Porous polyolefin membranes are the most widely used lithium
ion battery separators due to their good electrochemical and
chemical stability, very low moisture absorption, and excellent
tensile properties. However, the processes of making conventional
separators require precise stretching of the extruded thin film to
create pores [2e4]. Heat exposure to these stretched separators
initiates re-coiling of the elongated polymer chains, observed as
membrane shrinkage, which could significantly increase the risk of
battery shorting, especially for large format battery applications. In
addition, the melting temperature of polyolefin is normally in the
range of 120e170 C. Any local hot spots developed under abnormal
conditions could cause the melting of the separator further
increasing the contact area between the two electrodes.