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

Abstract

A manganese dioxide (gamma-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 (similar to 200 degrees C) revealed diffraction peaks confined to the orthorhombic phase of gamma-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 N-2 adsorption and Brunauer Emmett Teller (BET) studies, the average pore diameter and the surface area of the annealed gamma-MnO2 was determined to be 3.77 nm and 148 m(2) g(-1) respectively and thereby the mesoporous sample characteristics were confirmed. When employed in a Na/MnO2 cell, the mesoporous gamma-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.