SEPARATOR FOR NONAQUEOUS ELECTROLYTE SECONDARY BATTERY AND NONAQUEOUS ELECTROLYTE SECONDARY BATTERY INCLUDING THE SAME

An object of this invention is to improve battery performance such as a rate capability of a nonaqueous electrolyte solution secondary battery using a separator constituting a thermoplastic resin-based porous film containing a filler. This invention provides a nonaqueous electrolyte solution secondary battery separator which is formed from a porous film containing a thermoplastic resin and a filler contained in the thermoplastic resin and has a ratio of an average pore diameter (µm) to a maximum pore diameter (µm) defined by ASTM F316-86 of 0.6 or more as well as relates to a nonaqueous electrolyte solution secondary battery using this separator.