Separator for energy storage devices

Abstract

Provided is a separator (1) for a power storage device, the separator comprising a base material and a thermoplastic polymer-containing layer that is formed on at least one surface of the base material and that contains a thermoplastic polymer, wherein the thermoplastic polymer includes a particulate polymer (2); the thermoplastic polymer-containing layer has a dot pattern; and, on a cross-section passing through the center of the dot pattern, the ratio (RX>5 / X≥1) of a region in which more than 5 layers of the particulate polymer (2) are laminated to a region in which one or more layers of the particulate polymer (2) are present is 30% or less.

Description

[Technical Field]

[0001] This invention relates to separators for energy storage devices, etc. [Background technology]

[0002] In recent years, there has been active development of energy storage devices, such as non-aqueous electrolyte batteries. Typically, non-aqueous electrolyte batteries, such as lithium-ion batteries, 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 micropores.

[0003] In addition to conventionally required safety features such as the ability to quickly stop the battery reaction in the event of abnormal overheating (fuse characteristics) and the ability to maintain its shape even at high temperatures to prevent the dangerous situation of the positive and negative electrode materials directly reacting (short-circuit characteristics), separators are also required to improve adhesion to the electrodes from the perspective of uniformizing the charge and discharge current and suppressing lithium dendrite formation.

[0004] In addition to safety and adhesion to electrodes, various functions are being considered for the separator, including coating and lamination of functional layers onto microporous films (Patent Documents 1-6).

[0005] For example, Patent Document 1 describes a method for improving handling and adhesion when winding batteries, as well as lithium ion permeability, by forming a thermoplastic polymer-containing layer in a dot pattern on at least one side of a microporous film used as a separator substrate, and adjusting the average dot height, dot diameter, and inter-dot distance.

[0006] Patent Document 2 describes a method for improving the separation between a separator having a porous coating layer and an electrode, and the desorption phenomenon of inorganic particles within the porous coating layer, by coating the separator substrate with an inorganic particle-containing porous layer in a dot pattern, and adjusting the average dot thickness, average dot diameter, and inter-dot distance.

[0007] Patent Document 3 focuses on a technique for improving the absorption of electrolyte into electrodes by allowing the electrolyte to penetrate to the center of the positive or negative electrode when using an adhesive separator in a battery. However, regarding the dot-pattern coating of the adhesive layer on the separator substrate, it merely lists the average dot thickness, maximum dot diameter, and dot arrangement pitch.

[0008] Patent Document 4 illustrates a separator in which an acrylate-based adhesive layer is formed on at least one side of a porous substrate, with the aim of suppressing an increase in resistance acting inside the secondary battery when the separator, which includes an adhesive layer, is mounted on the secondary battery by a full-surface coating of the porous substrate. The diagram shows a dot-like pattern of the adhesive layer.

[0009] Patent documents 5 and 6 describe providing an acrylate-based adhesive layer on the surface of a porous coating layer, which is formed from a plurality of dots spaced apart from each other at predetermined intervals, in order to suppress a decrease in the bonding force between the separator containing inorganic particles in the porous coating layer and the electrode. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] International Publication No. 2014 / 017651 [Patent Document 2] Special Publication No. 2011-512005 [Patent Document 3] International Publication No. 2020 / 067208 [Patent Document 4] Special Publication No. 2018-535534 [Patent Document 5] Japanese Patent Publication No. 2015-99777 [Patent Document 6] Japanese Patent Publication No. 2015-99776 [Overview of the Initiative] [Problems that the invention aims to solve]

[0011] When a separator comprising a microporous film as a separator substrate and an adhesive layer disposed on at least one side of the microporous film is used in the cell assembly of an energy storage device, a decrease in capacity due to increased resistance or a decrease in energy density due to increased thickness of the separator-electrode winding may occur.

[0012] However, conventional separators for energy storage devices, which consist of a microporous film as a substrate and an adhesive layer of a predetermined average thickness formed on the substrate in a dot-like pattern, had room for improvement in suppressing the decrease in capacity and energy density due to the increase in resistance of the energy storage device.

