Separator for energy storage device, separator reel, and energy storage device

Abstract

Provided is a separator for an energy storage device, said separator including a porous base material, an inorganic filler-containing layer disposed on a first main surface of the porous base material, and a thermoplastic polymer-containing layer disposed on the surface of the inorganic filler-containing layer and on a second main surface of the porous base material, wherein the coverage area ratio Sc of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer is between 30% and 100% inclusive, the coverage area ratio Sp of the thermoplastic polymer-containing layer on the second main surface of the porous base material is more than 0% and less than 30%, and the thickness tc of the thermoplastic polymer-containing layer on the inorganic filler-containing layer and the thickness tp of the thermoplastic polymer-containing layer on the second main surface of the porous base material satisfy the relationship tc / tp > 1.00.

Description

Separator for power storage device, separator reel, and power storage device

[0001] The present invention relates to a separator for an electricity storage device, a separator reel, an electricity storage device, and the like.

[0002] In recent years, the development of energy storage devices, typified by nonaqueous electrolyte batteries, has been actively pursued. Nonaqueous electrolyte batteries, such as lithium-ion batteries, typically have a microporous membrane as a separator between the positive and negative electrodes. Such a separator prevents direct contact between the positive and negative electrodes and allows ions to pass through the electrolyte held in the microporous membrane.

[0003] Separators are required to have the safety performance that has traditionally been required, such as the ability to quickly stop the battery reaction in the event of abnormal heating (fuse characteristics) and the ability to maintain their shape even at high temperatures and prevent dangerous situations in which the positive and negative electrode materials directly react with each other (short-circuit characteristics).

[0004] In order to impart various functions to the separator in addition to safety, layer configurations such as coating a functional layer on a microporous membrane, lamination patterns of functional layers, and coating patterns such as dots have been investigated.

[0005] For example, Patent Document 1 discloses a separator for an electricity storage device, which comprises a polyolefin microporous membrane and a thermoplastic polymer coating layer that covers at least a portion of at least one surface of the polyolefin microporous membrane, and the thermoplastic polymer coating layer is provided in the form of dots on the polyolefin microporous membrane.

[0006] International Publication No. 2014 / 017651

[0007] A potential issue with separators is the tendency for static electricity to be generated (easily charged) when the separator is unwound from a reel or when it is run from the reel. If the separator is highly charged, static electricity discharges, creating pinholes that can cause short circuits in the battery. Another issue is that separators can be attracted to each other or stick to surrounding rolls, making the separators difficult to handle and reducing processability.

[0008] In view of the above circumstances, the present invention aims to provide a separator that suppresses the generation of static electricity that occurs when the separator is unwound from a reel, thereby suppressing the generation of pinholes and deterioration of handleability.

[0009] As a result of extensive research, the present inventors have found that the above problems can be solved by using a separator for an electricity storage device having the following configuration, and have completed the present invention. That is, the present invention is as follows: [Item 1] A separator comprising a porous substrate, an inorganic filler-containing layer disposed on a first main surface of the porous substrate, and a thermoplastic polymer-containing layer disposed on a surface of the inorganic filler-containing layer and on a second main surface of the porous substrate, wherein the coverage area ratio S of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer is ｃ is 30% or more and 100% or less, and the coverage area ratio S of the thermoplastic polymer-containing layer on the second main surface of the porous substrate is ｐ is more than 0% and less than 30%, and the thickness t of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer is ｃ and a thickness t of the thermoplastic polymer-containing layer on the second major surface of the porous substrate. ｐ But, t ｃ / t ｐ＞ [Item 2] A separator for an electric storage device, wherein the coverage area ratio S of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer satisfies the relationship of 1.00. ｃ and a coverage area ratio S of the thermoplastic polymer-containing layer on the second main surface of the porous substrate. ｐ But, S ｃ / S ｐ Item 3. The separator for an electric storage device according to Item 1, wherein the coverage area ratio S of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer satisfies the relationship: ｃ and a coverage area ratio S of the thermoplastic polymer-containing layer on the second main surface of the porous substrate. ｐ However, 55%≦S ｃ +S ｐItem 4. The electricity storage device separator according to any one of Items 1 to 3, wherein the particle size of the inorganic filler contained in the inorganic filler-containing layer satisfies the relationship 1.0≦D90 / D10≦5.0, and the particle size of the thermoplastic polymer contained in the thermoplastic polymer-containing layer on the second main surface of the porous substrate satisfies the relationship 1.0≦D90 / D10≦5.0. [Item 5] The electricity storage device separator according to any one of Items 1 to 4, wherein the peel charge amount when unwound from the reel is −15 kV or more and +15 kV or less. [Item 6] A reel formed by winding the electricity storage device separator according to any one of Items 1 to 5, wherein the surface pressure applied to the innermost layer is 5 MPa or less. [Item 7] The electricity storage device separator according to any one of Items 1 to 5, obtained by applying an aqueous slurry containing a thermoplastic polymer to the surface of the porous substrate or the inorganic filler-containing layer provided on the porous substrate. [Item 8] The electricity storage device separator according to any one of Items 1 to 5 and 7, wherein the thermoplastic polymer-containing layer is arranged in a dotted pattern. [Item 9] The electricity storage device separator according to any one of Items 1 to 5 and 7 to 8, wherein the thermoplastic polymer-containing layer contains a copolymer containing a monomer unit of a (meth)acrylic acid ester monomer. [Item 10] An electricity storage device comprising the electricity storage device separator according to any one of Items 1 to 5 and 7 to 9, a positive electrode, a negative electrode, and a non-aqueous electrolyte. [Item 11] A thickness t of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer ｃ Standard deviation s ｔｃ and a thickness t of the thermoplastic polymer-containing layer on the second major surface of the porous substrate. ｐ Standard deviation s ｔｐ But, s ｔｃ / s ｔｐItem 12: The separator for an electrical storage device according to any one of Items 1 to 5 and Items 7 to 9, wherein the separator satisfies the relationship of ≈1.0. [Item 12] ... comprises the steps of: preparing a porous substrate; applying a slurry containing an inorganic filler onto a first main surface of the porous substrate to form an inorganic filler-containing layer; and applying a slurry containing a thermoplastic polymer onto the surface of the inorganic filler-containing layer and onto a second main surface of the porous substrate to form a thermoplastic polymer-containing layer, wherein the viscosity of the slurry containing the thermoplastic polymer is －１ the viscosity of the slurry containing the thermoplastic polymer is 1 mPa·s or more and 20 mPa·s or less at a shear rate v ｃ and a shear rate v when applying the slurry containing the thermoplastic polymer onto the second main surface of the porous substrate. ｐ The method for producing a separator for an electricity storage device according to any one of Items 1 to 5 and Items 7 to 9, wherein the relationship of formulas (2) and (3) is satisfied. －１ ≦v ｃ ≦200,000 sec －１ ...Formula (2) 5000sec －１ ≦v ｃ -v ｐ ≦40,000 sec －１ ...Formula (3)

[0010] According to the present invention, it is possible to provide a separator that can suppress the generation of pinholes by suppressing the generation of static electricity when the separator is fed out. Also, according to the present invention, it is possible to provide a separator that is easy to handle by suppressing the generation of static electricity. Furthermore, a battery including the separator of the present invention has excellent cycle characteristics and rate characteristics.

[0011] Hereinafter, a detailed description will be given of an embodiment of the present invention (hereinafter referred to as "the present embodiment"). Note that the present invention is not limited to the following embodiment, and various modifications can be made within the scope of the gist of the present invention. Furthermore, unless otherwise specified, the characteristic values ​​described in the present embodiment are intended to be values ​​measured by the method described in the [Example] section or a method that would be understood by a person skilled in the art to be equivalent thereto.

[0012] In the following description, the upper or lower limit of a numerical range described in stages may be replaced with the upper or lower limit of another numerical range described in stages. Also, in the following description, the upper or lower limit of a certain numerical range may be replaced with a value described in an example. Furthermore, with regard to the term "step" in the following description, not only an independent step but also a step that cannot be clearly distinguished from other steps may be included in this term as long as the function of that "step" is achieved.

[0013] <Separator for Electricity Storage Device> The separator for an electricity storage device according to this embodiment (hereinafter also simply referred to as "separator") has a porous substrate, an inorganic filler-containing layer disposed on a first main surface of the porous substrate, and a thermoplastic polymer-containing layer disposed on a surface of the inorganic filler-containing layer and on a second main surface of the porous substrate, and the coverage area ratio S of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer is ｃ is 30% or more and 100% or less, and the coverage area ratio S of the thermoplastic polymer-containing layer on the second main surface of the porous substrate is ｐ is more than 0% and less than 30%, and the thickness t of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer is ｃ and a thickness t of the thermoplastic polymer-containing layer on the second major surface of the porous substrate. ｐ But, t ｃ / t ｐ >1.00.

[0014] Factors that determine the charge level of a separator are generally considered to be "contact area," "frictional force," "humidity," "pressure," and "temperature." In the manufacturing process of separators and batteries, it is preferable to eliminate moisture and maintain constant temperature and humidity. Therefore, it is difficult to arbitrarily change the environmental factors of "temperature" and "humidity." Therefore, the manufacturing process of separators and batteries is an environment where static electricity is likely to become a problem. Therefore, the present inventors conducted extensive research focusing on "contact area," "frictional force," and "pressure." Separators are primarily composed of a substrate, an inorganic filler-containing layer, and a thermoplastic polymer-containing layer. Through their research, the present inventors discovered that the contact between the inorganic filler-containing layer and the thermoplastic polymer-containing layer significantly affects the generation of static electricity. This is presumably because the inorganic filler-containing layer, which has a higher surface roughness and higher insulating properties than the substrate, contacts the thermoplastic polymer-containing layer, resulting in frictional charging in addition to peel charging when the separator is unwound from the reel. Therefore, the present inventors have completed the separator of the present embodiment, in which the contact area between the inorganic filler-containing layer and the thermoplastic polymer-containing layer is reduced by setting the coverage area and thickness of the thermoplastic polymer-containing layer, and further the particle size distribution of the inorganic filler and the thermoplastic polymer, at or above a certain level, while taking into consideration the balance with battery performance.

[0015] The separator of this embodiment includes a porous substrate, an inorganic filler-containing layer disposed on a first main surface of the porous substrate, and a thermoplastic polymer-containing layer disposed on the surface of the inorganic filler-containing layer and on a second main surface of the porous substrate. In this disclosure, the first main surface of the porous substrate refers to at least one surface of the porous substrate (in one aspect, one side of the porous substrate). In addition, in this disclosure, the second main surface of the porous substrate refers to the surface of the porous substrate opposite the first main surface. The separator of this embodiment has excellent heat resistance due to the inorganic filler-containing layer disposed on the first main surface of the porous substrate. Furthermore, the separator of this embodiment has excellent cycle characteristics due to the thermoplastic polymer-containing layer disposed on the surface of the inorganic filler-containing layer and on the second main surface of the porous substrate, which improves adhesion to the electrode.

[0016] The separator of this embodiment has a coverage area ratio S of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer. ｃ is preferably 30% or more and 100% or less, and the coverage area ratio S ｃ is more preferably 35% or more and 80% or less, and the coverage area ratio S ｃ In the separator of the present embodiment, the coverage area ratio S of the thermoplastic polymer-containing layer on the second main surface of the porous substrate is more preferably 40% or more and 70% or less. ｐ is preferably more than 0% and less than 30%, and the coverage area ratio S ｐ is more preferably 5% or more and 25% or less, and the coverage area ratio S ｐ From the viewpoint of reducing the contact area between the inorganic filler-containing layer and the thermoplastic polymer-containing layer, suppressing the generation of static electricity, and improving adhesion to the electrode while maintaining ion permeability, it is preferable that the coverage area ratio of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer and on the second main surface of the porous substrate be in the above-mentioned range.

[0017] Here, the coverage area ratio S of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer is ｃ and the coverage area ratio S of the thermoplastic polymer-containing layer on the second main surface of the porous substrate ｐ are calculated from the following formulas: ｃ (%) = Coverage area of ​​the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer / Surface area of ​​the inorganic filler-containing layer × 100 S ｐ (%) = Coverage area of ​​the thermoplastic polymer-containing layer on the second main surface of the porous substrate / Surface area of ​​the porous substrate × 100. The coverage area ratio S of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer is ｃ and the coverage area ratio S of the thermoplastic polymer-containing layer on the second main surface of the porous substrate ｐ can be measured by the method described in the Examples.

[0018] The separator of this embodiment has a thickness t of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer. ｃ and a thickness t of the thermoplastic polymer-containing layer on the second major surface of the porous substrate. ｐ But, tｃ / t ｐ It is preferable that the relationship of t > 1.00 is satisfied, and t ｃ / t ｐ It is more preferable that the relationship of t ≧ 1.40 is satisfied. ｃ / t ｐ It is more preferable that the relationship of t≧2.00 is satisfied. ｃ / t ｐ It is particularly preferable that the relationship of t ≧ 3.00 is satisfied. ｃ / t ｐ It is most preferable that the relationship of ≧4.00 is satisfied. From the viewpoint of reducing the contact area between the inorganic filler-containing layer and the thermoplastic polymer-containing layer and suppressing the generation of static electricity, it is preferable that the thickness ratio of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer and on the second main surface of the porous substrate is set to the above-mentioned range. The effect of this embodiment is achieved by setting the coverage area ratio and thickness ratio of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer and on the second main surface of the porous substrate to a predetermined range.

[0019] The thickness t of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer ｃ The thickness t of the thermoplastic polymer-containing layer on the second main surface of the porous substrate is preferably 0.1 μm or more and 5.0 μm or less, more preferably 0.5 μm or more and 4.0 μm or less, and even more preferably 1.0 μm or more and 3.0 μm or less. ｐ is preferably 0.1 μm or more and 3.0 μm or less, more preferably 0.1 μm or more and 2.0 μm or less, and even more preferably 0.1 μm or more and 1.0 μm or less. ｃ and a thickness t of the thermoplastic polymer-containing layer on the second major surface of the porous substrate. ｐ can be measured by the method described in the Examples.

[0020] The separator of this embodiment has a thickness t of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer. ｃ Standard deviation s ｔｃ and a thickness t of the thermoplastic polymer-containing layer on the second major surface of the porous substrate. ｐ Standard deviation s ｔｐBut, s ｔｃ / s ｔｐ It is preferable that the thickness t of the thermoplastic polymer-containing layer on the second main surface of the porous substrate satisfies the relationship t > 1.0. ｐ Standard deviation s ｔｐ the thickness t of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer relative to ｃ Standard deviation s ｔｃ Ratio of: s ｔｃ / s ｔｐ is preferably greater than 1, more preferably 3 or greater, even more preferably 5 or greater, and particularly preferably 7 or greater. From the viewpoint of reducing the contact area between the inorganic filler-containing layer and the thermoplastic polymer on the second main surface of the porous substrate when the separators are superposed and suppressing the generation of static electricity, the surface unevenness of the thermoplastic polymer on the surface of the inorganic filler-containing layer and the surface unevenness of the thermoplastic polymer on the second main surface of the porous substrate are separately adjusted, thereby making it possible to reduce the ratio of the standard deviations of the thickness of the thermoplastic polymer-containing layer: s ｔｃ / s ｔｐ It is preferable that the thickness t of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer is within the above-mentioned range. ｃ Standard deviation s ｔｃ and the thickness t of the thermoplastic polymer-containing layer on the second major surface of the porous substrate. ｐ Standard deviation s ｔｐ can be measured by the method described in the Examples.

[0021] The thickness t of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer ｃ Standard deviation s ｔｃ is the thickness t ｃ If the values ​​are the same, the standard deviation s ｔｃ A larger value of standard deviation s is preferable from the viewpoint of ensuring a clearance (preventing contact) between the surface of the inorganic filler-containing layer and the surface of the thermoplastic polymer-containing layer on the second main surface of the porous substrate when the separators are stacked. ｔｃ is preferably 0.01 μm or more, more preferably 0.05 μm or more, even more preferably 0.10 μm or more, and particularly preferably 0.30 μm or more. ｔｃFrom the viewpoint of maintaining a constant distance between the electrode and the separator inside the battery, the standard deviation s is preferably 1.50 μm or less, more preferably 1.00 μm or less, and even more preferably 0.70 μm or less. ｔｃ can be adjusted by the shear rate during coating and the particle size of the thermoplastic polymer particles when the thermoplastic polymer-containing slurry described below is applied to the surface of the inorganic filler-containing layer to form the thermoplastic polymer-containing layer. For example, when the shear rate during coating of the thermoplastic polymer-containing slurry is increased, the standard deviation s ｔｃ becomes larger, and when the shear rate during coating is reduced, the standard deviation s ｔｃ In addition, by increasing the particle size of the thermoplastic polymer particles, the standard deviation s ｔｃ becomes larger.

[0022] the thickness t of the thermoplastic polymer-containing layer on the second major surface of the porous substrate; ｐ Standard deviation s ｔｐ is the thickness t ｐ If the values ​​are the same, the standard deviation s ｔｐ If the value of is large, the thermoplastic polymer-containing layer on the second main surface of the porous substrate may locally come into contact with the surface of the inorganic filler-containing layer when the separator is superposed. Therefore, from the viewpoint of suppressing the generation of static electricity, the standard deviation s ｔｐ The smaller the value of standard deviation s, the better. ｔｐ is preferably 1.00 μm or less, more preferably 0.50 μm or less, even more preferably 0.30 μm or less, and particularly preferably 0.10 μm or less. ｔｐ From the viewpoint of improving the adhesion to the electrode, the standard deviation s is preferably 0.01 μm or more, more preferably 0.02 μm or more, even more preferably 0.03 μm or more, and particularly preferably 0.05 μm or more. ｔｐ can be adjusted by the shear rate during coating when a thermoplastic polymer-containing slurry, which will be described later, is applied to the surface of a porous substrate to form a thermoplastic polymer-containing layer. For example, when the shear rate during coating of the thermoplastic polymer-containing slurry is increased, the standard deviation s ｔｐ becomes larger, and when the shear rate during coating is reduced, the standard deviation s ｔｐ becomes smaller.

[0023] The separator of this embodiment has a coverage area ratio S of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer. ｃ and the coverage area ratio S of the thermoplastic polymer-containing layer on the second main surface of the porous substrate. ｐ But, S ｃ / S ｐ It is preferable that the relationship of S≧2.00 is satisfied. ｃ / S ｐ From the viewpoint of reducing the contact area between the inorganic filler-containing layer and the thermoplastic polymer-containing layer and suppressing the generation of static electricity, it is preferable that the area ratio of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer to the second main surface of the porous substrate be in the above-mentioned range.

