<i>In situ</i> X-ray spatial profiling reveals uneven compression of electrode assemblies and steep lateral gradients in lithium-ion coin cells
John Okasinski, Ilya A. Shkrob, Andrew Chihpin Chuang, Marco‐Tulio F. Rodrigues, Abhi Raj, Dennis W. Dees, Daniel P. Abraham
Abstract
Coin cells are used extensively as test devices in battery research for evaluation of new materials and optimization of cycling protocols. In this study, in situ X-ray diffraction profilometry is used to characterize spatial distribution of the active materials, lithiation, and phase distribution in electrodes of NCM523/graphite coin cells. The X-ray data indicate uneven areal compression of the electrode assembly in such cells, which we trace to a specific design feature that leads to elastic deformation of a metal spacer. Steep lithiation gradients observed in the electrodes imply radially-dependent resistivity, for which uneven compression of the separator is a likely cause. Electrochemical model calculations suggest that variable porosity of the polymer separator would account for the salient features of spatial profiles observed in these coin cells.