The unusual delamination phenomenon of three kinds of lithium‐ion battery separators

Abstract An unusual delamination phenomenon on three kinds of lithium‐ion battery separators was investigated in this study, which is closely associated with the compression resistance of the separator. The delamination trends of three kinds of polymer separators were analyzed systematically. Scanning electron microscopy, two‐dimensional wide‐angle X‐ray diffraction, compression and delamination tests show that a separator prepared by the dry process with uniaxial stretching delaminate hardest due to abundant connection or support structure along the thickness direction. However, the multilayer structure stacked along the thickness direction can be seen clearly for separators experiencing biaxial stretching, both for the dry process and wet process. In particular, a separator prepared by the wet process has the poorest connection or support structure along the thickness direction, leading to the strongest delamination trend and the worst compression resistance. Based on this, we control the delamination trend of the separator by adjusting the condensed structure of the precursor film. Besides, the delamination test can quantify the delamination trend of different kinds of separators accurately and further supplement the evaluation criteria of lithium‐ion battery separators, which can help us to better understand and design a separator with optimal microporous structure. © 2020 Society of Industrial Chemistry