[0013] In view of the above circumstances, the present invention aims to provide a separator for energy storage devices that can suppress a decrease in capacity or energy density due to an increase in the resistance of the energy storage device. [Means for solving the problem]

[0014] As a result of diligent research, the inventors have found that the above problems can be solved by specifying the number of layers of thermoplastic polymer-containing layers formed in a dot-like pattern on at least one side of the substrate, or the number of thermoplastic polymer particles or the filling configuration, and have completed the present invention. The embodiments of the present invention are listed below. (1) A separator for an energy storage device comprising a base material and a thermoplastic polymer-containing layer formed on at least one surface of the base material and containing a thermoplastic polymer, The thermoplastic polymer includes particulate polymer, The thermoplastic polymer-containing layer has a dot-like pattern, In a cross-section passing through the center of the dot-shaped pattern, the ratio of the region where the particulate polymer is stacked in five or more layers to the region where the particulate polymer is stacked in one or more layers (R X>5 / X≧1 A separator for energy storage devices, where the ratio is 30% or less. (2) A separator for a power storage device, comprising a base material and a thermoplastic polymer-containing layer formed on at least one surface of the base material and containing a thermoplastic polymer. The thermoplastic polymer includes a particulate polymer. The thermoplastic polymer-containing layer has a dot pattern. In a cross-section passing through the center of the dot pattern, the ratio (R 1<X≦3 / X≧1 ) of the region where one or more layers of the particulate polymer are stacked to the region where the particulate polymer is stacked in more than one layer and at most three layers is 40% or more and 100% or less. A separator for a power storage device. (3) In a cross-section passing through the center of the dot pattern, the ratio (R 0<X≦1(X=1) / X≧1 ) of the region where one layer of the particulate polymer is stacked to the region where one or more layers of the particulate polymer are present is 50% or less. The separator for a power storage device according to item 1 or 2. (4) In a cross-section passing through the center of the dot pattern, the ratio (R 1<X≦2 / X≧1 ) of the region where the particulate polymer is stacked in more than one layer and at most two layers to the region where one or more layers of the particulate polymer are present is defined as A, and the ratio (R 0<X≦1(X=1) / X≧1 ) of the region where one layer of the particulate polymer is stacked to the region where one or more layers of the particulate polymer are present is defined as B. When the ratio (R 0<X≦1(X=1) / X≧1 / R 1<X≦2 / X≧1 ) of B to A is 0 or more and 1 or less. The separator for a power storage device according to any one of items 1 to 3. (5) In a cross-section passing through the center of the dot pattern, for the ratio (R n<X≦n+1 / X≧1 ) of the region where the particulate polymer is stacked in more than n layers and at most (n + 1) layers to the region where one or more layers of the particulate polymer are present, the following formula: (R 1<X≦2 / X≧1 )≧(R 0<X≦1(x=1) / X≧1 )≧(R 2<X≦3 / X≧1 )≧(R n<X≦n+1 / X≧1 ) {In the formula, n is an integer of 3 or more} holds. The separator for a power storage device according to any one of items 1 to 4. (6) A separator for energy storage devices according to any one of items 1 to 5, wherein the average particle size of the particulate polymer is 0.10 μm or more and 0.80 μm or less. (7) A separator for an energy storage device according to any one of items 1 to 6, wherein the thermoplastic polymer has at least two glass transition temperatures, at least one of which is in the region of less than 20°C, and at least one of which is in the region of 40°C or more and 110°C or less. (8) A separator for an energy storage device according to any one of items 1 to 7, wherein the total coverage area ratio of the thermoplastic polymer to the surface of the substrate on at least one side is 3% or more and 60% or less. (9) The basis weight of the thermoplastic polymer-containing layer on at least one side is 0.03 g / m². 2 ~0.5g / m 2 A separator for energy storage devices as described in any one of items 1 to 8. (10) A separator for an energy storage device according to any one of items 1 to 9, wherein a porous layer containing an inorganic filler and a resin binder is formed between at least one side of the substrate and the thermoplastic polymer-containing layer. (11) A separator for an energy storage device according to item 10, wherein the pore size of the porous layer is 0.03 μm or more and 0.40 μm or less. (12) A separator for an energy storage device according to any one of items 1 to 11, wherein the thickness of the substrate or the ratio of the thickness of the thermoplastic polymer-containing layer to the thickness of the substrate and the porous layer is 0.10 or more and 0.40 or less. (13) A separator for an energy storage device according to any one of items 1 to 12, wherein the thermoplastic polymer-containing layer is provided on both sides of the substrate, the sum of the maximum heights of the dots on both sides is 0.2 μm or more and 4.5 μm or less, and the difference in the maximum heights of the dots on both sides is greater than 0.0 μm and 1.0 μm or less. (14) A method for manufacturing a separator for energy storage devices, The process of preparing the base material, The process includes a step of forming a thermoplastic polymer-containing layer by applying a coating solution containing a thermoplastic polymer to at least one surface of the substrate. The coating liquid has a solid content of 6% to 35% by mass of the total coating liquid, a viscosity of 10 mPa·s to 100 mPa·s, a surface tension of 10 mN / m to 45 mN / m, and a pH of 6 to 10. A method for manufacturing separators for energy storage devices. (15) Between the step of preparing the substrate and the step of forming the thermoplastic polymer-containing layer, The invention further comprises the step of forming an inorganic particle-containing layer by applying a coating solution containing inorganic particles to the surface of the substrate. A method for manufacturing a separator for energy storage devices as described in item 14. (16) An energy storage device comprising a positive electrode, a negative electrode, a separator for an energy storage device described in any one of items 1 to 13, and a non-aqueous electrolyte, wherein the separator for the energy storage device is arranged such that the side having the porous layer and the positive electrode face each other with respect to the substrate. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a separator for energy storage devices that can suppress the decrease in capacity and / or decrease in energy density due to the increase in resistance of the energy storage device. [Brief explanation of the drawing]

