| abstract |
PROBLEM TO BE SOLVED: To provide a high-performance lithium ion battery excellent in lithium ion permeability and mechanical strength, and to prevent a short circuit between a positive electrode and a negative electrode due to dendrite or impact. A resin microporous film is provided. A propylene-based resin microporous film of the present invention is a propylene-based resin microporous film in which micropores are formed by biaxially stretching a propylene-based resin film, and the propylene-based resin includes: The amount of components having a molecular weight of 50,000 or less is 25 to 60% by weight, the amount of components having a molecular weight of 700,000 or more is 19 to 30% by weight, the weight average molecular weight is 350,000 to 500,000, and the melt tension is 1. 1 to 3.2 g, and further, the air permeability of the propylene-based resin microporous film is 40 to 400 s / 100 mL, the porosity is 40 to 70%, and the maximum major axis of the open end of the micropore is 500 nm or less. It is characterized by being. [Selection figure] None |