Effects of Na+ contents on electrochemical properties of Li1.2Ni0.13Co0.13Mn0.54O2 cathode materials

The Li1.2−xNaxNi0.13Co0.13Mn0.54O2 (0 ≤ x ≤ 0.1) cathode materials have been synthesized by a solid-state reaction method. The effects of the Na+ contents on the structure, surface components and electrochemical performance are studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electrochemical techniques. The XRD data indicate that the Li1.2−xNaxNi0.13Co0.13Mn0.54O2 samples evolve from a sole layered structure (0 ≤ x ≤ 0.02) to a mixture of Na+-contained layered structure (0.02 < x ≤ 0.1), which would transform into the single layered structure after the initial charge and discharge process. XPS data demonstrate that some of the Na+ ions could be reversibly de-/re-intercalated for the Li1.2−xNaxNi0.13Co0.13Mn0.54O2 materials. An electrochemical test reveals that a small amount of Na+ (x ≤ 0.02) in the Li1.2−xNaxNi0.13Co0.13Mn0.54O2 materials can significantly increase the rate capacity, yet the capacity retention becomes worse. We also find that the capacity retention increases with the Na+ contents.