“…The slope of lines indicates a Warburg diffusion process, and the resistances of different separators are determined by the intersection of the spectrum line and x‐axis. The bulk resistances of the Celgard PP, PI nonwoven, PI‐2, and PI‐4 separators are 2.1, 0.7, 1.1, and 1.2 Ω, respectively. The ionic conductivities of the separators with liquid electrolyte are evaluated to be 0.59, 2.2, 1.43, and 1.31 mS cm −1 , respectively.…”