Development of Separators for Lithium-Ion Cells with High Temperature Melt Integrity

During charge and discharge at high rates and in high abuse situations, a battery can become quite hot, as the heat generated from internal chemical reactions can exceed the battery¿s capability to dissipate the heat. When internal temperatures become excessive, separator breakdown can result, even after separator shutdown, as the internal cell temperature continues to climb. Eventually the separator begins to melt and shrink. Upon shrinking, the electrodes can short circuit, leading to a thermal and/or electrochemical runaway, which possibly could result in explosion and fire. To develop high-melt-integrity (>200°C) separators, this project will pursue two approaches based upon traditional solution-based electro-spinning and melt-electro-spinning processes. During Phase I, a polyimide-based electrospun separator with melt integrity up to 400°C was produced via solution-based electro-spinning. This separator performed extremely well during performance testing in a lithium-ion cell. Phase II will include further development of the melt-based electro-spinning technology, incorporation of shutdown features for both melt and solution based technologies, and demonstration of manufacturing scalability of the electrospun separator. Commercial Applications and other Benefits as described by the awardee: Separators with higher melt temperatures (>200°C) would significantly improve a lithium-ion cell¿s resilience to the onset of a thermal runaway situation. This would greatly increase the safety of lithium batteries, which are used in a wide range of applications such as electric and hybrid electric vehicles, aerospace, medical, and military markets.