Synthesis and Electrochemical Characterization of a Sodium Manganese Oxide By Facile Reduction Reaction for Sodium Ion Batteries

A non-stoichiometric composition of sodium manganese oxide (Na_xMnO_2+δ) cathode useful for sodium batteries was synthesized by an ambient temperature strategy that involves the facile reduction of aqueous sodium permanganate in sodium iodide and subsequent heat treatment at 600 °C.  A combined powder X-ray diffraction (PXRD) and synchrotron X-ray diffraction (SXRD) analyses confirmed the annealed sample to belong to a Na_xMnO₂ phase with a P2-hexagonal structure. The ICP results confirmed the stoichiometry of the sample to be Na_0.53MnO_2+δ. Electron microscopy studies revealed the particle size of the electrode to be in the range of a few hundred nanometers. The Na_0.53MnO_2+δ cathode delivered average discharge capacities of 170 mAhg^-1 with a stable plateau at 2.1 V for the initial 25 cycles versus sodium. Ex-situ XANES studies confirmed the reversible intercalation of sodium into Na_0.53MnO_2+δ and suggested the accommodation of over-stoichiometric Mn⁴⁺ ions to contribute towards electrode performance.