Li+‐Ion Extraction/Insertion of Ni‐Rich Li1+x(NiyCozMnz)wO2 (0.005<x<0.03; y:z=8:1, w≈1) Electrodes: In Situ XRD and Raman Spectroscopy Study

We present the results of our in situ X-ray diffraction (XRD) and Raman spectroscopy measurements for the first Li-ion extraction/insertion (charge/discharge) processes of nickel-rich Li1+x(NiyCozMnz)(w)O-2 (0.005 < x < 0.03; y:z = 8:1, w is nearly 1) electrodes in Li cells. These cells were of a special design that provide in situ (at-work) measurements during electrochemical polarization and can be used for regular cycling tests of practical Li-battery electrodes. By using XRD measurements, it was established that, upon Li+ extraction, these cathode materials demonstrate structural transformations of the hexagonal phase (space group R-3m) H1 to another hexagonal phase H2 (with a lower Li-ion content in the lattice) and to domains comprising both of these two phases, coexisting at potentials E approximate to 4.2-4.3V. The above phases differ by the a and c lattice constants, which is in agreement with literature results. Evolution of the lattice constants with the electrode potential upon charge/discharge is shown to be in correlation with the differential capacity dQ/dE versus E plots and with some Raman parameters calculated from complementary in situ studies of these cathode materials by Raman spectroscopy.