Solid-state chemistry and electrochemistry of LiCo1/3Ni1/3Mn1/3O2 for advanced lithium-ion batteries

LiCo1/3Ni1/3Mn1/3O2 was prepared and characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), electron diffraction (ED), X-ray diffraction (XRD), and X-ray absorption fine structure (XAFS) to examine whether or not our first-principles calculation properly predicted a new lithium insertion material of LiCo1/3Ni1/3Mn1/3O2. High-resolution TEM image directly showed the layered structure having a cubic close-packed oxygen array. The [00.1] zone electron diffraction pattern showed a [root 3 x root 3]R30 degrees- type superlattice ordering in the transition metal layers. Rietveld analysis of powder XRD indicated that a structural model with a space group symmetry of P3(1)12 to present a [root 3 x 3]R30 degrees- type superlattice based on alpha-NaFeO2-structural type was adequate rather than that simply formulated with R (3) over barm. The Me-O bond lengths, i.e., 1.93, 2.03, and 1.92 angstrom, respectively, for Co, Ni, and Mn, obtained by K-edge EXAFS, were compared with those calculated from structural data determined by XRD assuming P3(1)12 and also with those of the first-principles calculation. These values were consistent with each other, which indicated that LiCo1/3Ni1/3Mn1/3O2 was a superlattice structure (P3(1)12; a = 4.959 angstrom, and c = 14.254 angstrom) consisting of Co3+ (t(2g)(6)e(g)(0)), Ni2+ (t(2g)(6)e(g)(2)), and Mn4+ (t(2g)(3)e(g)(0)). (c) 2005 The Electrochemical Society. All rights reserved.