Robust nanocube framework CoS2-based composites as high-performance anodes for Li- and Na-ion batteries

Robust hierarchical nanocube framework CoS2-based composites comprising of nanocrystalline CoS2 (-8-10 nm) encapsulated in a robust carbon-core matrix entangled in carbon nanotubes (CNTs) were synthesized, and their performance as electrodes for Li-ion batteries (LIBs) and Na-ion batteries (NIBs) was evaluated. The robust nanocube framework CoS2-C-CNT composites were synthesized from Co-based metal-organic frameworks by an efficient two-step synthesis process of carbonization and sulfidation. The structural phase change mechanism of CoS2 was systematically characterized by ex situ analysis tools, which revealed that it involved a conversion during Li/Na-insertion and a recombination reaction during Li/Na-extraction. The unique structural characteristics of the nanocube framework CoS2-C-CNT composites and the unique structural phase change mechanism of CoS2 are attributed to the superior Li/Na-storage performances. The nanocube framework CoS2-C-CNT composites delivered a large reversible capacity (LIB: 770 mAh g-1 and NIB: 629 mAh g-1), excellent cycling (LIB: 726 mAh g-1 after 250 cycles and NIB: 531 mAh g-1 after 100 cycles), and fast rate behavior (LIB: 613 mAh g-1 at 3C and NIB: 391 mAh g-1 at 2C rates). This remarkable robust nanocube framework composite structure is highly applicable to various LIB/NIB electrode materials owing to their excellent Li/Na-ion storage characteristics.