Lab-scale coin-cell supercapattery assembled with nickel cobaltite/rGO nanocomposite electrodes for hybrid energy storage

Hybrid energy storage devices that bridge the gap between batteries and supercapacitors are critical for next-generation portable and high-power applications. In this work, a lab-scale coin cell asymmetric supercapattery device is fabricated using nickel cobaltite/reduced graphene oxide (NiCo 2 O 4 /rGO) nanocomposites as the positive electrode and activated carbon as the negative electrode. NiCo 2 O 4 /rGO nanocomposites with varying rGO contents (1, 3, and 5 wt%) were synthesized via an in situ hydrothermal method, followed by calcination to enhance crystallinity. Electrochemical studies in an open-cell configuration using 2 M KOH revealed that the optimized NCOG5 electrode exhibited superior charge storage performance of having specific capacity of 1852 C g −1 at 1 A g −1 with low charge-transfer resistance (2.58 Ω). An asymmetric coin cell supercapattery (NCOG5//AC) was assembled and operated stably over a wide voltage window of 1.8 V. The device achieved a maximum specific power density of 801 W kg −1 with a specific energy density of 65 Wh kg −1 at a current density of 1 A g −1 . The full device demonstrated combined battery-type and capacitive behaviour, and retained 92.28% of its initial capacitance after 5000 charge–discharge cycles at 5 A g⁻¹ .