Mimics of microstructures of Ni substituted Mn1−xNixCo2O4 for high energy density asymmetric capacitors

The preparation of nanostructured hierarchical Mn1−xNixCo2O4 metal oxides as efficient supercapacitors of different structures and configurations especially for the miniaturized electronics is still a challenge. In this context, we report template free facile hydrothermal synthesis of hierarchical nanostructured Mn1−xNixCo2O4 with excellent supercapacitive performance. Significantly, the morphology of pure MnCo2O4 transformed from 3D microcubes to 1D nanowires with incorporation of Ni. The electrochemical study shows highest specific capacitance i.e. 1762 F/g for Mn0.4Ni0.6Co2O4 with high cycling stability of 89.2% which is much higher than pristine MnCo2O4 and NiCo2O4. Later, asymmetric capacitor has been fabricated successfully using Mn0.4Ni0.6Co2O4 nanowires as positive electrode and activated carbon (AC) as negative electrode in a KOH aqueous electrolyte. An asymmetric cell could be cycled reversibly in the high-voltage range of 0–1.5 V and displays intriguing performances with a specific capacitance of 112.8 F/g (6.87 F/cm3) and high energy density of 35.2 Wh/kg (2.1 mWh/cm3). Importantly, this asymmetric capacitor device exhibits an excellent long cycle life along with 83.2% specific capacitance retained after 2000 cycles.