Nonaqueous electrolyte secondary battery insulating porous layer and nonaqueous electrolyte secondary battery laminated separator

A laminated separator for a nonaqueous electrolyte secondary battery, the laminated separator comprising:

• a porous film containing a polyolefin at a proportion of not less than 50% by volume;
• and
• an insulating porous layer disposed on one or both surfaces of the porous film,
• the insulating porous layer containing a fine particle of a metal salt,
• the metal salt having a Lewis acid peak area per unit weight within a range of not less than 0.2 g−1 and not more than 3.6 g −1, the Lewis acid peak area per unit weight being measured by an infrared spectroscopy-based acid nature evaluation method for a solid surface,
• the insulating porous layer having a component volume per unit area for each surface within a range of 0.5 cm3/m2 to 20 cm3/m2,
• the fine particle of the metal salt having a volume-based particle size distribution having a first peak and a second peak, wherein the first peak corresponds to a particle size of not less than 0.4 μm and not more than 0.6 μm and the second peak corresponds to a particle size of not less than 5 μm and not more than 7 μm, wherein the first peak has a minus sieve cumulative distribution of not less than 10% and not more than 20%, and wherein the second peak has a minus sieve distribution of not less than 60% and not more than 80%,
• a Lewis acid peak area of a metal salt per unit weight being defined as a value resulting from dividing (i) an area of a peak present in a region of 1447 cm−1 to 1460 cm−1 of an infrared (IR) absorption spectrum measured of a sample on which pyridine was adsorbed and then desorbed by (ii) a weight of the metal salt;
• the infrared (IR) absorption spectrum being measured by (I) obtaining a background spectrum by measuring an infrared transmission spectrum of the fine particle of the metal salt on which fine particle pyridine has not been adsorbed, (II) preparing a sample by causing pyridine to be adsorbed on the fine particle of the metal salt and then desorbing the pyridine which has been physically adsorbed, (III) measuring an infrared transmission spectrum of the sample, and (IV) subtracting the background spectrum from the infrared transmission spectrum;
• wherein the peak area is an area of a portion surrounded by (a) a peak which is present in the region of 1447 cm−1 to 1460 cm−1 of the infrared (IR) absorption spectrum and (b) a baseline which is drawn to pass through opposite ends of the peak, and
• wherein the component volume per unit area is defined as the sum of values each resulting from multiplying a weight per unit area of the insulating porous layer by a weight concentration of each component of the insulating porous layer to obtain a weight per unit area of each component;
• and dividing the weight per unit area of each component by a true specific gravity of each component.