Electrochemical Impact of Inhomogeneous Binder Distribution in Lithium-Ion Battery Electrodes

Abstract

In recent years, the application possibilities of the lithium-ion battery (LIB) have increased significantly. Moreover, the demand for LIBs will rise in the next few years, especially in the automotive sector. This leads to an increasing importance of careful management of the limited lithium resources. Battery production offers high savings potential, as the current scrap rate is around 5-30% [1,2]. The scrap arises in the various process steps such as electrode production, battery conditioning or even from impure raw materials. Especially during the electrode production including mixing, coating, drying and calendaring, various defects can be implemented into the electrodes. Defects such as compositional inhomogeneities (e.g., inhomogeneous binder distribution), microstructural inhomogeneities (e.g., thickness variations), line defects, point defects or even foreign particle contamination can lead to increased scrap rates [3].For the detection of defects, there are already a few established methods such as computed thermography, camera-based optical systems, or post-mortem analyses. However, the detection of the defects might not be sufficient to evaluate the electrode usability since the influence might still be tolerable. Therefore, the impact of the defect type, size, and concentration and resulting determination of the tolerance limits is decisive for the reduction of production waste.In this work we focus on the influence of compositional inhomogeneities on the battery performance. Compositional inhomogeneities like inhomogeneous binder distribution can modify the local electrode characteristics e. g. porosity/tortuosity. This can lead to local higher or lower c-rate followed by faster or slower local degradation. In worst case these inhomogeneities can cause lithium plating or short circuits and shorten the lifetime of LIBs significantly.To determine the criticality and establish tolerance limits, we produced and analyzed defective and defect-free electrodes. For the determination of the impact of the inhomogeneities we developed a special experimental setup that allows us the analysis of the internal dynamics of the interaction between defect-containing (selective modification of the binder content) and defect-free (target binder content) electrodes. Therein, compensating currents continuously redistribute the inhomogeneous charges in electrodes with different binder content. This balancing effect was studied in terms of the caused accelerated aging.This experimental approach provides a foundation for further investigation and for deep understanding of the effect of electrode defects. This knowledge represents a basis for further developing of effective quality assurance strategies and reducing scrap rates accompanying by careful management of the limited lithium resources.[1] Gaines, L.; Dai, Q.; Vaughey, J. T.; Gillard, S.: Direct Recycling R&D at the ReCell Center. Recycling. 2021, 6 (2), 31. DOI: 10.3390/recycling6020031. [2] Brückner, L.; Frank, J.; Elwert, T.: Industrial Recycling of Lithium-Ion Batteries—A Critical Review of Metallurgical Process Routes. Metals 2020, 10 (8), 1107. DOI: 10.3390/met10081107. [3] du Baret de Limé, A.; Lein, T., Maletti, S.; Schmal, K.; Reuber, S.; Heubner, C. and Michaelis, A.: Impact of Electrode Defects on Battery Cell Performance: A Mini Review. Batteries & Supercaps 2022, 5, e202200239, doi.org/10.1002/batt.202200239.