[0016] [Figure 1] This is a schematic diagram illustrating how to determine the ratio of the region where particulate polymers are present to the region where they are layered. [Figure 2] This is a schematic cross-sectional view of a separator according to one embodiment of the present invention. [Figure 3]This is a schematic plan view defining the region where a thermoplastic polymer is present in order to explain a dot-like pattern according to one embodiment of the present invention. [Modes for carrying out the invention]

[0017] The embodiments for carrying out the present invention (hereinafter referred to as "embodiments") will be described in detail below. However, the present invention is not limited to the following embodiments and can be implemented in various ways within the scope of its gist.

[0018] <Separator for energy storage devices> The separator for energy storage devices according to this embodiment (hereinafter also simply referred to as "separator") comprises a base material and A thermoplastic polymer-containing layer is formed on the surface of at least one side of the substrate and includes a thermoplastic polymer, The thermoplastic polymer comprises particulate polymer, and the thermoplastic polymer-containing layer has a dot-like pattern.

[0019] The separator may have a thermoplastic polymer-containing layer directly on one or both sides of the substrate surface, and optionally, a porous layer may be present between the substrate surface and the thermoplastic polymer-containing layer, or on the substrate surface where the thermoplastic polymer-containing layer is not formed.

[0020] <Dot-like pattern of thermoplastic polymer-containing layer> The term "dot pattern" refers to a configuration on a substrate where portions containing a thermoplastic polymer and portions not containing a thermoplastic polymer exist, with the portions containing the thermoplastic polymer presenting as islands. Note that the thermoplastic polymer-containing layer may consist of independent portions.

[0021] The thermoplastic polymer-containing layer having a specific dot-like pattern provides excellent resistance suppression or liquid injection properties for the separator. In this specification, liquid injection properties refer to the ease with which the electrolyte penetrates the electrodes and separator during the electrolyte injection process in the cell assembly of an energy storage device using a separator, and are expressed as the short time required from the start of injection to the completion of penetration. From the viewpoint of improving liquid injection properties, it is preferable that the portion of the thermoplastic polymer-containing layer containing the thermoplastic polymer is independent.

