Electrochemical and Structural Characterization of LiNi1 − y Co y O 2 ( 0 ≤ y ≤ 0.2 ) Positive Electrodes during Initial Cycling

The initial charge/discharge behavior of LiNi 1-y Co y O 2 (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-y Co y O 2 (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-x Ni 1-y Co y O 2 are simultaneously oxidized and that the local structure of MO 6 (M = Ni, Co) octahedra is slightly distorted upon lithium deintercalation.