Non-destructive observation of plated lithium distribution in a large-scale automobile Li-ion battery using synchrotron X-ray diffraction

Automotive Li-ion batteries need to be rapidly chargeable to satisfy user requirements. However, increasing the charging rate of Li-ion batteries also increases the risk of metallic lithium precipitation, an unwanted side reaction. Therefore, the non-destructive detection of lithium electrodeposition is of significant interest to researchers and developers from numerous automobile manufacturers. In this study, we report the detection of electrodeposited lithium in an automotive prismatic battery using synchrotron X-ray diffraction (XRD). High-energy (61 keV) X-rays are used to non-destructively observe the spatial distribution of the deposited lithium in the large-scale battery. The relative amount of deposited lithium is determined by calculating the area of the Li 110 XRD peak, and the state of charge (SOC) of the positive electrode is estimated from the position of the 101 peak of the positive electrode material (LiNi1/3Co1/3Mn1/3O2). We record the XRD patterns at 72 points on the electrodeposited cell and map the concentrations of deposited lithium and SOC of the positive electrode; subsequently, we discuss the correlations between the two distributions. A unique finding of this study is the observation of unusual, nonuniform positive-electrode SOC in the cells where lithium electrodeposition occurs. This phenomenon merits further exploration toward concretely establishing the SOC-distribution–lithium-electrodeposition relationship.