Highly Efficient Nanocarbon Coating Layer on the Nanostructured Copper Sulfide-Metal Organic Framework Derived Carbon for Advanced Sodium-Ion Battery Anode.

High theoretical capacity and low-cost copper sulfide (CuS)-based anodes have gained great attention for advanced sodium-ion batteries (SIBs). However, their practical application may be hindered due to their unstable cycling performance and problems with the dissolution of sodium sulfides (NaS) into electrolyte. Here, we employed metal organic framework (MOF-199) as a sacrificial template to fabricate nanoporous CuS with a large surface area embedded in the MOF-derived carbon network (CuS-C) through a two-step process of sulfurization and carbonization via HS gas-assisted plasma-enhanced chemical vapor deposition (PECVD) processing. Subsequently, we uniformly coated a nanocarbon layer on the CuS-C through hydrothermal and subsequent annealing processes. The physico-chemical properties of the nanocarbon layer were revealed by the analytical techniques of high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS), and scanning electron microscopy (SEM). We acquired a higher SIB performance (capacity retention (~93%) with a specific capacity of 372 mAh/g over 110 cycles) of the nanoporous CuS-C/C core/shell anode materials than that of pure CuS-C. This encouraging SIB performance is attributed to the key roles of a nanocarbon layer coated on the CuS-C to accommodate the volume variation of the CuS-C anode structure during cycling, enhance electrical conductivity and prevent the dissolution of NaS into the electrolyte. With these physico-chemical and electrochemical properties, we ensure that the CuS-C/C structure will be a promising anode material for large-scale and advanced SIBs.