[0022] (First embodiment) In a cross-section passing through the center of the dot-shaped pattern of the thermoplastic polymer-containing layer according to the first embodiment, the ratio of the region where five or more layers of particulate polymer are stacked to the region where one or more layers of particulate polymer are present (R X>5 / X≧1 ) is 30% or less, preferably 20% or less, and more preferably 10% or less.

[0023] In the first embodiment, when the number of layers containing particulate polymer is X, the above ratio (R X>5 / X≧1 By optimizing so that the ratio of particulate polymers to less than 30%, the height of the thermoplastic polymer-containing layer can be controlled, and the formation of a coffee ring in the thermoplastic polymer-containing layer can be suppressed. This suppresses the decrease in capacity due to increased resistance of the energy storage device, and / or the decrease in energy density due to increased separator film thickness or increased thickness of the separator-electrode winding, and in turn, improves the performance of the energy storage device by making the distance between electrodes in the energy storage device uniform and narrowing it. X>5 / X≧1 By reducing the amount of particulate polymer (X≧1), the increase in the thickness of the separator and the thickness of the separator-electrode winding can be suppressed, thereby suppressing the decrease in energy density. Furthermore, by having one or more layers of particulate polymer in the thermoplastic polymer-containing layer, adhesion to the electrodes can be achieved while suppressing the increase in resistance, and the distance between electrodes can be maintained uniformly.

[0024] From the perspective of further suppressing the increase in separator resistance or film thickness, improving liquid injection properties, and further improving the performance of the energy storage device, the above ratio (R X>5 / X≧1 It is more preferably 0% to 9%, even more preferably 0% to 8%, and particularly preferably more than 0% to 7%.

[0025] (Second embodiment) In a cross-section passing through the center of the dot-shaped pattern of the thermoplastic polymer-containing layer according to the second embodiment, the ratio (R) of the region where particulate polymer is stacked in layers of more than one and three or fewer layers to the region where one or more layers of particulate polymer exist. 1<X≦3 / X≧1 ) is 40% to 100%, preferably 50% to 100%.

[0026] In the second embodiment, when the number of layers containing particulate polymer is X, the above ratio (R 1<X≦3 / X≧1 By optimizing the ratio to be between 40% and 100%, the height of the thermoplastic polymer-containing layer can be controlled, and the formation of a coffee ring in the thermoplastic polymer-containing layer can be suppressed. This suppresses the decrease in capacity due to increased resistance of the energy storage device, and / or the decrease in energy density due to increased separator film thickness or increased thickness of the separator-electrode winding, and consequently improves the performance of the energy storage device by making the distance between electrodes in the energy storage device uniform and narrowing it.

[0027] From the perspective of further suppressing the increase in separator resistance or film thickness, improving liquid injection properties, and further improving the performance of the energy storage device, the above ratio (R 1<X≦3 / X≧1 It is more preferable that the ratio is greater than 50% and 100% or less, even more preferable that it is 52% or more and less than 100%, and particularly preferable that it is 54% or more and 95% or less.

[0028] (Percentage of regions where particulate polymers exist and regions where particulate polymers are layered) Regarding the region where the particulate polymer exists and the ratio of the region where the particulate polymers are stacked, it will be described below with reference to FIGS. 1 and 2. FIG. 1 is a schematic diagram for explaining how to obtain the ratio of the region where the particulate polymer (2) exists and the stacked region, and FIG. 2 is a schematic cross-sectional view of the separator (1) according to the first or second embodiment.

[0029] The center of the pattern may be, for example, the center of one dot in the top view of the polymer-containing layer.

[0030] In the cross-sectional observation through the center of the dot-shaped pattern, the following constraints shall be observed: · Let X be the number of layers; · Do not count the particles in the depth direction; · At the boundary of the observation length, divide so that the whole of one particle remains (that is, divide so that only a part of one particle does not remain); · The maximum height of the dot containing the particulate polymer is the maximum thickness of the dot. · When a plurality of particulate polymers overlap in the vertical direction, the plurality of particulate polymers shall be either most densely packed or in contact in the vertical direction.

