Na Storage Capability Investigation of a Carbon Nanotube-Encapsulated Fe_1–<i>x</i>S Composite

A promising anode material consisting of Fe_1–<i>x</i>S nanoparticles and bamboo-like carbon nanotubes (CNTs) has been designed and prepared by an effective in situ chemical transformation. The resultant Fe_1–<i>x</i>S@CNTs with a three-dimensional network not only provide high conductivity paths and channels for electrons and ions but also offer the combined merits of iron sulfide and CNTs in electrochemical energy storage applications, leading to outstanding performance as an anode material for sodium-ion batteries. When tested in a half-cell, a high capacity of 449.2 mAh g^–1 can be retained after 200 cycles at 500 mA g^–1, corresponding to a high retention of 97.4%. Even at 8000 mA g^–1, a satisfactory capacity of 326.3 mAh g^–1 can be delivered. When tested in the full cell, a capacity of 438.5 mAh g^–1 with capacity retention of 85.0% is manifested after 80 cycles based on the mass of the anode. The appealing structure and electrochemical performance of this material demonstrate its great promise for applications in practical rechargeable batteries