Separator for non-aqueous electrolyte secondary battery

Abstract

To provide a separator for a non-aqueous electrolyte secondary battery that excels in both ion permeability and dendrite blocking.SOLUTION: The separator for a non-aqueous electrolyte secondary battery includes a porous film and a porous layer laminated on both surfaces of the porous film. "(Average pore area of one porous layer) / (average pore area of the other porous layer)≥1.7" and / or "(average equivalent circular diameter of one porous layer)-(average equivalent circular diameter of the other porous layer)≥2.0 nm." is satisfied.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a separator for a non-aqueous electrolyte secondary battery (hereinafter also simply referred to as "separator"). [Background technology]

[0002] Non-aqueous electrolyte secondary batteries, in particular lithium ion secondary batteries, have a high energy density and are therefore widely used as batteries for personal computers, mobile phones, portable information terminals, and the like, and recently they have been developed as batteries for use in vehicles.

[0003] In recent years, with the expansion of applications of non-aqueous electrolyte secondary batteries, the separator is required to have heat resistance in order to further improve the safety of the battery. Here, for example, as described in Patent Document 1, a separator in which a heat-resistant porous layer is laminated on at least one side of a porous substrate is known to be a separator with excellent heat resistance. In addition, an example of Patent Document 1 describes a separator in which a heat-resistant porous layer is laminated on both sides of a porous substrate. As described in the example of Patent Document 1, a separator in which a heat-resistant porous layer is laminated on both sides of a porous substrate is known to be a separator with better heat resistance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-60777 A Summary of the Invention [Problem to be solved by the invention]

[0005] In a separator in which a porous layer is laminated on both sides of a conventional porous substrate, the respective porous layers laminated on both sides of the porous substrate are generally porous layers having substantially the same or very similar properties. Here, the separator in which a porous layer is laminated on both sides of the conventional porous substrate has lower ion permeability than a separator in which a porous layer is laminated on one side of the porous substrate, and as a result, the battery performance of a non-aqueous electrolyte secondary battery including the separator may be deteriorated. On the other hand, it is known that the deterioration of the ion permeability can be prevented by adopting a porous layer with low air permeability as the porous layer laminated on both sides of the porous substrate. However, a separator in which a porous layer having the above-mentioned low air permeability is laminated on both sides of a porous substrate has low dendrite blocking properties. As a result, a short circuit may easily occur in a non-aqueous electrolyte secondary battery including the separator, and the safety may be deteriorated.

[0006] As described above, in a conventional separator in which a porous layer is laminated on both sides of a porous substrate, there is a trade-off between ion permeability and dendrite blocking property. Therefore, in a non-aqueous electrolyte secondary battery including a separator in which a porous layer is laminated on both sides of a conventional porous substrate, either the battery performance or the safety is deteriorated, and there is a problem in that it is not possible to achieve both excellent battery performance and excellent safety.

[0007] In order to solve the above problems, an object of the present invention is to provide a separator for a non-aqueous electrolyte secondary battery which is excellent in both ion permeability and dendrite blocking properties. [Means for solving the problem]

[0008] Means for Solving the Problems The present inventors have, as a result of intensive research, found that in a separator in which porous layers are laminated on both sides of a porous substrate (porous film), when there is a large difference in the size of pores on the surface between one side of the porous layer and the other side of the porous layer, it is possible to achieve both excellent ion permeability and excellent dendrite blocking properties, and have arrived at the present invention.

[0009] One aspect of the present invention is a separator for a non-aqueous electrolyte secondary battery, comprising a porous film containing a polyolefin resin as a main component and a porous layer laminated on both sides of the porous film, The porous layer contains a resin, The separator for a non-aqueous electrolyte secondary battery satisfies at least one of the following formula (A) and formula (B): (average pore area of ​​one porous layer) / (average pore area of ​​the other porous layer)≧1.7 (A) (Average circular equivalent diameter of one porous layer) - (Average circular equivalent diameter of the other porous layer) ≧ 2.0 nm (B) (In formula (A) and formula (B), of the porous layers laminated on both sides of the porous film, the porous layer having a larger average pore area is defined as one porous layer, and the porous layer having a smaller average pore area is defined as the other porous layer. The average pore area is the average value of the areas of the pores on the surface of the porous layer. The average equivalent circle diameter is the average value of the diameters of circles having the same area as the areas of the pores on the surface of the porous layer.) Effect of the Invention

[0010] The separator for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention exhibits the effects of being excellent in both ion permeability and dendrite blocking properties. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] An embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to each of the configurations described below, and various modifications are possible within the scope of the claims. The technical scope of the present invention also includes embodiments obtained by appropriately combining the technical means disclosed in different embodiments. In this specification, unless otherwise specified, "A to B" representing a numerical range means "A or more, B or less."

[0012] [Embodiment 1: Separator for non-aqueous electrolyte secondary battery] A separator for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention includes a porous film containing a polyolefin resin as a main component, and porous layers laminated on both sides of the porous film, the porous layers including a resin and satisfying at least one of the following formula (A) and formula (B): (average pore area of ​​one porous layer) / (average pore area of ​​the other porous layer)≧1.7 (A) (Average circular equivalent diameter of one porous layer) - (Average circular equivalent diameter of the other porous layer) ≧ 2.0 nm (B) (In formula (A) and formula (B), of the porous layers laminated on both sides of the porous film, the porous layer having a larger average pore area is defined as one porous layer, and the porous layer having a smaller average pore area is defined as the other porous layer. The average pore area is the average value of the areas of the pores on the surface of the porous layer. The average equivalent circle diameter is the average value of the diameters of circles having the same area as the areas of the pores on the surface of the porous layer.) Hereinafter, the separator for a nonaqueous electrolyte secondary battery according to one embodiment of the present invention and the separator for a nonaqueous electrolyte secondary battery according to another embodiment of the present invention will be collectively referred to as the "separator of the present invention." Each member constituting the separator of the present invention will be described in detail below.

[0013] [Porous film] The porous film in one embodiment of the present invention is mainly composed of a polyolefin resin. Here, "mainly composed of a polyolefin resin" means that the proportion of the polyolefin resin in the porous film is 50% by weight or more, preferably 90% by weight or more, and more preferably 95% by weight or more of the total material constituting the porous film.

[0014] The porous film has many interconnected pores inside, allowing gas and liquid to pass from one surface to the other.

[0015] The thickness of the porous film is preferably 4 to 40 μm, and more preferably 5 to 20 μm. If the thickness of the porous film is 4 μm or more, internal short circuit of the battery can be sufficiently prevented. On the other hand, if the thickness of the porous film is 40 μm or less, the nonaqueous electrolyte secondary battery can be prevented from becoming large.

[0016] The polyolefin resin has a weight average molecular weight of 5×10 5 ~15×10 6 It is more preferable that the polyolefin resin contains a high molecular weight component having a weight average molecular weight of 1,000,000 or more. In particular, it is more preferable that the polyolefin resin contains a high molecular weight component having a weight average molecular weight of 1,000,000 or more, since the strength of the obtained porous film and the separator containing the porous film is improved.

[0017] The polyolefin resin is not particularly limited, but examples thereof include thermoplastic resins such as homopolymers or copolymers obtained by polymerizing monomers such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, and 1-hexene. Examples of the homopolymers include polyethylene, polypropylene, and polybutene. Examples of the copolymers include ethylene-propylene copolymers.

[0018] Among these, polyethylene is more preferable because it can prevent (shut down) an excessive current from flowing through the separator at a lower temperature. Examples of the polyethylene include low-density polyethylene, high-density polyethylene, linear polyethylene (ethylene-α-olefin copolymer), and ultra-high molecular weight polyethylene having a weight-average molecular weight of 1,000,000 or more. Among these, the ultra-high molecular weight polyethylene is more preferable.

[0019] The weight per unit area of ​​the porous film can be appropriately determined in consideration of the strength, thickness, weight and handling properties. However, in order to increase the weight energy density and volume energy density of the nonaqueous electrolyte secondary battery, the weight per unit area is preferably 3 to 20 g / m. 2is preferably 3 to 12 g / m 2 More preferably, the thickness is 3 to 10 g / m 2 It is even more preferable that:

[0020] From the viewpoint of obtaining sufficient ion permeability, the air permeability of the porous film is preferably 30 to 500 sec / 100 mL, and more preferably 50 to 300 sec / 100 mL, in terms of Gurley value.

