The Role of Separators in Lithium-Ion Cell Safety

As the use of lithium-ion cells for high power applications becomes increasingly widespread, safety and reliability of these cells and battery packs is of paramount importance. Many of the multilayer separators are designed with a shutdown feature, where two of the layers have different phase transition temperatures. As the temperature of a cell increases, the lower melting component melts and fills the pores of the other solid layer and stops ion transport and current flow in the cell. Separator designs for ensuring safety should be considered for a specific battery size, application, and potential abuse scenarios. New designs, detailed modeling, and robust testing are all essential to ensure separators selected to meet both the performance and safety requirements for a given application. Ceramic/polymer composites and high melting point polymer materials offer some improvement in thermal stability and abuse tolerance for lithium-ion cell separators but, in general, there needs to be more evaluation work dedicated to quantifying the safety impact of new separators