Mesoporous NiS₂ Nanospheres Anode with Pseudocapacitance for High-Rate and Long-Life Sodium-Ion Battery

It is of great importance to exploit electrode materials for sodium-ion batteries (SIBs) with low cost, long life, and high-rate capability. However, achieving quick charge and high power density is still a major challenge for most SIBs electrodes because of the sluggish sodiation kinetics. Herein, uniform and mesoporous NiS₂ nanospheres are synthesized via a facile one-step polyvinylpyrrolidone assisted method. By controlling the voltage window, the mesoporous NiS₂ nanospheres present excellent electrochemical performance in SIBs. It delivers a high reversible specific capacity of 692 mA h g^-1 . The NiS₂ anode also exhibits excellent high-rate capability (253 mA h g^-1 at 5 A g^-1 ) and long-term cycling performance (319 mA h g^-1 capacity remained even after 1000 cycles at 0.5 A g^-1 ). A dominant pseudocapacitance contribution is identified and verified by kinetics analysis. In addition, the amorphization and conversion reactions during the electrochemical process of the mesoporous NiS₂ nanospheres is also investigated by in situ X-ray diffraction. The impressive electrochemical performance reveals that the NiS₂ offers great potential toward the development of next generation large scale energy storage.