Diffusion-Controlled Lithium Storage in Spinel LiCuFe₂O₄ for Aqueous Rechargeable Lithium-Ion Batteries

Spinel LiCuFe₂O₄ was synthesized by a co-precipitation route and evaluated as a cathode material for aqueous rechargeable lithium-ion batteries. The phase-pure cubic spinel structure was confirmed by powder X-ray diffraction, while scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy revealed aggregated particles with homogeneous distribution of Li, Cu, Fe and O. The electrochemical behaviour of LiCuFe₂O₄ was investigated in saturated Li₂SO₄ aqueous electrolyte using a three-electrode configuration by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy. Cyclic voltammograms display a well-defined Fe²⁺/Fe³⁺ redox couple with peak currents scaling linearly with the square root of the scan rate, indicating a predominantly diffusion-controlled lithium storage process. In half-cell tests, the LiCuFe₂O₄ electrode delivers an initial discharge capacity of 136 mAh g⁻¹ and maintains 121 mAh g⁻¹ over 200 cycles at a current density of 0.005 mA g⁻¹, demonstrating good capacity retention in aqueous media. A full cell assembled with LiCuFe₂O₄ as the cathode and carbon black as the anode exhibits stable cycling with high coulombic efficiency over extended cycling. Impedance analysis shows a relatively low charge-transfer resistance and a clear Warburg-type diffusion response, consistent with efficient Li⁺ transport at the electrode-electrolyte interface. These results identify co-precipitation-derived spinel LiCuFe₂O₄ as a promising cathode candidate for safe, aqueous rechargeable lithium-ion batteries.