[0024] The separator of this embodiment has a coverage area ratio S of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer. ｃ and the coverage area ratio S of the thermoplastic polymer-containing layer on the second main surface of the porous substrate. ｐ However, 55%≦S ｃ +S ｐ It is preferable that the relationship of 60%≦S ｃ +S ｐ It is more preferable that the relationship of ≦70% is satisfied. When the total coverage area ratio of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer and on the second main surface of the porous substrate is 55% or more, adhesion to the electrode is improved and cycle characteristics are excellent, which is preferable. Furthermore, when the total coverage area ratio of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer and on the second main surface of the porous substrate is 75% or less, ion permeability is not reduced and rate characteristics are excellent, which is preferable.

[0025] In the separator of this embodiment, it is preferable that the particle size of the inorganic filler contained in the inorganic filler-containing layer satisfies 1.0≦D90 / D10≦5.0, and the particle sizes of the thermoplastic polymer contained in the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer and on the second main surface of the porous substrate satisfy the relationship 1.0≦D90 / D10≦5.0. From the viewpoint of suppressing the generation of static electricity, it is preferable that the thickness of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer and on the second main surface of the porous substrate, and the particle sizes of the inorganic filler and the thermoplastic polymer, are set within predetermined ranges. The effects of this embodiment are achieved by setting the thickness of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer and on the surface of the porous substrate, and the particle sizes of the inorganic filler and the thermoplastic polymer, within predetermined ranges. The separator of this embodiment achieves excellent cycle characteristics by providing a thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer arranged on the first main surface of the porous substrate and on the second main surface of the porous substrate (in one embodiment, on both sides of the separator), and by controlling the coverage area ratios and thicknesses of the two types of thermoplastic polymer-containing layers, respectively, it is possible to suppress the generation of static electricity due to contact between the inorganic filler-containing layer and the thermoplastic polymer-containing layer.

[0026] (Dot Pattern of Thermoplastic Polymer-Containing Layer) The thermoplastic polymer-containing layer according to this embodiment may be arranged in a dot pattern.

[0027] The dot-like pattern indicates that there are portions containing a thermoplastic polymer and portions not containing a thermoplastic polymer on the substrate, and the portions containing the thermoplastic polymer are present in an island-like pattern. The dot-like pattern indicates that the dots are regularly arranged. Note that the portions containing the thermoplastic polymer in the thermoplastic polymer-containing layer may be independent. When the thermoplastic polymer-containing layer of the separator of this embodiment is arranged in a dot-like pattern, there are paths for Li ions (areas where no thermoplastic polymer is present on the substrate and which are particularly excellent in Li ion permeability), which is preferable because it reduces resistance and improves electrolyte permeability (injectability) during the battery manufacturing process.

[0028] In one embodiment, the dot pattern of the thermoplastic polymer-containing layer functions as an adhesive layer that bonds the electrode and the separator. The separator of this embodiment can suppress the generation of static electricity when the separator is unwound from the reel by reducing the contact area between the inorganic filler-containing layer and the thermoplastic polymer-containing layer. To reduce the contact area between the adhesive layer and the inorganic filler-containing layer, the coverage area ratio S of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer is set to 0.05. ｃ or increasing the coverage area ratio S of the thermoplastic polymer-containing layer on the second main surface of the porous substrate. ｐ This is achieved by reducing the

[0029] <Dot Diameter> The diameter of the dots in the thermoplastic polymer-containing layer is preferably 50 μm or more and 1000 μm or less, more preferably 100 μm or more and 500 μm or less, particularly preferably 150 μm or more and 300 μm or less, and most preferably 200 μm or more and 300 μm or less, from the viewpoints of reducing the resistance of the battery, facilitating air escape, increasing the permeability (pouring property) of the electrolyte, improving safety by preventing heat buildup, and suppressing the generation of static electricity or the generation of pinholes.

[0030] The dot diameter of the thermoplastic polymer-containing layer is measured using a microscope (model: VHX-7000, manufactured by Keyence Corporation). A sample separator is photographed at 100x magnification (coaxial epi-illumination), and the diameters of multiple dots (five points) are measured in measurement mode, and the average value is calculated as the dot diameter.

[0031] <Distance between dots> From the viewpoint of ensuring sufficient gaps between the multiple dots to ensure a permeation flow path for the electrolyte solution and to facilitate good air escape, as well as from the viewpoint of suppressing the generation of static electricity, the distance between dots in the thermoplastic polymer-containing layer is preferably 50 μm or more and 3000 μm or less, more preferably 100 μm or more and 2500 μm or less, even more preferably 150 μm or more and 2000 μm or less, and even more preferably 200 μm or more and 500 μm or less.

[0032] The distance between dots in the thermoplastic polymer-containing layer is measured using a microscope (model: VHX-7000, manufactured by Keyence Corporation). A sample separator is photographed at 100x magnification (coaxial epi-illumination), and in measurement mode, an arbitrary dot is selected. The distances between the center of the selected dot and the centers of dots positioned vertically, horizontally, and diagonally from the arbitrary dot are measured, and the average value of these distances is taken as the distance between dots.

[0033] From the viewpoint of achieving an excellent balance between maintaining adhesive strength with the electrode and injecting electrolyte solution, the distance between dots in the thermoplastic polymer-containing layer / diameter of the dots is preferably 0.3 or more and 5 or less, more preferably 0.5 or more and 4 or less, even more preferably 0.7 or more and 3.8 or less, and particularly preferably 1 or more and 3.5 or less.

[0034] The arrangement angle of the dots in the thermoplastic polymer-containing layer is preferably less than 40° from the viewpoint of improving air release, and the lower limit of the arrangement angle is not limited, but may be, for example, 0° or more.

[0035] (Uniformly Dispersed Coating of Thermoplastic Polymer-Containing Layer) When forming the thermoplastic polymer-containing layer according to this embodiment, the thermoplastic polymer can be coated onto the inorganic filler-containing layer and the porous substrate so as to be uniformly dispersed (in one embodiment, uniformly dispersed coating). In one embodiment, the uniformly dispersed coating may be performed so that the thermoplastic polymer-containing layer completely covers the surface to be coated (for example, the surface of the polyolefin microporous membrane or the inorganic filler-containing layer), or so that a part of the surface to be coated is exposed.

[0036] The components of the separator according to this embodiment will be described below.

[0037] [Thermoplastic Polymer-Containing Layer] The thermoplastic polymer-containing layer according to this embodiment contains a thermoplastic polymer.

[0038] (Thermoplastic Polymer) The thermoplastic polymer used in this embodiment is not particularly limited, but examples thereof include polyolefin resins such as polyethylene, polypropylene, and α-polyolefin; fluorine-containing resins such as polyvinylidene fluoride and polytetrafluoroethylene and copolymers containing these; diene-based polymers containing conjugated dienes such as butadiene and isoprene as monomer units or copolymers containing these and hydrogenated products thereof; acrylic polymers containing acrylic acid esters, methacrylic acid esters, etc. as monomer units or copolymers containing these and hydrogenated products thereof; rubbers such as ethylene propylene rubber, polyvinyl alcohol, and polyvinyl acetate; cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose; resins having a melting point and / or glass transition temperature of 180°C or higher, such as polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, and polyester, and mixtures thereof. Furthermore, monomers having a hydroxyl group, sulfonic acid group, carboxyl group, amide group, or cyano group can also be used as the monomer used in synthesizing the thermoplastic polymer.

[0039] Among these thermoplastic polymers, diene-based polymers, acrylic polymers, and fluorine-based polymers are preferred because they have excellent adhesion to the electrode active material, strength, and flexibility.

[0040] (Diene-Based Polymer) The diene-based polymer is not particularly limited, but is a polymer containing a monomer unit obtained by polymerizing a conjugated diene having two conjugated double bonds, such as butadiene or isoprene. Examples of conjugated diene monomers include, but are not particularly limited to, 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-phenyl-1,3-butadiene, 1,3-pentadiene, 2-methyl-1,3-pentadiene, 1,3-hexadiene, 4,5-diethyl-1,3-octadiene, and 3-butyl-1,3-octadiene. These may be polymerized alone or copolymerized.

[0041] The proportion of monomer units obtained by polymerizing a conjugated diene in the diene polymer is not particularly limited, but is, for example, 40% by mass or more, preferably 50% by mass or more, and more preferably 60% by mass or more of the total diene polymer.

[0042] The diene polymer is not particularly limited, but examples thereof include homopolymers of conjugated dienes such as polybutadiene and polyisoprene, and copolymers of conjugated dienes with copolymerizable monomers. The copolymerizable monomer is not particularly limited, but examples thereof include the (meth)acrylate monomers described below and the following monomers (hereinafter also referred to as "other monomers").

[0043] The "other monomers" are not particularly limited, but examples thereof include α,β-unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile; unsaturated carboxylic acids such as acrylic acid (AA), methacrylic acid (MAA), itaconic acid, and fumaric acid; styrene-based monomers such as styrene, chlorostyrene, vinyltoluene, t-butylstyrene, vinylbenzoic acid, methyl vinylbenzoate, vinylnaphthalene, chloromethylstyrene, hydroxymethylstyrene, α-methylstyrene, and divinylbenzene; olefins such as ethylene and propylene; halogen atom-containing monomers such as vinyl chloride and vinylidene chloride; vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate, and vinyl benzoate; methyl vinyl ether, ethyl vinyl vinyl ketones such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, isopropenyl vinyl ketone; heterocycle-containing vinyl compounds such as N-vinylpyrrolidone, vinylpyridine, and vinylimidazole; acrylic acid ester and / or methacrylic acid ester compounds such as methyl acrylate and methyl methacrylate; hydroxyalkyl group-containing compounds such as β-hydroxyethyl acrylate and β-hydroxyethyl methacrylate; and amide monomers such as acrylamide, N-methylolacrylamide, and acrylamido-2-methylpropanesulfonic acid, and the like. These may be used alone or in combination of two or more.

[0044] (Acrylic Polymer) The acrylic polymer is not particularly limited, but is preferably a polymer containing a monomer unit obtained by polymerizing a (meth)acrylate monomer. When the thermoplastic polymer-containing layer contains an acrylic polymer as the thermoplastic polymer, it preferably contains a copolymer containing a monomer unit of a (meth)acrylic acid ester monomer. If the thermoplastic polymer of the thermoplastic polymer-containing layer contains a copolymer containing a monomer unit of a (meth)acrylic acid ester monomer, the adhesive strength is improved when the separator has a low basis weight, which is preferable.

[0045] In this specification, "(meth)acrylic acid" refers to "acrylic acid or methacrylic acid", and "(meth)acrylate" refers to "acrylate or methacrylate".

[0046] The (meth)acrylate monomer is not particularly limited, but examples thereof include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, and decyl (meth)acrylate. alkyl (meth)acrylates such as acrylate, lauryl (meth)acrylate, n-tetradecyl (meth)acrylate, and stearyl (meth)acrylate; hydroxy group-containing (meth)acrylates such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and hydroxybutyl (meth)acrylate; amino group-containing (meth)acrylates such as aminoethyl (meth)acrylate; and epoxy group-containing (meth)acrylates such as glycidyl (meth)acrylate (GMA).

[0047] The proportion of monomer units obtained by polymerizing (meth)acrylate monomers is not particularly limited, but is, for example, 40% by mass or more, preferably 50% by mass or more, and more preferably 60% by mass or more of the total acrylic polymer. Examples of the acrylic polymer include homopolymers of (meth)acrylate monomers and copolymers of the same with copolymerizable monomers. Examples of copolymerizable monomers include the "other monomers" listed in the above section on diene polymers, and these may be used alone or in combination of two or more.

[0048] (Fluorine-based polymer) The fluorine-based polymer is not particularly limited, but examples thereof include a homopolymer of vinylidene fluoride and a copolymer of the homopolymer and a copolymerizable monomer. The fluorine-based polymer is preferable from the viewpoint of electrochemical stability.

[0049] The proportion of the monomer unit obtained by polymerizing vinylidene fluoride is not particularly limited, but for example, it is 40 mass% or more, preferably 50 mass% or more, more preferably 60 mass% or more. The monomer copolymerizable with vinylidene fluoride is not particularly limited, but examples thereof include fluorine-containing ethylenically unsaturated compounds such as vinyl fluoride, tetrafluoroethylene, trifluorochloroethylene, hexafluoropropylene, hexafluoroisobutylene, perfluoroacrylic acid, perfluoromethacrylic acid, and fluoroalkyl esters of acrylic acid or methacrylic acid; fluorine-free ethylenically unsaturated compounds such as cyclohexyl vinyl ether and hydroxyethyl vinyl ether; and fluorine-free diene compounds such as butadiene, isoprene, and chloroprene.

[0050] Among fluoropolymers, vinylidene fluoride homopolymers, vinylidene fluoride / tetrafluoroethylene copolymers, vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymers, etc. are preferred. A particularly preferred fluoropolymer is vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymer, the monomer composition of which is typically 30 to 90 mass% vinylidene fluoride, 9 to 50 mass% tetrafluoroethylene, and 1 to 20 mass% hexafluoropropylene. These fluororesin particles may be used alone or in combination of two or more.

[0051] Furthermore, as the monomer used in synthesizing the thermoplastic polymer, a monomer having a hydroxyl group, a carboxyl group, an amino group, a sulfonic acid group, an amide group, or a cyano group can also be used.

[0052] The monomer having a hydroxyl group is not particularly limited, but examples thereof include vinyl monomers such as penteneol.

[0053] The monomer having a carboxyl group is not particularly limited, but examples thereof include unsaturated carboxylic acids having an ethylenic double bond such as (meth)acrylic acid and itaconic acid, and vinyl monomers such as pentenoic acid.

[0054] The monomer having an amino group is not particularly limited, but examples thereof include 2-aminoethyl methacrylate.

[0055] The monomer having a sulfonic acid group is not particularly limited, but examples thereof include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth)allylsulfonic acid, styrenesulfonic acid, (meth)acrylic acid-2-ethyl sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, and 3-allyloxy-2-hydroxypropanesulfonic acid.

[0056] The monomer having an amide group is not particularly limited, but examples thereof include acrylamide (AM), methacrylamide, N-methylol acrylamide, and N-methylol methacrylamide.

[0057] The monomer having a cyano group is not particularly limited, but examples thereof include acrylonitrile (AN), methacrylonitrile, α-chloroacrylonitrile, and α-cyanoethyl acrylate.

[0058] The thermoplastic polymer used in this embodiment may be a single polymer or a mixture of two or more types, but preferably contains two or more types of polymers. The thermoplastic polymer may be used together with a solvent. The solvent may be any solvent that can uniformly and stably disperse the thermoplastic polymer, such as N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, water, ethanol, toluene, hot xylene, methylene chloride, hexane, etc., and among these, aqueous solvents such as water are preferred. The thermoplastic polymer may also be used in the form of a latex.

[0059] (Glass Transition Temperature of Thermoplastic Polymer) From the viewpoints of ensuring adhesion to the substrate, suppressing blocking, and exhibiting adhesive strength between the separator and the electrode, while also being able to ensure the distance between the electrode and the separator in the electricity storage device, and shortening the injection time of the electrolyte solution, the thermoplastic polymer constituting the thermoplastic polymer-containing layer preferably has thermal properties such that at least one of the glass transition temperatures is in a range of 20°C or less, and at least one of the glass transition temperatures is in a range of 30°C or more and 150°C or less.

[0060] The glass transition temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC). In the present disclosure, the glass transition temperature may also be expressed as Tg.

[0061] Specifically, it is determined by the intersection of a line extending from the low-temperature side baseline of the DSC curve to the high-temperature side and a tangent to the inflection point of the step-like change in the glass transition. For more details, see the method described in the Examples.

[0062] Here, "glass transition" refers to a change in heat quantity that occurs on the endothermic side in DSC due to a change in the state of the polymer test piece. Such a change in heat quantity is observed as a step-like change or a combination of a step-like change and a peak in the DSC curve.

[0063] The term "step change" refers to the portion of a DSC curve where the curve leaves the previous baseline and transitions to a new baseline, and includes a combination of a peak and a step change.

[0064] The "inflection point" refers to the point at which the gradient of the step-like change portion of the DSC curve is maximized. It can also be expressed as the point at which the step-like change portion changes from an upwardly convex curve to a downwardly convex curve.

[0065] The term "peak" refers to the portion of a DSC curve from when the curve leaves the baseline until when it returns to the baseline.

[0066] "Baseline" refers to the DSC curve in the temperature region where no transition or reaction occurs in the test specimen.

[0067] In this embodiment, at least one of the glass transition temperatures of the thermoplastic polymers used is in the range of 20°C or less, thereby providing excellent adhesion to the porous substrate or the inorganic filler-containing layer and suppressing blocking, thereby achieving the effect of providing excellent adhesion between the separator and the electrode. The glass transition temperature is preferably -100°C or higher, more preferably -50°C or higher, even more preferably -40°C or higher, or particularly preferably -6°C or higher, from the viewpoint of handleability and blocking resistance, and is preferably 20°C or lower, more preferably 10°C or lower, or particularly preferably 0°C or lower, from the viewpoint of adhesion to the porous substrate or the inorganic filler-containing layer.

[0068] In this embodiment, at least one of the glass transition temperatures of the thermoplastic polymers used is in the range of 30° C. or higher and 150° C. or lower, thereby providing excellent adhesion and handling between the separator and the electrode, and further enabling the distance between the electrode surface and the separator substrate surface in an electricity storage device to be maintained, and shortening the injection time of the electrolyte solution. The glass transition temperature is preferably 30° C. or higher, more preferably 40° C. or higher, even more preferably 60° C. or higher, or particularly preferably 85° C. or higher, from the viewpoint of handleability and blocking resistance, and is preferably 150° C. or lower, more preferably 130° C. or lower, or particularly preferably 120° C. or lower, from the viewpoint of adhesive strength.

[0069] The thermoplastic polymer having two glass transition temperatures can be achieved, for example, by blending two or more types of thermoplastic polymers, but is not limited to this method.

