Impact of Electrode Defects on Battery Cell Performance: A Review

Abstract

The continuing rise of electric mobility is driving demand for lithium‐ion batteries to unprecedented levels. To ensure efficient production of high quality, yet affordable battery cells, while making the best use of available raw materials and processes, reasonable quality assurance criteria are needed. A step of particular importance, affecting all downstream processes, lies in electrode manufacturing including mixing, coating, drying, and calendering. Several classes of defects which originate in these processes are well‐known and detectable using various methods. The crucial point, however, lies in the quantification of their electrochemical significance, i. e., in an evaluation, which defect types, sizes and concentrations can be tolerated without impacting cell performance. Herein, we review the still scarce literature on that topic. It is found that, although the impact of some defects is quite well understood, others almost completely lack an evaluation of their criticality. We finally make suggestions for further studies paving the way to deduce knowledge‐based quality assurance criteria for the large variety of coating defects occurring in lithium‐ion battery electrodes.

Efficient Analysis of Interdependencies in Electrode Manufacturing Through Joint Application of Design of Experiments and Explainable Machine Learning

“…This decision was driven by various factors, including the need to limit the number of experiments to underscore the benefits of DoE for cross-process analysis, the available coating technology using a doctor blade, along comprehensive reviews available in the literature concerning defects. [19,20] To ensure an exhaustive cross-process analysis with independent input variables, the electrode porosity after calendering and the mass loading were chosen as input variables, eliminating the third dependent variable, the thickness. Due to the complexity involved in the digitalization of adhesion, with only offline characterization methods available, [13] and the difficulty in defining appropriate levels for the DoE, the temperature of the second dryer was chosen as an influential factor impacting adhesion.…”

“…While the topic of defects in both the coating process – primarily caused by slot‐die coating or inhomogeneous slurry – and the calendering process is noteworthy, these parameters were not considered for the analysis in the DoE. This decision was driven by various factors, including the need to limit the number of experiments to underscore the benefits of DoE for cross‐process analysis, the available coating technology using a doctor blade, along comprehensive reviews available in the literature concerning defects [19,20] . To ensure an exhaustive cross‐process analysis with independent input variables, the electrode porosity after calendering and the mass loading were chosen as input variables, eliminating the third dependent variable, the thickness.…”

Surface-Scan MRI Diagnostics of Li-Ion Cells: Boosting the Sensitivity with High-Performance Unilateral RF Sensors

“…However, flammable and heat-generating components of battery cells pose risks of thermal runaway. Such risks can increase due to the presence of degraded or substandard electrochemical materials and mechanical defects in individual cells. − A screening technology providing accurate identification of hazardous cells can significantly mitigate these risks. Recent advances in battery cell diagnostics have been achieved with a magnetic resonance imaging technique (Surface-Scan MRI) tailored for accurate and rapid mapping of strongly inhomogeneous magnetic fields.…”

Measuring Instruments for Characterization of Intermediate Products in Electrode Manufacturing of Lithium‐Ion Batteries

“…In addition to edge elevation, compositional inhomogeneity, and microstructural heterogeneity, other defects, such as pinholes or agglomerates, can occur during the coating and drying processes. A comprehensive review of different defect types with their influence on the electrochemical performance of the battery cell is provided by Du Baret de Limé et al [ 62 ] Infrared (IR) thermography or visual inspection systems using a camera can be adopted to identify electrode surface defects. [ 63 ] Depending on the pixel size and optics, such systems can have resolutions in the μm range.…”

“…Another quality-critical aspect that can have an irreversible impact on cell performance is the electrode's defects, such as pinholes or stripes. [62,63] To ensure that all potential defects arising during the coating and drying process are detected, the measuring systems are most often installed after the drying section of the coating line. Hence, these are listed in Section 3.3.…”