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Abstract :
[en] Doped sodium-ion oxide materials have attracted increasing attention due to their potential to enhance the structural, electronic, and electrochemical properties of electrode materials. Among them, layered AMO2-type oxides remain, for more than three decades, highly promising cathode candidates for both fundamental research and practical sodium-ion battery applications. In this work, Na2/3Mn0.8 Mg0.2 O2 was successfully synthesized by the solid-state reaction method and crystallized in an orthorhombic structure with the Cmcm space group. Structural analysis revealed that Mg2+ incorporation induces a compression of the MnO6 octahedra. The electrical and dielectric investigations, performed as a function of temperature and frequency, evidenced contributions associated with sodium ions mobility. The weak temperature dependence of the conductivity confirms a thermally activated transport process. The activation energies related to grain conductivity, grain-boundary conductivity, relaxation frequencies (ωmax1,2) and DC conductivity, extracted respectively from Nyquist plots, electric modulus formalism, and JPL fitting, were found to be lower than 0.1 eV. Furthermore, the evolution of the frequency exponent s and the obtained activation energies indicate that the charge transport mechanism is governed by the overlapping large polaron tunneling (OLPT(i)) model, with a lower hopping energy WH0 compared to the undoped compound. These findings suggest that sodium-ion migration occurs through a tunnelling process between localized states. The present study provides valuable insights into the conduction mechanism of Mgdoped sodium manganese oxides and highlights their potential for next generation sodium-ion battery technologies.
