electrical conductivity of 6.02 S m-1 and a high specific BET surface area of 630 m2 with the presence of micro-, mesopores (up to 4 nm) and macropores (>>50 nm) simultaneously. A combined analysis of gas sorption measurements and elemental mapping using EFTEM after sulfur vapor deposition revealed that only the micro- and mesopores were accessible and that the sulfur is encapsulated within the double hierarchy. Hence, the electric percolation remains high without losing the necessary outer conductivity. Thereafter, these composites were employed in a proof-of-concept study as a sulfur cathode, demonstrating the importance of predesigning an electrode structure, shown in electrochemical performance data. With the aid of this hierarchical 3D composite structure, it is possible to achieve a stability over 100 cycles with $\approx$ 5.8 mAh cm-1 as a sulfur cathode in lithium half-cell tests.