NiGa2O4 Nanosheets in a Microflower Architecture as Anode Materials for Li-Ion Capacitors

Because of its lower toxicity, lower cost, high chemical and thermodynamic stability, and abundant reserves, NiO has attracted extensive attention and research in the field of energy storage. However, its application for Li-ion hybrid capacitors (LIHC) is limited by its single energy storage mechanism, large volume expansion during the cycling process, and slow kinetics process, which makes it difficult to match with carbon electrode. Here, through simple hydrothermal growth and subsequent calcination treatment, a NiGa2O4 material that is deposited by nanosheets into nanoflower shape is obtained. X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) were used to characterize the sample. The results showed that NiGa2O4 with the self-assembled micronflower with nanosheet was successfully prepared without heterophase. Subsequently, half-cells electrochemical test showed that the material had a mixed energy storage mechanism combining the alloy reaction to Ga with the conversion reaction to Ni. The combination of the two energy storage mechanisms makes NiGa2O4 have better cyclic stability than NiO. By calculation of the relationship between peak current and scanning speed, b = 0.94 of NiGa2O4 is obtained, and its electrochemical behavior is closer to the pseudocapacitance behavior caused by surface redox reaction than NiO. Consequently, the NiGa2O4//AC LIHC device exhibits excellent cycling stability (capacity retention of 82% after 8000 cycles), high energy density of 104.89 Wh kg(-1) (at 200 W kg(-1)), and high power density of 3999 W kg(-1) (at 25.44 Wh kg(-1)). Therefore, this NiGa2O4 with nanosheets in a microflower architecture, double energy storage mechanism, and fast kinetic process is expected to replace NiO as the next generation of research hotspot.