Electrical and Optical Properties of Na2/3MnO2 Compound

Sodium-ion batteries (SIBs) are considered to be an important substitute for lithium-ion batteries (LIBs) [1–3] in large-scale electrochemical energy storage systems due to their low cost, widely used raw materials and reaction mechanism that is similar to lithium-ion batteries (LIBs) [4–6]. Among them, layered NaxMnO2 (M is a transition metal) is considered one of the most promising SIB cathode materials and can provide a stable two-dimensional (2D) ion diffusion channel for sodium ion extraction and insertion. Na2/3MnO2 was synthesized by the conventional solid-state reaction. The x-ray diffraction show the Na2/3MnO2 sample crystallize in orthorhombic system with Cmcm space group and the cell parameter are a=2.8384Å, b=5.3137 and c=11.1503Å, the optical properties were studied and showed a gap energy equal to 3.5eV which confirms the semiconductor character of this compound. The analysis of the electrical data of the impedance spectra and the imaginary part of the complex modulus shows the presence of two types of relaxations corresponding to the grain and grain boundary effects in the two compounds. The equivalent circuit was chosen and the electrical conductivity was analyzed. In addition, the frequency behavior of the AC conductivity of this sample was analyzed using Joncher's universal law.