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

While lithium-ion batteries are rapidly penetrating the laptop and cell-phone markets because of their high specific energy, safety is one of the key challenges to be addressed before lithium-ion batteries can replace the nickel-metal-hydride batteries that are commonly used in today¿s Hybrid Electric Vehicles (HEVs). The major safety concern is the possibility of an internal short-circuit, due to shrinkage of the separator when exposed to high temperatures, possibly resulting in explosion and fire. 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 project will develop new separators with high melt integrity and chemical stability via an enhanced electrospinning process, a technique that has been widely used in the textile and filter industries. However, with traditional electrospinning techniques, many high-melt-integrity candidates do not readily dissolve into solvents at temperatures much below their melting point. Therefore, the electrospinning of these polymers will be explored through the use of precursor solutions or via the molten state. In addition to the measurement of physical properties such as thickness and porosity, the electrospun separators will be characterized for thermal and electrochemical stability. Commercial Applications and other Benefits as described by the awardee: The new separators for the HEV market should provide the same benefits (in terms of porosity, thickness, cost, etc.) as current state-of-the-art lithium-ion separators that are used in other markets. For the year 2007, sales of HEVs were projected to reach 375,000 automobiles.