Conduction mechanism and electrochemical properties of P2-Na2/3Fe1/3Mn2/3O2 for Na-ion batteries

Abstract

Layered transition metal oxides Na_xFe_1-yMn_yO₂ represent a cutting-edge cathode material for sodium-ion batteries because they demonstrate high capacity, excellent cycle rate, good electrochemical stability, and long lifetime. The widely used solid-state reaction method was utilized to prepare Na_2/3Fe_1/2Mn_2/3O₂ cathode active material. Using Rietveld refinement of X-ray diffraction data, the hexagonal system with P6₃/mmc space group and lattice constants a = b = 2.9184(9) Å and c = 11.2525(6) Å was identified. Scanning electron microscope analysis enables us to examine the morphology of this material. The optical band gap was calculated throughout the UV–visible spectroscopy in the 200–800 nm wavelength range. The gap energy was estimated to be equal to 2.60 eV. The electrical study relying on the complex impedance of the P2 compound confirms the presence of the three distinct phases with different conductivity behaviors. The semiconducting behavior has two phases: the first occurs for T ≤ 383 K with the NSPT mechanism, and the second occurs for T ≥ 423 K with the CBH mechanism. The electrochemical performance of this material was assessed on CR2032 coin-type half-cell configurations by investing galvanostatic charge-discharge cycling in the voltage range of 2–4.2 V. Up to 120 mAh g⁻¹, the cathode active material shows a high discharge capacity. When the scan rate is raised, the redox peaks exhibit a slight shift, indicating that the material has good structural stability and minimal polarization.