[0021] The porosity of the porous film is preferably 20 to 80% by volume, more preferably 30 to 75% by volume, so as to increase the amount of electrolyte retained and to reliably prevent the flow of excessive current at a lower temperature. The pore size of the pores in the porous film is preferably 0.3 μm or less, more preferably 0.14 μm or less, so as to obtain sufficient ion permeability.

[0022] [Method of manufacturing porous film] The manufacturing method of the porous film is not particularly limited. For example, a polyolefin resin, a pore-forming agent such as an inorganic filler or a plasticizer, and optionally an antioxidant are kneaded and then extruded to prepare a sheet-shaped polyolefin resin composition. Then, the pore-forming agent is removed from the sheet-shaped polyolefin resin composition using a suitable solvent. Then, the polyolefin resin composition from which the pore-forming agent has been removed is stretched to produce the porous film.

[0023] The inorganic filler may be an inorganic filler, specifically, calcium carbonate, etc. The plasticizer may be a low molecular weight hydrocarbon such as liquid paraffin.

[0024] [Porous layer] In one embodiment of the present invention, the porous layer is laminated on both sides of the porous film. That is, in one embodiment of the present invention, a porous layer is laminated on one side of the porous film, and another porous layer is laminated on the side of the porous film opposite to the side on which the porous layer is laminated.

[0025] The porous layer is composed of a resin and, optionally, a filler. Here, the resin may be fibril-like, and a plurality of pores are formed by combining the fibril-like resin. As a result, the porous layer has a porous structure. By having the porous structure, the porous layer can pass gas and liquid from one surface to the other surface. The other porous layer also has a porous structure like the porous layer.

[0026] In one embodiment of the present invention, the porous layer satisfies at least one of the following formula (A) and formula (B). (average pore area of ​​one porous layer) / (average pore area of ​​the other porous layer)≧1.7 (A) (Average circular equivalent diameter of one porous layer) - (Average circular equivalent diameter of the other porous layer) ≧ 2.0 nm (B) The average pore area is the average value of the areas of the pores on the surface of the porous layer. The average equivalent circle diameter is the average of the equivalent circle diameters of the pores on the surface of the porous layer, and the equivalent circle diameter is the diameter of a circle having the same area as the area of ​​the pores. Specifically, the equivalent circle diameter d (nm) is calculated by multiplying the area S (nm 2 ) and the value that satisfies the relationship shown in the following equation (1).

[0027] S = π × (d / 2) 2 (1) Therefore, the circle equivalent diameter is larger as the area of ​​the pores is larger. Therefore, when the average pore area is large, the average circle equivalent diameter is also larger. Here, the pores on the surface of the porous layer refer to pores with openings on the surface of the porous layer. Therefore, the area of ​​the pores refers to the area of ​​each opening on the surface of the porous layer. The average pore area and the average circle equivalent diameter can be calculated, for example, by analyzing an SEM image (hereinafter also referred to as a "surface image") obtained by observing the surface of the porous layer using a scanning electron microscope (SEM) using commercially available image analysis software. Specifically, the average pore area and the average circle equivalent diameter can be calculated by the method described in the examples. In addition, in one embodiment of the present invention, the surface of the porous layer refers to the surface of the porous layer opposite to the surface that contacts the porous film.

[0028] In addition, the conditions of SEM photography when obtaining the surface image, such as acceleration voltage, working distance, image resolution, and magnification, are not particularly limited as long as the pores having an opening can be identified and the area of ​​each pore on the surface of the porous layer can be calculated. The conditions of the photography may be, for example, the photography conditions described in the Examples. In addition, in obtaining the surface image, an operation to adjust the obtained SEM image may be performed using, for example, an autofocus function and an autocontrast function. Furthermore, in the case of measuring the aperture ratio described later, the conditions of SEM photography when obtaining the surface image are not particularly limited as long as the pores having an opening can be identified and the aperture ratio can be calculated.

[0029] In addition, in the separator of the present invention, of the porous layers laminated on both sides of the porous film, the porous layer having the larger average pore area is defined as "one porous layer", and the porous layer having the smaller average pore area is defined as "the other porous layer". Thus, the separator of the present invention satisfies the relationship of (average pore area of ​​one porous layer)>(average pore area of ​​the other porous layer) in the formula (A). As described above, when the average pore area is large, the average equivalent circle diameter is also large, so that the one porous layer defined above has a larger average equivalent circle diameter than the other porous layer. Thus, the separator of the present invention satisfies the relationship of (average equivalent circle diameter of one porous layer)>(average equivalent circle diameter of the other porous layer) in the formula (B).

[0030] As described above, both the average pore area and the average equivalent circle diameter are parameters that represent the area (size) of the openings on the surface of the porous layer. Satisfying at least one of the formula (A) and the formula (B) means that there is provided "one porous layer" and "the other porous layer". The "one porous layer" is a porous layer in which the average pore area and / or the average equivalent circle diameter are large, i.e., the area of ​​the openings of the pores is large. The "other porous layer" is a porous layer in which the average pore area and / or the average equivalent circle diameter are small, i.e., the area of ​​the openings of the pores is small.

[0031] Here, in one embodiment of the present invention, the "one porous layer" having pores with large openings allows gas and liquid to pass through the large openings. Therefore, the "one porous layer" has a small air permeability and high ion permeability. On the other hand, the porous layer having large openings on its surface has a rough structure, and dendrites that are generated and grow in the electrode (negative electrode) of the non-aqueous electrolyte secondary battery easily penetrate the porous layer and the separator including the porous layer. Therefore, in one embodiment of the present invention, the "other porous layer" having a small opening area of ​​the pores has a dense layer structure, and is therefore difficult to be penetrated by the growing dendrites. Therefore, the "other porous layer" has high dendrite blocking properties.

[0032] Therefore, by satisfying the formula (A) and / or formula (B), the separator of the present invention has "one porous layer" with high ion permeability and "the other porous layer" with high dendritic blocking property laminated on each side of the porous film.

[0033] Conventional separators in which porous layers are laminated on both sides of a porous film include the following two types of separators. A separator in which both of the porous layers have high ion permeability but low dendrite blocking properties (hereinafter, referred to as "conventional separator 1"). A separator in which both of the porous layers have low ion permeability but high dendrite blocking properties (hereinafter, referred to as "conventional separator 2").

[0034] The separator of the present invention has an "other porous layer" with high dendrite blocking properties compared to conventional separator 1, and thereby improves the dendrite blocking properties of the entire separator. Also, the separator of the present invention has an "one porous layer" with high ion permeability compared to conventional separator 2, and thereby improves the ion permeability of the entire separator. As a result, the separator of the present invention, unlike conventional separator 1 and conventional separator 2, exhibits the effect of being excellent in both ion permeability and dendrite blocking properties.

[0035] From the viewpoint of improving both the ion permeability and the dendrite blocking property, it is preferable that the separator of the present invention satisfies both the formula (A) and the formula (B). From the same viewpoint, when the separator of the present invention satisfies the formula (A), the "(average pore area of ​​one porous layer) / (average pore area of ​​the other porous layer)" (hereinafter also referred to as "ratio A of the present invention") in the formula (A) is preferably 1.7 or more, more preferably 1.9 or more. From the same viewpoint, when the separator of the present invention satisfies the formula (B), the "(average circular equivalent diameter of one porous layer)-(average circular equivalent diameter of the other porous layer)" (hereinafter also referred to as "difference A of the present invention") in the formula (B) is preferably 2.0 nm or more, more preferably 3.3 nm or more.

