In this study, NiCo₂O₄-based electrode materials (NiCo<inf>2</inf>O<inf>4</inf>-B, NiCo<inf>2</inf>O<inf>4</inf>-P, NiCo<inf>2</inf>O<inf>4</inf>-O, and NiCo<inf>2</inf>O<inf>4</inf>-E) were successfully synthesized using a facile chemical oxidation method, incorporating different additives such as polyvinylpyrrolidone (PVP), oleylamine, and ethylenediaminetetraacetic acid (EDTA). All samples exhibited hexagonal platelet morphology, with NiCo₂O₄-E showing a more porous structure. Electrochemical evaluation in a three-electrode system revealed battery-type behavior with prominent redox peaks. NiCo₂O₄-E delivered the highest specific capacitance of 2254 F/g at 1 mV/s, outperforming the other variants (NiCo₂O₄-B: 1201 F/g, NiCo₂O₄-P: 1529 F/g, NiCo₂O₄-O: 1606 F/g). GCD studies confirmed its high capacity of 700 C/g at 1 A/g. Transatti analysis indicated dominant inner-surface charge contribution (93.3%), and the material exhibited the highest active site density (9.76 × 1018). Although NiCo₂O₄-E retained 60% of its capacity after 5000 cycles, all samples showed nearly 100% coulombic efficiency. To evaluate practical applicability, a two-electrode solid-state asymmetric supercapacitor was fabricated using NiCo₂O₄-E as the positive electrode and activated carbon as the negative electrode. The device showed clear redox peaks in the CV profiles (0.0–1.5 V) and delivered stable GCD behavior up to 3 A/g. Notably, it retained 96% of its initial capacitance after 10,000 cycles at 3 A/g, with a consistent coulombic efficiency of 96%. Post-cycling EIS analysis confirmed improved charge transfer characteristics. These findings demonstrate that the EDTA-assisted NiCo₂O₄-E electrode exhibits excellent electrochemical performance and long-term cycling stability, making it a promising candidate for high-performance energy storage devices. © 2025 Elsevier B.V., All rights reserved.