| abstract |
A separator of a battery wherein an organic electrolyte is used, which is made of a microporous film having a matrix constituted of a polyethylene having such a molecular weight distribution that a portion having a molecular weight of 1,000,000 or above accounts for 10 wt.% or above and a portion having a molecular weight of 100,000 or less accounts for 5 wt.% or above and a polypropylene having a weight-average molecular weight of 10,000 to 1,000,000 in an amount of 5 to 45 wt.% of the total amount of polyethylene and polypropylene. The microporous film has a thickness of 10 to 500 µm, a porosity of 40 to 85% and a maximum pore diameter of 0.05 to 5 µm. This battery separator can be readily produced by extrusion-molding a mixture of the polyethylene having the above-specified molecular weight distribution, the polypropylene having the above-specified weight-average molecular weight, an organic liquid and fine inorganic powder to form a film, and then extracting the organic liquid and the inorganic powder from the film. It has not only excellent stability but also excellent chemical resistance, mechanical strength and ion permeability, and is extremely useful as the separators of not only a lithium cell but also other primary and secondary cells wherein an organic electrolyte is used. |