Neutron diffraction and electrochemical studies of Na _0.79CoO₂ and Na_0.79Co_0.7Mn _0.3O₂ cathodes for sodium-ion batteries

Na_0.79CoO₂ and Na_0.79Co _0.7Mn_0.3O₂ 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 Na_0.79Co _0.7Mn_0.3O₂ composition showing a more stable discharge capacity up to 60 cycles.