Thermally tuned phase engineering of FeCo₂O₄ spinel electrodes for enhanced diffusion-controlled charge storage in battery-type supercapacitors

Controlled thermal treatment of spinel oxide electrodes is a critical technique to produce high-performance supercapacitor materials. Upon synthesis of FeCo₂O₄ nanoparticles via one step hydrothermal method, drop dried FeCo 2 O 4 /NF electrodes are heat treated at 200°C and 350°C to obtain the electrodes. Thermal treatment has altered morphology, crystallinity, phase evolution, subsequently affecting the electrochemical properties. The electrodes heated at 200°C has resulted in the moderate change in nanograin architecture of pours nature while enhancing crystallinity compared to the 350°C heat treated electrode. At higher temperature heating induces particle coalescence and particle phase segregation compared to the as synthesized nanoparticles. FeCo₂O₄-200 electrode demonstrates the superior electrochemical performance showing a specific capacity of 247.54 mAh g⁻¹ at 2 mA cm⁻² with a substantial diffusion-limited contribution (∼81%), indicating efficient ion transport and battery-type behavior. Electrochemical kinetics is optimized by heat treatment to obtain improved cycling stability (88.52% retention over 2500 cycles) and reduced charge transfer. FeCo₂O₄-200//FeCo₂O₄-200 A symmetric device showed high energy density of 11.33 Wh kg⁻¹ at 130.14 W kg⁻¹, capacitance enhancement (119.22%) was also enhanced due to the surface reconstruction and electrochemical activation. The study demonstrates that thermal engineering optimizes the porosity, number of active sites, to achieve the structure-property relationship to obtain high-performance spinel structure-based energy storage systems.