US-12620675-B2 - Separator including mixed layer of heat-resistant resin and porous polyolefin film, and nonaqueous electrolyte secondary battery including the same

US12620675B2US 12620675 B2US12620675 B2US 12620675B2US-12620675-B2

Abstract

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.

Inventors

Riku Matsumine
Akihiko SHIN

Assignees

SUMITOMO CHEMICAL COMPANY, LIMITED

Dates

Publication Date: 20260505
Application Date: 20230303
Priority Date: 20220304

Claims (8)

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.

Description

This Nonprovisional application claims priority under 35 U.S.C. § 119 on Patent Application No. 2022-033934 filed in Japan on Mar. 4, 2022, the entire contents of which are hereby incorporated by reference. TECHNICAL FIELD The present invention relates to a separator for a nonaqueous electrolyte secondary battery (hereinafter referred to as a “nonaqueous electrolyte secondary battery separator”), a member for a nonaqueous electrolyte secondary battery (hereinafter referred to as a “nonaqueous electrolyte secondary battery member”), and a nonaqueous electrolyte secondary battery. BACKGROUND ART Nonaqueous electrolyte secondary batteries such as lithium secondary batteries are currently in wide use as (i) batteries for devices such as personal computers, mobile telephones, and portable information terminals or (ii) on-vehicle batteries. As separators for the nonaqueous electrolyte secondary batteries, known are separators the heat resistance of each of which is improved by causing a part of a resin, which constitutes a heat-resistant layer formed on a porous film containing polyolefin as a main component, to penetrate into a part of the porous film (for example, Patent Literatures 1 to 3). CITATION LIST Patent Literature [Patent Literature 1] Published Japanese Translation of PCT International Application Tokuhyo No. 2013-511818 [Patent Literature 2] Japanese Patent Application Publication Tokukai No. 2013-46998 [Patent Literature 3] Pamphlet of PCT International Publication No. WO 2019/107219 SUMMARY OF INVENTION Technical Problem However, in each of the above conventional separators, a degree of penetration of the resin, which constitutes the heat-resistant layer, into the porous film is suppressed, from the viewpoint of ensuring a good shutdown characteristic and preventing an excessive increase in resistance. Therefore, the conventional separators each have a problem that the heat resistance is insufficient particularly in a region in which a weight per unit area is low and a problem that there is room for improvement in safety. Furthermore, in each of the conventional separators, there is also room for improvement in battery performance, such as ion permeability and a resistance maintaining property in a coin cell. The object of an aspect of the present invention is to provide a nonaqueous electrolyte secondary battery separator which has more excellent heat resistance and also more excellent battery performance, such as ion permeability and a resistance maintaining property in a coin cell, than conventional separators. Solution to Problem The inventors of the present invention found that the heat resistance of each of the separators can be more improved by improving the degree of penetration of the resin, which constitutes the heat-resistant layer, into the porous film. The inventors of the present invention also found that the ion permeability and the resistance, which had been predicted to significantly deteriorate, did not deteriorate more than predicted. As a result, the inventors of the present invention conceived of the present invention. The present invention includes the following aspects <1> to <10>. <1> A nonaqueous electrolyte secondary battery separator including a mixed layer which contains a heat-resistant resin and a porous base material that includes a porous film containing a polyolefin-based resin as a main component,in the mixed layer, a weight ratio (W1/W0) between a weight W1 of the heat-resistant resin and a weight W0 of the porous base material being not less than 0.07. <2> The nonaqueous electrolyte secondary battery separator as described in <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 described in <1> or <2>, wherein a heat-resistant layer which contains the heat-resistant resin is formed on the mixed layer. <4> The nonaqueous electrolyte secondary battery separator as described in <3>, wherein the heat-resistant layer further contains a filler. <5> The nonaqueous electrolyte secondary battery separator as described in <4>, 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. <6> The nonaqueous electrolyte secondary battery separator as described in any one of <3> to <5>, wherein a value, represented by the following expression (1), of the heat-resistant layer is not less than 5%: a luminance X1(%)−a luminance X2(%) (1) where the luminance X1 indicates an average value of luminances of a part 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 X2 indicates an average value of luminances of a part from an outermost surface of the heat-resistant layer to a depth of 20% of the thickness of the hea