Separator including mixed layer of heat-resistant resin and porous polyolefin film, and nonaqueous electrolyte secondary battery including the same
As a nonaqueous electrolyte secondary battery separator which has excellent heat resistance and excellent battery performance, provided is a nonaqueous electrolyte secondary battery separator including a mixed layer which contains a heat-resistant resin and a porous base material that includes a polyolefin porous film, in the mixed layer, a weight ratio (W 1 /W 0 ) between a weight W 1 of the heat-resistant resin and a weight W 0 of the porous base material being not less than 0.07.
1 . A nonaqueous electrolyte secondary battery separator comprising:
a mixed layer which contains a heat-resistant resin and a porous base material that includes a porous film containing a polyolefin-based resin in an amount of not less than 50% by volume relative to a total volume of components of the porous film,
in the mixed layer, a weight ratio (W 1 /W 0 ) between a weight W 1 of the heat-resistant resin and a weight W 0 of the porous base material being not less than 0.07,
wherein a heat-resistant layer which contains the heat-resistant resin is formed on the mixed layer,
wherein a value of expression (1) of the heat-resistant layer is not less than 5%:
a luminance X 1 (%)−a luminance X 2 (%) (1)
where the luminance X 1 represents an average value of luminances of a part of the heat-resistant layer from an interface between the heat-resistant layer and the mixed layer to a depth of 20% of a thickness of the heat-resistant layer from the interface,
the luminance X 2 represents an average value of luminances of a part of the heat-resistant layer from an outermost surface of the heat-resistant layer to a depth of 20% of the thickness of the heat-resistant layer from the outermost surface, and
an average value of luminances of the entire heat-resistant layer is 100%.
2 . The nonaqueous electrolyte secondary battery separator as set forth in claim 1 , wherein a shutdown temperature of the nonaqueous electrolyte secondary battery separator is not lower than 150° C.
3 . The nonaqueous electrolyte secondary battery separator as set forth in claim 1 , wherein an air permeability of the nonaqueous electrolyte secondary battery separator is not more than 500 sec/100 mL.
4 . The nonaqueous electrolyte secondary battery separator as set forth in claim 1 , wherein the heat-resistant resin is an aramid resin.
5 . The nonaqueous electrolyte secondary battery separator as set forth in claim 1 , wherein the heat-resistant layer further contains a filler.
6 . The nonaqueous electrolyte secondary battery separator as set forth in claim 5 , wherein an amount of the filler contained in the heat-resistant layer is not less than 20% by weight and not more than 90% by weight, relative to a total weight of the heat-resistant layer.
7 . A nonaqueous electrolyte secondary battery comprising a nonaqueous electrolyte secondary battery separator recited in claim 1 .
8 . A nonaqueous electrolyte secondary battery member comprising:
a positive electrode;
a nonaqueous electrolyte secondary battery separator recited in claim 1 ; and
a negative electrode,
the positive electrode, the nonaqueous electrolyte secondary battery separator, and the negative electrode being disposed in this order.