[0036] When the present invention satisfies the formula (A), the ratio A of the present invention being excessively large means that the average pore area of ​​one porous layer is excessively large and / or the average pore area of ​​the other porous layer is excessively small. When the average pore area of ​​one porous layer is excessively large, the dendrite blocking property of one porous layer may be excessively reduced, and the dendrite blocking property of the entire separator may be reduced. When the average pore area of ​​the other porous layer is excessively small, the ion permeability of the other porous layer may be excessively reduced, and the ion permeability of the entire separator may be reduced. Therefore, in terms of preventing the above-mentioned dendrite blocking property and / or the ion permeability of the entire separator from being reduced, it is preferable that the ratio A of the present invention is equal to or less than a predetermined upper limit. Specifically, the ratio A of the present invention is preferably equal to or less than 12.0, more preferably equal to or less than 6.0.

[0037] When the present invention satisfies the formula (B), the difference A of the present invention being excessively large means that the average equivalent circle diameter of one porous layer is excessively large and / or the average equivalent circle diameter of the other porous layer is excessively small. When the average equivalent circle diameter of one porous layer is excessively large, the dendrite block property of one porous layer may be excessively decreased, and the dendrite block property of the entire separator may be decreased. When the average equivalent circle diameter of the other porous layer is excessively small, the ion permeability of the other porous layer may be excessively decreased, and the ion permeability of the entire separator may be decreased. Therefore, in terms of suitably preventing the above-mentioned decrease in the dendrite block property of the entire separator and / or the ion permeability of the entire separator, it is preferable that the difference A of the present invention is a predetermined upper limit value or less. Specifically, the difference A of the present invention is preferably 11.0 nm or less, and more preferably 9.3 nm or less.

[0038] In the separator of the present invention, the average pore area of ​​one porous layer and the average pore area of ​​the other porous layer are adjusted within the range described below to satisfy the formula (A), and preferably, the ratio A of the present invention can be controlled within the preferred range described above. 2 It is preferable to adjust the wavelength to 500 nm or more. 2 More preferably, the wavelength is adjusted to 700 nm or more. 2 It is more preferable to adjust the average pore area of ​​one of the porous layers to 5000 nm or more. 2 It is preferable to adjust the wavelength to 3000 nm or less. 2 It is more preferable to adjust the wavelength to 1000 nm or less. 2 It is more preferable to adjust the wavelength to 900 nm or less. 2 It is particularly preferable to adjust the average pore area of ​​the other porous layer to 100 nm or less. 2 It is preferable to adjust the wavelength to 130 nm or more. 2 It is more preferable to adjust the average pore area of ​​the other porous layer to 3000 nm or more. 2 It is preferable to adjust the wavelength to 1800 nm or less. 2 It is more preferable to adjust the wavelength to 500 nm or less. 2 It is more preferable to adjust the wavelength to 400 nm or less. 2 It is particularly preferable to adjust the average pore area of ​​one porous layer to be equal to or less than the above-mentioned preferable lower limit. More specifically, by adjusting the average pore area of ​​one porous layer to be equal to or less than the above-mentioned preferable upper limit, the ratio A of the present invention can be suitably controlled to 1.7 or more. The average pore area of ​​one porous layer and the average pore area of ​​the other porous layer can be controlled within a suitable range by the method described later in the section [Method of manufacturing porous layer].

[0039] In the separator of the present invention, the average equivalent circle diameter of one porous layer and the average equivalent circle diameter of the other porous layer are adjusted within the range described below to satisfy the formula (B), and preferably, the difference A of the present invention can be controlled within the above-mentioned preferred range. Specifically, it is preferable to adjust the average equivalent circle diameter of one porous layer to 18 nm or more, and more preferably to adjust it to 19 nm or more. In addition, it is preferable to adjust the average equivalent circle diameter of one porous layer to 80 nm or less, more preferably to adjust it to 60 nm or less, even more preferably to adjust it to 24 nm or less, and particularly preferably to adjust it to 22 nm or less. Furthermore, it is preferable to adjust the average equivalent circle diameter of the other porous layer to 8 nm or more, and more preferably to adjust it to 10 nm or more. In addition, it is preferable to adjust the average equivalent circle diameter of the other porous layer to 60 nm or less, more preferably to adjust it to 45 nm or less, and even more preferably to adjust it to 18 nm or less. More specifically, by adjusting the average equivalent circular diameter of one porous layer to the above-mentioned preferable lower limit or more and adjusting the average equivalent circular diameter of the other porous layer to the above-mentioned preferable upper limit or less, the difference A of the present invention can be suitably controlled to 2.0 nm or more. The average equivalent circular diameter of one porous layer and the average equivalent circular diameter of the other porous layer can also be controlled within a suitable range by the method described later in the section [Method of manufacturing porous layer].

[0040] In the separator of the present invention, from the viewpoint of further improving both ion permeability and dendrite blocking property, "(the average pore area of ​​one porous layer) - (the average pore area of ​​the other porous layer)" (hereinafter also referred to as "difference B of the present invention) is 100 nm 2 It is preferable that the thickness is 300 nm or more. 2 From the same viewpoint, the difference B of the present invention is preferably 2000 nm or more. 2 It is preferable that the thickness is less than 1200 nm. 2 More preferably, it is 600 nm or less. 2 It is even more preferable that:

[0041] In the separator of the present invention, from the viewpoint of further improving both ion permeability and dendrite blocking property, "(average circular equivalent diameter of one porous layer) / (average circular equivalent diameter of the other porous layer)" (hereinafter also referred to as "ratio B of the present invention") is preferably 1.2 or more. From the same viewpoint, ratio B of the present invention is preferably 4.5 or less, and more preferably 2.0 or less.

[0042] When the "opening ratio", which is the area of ​​the openings relative to the total surface area of ​​the porous layer, is high, the porous layer allows gas and liquid to pass through easily, the air permeability value is small, and ion permeability is improved, for the same reasons as when the average pore area and the average equivalent circle diameter are large. On the other hand, when the "opening ratio" is low, the porous layer is difficult to be penetrated by the growing dendrites, and dendrite blocking properties are improved, for the same reasons as when the average pore area and the average equivalent circle diameter are small. Therefore, from the viewpoint of further improving both the ion permeability and the dendrite blocking properties, it is preferable that the opening ratio of one porous layer is significantly different from the opening ratio of the other porous layer in the separator of the present invention.

[0043] Specifically, in the separator of the present invention, the "opening ratio of one porous layer / opening ratio of the other porous layer" (hereinafter referred to as "ratio C of the present invention") is preferably 2.0 or more, and more preferably 3.0 or more. Also, in the separator of the present invention, the "opening ratio of one porous layer - opening ratio of the other porous layer" (hereinafter referred to as "difference C of the present invention") is preferably 1.5% or more, more preferably 10.0% or more, and even more preferably 18.0% or more.

[0044] Furthermore, when the ratio C of the present invention and / or the difference C of the present invention are excessively large, the dendrite block property and / or ion permeability may decrease for the same reason as when the ratio A of the present invention and / or the difference A of the present invention are excessively large. Therefore, in order to more suitably prevent the above-mentioned dendrite block property of the entire separator and / or the ion permeability of the entire separator from decreasing, it is preferable that the ratio C of the present invention and / or the difference C of the present invention are not more than a predetermined upper limit. Specifically, the ratio C of the present invention is preferably not more than 16.0, and more preferably not more than 10.0. Furthermore, the difference C of the present invention is preferably not more than 26.0%, and more preferably not more than 22.0%.

[0045] The aperture ratio can also be calculated by, for example, analyzing the surface image using commercially available image analysis software, similarly to the average pore area and the average equivalent circle diameter. Specifically, the aperture ratio can also be calculated by the method described in the Examples.

[0046] In the separator of the present invention, the ratio C of the present invention and / or the difference C of the present invention can be controlled within the above-mentioned preferred range by adjusting the aperture ratio of one porous layer and the aperture ratio of the other porous layer within the range described below. Specifically, the aperture ratio of one porous layer is preferably adjusted to 10.0% or more, more preferably adjusted to 20.0% or more. In addition, the aperture ratio of one porous layer is preferably adjusted to 40.0% or less, more preferably adjusted to 30.0% or less. Furthermore, the aperture ratio of the other porous layer is preferably adjusted to 1.0% or more, more preferably adjusted to 1.5% or more. In addition, the aperture ratio of the other porous layer is preferably adjusted to 12.0% or less, more preferably adjusted to 7.0% or less. The aperture ratio of one porous layer and the aperture ratio of the other porous layer can also be controlled within a preferred range by the method described in the section [Method of manufacturing a porous layer] described below.

