Li⁺-Ion Extraction/Insertion of Ni-Rich Li_1+x(Ni_yCo_zMn_z)_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 insitu X-ray diffraction (XRD) and Raman spectroscopy measurements for the first Li-ion extraction/insertion (charge/discharge) processes of nickel-rich Li_1+x(Ni_yCo_zMn_z)_wO₂ (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 insitu (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≈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 insitu studies of these cathode materials by Raman spectroscopy.