Improving Na Diffusion and Performance of P2-Type Layered NaLiMnCoNiO by Expanding the Interplanar Spacing.

Because of their high reversible capacity and wide operation voltage window, P2-type layered transition metal oxides are considered as one type of potential cathode candidate for sodium-ion batteries. However, they still suffer from low kinetics, phase degeneration, and ambiguous mechanism of Na diffusion. Here, we synthesized a P2-type NaLiMnCoNiO with a high Na diffusion performance by sintering a nanoplate-structural precursor with alkali metal salt and proposed a possible mechanism for improving Na diffusion. The as-prepared P2-type layered oxide presents a quasi-hexagon shape and demonstrates a discharge capacity of 87 mAh g at a current density of 875 mA g (5 C rate), twice that of the sample synthesized from a non-nanoplate particle precursor. Rietveld refinement and results of X-ray photoelectron spectroscopy reveal the probable mechanism that the expanded interplanar spacing along the c-axis orientation would facilitate Na diffusion during Na intercalation/deintercalation processes, and the expanded interplanar spacing may arise from a high oxidation state of transition metal ions.