[0047] The aperture ratio can be controlled to a suitable range, for example, by adjusting the average pore size and / or the average equivalent circle size to the above-mentioned preferred ranges, and then adjusting the density of the apertures on the porous surface to a predetermined range. Specifically, the density of the apertures is 70 pores / μm 2 More preferably, 100 particles / μm 2 It is more preferable that the density of the openings is 280 / μm or more. 2 It is preferable that the number of particles is less than 240 / μm. 2 It is more preferable that the density of the openings is not more than 100%. The density of the openings can be controlled within a suitable range by the method described in the section [Method of manufacturing the porous layer] below.

[0048] In the separator of the present invention, it is preferable that the ratio C of the present invention and the difference C of the present invention have a relationship that satisfies the following formula (C).

[0049] (Proportion of the present invention C) < (Difference of the present invention C) (C) In the separator of the present invention, by satisfying the above formula (C), the ion permeability and the dendrite blocking property can be more suitably improved.

[0050] [resin] In one embodiment of the present invention, the porous layer contains a resin. When the porous layer contains a filler described below, the resin can function as a binder resin that bonds the fillers together, the filler and the positive electrode or the negative electrode, or the filler and the porous film.

[0051] In one embodiment of the present invention, the resin is preferably insoluble in the electrolyte of the battery and is electrochemically stable within the range of use of the battery. The resin is also preferably a heat-resistant resin.

[0052] The resin is not particularly limited. Specific examples of the resin include polyolefin, (meth)acrylate resin, fluorine-containing resin, polyamide resin, polyimide resin, polyester resin, rubber, resin with a melting point or glass transition temperature of 180° C. or higher, water-soluble polymer, polycarbonate, polyacetal, polyether ether ketone, etc. The resin may be one type or a mixture of two or more types of resins.

[0053] Among the specific examples of the resins, (meth)acrylate resins, fluorine-containing resins, polyamide resins and polyester resins are preferred.

[0054] Examples of polyamide resins include aromatic polyamides, preferably fully aromatic polyamides (aramid resins). Examples of polyester resins include polyarylates and liquid crystal polyesters. Examples of fluorine-containing resins include polyvinylidene fluoride resins. Examples of water-soluble polymers include polyvinyl alcohol, polyethylene glycol, cellulose ether, sodium alginate, polyacrylic acid, polyacrylamide, polymethacrylic acid, and the like.

[0055] Specific examples of the aramid resin include poly(paraphenylene terephthalamide), poly(metaphenylene isophthalamide), poly(parabenzamide), poly(metabenzamide), poly(4,4'-benzanilide terephthalamide), poly(paraphenylene-4,4'-biphenylenedicarboxylic acid amide), poly(metaphenylene-4,4'-biphenylenedicarboxylic acid amide), poly(paraphenylene-2,6-naphthalenedicarboxylic acid amide), poly(metaphenylene-2,6-naphthalenedicarboxylic acid amide), poly(para ... Examples of the poly(4,4'-diphenylsulfonyl terephthalamide) include poly(2-chloroparaphenylene terephthalamide), paraphenylene terephthalamide / 2,6-dichloroparaphenylene terephthalamide copolymer, metaphenylene terephthalamide / 2,6-dichloroparaphenylene terephthalamide copolymer, poly(4,4'-diphenylsulfonyl terephthalamide), paraphenylene terephthalamide / 4,4'-diphenylsulfonyl terephthalamide copolymer, etc. Among these, poly(paraphenylene terephthalamide) is more preferred.

[0056] The method for producing the resin is not particularly limited, and any conventionally known method can be used as appropriate.

[0057] [Filler] In one embodiment of the present invention, the porous layer may contain a filler, the content of which is preferably 30% by weight or more and 99% by weight or less, more preferably 40% by weight or more and 85% by weight or less, and even more preferably 40% by weight or more and 70% by weight or less, based on the total weight of the porous layer.

[0058] In one embodiment of the present invention, the material constituting the filler is not particularly limited. The filler may be composed of only one type of filler material, or may be composed of two or more types of fillers each having a different constituent material.

[0059] The filler may be an inorganic filler or an organic filler. Examples of the inorganic filler include fillers made of inorganic substances such as calcium carbonate, talc, clay, kaolin, silica, hydrotalcite, diatomaceous earth, magnesium carbonate, barium carbonate, calcium sulfate, magnesium sulfate, barium sulfate, aluminum hydroxide, boehmite, magnesium hydroxide, calcium oxide, magnesium oxide, titanium oxide, titanium nitride, alumina (aluminum oxide), aluminum nitride, mica, zeolite, and glass. Among these, the inorganic filler is preferably a filler made of an inorganic oxide such as silica, calcium oxide, magnesium oxide, titanium oxide, alumina, mica, zeolite, aluminum hydroxide, or boehmite, more preferably a filler made of calcium oxide, magnesium oxide, or alumina, and even more preferably a filler made of alumina. In addition, examples of the organic filler include fillers made of resin.

[0060] The shape of the filler is not particularly limited and may be, for example, spherical, elliptical, plate-like, rod-like, or irregular. Among these, the shape of the filler is preferably spherical.

[0061] The average particle size of the filler is preferably 0.01 μm or more and 10 μm or less, and more preferably 0.02 μm or more and 5 μm or less.

[0062] [Properties of the porous layer] The thickness of the porous layer is preferably 0.5 to 15 μm, and more preferably 1 to 10 μm. When the thickness is within this range, it is suitable for preventing internal short circuits due to damage to the nonaqueous electrolyte secondary battery, for retaining the electrolyte in the porous layer, and for preventing deterioration of rate characteristics or cycle characteristics.

[0063] The weight per unit area of ​​the porous layer can be appropriately determined in consideration of the strength, film thickness, weight and handling property of the porous layer. The weight per unit area of ​​the porous layer is 0.5 to 20 g / m 2It is preferable that the thickness is 0.5 to 10 g / m 2 By setting the weight per unit area within these numerical ranges, it is possible to increase the weight energy density and volume energy density of the nonaqueous electrolyte secondary battery.

[0064] The porosity of the porous layer is preferably 40% or more and 80% or less, and more preferably 50% or more and 70% or less. When the porosity is within the above range, the separator and the nonaqueous electrolyte secondary battery including the separator can obtain sufficient ion permeability.

[0065] The pores in the porous layer preferably have a pore size of 1.0 μm or less, more preferably 0.5 μm or less. By setting the pore size to this size, the separator and the nonaqueous electrolyte secondary battery including the separator can obtain sufficient ion permeability.

[0066] The porous layer may contain other components in addition to the resin and the filler. Examples of the other components include a surfactant and a wax. The content of the other components is preferably 0% by weight to 10% by weight based on the total weight of the porous layer.

[0067] In one embodiment of the present invention, it is preferable that the composition of the "one porous layer" and the composition of the "other porous layer" are substantially the same. Here, "substantially the same composition" means that the type of resin as a constituent material and the type of filler as an optional constituent material are the same between the "one porous layer" and the "other porous layer". In addition, the difference in the weight ratio (content) of the resin and the weight ratio (content) of the filler with respect to the weight of the entire porous layer between the "one porous layer" and the "other porous layer" is more preferably 30% or less, even more preferably 15% or less, and particularly preferably 0%. The difference in the weight ratio (content) of the resin and the weight ratio (content) of the filler being 0% means that the contents of the resin and the filler are the same.

[0068] [Method of manufacturing the porous layer] The method for producing the porous layer includes, for example, preparing a coating liquid by dissolving the resin in a solvent, applying the coating liquid to a substrate to form a coating layer, and then removing the solvent from the coating layer to form the porous layer. The substrate can be, for example, the porous film. In addition, when the porous layer contains the filler, the coating liquid can be prepared by dissolving the resin in a solvent and dispersing the filler.

