| abstract |
The invention relates to a microporousnmembrane, which is provided with high safety even underna condition that the interior temperature of a batterynbecomes high, and which has high permeability and highnmechanical strength at the same time. n The polyolefin microporous membrane isncharacterized by a membrane thickness of 5 to 50 µm, anvoid content of 30 to 60%, a gas transmission rate ofn40 to 300 sec/100cc/20µm, a piercing strength of notnless than 2.5 N/20µm and a break through temperature ofnnot lower than 110°C. n The separator in accordance with the presentninvention is used to exhibit high safety under a highntemperature condition as well as high permeability, andntherefore it is particularly useful as a separator fornminiaturized high capacity batteries of a non-aqueousnelectrolytic solution type. |