[0070] In particular, polymer blends can control the glass transition temperature of the entire thermoplastic polymer by combining polymers with high and low glass transition temperatures. Furthermore, multiple functions can be imparted to the entire thermoplastic polymer. For example, blending two or more polymers, particularly those with a glass transition temperature in the range of 30°C or higher and those with a glass transition temperature in the range of 20°C or lower, can achieve both stickiness resistance and wettability to a polyolefin microporous membrane. The blending ratio of the polymer with a glass transition temperature in the range of 30°C or higher to the polymer with a glass transition temperature in the range of 20°C or lower is preferably in the range of 0.1:99.9 to 99.9:0.1, more preferably 5:95 to 95:5, even more preferably 50:50 to 95:5, and even more preferably 60:40 to 90:10. Viscoelasticity can also be controlled by combining a highly viscous polymer with a highly elastic polymer.

[0071] In this embodiment, the glass transition temperature (Tg) of the thermoplastic polymer can be adjusted appropriately by, for example, changing the monomer components and the ratio of each monomer used to produce the thermoplastic polymer. That is, the Tg can be roughly estimated from the Tg of the homopolymer generally indicated for each monomer used to produce the thermoplastic polymer (for example, as described in "Polymer Handbook" (A Wiley-Interscience Publication)) and the blending ratio of the monomers. For example, copolymers containing high proportions of monomers such as styrene, methyl methacrylate, and acrylonitrile, which give polymers with Tg of about 100°C, have high Tg. Copolymers containing high proportions of monomers such as butadiene, which gives polymers with Tg of about -80°C, or n-butyl acrylate and 2-ethylhexyl acrylate, which give polymers with Tg of about -50°C, have low Tg.

[0072] The Tg of the polymer can be roughly calculated by the FOX formula (the following formula (1)). The glass transition point of the thermoplastic polymer in this embodiment is measured by the above-mentioned method using DSC. 1 / Tg=W １ / Tg １ +W ２ / Tg ２ +...+W ｉ / Tg ｉ +...W ｎ / Tg ｎ (1) {In formula (1), Tg(K) is the Tg of the copolymer, Tg ｉ (K) is the Tg of the homopolymer of each monomer i, W ｉ indicates the mass fraction of each monomer.}

[0073] The glass transition temperature of a thermoplastic polymer can be determined by the following method. An appropriate amount of the thermoplastic polymer coating liquid is placed on an aluminum dish and dried in a hot air dryer at 130°C for 30 minutes. Approximately 5 mg of the dried film after drying is placed in an aluminum container for measurement, and a DSC curve and a DDSC curve are obtained under a nitrogen atmosphere using a DSC measurement device (TA Instruments, DSC Q2000). The measurement conditions are as follows: (First-stage heating program) Start at 40°C, increase the temperature at a rate of 50°C per minute. After reaching 200°C, maintain this temperature for 5 minutes. (Second-stage heating program) Reduce the temperature from 200°C at a rate of 20°C per minute. After reaching -50°C, maintain this temperature for 5 minutes. (Third-stage heating program) Increase the temperature from -50°C to 200°C at a rate of 20°C per minute. DSC and DDSC data are obtained during this third heating stage. According to the method described in JIS-K7121, the glass transition temperature (Tg) is determined as the intersection of the baseline (a straight line extending the baseline of the obtained DSC curve toward the higher temperature side) and the tangent at the inflection point (the point where the upward convex curve changes to a downward convex curve).

[0074] (Structure of Thermoplastic Polymer-Containing Layer) In the thermoplastic polymer-containing layer, it is preferred that a thermoplastic resin having a glass transition temperature of 30°C or higher and 150°C or lower is present on the outermost surface side of the electricity storage device separator, and a thermoplastic resin having a glass transition temperature of 20°C or lower is present on the interface side between the polyolefin microporous membrane and the thermoplastic polymer-containing layer. The "outermost surface" refers to the surface of the thermoplastic polymer-containing layer that contacts the electrode when the electricity storage device separator and the electrode are laminated together. The "interface" refers to the surface of the thermoplastic polymer-containing layer that contacts the polyolefin microporous membrane.

[0075] In the thermoplastic polymer-containing layer, the presence of a thermoplastic polymer having a glass transition temperature of 30°C or higher and 150°C or lower on the outermost surface side of the separator for an electricity storage device tends to provide better adhesion to the microporous membrane, and as a result, better adhesion between the separator and the electrodes. Furthermore, the presence of a thermoplastic polymer having a glass transition temperature of 20°C or lower on the interface side between the polyolefin microporous membrane and the thermoplastic polymer-containing layer tends to provide better adhesion and handleability between the separator and the electrodes. By having such a thermoplastic polymer-containing layer, the separator tends to have better adhesion and handleability between the separator and the electrodes.

[0076] The above-mentioned structure can be achieved by, for example, (a) the thermoplastic polymer comprises a particulate thermoplastic polymer and a binder polymer that adheres the particulate thermoplastic polymer to the polyolefin microporous membrane with the particulate thermoplastic polymer exposed on the surface, the particulate thermoplastic polymer having a glass transition temperature in the range of 30°C to 150°C, and a thermoplastic polymer having a glass transition temperature of 20°C or lower present at the interface between the polyolefin microporous membrane and the thermoplastic polymer-containing layer, or (b) the thermoplastic polymer has a laminated structure, the glass transition temperature of the thermoplastic polymer in the part that will become the outermost layer in the separator is in the range of 30°C to 150°C, and a thermoplastic polymer having a glass transition temperature of 20°C or lower present at the interface between the polyolefin microporous membrane and the thermoplastic polymer-containing layer. Note that (b) the thermoplastic polymer may have a laminated structure of polymers with different Tg.

[0077] (Particle size of thermoplastic polymer) The structure of the thermoplastic polymer in this embodiment is not particularly limited, but may be, for example, granular. Such a structure tends to improve the adhesiveness between the separator and the electrode and the handleability of the separator. Here, granular refers to a state in which individual thermoplastic polymer particles have contours as measured with a scanning electron microscope (SEM), and may be elongated, spherical, polygonal, or the like.

[0078] The particle size distribution and D10, D50, and D90 of the granular thermoplastic polymer are obtained by measuring the thermoplastic polymer particle dispersion using a laser particle size distribution analyzer (Microtrac MT3300EX, manufactured by Nikkiso Co., Ltd.). If necessary, the particle size distribution of the thermoplastic polymer particle dispersion can be adjusted using the particle size distribution of the dispersion solvent or binder polymer as a baseline. The particle sizes at which the cumulative frequencies are 10%, 50%, and 90% are defined as the average volume particle size D10 of the thermoplastic polymer particles, the average volume particle size D50 of the thermoplastic polymer particles, and the average volume particle size D90 of the thermoplastic polymer particles, respectively.

[0079] The particle size of the thermoplastic polymer contained in the thermoplastic polymer-containing layer of this embodiment preferably satisfies the relationship 1.0≦D90 / D10≦5.0, more preferably satisfies the relationship 1.0≦D90 / D10≦3.0, and even more preferably satisfies the relationship 1.0≦D90 / D10≦2.0. Setting the particle size ratio of the thermoplastic polymer particles contained in the thermoplastic polymer-containing layer to a predetermined range is preferable because it can maintain a constant particle size distribution of the thermoplastic polymer and control the friction and contact area between the thermoplastic polymer and the inorganic filler, thereby suppressing the generation of static electricity.

[0080] In the particle size distribution of the slurry containing the thermoplastic polymer, the average particle size D90 of the thermoplastic polymer particles is preferably 0.5 μm or more and 1.5 μm or less, more preferably 0.5 μm or more and 1.0 μm or less. A D90 of 0.5 μm or more is preferred from the viewpoint of improving the ion permeability of the separator, and a D90 of 1.5 μm or less is preferred from the viewpoint of preventing sedimentation of the thermoplastic polymer particles when the slurry is left to stand.

[0081] In the particle size distribution of the slurry containing the thermoplastic polymer, the average particle size D50 of the thermoplastic polymer particles is preferably 0.3 μm or more and 1.5 μm or less, more preferably 0.5 μm or more and 1.0 μm or less, and even more preferably 0.5 μm or more and 0.7 μm or less. A D50 of 0.3 μm or more is preferred from the viewpoint of increasing the anchor strength with the electrode surface and realizing high adhesiveness, and a D50 of 1.5 μm or less is preferred from the viewpoint of increasing the adhesion with the electrode surface and realizing high adhesiveness.

[0082] In the particle size distribution of the slurry containing the thermoplastic polymer, the average particle size D10 of the thermoplastic polymer particles is preferably 0.2 μm or more and 1.0 μm or less, more preferably 0.3 μm or more and 0.5 μm or less. A D10 of 0.2 μm or more is preferred from the viewpoint of preventing the thermoplastic polymer particles from entering the pores of the porous substrate and inhibiting ion permeation, and a D10 of 1.0 μm or less is preferred from the viewpoint of improving the dot-forming properties of the thermoplastic polymer particles.

[0083] (Basis Weight per Side of Thermoplastic Polymer-Containing Layer) In the separator according to this embodiment, the basis weight per side of the thermoplastic polymer-containing layer is set to 0.03 g / m from the viewpoint of achieving both adhesive strength with the electrode and ion permeability. ２ 0.50g / m or more ２ It is preferable that the content is 0.04 g / m or less. ２ 0.45g / m or more ２ More preferably, it is 0.06 g / m or less, and most preferably, it is 0.06 g / m ２ 0.40g / m or more ２ The basis weight of the thermoplastic polymer-containing layer can be adjusted by changing the polymer concentration of the coating liquid or the amount of the polymer solution applied. From the viewpoint of improving the cycle characteristics of the battery by suppressing deformation of the cell shape due to expansion and contraction of the electrodes, within a range that does not impair the effects of this embodiment, it is preferable to set the basis weight to 0.06 g / m ２ The above range is preferred.

[0084] [Substrate] Because a separator needs to have insulating properties and ion permeability, the separator substrate (hereinafter referred to as a porous substrate or substrate) is generally formed from an insulating material having a porous structure, such as paper, a polyolefin nonwoven fabric, or a resin microporous membrane. In particular, as a separator substrate used in an electricity storage device such as a nonaqueous secondary battery comprising a positive electrode and a negative electrode capable of absorbing and releasing lithium and a nonaqueous electrolyte solution obtained by dissolving an electrolyte in a nonaqueous solvent, a polyolefin microporous membrane that has oxidation-reduction resistance and can form a dense and uniform porous structure is preferred.

[0085] (Polyolefin microporous membrane) The polyolefin microporous membrane in this embodiment is not particularly limited, but examples include microporous membranes composed of a polyolefin resin composition containing polyolefin, and a microporous membrane composed mainly of polyolefin resin is preferred. The polyolefin microporous membrane in this embodiment is not particularly limited in polyolefin resin content, but from the viewpoint of shutdown performance when used as a separator for an electrical storage device, a microporous membrane composed of a polyolefin resin composition in which polyolefin resin accounts for 50% to 100% by mass of all components constituting the microporous membrane is preferred. The proportion of polyolefin resin is more preferably 60% to 100%, and even more preferably 70% to 100%.

[0086] The polyolefin resin is not particularly limited, but refers to a polyolefin resin used in ordinary extrusion, injection, inflation, blow molding, etc., and can be a homopolymer, copolymer, multistage polymer, etc. of ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, etc. Furthermore, polyolefins selected from the group consisting of these homopolymers, copolymers, and multistage polymers can be used alone or in combination.

[0087] Representative examples of polyolefin resins include, but are not limited to, polyethylenes such as low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, and ultra-high molecular weight polyethylene; polypropylenes such as isotactic polypropylene and atactic polypropylene; ethylene-propylene random copolymers; polybutene; and ethylene-propylene rubber.

[0088] When the separator of this embodiment is used as a battery separator, it is preferable to use polyethylene as the main component because of its low melting point and high strength, and it is particularly preferable to use a resin whose main component is high-density polyethylene.

[0089] From the viewpoint of improving the heat resistance of the microporous membrane, it is more preferable to use a microporous membrane made of a resin composition containing polypropylene and a polyolefin resin other than polypropylene. Here, the three-dimensional structure of the polypropylene is not limited, and it may be any of isotactic polypropylene, syndiotactic polypropylene, and atactic polypropylene.

[0090] The proportion of polypropylene relative to the total polyolefins in the polyolefin resin composition is not particularly limited, but from the viewpoint of achieving both heat resistance and a good shutdown function, it is preferably 1 to 35% by mass, more preferably 3 to 20% by mass, and even more preferably 4 to 10% by mass. In this case, there are no limitations on the polyolefin resins other than polypropylene, and examples include homopolymers or copolymers of olefin hydrocarbons such as ethylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene. Specific examples include polyethylene, polybutene, and ethylene-propylene random copolymers.

[0091] From the viewpoint of the shutdown property in which pores are closed by thermal melting, it is preferable to use polyethylene such as low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, and ultra-high molecular weight polyethylene as the polyolefin resin other than polypropylene. Among these, from the viewpoint of strength, polyethylene having a density of 0.93 g / cm as measured in accordance with JIS K 7112 is preferred. ３ 0.97g / cm or more ３ It is more preferable to use polyethylene that is:

[0092] The viscosity average molecular weight of the polyolefin resin constituting the polyolefin microporous membrane is not particularly limited, but is preferably from 30,000 to 12 million, more preferably from 50,000 to less than 2 million, even more preferably from 100,000 to less than 1.2 million, and most preferably from 500,000 to less than 1 million. A polyolefin resin with a viscosity average molecular weight of 30,000 or more is preferred because it increases the melt tension during melt molding, improving moldability, and tends to have high strength due to entanglement of the polymers. On the other hand, a polyolefin resin with a viscosity average molecular weight of 12 million or less is preferred because it facilitates uniform melt-kneading and tends to have excellent sheet moldability, particularly thickness stability. Furthermore, a polyolefin resin with a viscosity average molecular weight of less than 1 million is preferred because it tends to easily block pores when the temperature rises, resulting in a good shutdown function. For example, instead of using a polyolefin with a viscosity average molecular weight of less than 1 million alone, a mixture of a polyolefin with a viscosity average molecular weight of 2 million and a polyolefin with a viscosity average molecular weight of 270,000, wherein the viscosity average molecular weight is less than 1 million, may be used.

[0093] The polyolefin microporous membrane of the present embodiment can contain any additive. Such additives are not particularly limited, and examples thereof include polymers other than polyolefins; inorganic particles; phenolic, phosphorus-based, sulfur-based, and other antioxidants; metal soaps such as calcium stearate and zinc stearate; ultraviolet absorbers; light stabilizers; antistatic agents; antifogging agents; coloring pigments, etc. The total content of these additives is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less, per 100 parts by mass of the polyolefin resin composition.

[0094] (Physical properties of polyolefin microporous membrane) The basis weight (g / m) of the polyolefin microporous membrane (in one embodiment, the PO microporous membrane) ２ The puncture strength when converted into basis weight (hereinafter referred to as basis weight converted puncture strength) is 50 gf / (g / m ２ ) or more, or 60 gf / (g / m ２ ) or more. ２ ) or more or 60 gf / (g / m ２ A PO microporous membrane having a pin puncture strength equivalent to basis weight of 70 gf / (g / m) or more tends to be less likely to break in an impact test of an electricity storage device. From the viewpoint of improving the safety, for example, impact resistance, of an electricity storage device while maintaining the strength of the PO microporous membrane, the pin puncture strength equivalent to basis weight is more preferably 70 gf / (g / m) or more. ２ ) or more, more preferably 80 gf / (g / m ２ The puncture strength converted into basis weight is not limited, but is, for example, 200 gf / (g / m ２ ) or less, or 150 gf / (g / m ２ ) or less, or 140 gf / (g / m ２ ) can be:

[0095] The lower limit of the pin puncture strength of the PO microporous membrane not converted into basis weight (hereinafter simply referred to as pin puncture strength) is preferably 100 gf or more (preferably 0.98 N or more), more preferably 200 gf or more, and even more preferably 300 gf or more. A pin puncture strength of 100 gf or more is preferred from the viewpoint of preventing breakage of the PO microporous membrane in an impact test. From the viewpoint of stability during membrane production, the upper limit of the pin puncture strength of the PO microporous membrane is preferably 1000 gf or less, more preferably 800 gf or less, and even more preferably 700 gf or less. Any lower limit can be used as long as it allows stable production of membranes and battery manufacturing. The upper limit is set by balancing with other properties. The pin puncture strength can be increased by increasing the shear force applied to the molded product during extrusion or by increasing the molecular chain orientation due to stretching. However, since increased strength leads to deterioration of thermal stability due to increased residual stress, it is controlled according to the purpose.

[0096] The basis weight of the polyolefin microporous membrane in this embodiment is not particularly limited, but is preferably 2.8 g / m ２ More preferably, 3.5 g / m ２ More preferably, 4.0 g / m ２ or more, and preferably 6.4 g / m ２ or less, more preferably 5.4 g / m ２ More preferably, 4.8 g / m or less ２ The following is the result.

[0097] The porosity of the polyolefin microporous membrane in this embodiment is not particularly limited, but is preferably 20% or more, more preferably 35% or more, even more preferably 40% or more, particularly preferably 45% or more, and preferably 80% or less, more preferably 60% or less, and even more preferably 55% or less. A porosity of 20% or more is preferred from the viewpoint of ensuring the permeability of the separator. On the other hand, a porosity of 80% or less is preferred from the viewpoint of ensuring pin puncture strength. The porosity of the polyolefin microporous membrane can be adjusted by changing the stretching ratio, etc.

[0098] The thickness of the polyolefin microporous membrane in this embodiment is not particularly limited, but is preferably 2 μm or more, more preferably 4.5 μm or more, even more preferably 5.5 μm or more, and particularly preferably 6 μm or more. The thickness of the polyolefin microporous membrane is preferably 30 μm or less, more preferably 20 μm or less, even more preferably 16 μm or less, particularly preferably 12 μm or less, and most preferably 9 μm or less. A polyolefin microporous membrane thickness of 2 μm or more is preferred from the viewpoint of improving mechanical strength. On the other hand, a polyolefin microporous membrane thickness of 30 μm or less is preferred because it reduces the volume occupied by the separator, which tends to be advantageous in terms of increasing the capacity of the battery.

[0099] The air permeability of the polyolefin microporous membrane in this embodiment is not particularly limited, but is preferably 10 sec / 100 cm ３ More preferably, 20 sec / 100 cm ３ More preferably, 30 sec / 100 cm ３ More preferably 90 sec / 100 cm ３ More than 100 sec / 100 cm, most preferably ３ The air permeability of the polyolefin microporous membrane is preferably 300 sec / 100 cm ３ Less than 200 sec / 100 cm, more preferably ３ More preferably, 180 sec / 100 cm or less ３ Below 140 sec / 100 cm, particularly preferably ３ The air permeability of the polyolefin microporous membrane is 10 sec / 100 cm or less. ３ On the other hand, it is preferable to set the air permeability of the polyolefin microporous membrane to 300 sec / 100 cm or more from the viewpoint of suppressing self-discharge of the electricity storage device. ３ The following conditions are preferable from the viewpoint of obtaining good charge / discharge characteristics. The air permeability can be adjusted by changing the stretching temperature, stretching ratio, etc.

