Quantitative analysis of Li contents in Li_xCoO_2 cathodes via Rietveld refinement

摘要

Rietveld refinement of Li_xCoO_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) A, c= 14.052(1) A. The error convention used in this paper is 3σ of standard deviations obtained from Rietveld refinement output.