In Situ Imaging of Electrode Thickness Growth and Electrolyte Depletion in Single-Crystal vs Polycrystalline LiNixMnyCozO₂/Graphite Pouch Cells using Multi-Scale Computed Tomography

Abstract

Single-crystal LiNixMnyCozO2 (NMC) materials have recently garnered significant academic and commercial interest as they have been shown to provide exceptional long-term charge-discharge cycling stability in Li-ion cells. Understanding the degradation mechanisms occurring in conventional polycrystalline NMC materials in comparison to the more stable single-crystal equivalents has become a topic of significant interest. In this study, we demonstrate how multi-scale, in-situ computed tomography can be used to characterize important changes occurring in wound pouch cells containing polycrystalline or single-crystal NMC. These changes include cell-level phenomena (such as deformation of the jelly roll and electrolyte depletion) as well as electrode-scale phenomena (such as electrode thickness growth and electrode cracking). A set of twenty-one cells were scanned in total, consisting of three different electrodes: polycrystalline NMC622, single-crystal NMC811, and single-crystal NMC532. These studies were designed to characterize the effects of varying C-rate, depth of discharge, and duty cycle, so this work includes an analysis of these factors as they relate to physical changes taking place at the cell and electrode level.

Quantifying the Impact of Charge Rate and Number of Cycles on Structural Degeneration of Li-Ion Battery Electrodes

“…The increasing porosity of particles was hypothesized to cause the irreversible expansion of cells throughout their cycle life by increasing the porosity of electrodes and therefore the volume. 34 The thickness of the NMC electrodes were quantified from the SEM images, however as seen in Fig. 5b the standard deviation of thicknesses measured was too large to confidently determine a trend.…”

From material properties to device metrics: a data-driven guide to battery design

“…For instance, silicon negative electrodes improve the energy density over traditional graphite electrodes in lithium-ion batteries even though they require lower active mass fractions (B90% vs. B96%) and higher porosities (B40% vs. B25%). [68][69][70][71] Fig. 3b also provides correlations for cell performance parameters.…”

Nondestructive Defect Detection in Battery Pouch Cells: A Comparative Study of Scanning Acoustic Microscopy and X‐Ray Computed Tomography

“…X-ray CT is the most widespread method for nondestructive testing to identify production-related defects in the battery industry. [30][31][32][33][34][35] The typical implementation in engineering fields utilizes a rotating sample stage between an X-ray tube and a flat panel detector, as illustrated in Figure 2. [36,37] CT measurements with synchrotron radiation are also possible.…”