Li⁺‐Ion Extraction/Insertion of Ni‐Rich Li_1+<i>x</i>(Ni_<i>y</i>Co_<i>z</i>Mn_<i>z</i>)_<i>w</i>O₂ (0.005&lt;<i>x</i>&lt;0.03; <i>y</i>:<i>z</i>=8:1, <i>w</i>≈1) Electrodes: In Situ XRD and Raman Spectroscopy Study

Abstract

Abstract 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 Li 1+ x (Ni y Co z Mn z ) w O 2 (0.005&lt; x &lt;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 ‐3 m ) 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 ≈4.2–4.3 V. 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 d Q /d E versus E plots and with some Raman parameters calculated from complementary in situ studies of these cathode materials by Raman spectroscopy.