Improving\nthe Performance of the Layered Nickel Manganese\nOxide Cathode of Sodium-Ion Batteries by Direct Coating with Sodium\nNiobium Oxide

This research highlights\nthe efficacy of NaNbO<sub>3</sub> as a\ncoating for P2-Na<sub>2/3</sub>Ni<sub>1/3</sub>Mn<sub>2/3</sub>O<sub>2</sub> cathodes in sodium-ion batteries. The coating enhances the\nkinetic behavior and cyclability of the electrochemical cells, as\nshown by electrochemical measurements. XRD analysis indicates that\nNb does not incorporate into the cathode structure, implying a physical\ninteraction between the coating and the cathode material. XRF analysis\nand EDX mapping confirm the actual composition and uniform dispersion\nof elements throughout the sample, while the electron micrographs\nevidence the occurrence of NaNbO<sub>3</sub> particles modifying the\nsurface of the layered oxide. The Ni<sup>4+</sup>/Ni<sup>3+</sup> and\nNi<sup>3+</sup>/Ni<sup>2+</sup> redox pairs, along with the partially\nreversible oxidation of oxide to peroxide anions, contribute significantly\nto cell capacity, as revealed by XPS spectra. This last effect and\nthe appearance of a co-intercalated phase at high voltage are positive\nfactors to provide fast kinetics. Cyclic voltammograms show that samples\ncoated with 2–3% NaNbO<sub>3</sub> have superior rate capability,\nwith high capacitive response and apparent diffusion coefficients.\nThese samples also have low impedance at the electrode–electrolyte\ninterface, which helps deliver a high capacity at 5C. Further cycling\nat 1C shows improved cyclability in the bare and 3% coated samples,\ndue to their higher diffusion coefficients on charging. Notably, the\n3% NaNbO<sub>3</sub>-coated sample exhibits excellent cyclability\nbelow 0 °C, making it a promising cathode material for sodium-ion\nbatteries.