Neutron Diffraction and Electrochemical Studies of Na0.79CoO2 and Na0.79Co0.7Mn0.3O2 Cathodes for Sodium-Ion Batteries

Na0.79CoO2 and Na0.79Co0.7Mn0.3O2 with a layered hexagonal structure (P2-type) were synthesized by the Pechini process followed by heat-treatment at elevated temperatures in order to achieve the crystalline phases. The samples were characterized with X-ray diffraction, neutron diffraction, magnetic measurements and electrochemical charge-discharge cycling. X-ray diffraction confirmed the presence of P2 layered hexagonal structure after heat-treatment at 900°C in air. Neutron diffraction patterns confirm Mn substitution on Co sites without forming pronounced Mn-Co ordering. Cyclic voltammetry showed the oxidation and reduction peaks of Co and Mn, indicating the intercalation and de-intercalation behavior of the Na ions. A discharge capacity of 60 mAh/g was achieved for both compositions, with the Na0.79Co0.70Mn0.3O2 composition showing a more stable discharge capacity up to 60 cycles.