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 R (3) over barm 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 double right arrow O1 double right arrow P3 double right arrow P1 phases with an increased 'c' parameter, while the 'a' parameter remains almost unchanged.