A non-aqueous electrolyte secondary battery such as a lithium-ion secondary battery has high energy density. Recently, therefore, the non-aqueous electrolyte secondary battery is widely used as batteries for use in apparatuses such as a personal computer, a mobile phone, and a portable information terminal.
In order to enhance properties (such as safety) of the non-aqueous electrolyte secondary battery, various attempts have been made to improve a separator which is provided between a positive electrode and a negative electrode. In particular, a porous film made of polyolefin is excellent in electrical insulating property and exhibits good ion permeability. Therefore, such a porous film made of polyolefin is widely used as a separator for a non-aqueous electrolyte secondary battery, and various proposals relating to the separator have been made.
For example, Patent Literature 1 proposes a non-aqueous electrolyte battery separator that is a multilayer porous membrane (i) in which a porous layer that contains an inorganic filler or a resin having a melting point and/or a glass transition temperature of 180° C. or higher and has a thickness of 0.2 μm or more and 100 μm or less is provided on at least one surface of a polyolefin resin porous membrane and (ii) which has air permeability of 1 second to 650 seconds/100 cc.
Patent Literature 2 proposes a non-aqueous electrolyte battery separator which is a separator including a polyolefin layer and a heat-resistant insulating layer that (i) is provided on one surface or each of both surfaces of the polyolefin layer, (ii) contains a heat-resistant resin and oxidation-resistant ceramic particles, and (iii) contains the oxidation-resistant ceramic particles at a ratio of 60% to 90%.