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.