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. "The ratio of an area of communicating holes in one porous layer (referred to as "ratio 1") to an area of the communicating holes in the other porous layer (referred to as "ratio 2")>1.45 (B)" 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] As a result of extensive research, the inventors have 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 proportion of communicating pores, which are pores having a certain depth, between one side 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, A separator for a nonaqueous electrolyte secondary battery, in which the ratio (%) of the area of ​​the communicating holes in the surface of one of the porous layers to the entire surface area of ​​the one of the porous layers and the ratio (%) of the area of ​​the communicating holes in the surface of the other of the porous layers to the entire surface area of ​​the other of the porous layers satisfy the following relationships (A) and (B): (Ratio of the area of ​​the continuous holes to the total surface area of ​​one of the porous layers)>(Ratio of the area of ​​the continuous holes to the total surface area of ​​the other porous layer) (A) (Ratio of the area of ​​the interconnecting holes to the total surface area of ​​one of the porous layers) / (Ratio of the area of ​​the interconnecting holes to the total surface area of ​​the other porous layer)>1.45 (B) 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. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is a schematic diagram showing an aspect of a porous layer laminated on a porous film in one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] 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."

[0013] [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 is a separator for a non-aqueous electrolyte secondary battery comprising a porous film mainly composed of a polyolefin resin and porous layers laminated on both sides of the porous film, wherein the porous layers contain a resin, and the ratio (%) of the area of ​​communicating holes on one surface of the porous layer to the entire surface area of ​​the one porous layer and the ratio (%) of the area of ​​communicating holes on the other surface of the porous layer to the entire surface area of ​​the other porous layer satisfy the following relationships (A) and (B):

[0014] (Ratio of the area of ​​the continuous holes to the total surface area of ​​one of the porous layers)>(Ratio of the area of ​​the continuous holes to the total surface area of ​​the other porous layer) (A) (Ratio of the area of ​​the interconnecting holes to the total surface area of ​​one of the porous layers) / (Ratio of the area of ​​the interconnecting holes to the total surface area of ​​the other porous layer)>1.45 (B) 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.

[0015] [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.

[0016] The porous film has many interconnected pores inside, allowing gases and liquids to pass from one surface to the other.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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. 2 is preferably 3 to 12 g / m 2 More preferably, the thickness is 3 to 10 g / m 2 It is even more preferable that:

[0022] 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.

[0023] 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.

[0024] [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.

[0025] 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.

[0026] [Porous layer] The porous layer in one embodiment of the present invention is laminated on both sides of the porous film. Here, the embodiment of the porous layer will be described with reference to FIG. 1. FIG. 1 is a schematic diagram showing an embodiment of a porous layer laminated on a porous film in one embodiment of the present invention. As shown in FIG. 1, in one embodiment of the present invention, a porous layer 2 is laminated on a porous film 1. Note that FIG. 1 shows only the porous film 1 and the porous layer 2 laminated on one side of the porous film 1. However, in the separator of the present invention, another porous layer is laminated on the surface of the porous film 1 opposite to the surface on which the porous layer 2 is laminated. The other porous layer has a porous structure including communicating holes, which will be described later, similar to the porous layer 2.

[0027] The porous layer 2 is composed of a resin 3 and, optionally, a filler 4. Here, the resin 3 may be fibril-like, and a plurality of pores are formed by combining the fibril-like resins. As a result, the porous layer 2 has a porous structure. By having the porous structure, the porous layer 2 is capable of passing gas and liquid from one surface to the other surface.

[0028] The porous layer 2 has a continuous hole. The connecting hole is a hole that has an opening on the surface of the porous layer 2 and has depth, as shown by the arrow in FIG. 1, among the holes that constitute the porous structure. Here, the surface means the surface of the porous layer 2 opposite to the surface on the porous film 1 side. The depth means that the depth of the hole, that is, the distance from the surface of the porous layer 2 to the bottom of the hole in the vertical direction to the surface of the porous layer 2, is a specific value or more with respect to the film thickness of the porous layer 2. Here, as a method for identifying the hole corresponding to the connecting hole, for example, a method of image analysis of an SEM image of the surface of the porous layer described later can be mentioned. In the SEM image, it is known that there is a correlation between the depth of the hole and the blackness (color intensity). Therefore, in the image analysis described later, the part detected by adjusting the threshold to fall within 2 to 3% is a part with a certain degree of blackness or more, and is a part where the hole corresponding to the connecting hole has a depth of a specific value or more with respect to the film thickness of the porous layer. Specifically, the pores corresponding to the communicating holes have a depth of 7% or more and 100% or less with respect to the film thickness of the porous layer 2. The depth can be measured by observing the porous layer 2 from the surface direction using, for example, a scanning probe microscope.

