In situ formation of ultrafine CoS2 nanoparticles uniformly encapsulated in N/S-doped carbon polyhedron for advanced sodium-ion batteries

A dragon fruit-like nanostructure consisting of CoS2 nanoparticles and co-doped carbon polyhedron is effectively prepared through adjusting the pyrolysis processes of a Co-based zeolitic imidazolate framework (ZIF-67) precursor and subsequent heating sulfidation treatment. It was revealed that ultrafine CoS2 nanoparticles with an average particle size of 8 nm are uniformly dispersed and completely encapsulated in the N/S-doped carbon matrix. Such a multifunctional architecture achieves the integration of the favorite traits of ultrafine active nanoparticles and heteroatom-doped carbon matrix, thus giving rise to much improved electron transfer and ion transport, and upholding the structural integrity of the electrode and electrode/electrolyte interface. As an anode for sodium-ion batteries (SIBs), the as-prepared CoS2/C polyhedron electrodes exhibit high reversible capacity and good cycling stability. For example, a reversible specific capacity of 563 mA h g(-1) and a capacity retention rate of (0% with a remaining capacity of 510 mA h g(-1) are obtained after 100 cycles at 100 mA g(-1). In addition, a superior fast charge-discharge capability is also demonstrated with reversible specific capacities of 307 and 288 mA h g(-1) at large current densities of 1500 and 2000 mA g(-1), respectively. These impressive results indicate that the ZIF-derived synthetic strategy is highly adaptable to design dragon fruit-like nanostructure consisting of metal compounds/carbon nanomaterials with potential applications in high performance electrochemical energy storage devices and other environmental technology fields.