Small-Sized CuS Nanoparticles/N, S Co-Doped rGO Composites as the Anode Materials for High-Performance Lithium-Ion Batteries

In this work, small-sized CuS nanoparticles/N, S co-doped rGO composites (CuS@N/S-G-C _n ) are synthesized by a facile route with the metal-containing ionic liquids (MILs) [C _n MMim] ₂ [CuCl ₄ ] (n is 6, 8, 10 representing the number of C atoms in the alkyl chain of imidazolium cation) as the precursors. In the composites, the CuS nanoparticles with small size of sub-20 nm are homogeneously dispersed in nitrogen and sulfur co-doped reduced graphene oxide (rGO). The highly dispersed nanosized CuS are embedded on excellent conductive doped rGO substrates to supply not only large quantity of accessible active sites for lithium-ion insertion but also short diffusion length for lithium ions, while the N and S co-doping in rGO can efficiently restrain the polysulfides dissolution and circumvent the volume expansion/contraction associated with lithium insertion/extraction during charge–discharge processes. Bestowed by these advantages, the CuS@N/S-G-C _n composites exhibit enhanced electrochemical performance for lithium storage. Especially, when [C ₆ MMim] ₂ [CuCl ₄ ] is chosen as the precursor, the obtained electrode material CuS@N/S-G-C ₆ delivers a reversible capacity as high as 603.5 mAh g ⁻¹ at 200 mA g ⁻¹ after 300 cycles and 530 mAh g ⁻¹ at 2 A g ⁻¹ after 1000 cycles.