Synthesizing nickel-based transition bimetallic oxide via nickel precursor-free hydrothermal synthesis for battery supercapacitor hybrid devices

The Ni foam can act as the nickel ion source and the current collector for synthesizing Ni-based compounds using the hydrothermal synthesis especially in the acid condition. Using Ni foam as the Ni²⁺ source can grow materials on the substrate directly and uniformly since nickel ions are released from substrate thoroughly. Nickel-based bimetallic oxides are intensively investigated as battery-type materials for battery supercapacitor hybrid devices (BSHD) because of high electrical conductivities and abundant transition states for inducing multiple redox reactions. In this study, Mo, Mn, Al, and W precursors are simply added in Ni precursor-free acid solution for hydrothermal synthesis using Ni foam as the nickel ion source and the current collector to synthesize Ni-based bimetallic oxide electrodes for BSHD. The morphology of nickel-based bimetallic oxide prepared with and without incorporating the structure-directing agent is also carefully discussed. The highest specific capacitance (C_F) of 1.80 F/cm² corresponding to the capacity of 4.54 mAh/cm² at 5 mA/cm² is attained for the nickel molybdenum oxide (Ni-Mo oxide) electrode. The Ni-Mo oxide-based BSHD shows a potential window of 1.8 V, a C_F value of 223.53 mF/cm² corresponding to the capacity of 1.45 mAh/cm² at 5 mA/cm², the maximum energy density of 4.60 Wh/kg at the power density of 0.21 kW/kg, and the C_F retention of 90% after 6000 times charging/discharging process.