[0100] The average pore size of the polyolefin microporous membrane in this embodiment is preferably 0.15 μm or less, more preferably 0.1 μm or less. The average pore size of the polyolefin microporous membrane is preferably 0.01 μm or more. When the polyolefin microporous membrane is used as a separator for an electrical storage device, it is preferable to set the average pore size of the polyolefin microporous membrane to 0.15 μm or less, from the viewpoint of suppressing self-discharge of the electrical storage device and suppressing capacity reduction. Furthermore, when the average pore size of the polyolefin microporous membrane is within the above range, it is preferable because the contact angle of the adhesive coating liquid with the surface of the substrate on which the thermoplastic polymer-containing layer is provided or the inorganic filler-containing layer (in one embodiment, the surface coated with the thermoplastic polymer) can be controlled within the specified range in this application. The average pore size can be adjusted by changing the stretching ratio when producing the polyolefin microporous membrane, for example.

[0101] The polyolefin microporous membrane of the present embodiment has a short-circuit temperature, which is an index of heat resistance, of preferably 140° C. or higher, more preferably 150° C. or higher, and even more preferably 160° C. or higher. When the membrane is used as a separator for an electricity storage device, a short-circuit temperature of 140° C. or higher is preferred from the viewpoint of safety of the electricity storage device.

[0102] The viscosity average molecular weight of the polyolefin microporous membrane in this embodiment is not particularly limited, but is preferably from 100,000 to 5,000,000, more preferably from 300,000 to 1,500,000, and even more preferably from 500,000 to 1,000,000. A viscosity average molecular weight of from 100,000 to 5,000,000 is preferred from the viewpoints of the pin puncture strength, permeability, heat shrinkage, and shutdown function of the polyolefin microporous membrane.

[0103] (Method for producing polyolefin microporous membrane) The method for producing the polyolefin microporous membrane in this embodiment is not particularly limited, and known production methods can be used. For example, a method in which a polyolefin resin composition and a plasticizer are melt-kneaded to form a sheet, and then optionally stretched, and then the plasticizer is extracted to make the membrane porous; a method in which a polyolefin resin composition is melt-kneaded and extruded at a high draw ratio, and then heat-treated and stretched to peel the polyolefin crystal interface to make the membrane porous; a method in which a polyolefin resin composition and an inorganic filler are melt-kneaded to form a sheet, and then stretched to peel the interface between the polyolefin and the inorganic filler to make the membrane porous; a method in which a polyolefin resin composition is dissolved and then immersed in a poor solvent for the polyolefin, and the polyolefin is solidified while the solvent is simultaneously removed to make the membrane porous, etc. will be described below as an example of a method for producing a microporous membrane.

[0104] First, the polyolefin resin composition and the plasticizer are melt-kneaded. Examples of melt-kneading methods include adding the polyolefin resin and, if necessary, other additives to a resin kneading device such as an extruder, kneader, lab plastomill, kneading roll, or Banbury mixer, and then introducing and kneading the plasticizer at a desired ratio while heating and melting the resin components. In this case, it is preferable to pre-knead the polyolefin resin, other additives, and plasticizer in a predetermined ratio using a Henschel mixer or the like before adding them to the resin kneading device. More preferably, only a portion of the plasticizer is added during pre-kneading, and the remaining plasticizer is kneaded while side-feeding the resin kneading device. This improves the dispersibility of the plasticizer, allowing the sheet-shaped molded product of the melt-kneaded mixture of the resin composition and the plasticizer to be stretched at a high ratio without film rupture in a subsequent process.

[0105] As the plasticizer, a non-volatile solvent capable of forming a homogeneous solution at or above the melting point of the polyolefin can be used. Specific examples of such non-volatile solvents include hydrocarbons such as liquid paraffin and paraffin wax; esters such as dioctyl phthalate and dibutyl phthalate; and higher alcohols such as oleyl alcohol and stearyl alcohol. Among these, liquid paraffin is preferred because it has high compatibility with polyethylene and polypropylene, and is less likely to cause interfacial peeling between the polyolefin resin composition and the plasticizer even when the molten kneaded product is stretched, making it easier to perform uniform stretching.

[0106] The ratio of the polyolefin resin composition to the plasticizer is not particularly limited as long as they can be uniformly melt-kneaded and molded into a sheet. For example, the mass fraction of the plasticizer in a composition consisting of the polyolefin resin composition and the plasticizer is preferably 30 to 80% by mass, more preferably 40 to 70% by mass. When the mass fraction of the plasticizer is 80% by mass or less, the melt tension during melt molding is less likely to be insufficient, and moldability tends to be improved. On the other hand, when the mass fraction of the plasticizer is 30% by mass or more, polyolefin chain scission does not occur even when the mixture of the polyolefin resin composition and the plasticizer is stretched at a high ratio, and a uniform and fine pore structure is formed, which also tends to increase strength.

[0107] Next, the molten mixture is molded into a sheet. Examples of methods for producing a sheet-shaped molded product include extruding the molten mixture into a sheet through a T-die or the like, contacting it with a heat conductor, and cooling it to a temperature sufficiently lower than the crystallization temperature of the resin component to solidify it. Heat conductors used for cooling and solidifying can include metal, water, air, or the plasticizer itself, but metal rolls are preferred due to their high thermal conductivity. In this case, sandwiching the sheet between the metal rolls when contacting it further increases the thermal conductivity, orients the sheet, increasing film strength and improving the surface smoothness of the sheet, making it more preferable. When extruding into a sheet through a T-die, the die lip spacing is preferably 400 μm or more and 3000 μm or less, and more preferably 500 μm or more and 2500 μm or less. A die lip spacing of 400 μm or more reduces scum and other deposits, minimizing the impact on film quality such as streaks and defects, and tends to prevent film rupture during the subsequent stretching process. On the other hand, when the die lip gap is 3000 μm or less, the cooling rate is fast, which prevents uneven cooling and tends to maintain the thickness stability of the sheet.

[0108] The sheet-like molded article thus obtained is preferably stretched. Either uniaxial stretching or biaxial stretching can be suitably used as the stretching treatment, but biaxial stretching is preferred from the viewpoint of the strength of the resulting microporous membrane. When the sheet-like molded article is stretched in the biaxial direction at a high ratio, the molecules are oriented in the plane direction, and the finally obtained microporous membrane is less likely to tear and has high pin puncture strength. Examples of stretching methods include simultaneous biaxial stretching, sequential biaxial stretching, multistage stretching, and multiple stretching, and simultaneous biaxial stretching is preferred from the viewpoints of improved pin puncture strength, stretching uniformity, and shutdown properties.

[0109] Here, simultaneous biaxial stretching refers to a stretching method in which stretching in the MD direction (the machine direction of the microporous membrane) and stretching in the TD direction (the direction crossing the MD of the microporous membrane at an angle of 90°) are performed simultaneously, and the stretching ratios in each direction may be different. Sequential biaxial stretching refers to a stretching method in which stretching in the MD direction or the TD direction is performed independently, and while stretching is performed in the MD direction or the TD direction, the other direction is unconstrained or fixed at a fixed length.

[0110] The areal stretching ratio is preferably in the range of 20 to 100 times, more preferably 25 to 50 times. The stretching ratio in each axial direction is preferably in the range of 4 to 10 times in the MD direction and 4 to 10 times in the TD direction, more preferably 5 to 8 times in the MD direction and 5 to 8 times in the TD direction. A total areal stretching ratio of 20 times or more tends to impart sufficient strength to the resulting microporous membrane, while a total areal stretching ratio of 100 times or less tends to prevent membrane breakage during the stretching step and achieve high productivity.

[0111] The sheet-like molded product may also be rolled. Rolling can be carried out, for example, by a pressing method using a double belt press or the like. Rolling can particularly increase the orientation of the surface layer portion. The rolling areal ratio is preferably greater than 1 and not greater than 3, and more preferably greater than 1 and not greater than 2. If the rolling ratio is greater than 1, the planar orientation tends to increase, and the membrane strength of the microporous membrane finally obtained tends to increase. On the other hand, if the rolling ratio is 3 or less, the difference in orientation between the surface layer portion and the central interior tends to be small, and a uniform porous structure tends to be formed in the thickness direction of the membrane, which is preferable.

[0112] Next, the plasticizer is removed from the sheet-like molding to produce a microporous membrane. Examples of methods for removing the plasticizer include immersing the sheet-like molding in an extraction solvent to extract the plasticizer and then thoroughly drying the resulting material. The plasticizer extraction method may be either a batch method or a continuous method. To prevent shrinkage of the microporous membrane, it is preferable to restrain the edges of the sheet-like molding during the immersion and drying process. Furthermore, it is preferable that the amount of plasticizer remaining in the microporous membrane be less than 1% by mass.

[0113] It is preferable to use an extraction solvent that is a poor solvent for the polyolefin resin composition and a good solvent for the plasticizer, and that has a boiling point lower than the melting point of the polyolefin resin. Examples of such extraction solvents include hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane; non-chlorine-based halogenated solvents such as hydrofluoroethers and hydrofluorocarbons; alcohols such as ethanol and isopropanol; ethers such as diethyl ether and tetrahydrofuran; and ketones such as acetone and methyl ethyl ketone. These extraction solvents may be recovered by distillation or other procedures and reused.

[0114] To suppress shrinkage of the microporous membrane, heat treatment such as heat setting or heat relaxation can be performed after the stretching step or after the formation of the microporous membrane. The microporous membrane may also be subjected to post-treatment such as hydrophilization treatment with a surfactant or crosslinking treatment with ionizing radiation or the like.

[0115] [Inorganic Filler-Containing Layer] The separator for an electricity storage device according to this embodiment may also include an inorganic filler-containing layer (in this embodiment, the inorganic filler-containing layer may be referred to as a porous layer) containing an inorganic filler and a resin binder. The inorganic filler-containing layer may be located on at least a portion of the surface of the polyolefin microporous membrane, at least a portion of the surface of the thermoplastic polymer-containing layer, and / or between the polyolefin microporous membrane and the thermoplastic polymer-containing layer. In one aspect, the inorganic filler-containing layer of this embodiment is located between the polyolefin microporous membrane and the thermoplastic polymer-containing layer. The separator according to this embodiment may include an inorganic filler-containing layer on one and / or both sides of the polyolefin microporous membrane.

[0116] (Inorganic Filler) The inorganic filler used in the inorganic filler-containing layer is not particularly limited, but is preferably one that has a melting point of 200°C or higher, high electrical insulation properties, and is electrochemically stable within the range of use of lithium ion secondary batteries.

[0117] Examples of inorganic filler materials include oxide ceramics such as alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide; nitride ceramics such as silicon nitride, titanium nitride, and boron nitride; ceramics such as silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, barium sulfate, aluminum hydroxide, aluminum oxide hydroxide, or boehmite, potassium titanate, talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; and glass fiber. Among these, at least one selected from the group consisting of alumina, boehmite, and barium sulfate is preferred from the viewpoint of stability in lithium-ion secondary batteries. Furthermore, synthetic boehmite is preferred as the boehmite, as it can reduce ionic impurities that adversely affect the characteristics of electrochemical devices.

[0118] Examples of the shape of the inorganic filler include plate-like, scale-like, polyhedral, needle-like, columnar, granular, spherical, spindle-like, and block-like shapes, and a combination of multiple types of inorganic fillers having the above shapes may be used. Among these, the block-like shape is preferred from the viewpoint of the balance between permeability and heat resistance.

[0119] The aspect ratio of the inorganic filler is preferably 1.0 or more and 5.0 or less, more preferably 1.1 or more and 3.0 or less. The aspect ratio of the inorganic filler of 5.0 or less is preferred from the viewpoints of suppressing the amount of water adsorption in the multilayer porous membrane (in one embodiment, the inorganic filler-containing layer and the polyolefin microporous membrane) and suppressing capacity deterioration after repeated cycles, and suppressing deformation at temperatures exceeding the melting point of the polyolefin microporous membrane.

[0120] The specific surface area of ​​the inorganic filler is 3.0 m ２ / g or more 17m ２ / g or less, and more preferably 5.0m ２ / g or more 15m ２ / g or less, and more preferably 6.5m ２ / g or more 13m ２ / g or less. The specific surface area of ​​the inorganic filler is 17 m ２ When the specific surface area of ​​the inorganic filler is 3.0 m / g or less, the amount of water adsorption by the multilayer porous film is suppressed, and deterioration of the capacity during repeated cycles is suppressed, which is preferable. ２ / g or more is preferable from the viewpoint of suppressing deformation at a temperature exceeding the melting point of the polyolefin microporous membrane. The specific surface area of ​​the inorganic filler is measured using the BET adsorption method.

[0121] The particle size of the inorganic filler contained in the inorganic filler-containing layer of this embodiment preferably satisfies the relationship 1.0≦D90 / D10≦5.0, and more preferably satisfies the relationship 2.0≦D90 / D10≦4.0. Setting the particle size ratio of the inorganic filler contained in the inorganic filler-containing layer within a predetermined range is preferable because it can keep the particle size distribution of the inorganic filler constant and control the friction and contact area between the thermoplastic polymer and the inorganic filler, thereby suppressing the generation of static electricity.

[0122] Examples of methods for adjusting the particle size distribution of the inorganic filler within the above range include a method of pulverizing the inorganic filler using a ball mill, a bead mill, a jet mill, or the like to obtain a desired particle size distribution, and a method of preparing fillers with multiple particle size distributions and then blending them.

[0123] In the particle size distribution of the slurry containing the inorganic filler, the inorganic filler particles have an average particle size D90 of preferably 0.1 μm or more and 2.5 μm or less, more preferably 0.3 μm or more and 1.5 μm or less, and even more preferably 0.50 μm or more and 1.0 μm or less. An average particle size D90 of 0.1 μm or more is preferred from the viewpoint of improving the ion permeability of the separator, and a D90 of 2.5 μm or less is preferred from the viewpoint of improving the heat resistance of the separator.

[0124] In the particle size distribution of the slurry containing the inorganic filler, the inorganic filler particles have an average particle size D50 of preferably 0.10 μm or more and 1.50 μm or less, more preferably 0.20 μm or more and 1.0 μm or less, and even more preferably 0.40 μm or more and 0.70 μm or less. If the inorganic filler particles have an average particle size D50 of 0.10 μm or more, this is preferable from the viewpoint of preventing the inorganic filler from penetrating the pores of the substrate and increasing the battery resistance, and thus preventing capacity deterioration over repeated cycles. If the inorganic filler particles have an average particle size D50 of 1.50 μm or less, this is preferable from the viewpoint of easily forming a thin inorganic filler-containing layer, and preventing an increase in battery capacity and deterioration of rate characteristics.

[0125] In the particle size distribution of the slurry containing the inorganic filler, the inorganic filler particles have an average particle size D10 of preferably 0.08 μm or more and 0.80 μm or less, more preferably 0.09 μm or more and 0.50 μm or less, and even more preferably 0.20 μm or more and 0.35 μm or less. An average particle size D10 of the inorganic filler particles of 0.08 μm or more is preferred from the viewpoint of suppressing the amount of water adsorption of the multilayer porous membrane and suppressing capacity deterioration after repeated cycles, and an average particle size D10 of the inorganic filler particles of 0.80 μm or less is preferred from the viewpoint of suppressing deformation at temperatures exceeding the melting point of the polyolefin microporous membrane.

[0126] The particle size distribution and D10, D50, and D90 of the inorganic filler particles are obtained by measuring the inorganic filler particle dispersion using a laser particle size distribution measuring device (Microtrac MT3300EX, manufactured by Nikkiso Co., Ltd.). If necessary, the particle size distribution of the inorganic filler particle dispersion solvent or binder polymer can be used as a baseline to adjust the particle size distribution of the inorganic filler particle dispersion. The particle size at which the cumulative frequency is 10% is the average volume particle size D10 of the inorganic filler particles, the particle size at which the cumulative frequency is 50% is the average volume particle size D50 of the inorganic filler particles, and the particle size at which the cumulative frequency is 90% is the average volume particle size D90 of the inorganic filler particles.

[0127] The proportion of the inorganic filler in the inorganic filler-containing layer can be appropriately determined from the viewpoints of the adhesion of the inorganic filler, the permeability and heat resistance of the multilayer porous membrane, etc., but is preferably 50% by mass or more and less than 100% by mass, more preferably 70% by mass or more and 99.99% by mass or less, even more preferably 80% by mass or more and 99.9% by mass or less, and particularly preferably 90% by mass or more and 99% by mass or less.

[0128] (Resin Binder) The type of resin binder is not particularly limited, but when the multilayer porous membrane in the present embodiment is used as a separator for a lithium ion secondary battery, it is preferable to use a resin binder that is insoluble in the electrolyte solution of the lithium ion secondary battery and is electrochemically stable within the range of use of the lithium ion secondary battery.

[0129] Specific examples of resin binders include the following 1) to 7): 1) polyolefins: for example, polyethylene, polypropylene, ethylene propylene rubber, and modified products thereof; 2) conjugated diene polymers: for example, styrene-butadiene copolymers and hydrogenated products thereof, acrylonitrile-butadiene copolymers and hydrogenated products thereof, acrylonitrile-butadiene-styrene copolymers and hydrogenated products thereof; 3) acrylic polymers: for example, methacrylic acid ester-acrylic acid ester copolymers, styrene-acrylic acid ester copolymers, acrylonitrile-acrylic acid ester copolymers; 4) polyvinyl alcohol resins: for example, polyvinyl alcohol, polyvinyl acetate; 5) fluorine-containing resins: for example, polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymers, ethylene-tetrafluoroethylene copolymers; 6) cellulose derivatives: for example, ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose; 7) Resins having a melting point and / or glass transition temperature of 180°C or higher, or polymers having no melting point but a decomposition temperature of 200°C or higher: for example, polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, polyester.

[0130] From the viewpoint of further improving safety in the event of a short circuit, 3) acrylic polymers, 5) fluorine-containing resins, and 7) polyamides as polymers are preferred. As polyamides, wholly aromatic polyamides, particularly polymetaphenylene isophthalamide, are preferred from the viewpoint of durability.

