Effect of active material morphology on PTFE-fibrillation, powder characteristics and electrode properties in dry electrode coating processes

This study investigates the significant impact of different active material particle morphologies – platelet-like graphite, spherical highly porous LFP, and spherical NCM – on PTFE fibrillation during mixing and calendering steps of a dry coating process. Graphite's platelet-like structure slows PTFE fibrillation compared to LFP's structure, which exhibits prolonged PTFE fibrillation due to its fine particle content. NCM, with higher density and compaction speed, promotes faster PTFE fibrillation during mixing. The hierarchical morphology of the fibrils determines the powder blend properties. Consequently, powder behaviour in the calender gap was characterised using uniaxial compression and ring shear cell tests. Uniaxial compression tests revealed that NCM-based powder requires higher compression stress. Under consistent calendering conditions, it forms thicker dry-coated films compared to the graphite-based powder, which requires lower compression stress and forms thinner films. These findings are supported by ring shear cell tests, which showed lower wall friction for graphite-based powder and a higher wall friction angle for NCM-based powder. Additionally, the porosity of the free-standing films can be predicted using uniaxial compression tests. These results highlight the need for tailored mixing and calendering processes for each active material to optimize electrode properties in dry coating processes for lithium-ion batteries. • PTFE fibrillation varies significantly with particle morphology during dry mixing. • Dry-coated film properties correlate with shear cell and compaction test results. • Uniaxial compression tests on powders determine the porosity of dry-coated films.