[0029] The communicating holes allow gas and liquid to pass through more effectively than other pores. Therefore, the greater the proportion of the connecting holes in the surface of the porous layer, the greater the number of the connecting holes, and the easier it is for gas and liquid to pass through the porous layer. As a result, the air permeability of the porous layer is reduced, and ion permeability is improved. On the other hand, the thickness of the porous layer is locally thin at the location where the connecting holes are present, and dendrites that are generated and grow in the electrode (negative electrode) of the non-aqueous electrolyte secondary battery are more likely to pass through and penetrate the porous layer and the separator including the porous layer. Therefore, the smaller the proportion of the connecting holes in the surface of the porous layer, the harder it is for the dendrites to pass through and penetrate the porous layer due to their growth. As a result, the dendrite blocking property of the porous layer is improved.

[0030] In the separator of the present invention, the ratio (%) of the area of ​​the communicating holes in the surface of one of the porous layers to the total surface area of ​​the one of the porous layers (hereinafter referred to as "ratio 1") and the ratio (%) of the area of ​​the communicating holes in the surface of the other of the porous layers to the total surface area of ​​the other of the porous layers (hereinafter referred to as "ratio 2") satisfy the following relationship (A). Note that the area of ​​the communicating holes in the surface of the porous layer means the area of ​​the openings of the communicating holes. (Ratio 1)>(Ratio 2) (A)

[0031] Satisfying the relationship (A) means that, in the separator of the present invention, of the porous layers laminated on both sides of the porous film, the porous layer having a larger ratio (%) of the area of ​​communicating holes to the entire surface area at the surface is defined as "one porous layer," and the porous layer having a smaller ratio (%) of the area of ​​communicating holes to the entire surface area at the surface is defined as "the other porous layer."

[0032] In the separator of the present invention, "ratio 1" and "ratio 2" satisfy the following relationship (B). (Ratio 1) / (Ratio 2)>1.45 (B)

[0033] Satisfying the relationship (B) means that in "one porous layer," the connecting pores account for a "proportion 1," i.e., a large proportion of the surface, and in "the other porous layer," the connecting pores account for a "proportion 2," i.e., a small proportion of the surface, in the "one porous layer." Thus, in the separator of the present invention, "one porous layer" having high ion permeability but low dendrite blocking property and "the other porous layer" having low ion permeability but high dendrite blocking property are laminated on each of both sides of the porous film.

[0034] 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").

[0035] 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.

[0036] From the viewpoint of improving both the above-mentioned ion permeability and dendrite blocking property, in the separator of the present invention that satisfies the requirement (B), the value of (ratio 1) / (ratio 2) is preferably 1.47 or more, and more preferably 1.50 or more.

[0037] The excessively high value of (Ratio 1) / (Ratio 2) means that in the separator of the present invention, the (Ratio 1) is excessively large or the (Ratio 2) is excessively small. Here, in the separator of the present invention, if the (Ratio 1) is excessively large, the dendrite blocking property of the "one porous layer" may be excessively decreased, and the dendrite blocking property of the entire separator may be decreased. In addition, in the separator of the present invention, if the (Ratio 2) 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, it is more preferable that the (Ratio 1) and the (Ratio 2) are within a predetermined range in terms of preventing the decrease in the dendrite blocking property and the decrease in the ion permeability. From the above viewpoint, the upper limit value of the (Ratio 1) is preferably 5% or less, more preferably 3% or less. Similarly, the (Ratio 2) is preferably 0.1% or more, more preferably 0.3% or more.

[0038] From the viewpoint of preventing the above-mentioned deterioration in dendritic block property and deterioration in ion permeability, in the separator of the present invention satisfying the requirement (B), the value of (ratio 1) / (ratio 2) is preferably 2.20 or less, and more preferably 2.10 or less.

