Oxygen Vacancies and Intermediate Spin Trivalent Cobalt Ions in Lithium-Overstoichiometric LiCoO₂

Abstract

Thermal treatments under a very wide range of oxygen pressures were used to probe the composition and defect nature of a lithium-overstoichiometric “Li x 0 CoO2” (x 0 > 1) sample using X-ray powder diffraction, 7Li NMR, and electrochemical tests. It was found that at 900 °C, under atmospheric and elevated oxygen pressures, the lithium-overstoichiometric sample gradually transformed to stoichiometric LiCoO2 by losing excess lithium in the form of Li2O. In addition, it was shown that the defect associated with Co2+ and oxygen deficiency as reported by Gorshkov et al. and Karelina et al. had a different NMR signature than that present in Li-overstoichiometric samples. Therefore, it is believed that oxygen vacancies are present but Co2+ ions are not present in Li x 0 CoO2 (x 0 > 1). This leads to a formula [Li]interslab[CoIII 1 - 3tCo3+(IS) 2tLit]slab[O2 - t], involving an intermediate spin configuration for 2t Co3+ ions in a square-based pyramidal site. This new model was supported by the NMR and magnetic data of the lithium-overstoichiometric sample and its deintercalated compounds. The effect of the defect on the end-of-discharge voltage profile during cycling was also discussed.

X‐ray Absorption Spectroscopic Study of LiCoO2 as the Negative Electrode of Lithium‐Ion Batteries

“…In contrast, the small decrease in the intensity of the peak around + 11 eV for the sample annealed at 850 8C could be indicative of a diminution in the ionicity of the cobalt by the annealing of possible traces of Co 3 + species near defect sites of the structure, that do not affect the XANES results to a great extent. The apparent shift falls within the experimental error and, thus, there is no clear evidence of cobalt oxidation during annealing, in agreement with Levasseur et al [24] Figure 2 shows the EXAFS spectra and corresponding Fourier transforms (corrected with the phase shift of the first shell) of the as-received, ground for 180 min, and heated at 850 8C LiCoO 2 samples. The distances computed from fitting with EXCURV98 are shown in Table 1.…”

Electronic phase diagram of the layered cobalt oxide systemLixCoO2(0.0≤xMotohashi1, Ono2, Sugimoto3 et al. 2009Phys. Rev. B838800View full textAdd to dashboardCite

“…This result is in good agreement with those previously reported. 28 On the other hand, the Li-deficient samples exhibit complicated magnetic behaviors. For x = 0.67 and 0.70, the value slightly increases with lowering temperature and then suddenly decreases at T t = 175-185 K. The magnetic anomaly involves temperature hysteresis of ⌬T = 4 K between the heating and cooling curves.…”

Synthesis of LiNi1/3Co1/3Mn1/3O2 cathode materials by using a supercritical water method in a batch reactor

“…3, the XRD pattern for LiNi 1/3 Co 1/3 Mn 1/3 O 2 is similar to that of Li 1.15 CoO 2 , both having a layered structure [21,33] Table 3. LiCoO 2 was identified as a layered structure with the space group symmetry of R-3m, in which lithium and cobalt were located at the octahedral 3a and 3b sites in an AB CA BC cubic-close-packed oxygen array [50]. The lattice parameters of Li 1.15 CoO 2 samples obtained from the Rietveld method are a = 2.816(4) Å and c = 14.052(1) Å, which are in good agreement with the literature data [3,21,44,51,52].…”

“…8. It is because the final composition of LiCoO 2 prepared by using the SCW method in this study is Li 1.15 CoO 2 , and this overlithiated Li 1.15 CoO 2 delivers a reduced discharge capacity even at the high C-rate range [44,50].…”