High-temperature supercapacitive performance of NiCo₂O₄ nanosheets: Effect of calcination and device operating temperature

Reliable energy storage and on-demand energy delivery are crucial during times of scarcity. Aqueous electrolytes are widely used in energy storage devices, but their performance is influenced by ambient temperature, especially in regions with significant temperature fluctuations. This study reports synthesis of NiCo₂O₄ (NCO) nanosheets through a solvothermal method, followed by calcination at different temperatures (300 °C, 400 °C, and 500 °C). A symmetric supercapacitor cell is fabricated and tested with 3 M Potassium hydroxide (KOH) electrolyte within an elevated temperature range [40 °C-80 °C], using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and impedance spectroscopy (EIS). Structural analysis confirms the formation of NCO-nanosheets with specific surface area of 110 m²/g, and X-ray Photoelectron Spectroscopy (XPS) analysis verifies the oxidation states. The NCO 300 sample exhibits the highest specific capacitance of ∼531 F/g at 10 mV/s and ∼244 F/g at 2 A/g. Impedance analysis reveals low bulk/charge transfer resistance, along with reduced activation energy, as confirmed by Arrhenius plot. NCO300 achieves a peak energy density of 33.87 Wh/kg at a power density of 842.07 W/kg. Capacitance increases with temperature across all samples, demonstrating excellent thermal stability of device. Practical application is confirmed by successfully illuminating a red light-emitting diode (LED), highlighting the potential of NCO-based supercapacitors for real-world high temperature energy storage solutions.