| abstract |
A porous film is provided that excels, when used as a separator for a lithium-ion battery, not only in separator followability to expansion and contraction of an electrode during charging and discharging, but also in charging and discharging cycle characteristics. The porous film of the present invention is characterized in that, denoting the thickness of a circular region having a diameter of 10 mm as an initial thickness to after a load of 50 g is applied onto the circular region for 10 seconds, as a thickness t after a load of 500 g is subsequently applied onto the same region for 10 seconds, and as a thickness t 1 after 10 seconds has passed after the load applied onto the same region is subsequently changed to 50 g, the thickness change rate expressed by equation (1) is 10% to 50%, and the thickness (t 1 ) recovery rate expressed by equation (2) is 80% to 99.9%: Thickness change rate % = t 0 - t / t 0 × 100 Thickness t 1 recovery rate % = t 1 / t 0 × 100 |