| 摘要 |
The present invention relates a microporous polyethylene film with improved mechanical strength, porosity, pore size and, particularly, improved surface energy, thereby having improved electrolyte wettability and being adequate for use as separators in high-capacity and long lifetime lithium secondary batteries. The microporous polyethylene film of the present invention is characterized by having a surface energy of at least 50 dynes/cm2, an air permeability (Darcy's permeability constant) of at least 2.0x10-5, a puncture strength of at least 0.17 N/m, a product of the air permeability and the puncture strength of at least 0.34x10-5 Darcy.N/m, a weighted average pore size of at least 30 nm, and a film shrinkage in the transverse and machine directions of not more than 5% at 105° C. for 10 minutes and not more than 15% at 120° C. for 60 minutes, respectively. The microporous polyethylene film is prepared by compounding raw materials in an extruder such that a thermodynamic single phase is formed above the temperature of liquid-liquid phase separation, inducing sufficient phase separation in a phase separation zone formed inside the extruder by controlling the temperature below the temperature of liquid-liquid phase separation, forming through a die, and carrying out plasma treatment in order to enhance surface energy.
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