Na 10 Mn 4 O 9 : Synthesis, Structure, and Electrochemical Properties

In the search for sustainable cathode materials for Na–ion batteries, Mn-based oxides have emerged as attractive candidates owing to their earth abundance and structural versatility. In this context, a comprehensive investigation of the electrochemical behavior of the sodium-rich Mn 2+ oxide Na 10 Mn 4 O 9 toward sodium extraction/insertion is presented. The structural framework of this phase, prepared through a simple solid-state synthesis at 450 °C, is built on MnO 4 and MnO 3 polyhedra. Seven sodium ions per unit formula can be extracted during the first charge, and XAS analysis reveals the main transformation into a layered Na x MnO 2 ·Na 2 O composite. Upon further cycling, once this phase is formed, the material delivers a reversible capacity of 110 mAh g –1 at an average potential of 2.24 V vs Na + /Na.