Impact of P-Doped in Spinel LiNi0.5Mn1.5O4 on Degree of Disorder, Grain Morphology, and Electrochemical Performance

LiNi0.5-xP2xMn1.5-xO4 (x = 0, 0.005, 0.01, and 0.02) submicrograins in regular octahedral shape with merely {111} surface facets and truncated octahedral shape with both {111} and {100} surface planes were obtained by the solid-state reaction method. The effect of doping P on ions arrangement, grain morphology, and the electrochemical performance of lithium nickel manganese oxide was investigated. The characterizations of X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), and selected area electron diffraction (SAED) confirm more Mn3+ ions in the structure to enhance the cationic disorder degree of LiNi0.5Mn1.5O4 after P-doping. Comparing the LiNi0.5Mn1.5O4 and LiNi0.495P0.01Mn1.495O4 samples both with regular octahedral morpology, their electrochemical performance could be remarkably improved by more disordered transition metal ions arrangement leading to higher conductivity of Li-ions and electrons. However, when the amount of P-doping further increased, the rate and cycle ability of the LiNi0.480P0.04Mn1.480O4 sample in truncated octahedral shape worsen dramatically even with a higher degree of cationic disorder. This could be on account of the crystal planes starting to dominate the electrochemical performance instead of ions arrangement under high voltage and large rate: the {111} facet is more favorable to the lithium ion transport than the {100} crystal plane for LiNi0.5Mn1.5O4 submicrograins during charge and discharge.