[0069] The solvent (dispersion medium) is sufficient if it does not adversely affect the substrate such as a porous film and can dissolve the resin uniformly and stably, and if the filler is included, it is sufficient if it can disperse the filler uniformly and stably. Specific examples of the solvent include water; lower alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, and t-butyl alcohol; acetone, toluene, xylene, hexane, N-methylpyrrolidone (NMP), N,N-dimethylacetamide, and N,N-dimethylformamide. The solvent may be used alone or in combination of two or more.

[0070] The coating liquid may be formed by any method as long as it satisfies the conditions such as the resin solid content (resin concentration) required to obtain a desired porous layer, and the amount of the filler, if a filler is included. Specific examples of the forming method include mechanical stirring, ultrasonic dispersion, high pressure dispersion, and media dispersion. In addition, if the filler is included, the filler may be dispersed in the solvent using a conventionally known dispersing machine such as a three-one motor. In addition, the coating liquid may contain additives such as a dispersant, a plasticizer, a surfactant, and a pH adjuster, in addition to the resin and the filler, as long as the purpose of the present invention is not impaired.

[0071] The method of applying the coating liquid to the substrate is not particularly limited. For example, a sequential lamination method in which a porous layer is formed on one side of the substrate and then a porous layer is formed on the other side, or a simultaneous lamination method in which porous layers are simultaneously formed on both sides of the substrate, etc. may be used.

[0072] The method for applying the coating liquid to the substrate may be any method that can achieve the required basis weight and coating area. For example, a conventionally known method such as a gravure coater method may be used as the coating method.

[0073] The method for forming the porous layer is not particularly limited, and examples thereof include the following method (a) or (b).

[0074] (a) A method in which the coating layer is immersed in a deposition solution to deposit the coating layer, and then the coating layer is washed with water and dried to remove the solvent, thereby forming the porous layer (hereinafter referred to as the "immersion precipitation method").

[0075] (b) A method in which the substrate on which the coating layer has been formed is exposed to air containing water vapor to cause the coating layer to precipitate, and then the coating layer is washed with water and dried to remove the solvent, thereby forming the porous layer (hereinafter referred to as the "humidity precipitation method").

[0076] In the immersion precipitation method, the method of immersing the coating layer in the precipitation liquid is not particularly limited. The coating layer and the substrate may be immersed together in the precipitation liquid, or only the coating layer may be immersed in the precipitation liquid.

[0077] The precipitating liquid may be a mixture of a solvent that cannot dissolve the resin and an organic solvent that can dissolve the resin. In the precipitating liquid, the precipitating rate of the resin can be controlled by adjusting the mixing ratio of the solvent that cannot dissolve the resin and the organic solvent. Specifically, when the mixing ratio of the organic solvent is small, the precipitating rate of the resin is high.

[0078] The solvent incapable of dissolving the resin is not particularly limited, and may be, for example, water, etc. The organic solvent is not particularly limited, and may be, for example, NMP, etc.

[0079] In the humidity precipitation method, the rate at which the resin is precipitated can be controlled by adjusting the temperature and humidity of the air containing water vapor. Specifically, the higher the temperature of the air containing water vapor, the faster the resin is precipitated. Also, the higher the humidity of the air containing water vapor, the faster the resin is precipitated.

[0080] Furthermore, in general, the immersion precipitation method provides a faster precipitation rate of the resin than the humidity precipitation method.

[0081] When the resin deposition rate is high, the resin is mainly deposited on the surface of the porous layer, and as a result, a film with a high resin ratio is formed on the surface of the porous layer. In a film with a high resin ratio, the effect of opening the holes by the filler is reduced. Therefore, the pores in the film with a high resin ratio are easily blocked. As a result, the pores on the surface of the porous layer are blocked, and the area of ​​the openings is reduced. Therefore, when the resin deposition rate is increased to form a porous layer using the above-mentioned method, the average pore area and / or the average equivalent circle diameter can be controlled to a small range in the obtained porous layer. Conversely, when the resin deposition rate is decreased to form a porous layer, the average pore area and / or the average equivalent circle diameter can be controlled to a large range in the obtained porous layer.

[0082] Therefore, the separator of the present invention can be produced by a method including the following steps (i) and (ii).

[0083] (i) A step of forming the "one porous layer" on one side of the porous film by slowing down the deposition rate of the resin.

[0084] (ii) A step of forming the "other porous layer" on the other side of the porous film by increasing the resin deposition rate.

[0085] A specific method for producing the separator of the present invention can include, for example, a method in which the "one porous layer" is formed on one side of the porous film by the humidity precipitation method, and the "other porous layer" is formed on the other side of the porous film by the immersion precipitation method.

[0086] When the step (i) and the step (ii) are performed, the step (i) may be performed first and then the step (ii), the step (ii) may be performed first and then the step (i), or the step (i) and the step (ii) may be performed simultaneously.

[0087] In the steps (i) and (ii), the operation of washing and drying the deposited coating layer may be performed in common. In other words, in the production of the separator of the present invention, after depositing the coating layer on both sides of the porous film, the coating layer or a laminate consisting of the coating layer and the porous film may be washed and dried in one go to form the porous layer on both sides of the porous film.

[0088] The conditions for forming the porous layer include, for example, the temperature and humidity of the air containing water vapor when the humidity deposition method is adopted, and the mixing ratio of the solvent that cannot dissolve the resin and the organic solvent in the deposition solution when the immersion deposition method is adopted. When the porous layer is formed on one side of each of the porous films, the average pore area and / or the average equivalent circle diameter can be controlled within a suitable range by appropriately adjusting the type of the formation method and the formation conditions in the formation of each of the porous layers. As a result, the separator of the present invention can be suitably manufactured.

[0089] In addition, when the precipitation speed of the resin is fast, the area of ​​the openings on the surface of the obtained porous layer is likely to be small, and therefore the density of the openings is likely to be low. Therefore, when the precipitation speed of the resin is fast to form a porous layer, the average pore area and / or the average equivalent circle diameter can be small in the obtained porous layer, and the opening ratio can also be small. Conversely, when the precipitation speed of the resin is slow to form a porous layer, the average pore area and / or the average equivalent circle diameter can be large in the obtained porous layer, and the opening ratio can also be large.

[0090] Furthermore, when the porous layer contains the filler, the filler functions as a pore-forming agent. Therefore, when the filler is used as a raw material in the manufacturing method of the porous layer, the number of pores formed can be increased by increasing the amount of the filler used, and the density of the openings can be increased. Therefore, the opening ratio can be increased in the obtained porous layer by increasing the amount of the filler used. Conversely, the number of pores formed can be decreased by decreasing the amount of the filler used, and the density of the openings can be decreased. Therefore, the opening ratio can be reduced in the obtained porous layer by decreasing the amount of the filler used.

[0091] As described above, in the above-mentioned manufacturing method, when the porous layer is formed on each side of the porous film, the opening ratio can be controlled within a suitable range by appropriately adjusting the amount of filler used, the type of formation method, and the formation conditions.

[0092] [Embodiment 2: Nonaqueous electrolyte secondary battery member, Embodiment 3: Nonaqueous electrolyte secondary battery] The nonaqueous electrolyte secondary battery member according to one embodiment of the present invention includes a positive electrode, a separator according to one embodiment of the present invention, and a negative electrode arranged in this order. The nonaqueous electrolyte secondary battery according to one embodiment of the present invention includes the separator according to one embodiment of the present invention.

[0093] The nonaqueous electrolyte secondary battery member, by including the separator, exhibits the effect of providing excellent battery performance and safety in the nonaqueous electrolyte secondary battery. The nonaqueous electrolyte secondary battery, by including the separator, exhibits the effect of providing excellent battery performance and safety.

[0094] In non-aqueous electrolyte secondary batteries, dendrites usually form and grow on the negative electrode. Therefore, in the non-aqueous electrolyte secondary battery member and the non-aqueous electrolyte secondary battery, it is preferable from the viewpoint of further improving the above-mentioned safety that the separator of the present invention is disposed so that the "other porous layer" having high dendrite blocking property is located on the negative electrode side.

