Stepwise Analysis of the Dry Graphite Anode Process via PTFE-Crystallinity-Induced Fibrillation

Abstract

The rapid growth of electric vehicles is driving demand for lithium-ion batteries with higher energy density and lower manufacturing costs. Thick electrodes are a key route at the cell level, but the conventional NMP-based slurry process suffers from high manufacturing energy, solvent toxicity, and poor scalability to thick electrodes. Dry electrode processing using polytetrafluoroethylene (PTFE) as a fibrillating binder can address these issues, yet the coupled effects of PTFE crystallinity and kneading time on shear-induced fibrillation, intermediate products properties, and final electrode performance are still poorly understood. In this study, the dry graphite anode process was analyzed stepwise using a combination of a monosodium glutamate monosodium glutamate (MSG)/PTFE model system and a practical graphite/PTFE system. PTFE fibrillation was first quantified as a function of kneading time by tracking the decrease of fibrillation-sensitive (107) and (108) XRD reflections in the MSG/PTFE model, while complementary cryo-SEM revealed the evolution from primary particles to a fibrillar network and to fibril cleavage under over-kneading. In the actual dry graphite dough, the degree of fibrillation was further quantified via the CF₂/C–C peak area ratio from XPS, which increased and saturated at 12 min kneading, indicating an optimal fibrillation window. Building on this framework, three PTFE grades with similar molecular weights but different (107), (108) crystallinities were compared. Higher (107) and (108) crystallinity promoted more extensive fibrillation at a fixed kneading condition, leading to larger granule d50, higher film-level cohesion, increased edge roughness, and higher electrode tortuosity and ionic resistance. Consequently, highly crystalline PTFE improved mechanical robustness and cycle stability but degraded rate capability, whereas low-crystallinity PTFE showed the opposite trade-off. The results clarify the inherent trade-offs between mechanical strength, processability, and electrochemical performance in PTFE-based dry graphite anodes by jointly mapping the roles of PTFE crystallinity. Based on this understanding, the study proposes practical processing windows and design guidelines in dry anode process.