Understanding Powder Behavior in Battery Manufacturing
*This article is revised from Freeman Technology’s document AP113 for Japanese customers*
The Relationship between Batteries, Slurry, and Powders
Lithium-ion (Li-ion) batteries are used as rechargeable batteries in a wide range of applications, including consumer electronics, power tools, automotive and aerospace industries, due to their high energy density, resistance to self-discharge, and minimal memory effect.
Figure: Typical Process Stages in Lithium-ion Battery Manufacturing
The various stages within the process largely depend on the quality of the slurry created at the start of the process. The characteristics of the slurry depend on the properties of the powder mixed with the binder and solvent, and the behavior during the mixing process.
To ensure optimal process performance and a high-quality final product, it is necessary to meet critical criteria such as fine powder content, viscosity, and solids in the slurry state. Particularly, the uniformity of the solids affects the coating efficiency of the substrate from the slurry. Therefore, ensuring that powders do not agglomerate during mixing and dispersion is crucial.
Evaluation of Powder Properties Related to the Process
The flow properties of powders determine the mixing and dispersion performance during slurry formation, affecting characteristics such as flow behavior and agglomeration. The following data shows how the properties measured using the Powder Rheometer FT4® correlate with processing within the Li-ion battery manufacturing process.
Anodes were manufactured using three LiFePO4 batches sourced from different suppliers. While homogeneous slurry generation was observed with Batch 1, Batches 2 and 3 lacked homogeneity, resulting in blockages leading to system shutdowns or off-spec products.
The analysis of the material powders at that time is shown in the figure above. SE quantifies the extent of physical interlocking and friction between particles. The low SE value of Batch 1 suggests the ability to disperse particles more freely, indicating a low likelihood of agglomerate formation through binding.
Air permeability of powders was also examined.
Permeability represents the property of powders to release or retain incoming air. The increase in pressure drop recorded for Batch 1 indicates reduced permeability, likely due to more efficient packing of the powder layer. Typically, powdered substances with regularity in the packing structure flow more freely and can thus disperse more freely and uniformly. Additionally, lower adhesion strength also reduces the risk of agglomeration.
These results suggest that powders with low physical interlocking and friction extent and low permeability are useful for creating homogeneous slurry for anode manufacture in Li-ion battery production. The multivariate approach of the Powder Rheometer FT4 allows precise quantification of these characteristics, ensuring powder specifications are accurately defined.
Powder Rheometer FT4
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