A Polyol‐Mediated Synthesis of Li 0.5 Co x Fe 2.5– x O 4 ( x = 0, 0.5, 1.0, 1.5, 2.0, 2.5) and Its Characterization for a High‐Performance Supercapacitor

In this work, nanostructured Li 0.5 Fe 2.5 –x Co x O 4 was synthesized via the polyol method, a simple yet highly controllable and regenerative route that enables precise tuning of particle size, an essential criterion for next‐generation energy storage devices. Structural analysis by X‐ray diffraction, Fourier transform infrared spectroscopy, and Raman spectra confirmed the formation of a pure spinel phase, with crystallite sizes calculated using the Scherrer equation and Halder–Wagner plot. Morphological, energy‐dispersive spectroscopy, and X‐ray photoelectron spectroscopy analysis studies displayed nearly spherical nanoparticles with uniform distribution and oxidation state of constituent elements. Electrochemical characterization demonstrated notably, the electrode achieved a specific capacitance of 1303.33 F/g at 5 mA/cm 2 . Importantly, the electrode exhibited excellent cyclic stability, retaining 91.33% capacitance after 5 000 GCD cycles, demonstrating strong resistance to structural degradation during long‐term operation. The electrochemical impedance spectroscopy analysis further revealed a significant reduction in both series resistance ( R s ) and charge transfer resistance ( R ct ) with increasing cobalt substitution, confirming improved conductivity and accelerated redox kinetics. The superior performance achieved highlights the novelty and promise of Co‐substituted lithium oxide as a robust electrode material. Their rare combination of high capacitance, stable redox activity, and structural integrity positions them as strong candidates for future supercapacitor technologies and next‐generation energy storage solutions.