[0039] The (ratio 1) can be measured by a method including the following steps (1) to (3). (1) A step of measuring the depth of each pore having an opening on the surface of the "one porous layer" by a known method, and determining which pores correspond to the connected pores from the obtained pore depths. (2) A process of measuring the area of ​​the opening of each of the holes corresponding to the connecting holes identified in step (1) using a known method, and calculating the total area of ​​the openings of the holes corresponding to the connecting holes. (3) A step of calculating the ratio of the total area of ​​the openings of the pores corresponding to the connecting pores calculated in step (2) to the total surface area of ​​the "one of the porous layers" to give the ratio (ratio 1).

[0040] The (ratio 2) can be measured in the same manner as the (ratio 1) described above, except that the "other porous layer" is used instead of the "one porous layer".

[0041] Hereinafter, the "one porous layer" and the "other porous layer" are collectively referred to simply as "porous layers." The method for measuring the depth of the pores and the method for measuring the area of ​​the openings of the pores corresponding to the connecting pores are not particularly limited, and can be measured, for example, by subjecting a scanning electron microscope (SEM) image of the surface of the porous layer to image processing, which will be described later.

[0042] A specific method for measuring the above (Ratio 1) and (Ratio 2) can include, for example, a method including the following steps 1. to 6. 1. A step of photographing the surface of the porous layer using an SEM to obtain an SEM image of the surface of the porous layer. 2. A step of removing by trimming the SEM image obtained in step 1, except for the imaged portion, to obtain an image for analysis. 3. A process of opening the image for analysis obtained in 2. with the image analysis software Image J (provided by the National Institutes of Health (NIH)), selecting [Type] from [Image] on the toolbar of the image analysis software, checking [8-bit], and specifying the image type. The operation in 3. specifically means a process of lowering the bit depth of the image for analysis and reducing intermediate colors in the black and white of the image. 4. After the operation of 3., select [Threshold] from [Adjust] in the [Image] toolbar of the image analysis software, and in the window that opens, set the upper setting bar to 0, and adjust the lower setting bar so that the threshold falls within 2-3%. The operation in 4. specifically means the process of selecting the darker black parts of the image for analysis. 5. After the operation of 4., select [Set Scale] from [Analyze] on the toolbar of the image analysis software, change the image dimensions from Pixels to μm, then select [Analyze Particles] from [Analyze], set Size to [0.001-Infinity], press [OK] in the [Analyze Particles] window, and display the [Summary] window. The operation in step 5 specifically means a process for calculating the area in μm. 6. A process of obtaining the value displayed in [Area Fraction] in the [Summary] window displayed as a result of the operation of 5., as the ratio of the total area of ​​the openings of the communicating holes to the area of ​​the image for analysis, i.e., the entire surface area of ​​the porous layer. 7. A process of setting the value obtained in 6. as the (Ratio 1) or (Ratio 2) value.

[0043] The conditions for SEM photography in step 1, such as acceleration voltage, working distance, image resolution, and magnification, are not particularly limited as long as the pores corresponding to the connecting pores can be identified by the above-mentioned method, and the ratio of the area of ​​the openings of the pores corresponding to the connecting pores to the area of ​​the entire surface of the porous layer can be calculated. The photographing conditions can be, for example, the photographing conditions described in the Examples. In addition, in obtaining the SEM image in step 1, an operation for adjusting the obtained SEM image can be performed, for example, using an autofocus function and an autocontrast function.

[0044] In step 4, if multiple thresholds can be set in the range of 2 to 3%, steps 4 to 6 are performed for all of the multiple thresholds, and the ratio of the total area of ​​the openings of the communicating holes to the total area of ​​the image for analysis, i.e., the porous layer, is calculated for all thresholds. Then, instead of step 7, a step is carried out in which an average value of the ratio of the total area of ​​the openings of the communicating holes to the total area of ​​the porous layer is calculated for all thresholds, and the average value is set as the value of (Ratio 1) or (Ratio 2).

[0045] [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.

[0046] 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.

[0047] 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.

[0048] Among the specific examples of the resins, (meth)acrylate resins, fluorine-containing resins, polyamide resins and polyester resins are preferred.

[0049] 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.

[0050] 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.

