Abstract
High theoretical capacity and low-cost copper sulfide (CuxS)-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 (NaxS) into electrolyte. Here, we employed metal organic framework (MOF-199) as a sacrificial template to fabricate nanoporous CuxS with a large surface area embedded in the MOF-derived carbon network (CuxS-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 Cu1.8S-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 Cu1.8S-C/C core/shell anode materials than that of pure Cu1.8S-C. This encouraging SIB performance is attributed to the key roles of a nanocarbon layer coated on the Cu1.8S-C to accommodate the volume variation of the Cu1.8S-C anode structure during cycling, enhance electrical conductivity and prevent the dissolution of NaxS into the electrolyte. With these physico-chemical and electrochemical properties, we ensure that the Cu1.8S-C/C structure will be a promising anode material for large-scale and advanced SIBs.
Highlights
Sodium ion batteries (SIBs) have drawn great attention as an alternative to lithium ion batteries (LIBs) for large-scale energy storage systems (ESS) such as home solar-power storage, microgrids, and load leveling, owing to the abundant resource and low cost of Na [1,2]
Metal organic frameworks (MOF)-199 was completely transformed into the copper sulfide that the as-synthesized MOF-199 was completely transformed into the copper sulfide (Cux S) that (CuxS) that was incorporated in the MOF-derived carbon network
These results suggest that the Cu1.8S-C/C could offer facilitated Na+ ion diffusion and reaction, inter-space volume to accommodate volume change, and a large contact area of the electrode/electrolyte interface during cycling process, leading to enhanced sodium-ion batteries (SIBs) performance [18]
Summary
Sodium ion batteries (SIBs) have drawn great attention as an alternative to lithium ion batteries (LIBs) for large-scale energy storage systems (ESS) such as home solar-power storage, microgrids, and load leveling, owing to the abundant resource and low cost of Na [1,2]. Digenite Cu1.8 S-C (showing the highest capacity among the polymorphs of Cux S investigated in this study) was coated by a nanocarbon layer to form a core/shell structure, demonstrating a specific capacity of 372 mAh/g at 2C over 110 cycles, superior to that of the pure Cu1.8 S-C anode, and a higher cycling stability with ~93% retention. Considering these results, we ensure that the highly nanoporous Cu1.8 S-C/C core/shell anode structure can shed light on resolving the remaining issues of Cux S-based anodes for large-scale, next-generation SIBs
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