Ether-Functionalized Polybenzimidazole Composite Separators for Enhanced Performance and Sustainable Lithium-Ion Batteries

Polybenzimidazole (PBI) is a promising separator for lithium-ion batteries (LIBs) owing to its excellent thermal/chemical stability and mechanical strength, but its application is limited by poor solubility and processability. Herein, a novel ether-functionalized PBI was synthesized, and three-layer composite separators (PBIPHPE) were fabricated by electrospinning PBI/PVDF-HFP blends onto polyethylene (PE) substrate. The PBIPHPE separator exhibits high porosity (73.1%), superior electrolyte uptake (211.2%), and excellent ionic conductivity (1.125 mS/cm), with no dimensional change after thermal treatment at 150 °C for 0.5 h. Lithium-ion batteries assembled with PBIPHPE deliver an initial specific capacity of 157.7 mAh/g, retain 86.0% capacity after 400 cycles at 2 C, and show only 15.7% capacity decay from 0.2 C to 5 C. Molecular dynamics simulations of the composite separator–electrolyte system were performed to reveal Li+ transport behaviors. The results confirm that ether-functionalized PBIPHPEs enhance Li+ transport and cycling stability, providing a promising route for high-performance separators.