The interdependence of single crystal content and polytetrafluoroethylene fibrillation in dry-coated nickel-rich lithium-ion cathodes

This study investigates the role of fine single crystal (SC) particles as cathode active material (CAM) in blends with polycrystal (PC) CAM particles for Polytetrafluoroethylene (PTFE) fibrillation, processing, and performance in thin dry-coated, nickel-rich cathodes (~60 μm, 3.9 mAh cm −2 , 1.5 wt% PTFE). Pure SC powders show high bulk porosity and, under the same fill level and mixing protocol, exhibit a higher specific mixing energy (~300 kJ kg −1 ), resulting in functional but insufficiently fibrillated electrodes. However, theoretical considerations indicate that a moderate SC fraction of about 18.9 wt% can fill PC voids during high compaction, resulting in denser electrodes with finer PTFE fibrillation, which results in a more homogenous electrode structure. Powder flow measurements show that wall-friction angles correlate with film thickness during the initial film formation step. Calendering further refines PTFE fibrils, increases tensile strength of free-standing films, and decreases electrical electrode resistivity, probably by releasing carbon black embedded within PTFE. Within the investigated parameter window and electrode designs, cathodes with the theoretically derived 18.9 wt% fraction exhibit balanced properties and the highest energy density (~2200 Wh L −1 at 0.1C). The findings provide practical guidance for tailoring SC/PC blends and processing parameters in advanced dry-coated nickel-rich cathodes.