[0131] From the viewpoint of compatibility between the resin binder and the electrode, the above 2) conjugated diene polymer is preferred, and from the viewpoint of voltage resistance, the above 3) acrylic polymer and 5) fluorine-containing resin are preferred.

[0132] The conjugated diene polymer 2) is a polymer containing a conjugated diene compound as a monomer unit.

[0133] Examples of the conjugated diene compound include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, substituted linear conjugated pentadiene compounds, and substituted and side-chain conjugated hexadienes, and these may be used alone or in combination of two or more. Among these, 1,3-butadiene is particularly preferred.

[0134] The acrylic polymer (3) is a polymer containing a (meth)acrylic compound as a monomer unit, and the (meth)acrylic compound is at least one selected from the group consisting of (meth)acrylic acid and (meth)acrylic acid esters.

[0135] Examples of the (meth)acrylic acid ester used in the acrylic polymer 3) include (meth)acrylic acid alkyl esters such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, and 2-ethylhexyl methacrylate; and epoxy group-containing (meth)acrylic acid esters such as glycidyl acrylate and glycidyl methacrylate; these may be used alone or in combination of two or more. Of the above, 2-ethylhexyl acrylate (EHA) and butyl acrylate (BA) are particularly preferred.

[0136] From the viewpoint of safety in a crash test, the acrylic polymer is preferably a polymer containing EHA or BA as a main structural unit. The main structural unit refers to a polymer portion corresponding to a monomer that accounts for 40 mol % or more of all raw materials for forming the polymer.

[0137] The above 2) conjugated diene polymer and 3) acrylic polymer may be obtained by copolymerizing other monomers copolymerizable therewith. Examples of the copolymerizable other monomers include unsaturated carboxylic acid alkyl esters, aromatic vinyl monomers, vinyl cyanide monomers, unsaturated monomers containing a hydroxyalkyl group, unsaturated carboxylic acid amide monomers, crotonic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, etc., which may be used alone or in combination of two or more. Among the above, unsaturated carboxylic acid alkyl ester monomers are particularly preferred. Examples of unsaturated carboxylic acid alkyl ester monomers include dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, dimethyl itaconate, monomethyl fumarate, monoethyl fumarate, etc., which may be used alone or in combination of two or more.

[0138] The conjugated diene polymer 2) may be obtained by copolymerizing the above (meth)acrylic compound as another monomer.

[0139] The resin binder is preferably in the form of latex, and more preferably an acrylic polymer latex, from the viewpoint of providing strong adhesion between multiple inorganic particles even at high temperatures exceeding room temperature and suppressing thermal shrinkage.

[0140] The average particle size of the resin binder is preferably 50 nm or more and 500 nm or less, more preferably 60 nm or more and 460 nm or less, and even more preferably 80 nm or more and 250 nm or less. When the average particle size of the resin binder is 50 nm or more, when an inorganic filler-containing layer containing an inorganic filler and a resin binder is laminated on at least one side of a polyolefin microporous membrane, ion permeability is less likely to decrease and high output characteristics are easily obtained. In addition, even when the temperature rises rapidly during abnormal heat generation, smooth shutdown characteristics are exhibited and high safety is easily achieved. When the average particle size of the resin binder is 500 nm or less, good adhesion is exhibited, and when formed into a multilayer porous membrane, thermal shrinkage is good and safety tends to be excellent.

[0141] The average particle size of the resin binder can be controlled by adjusting the polymerization time, polymerization temperature, raw material composition ratio, raw material charging order, pH, and the like.

[0142] A dispersant such as a surfactant may be added to the inorganic filler coating liquid to stabilize dispersion or improve coating properties. The dispersant is adsorbed to the surface of inorganic filler particles in the slurry and stabilizes the inorganic filler particles by electrostatic repulsion or the like, and examples of such dispersants include polycarboxylates, sulfonates, and polyoxyethers. The amount of dispersant added is preferably 0.2 parts by weight or more and 5.0 parts by weight or less, more preferably 0.3 parts by weight or more and 1.0 parts by weight or less, calculated as solid content, per 100 parts by weight of the inorganic filler.

[0143] (Physical Properties, Structure, and Formation Method of Inorganic Filler-Containing Layer) The thickness of the inorganic filler-containing layer is preferably 0.1 μm or more and 4.0 μm or less, more preferably 0.2 μm or more and 3.0 μm or less, even more preferably 0.5 μm or more and 2.0 μm or less, and particularly preferably 1.0 μm or more and 1.5 μm or less. A thickness of 0.1 μm or more of the inorganic filler-containing layer is preferred from the viewpoint of preventing deterioration of performance and safety due to the occurrence of micro-short circuits due to the inability to resist the shrinkage stress of the substrate during storage tests, and suppressing deformation at temperatures above the melting point of the microporous membrane. A thickness of 4.0 μm or less of the inorganic filler-containing layer is preferred from the viewpoint of increasing battery capacity, suppressing deterioration of rate characteristics, and suppressing the amount of moisture adsorption of the multilayer porous membrane. The thickness of the inorganic filler-containing layer is measured by the method described in the Examples.

[0144] The layer density in the inorganic filler-containing layer is 1.10 g / (m ２ ・μm) or more 3.00g / (m ２ .μm) or less, and more preferably 1.20 g / (m ２ ・μm) or more 2.90g / (m ２ μm) or less, more preferably 1.40 g / (m ２ ・μm) or more 2.70g / (m ２ μm) or less, particularly preferably 1.50 g / (m ２ ・μm) or more 2.50g / (m ２ The layer density in the inorganic filler-containing layer is 1.10 g / (m ２ It is preferable that the layer density of the inorganic filler-containing layer is 3.00 g / (m ２ It is preferable that the thickness is 1 μm or less from the viewpoint of maintaining the ion permeability of the inorganic filler-containing layer and suppressing capacity deterioration during repeated cycles.

[0145] An example of a method for forming the inorganic filler-containing layer is a method in which a coating liquid (in one embodiment, an inorganic filler-containing slurry) containing an inorganic filler, a resin binder, and a solvent is applied to at least one surface of a microporous membrane containing a polyolefin resin as a main component (e.g., the first main surface of a porous substrate) to form the inorganic filler-containing layer.

[0146] The solvent for the coating liquid containing the inorganic filler and the resin binder is preferably one that can disperse the inorganic filler and the resin binder uniformly and stably, and examples thereof include N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, water, ethanol, toluene, hot xylene, methylene chloride, and hexane.

[0147] To the coating liquid containing the inorganic filler and the resin binder, various additives may be added, such as dispersants such as surfactants, thickeners, wetting agents, antifoaming agents, pH adjusters containing acids and alkalis, in order to stabilize dispersion and improve coating properties. These additives are preferably removable when the solvent is removed, but may remain in the inorganic filler-containing layer as long as they are electrochemically stable within the range of use of the lithium ion secondary battery, do not inhibit the battery reaction, and are stable up to about 200°C.

[0148] The method for dispersing the inorganic filler and the resin binder in the solvent of the coating liquid is not particularly limited as long as it can realize the dispersion characteristics of the coating liquid required for the coating step, and examples thereof include a ball mill, a bead mill, a planetary ball mill, a vibrating ball mill, a sand mill, a colloid mill, an attritor, a roll mill, high-speed impeller dispersion, a disperser, a homogenizer, a high-speed impact mill, ultrasonic dispersion, and mechanical stirring using a stirring blade or the like.

[0149] The method for applying the coating liquid containing the inorganic filler and the resin binder to the microporous membrane is not particularly limited as long as it can achieve the required thickness and coverage area of ​​the inorganic filler-containing layer, and examples include a gravure coater method, a small-diameter gravure coater method, a reverse roll coater method, a transfer roll coater method, a kiss coater method, a dip coater method, a knife coater method, an air doctor coater method, a blade coater method, a rod coater method, a squeeze coater method, a cast coater method, a die coater method, a screen printing method, and a spray coating method.

[0150] Furthermore, prior to application of a coating liquid containing an inorganic filler and a resin binder, it is preferable to subject the surface of the microporous membrane serving as the separator substrate to a surface treatment, since this facilitates application of the coating liquid and improves adhesion between the inorganic filler-containing layer and the microporous membrane surface after application. The surface treatment method is not particularly limited as long as it does not significantly impair the porous structure of the microporous membrane, and examples include corona discharge treatment, mechanical graining, solvent treatment, acid treatment, and ultraviolet oxidation.

[0151] The method for removing the solvent from the coating film after application of a coating liquid containing an inorganic filler and a resin binder is not particularly limited as long as it does not adversely affect the microporous membrane, and examples include a method in which the microporous membrane is fixed while drying at a temperature below its melting point, and a method in which the microporous membrane is dried under reduced pressure at a low temperature. Drying at normal pressure is preferred from the viewpoint of preventing the ion permeability of the separator from being impaired while allowing the binder polymer, which is the binding component of the resin binder, to exhibit binding strength with the microporous membrane or inorganic filler-containing layer (in one embodiment, the porous layer) as the substrate and binding strength between particulate binders. From the viewpoint of controlling the shrinkage stress in the MD direction of the microporous membrane and the multilayer porous membrane, it is preferred to appropriately adjust the drying temperature, winding tension, etc.

[0152] [Physical Properties and Configuration of Separator] From the viewpoints of excellent electrolyte injectability, less air pockets, and a short injection time, the separator of this embodiment preferably has a contact angle of the electrolyte of 0° to 20°, more preferably 2° to 18°, and even more preferably 4° to 16°. The contact angle of the electrolyte is more preferably measured on a surface of the separator where the thermoplastic polymer-containing layer is formed in a dot pattern.

[0153] The lower limit of the total thickness of the separator for an electricity storage device of this embodiment is preferably 5 μm or more, more preferably 6 μm or more, and even more preferably 8 μm or more. The upper limit is preferably 20 μm or less, more preferably 17 μm or less, even more preferably 15 μm or less, and particularly preferably 11.5 μm or less. A total thickness of 5 μm or more of the separator for an electricity storage device is suitable from the viewpoint of ensuring the strength and safety of the separator for an electricity storage device. On the other hand, a total thickness of 20 μm or less of the separator for an electricity storage device is preferred from the viewpoint of reducing the resistance of the battery and obtaining good charge / discharge characteristics. The total thickness of the separator for an electricity storage device is preferably 5 μm or more and 20 μm or less, more preferably 6 μm or more and 17 μm or less, even more preferably 7 μm or more and 15 μm or less, and particularly preferably 8 μm or more and 11.5 μm or less. The total thickness of the separator of this embodiment is determined by the following method. The thickness of the separator is measured at room temperature (23±2° C.) using a micro thickness measuring instrument "KBM (trademark)" manufactured by Toyo Seiki Co., Ltd.

[0154] The lower limit of the basis weight of the separator for an electricity storage device of this embodiment is preferably 5.0 g / m ２ More preferably, 6.1 g / m ２ More preferably, it is 7.5 g / m or more. ２ The upper limit is preferably 13.5 g / m ２ or less, more preferably 12.0 g / m ２ More preferably, 7.6 g / m or less ２ The basis weight of the separator for an electricity storage device of this embodiment is 5.0 g / m ２ On the other hand, it is preferable that the basis weight of the separator for an electricity storage device of this embodiment is 13.5 g / m or more from the viewpoint of ensuring strength and safety. ２ The following is preferable from the viewpoint of obtaining good charge / discharge characteristics because it reduces the resistance of the battery.

[0155] The lower limit of the air permeability of the separator for an electricity storage device of this embodiment is preferably 10 sec / 100 cm ３ More preferably, 20 sec / 100 cm ３ More preferably, 30 sec / 100 cm ３More preferably, it is 50 sec / 100 cm or more. ３ The upper limit of the air permeability of the separator for an electricity storage device of this embodiment is preferably 200 sec / 100 cm ３ Less than 180 sec / 100 cm, more preferably ３ More preferably, 150 sec / 100 cm or less ３ Below 120 sec / 100 cm, most preferably ３ The air permeability of the separator for an electricity storage device of this embodiment is 10 sec / 100 cm ３ Setting the air permeability to 200 sec / 100 cm or more is preferable from the viewpoint of suppressing the occurrence of micro-short circuits during storage tests, the deterioration of performance and safety, and further suppressing self-discharge of the electricity storage device when producing a separator for an electricity storage device. ３ The following is preferable from the viewpoint of reducing the resistance of the battery and obtaining good charge / discharge characteristics. The air permeability of the separator for an electricity storage device of this embodiment can be adjusted by changing the stretching temperature and stretching ratio when producing the polyolefin microporous membrane, the area ratio and form of the thermoplastic polymer, etc.

[0156] The lower limit of the puncture strength of the separator for an electric storage device of this embodiment is preferably 200 gf or more, more preferably 300 gf or more, even more preferably 400 gf or more, and particularly preferably 450 gf or more. A puncture strength of 200 gf or more of the separator for an electric storage device of this embodiment is preferred from the viewpoint of preventing film rupture due to fallen active material, etc., when the separator is wound with electrodes, preventing short circuits due to expansion and contraction of electrodes during charge and discharge, and improving the impact resistance of the electric storage device. Furthermore, the upper limit of the puncture strength of the separator for an electric storage device of this embodiment is preferably 800 gf or less, more preferably 700 gf or less, and even more preferably 600 gf or less, from the viewpoint of reducing width contraction due to orientation relaxation during heating.

[0157] Regarding the heat shrinkage of the separator for an electric storage device of this embodiment, the TD heat shrinkage at 150°C for 1 hour is preferably −3% to 10%, more preferably −1% to 8%, and even more preferably 0% to 5%. Here, a TD heat shrinkage of −3% or more at 150°C for 1 hour suppresses negative shrinkage (expansion) of the separator, leading to separator twisting and the like, thereby reducing the risk of short circuits between electrodes and a decrease in performance and safety. A TD heat shrinkage of 10% or less at 150°C for 1 hour suppresses the occurrence of micro-short circuits during storage tests and a decrease in performance and safety. The heat shrinkage of the separator of this embodiment can be adjusted by appropriately combining the stretching operation and heat treatment of the substrate. While suppressing the TD heat shrinkage at 150°C for 1 hour, the MD heat shrinkage is also preferably −3% to 10%, more preferably −1% to 8%, and even more preferably 0% to 5%. In this disclosure, longitudinal direction (MD) means the machine direction of the continuous microporous membrane molding, and transverse direction (TD) means the direction crossing the MD of the microporous membrane at a 90° angle.

[0158] The separator for an electricity storage device of this embodiment has a shutdown temperature, which is an indicator of the safety of the electricity storage device, of preferably 160°C or less, more preferably 155°C or less, even more preferably 150°C or less, and most preferably 145°C or less.

[0159] The separator for an electricity storage device of this embodiment has a short-circuit temperature, which is an index of heat resistance, of preferably 140° C. or higher, more preferably 150° C. or higher, and even more preferably 160° C. or higher. When the separator of this embodiment is used as a separator for an electricity storage device, a short-circuit temperature of 160° C. or higher is preferable from the viewpoint of the safety of the electricity storage device.

[0160] [Method for manufacturing separator] The method for manufacturing a separator for an electricity storage device according to this embodiment includes the steps of: preparing a porous substrate; forming an inorganic filler-containing layer on a first main surface of the porous substrate; and applying a slurry containing a thermoplastic polymer to the surface of the inorganic filler-containing layer provided on the first main surface of the porous substrate and to the second main surface of the porous substrate, thereby forming a thermoplastic polymer-containing layer.

[0161] In one aspect, a method for producing a separator for an electricity storage device according to the present embodiment includes the steps of: preparing a porous substrate; applying a slurry containing an inorganic filler onto a first main surface of the porous substrate to form an inorganic filler-containing layer; and applying a slurry containing a thermoplastic polymer onto the surface of the inorganic filler-containing layer and onto a second main surface of the porous substrate to form a thermoplastic polymer-containing layer, wherein the viscosity of the slurry containing the thermoplastic polymer is 60,000 s at a shear rate of 60,000 s. －１ the viscosity is 1 mPa s or more and 20 mPa s or less at a shear rate v when applying the slurry containing the thermoplastic polymer onto the surface of the inorganic filler-containing layer. ｃ and a shear rate v when applying the slurry containing the thermoplastic polymer onto the second main surface of the porous substrate. ｐ However, equations (2) and (3): 30000 sec －１ ≦v ｃ ≦200,000 sec －１ ...Formula (2) 5000sec －１ ≦v ｃ -v ｐ ≦40,000 sec －１ The method for producing a separator for an electricity storage device satisfies the relationship of formula (3).

[0162] <Step of Preparing a Porous Substrate> The manufacturing method of this embodiment includes the step of preparing a porous substrate. The step of preparing a porous substrate includes, for example, the formation of a microporous membrane by the above-described method for manufacturing a substrate and the surface treatment of the substrate described below.

[0163] <Step of forming inorganic filler-containing layer> The manufacturing method of this embodiment includes a step of forming an inorganic filler-containing layer on the first main surface of the porous substrate. As a method for forming the inorganic filler-containing layer, for example, the method described above for forming an inorganic filler-containing layer can be carried out.

[0164] <Step of forming a thermoplastic polymer-containing layer> The manufacturing method of this embodiment includes a step of applying a slurry containing a thermoplastic polymer to the surface of the inorganic filler-containing layer provided on the first main surface of the porous substrate and to the second main surface of the porous substrate to form a thermoplastic polymer-containing layer. The method of applying the slurry is not particularly limited, and examples thereof include a method of applying a slurry containing a thermoplastic polymer and a solvent (in one embodiment, a thermoplastic polymer-containing coating liquid) to a polyolefin microporous membrane (in one embodiment, a porous substrate) or an inorganic filler-containing layer.

[0165] When a slurry containing a thermoplastic polymer is applied to a polyolefin microporous membrane or an inorganic filler-containing layer, if the slurry penetrates into the interior of the polyolefin microporous membrane or the inorganic filler-containing layer, the thermoplastic polymer will fill the surfaces and interiors of the pores of the microporous membrane, reducing ion permeability. Therefore, the solvent for the slurry is preferably a poor solvent for the thermoplastic polymer.

[0166] When a poor solvent for the thermoplastic polymer is used as the solvent for the slurry containing the thermoplastic polymer, the coating liquid does not penetrate into the interior of the polyolefin microporous membrane or the inorganic filler-containing layer, and the thermoplastic polymer is mainly present on the surface of the microporous membrane, which is preferable from the viewpoint of suppressing a decrease in ion permeability. For example, water is a preferred solvent for the thermoplastic polymer. Furthermore, solvents that can be used in combination with water are not particularly limited, but examples include ethanol and methanol. If desired, an antifoaming agent (e.g., KM-73 from Shin-Etsu Chemical Co., Ltd., SK-14 from Nissin Chemical Industry Co., Ltd., etc.) may be added to the slurry.

