Synthesis of Ternary Metal Oxides for Battery-Supercapacitor Hybrid Devices: Influences of Metal Species on Redox Reaction and Electrical Conductivity

Designing battery-type materials with good electrocapacitive performance and high electrical conductivity is necessary to improve the energy-storage capability of an battery-supercapacitor hybrid devices (BSH). Ternary metal oxides are synthesized by using a hydrothermal reaction with an extra metal of Mo, Fe, Cu, Zn, or Al incorporated in the nickel cobalt oxide as the battery-type material to enhance the electrical conductivity and generate numerous Faradaic reactions via the multiple oxidation state of transition metals. Because of the larger surface area of the nanosheet structure and the smaller charge transfer resistance with the participation of molybdenum, the best electrocapacitive performance among the ternary metal oxide electrodes is attained for the NixCoyMozO electrode, which is further optimized by tuning the Mo ratios in the precursor solution. An optimized NixCoyMozO electrode is prepared by using the Ni:Co:Mo ratio of 1:2:2. This electrode achieves an areal capacitance (CF) of 2.94 F/cm2, which is higher than those for the binary metal oxide electrodes of NixMoyO (1.11 F/cm2), CoxMoyO (1.63 F/cm2), and NixCoyO (1.45 F/cm2), inferring the success to improve the energy-storage ability of the electrode by incorporating more transition metals in the oxide as the electrocapacitive material. An BSH based on the NixCoyMozO positive electrode and an activated carbon negative electrode shows a CF value of 126 mF/cm2 at 10 mA/cm2, a potential window of 1.8 V, and a maximum energy density of 22.02 Wh/kg at a power density of 3.50 W/kg. This result provides new blueprints for constructing multiple metal oxides as the battery-type material for achieving more Faradaic reactions and higher electrical conductivity, and hence for enhancing the energy-storage capability of an BSH.

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