Nickel Fluoride Nanorods as Anode Materials for Li-Ion Hybrid Capacitors

Lithium-ion hybrid capacitors (LIHCs) are considered as promising energy storage devices due to their high energy density of lithium-ion batteries and excellent power density of supercapacitors. The electrode material is the key to the performance of LIHCs. Therefore, a rod-like nanostructure of NiF2 with a clear morphology was prepared by a simple hydrothermal method. The nanorod structure of NiF2 shortens the transport distance of lithium ions and provides more active sites, thus showing excellent electrochemical performance. The specific capacity of the NR-NiF2 electrode can reach 379 mA h g–1 after 500 cycles at 0.1 A g–1 and remains at 61 mA h g–1 after 10,000 cycles (a current density of 2 A g–1). Meanwhile, according to the fitting results of the peak current and sweep rate, b = 0.95 is obtained, indicating that the electrochemical behavior of the NR-NiF2 material is dominated by pseudocapacitance. Furthermore, the LIHCs of NR-NiF2//AC are constructed and exhibit a high energy density of 87 W h kg–1(at 96 W kg–1), a high power density of 6079 W kg–1 (at 27 W h kg–1), and an excellent cycle stability (capacity retention of 69% after 5000 cycles at 1 A g–1). Hence, NiF2 nanorods with fast kinetic properties are a promising choice as an anode material for LIHCs.