Scientific papers
This study explores how the particle morphology of active materials—platelet-like graphite, spherical highly porous LFP, and spherical NCM—significantly influences PTFE fibrillation during the mixing and calendering stages of a dry coating process. Graphite's platelet-like structure slows PTFE fibrillation, whereas LFP's fine particle content extends the fibrillation process. In contrast, NCM's higher density and faster compaction speed accelerate PTFE fibrillation during mixing. The hierarchical morphology of the fibrils plays a key role in shaping the powder blend's properties.
To better understand powder behavior in the calender gap, uniaxial compression and ring shear cell tests were conducted. Uniaxial compression tests revealed that NCM-based powders require higher compression stress and produce thicker dry-coated films under similar calendering conditions, compared to graphite-based powders, which need lower compression stress and form thinner films. Ring shear cell tests corroborated these findings, showing lower wall friction for graphite-based powders and a higher wall friction angle for NCM-based powders. Additionally, uniaxial compression tests proved useful in predicting the porosity of free-standing films.
These findings underscore the importance of customizing mixing and calendering processes for each active material to optimize electrode properties in dry coating applications for lithium-ion batteries.
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