[0167] In one embodiment, the slurry is prepared by dispersing a thermoplastic polymer in a solvent. In one embodiment, the solvent for dispersing the thermoplastic polymer may be a poor solvent for the thermoplastic polymer. As the poor solvent for the thermoplastic polymer, organic solvents and water are preferred, and water is more preferred from the viewpoint of suppressing static electricity. In one embodiment, the thermoplastic polymer-containing coating liquid (in one embodiment, the thermoplastic polymer-containing slurry) may be an aqueous slurry using water as the solvent.

[0168] From the viewpoint of preventing the coating liquid from flowing and making it impossible to maintain the dot shape of the thermoplastic polymer-containing layer, and from the viewpoint of controlling the thickness distribution of the coating layer, the solid content in 100% by mass of the thermoplastic polymer-containing slurry is preferably 6% by mass or more and 40% by mass or less, more preferably 10% by mass or more and 35% by mass or less, even more preferably 15% by mass or more and 33% by mass or less, and particularly preferably 20% by mass or more and 31% by mass or less.

[0169] From the viewpoint of preventing the coating liquid from flowing and thus making it impossible to maintain the dot shape of the thermoplastic polymer-containing layer, and from the viewpoint of controlling the thickness distribution of the coating layer, the viscosity of the thermoplastic polymer-containing slurry at 20° C. is preferably from 5 mPa·s to 150 mPa·s, more preferably from 10 mPa·s to 100 mPa·s, and even more preferably from 25 mPa·s to 80 mPa·s. The viscosity of the thermoplastic polymer-containing slurry at 20° C. is measured by the method described in the Examples.

[0170] From the viewpoint of preventing the coating liquid from flowing and making it impossible to maintain the dot shape of the thermoplastic polymer-containing layer, and from the viewpoint of controlling the thickness distribution of the coating layer, the surface tension of the thermoplastic polymer-containing slurry is preferably 10 mN / m or more and 70 mN / m or less, more preferably 20 mN / m or more and 60 mN / m or less, and even more preferably 25 mN / m or more and 50 mN / m or less.

[0171] From the viewpoint of preventing aggregation of the coating liquid, the pH of the thermoplastic polymer-containing slurry is preferably 6 or more and 10 or less, and more preferably 7 or more and 9 or less.

[0172] The viscosity of the thermoplastic polymer-containing slurry was 60,000 sec at a shear rate of －１ The viscosity of the thermoplastic polymer-containing slurry is preferably 1 mPa·s or more and 20 mPa·s or less, more preferably 3 mPa·s or more and 15 mPa·s or less, and even more preferably 5 mPa·s or more and 10 mPa·s or less at a shear rate of 90,000 sec. －１ From the viewpoint of preventing the coating liquid from flowing and making it impossible to maintain the dot shape of the thermoplastic polymer-containing layer, and from the viewpoint of controlling the thickness distribution of the coating layer, the viscosity is preferably from 3 mPa·s to 25 mPa·s at a shear rate of 60,000 sec －１ and 90,000 sec －１ The viscosity of the thermoplastic polymer-containing slurry (in one embodiment, high shear viscosity) at a shear rate of 90,000 sec is preferably controlled within a predetermined range. －１ The high shear viscosity at a shear rate of 60,000 sec －１ It is preferable that the high shear viscosity is higher than that at a shear rate of 60,000 sec. －１ and 90,000 sec －１ The high shear viscosity is measured by the method described in the Examples.

[0173] The shear rate v when applying the slurry containing the thermoplastic polymer onto the surface of the inorganic filler-containing layer is ｃ and a shear rate v when applying the slurry containing the thermoplastic polymer onto the second main surface of the porous substrate. ｐ It is preferable that the relationship between the following formulas (2) and (3) is satisfied: －１ ≦v ｃ ≦200,000 sec －１ ...Formula (2) 5000sec －１ ≦v ｃ -v ｐ ≦40,000 sec －１ ...Formula (3)

[0174] By increasing the shear rate and increasing the viscosity of the thermoplastic polymer-containing slurry (in one embodiment, the viscosity of the thermoplastic polymer-containing slurry in a sheared state during coating), the thickness t of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer can be increased. ｃ varies, with a standard deviation of s ｔｃ Since the value of is large, it becomes easier to ensure a clearance (prevent contact) between the surface of the inorganic filler-containing layer and the surface of the thermoplastic polymer-containing layer on the second main surface of the porous substrate when the separator is superposed. For the above-mentioned reasons, when the slurry containing the thermoplastic polymer is applied onto the surface of the inorganic filler-containing layer, the shear rate v ｃ is preferably 30,000 sec －１ More preferably, 50,000 seconds －１ More preferably, 60,000 seconds －１ More preferably, 75,000 seconds or more －１ More than 76,000 sec, especially preferred －１ More than 90,000 seconds, most preferably －１ In addition, from the viewpoint of preventing coating streaks and rubbing, the shear rate v ｃ is preferably 200,000 sec －１ Less than 150,000 seconds, more preferably －１ More preferably, 100,000 seconds or less －１ Below 95,000 sec, particularly preferably －１ In addition, from the viewpoint of dot formation, v ｃ is 30,000 seconds －１ More than 200,000 seconds －１ Preferably less than 50,000 sec －１ More than 150,000 seconds －１ Less than 60,000 seconds is more preferable. －１ More than 100,000 seconds －１ The following are particularly preferred:

[0175] By reducing the shear rate and lowering the viscosity of the thermoplastic polymer-containing slurry (in one embodiment, the viscosity of the thermoplastic polymer-containing slurry in a sheared state during coating), the thickness t of the thermoplastic polymer-containing layer on the second main surface of the porous substrate can be reduced.ｐ becomes uniform, and the standard deviation s ｔｐ Since the value of is small, when the separator is superposed, it is possible to reduce the local contact of the thermoplastic polymer-containing layer on the second main surface of the porous substrate with the surface of the inorganic filler-containing layer. For the above-mentioned reasons, it is possible to reduce the shear rate v ｐ is preferably 100,000 sec －１ Less than 90,000 seconds, more preferably －１ More preferably, 80,000 seconds or less －１ Below 60,000 sec, particularly preferably －１ In addition, from the viewpoint of pattern formation, the shear rate v ｐ is preferably 10,000 sec －１ More preferably, 20,000 seconds －１ More preferably, 30,000 seconds －１ More than 50,000 sec, especially preferred －１ That's all.

[0176] The shear rate v when applying the slurry containing the thermoplastic polymer onto the surface of the inorganic filler-containing layer is ｃ and the shear rate v when applying the slurry containing the thermoplastic polymer onto the second main surface of the porous substrate. ｐ By controlling the difference between the thickness of the thermoplastic polymer-containing layer on both sides of the separator to a certain range, the standard deviation s ｔｃ and standard deviation s ｔｐ When the separator is laminated, the thermoplastic polymer-containing layer and the inorganic filler-containing layer on the second main surface of the porous substrate are less likely to come into contact with each other. For the above-mentioned reasons, the shear rate v ｃ and a shear rate v when applying the slurry containing the thermoplastic polymer onto the second main surface of the porous substrate. ｐ Difference with: v ｃ -v ｐ is preferably 5000 sec －１ More preferably, 10,000 seconds －１ More preferably, 15,000 seconds－１ More than 30,000 sec, especially preferred －１ That's all. ｃ -v ｐ is preferably 40,000 sec －１ Less than 35,000 seconds, more preferably －１ Below 30,000 sec, particularly preferably －１ Below is the result. ｃ -v ｐ is preferably 5000 sec －１ Over 40,000 seconds －１ Less than 10,000 seconds, more preferably 10,000 seconds －１ More than 35000 seconds －１ Below 15,000 sec, particularly preferably －１ More than 30000 seconds －１ The shear rate when applying the thermoplastic polymer-containing slurry to the porous substrate and the inorganic filler-containing layer is measured by the method described in the Examples. ｃ and shear rate v ｐ is 70,000 seconds －１ If the value is equal to or greater than this, the shear rate is considered to be high.

[0177] Furthermore, without being bound by theory, when the shear rate when the thermoplastic polymer-containing slurry is applied to the porous substrate and the inorganic filler-containing layer is small, the viscosity of the thermoplastic polymer-containing slurry during application tends to be low, and the thickness of the thermoplastic polymer-containing layer tends to be uniform. On the other hand, when the shear rate when the thermoplastic polymer-containing slurry is applied to the porous substrate and the inorganic filler-containing layer is large, the viscosity of the thermoplastic polymer-containing slurry during application tends to be high, and the thickness of the thermoplastic polymer-containing layer tends to vary.

[0178] The method for applying the thermoplastic polymer-containing coating liquid to the microporous membrane and the inorganic filler-containing layer is not particularly limited as long as it can achieve the required coverage area ratio and thickness of the thermoplastic polymer-containing layer. Examples include gravure coater method, small-diameter gravure coater method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife coater method, air doctor coater method, blade coater method, rod coater method, squeeze coater method, cast coater method, die coater method, screen printing method, spray coating method, spray coater coating method, inkjet coating, etc. Among these, gravure coater method or spray coating method is preferred from the viewpoint of high flexibility in the coating shape of the thermoplastic polymer and easy achievement of a desired coverage area ratio. Furthermore, gravure coater method or inkjet coating is preferred from the viewpoint of adjusting the dot pattern of the thermoplastic polymer-containing layer as described above, and a coating method that makes it easy to adjust the printing plate is preferred.

[0179] From the viewpoint of adjusting the dot pattern of the thermoplastic polymer-containing layer as described above, it is preferable to optimize the thermoplastic polymer-containing coating liquid using the thermoplastic polymer and its poor solvent described above.

[0180] The thermoplastic polymer-containing coating solution was applied in an amount of 0.03 g / m per side of the separator in order to achieve both adhesive strength to the electrode and ion permeability. ２ 0.50g / m or more ２ It is preferable that the content is 0.04 g / m or less. ２ 0.45g / m or more ２ More preferably, it is 0.06 g / m or less, and most preferably, it is 0.06 g / m ２ 0.40g / m or more ２ The following is the result.

[0181] Furthermore, prior to application of the thermoplastic polymer-containing coating liquid, it is preferable to surface-treat the porous substrate as the separator substrate, since this makes it easier to apply the thermoplastic polymer-containing coating liquid and improves the adhesion between the porous substrate or the inorganic filler-containing layer and the thermoplastic (adhesive) polymer. The surface treatment method is not particularly limited as long as it does not significantly impair the porous structure of the porous substrate, and examples thereof include corona discharge treatment, plasma treatment, mechanical roughening, solvent treatment, acid treatment, and ultraviolet oxidation.

[0182] In the case of the corona discharge treatment method, from the viewpoint of adjusting the contact angle of the thermoplastic polymer-containing layer or separator with the electrolyte to within the above-described numerical range, the corona treatment intensity of the substrate surface is 1 W / (m ２ / min) or more 40W / (m ２ / min) or less, and ２ / min) or more 32W / (m ２ / min) or less, and more preferably 5W / (m ２ / min) or more 25W / (m ２ / min) or less. By using a corona treatment intensity within the above range, the affinity with the electrolyte solution is improved by introducing a hydrophilic group into the substrate surface, and wettability tends to be improved. Furthermore, it is also preferable to perform a corona discharge treatment after the dot pattern of the thermoplastic polymer-containing layer is formed.

[0183] The method for removing the solvent from the coating film after applying the thermoplastic polymer is not particularly limited as long as it does not adversely affect the porous substrate. Examples include a method in which the porous substrate is fixed while being dried at a temperature below its melting point, a method in which the porous substrate is dried under reduced pressure at a low temperature, and a method in which the porous substrate is immersed in a poor solvent for the adhesive polymer to coagulate the adhesive polymer and simultaneously extract the solvent.

[0184] <Drying Step> The manufacturing method of this embodiment may include a step of drying the slurry after applying the slurry containing a thermoplastic polymer to at least one surface of the porous substrate.

[0185] In drying the slurry, the drying rate is 0.03 g / (m ２・s) or more 4.0g / (m ２ s) or less, and ２ ・s) or more 3.5g / (m ２ s) or less, and more preferably 0.08 g / (m ２ ・s) or more 3.0g / (m ２ It is more preferable that the drying rate is within the range of s). When the drying rate is within this range, the appropriate drying rate suppresses leveling, and an uneven structure of the thermoplastic polymer particles is formed on the dot surface, tending to improve wettability. From the same viewpoint, when drying the coating film, it is also preferable to increase the temperature by heating or heating to an extent that does not damage the particle shape of the thermoplastic polymer-containing layer.

[0186] [Separator Reel] A separator wound around a core is called a separator reel (in one embodiment, a reel). In recent years, there has been a trend toward longer separators wound on reels to improve productivity. However, as separators become longer, the issue of static electricity generation is expected to become more pronounced. Static electricity worsens as the "pressure" applied to the separator increases. The separator is more susceptible to pressure on the inner layer side when reeled, and the closer to the innermost layer, the higher the risk of static electricity generation. In this disclosure, the innermost layer of a separator reel refers to the surface where the core and separator come into direct contact. The inventors have discovered that when actually unwinding a separator from a reel, the amount of peeling charge increases as the separator approaches the innermost layer.

[0187] Another trend is to make separators thinner (for example, a polyolefin microporous membrane with a thickness of about 6 to 9 μm and an inorganic filler-containing layer with a thickness of about 1 to 1.5 μm) in order to improve energy density. However, thinner separators tend to increase the pressure on the inner layer, which is expected to increase the risk of static electricity. Therefore, it is preferable to wind the separator to produce a reel while controlling the inner layer pressure to a certain level or less.

[0188] The reel can be produced by winding the separator around any core (for example, made of resin, paper, or glass) at any winding tension (for example, 0.01 to 1.50 N / mm).

[0189] The amount of charge at peeling and the stickiness due to static electricity are used as indicators for evaluating the effect of static electricity on separators.

[0190] The separator of this embodiment has a peel charge of preferably −15 kV or more and +15 kV or less, more preferably −10 kV or more and +10 kV or less, and even more preferably −8 kV or more and +8 kV or less, when unwound from a reel. The separator of this embodiment can prevent pinholes from occurring when unwound from the separator by suppressing static electricity and the associated sparks.

[0191] The amount of peeling charge when the separator of this embodiment is unwound from the separator reel of this embodiment, which is formed by winding the separator around a core, is determined by the following method. A separator reel sample for evaluation (hereinafter referred to as a reel) is prepared by winding 4000 m of the sample separator around a core having an outer diameter of 6 inches and made of acrylonitrile-butadiene-styrene (ABS) so that the entire reel surface faces the second main surface of the porous substrate. After unwinding 3000 m of the separator from the circular reel, the amount of peeling charge is measured when 50 m of the separator is pulled tangentially from the reel and unwound at a rate of 10 m / min, and the average value is taken as the amount of peeling charge when the separator is unwound from the separator reel of this embodiment. A static electricity measuring instrument (model: FMA-004, manufactured by Simco Japan Co., Ltd.) was installed at a position 20 mm from the point where the separator separates from the reel (hereinafter referred to as the peeling point) in the direction in which the separator is unwound and 25 mm in the direction perpendicular to the surface of the unwound separator, and the amount of charge due to peeling was measured. The measurement was carried out in an environment with a temperature of 23°C and a humidity of 20%.

[0192] The static cling when unwinding a separator from a separator reel of this embodiment, which is formed by winding the separator around a core, is determined by the following method. A 4000 m length of a sample separator is wound around a 6-inch outer diameter core made of acrylonitrile-butadiene-styrene (ABS) so that the entire reel surface faces the second main surface of the porous substrate, to prepare a separator reel sample for evaluation (hereinafter, "reel"). After unwinding 3000 m of the separator from the circular reel, the separator is pulled from the reel in the tangential direction of the reel at a rate of 10 m / min. After cutting the separator with scissors at a position 20 cm from the peeling point, the percentage of the separator that is pulled toward the reel is used as an index of static cling. Measurements are performed in an environment with a temperature of 23°C and a humidity of 20%.

[0193] In the separator reel of this embodiment, the surface pressure applied to the innermost layer is preferably 5 MPa or less. In one aspect, when the separator of this embodiment is wound to produce a reel, the surface pressure applied to the innermost layer is preferably 5 MPa or less, more preferably 3 MPa or less, and even more preferably 2 MPa or less. By keeping the surface pressure applied to the innermost layer within a predetermined range, the separator reel of this embodiment can prevent the generation of static electricity.

[0194] The surface pressure applied to the innermost layer of a separator reel of this embodiment, which is formed by winding the separator of this embodiment around a core, is determined by the following method. A sensor sheet (FlexiForce A201-25, manufactured by Nitta Corporation) is attached to a core with an outer diameter of 6 inches made of acrylonitrile-butadiene-styrene (ABS), and the separator is wound around the core for 4000 m so that the entire reel surface layer faces the second main surface of the porous substrate, to prepare an evaluation reel. The resistance value applied to the sensor sheet is measured using a digital multimeter (RD701, manufactured by SANWA Corporation), and the surface pressure applied to the innermost layer is calculated by applying the measured resistance value to a calibration curve prepared in advance. The calibration curve is prepared by the following method. When a constant pressure is applied to the pressure-sensitive portion of the sensor sheet, the resistance value detected by the digital multimeter is recorded. This is repeated while changing the pressure applied to the sensor sheet, and the pressure and resistance values ​​are plotted on a graph to create a calibration curve. A calibration curve is created by plotting data so that at least five points of pressure between 0 MPa and 5 MPa are included.

[0195] [Laminate] The laminate according to this embodiment is formed by laminating a separator and an electrode. The separator according to this embodiment can be used as a laminate by adhering it to an electrode. The laminate according to this embodiment has excellent handling properties when wound, and excellent cycle characteristics and rate characteristics of an electricity storage device. Furthermore, the laminate suppresses the generation of static electricity when the separator is unwound, thereby suppressing the occurrence of pinholes. Therefore, the use of the laminate is not particularly limited, and it can be suitably used, for example, in batteries such as non-aqueous electrolyte secondary batteries, and electricity storage devices such as condensers and capacitors.