[0095] A conventionally known manufacturing method can be used as the manufacturing method of the nonaqueous electrolyte secondary battery. For example, the nonaqueous electrolyte secondary battery member is formed by arranging a positive electrode, the separator, and a negative electrode in this order. Here, the porous layer of the separator is between the porous film and at least one of the positive electrode and the negative electrode. Next, the nonaqueous electrolyte secondary battery member is placed in a container that will become the housing of the nonaqueous electrolyte secondary battery. After filling the container with the nonaqueous electrolyte, the container is sealed while reducing the pressure. This allows the nonaqueous electrolyte secondary battery to be manufactured.

[0096] <Positive electrode> The positive electrode in one embodiment of the present invention is not particularly limited as long as it is generally used as a positive electrode of a non-aqueous electrolyte secondary battery. For example, a positive electrode sheet having a structure in which an active material layer containing a positive electrode active material and a binder is formed on a positive electrode current collector can be used as the positive electrode. The active material layer may further contain a conductive agent.

[0097] The positive electrode active material may be, for example, a material capable of doping / dedoping metal ions such as lithium ions or sodium ions, etc. Examples of such materials include lithium composite oxides containing at least one transition metal such as V, Mn, Fe, Co, and Ni.

[0098] The conductive agent may be, for example, one or more selected from carbonaceous materials such as natural graphite, artificial graphite, cokes, carbon black, pyrolytic carbons, carbon fibers, and baked organic polymer compounds.

[0099] Examples of the binder include fluorine-based resins such as polyvinylidene fluoride (PVDF), acrylic resins, and styrene-butadiene rubber.

[0100] The positive electrode current collector may be made of a conductor such as Al, Ni, or stainless steel.

[0101] Examples of methods for producing a positive electrode sheet include a method in which a positive electrode active material, a conductive agent, and a binder are pressure-molded on a positive electrode current collector.

[0102] <Negative electrode> The negative electrode in one embodiment of the present invention is not particularly limited as long as it is generally used as a negative electrode of a non-aqueous electrolyte secondary battery. For example, a negative electrode sheet having a structure in which an active material layer containing a negative electrode active material and a binder is formed on a negative electrode current collector can be used as the negative electrode. The active material layer may further contain a conductive agent.

[0103] The negative electrode active material may be, for example, a material capable of doping / de-doping metal ions such as lithium ions or sodium ions, etc. Examples of such materials include carbonaceous materials such as natural graphite.

[0104] The negative electrode current collector may be made of, for example, Cu, Ni, stainless steel, or the like.

[0105] The negative electrode sheet can be produced, for example, by pressurizing and molding a negative electrode active material on a negative electrode current collector.

[0106] <Nonaqueous electrolyte> The nonaqueous electrolyte in one embodiment of the present invention is not particularly limited as long as it is a nonaqueous electrolyte generally used in nonaqueous electrolyte secondary batteries. For example, a nonaqueous electrolyte obtained by dissolving a lithium salt in an organic solvent can be used as the nonaqueous electrolyte. For example, LiClO 4 , LiPF 6 , LiAsF 6 , LiSbF 6 , LiBF4 , LiCF 3 SO 3 , LiN(CF 3 SO 2 ) 2 , LiC(CF 3 SO 2 ) 3 , Li 2 B 10 Cl 10 , lithium salts of lower aliphatic carboxylic acids and LiAlCl 4 One or more selected from the above can be mentioned.

[0107] Examples of the organic solvent constituting the nonaqueous electrolyte solution include one or more selected from carbonates, ethers, esters, nitriles, amides, carbamates, sulfur-containing compounds, and fluorine-containing organic solvents obtained by introducing a fluorine group into these organic solvents.

[0108] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0109] [summary] One embodiment of the present invention may include the following inventions [1] to [6]. [1] A separator for a non-aqueous electrolyte secondary battery, comprising a porous film containing a polyolefin resin as a main component and a porous layer laminated on both sides of the porous film, The porous layer contains a resin, A separator for a non-aqueous electrolyte secondary battery, which satisfies at least one of the following formulas (A) and (B): (average pore area of ​​one porous layer) / (average pore area of ​​the other porous layer)≧1.7(A) (Average circular equivalent diameter of one porous layer) - (Average circular equivalent diameter of the other porous layer) ≧ 2.0 nm (B) (In formula (A) and formula (B), of the porous layers laminated on both sides of the porous film, the porous layer having a larger average pore area is defined as one porous layer, and the porous layer having a smaller average pore area is defined as the other porous layer. The average pore area is the average value of the areas of the pores on the surface of the porous layer. The average equivalent circle diameter is the average value of the diameters of circles having the same area as the areas of the pores on the surface of the porous layer.) [2] The porous layer contains a filler, The separator for a non-aqueous electrolyte secondary battery according to [1], wherein a content of the filler in the porous layer is 30% by weight or more and 99% by weight or less, based on a total weight of the porous layer. [3] The separator for a non-aqueous electrolyte secondary battery according to [1] or [2], wherein the resin is at least one selected from the group consisting of (meth)acrylate-based resins, fluorine-containing resins, polyamide-based resins, and polyester-based resins. [4] The separator for a non-aqueous electrolyte secondary battery according to [3], wherein the resin comprises a polyamide-based resin, and the polyamide-based resin is an aramid resin. [5] A member for a non-aqueous electrolyte secondary battery, comprising a positive electrode, the separator for a non-aqueous electrolyte secondary battery according to any one of [1] to [4], and a negative electrode, arranged in this order. [6] A non-aqueous electrolyte secondary battery comprising the separator for a non-aqueous electrolyte secondary battery according to any one of [1] to [4].

[0110] The scope of the nonaqueous electrolyte secondary battery separator, nonaqueous electrolyte secondary battery member, and nonaqueous electrolyte secondary battery according to one embodiment of the present invention may include any combination of the features described in the above-mentioned configurations within the scope of the claims. EXAMPLES

[0111] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0112] [Measurement methods for various physical properties] Various physical properties in Examples 1 to 3 and Comparative Examples 1 and 2 were measured by the following methods.

[0113] [Total thickness of porous layer] The thicknesses (unit: μm) of the porous films and separators described in Examples 1 to 3 and Comparative Examples 1 and 2 were measured using a high-precision digital length measuring machine (Litematic VL-50B) manufactured by Mitutoyo Corporation. Then, the difference between the thickness of the separator and the thickness of the porous film was calculated, and the calculated value was taken as the total thickness (unit: μm) of the porous layers included in the separator. Here, the total thickness of the porous layers means the sum of the thicknesses of the porous layers formed on both sides (front and back) of the porous film in the separator.

[0114] [Air permeability per film thickness of porous layer] <Measurement and calculation of air permeability of porous layer> From the porous film and separator described in Examples 1 to 3 and Comparative Examples 1 and 2, a square of 60 mm x 60 mm in size was cut out to obtain a sample for measuring the air permeability of the porous film and the separator. The sample for measuring the air permeability of the porous film and the separator was placed in a digital type Oken type air permeability tester EGO1 manufactured by Asahi Seiko Co., Ltd., and the air permeability of the porous film and the separator was measured, respectively, to obtain the air permeability (A) (unit: s / 100 ml) of the porous film and the air permeability (B) (unit: s / 100 ml) of the separator. Then, the air permeability (C) (unit: s / 100 ml) of the porous layer was calculated from the measured values ​​of (A) and (B) according to the following formula. Air permeability of porous layer (C) = Air permeability of separator (B) - Air permeability of porous film (A)

[0115] <Calculation of air permeability per film thickness of porous layer> The air permeability (C) (unit: s / 100 ml) of the porous layer obtained by the above-mentioned method was divided by the film thickness (unit: μm) of the porous layer calculated by the method described in the "Film thickness of porous layer" column above to calculate the air permeability per unit film thickness of the porous layer (unit: (s / 100 ml) / μm).

[0116] [Average pore area, average equivalent circle diameter, and aperture ratio of porous layer]

[0117] The laminated separator for non-aqueous electrolyte secondary batteries manufactured in the examples and comparative examples were used as measurement samples. In the measurement samples, the surface of one of the porous layers laminated on both sides of the porous film (hereinafter referred to as the "first side") was vapor-deposited with osmium (Os). The first side on which Os was vapor-deposited was observed using a scanning electron microscope (SEM, S-4800 (manufactured by Hitachi High-Technologies Corporation)) to obtain a surface image of the porous layer. The conditions at that time were as shown below. Acceleration voltage: 0.8kV Working distance (WD): 3mm Probe current: High Condenser lens 1:1 Condenser lens 2:1 Emission current: 20uA ·Backscattered electron image ·Image resolution 4.96nm / pix In this way, five or more surface images were obtained for the first surface.