[0031] For example, as shown in FIG. 1, two particulate polymers (2, 2) can be most densely packed (1 < X < 2) or in contact in the vertical direction (X = 2). Also, as shown in FIG. 1, three particulate polymers (2, 2, 2) can not only be completely in contact in the vertical direction (X = 3), but can also be most densely packed to be 1 < X ≤ 2 or 2 < X < 3. In the case of four particulate polymers, five particulate polymers, or six or more particulate polymers (not shown), they may overlap in the same manner as above.

[0032] In this specification, in the region where one or more layers of particulate polymers exist, since at least one grain exists as the primary particle of the particulate polymer, it is always one or more layers (that is, there is no concept of 0.5 layer or less). As shown in FIG. 1, when the number of layers of the particulate polymer (2) is X, X = 1 in the region where one layer of the particulate polymer (2) exists.

[0033] As shown in Figure 2, when a single cross-section passing through the center of a single dot is observed at a magnification sufficient to measure the number of layers of thermoplastic polymer (for example, 5000x for 1.0kV SEM observation), the length of the region in which particulate polymer (2) exists in one field of view, i.e., the length of the continuous region in which one or more layers (X≧1) of particulate polymer (2) exist in one field of view, is defined as the observation length L of the region. Total length refers to the sum of the observation lengths L when the entire diameter of a single dot is observed at a magnification sufficient to measure the number of layers of thermoplastic polymer (for example, 5000x for 1.0kV SEM observation). Furthermore, there may be regions in the diameter of the dot where particulate polymer (2) does not exist, and from the viewpoint of achieving both appropriate adhesive strength and liquid injection properties, the ratio of total length / dot diameter is preferably 30% to 90%, more preferably 35% to 80%, and even more preferably 40% to 70%.

[0034] Ratio (R X>5 / X≧1 One example of how to find ) is as follows: The cross-section passing through the center of the dot-shaped pattern is observed using a scanning electron microscope (SEM). The length of the region where the particulate polymer is stacked in more than 5 layers is determined relative to the length of the region where one or more layers of particulate polymer are present, and the ratio is calculated using the following formula. R X>5 / X≧1 = {Length of the region where particulate polymer is stacked in 5 or more layers / Length of the region where particulate polymer is present} × 100 (%)

[0035] Ratio (R 1<X≦3 / X≧1 One example of how to find ) is as follows: Observe the cross-section passing through the center of the dot-shaped pattern using a scanning electron microscope (SEM). Determine the length of the region where the particulate polymer is stacked in layers of more than one or more layers, and then calculate the ratio using the following formula. R 1<X≦3 / X≧1 = {Length of the region where particulate polymer is stacked in layers greater than 1 or less than 3 layers / Length of the region where particulate polymer is present} × 100 (%)

[0036] Regarding the direction of the length of the region where the particulate polymer is present, from the viewpoint of controlling the variation in length, it is preferably at least in the MD direction (mechanical direction of the microporous membrane), and more preferably in the MD and TD directions (directions that cross the MD of the microporous membrane at a 90° angle).

[0037] The proportion according to the first embodiment (R X>5 / X≧1 ) and the ratio relating to the second embodiment (R 1<X≦3 / X≧1 ) can be combined.

[0038] In the first and / or second embodiments, from the viewpoint of further suppressing the increase in separator resistance or film thickness, improving liquid injection properties, and further improving the performance of the energy storage device, the ratio of the region where one layer of particulate polymer is stacked to the region where one or more layers of particulate polymer exist in a cross section passing through the center of the dot-shaped pattern (R 0<X≦1(X=1) / X≧1 ) is preferably 50% or less, more preferably 0% to 45%, even more preferably 1% to 40%, and particularly preferably 2% to 38%.

