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 (Cu(x)S)-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 (Na(x)S) into electrolyte. Here, we employed metal organic framework (MOF-199) as a sacrificial template to fabricate nanoporous Cu(x)S with a large surface area embedded in the MOF-derived carbon network (Cu(x)S-C) through a two-step process of sulfurization and carbonization via H(2)S gas-assisted plasma-enhanced chemical vapor deposition (PECVD) processing. Subsequently, we uniformly coated a nanocarbon layer on the Cu(1.8)S-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 Cu(1.8)S-C/C core/shell anode materials than that of pure Cu(1.8)S-C. This encouraging SIB performance is attributed to the key roles of a nanocarbon layer coated on the Cu(1.8)S-C to accommodate the volume variation of the Cu(1.8)S-C anode structure during cycling, enhance electrical conductivity and prevent the dissolution of Na(x)S into the electrolyte. With these physico-chemical and electrochemical properties, we ensure that the Cu(1.8)S-C/C structure will be a promising anode material for large-scale and advanced SIBs.