N-doped CNTs wrapped sulfur-loaded hierarchical porous carbon cathode for Li-sulfur battery studies

Lithium-sulfur (Li-S) batteries are considered promising next-generation energy storage devices due to their low cost and high energy density (2600 W h kg^-1). However, the practical applicability of Li-S batteries is hindered by the insulating nature of sulfur cathodes, and the high solubility of polysulfides (Li₂S, 3 < x ≤ 8) which are formed during the electrochemical process. Integrating sulfur into the carbon host is an effective way to enhance the conductivity of the electrode which hampers the shuttling effect of the polysulfides. Here in this study, hierarchical porous carbon structures (HPC) are prepared from spent coffee waste (SCW) by the KOH activation process and are encapsulated with sulfur (SHPC) which increases the interaction between sulfur and carbon and enhances both the electronic and ionic conductivities. Further wrapping of SHPC with N-doped multi-walled carbon nanotubes (NCNTs) gives a SHPC-NCNT composite, which alleviates the shuttling of polysulfides by trapping them and ensures the required conductivity to the sulfur cathode during the Li⁺ reactions. When studied as a cathode material for Li-S batteries, the prepared cathode showed 664 and 532 mA h g^-1 specific capacities after 150 cycles at 0.2C and 0.5C, respectively. The stable cyclability and rate capability properties of SPHCNCNT suggest that the prepared sulfur composite is suitable as a cathode material for Li⁺ energy storage applications.