[0039] In the first and / or second embodiments, from the viewpoint of further suppressing the increase in separator resistance or film thickness, improving liquid injection properties, and further improving the performance of the energy storage device, in a cross-section passing through the center of the dot-shaped pattern, the ratio (R) of the region where the particulate polymer is stacked in more than one layer but two or fewer layers to the region where one or more layers of the particulate polymer exist. 1<X≦2 / X≧1 Let A be the region where the particulate polymer is present in one or more layers, and the ratio of the region where the particulate polymer is present in one layer to the region where the particulate polymer is present in one or more layers (R 0<X≦1(X=1) / X≧1 When B is the ratio of A to B, (R 0<X≦1(X=1) / X≧1 / R 1<X≦2 / X≧1 It is preferable that the value is between 0 and 1, and more preferably that it is greater than 0 and less than or equal to 1.

[0040] In the first and / or second embodiments, from the viewpoint of further suppressing the increase in separator resistance or film thickness, improving liquid injection properties, and further improving the performance of the energy storage device, in a cross-section passing through the center of the dot-shaped pattern, the ratio (R) of the region where particulate polymer is stacked to more than n layers and (n+1) layers or less to the region where one or more layers of particulate polymer exist. n<X≦n+1 / X≧1 Regarding ), see the following formula: (R 1<X≦2 / X≧1 )≧((R 0<X≦1(X=1) / X≧1 ) and (R 2<X≦3 / X≧1 ))≧(R n<X≦n+1 / X≧1 ) {In the formula, n is a positive integer from 3 onwards.} It is preferable that the relationship expressed by the following equation holds, and also, the following equation: (R 1<X≦2 / X≧1 )≧(R 0<X≦1(X=1) / X≧1 )≧(R 2<X≦3 / X≧1 )≧(R n<X≦n+1 / X≧1 ) {In the formula, n is a positive integer from 3 onwards.} It is preferable that the relationship expressed by (R) holds. Also, from the perspective of being able to suppress the blocking problem, which refers to the adhesion of separators to each other, 1<X≦2 / X≧1 ), (R 0<X≦1(X=1) / X≧1 ), and (R 2<X≦3 / X≧1 It is preferable that the sum of ) exceeds 50%.

[0041] The proportion of the region where the particulate polymer is present and the region where the particulate polymer is layered, as described above, can be achieved, for example, in the separator manufacturing process by controlling the solid content concentration, particle size distribution, viscosity or surface tension of the coating solution containing the particulate polymer; the number of binder particles per unit volume of the coating droplet; the penetration of the coating solution into the substrate; the pore size and wettability of the substrate or backing layer; and the suppression of coffee ring formation.

[0042] (Dot pattern) When there are thermoplastic polymer-containing layers on both sides of the substrate, it is preferable that the sum of the maximum heights of the dots on both sides is 0.2 μm or more and 4.5 μm or less, and / or that the difference in the maximum heights of the dots on both sides is greater than 0.0 μm and 1.0 μm or less. When the maximum heights of the dots on both sides are adjusted as described above, it becomes easier to control the height of the thermoplastic polymer-containing layer, and it tends to be easier to suppress the decrease in capacity due to the increase in resistance of the energy storage device, and / or the decrease in energy density due to the increase in separator film thickness or the increase in the thickness of the separator-electrode winding. Considering this tendency, it is more preferable that the sum of the maximum heights of the dots on both sides is 0.5 μm or more and 3.5 μm or less, and / or that the difference in the maximum heights of the dots on both sides is greater than 0.0 μm and 0.5 μm or less.

[0043] The dot diameter of the thermoplastic polymer-containing layer is preferably 20 μm to 1000 μm, more preferably 50 μm to 800 μm, even more preferably 100 μm to 700 μm, particularly preferably 145 μm to 600 μm, and most preferably 150 μm to 600 μm, from the viewpoint of separator adhesion or liquid injection. Note that the dot diameter refers to 'a' as shown in Figure 3. In relation to multiple dots, each dot may be controlled to have a uniform predetermined diameter, or each dot may have a different diameter, but it is preferable that each dot is controlled to have a uniform predetermined diameter.

