The metal oxides based various nanostructures are believed to be a promising candidate for the development of high-performance electrochemical energy storage devices. Nickel oxide (NiO) based nanostructures such as nanoplate, nanoflower, nanorod, and nanosheet have been successfully synthesized by facile, solution-based hydrothermal method. The electrochemical performances of different NiOs nanostructures have been investigated using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) techniques. When NiOs are used as an electrode in a three-electrode system, the maximum achieved specific capacity values are 355 C g-1, 294 C g-1, 284 C g-1, and 432 C g-1 at 1 A g-1 for NiO nanoplate, nanoflower, nanorod, and nanosheet respectively. The solid-state asymmetric supercapacitor device (NiO//AC) has been fabricated using a NiO nanosheet as an anode and activated carbon derived from sunflower seed (AC) as a cathode. The Asymmetric supercapacitor NiO//AC device exhibits a specific capacity of 83 C g-1 at a current density of 1 A g-1. In addition, NiO//AC delivers a maximum energy density of 39.49 Wh Kg-1 at a power density of 1.7 kW Kg-1 and a retention of 107.9 % is observed at 10000 charge/discharge cycles. © 2023, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.