[0118] For each of the five or more surface images, a two-dimensional quantitative analysis of the pores was performed using software from Ratoc Systems Engineering (TRI / 3D-BON-FCS: 2D particle analysis option), and the average pore area, average equivalent circle diameter, and aperture ratio in the surface image to be measured were calculated. The average values ​​of the calculated average pore area, average equivalent circle diameter, and aperture ratio were calculated using the number of surface images. The calculated average values ​​were taken as the average pore area, average equivalent circle diameter, and aperture ratio in the first surface.

[0119] The two-dimensional quantitative analysis was carried out using the above software by a method consisting of the following steps (a) to (i). (a) The surface image was subjected to two-tone gradation for the pores and the substance of the porous layer, to obtain image a in which the pores and the substance of the porous layer were in two gradations. (b) Using image a obtained in step (a), two-dimensionally isolated pores were identified and labeled. The number of labeled pores was more than 3,000 per image. (c) The area of ​​each of the pores labeled in step (b), i.e., the pore area S (nm 2 ) was calculated. (d) The pore area S (nm ) of each pore in the surface image to be measured calculated in step (c). 2 ) the equivalent circle diameter d (nm) of each pore was calculated so as to satisfy the following formula (1). S = π × (d / 2) 2 (1) (e) The pore areas of all pores calculated in step (c) are added together to obtain the total area S of the pores in the surface image to be measured. tot (nm 2 ) was calculated. (f) The total pore area S calculated in step (e) tot (nm 2 ) and the number n (of pores) labeled in step (b), the average pore area S in the surface image to be measured is calculated based on the following formula (2): av was calculated. S av =S tot / n (2) (g) The circular equivalent diameters of all pores calculated in step (d) are added together to obtain the sum d of the circular equivalent diameters of the pores in the surface image to be measured. tot (nm) was calculated. (h) The sum of the circle equivalent diameters of each pore calculated in step (g), d tot Using the surface area (nm) and the number n of pores labeled in step (b), the average pore area d av was calculated. d av =d tot / n (3) (i) The total area S of the pores in the surface image to be measured calculated in step (e) tot (nm2 ) and the area (nm 2 ) was used to calculate the aperture ratio in the surface image to be measured based on the following formula (4). Opening rate (%) = (total area of ​​pores) / (area of ​​surface image) (4)

[0120] Next, the average pore area, average equivalent circle diameter and opening ratio of the other porous layer surface of the measurement sample (hereinafter referred to as the "second side") were calculated using the same method as that used for the first side described above.

[0121] Next, the average pore area on the first surface was compared with the average pore area on the second surface, and the porous layer having the surface with the larger average pore area was designated as "one porous layer," and the porous layer having the surface with the smaller average pore area was designated as "the other porous layer."

[0122] Then, the ratio of the "average pore area of ​​one porous layer" to the "average pore area of ​​the other porous layer", that is, the ratio A of the present invention, was calculated. The difference between the "average circle equivalent diameter of one porous layer" and the "average circle equivalent diameter of the other porous layer", that is, the difference A of the present invention, was calculated. The difference between the "average pore area of ​​one porous layer" and the "average pore area of ​​the other porous layer", that is, the difference B of the present invention, was calculated. The ratio of the "average circle equivalent diameter of one porous layer" to the "average circle equivalent diameter of the other porous layer", that is, the ratio B of the present invention, was calculated. The ratio of the "opening ratio of one porous layer" to the "opening ratio of the other porous layer", that is, the ratio C of the present invention, was calculated. The difference between the "opening ratio of one porous layer" and the "opening ratio of the other porous layer", that is, the difference C of the present invention, was calculated.

[0123] [Trickle test] <Preparation of non-aqueous electrolyte secondary battery for testing> Using the laminated separators for nonaqueous electrolyte secondary batteries obtained in Examples 1 to 3 and Comparative Examples 1 and 2, nonaqueous electrolyte secondary batteries for testing were fabricated by the methods shown in 1. to 4. below. 1. A positive electrode and a negative electrode were prepared. The positive electrode had a thickness of 57.9 μm and a density of 2.52 g / cm3 The positive electrode active material was LiNi 0.5 Mn 0.3 Co 0.2 O 2 The negative electrode had a thickness of 48.4 μm and a density of 1.41 g / cm. 3 The negative electrode active material had a composition of 98 parts by weight of natural graphite, 1 part by weight of a binder (styrene butadiene rubber), and 1 part by weight of carboxymethyl cellulose. 2. The positive electrode, the separator and the negative electrode were laminated in this order in a laminate pouch to prepare a member for a non-aqueous electrolyte secondary battery. 3. The nonaqueous electrolyte secondary battery member was placed in a bag formed by laminating an aluminum layer and a heat seal layer, and a nonaqueous electrolyte was poured in. The nonaqueous electrolyte was a mixture of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate in a volume ratio of 3:5:2, and LiPF with a concentration of 1 mol / L was poured into the mixture. 6 The dissolved one was used. 4. The bag was heat sealed while the pressure inside the bag was reduced, thereby producing a non-aqueous electrolyte secondary battery for testing.

[0124] <Trickle test> Next, a trickle test was performed according to the following procedures 1 to 3, and the test time was measured when the current value during the trickle test reached 0.4 mA or more. The measured test time is the time (unit: hour) until a micro-short circuit caused by the formation and growth of dendrites occurred in the trickle test. 1. The test nonaqueous electrolyte secondary battery was subjected to one initial charge / discharge cycle under the following conditions: temperature: 25° C., voltage range: 2.7 to 4.2 V, current value: 0.1 C (charge), 0.2 C (discharge). Here, 1 C is the current value at which the rated capacity based on the discharge capacity per hour rate is discharged in one hour. 2. After the initial charge / discharge, the test nonaqueous electrolyte secondary battery was subjected to 10 cycles of charge / discharge under the following conditions: temperature: 25°C, voltage range: 2.7 to 4.2V, current value: 1C (charge), 5C (discharge), to age the test nonaqueous electrolyte secondary battery. 3. After the aging, the test non-aqueous electrolyte secondary battery was charged at a voltage of 4.5 V (i.e., 4.6 V (vs Li / Li)) at a temperature of 25° C. and a current value of 1 C (charging). + After the constant current charging, the test nonaqueous electrolyte secondary battery was charged at 45° C. and 4.5 V (i.e., 4.6 V (vs Li / Li + )) and a 450-hour trickle charge was performed.

[0125] [Production Example 1: Preparation of Coating Fluid] As the resin constituting the porous layer, poly(paraphenylene terephthalamide) (hereinafter referred to as "PPTA"), which is a type of aramid resin, was synthesized by the following method.

[0126] A 3 L separable flask equipped with a stirring blade, a thermometer, a nitrogen inlet, and a powder addition port was used as a synthesis vessel. 2200 g of N-methyl-2-pyrrolidone (NMP) was charged into a thoroughly dried flask. 151.07 g of calcium chloride powder was added thereto, and the mixture was heated to 100°C to completely dissolve, obtaining an NMP solution of calcium chloride. The calcium chloride powder used was previously vacuum dried at 200°C for 2 hours.

[0127] Next, the temperature of the NMP solution of calcium chloride was returned to room temperature, and 68.23 g of paraphenylenediamine was added and completely dissolved to obtain solution A. While keeping the temperature of solution A at 20°C ± 2°C, 124.25 g of terephthalic acid dichloride was added to solution A in four portions at intervals of about 10 minutes to obtain solution B. Thereafter, while continuing stirring, solution B was aged for 1 hour while keeping the temperature at 20°C ± 2°C to obtain an aramid polymerization liquid containing 6 wt% of PPTA. The intrinsic viscosity of PPTA contained in the aramid polymerization liquid was 1.5 g / dL.

