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

Abstract

High theoretical capacity and low-cost copper sulfide (Cu_xS)-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_xS) into electrolyte. Here, we employed metal organic framework (MOF-199) as a sacrificial template to fabricate nanoporous Cu_xS with a large surface area embedded in the MOF-derived carbon network (Cu_xS-C) through a two-step process of sulfurization and carbonization via H₂S gas-assisted plasma-enhanced chemical vapor deposition (PECVD) processing. Subsequently, we uniformly coated a nanocarbon layer on the Cu_1.8S-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_1.8S-C/C core/shell anode materials than that of pure Cu_1.8S-C. This encouraging SIB performance is attributed to the key roles of a nanocarbon layer coated on the Cu_1.8S-C to accommodate the volume variation of the Cu_1.8S-C anode structure during cycling, enhance electrical conductivity and prevent the dissolution of Na_xS into the electrolyte. With these physico-chemical and electrochemical properties, we ensure that the Cu_1.8S-C/C structure will be a promising anode material for large-scale and advanced SIBs.