Quantitative Analysis of Electrode Gaps in Prismatic Format Lithium-Ion Cells

Inside a lithium-ion cell, many layers of positive and negative electrodes are separated by an electrolyte-soaked separator. The positive and negative electrodes are engineered to be parallel so that the current distribution is uniform between each set of electrodes. This uniform current density further leads to uniform and predictable operation of the cell. During manufacturing, gaps can be introduced between the electrode layers. This is especially prevalent in prismatic cells because the cell manufacturing process involves inserting the pliable cell windings into a rigid cell housing and applying vacuum during electrolyte filling. These electrode gaps lead to non-uniform current densities, resulting in adverse effects such as incomplete lithiation, electrolyte degradation and possibly lithium plating. One method of non-destructively visualizing internal cell features is computed tomography (CT) scanning. Collecting data via this method is relatively fast with a typical cell scan takes ~1 hr and multiple cells being scanned at once. The output is commonly a set of 16-bit .tiff images that can be loaded and analyzed by a variety of software packages, with Volume Graphics Studio and Avizo being two common programs. These programs can be used to make a variety of measurements on individual datasets, but they lack the ability to conduct high-throughput analysis of many datasets. In this work, we have collected computed tomography data on prismatic cells cycled at a series of temperatures throughout their cycle life of up to 500 cycles. This data is analyzed for electrode gap features using a python code written to extract the number of gaps, gap locations, and gap volume for each dataset. This data is then aggregated for all datasets and analyzed for macroscopic trends. One finding from the study is that cells cycled at lower temperatures showed less expansion/contraction because of kinetics and less capacity passed overall, while cells cycled at higher temperatures showed increased gap volume due to material growth between layers. Additional findings and opportunities for future work will be presented. Image upload: Horizontal mapping of gap locations in individual cells from the three different temperature groups, where the size of the bubble correlates to the size of the gap. (0 Cycles: yellow, 100 & 200 cycles: blue, 500 cycles: purple) Figure 1