Nanostructured transition metal oxide synthesis possessing high energy density and stability is desirable for supercapacitors. Herein, we synthesize three-dimensional NiCo2O4 (NCO) nanosheets with oxygen vacancies induced by sustainable and environmentally benign electrodeposition assisted chemical reduction process. Oxygen vacancies increase the conductivity, adsorptivity, and the active surface area, thereby enhancing the charge storage capabilities. The binder-free NCO delivers the highest specific capacitance (Csp) of 2065 F g−1 at 1 A g−1, retaining 89.30 % of its initial value at 10 A g−1 after 10,000 continuous charge-discharge (CD) cycles. An asymmetric supercapacitor (ASC) fabricated shows remarkable electrochemical properties with high energy density (Emax) of 28.6 Wh kg−1 and power density (Pmax) of 7.5 kW kg−1. The assembled ASC reports exceptional cyclic retention of 90.6 % for 10,000 CD cycles with practical demonstration. The approach used herein is suitable for eco-friendly supercapacitor electrode fabrication with large scale manufacturing capability and less capital investment. © 2020 Wiley-VCH GmbH