NiS2 nanosheet arrays on stainless steel foil as binder-free anode for high-power sodium-ion batteries

Owing to the wide range and low cost of sodium resources, sodium-ion batteries (SIBs) have received extensive attention and research. Metal sulfides with high theoretical capacity are used as promising anode materials for SIBs. This paper presents the electrochemical performance of the binder-free NiS2 nanosheet arrays grown on stainless steel (SS) substrate (NiS2/SS) using an in situ growth and sulfidation strategy as anode for sodium ion batteries. Owing to the close connection between the NiS2 nanosheet arrays and the SS current collector, the NiS2/SS anode demonstrates high rate capability with a reversible capacity of 492.5 mAh.g(-1) at 5.0C rate. Such rate capability is superior to that of NiS2 nanoparticles (NiS2/CMC: 41.7 mAh.g(-1) at 5.0C, NiS2/PVDF: 7.3 mAh.g(-1) at 5.0C) and other Ni sulfides (100-450 mAh.g(-1) at 5.0C) reported. Furthermore, the initial reversible specific capacity and Coulombic efficiency of NiS2/SS are 786.5 mAh.g(-1) and 81%, respectively, demonstrating a better sodium storage ability than those of most NiS2 anodes reported for SIBs. In addition, the amorphization and conversion mechanism during the sodiation/desodiation process of NiS2 are proposed after investigation by in situ X-ray diffraction (XRD) measurements of intermediate products at successive charge/discharge stages.