[0128] 100 parts by weight of the aramid polymerization liquid was weighed out in another flask, and 6.0 parts of alumina A (average particle size: 13 nm) was added to obtain a mixed liquid A. In the mixed liquid A, the weight ratio of PPTA to alumina A was 1:1. Next, NMP was added to the mixed liquid A so that the solid content was 4.5% by weight, and the mixture was stirred for 240 minutes to obtain a mixed liquid B. The "solid content" here refers to the total weight of PPTA and alumina A. Next, 0.73 parts of calcium carbonate was added to the mixed liquid B and the mixture was stirred for 240 minutes to neutralize the solution, thereby obtaining a neutralized liquid. Then, the neutralized liquid was degassed under reduced pressure to prepare a slurry coating liquid.

[0129] [Example 1] Porous film (Porous polyethylene film, thickness: 9μm, weight: 4.7g / m 2) was conveyed, a slurry coating liquid was applied to one side (front side) of the porous film, forming a coating film on one side of the porous film. Then, while conveying the porous film on which the coating film was formed, the coating film and the porous film were passed through a deposition tank set at 50°C and a relative humidity of 70%, and the coating film was exposed to air containing water vapor at 50°C and a relative humidity of 70%. As a result, PPTA was precipitated on one side (front side) of the porous film, forming a coating layer. Next, a slurry coating liquid was applied to the other side (rear side) of the porous film, forming another coating film. Then, while conveying the porous film on which the other coating film was formed, the other coating film and the porous film were passed through an immersion tank filled with a mixture of ion-exchanged water:NMP=40:60 (weight ratio). As a result, PPTA was precipitated on the other side (rear side) of the porous film, forming another coating layer. Next, the porous film and a laminate consisting of the coating layer and another coating layer deposited on both sides of the porous film were washed with water to remove calcium chloride and the solvent from the coating layer and the other coating layer. The laminate was then dried to form a porous layer on both sides of the porous film. As a result, a double-sided laminated separator wound body (1) was obtained in which a porous layer was laminated on both sides of the porous film. The double-sided laminated separator wound body (1) was used as a separator (1).

[0130] [Example 2] A double-sided laminated separator wound body (2) was obtained by the same operation as in Example 1, except that the mixture filled in the immersion tank was changed to ion-exchanged water:NMP=50:50 (weight ratio). The double-sided laminated separator wound body (2) was used as the separator (2).

[0131] [Example 3] A double-sided laminated separator wound body (3) was obtained by the same operation as in Example 1, except that the mixture filled in the immersion tank was changed to ion-exchanged water:NMP=60:40 (weight ratio). The double-sided laminated separator wound body (3) was used as the separator (3).

[0132] [Comparative Example 1] The same operations as in Example 1 were carried out, except that instead of passing the other coating film and the porous film through an immersion tank, the other coating film and the porous film were passed through a precipitation tank set at 50°C and a relative humidity of 70%, and the other coating film was exposed to air containing water vapor at 50°C and a relative humidity of 70%, to obtain a double-sided laminated separator wound body (4). The double-sided laminated separator wound body (4) was used as a separator (4).

[0133] [Comparative Example 2] While conveying the same porous film as the porous film used in Example 1, a slurry coating liquid was applied to one side (surface) of the porous film to form a coating film on one side of the porous film. Then, while conveying the porous film on which the coating film was formed, the coating film and the porous film were passed through an immersion tank filled with ion-exchanged water to precipitate PPTA on one side (surface) of the porous film to form a coating layer. Next, the same operation was performed on the other side (rear side) of the porous film to precipitate PPTA on the other side (rear side) of the porous film to form another coating layer. Next, the porous film and a laminate consisting of the coating layer and another coating layer precipitated on both sides of the porous film were washed with water to remove calcium chloride and the solvent from the coating layer and the other coating layer. Then, the laminate was dried to form a porous layer on both sides of the porous film. As a result, a double-sided laminated separator wound body (5) was obtained in which porous layers were laminated on both sides of the porous film. The double-sided laminated separator wound body (5) was used as a separator (5).

[0134] [result] The physical properties of the separators (1) to (5) described in Examples 1 to 3 and Comparative Examples 1 and 2 were measured by the above-mentioned methods, and the results are shown in Tables 1 to 3 below. In the separators (1) to (3), the porous layer formed by the method of exposing the coating film to air containing water vapor (humidity precipitation method) was the "one porous layer". In the separators (1) to (3), the porous layer formed by the method of passing the other coating film and the porous film through an immersion tank filled with a mixed liquid (immersion precipitation method) was the "other porous layer". [Table 1] [Table 2] [Table 3]

[0135] As shown in Table 1, separators (1) to (3) produced in Examples 1 to 3 satisfy at least one of the following formulas (A) and (B), and therefore correspond to the separators of the present invention. On the other hand, separators (4) and (5) produced in Comparative Examples 1 and 2 do not satisfy the following formulas (A) and (B), and therefore do not correspond to the separators of the present invention. (average pore area of ​​one porous layer) / (average pore area of ​​the other porous layer)≧1.7 (A) (Average circular equivalent diameter of one porous layer) - (Average circular equivalent diameter of the other porous layer) ≧ 2.0 nm (B) In addition, the above formula (A) essentially means that "the ratio A of the present invention is 1.7 or more," and the above formula (B) essentially means that "the difference A of the present invention is 2.0 nm or more."

[0136] The separators (1) to (3) have a longer test time measured in the trickle test, i.e., a longer time until a micro-short circuit occurs due to the generation and growth of dendrites, compared to the separator (4). Therefore, it was found that the separators (1) to (3) have a better dendrite blocking property than the separator (4). In addition, it was found that the separators (1) to (3) have a smaller air permeability value per film thickness of the porous layer than the separator (5), and have a better ion permeability. Therefore, it was found that the separators (1) to (3) are superior in both ion permeability and dendrite blocking property, unlike the separators (4) and (5).

[0137] As described above, it has been found that the separator according to one embodiment of the present invention has the effect of exhibiting excellent ion permeability and dendrite blocking properties by satisfying at least one of the formula (A) and the formula (B). [Industrial Applicability]

[0138] The separator according to one embodiment of the present invention can be used to manufacture a non-aqueous electrolyte secondary battery that has both excellent battery performance and excellent safety.

Claims

1. A separator for a non-aqueous electrolyte secondary battery comprising a porous film mainly composed of a polyolefin resin and a porous layer laminated on both sides of the porous film, The porous layer contains a resin, A separator for a non-aqueous electrolyte secondary battery, which satisfies at least one of the following formulas (A) and (B): (average pore area of ​​one porous layer) / (average pore area of ​​the other porous layer)≧1.7 (A) (Average circular equivalent diameter of one porous layer)−(Average circular equivalent diameter of the other porous layer)≧2.0 nm (B) (In formulas (A) and (B), of the porous layers laminated on both sides of the porous film, the porous layer having a larger average pore area is defined as one porous layer, and the porous layer having a smaller average pore area is defined as the other porous layer. The average pore area is the average value of the areas of the pores on the surface of the porous layer. The average equivalent circle diameter is the average value of the diameters of circles having the same area as the areas of the pores on the surface of the porous layer.)

2. the porous layer includes a filler, 2 . The separator for a non-aqueous electrolyte secondary battery according to claim 1 , wherein a content of the filler in the porous layer is 30% by weight or more and 99% by weight or less based on a total weight of the porous layer.

3. 2. The separator for a non-aqueous electrolyte secondary battery according to claim 1, wherein the resin is at least one selected from the group consisting of (meth)acrylate-based resins, fluorine-containing resins, polyamide-based resins, and polyester-based resins.

4. The resin includes a polyamide resin, 4. The separator for a non-aqueous electrolyte secondary battery according to claim 3, wherein the polyamide resin is an aramid resin.

5. A member for a non-aqueous electrolyte secondary battery, comprising a positive electrode, the separator for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, and a negative electrode, arranged in this order.

6. A non-aqueous electrolyte secondary battery comprising the separator for non-aqueous electrolyte secondary batteries according to any one of claims 1 to 4.

Images