Comparison of kinetic properties of LiCoO2 and LiTi0.05Mg0.05Ni0.7Co0.2O2 by impedance spectroscopy

New material based on LiNiO2 with some nickel atoms substituted for other metals has become increasingly popular as cathode materials for Li-ion battery due to higher capacity of LiNiO2 compared to traditionally used LiCoO2 and improved material stability and safety due to substitutes. However, rate capability of new materials was not extensively researched. The purpose of this investigation is to characterize by impedance spectroscopy all major kinetic steps of Li intercalation into conventional LiCoO2 and substitution-stabilized material LiTi0.05Mg0.05Ni0.07Co0.02O2 samples, provided by FMC. Very wide frequency range of impedance measurements (to 200 muHz) with acceptable duration was made possible by using Kumho Chemical Laboratories' one-shot FFT-impedance spectrometer. Availability of such low frequency data allowed confident estimation of diffusion and phase-change kinetic parameters. Results were analyzed in terms of transmission line model considering composite structure of electrode. Effects of particle size and mechanism of sample degradation with cycling were also investigated. (C) 2003 Elsevier B.V. All rights reserved.