[0051] The method for producing the resin is not particularly limited, and any conventionally known method can be used as appropriate.

[0052] [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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] [Properties of 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] [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.

[0064] 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.

[0065] 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 dispersants, plasticizers, surfactants, and pH adjusters in addition to the resin and the filler, as long as the purpose of the present invention is not impaired.

[0066] 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.

[0067] 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.

[0068] The method for forming the porous layer is not particularly limited, and examples thereof include the following method (a) or (b). (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"). (b) A method in which the substrate on which the coating layer has been formed is exposed to air containing water vapor to precipitate 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 "humidity precipitation method").

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] Furthermore, in general, the immersion precipitation method provides a faster precipitation rate of the resin than the humidity precipitation method.

[0074] 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 holes by the filler is reduced. Therefore, the pores in the film with a high resin ratio are easily blocked. As a result, the continuous holes are difficult to form in the porous layer. Therefore, when the resin deposition rate is increased to form a porous layer using the above-mentioned method, the "ratio 1" or the "ratio 2" 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 "ratio 1" or the "ratio 2" can be controlled to a large range in the obtained porous layer.

[0075] Therefore, the separator of the present invention can be produced by a method including the following steps (i) and (ii). (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. (ii) A step of forming the "other porous layer" on the other side of the porous film by increasing the resin deposition rate.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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 "ratio 1" and "ratio 2" 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.

[0080] [Embodiment 3: Nonaqueous electrolyte secondary battery member, Embodiment 4: 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] <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.

[0085] 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.

[0086] 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.

[0087] Examples of the binder include fluorine-based resins such as polyvinylidene fluoride (PVDF), acrylic resins, and styrene-butadiene rubber.

[0088] The positive electrode current collector may be made of a conductor such as Al, Ni, or stainless steel.

[0089] 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.

[0090] <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.

[0091] 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.

[0092] The negative electrode current collector may be made of, for example, Cu, Ni, stainless steel, or the like.

[0093] The negative electrode sheet can be produced, for example, by pressurizing and molding a negative electrode active material on a negative electrode current collector.

[0094] <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 and the like. One or more selected from the group consisting of

[0095] Examples of the organic solvent constituting the non-aqueous electrolyte 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.

[0096] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in 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.

[0097] [Summary] One embodiment of the present invention may include the inventions shown in the following [1] to [6]. [1] A separator for a non-aqueous electrolyte secondary battery including a porous film mainly composed of a polyolefin resin and porous layers laminated on both surfaces of the porous film, wherein the porous layer contains a resin, and the ratio (%) of the area of the communication holes to the total area of the surface of one of the porous layers on the surface of one of the porous layers and the ratio (%) of the area of the communication holes to the total area of the surface of the other porous layer on the surface of the other porous layer satisfy the following relationships (A) and (B). A separator for a non-aqueous electrolyte secondary battery. (Ratio of the area of the communication holes to the total area of the surface of one of the porous layers) > (Ratio of the area of the communication holes to the total area of the surface of the other porous layer) (A) (Ratio of the area of ​​the interconnecting holes to the total surface area of ​​one of the porous layers) / (Ratio of the area of ​​the interconnecting holes to the total surface area of ​​the other porous layer)>1.45 (B) [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 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 [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].

[0098] 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

[0099] 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.

[0100] [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.

[0101] [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.

[0102] [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)

[0103] <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).

