Electrochemical and structural characterization of LiNi_1-yCo_yO₂ (0 ≤ y ≤ 0.2) positive electrodes during initial cycling

The initial charge/discharge behavior of LiNi_1-yCo_yO₂ (0 ≤ y ≤ 0.2) positive electrodes has been closely examined by neutron diffraction, X-ray diffraction, X-ray absorption, and electrochemical methods. Charge/discharge experiments and neutron diffraction refinements show that capacity loss during the initial cycling of LiNi_1-yCo_yO₂ (0 ≤ y ≤ 0.2) increases linearly with the excess nickel content controlled by cobalt substitution for nickel. Charge/discharge cycling with gradually increasing depth of charge indicates that most of the initial capacity loss takes place in the early stages of the first charge. X-ray absorption near-edge spectra reveal that the nickel and cobalt ions in Li_1-xNi_1-yCo_yO₂ are simultaneously oxidized and that the local structure of MO₆ (M = Ni, Co) octahedra is slightly distorted upon lithium deintercalation.