[0196] The electrodes used in the laminate of this embodiment can be those described in the section on power storage devices below. The method for producing a laminate using the separator of this embodiment is not particularly limited, but for example, the laminate can be produced by stacking the separator of this embodiment and an electrode, and heating and / or pressing as necessary. Heating and / or pressing can be performed when stacking the electrode and separator. Alternatively, the laminate can be produced by stacking the electrode and separator, and then winding them into a circular or flat spiral shape, and then heating and / or pressing the resulting wound body.

[0197] The laminate can also be produced by laminating a positive electrode, a separator, a negative electrode, a separator, or a negative electrode, a separator, a positive electrode, and a separator in this order into a flat plate, and then heating and / or pressing as necessary. In order to efficiently achieve the effects of this embodiment, it is preferable that the separator is disposed so that the side of the separator having the inorganic filler-containing layer described above faces the positive electrode, with the separator substrate as the reference.

[0198] More specifically, the separator of this embodiment is prepared as a vertically elongated separator having a width of 10 to 500 mm (preferably a width of 50 to 500 mm) and a length of 200 to 4000 m (preferably a length of 1000 to 4000 m), and the separators are stacked in the order of positive electrode-separator-negative electrode-separator, or negative electrode-separator-positive electrode-separator, and heated and / or pressed as necessary to produce the separator.

[0199] The heating temperature is preferably 40 to 120°C. The heating time is preferably 5 seconds to 30 minutes. The pressure during pressing is preferably 1 to 30 MPa. The pressing time is preferably 5 seconds to 30 minutes. The order of heating and pressing may be heating followed by pressing, pressing followed by heating, or simultaneous pressing and heating. Of these, simultaneous pressing and heating are preferred.

[0200] <Electricity storage device> The separator according to this embodiment can be used as a separator or for separating substances in batteries, condensers, capacitors, etc. In particular, when used as a separator for an electricity storage device, it is possible to impart adhesion to electrodes and excellent battery performance. Below, a preferred embodiment in which the electricity storage device is a non-aqueous electrolyte secondary battery will be described.

[0201] The power storage device according to the present embodiment includes a positive electrode, a negative electrode, a separator for a power storage device according to the present embodiment, and a non-aqueous electrolyte. When a non-aqueous electrolyte secondary battery is manufactured using the separator according to the present embodiment, the positive electrode, the negative electrode, and the non-aqueous electrolyte are not limited, and known electrolytes can be used.

[0202] The positive electrode material is not particularly limited, but may be, for example, LiCoO ２ , LiNiO ２ , spinel-type LiMnO ４ , olivine-type LiFePO ４ Examples of lithium-containing composite oxides include those mentioned above.

[0203] The negative electrode material is not particularly limited, but examples thereof include carbon materials such as graphite, non-graphitizable carbon, easily graphitizable carbon, and composite carbon; silicon, tin, metallic lithium, and various alloy materials.

[0204] The non-aqueous electrolyte is not particularly limited, but an electrolyte solution in which an electrolyte is dissolved in an organic solvent can be used. Examples of the organic solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Examples of the electrolyte include LiClO ４ , LiBF ４ , LiPF ６ Examples of lithium salts include:

[0205] The method for producing an electricity storage device using the separator of the present embodiment is not particularly limited. When the electricity storage device is a secondary battery, for example, the separator of the present embodiment is prepared as a vertically elongated separator having a width of 10 to 500 mm (preferably a width of 50 to 500 mm) and a length of 200 to 4000 m (preferably a length of 1000 to 4000 m), and the separators are stacked in the order of positive electrode-separator-negative electrode-separator, or negative electrode-separator-positive electrode-separator, and the stack is wound into a circular or flat spiral to obtain a wound body, which is then housed in a battery can and further injected with an electrolytic solution, thereby producing the electricity storage device.

[0206] In this case, the wound body may be heated and / or pressed to form the above-mentioned laminate. Alternatively, the wound body may be produced by winding the above-mentioned laminate into a circular or flat spiral shape. The power storage device may also be produced by laminating the above-mentioned laminate in the order of positive electrode-separator-negative electrode-separator, or negative electrode-separator-positive electrode-separator, in a flat plate shape, or by laminating the above-mentioned laminate with a bag-shaped film, followed by a step of injecting an electrolyte solution and, optionally, a step of heating and / or pressing. The above-mentioned heating and / or pressing step may be carried out before and / or after the step of injecting the electrolyte solution.

[0207] In an electricity storage device including a positive electrode, a negative electrode, the separator according to the present embodiment, and a non-aqueous electrolyte solution, the separator is preferably disposed such that the side having the inorganic filler-containing layer described above faces the positive electrode relative to the substrate, from the viewpoint of efficiently exhibiting the effects of the present embodiment.

[0208] The electricity storage device of this embodiment can be manufactured by the same method as the method for manufacturing the battery used in the rate characteristic test, cycle characteristic test, etc. described in the Examples below.

[0209] Unless otherwise specified, the measured values ​​of the various parameters described above are values ​​measured in accordance with the measurement methods in the examples described below.

[0210] The present invention will be described in detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. The methods for measuring and evaluating various physical properties used in the following Production Examples, Examples, and Comparative Examples are as follows. Unless otherwise specified, the various measurements and evaluations were carried out at room temperature of 23°C, at 1 atmospheric pressure, and at a relative humidity of 50%.

[0211] [Measurement Method] <Viscosity Average Molecular Weight (hereinafter also referred to as "Mv")> Based on ASRM-D4020, the intrinsic viscosity [η] at 135°C in decalin solvent was determined, and the Mv of the polyethylene was calculated using the following formula: [η] = 0.00068 × Mv ０．６７ The Mv of polypropylene was calculated using the following formula: [η] = 1.10 × 10 －４ Mv ０．８０

[0212] <Volume Average Particle Diameter of Thermoplastic Polymer Particles and Inorganic Filler Particles> The particle size distribution and D10, D50, and D90 of the thermoplastic polymer particles and inorganic filler particles were obtained by measuring the thermoplastic polymer particle dispersion and the inorganic filler particle dispersion using a laser particle size distribution measuring device (Microtrac MT3300EX manufactured by Nikkiso Co., Ltd.). If necessary, the particle size distribution of the thermoplastic polymer particle dispersion, the inorganic filler particle dispersion, or the binder polymer may be used as a baseline to adjust the particle size distribution of the thermoplastic polymer particles and the inorganic filler particle dispersion. The particle size at which the cumulative frequency of the thermoplastic polymer particles and the inorganic filler particles is 10% is defined as the average volume particle diameter D10 of the thermoplastic polymer particles and the inorganic filler particles, the particle size at which the cumulative frequency of the thermoplastic polymer particles and the inorganic filler particles is 50% is defined as the average volume particle diameter D50 of the thermoplastic polymer particles and the inorganic filler particles, and the particle size at which the cumulative frequency of the thermoplastic polymer particles and the inorganic filler particles is 90% is defined as the average volume particle diameter D90 of the thermoplastic polymer particles and the inorganic filler particles.

[0213] <Basis Weight of Polyolefin Microporous Membrane and Basis Weight of Separator> A 10 cm x 10 cm square sample was cut out from the polyolefin microporous membrane (porous substrate), and its weight was measured using an electronic balance AEL-200 manufactured by Shimadzu Corporation. The weight obtained was multiplied by 100 to obtain the basis weight of 1 m２ Weight of the polyolefin microporous membrane per unit area (g / m ２ A 10 cm x 10 cm square sample was cut out from the separator of this embodiment, and its weight was measured using an electronic balance AEL-200. The weight obtained was multiplied by 100 to calculate the 1 m ２ Weight of separator per unit (g / m ２ ) was calculated.

[0214] <Porosity (%) of Polyolefin Microporous Membrane> A 10 cm x 10 cm square sample was cut out from a polyolefin microporous membrane, and its volume (cm ３ ) and mass (g), and the film density was calculated to be 0.95 (g / cm ３ ) was calculated using the following formula: Porosity = (volume - mass / film density) / volume x 100

[0215] <Air permeability (sec / 100 cm) of polyolefin microporous membrane and separator ３ The air permeability was determined as the air resistance of the polyolefin microporous membrane and separator measured in accordance with JIS P-8117 using a Gurley air permeability meter G-B2 (trademark) manufactured by Toyo Seiki Co., Ltd.

[0216] <Thickness of Polyolefin Microporous Membrane and Separator> The thickness of the polyolefin microporous membrane and the separator was measured at room temperature (23±2° C.) using a micro thickness measuring instrument "KBM (trademark)" manufactured by Toyo Seiki Co., Ltd.

[0217] <Glass Transition Temperature (°C) of Thermoplastic Polymer> An appropriate amount of the thermoplastic polymer-containing coating solution (non-volatile content = 30%) was placed on an aluminum dish and dried for 30 minutes in a hot air dryer at 130°C. Approximately 5 mg of the dried film after drying was placed in an aluminum container for measurement, and a DSC curve and a DDSC curve were obtained under a nitrogen atmosphere using a DSC measurement device (TA Instruments, DSC Q2000). The measurement conditions were as follows: (First-stage heating program) Start at 40°C, heat up at a rate of 50°C per minute. After reaching 200°C, maintain this temperature for 5 minutes. (Second-stage heating program) Heat down from 200°C at a rate of 20°C per minute. After reaching -50°C, maintain this temperature for 5 minutes. (Third-stage heating program) Heat up from -50°C to 200°C at a rate of 20°C per minute. DSC and DDSC data were obtained during this third-stage heating. According to the method described in JIS-K7121, the intersection of the baseline (a straight line extending the baseline of the obtained DSC curve toward the higher temperature side) and the tangent at the inflection point (the point where the upward convex curve changes to a downward convex curve) was determined as the glass transition temperature (Tg).

[0218] <Coverage Area Ratio (%) of the Thermoplastic Polymer-Containing Layer on the Surface of the Inorganic Filler-Containing Layer and on the Second Main Surface of the Porous Substrate> The coverage area ratio of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer and on the second main surface of the porous substrate is expressed as the ratio (area %) of the total coverage area of ​​the thermoplastic polymer-containing layer to the surface area of ​​the inorganic filler-containing layer or the surface area of ​​the second main surface of the porous substrate. A microscope (model: VHX-7000, manufactured by Keyence Corporation) was used to measure the coverage area ratio. After photographing the separator sample at 100x magnification (coaxial epi-illumination), "Automatic Area Measurement (Particle Count)," "Extraction Method: Brightness (Standard)," and "Fill Holes" were selected from the "Measurement & Scale" command, and the total coverage area of ​​the thermoplastic polymer-containing layer was measured using binarization processing using the Otsu method. Ten locations per sample were measured, and the arithmetic mean value for each sample was calculated. If the contrast of the photographed image is unclear, the brightness of the light source can be adjusted appropriately, or a different light source (model: PD2-1024, manufactured by CCS Inc.) can be used for photographing.

[0219] <Measurement of thickness of inorganic filler-containing layer and thermoplastic polymer-containing layer> A cross section of a separator sample was processed using a broad ion beam (BIB). The cross section was processed using an IM4000 manufactured by Hitachi High-Tech Corporation under the following processing conditions: argon beam, 3 kV acceleration voltage, and 25 to 35 μA beam current. During processing, the sample was cooled down to just before processing as needed to suppress thermal damage. Specifically, the sample was left overnight in a cooling device at -40°C. This resulted in a smooth separator cross section. The thickness t of the inorganic filler-containing layer and the thermoplastic polymer-containing layer ｃ and t ｐ was measured using a scanning electron microscope (SEM) (model: S-4800, manufactured by Hitachi Corporation). The sample was osmium-deposited and observed under conditions of an acceleration voltage of 1.0 kV and 5000x magnification, and the thicknesses of the inorganic filler-containing layer and the thermoplastic polymer-containing layer were calculated. For the thermoplastic polymer-containing layer, measurements were taken at 10 points per sample for the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer and the thermoplastic polymer-containing layer on the second main surface of the porous substrate, and the arithmetic mean value was calculated to obtain t ｃ and t ｐ was calculated.

[0220] <Standard deviation of coating layer (thermoplastic polymer-containing layer) thickness: s ｔｃ and s ｔｐ > The cross section of the separator sample was processed in the same manner as in <Measurement of the thickness of the inorganic filler-containing layer and the thermoplastic polymer-containing layer> above. The thickness of the thermoplastic polymer-containing layer (dots) on the surface of the inorganic filler-containing layer and the thickness of the thermoplastic polymer-containing layer on the second main surface of the porous substrate were measured using an SEM under the same conditions as in <Measurement of the thickness of the inorganic filler-containing layer and the thermoplastic polymer-containing layer> at 10 locations where one or more thermoplastic polymer particles were present in the cross section-processed sample, and the arithmetic mean value was calculated to calculate the thickness of each coating layer (thermoplastic polymer-containing layer). Standard deviation of the thickness of each coating layer (thermoplastic polymer-containing layer): s ｔｃ and s ｔｐ (corresponding to s in formula 1) is represented by formula 1: (where N is the number of measurement points, x ｉ is the measured data, and x(-) is the average of the measured data), where: measured data: x ｉ The thickness of each coating layer calculated above (the thickness of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer and the thickness of the thermoplastic polymer-containing layer on the second main surface of the porous substrate) was applied to the above formula 1 to calculate the thickness.

[0221] <Shear rate when applying the thermoplastic polymer-containing slurry: v ｃ and v ｐ > shear rate v during application of the thermoplastic polymer-containing slurry ｃ and v ｐ (corresponding to γ ​​in formula 2) is expressed by formula 2: (where RPM is the number of rotations of the roll (revolutions per minute), R roll is the radius of the roll (m), and h is the gap between the roll and the blade (m). h was calculated by applying h, etc., determined by the following method, to the above equation 2. h was determined by placing a high-speed camera facing the axial surface of the gravure roll and capturing an image of the gap between the gravure roll and the blade during coating. The shutter speed of the high-speed camera can be adjusted as needed to avoid blurring. If the camera is capable of displaying a scale bar, the scale bar was used to calculate the gap between the gravure roll and the blade in the resulting image. If the camera is not capable of displaying a scale bar, a ruler was placed next to the object during shooting to serve as a scale bar, and the gap between the gravure roll and the blade was calculated. h can be controlled by the type of blade (material and thickness), how the blade is applied (angle, pressure, contact point), and the type of gravure roll (surface material and surface roughness).

[0222] <Viscosity> The viscosity of the thermoplastic polymer-containing slurry was measured at a temperature of 20°C using a viscometer TVB10M (manufactured by Toki Sangyo Co., Ltd.).

[0223] <High Shear Viscosity> Using a high shear rotational viscometer PM9002HV (manufactured by Mitsui Electric Seiki Co., Ltd.) equipped with an E-type bob, measurements were carried out at a rotation speed of 0 rpm to 12,000 rpm, a maximum rotation speed of 8,800 rpm, at room temperature, and with an acceleration time of 10 seconds. －１ and 90,000 sec －１ The viscosity (high shear viscosity) of the thermoplastic polymer-containing slurry was determined at this temperature.

[0224] <Distance between dots in thermoplastic polymer-containing layer> The distance between dots in the thermoplastic polymer-containing layer was measured using a microscope (model: VHX-7000, manufactured by Keyence Corporation). A sample separator was photographed at 100x magnification (coaxial epi-illumination), and in measurement mode, an arbitrary dot was selected, and the distances between the center of the selected dot and the centers of dots positioned vertically, horizontally, and diagonally to the arbitrary dot were measured, and the average value of these distances was taken as the distance between dots.

[0225] <Dot diameter of thermoplastic polymer-containing layer> The dot diameter of the thermoplastic polymer-containing layer was measured using a microscope (model: VHX-7000, manufactured by Keyence Corporation). A sample separator was photographed at 100x magnification (coaxial epi-illumination), and the diameters of multiple dots (5 points) were measured in measurement mode, and the average value was calculated as the dot diameter.

[0226] <Preparation of Positive Electrode and Negative Electrode for Rate Characteristics and Cycle Characteristics Test> Nickel, manganese, and cobalt composite oxide (NMC) (Ni:Mn:Co=1:1:1 (element ratio), density 4.70 g / cm 3) was used as the positive electrode active material. 3 ) as 90.4 mass%, graphite powder (KS6) (density 2.26 g / cm 3 1.6 mass% of acetylene black powder (AB) (density 1.95 g / cm 3 3.8 mass% of polyvinylidene fluoride (PVdF) (density 1.75 g / cm3) as a binder. 3) were mixed in a ratio of 4.2 mass %, and dispersed in N-methylpyrrolidone (NMP) to prepare a slurry. This slurry was applied to one side of a 20 μm thick aluminum foil serving as a positive electrode current collector using a die coater, dried at 130°C for 3 minutes, and then compression-molded using a roll press to prepare a positive electrode. The amount of positive electrode active material applied at this time was 109 g / m 2 As the negative electrode active material, graphite powder A (density 2.23 g / cm 3 87.6 mass% of graphite powder B (density 2.27 g / cm 3 A slurry was prepared by dispersing 9.7% by mass of carboxymethylcellulose (number average particle diameter 6.5 μm) and 1.4% by mass (solids content equivalent) of ammonium salt of carboxymethylcellulose (aqueous solution with a solids content of 1.83% by mass) and 1.7% by mass (solids content equivalent) of diene rubber latex (aqueous solution with a solids content of 40% by mass) in purified water as binders. This slurry was applied to one side of a 12 μm-thick copper foil serving as a negative electrode current collector using a die coater, dried at 120° C. for 3 minutes, and then compression-molded using a roll press to produce a negative electrode. The amount of negative electrode active material applied at this time was 5.2 g / m 2 It was.

[0227] <Preparation of non-aqueous electrolyte for rate characteristic and cycle characteristic test> A non-aqueous electrolyte was prepared by dissolving LiPF as a solute in a mixed solvent of ethylene carbonate:ethyl methyl carbonate = 1:2 (volume ratio) containing 1 wt% vinylene carbonate to a concentration of 1.0 mol / L.

[0228] <Battery Assembly> The separator or substrate was cut into a 24 mm diameter circle, and the positive and negative electrodes for measuring rate and cycle characteristics were each cut into a 16 mm diameter circle. The negative electrode, separator or substrate, and positive electrode were stacked in this order, with the active material surfaces of the positive and negative electrodes facing each other, and then placed in a lidded stainless steel container. The container and lid were insulated, with the container in contact with the copper foil of the negative electrode, and the lid in contact with the aluminum foil of the positive electrode. A simple battery (energy storage device) was assembled by pouring 0.4 mL of nonaqueous electrolyte for measuring rate and cycle characteristics into the container and sealing it.