[0104] [Ratio of area of ​​interconnected pores to the total surface area (Ratio 1, Ratio 2)] The following operations 1. to 8. were carried out on one of the porous layers laminated on both sides of the porous film in the separators described in Examples 1 to 3 and Comparative Examples 1 and 2. As a result, the ratio (%) of the area of ​​the communicating pores to the area of ​​the entire surface of the one porous layer was measured. 1. The surface of the porous layer was photographed using a scanning electron microscope (SEM, S-4800 (Hitachi High-Tech Corporation)) to obtain an SEM image of the surface of the porous layer. The photographing conditions were accelerating voltage: 2 kV, working distance (WD): 5 mm, secondary electron image, image resolution: 496 nm / pix, magnification: 20,000 times, and image quality was adjusted using the autofocus function, autocontrast function, etc. The portions of the SEM image obtained in 2.1 other than the imaged portion were removed by trimming to obtain an image for analysis. The image for analysis obtained in 3.2 was opened in the image analysis software Image J (provided by the National Institutes of Health (NIH)), and then [Type] was selected from [Image] on the toolbar of the image analysis software, and [8-bit] was checked to specify the image type. After performing the operation in 4.3, select [Image] > [Adjust] > [Threshold] from the toolbar in the image analysis software, and in the window that appears, set the upper setting bar to 0 and adjust the lower setting bar so that the threshold is within 2-3%. After the operation in 5.4, [Set Scale] was selected from [Analyze] on the toolbar of the image analysis software, and the image dimensions were changed from Pixels to μm. Next, [Analyze Particles] was selected from [Analyze], Size was set to [0.001-Infinity], and [OK] was pressed in the [Analyze Particles] window to display the [Summary] window. The value displayed in the [Area Fraction] in the [Summary] window displayed as a result of the operation in 6.5. was obtained as the ratio of the total area of ​​the openings of the communicating holes to the area of ​​the image for analysis, i.e., the entire surface of the porous layer.

[0105] Next, the same operations as those in 1 to 6 were carried out on another of the porous layers laminated on both sides of the porous film in the separator, and as a result, the ratio (%) of the area of ​​the communicating pores to the area of ​​the entire surface of the other porous layer was measured.

[0106] Of the one porous layer and the other porous layer, the one having a larger ratio (%) of the area of ​​the communicating holes to the total surface area was defined as "one porous layer," and the obtained ratio (%) of the area of ​​the communicating holes to the total surface area was defined as "ratio 1." Furthermore, of the one porous layer and the other porous layer, the one having a smaller ratio (%) of the area of ​​the communicating holes to the total surface area was defined as "the other porous layer," and the obtained ratio (%) of the area of ​​the communicating holes to the total surface area was defined as "ratio 2."

[0107] In all examples and comparative examples, multiple thresholds could be set in the range of 2 to 3% in the operation of 4., and the operations of 4. to 6. were performed for all of the multiple thresholds. As a result, the ratio of the total value of the opening area of ​​the communicating holes to the entire surface area was calculated for all of the thresholds. Then, the average value of the calculated ratio of the total value of the opening area of ​​the communicating holes to the entire surface area for all of the thresholds was calculated. The calculated average value was taken as the ratio (%) of the area of ​​the communicating holes to the entire surface area of ​​the porous layer to be measured.

[0108] [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 / cm 3 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.

[0109] <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.

[0110] [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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] [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).

[0115] [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).

[0116] [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).

[0117] [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).

[0118] [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).

[0119] [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 Table 1 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]

[0120] As shown in Table 1, separators (1) to (3) produced in Examples 1 to 3 correspond to the separators of the present invention because (Ratio 1) and (Ratio 2) satisfy the requirements (A) and (B) shown below. On the other hand, separators (4) and (5) produced in Comparative Examples 1 and 2 do not correspond to the separators of the present invention because (Ratio 1) and (Ratio 2) do not satisfy the requirement (B) shown below. (Ratio 1)>(Ratio 2) (A) (Ratio 1) / (Ratio 2)>1.45 (B)

[0121] 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).

[0122] As described above, it has been found that the separator according to one embodiment of the present invention satisfies the requirements (A) and (B) and thereby exhibits the effects of being excellent in both ion permeability and dendrite blocking properties. [Industrial Applicability]

[0123] 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. [Explanation of symbols]

[0124] 1. Porous film 2 Porous layer 3. Resin 4. Filler

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 nonaqueous electrolyte secondary battery, in which a ratio (%) of an area of ​​communicating holes in the surface of one of the porous layers to an entire surface area of ​​the one of the porous layers and a ratio (%) of an area of ​​communicating holes in the surface of the other of the porous layers to an entire surface area of ​​the other of the porous layers satisfy the following relationships (A) and (B): (The ratio of the area of ​​the continuous pores to the total surface area of ​​one of the porous layers)>(The ratio of the area of ​​the continuous pores to the total surface area of ​​the other porous layer) (A) (ratio of the area of ​​the communicating holes to the entire surface area of ​​one of the porous layers) / (ratio of the area of ​​the communicating holes to the entire surface area of ​​the other porous layer)>1.45 (B)

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. 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.

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