Mesoporous manganese dioxide cathode prepared by an ambient temperature synthesis for Na-ion batteries

Abstract

A manganese dioxide (γ-MnO₂) cathode was prepared by a simple ambient temperature redox reaction method for Na-ion batteries. The X-ray diffraction (XRD) pattern of the as-prepared sample annealed to low-temperatures (∼200 °C) revealed diffraction peaks confined to the orthorhombic phase of γ-MnO₂. The particle morphology of the sample, as revealed by the electron microscopy studies, was comprised of aggregated nanowire crystallites with diameters and lengths in the range of 2–3 and 25–40 nm, respectively. From the N₂ adsorption and Brunauer Emmett Teller (BET) studies, the average pore diameter and the surface area of the annealed γ-MnO₂ was determined to be 3.77 nm and 148 m² g⁻¹ respectively and thereby the mesoporous sample characteristics were confirmed. When employed in a Na/MnO₂ cell, the mesoporous γ-MnO₂ cathode registered initial discharge and charge capacities of 234 and 233 mA h g⁻¹ with almost 100% Coulombic efficiency. Although gradual capacity fading was observed on successive electrochemical cycling, the present study confirms the use of mesoporous electrodes as suitable Na-intercalation/de-intercalation hosts for emerging sodium battery applications.