Controlling polyethylene fibrillation in PFAS-free dry electrodes for processability and electrochemical performance

Ultra-high-molecular-weight polyethylene (UHMWPE) is a more sustainable binder alternative to polytetrafluoroethylene (PTFE) for producing PFAS-free Li-ion battery electrodes using a solvent-free PE fibrillation process. We show that PE fibrillation is thermo-activated and can be controlled to produce an extensive network of nano-fibrils with a median size of 20-40 nm. PE-containing graphite electrode ultimate tensile strength (UTS), critical for roll-to-roll processing, improved more than 20-fold when the electrode calendering temperature increased from 100 to 160-200 °C, providing mechanical stability superior to equivalent PTFE-containing electrodes. PE-containing electrodes calendered at lower temperatures (120-140 °C) showed comparable charging rate performance but superior capacity retention of ∼90% after 100 cycles when compared with PTFE-containing electrodes. Removing PTFE by calcination to mimic direct recycling required temperatures > 600 °C and led to PFAS emissions. In contrast, PE removal was PFAS-free and achieved at 300-400 °C, aided by the catalytic effect of graphite on PE decomposition making PE-containing electrodes more suitable with direct recycling. Overall, integrating across fabrication, mechanical, electrochemical and end-of-life considerations, PE-containing electrodes offer significant potential for more sustainable solvent-free Li-ion batteries.