Understanding the role played by Cu nanoparticles embedded in situ in a carbonaceous matrix as sulfur host for lithium-sulfur batteries

•C-embedded Cu nanoparticles were obtained from a Cu-oleate complex as single source.•Cu maintained its structure in the C/Cu@S composite ruling out the CuxS formation.•The values both the areal and specific capacity improve with increasing Cu content.•Cu nanoparticles act as electrocatalysts to enhance the redox reaction kinetics.•The Cu conductivity and its affinity towards LiPSs are the keys to this behavior. The lithium-sulfur (Li-S) battery is a promising alternative to Li-ion batteries as an energy storage system, owing to its higher capacity and specific energy values. To tackle its intrinsic problems, the element copper (Cu) is an attractive option given both its excellent conductivity and its ability to interact with highly reactive polysulfides. Here, we propose the use of a carbon/copper composite (90.5:9.5 wt ratio) obtained by thermal decomposition of a single precursor based on a Cu(II) oleate/oleic acid complex and eliminating the use of H2 as a reducing agent as commonly reported. Cu nanoparticles (mean particle size around 15 nm in diameter) which are highly dispersed on an amorphous carbon matrix derived from an organic framework, enhance both the conductivity and the ability for the chemical adsorption of lithium polysulfides (LiPSs), and thus increasing the reaction efficiency. Poor cycling stability, less specific capacity, and diminished rate capability were observed when the Cu content was reduced to around 70 % through treatment with concentrated nitric acid. This confirms the electrocatalytic role of the metal. [Display omitted]