Patent ID: 7585587

Claim:
A separator for a non-aqueous electrolyte cell comprising a microporous film formed by adding a phosphazene derivative and/or an isomer of a phosphazene derivative to a polymer, wherein the phosphazene derivative is a phosphazene derivative having a viscosity at 25° C. of not more than 300 mPa.s (300 cP) and represented by the following formula (I) or (II): (wherein R 1 , R 2 and R 3 are independently a monovalent substituent or a halogen element; X 1 is a substituent containing at least one element selected from the group consisting of carbon, silicon, germanium, tin, nitrogen, phosphorus, arsenic, antimony, bismuth, oxygen, sulfur, selenium, tellurium and polonium; and Y 1 , Y 2 and Y 3 are independently a bivalent connecting group, a bivalent element or a single bond); (NPR 4 2 ) n (II) (wherein R 4 is independently a monovalent substituent or a halogen element and n is 3-15), and wherein the phosphazene derivative of the formula (II) is a phosphazene derivative represented by the following formula (III): (NPF 2 ) n (III) (wherein n is 3-13).