The present study reports the successful green synthesis of Nickel (Ni) and Nickel–Lithium Oxide (Ni–Li₂O) composite nanoparticles. Powder X-ray diffraction (XRD) analysis confirmed the formation of both Ni and Ni–Li₂O composite nanoparticles with a Face-Centered Cubic (FCC) crystal structure. The average crystallite size of the Nickel nanoparticles was found to be 37.97 nm, while that of the Ni–Li₂O composite nanoparticles was 39.60 nm. The respective lattice parameters obtained for both Nickel (Ni) and Nickel–Lithium Oxide (Ni–Li₂O) composite nanoparticles showed good agreement with their reference JCPDS data. The morphological analysis of the synthesized Ni and Ni–Li₂O nanoparticles revealed noticeable agglomeration and cluster formation among the particles. The UV-Visible Spectroscopy analysis results and the tauc plot showed that, the Band gap of Nickel (Ni) nanoparticles was found to be 2.1 eV and the Band gap of Nickel-Lithium Oxide (Ni-Li2O) composite nanoparticles was found to be 1.9 eV. The FTIR results showed that the various functional groups present in the Nickel (Ni) and Nickel-Lithium Oxide (Ni-Li2O) composite nanoparticles such as stretching vibration bond of nickel and lithium oxide nanoparticles. It is found that these functional groups are responsible for reducing the required nanoparticles from the precursors. The electrochemical performance, evaluated through Cyclic Voltammetry (CV), revealed that the Nickel–Lithium Oxide (Ni–Li₂O) composite nanoparticles exhibited enhanced behavior when tested with electrolytes such as sulfuric acid (H₂SO₄) and disodium sulfate decahydrate (Na₂SO₄•10H₂O). The Ni–Li₂O composite nanoparticles demonstrated superior performance, making them promising candidates for battery applications. The average specific capacitance of the Ni–Li₂O nanoparticles was found to be approximately 320.38 F/g.
