Polyester Separators for Lithium-Ion Cells: Improving Thermal Stability and Abuse Tolerance

This report describes the preparation and performance of electro-spun polyester-based separators for lithium-ion batteries. Polyester fibers (200500 nm) are electro-spun into nonwoven mats and pressed into separator sheets approximate to 55 m thick. The resulting polyester separators are 75% porous, highly permeable (Gurley number (s/100 mL) = 6), and have good wettability with conventional carbonate-based electrolyte. In NMC/graphite lithium-ion cells, results show comparable performance to commercially available polyolefin separators (rate, capacity fade, and reactivity) but with improved thermal stability to >200 degrees C. The use of this higher melting temperature polymer separator is one approach to close the gap between potential thermal instabilities (softening, shrinking, melting, etc.) of separators and the onset of thermal runaway reactions of commonly used cathode materials.