<p>Microwave plasma was used to improve the electrochemical and energy storage properties of Zn-doped NiO nanocomposites for supercapacitor application. The Zn-doped NiO nanocomposites were produced and their structural and electrochemical behavior was improved using a microwave plasma discharge. The plasma tailored structural and electrochemical properties of the nanocomposites showed notable changes in their specific capacitance and dielectric behavior. The modified nanocomposites exhibited porous morphology and defect-rich formation, which facilitates the ion diffusion and redox kinetics. The structural analysis confirmed the growth of FCC structures in the Zn-doped NiO nanocomposites. During plasma-nanocomposite interaction, the highly reactive species in the plasma discharge drove the etching and oxidation process, which resulted in an increase in activation and porosity of the surface. FTIR analysis of both pristine and modified nanocomposites verified the occurrence of Ni–O, Zn–O, and O–H vibrations in the nanostructures. The UV–vis absorption spectroscopy confirmed the narrowing of the energy band gap in the plasma modified nanocomposites. Dielectric measurements revealed a dielectric loss of 0.26, 1.27, and 0.33 for 5%, 10%, and 15% Zn-doping, respectively. The dielectric loss reduced to 0.25, 0.30, and 0.19, respectively, in the plasma modified nanocomposites. Electrochemical analyses of the plasma modified nanocomposites confirmed a high specific capacitance of 1176&#xa0;F/g in a 1&#xa0;M KOH electrolyte at a current density of 1&#xa0;A/g. The energy density and power density of the modified nanocomposites were estimated around 49.96 Wh/kg and 276&#xa0;W/kg, respectively.</p>