Synthesis, Structure, and Electrochemical Properties of the Layered Sodium Insertion Cathode Material: NaNi1/3Mn1/3Co1/3O2

A layered phase, NaNi1/3Mn1/3Co1/3O2 (NaNMC), isostructural to NaCoO2 has been synthesized. Stoichiometric NaNMC crystallizes in a rhombohedral R3̅m space group where Na is in an octahedral environment (O3-Type). Galvanostatic cycling on NaNMC vs Na cell indicated a reversible intercalation of 0.5 Na, leading to a capacity of 120 mAh·g–1 in the voltage range of 2–3.75 V and indicating its possible application in Na-ion batteries. The electrochemically driven Na insertion/deinsertion in NaNMC is associated with several phase transitions and solid solution regimes which are studied by in situ X-ray diffraction. Sodium deinsertion in NaxNMC resulted in sequential phase transitions composed of biphasic and monophasic domains. The composition driven structural evolution in NaxNMC follows the sequence O3 ⇒ O1 ⇒ P3 ⇒ P1 phases with an increased 'c' parameter, while the 'a' parameter remains almost unchanged.