Abstract: Spinel LiMn^₂O^₄ and LiNi_yCo_0.1－yMn_1.9O₄ (y=0, 0.05, 0.10) samples were prepared by a precipitation method. The structure, morphology, and electrochemical performance of the samples were characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), scanning electron micrographs (SEM), charge-discharge measurements, and electrochemical impedance spectra (EIS). The results of FT-IR and XRD indicated that the absorption band at about 519 cm^-1 shifts to the high frequency with the decrease of Ni content in LiNi_yCo_0.1－yMn_1.9O₄ samples and the lattice parameter(a) of LiMn^₂O^₄ samples decreases with the addition of Ni, Co, or Ni/Co. The SEM observation displayed that the LiNi_yCo_0.1－yMn_1.9O₄ samples have lower agglomeration degree and smaller particle size. The results of the electrochemical experiments showed that the improvements on the electrochemical performance of substituted samples have some different reasons, and the LiNi_yCo_0.1－yMn_1.9O₄ sample manifests better electrochemical performance in 4 V region due to its lower electrochemical polarization and larger diffusion coefficient of Li⁺ ions.

Key words: Lithium ion batteries, Substituted manganese spinel oxide, Precipitation, Electrochemical properties