[0229] <Preparation of Evaluation Reel> A separator reel sample for evaluation was prepared by winding 4000 m of the sample separator around a core having an outer diameter of 6 inches made of acrylonitrile-butadiene-styrene (ABS) so that the entire reel surface layer was on the second main surface side of the porous substrate. For the reel used for pressure evaluation test evaluation, the evaluation reel was prepared in the same manner as above, except that a sensor sheet (FlexiForce A201-25 manufactured by Nitta Corporation) was attached to the core. The winding tension when winding the separator around the reel was 0.10 N / mm in Example 15, 0.15 N / mm in Example 16, and 0.06 N / mm in the other examples.

[0230] <Amount of peeling charge when unwinding separator from separator reel> After unwinding 3,000 m of separator from a circular evaluation reel, 50 m of separator was pulled tangentially from the reel at a speed of 10 m / min, and the amount of peeling charge was measured and averaged. A static electricity meter (model: FMA-004, manufactured by Simco Japan Co., Ltd.) was installed 20 mm in the direction of unwinding the separator and 25 mm in the direction perpendicular to the surface of the unwound separator from the point where the separator separated from the reel (hereinafter referred to as the peeling point) to measure the amount of peeling charge. The measurement was performed in an environment with a temperature of 23°C and a humidity of 20%. Because the porous substrate is more likely to be negatively charged than the inorganic filler-containing layer, when the surface on the porous substrate side is facing the static electricity meter, a negative value is obtained, and when the surface on the inorganic filler-containing layer side is facing the static electricity meter, a positive value is obtained. In the examples, all measurements were made on the surface of the porous substrate side, and therefore all measured values ​​were 0 or less.

[0231] <Static Sticking> After unwinding 3,000 m of separator from a circular evaluation reel, the separator was pulled tangentially from the reel at a speed of 10 m / min. The separator was cut with scissors at a position 20 cm from the peel point, and the rate at which the separator was pulled toward the reel was used as an index of static sticking. Measurements were performed in an environment with a temperature of 23°C and a humidity of 20%. A separator rated A to C can be suitably used as the separator of this embodiment. A: Static sticking occurred in 15 or fewer of 100 reels. B: Static sticking occurred in more than 15 but not more than 30 of 100 reels. C: Static sticking occurred in more than 30 but not more than 50 of 100 reels. D: Static sticking occurred in more than 50 of 100 reels.

[0232] <Pressure of the innermost layer of the reel> After preparing the evaluation reel, the resistance value applied to the sensor sheet was measured using a digital multimeter (RD701, manufactured by SANWA Corporation). The pressure of the innermost layer was calculated by applying the measured resistance value to a calibration curve prepared in advance. A constant pressure was applied to the pressure-sensitive part of the sensor sheet, and the resistance value detected by the digital multimeter was recorded. This was repeated while changing the pressure applied to the sensor sheet, and the pressure and resistance value were plotted on a graph to create a calibration curve. The calibration curve was created by plotting data so that at least five points with a pressure of 0 MPa or more and 5 MPa or less were included.

[0233] <Rate Characteristics> The assembled simplified battery was charged at 25°C at a current of 3 mA (approximately 0.5 C) to a battery voltage of 4.2 V, and then tapered from 3 mA to maintain 4.2 V. This initial charge (initial charge) was performed for a total of approximately 6 hours. The battery was then discharged at a current of 3 mA to a battery voltage of 3.0 V. Next, at 25°C, the battery was charged at a current of 6 mA (approximately 1.0 C) to a battery voltage of 4.2 V, and then tapered from 6 mA to maintain 4.2 V, for a total of approximately 3 hours. The discharge capacity at 6 mA to a battery voltage of 3.0 V was recorded as the 1 C discharge capacity (mAh). Next, at 25°C, the battery was charged at a current of 6 mA (approximately 1.0 C) to a battery voltage of 4.2 V, and then tapered from 6 mA to maintain 4.2 V, for a total of approximately 3 hours. Thereafter, the discharge capacity when the battery was discharged to a battery voltage of 3.0 V at a current value of 12 mA (approximately 2.0 C) was taken as the 2C discharge capacity (mAh). The ratio of the 2C discharge capacity to the 1C discharge capacity was then calculated, and this value was taken as the rate characteristic. Note that a current value of 6 mA corresponds to approximately 1C when charging and discharging a simple battery at a temperature of 25°C. If the evaluation is A to B, the separator can be suitably used for the present embodiment. Rate characteristic (%) = (2C discharge capacity / 1C discharge capacity) x 100 Evaluation criteria A (good): Rate characteristic is greater than 85% B (fair): Rate characteristic is greater than 80% and not greater than 85% C (poor): Rate characteristic is not greater than 80%

[0234] <Cycle Characteristics> The battery tested in the above <Rate Characteristics> was discharged at a discharge current of 1 C to a discharge cut-off voltage of 3 V at a temperature of 45° C., and then charged at a charge current of 1 C to a charge cut-off voltage of 4.2 V. This constituted one cycle, and charge and discharge were repeated. The cycle characteristics were evaluated according to the following criteria, using the capacity retention rate after 300 cycles relative to the initial capacity (capacity at the first cycle). If the evaluation was A to B, the battery can be suitably used as the separator of this embodiment. A (Good): Capacity retention rate of 65% or more B (Fair): Capacity retention rate of 60% or more but less than 65% C (Poor): Capacity retention rate of less than 60%

[0235] <Preparation of Thermoplastic Polymer> <Preparation of Thermoplastic Polymer a1> 70.4 parts by mass of ion-exchanged water, 0.5 parts by mass of "Aqualon KH1025", and 0.5 parts by mass of "ADEKA REASOAP SR1025" were initially charged into a reaction vessel equipped with a stirrer, a reflux condenser, a dropping tank, and a thermometer, and the temperature inside the reaction vessel was raised to 95° C. Thereafter, while maintaining the temperature inside the vessel at 95° C., 7.5 parts by mass of ammonium persulfate (2% aqueous solution) (referred to as "APS(aq)" in the table; the same applies hereinafter) was added.

[0236] On the other hand, 0.1 parts by mass of methacrylic acid (MAA), 0.1 parts by mass of acrylic acid (AA), 38.5 parts by mass of methyl methacrylate (MMA), 19.6 parts by mass of n-butyl acrylate (BA), 31.9 parts by mass of 2-ethylhexyl acrylate (EHA), 2 parts by mass of 2-hydroxyethyl methacrylate (HEMA), 5 parts by mass of acrylamide (AM), 2.8 parts by mass of glycidyl methacrylate (GMA), 0.7 parts by mass of trimethylolpropane triacrylate (A-TMPT) (manufactured by Shin-Nakamura Chemical Co., Ltd.), 0.3 parts by mass of γ-methacryloxypropyltrimethoxysilane (AcSi), 3.0 parts by mass of KH1025, SR1025 A mixture of 3.0 parts by mass of ammonium persulfate, 0.05 parts by mass of sodium p-styrenesulfonate (NaSS), 7.5 parts by mass of ammonium persulfate (2% aqueous solution), and 52 parts by mass of ion-exchanged water was mixed for 5 minutes using a homomixer to prepare an emulsion. The resulting emulsion was added dropwise from the dropping tank to the reaction vessel. Dropping began 5 minutes after the addition of the aqueous ammonium persulfate solution to the reaction vessel, and the entire amount of the emulsion was added dropwise over 150 minutes. During the dropwise addition of the emulsion, the temperature inside the vessel was maintained at 80°C. At this time, the stirring bar placed in the reaction vessel was constantly stirred using a magnetic stirrer.

[0237] After the dropwise addition of the emulsified liquid was completed, the temperature inside the reaction vessel was maintained at 80°C for 90 minutes, and then cooled to room temperature to obtain an emulsion. The pH of the obtained emulsion was adjusted to 9.0 using an aqueous ammonium hydroxide solution (25% aqueous solution), yielding an acrylic copolymer latex with a concentration of 40% (thermoplastic polymer a1). The glass transition temperature (Tg) of the thermoplastic polymer contained in the obtained thermoplastic polymer a1 was evaluated using the method described above. The results are shown in Table 3-1 below.

[0238] <Preparation of Thermoplastic Polymers a2 to a4> Thermoplastic polymers a2 to a4 were obtained in the same manner as for thermoplastic polymer a1, except that the composition of the emulsion was changed as shown in Table 3-1, and the glass transition temperature (Tg) was evaluated by the method described above. The obtained results are shown in Table 3-1.

[0239] Thermoplastic polymers a1 to a4 were mixed in the combinations and content ratios shown in Table 3-2 to prepare thermoplastic polymer-containing paints A1 to A3. The volume average particle diameters (D10, D50, and D90) of the obtained thermoplastic polymer-containing paints A1 to A3 were measured by the above-mentioned method. The results are shown in Table 3-2.

[0240] <Explanation of abbreviations in the table> Emulsifiers KH1025: "Aqualon KH1025" registered trademark, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., 25% aqueous solution SR1025: "Adeka Reasoap SR1025" registered trademark, manufactured by ADEKA Corporation, 25% aqueous solution NaSS: sodium p-styrenesulfonate

[0241] Initiator APS (aq): ammonium persulfate (2% aqueous solution)

[0242] Monomers MAA: methacrylic acid AA: acrylic acid MMA: methyl methacrylate BA: n-butyl acrylate EHA: 2-ethylhexyl acrylate CHMA: cyclohexyl methacrylate St: styrene AN: acrylonitrile HEMA: 2-hydroxyethyl methacrylate AM: acrylamide GMA: glycidyl methacrylate A-TMPT: trimethylolpropane triacrylate AcSi: γ-methacryloxypropyltrimethoxysilane

[0243] <Preparation of inorganic filler-containing slurries> The inorganic filler materials listed in Table 2 were dispersed in water to prepare inorganic filler-containing slurries C1 to C4. The physical properties (average volume particle diameters D10, D50, and D90) of the inorganic fillers used in slurries C1 to C4 were measured using the methods described above. The results are shown in Table 2.

[0244] Example 1 Production of Polyolefin Microporous Membrane B1 47 parts by mass of homopolymer high-density polyethylene having an Mv of 700,000, 46 parts by mass of homopolymer high-density polyethylene having an Mv of 300,000, and 7 parts by mass of homopolymer polypropylene having an Mv of 700,000 were dry-blended using a tumbler blender. 1 part by mass of tetrakis-[methylene-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane as an antioxidant was added to 99 parts by mass of the obtained polyolefin mixture, and the mixture was again dry-blended using the tumbler blender to obtain a mixture. The obtained mixture was supplied to a twin-screw extruder using a feeder under a nitrogen atmosphere. Liquid paraffin (kinematic viscosity at 37.78°C: 7.59 x 10) was also added. －５ m ２ The operating conditions of the feeder and pump were adjusted so that the proportion of liquid paraffin in the entire mixture to be extruded was 68 parts by mass, i.e., the polymer concentration was 32 parts by mass.

[0245] Next, they were melt-kneaded in a twin-screw extruder while being heated to 160°C, and the resulting melt-kneaded product was extruded through a T-die onto a cooling roll controlled at a surface temperature of 80°C. The extrudate was brought into contact with the cooling roll and cast, followed by cooling and solidification to obtain a sheet-like molded product. This sheet was stretched in a simultaneous biaxial stretching machine at a stretching ratio and temperature satisfying the physical properties B1 listed in Table 1, then immersed in methylene chloride to extract and remove the liquid paraffin, dried, and stretched in a tenter stretching machine at a temperature and stretching ratio satisfying the physical properties B1 listed in Table 1. The stretched sheet was then relaxed by about 10% in the width direction and heat-treated to obtain polyolefin microporous membrane B1.

[0246] The physical properties (membrane basis weight, porosity, air permeability, thickness, etc.) of the obtained polyolefin microporous membrane B1 were measured by the above-mentioned methods as necessary. The obtained results are shown in Table 1.

[0247] (Production of polyolefin microporous membrane B2) Polyolefin microporous membrane B2 was obtained in the same manner as B1, except that the production conditions were appropriately changed so as to satisfy the physical properties (membrane basis weight, porosity, air permeability, thickness, etc.) shown in Table 1. The physical properties of the obtained polyolefin microporous membrane B2 were evaluated by the methods described above. The obtained results are shown in Table 1.

[0248] Example 1 An inorganic filler-containing slurry C1 having the composition shown in Table 2 was applied to one surface of a polyolefin microporous membrane B1 (in one embodiment, the first main surface of the substrate) to a coating thickness of 1.5 μm to form an inorganic filler-containing layer. Then, a thermoplastic polymer-containing coating A1 having the composition shown in Table 3-2 was dot-coated by gravure coating on the surface of the inorganic filler-containing layer to a coating layer thickness t ｃ and coverage area ratio S ｃ The thermoplastic polymer-containing coating material A1 was dot-coated by gravure coating on the other surface of the polyolefin microporous membrane B1 (in one embodiment, the second main surface of the substrate) to form a coating layer having a thickness t ｐ and coverage area ratio S ｐA thermoplastic polymer-containing layer (the second layer in the table) having the above structure was formed. In this way, a separator for a storage battery device was obtained, which had a thermoplastic polymer-containing layer in a dot pattern on the surface of the inorganic filler-containing layer and the polyolefin microporous membrane. The physical properties of the obtained separator were evaluated by the above-mentioned methods, and the results are shown in Table 4.

[0249] (Uniformly dispersed coating of thermoplastic polymer-containing layer on polyolefin microporous membrane or inorganic filler-containing layer) Uniformly dispersed coating was performed by gravure coating or bar coating, in which the thermoplastic polymer-containing coating material was uniformly coated over the entire surface of the polyolefin microporous membrane or inorganic filler-containing layer.

[0250] Examples 2 to 21, Comparative Examples 1 to 8 Electrical storage device separators comprising a thermoplastic polymer-containing layer (first layer) on the surface of the inorganic filler-containing layer and a thermoplastic polymer-containing layer (second layer) on the second main surface of the polyolefin microporous membrane were obtained in the same manner as in Example 1, except that the conditions, such as the polyolefin microporous membrane, inorganic filler-containing slurry, thermoplastic polymer-containing coating material, coating shape of the thermoplastic polymer-containing layer, coverage area ratio of the thermoplastic polymer, and thickness of the thermoplastic polymer coating layer, were changed as shown in Table 4. The physical properties of the obtained separators were evaluated using the methods described above. The results are also shown in Table 4.

[0251]

[0252]

[0253]

[0254]

[0255]

[0256]

[0257]

[0258]

[0259]

[0260]

[0261]

[0262]

Claims

1. A porous substrate, an inorganic filler-containing layer disposed on a first main surface of the porous substrate, and a thermoplastic polymer-containing layer disposed on a surface of the inorganic filler-containing layer and on a second main surface of the porous substrate, wherein the coverage area ratio S of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer is ｃ is 30% or more and 100% or less, and the coverage area ratio S of the thermoplastic polymer-containing layer on the second main surface of the porous substrate is ｐ is more than 0% and less than 30%, and the thickness t of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer is ｃ and a thickness t of the thermoplastic polymer-containing layer on the second major surface of the porous substrate. ｐ But, t ｃ / t ｐ A separator for an electricity storage device, which satisfies the relationship:

2. Coverage area ratio S of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer ｃ and a coverage area ratio S of the thermoplastic polymer-containing layer on the second main surface of the porous substrate. ｐ But, S ｃ / S ｐ The separator for an electricity storage device according to claim 1 , wherein the relationship of ≧2.00 is satisfied.

3. Coverage area ratio S of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer ｃ and a coverage area ratio S of the thermoplastic polymer-containing layer on the second main surface of the porous substrate. ｐ However, 55%≦S ｃ +S ｐ The separator for an electricity storage device according to claim 1 or 2, which satisfies the relationship: ≦75%.

4. The separator for an electricity storage device according to claim 1 or 2, wherein the particle size of the inorganic filler contained in the inorganic filler-containing layer satisfies the relationship 1.0≦D90 / D10≦5.0, and the particle size of the thermoplastic polymer contained in the thermoplastic polymer-containing layer on the second main surface of the porous substrate satisfies the relationship 1.0≦D90 / D10≦5.

0.

5. The separator for an electricity storage device according to claim 1 or 2, wherein the peel charge when unwound from the reel is −15 kV or more and +15 kV or less.

6. A reel wound with the separator for an electricity storage device according to claim 1 or 2, wherein the surface pressure applied to the innermost layer is 5 MPa or less.

7. The separator for an electricity storage device according to claim 1 or 2, which is obtained by applying an aqueous slurry containing a thermoplastic polymer to the surface of the porous substrate or the inorganic filler-containing layer provided on the porous substrate.

8. The separator for an electricity storage device according to claim 1 or 2, wherein the thermoplastic polymer-containing layer is arranged in a dotted pattern.

9. The separator for an electricity storage device according to claim 1 or 2, wherein the thermoplastic polymer-containing layer contains a copolymer containing a monomer unit of a (meth)acrylic acid ester monomer.

10. An electricity storage device comprising the separator for an electricity storage device according to claim 1 or 2, a positive electrode, a negative electrode, and a non-aqueous electrolyte.

11. The thickness t of the thermoplastic polymer-containing layer on the surface of the inorganic filler-containing layer ｃ Standard deviation s ｔｃ and a thickness t of the thermoplastic polymer-containing layer on the second major surface of the porous substrate. ｐ Standard deviation s ｔｐ But, s ｔｃ / s ｔｐ The separator for an electricity storage device according to claim 1 or 2, which satisfies the relationship: ∇ > 1.

0.

12. A method for manufacturing a porous substrate, comprising the steps of: preparing a porous substrate; applying a slurry containing an inorganic filler onto a first main surface of the porous substrate to form an inorganic filler-containing layer; and applying a slurry containing a thermoplastic polymer onto the surface of the inorganic filler-containing layer and onto a second main surface of the porous substrate to form a thermoplastic polymer-containing layer, wherein the viscosity of the slurry containing the thermoplastic polymer is 60,000 s at a shear rate of 60,000 s. －１ the viscosity of the slurry containing the thermoplastic polymer is 1 mPa·s or more and 20 mPa·s or less at a shear rate v ｃ and a shear rate v when applying the slurry containing the thermoplastic polymer onto the second main surface of the porous substrate. ｐ The method for producing a separator for an electricity storage device according to claim 1 or 2, wherein the relationship between formulas (2) and (3) is satisfied. －１ ≦v ｃ ≦200,000 sec －１ ...Formula (2) 5000sec －１ ≦v ｃ -v ｐ ≦40,000 sec －１ ...Formula (3)

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