Porous film, separator for electric storage device, and electric storage device

摘要

A porous film 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, when the thickness of a circular region having a diameter of 10 mm as an initial thickness t0 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 t1 after 10 seconds has passed after the load applied onto the same region is subsequently changed to 50 g, the thickness change rate is 10% to 50%, and the thickness (t1) recovery rate is 80% to 99.9%.

主权项

1. A porous film having through-pores, containing:
a polyolefin-based resin is a polypropylene resin having a melt flow rate of 4 to 30 g/10 min; and 70% to 99% by mass of the polypropylene resin having the melt flow rate of 4 to 30 g/10 min and 1% to 30% by mass of a propylene-ethylene copolymer having a melt flow rate of 0.1 to less than 4 g/10 min; or 80% to 99% by mass of the polypropylene resin having the melt flow rate of 4 to 30 g/10 min and 1% to 20% by mass of an elastomer containing at least propylene or butane as a constituent unit, wherein, when thickness of a circular region having a diameter of 10 mm as an initial thickness t0 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 the thickness t1 after 10 seconds has passed after the load applied onto the same region is subsequently changed to 50 g, a thickness change rate (%) of the film as expressed by Equation (1) is 10% to 50%, and a thickness (t1) recovery rate (%) of the film as expressed by Equation (2) is 80% to 99.9%:
Thickness change rate (%)=[(t0−t)/t0]×100  (1), andThickness (t1) recovery rate (%)=(t1/t0)×100  (2).