Electrochemical and ion-kinetics performances of BMOF-derived Co3O4/CaO cathodes for calcium-ion batteries

Despite its theoretically appealing potential, the challenge to discover high-performance cathode materials with high energy density and low production cost for calcium-ion batteries (CIBs) remains unsolved. Therefore, this study examines the synthesis and characterization of calcium/cobalt-based oxides derived from bimetallic-organic frameworks (Ca/Co-BMOFs) in calcium-based organic electrolytes. The Ca/Co-BMOF precursors are synthesized using a simple room temperature co-precipitation method and further annealed in an air atmosphere to produce Ca/Co-oxides composites. By modulating the metal ratio in precursor, two MOF-derived metal oxides are produced, namely Co₃O₄/CaO and CaCO₃/Ca₂Co₂O₅. X-ray diffraction (XRD) spectroscopy and field-emission scanning electron microscopy (FESEM) reveal that the modulations of metal in precursor resulted in different bimetallic oxides with structure and morphology variations which influence the Ca²⁺ ion kinetics. The ion kinetics analysis reveals that cathode charge storage reactions are surface and diffusion-controlled. CaCO₃/Ca₂Co₂O₅’s capacitive contributions increase significantly with increasing scan rate, indicating a more dominant surface-controlled mechanism at high scan speeds, contributing to the lower overall electrochemical performance at higher rates. Further, the electrochemical studies demonstrate that nanosphere Co₃O₄/CaO produces a competitive specific capacity of 165.56 mAh g⁻¹ at 250 mA g⁻¹ and retains 85% of its reversible capacity after 70 cycles at various current densities ranging from 500–2000 mA g⁻¹, which is superior to the nanoplate CaCO₃/Ca₂Co₂O₅. This study highlights the feasibility of metal–organic framework (MOF)-derived metal oxides to be used as cathode materials for CIB applications.

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