Investigation of the Structural Changes in Li[NiyMnyCo(1−2y)]O2 (y = 0.05) upon Electrochemical Lithium Deintercalation

A systematic study has been performed to investigate the structural changes of Li[Ni 0.05 Mn 0.05 Co 0.90 ]O 2, one member of the Li[Ni y Mn y Co (1−2 y ) ]O 2 series with low Ni/Mn content, upon electrochemical lithium deintercalation. X-ray diffraction (XRD), X-ray absorption near-edge spectroscopy (XANES), and nuclear magnetic resonance (NMR) measurements were performed, and the results from these experiments provided a detailed picture of the whole delithiation process. Oxidation of not only Ni 2+, but also some Co 3+, is seen in the beginning of Li extraction (less than 0.15 mol removed), the ions located closest to Mn 4+ being extracted first. Further deintercalation (additional 0.2 mol of Li removal) induces an insulator to metal transition that is similar to that reported for LiCoO 2 . However, this reaction follows a solid solution mechanism even for this low level of substitution, rather than the two-phase reaction reported for the Ni, Mn-free oxide. When half of the Li ions are extracted, the electrochemical signature for lithium vacancy ordering in the host framework is observed. The NMR results for deintercalation of more than 50% Li were compared to those for Li x CoO 2 at similar stages of charge, which are reported here for the first time; they indicate that the behavior of these two phases at these potentials is very similar. When the batteries are charged to voltages higher than 4.6 V, very few lithium ions remain in the structure and the O3 to O1 phase transition occurs.