Methods—Spatially Resolved Diffraction Study of the Uniformity of a Li-Ion Pouch Cell

Abstract

A lab-made, multilayered Li-ion battery pouch cell is investigated using in-operando neutron powder diffraction (NPD) and spatially resolved powder X-ray diffraction (SR-PXRD) with the aim of investigating how to compare the information obtained from the two complementary techniques on a cell type with a complicated geometry for diffraction. The work focusses on the anode and cathode lithiation as obtained from the LiC6/LiC12 weight ratio and the NMC111 c/a-ratio, respectively. Neutron powder diffractograms of a sufficient quality for Rietveld refinement are measured using a rotation stage to minimize geometrical effects. Using SR-PXRD, the cell is shown to be non-uniform in its anode and cathode lithiation, with the edges of the cell being less lithiated/delithiated than the center in the fully charged state. The non-uniformity is more pronounced for high charging current than low charging current. The averaged SR-PXRD data is found to match the bulk NPD data well. This is encouraging as it seems to allow comparisons between studies using either of these complementary techniques. This work will also serve as a benchmark for our future studies on pouch cells with novel non-commercial cathode and/or anode materials.

Potential and Limitations of Research Battery Cell Types for Electrochemical Data Acquisition

“…The use of commercial, homogenous high quality electrodes [15] is absolutely necessary to show reproducible benchmark performance and guarantee that only cell building factors contribute to variances in electrochemical data. Therefore, commercial NMC111 as the cathode active material with an areal capacity of 1.75 mAh/cm 2 and graphite as the anode material with an areal capacity of 2.10 mAh/cm 2 (both measured @at 1 C in half‐cells, see Figures S6 and S7), resulting in a N/P ratio of 1.2, were investigated in calendered (cal) state for single‐sided coated (SS) electrodes, as well as in calendered (cal) vs. non‐calendered (uncal) state for double‐sided coated (DS) electrodes.…”