| abstract |
A separator which comprises a microporous polyethylene film and a heat-resistant porous layer. It has a sufficient shutdown function and heat resistance and can have a reduced thickness. It is effective in mitigating a problem concerning slipping properties. The separator for nonaqueous secondary batteries comprises a microporous film consisting mainly of polyethylene and a heat-resistant porous layer consisting mainly of a heat-resistant polymer and formed on at least one surface of the microporous film. It is characterized in that (1) the microporous film has a Gurley value of 25-35 sec/100 cc•µm per unit thickness, (2) the heat-resistant porous layer contains fine inorganic particles having an average particle diameter of 0.1-1.0 µm, (3) the fine inorganic particles account for 40-80% by volume of the sum of the heat-resistant polymer and the fine inorganic particles, and (4) the heat-resistant porous layer has a total thickness of 3-12 µm. |