Quantitative analysis of Li contents in Li x CoO 2 cathodes via Rietveld refinement

Rietveld refinement of Li x CoO 2 -type cathodes (where x =0.59–1.00) has been demonstrated to yield quantitative information about the Li occupancy with an error of about ∼10%. With careful X-ray diffraction (XRD) data collection, refinement, and proper calibration, accurate values can be obtained. Rietveld refinement tends to under-predict the Li occupancy values in charged (de-lithiated) cathodes as compared to ICP measurements. A Li-gradient model that assumes a decreasing concentration of Li from the particle core to its surface is discussed to explain this observation. The observed lattice parameters for the fully lithiated LiCoO 2 standard phase (R-3m symmetry) were a =2.8155(1) Å, c =14.052(1) Å. The error convention used in this paper is 3σ of standard deviations obtained from Rietveld refinement output.