Synthesis and physical properties of NaxTO2 (T = Mn, Co) nanostructures for cathode materials in Na-ion batteries

We prepared NaxTO2 (T = Mn, Co) nanostructures to use as cathode material in Na-ion batteries. The Rietveld refinement of X-ray diffraction data confirms the hexagonal symmetry. Scanning and transmission electron microscopy measurements show hexagonal and rod-shape morphology for T = Co and Mn, respectively. The magnetic measurements indicate the presence of variable oxidation states of Mn/Co ions, but no long range ordering till 5K. We find that the Na0.6MnO2 is highly insulating whereas Na0.7CoO2 is semiconducting in nature. The conduction in Na0.7CoO2 takes place through both variable range hopping (VRH) as well as activation mechanisms in different temperature ranges. However, for Na0.6MnO2 the VRH prevails at elevated temperatures. Furthermore, the coin cells have been fabricated and tested the electrochemical behavior using cyclic voltammetry, which confirms the reversibility of Na-ions during intercalation/de-intercalation.