[0044] The inter-dot distance in the thermoplastic polymer-containing layer is preferably 50 μm or more, more preferably 100 μm to 3000 μm, even more preferably 200 μm to 2500 μm, even more preferably 400 μm to 2000 μm, and particularly preferably 501 μm to 1500 μm, from the viewpoint of the separator's air release or liquid injection properties. Note that the inter-dot distance refers to the distance b between two dots that are different in proximity to each other, as shown in Figure 3. The distance between dots may be controlled so that the dot pattern has a regular pattern, or the distance between dots may be controlled to be different so that the dot pattern has an irregular pattern. However, it is preferable that the distance between dots is controlled to be a predetermined distance so that the dot pattern has a regular pattern. As shown in Figure 3, a dot refers to a shaded area where particulate polymers are continuously present, and thermoplastic polymers or particulate polymers scattered outside the shaded area are considered particle dispersion areas (4). The dot diameter and inter-dot distance are calculated based on the shaded area.

[0045] The dot-to-dot distance / dot diameter of the thermoplastic polymer-containing layer is preferably 0.5 to 4, more preferably 0.7 to 3.8, even more preferably 1 to 3.5, and particularly preferably 2 to 3.3, from the viewpoint of achieving an excellent balance between adhesion to the electrode and the ease of electrolyte injection.

[0046] Regarding the dot-like pattern of the thermoplastic polymer-containing layer, the average dot height is preferably 0.2 μm to 10 μm, more preferably 0.4 μm to 10 μm, even more preferably 0.5 μm to 4 μm, even more preferably 0.5 μm to 3 μm, and particularly preferably 1 μm to 3 μm, from the viewpoint of the distance between the separator and the electrode and the wettability of the separator.

[0047] From the viewpoint of ensuring good air release, the arrangement angle of the dots in the thermoplastic polymer-containing layer is preferably less than 40°, and although the lower limit of the arrangement angle is not limited, it may be, for example, 0° or greater.

[0048] The dot-like pattern of the thermoplastic polymer-containing layer identified above can be achieved, for example, in the separator manufacturing process by optimizing the thermoplastic polymer-containing coating solution, adjusting the polymer concentration or amount of the coating solution and the coating method or conditions, or by modifying the printing plate.

[0049] The components of the separator are described below.

[0050] [Thermoplastic polymer-containing layer] The thermoplastic polymer-containing layer according to this embodiment contains a thermoplastic polymer. The thermoplastic polymer layer contains particulate polymer.

[0051] [Contact angle between thermoplastic polymer-containing layer and electrolyte] From the viewpoint of excellent electrolyte pouring properties, resistance to air pockets, and short pouring time, the thermoplastic polymer-containing layer preferably has a contact angle with the electrolyte of 0° to 20°, more preferably 2° to 18°, and even more preferably 4° to 16°. The contact angle of the thermoplastic polymer-containing layer with the electrolyte is preferably within the above numerical range at least on the surface where the thermoplastic polymer-containing layer is formed with a dot-like pattern.

[0052] The contact angle between the thermoplastic polymer-containing layer and the electrolyte can be adjusted to within the numerical range described above by controlling, for example, the ratio of the total coverage area of ​​the thermoplastic polymer to the substrate surface, the particle size of the thermoplastic polymer, the corona treatment intensity of the substrate surface, the drying rate, the viscosity of the paint, and the pH of the paint during the process of forming the thermoplastic polymer-containing layer.

[0053] (Thermoplastic polymer) The thermoplastic polymer used in this embodiment is not particularly limited, but examples include: polyolefin resins such as polyethylene, polypropylene, and α-polyolefin; fluorine-containing resins such as polyvinylidene fluoride and polytetrafluoroethylene and copolymers containing these; diene polymers containing conjugated dienes such as butadiene and isoprene as monomer units, or copolymers containing these and their hydrides; acrylic polymers containing acrylic acid esters, methacrylic acid esters, etc. as monomer units, or copolymers containing these and their hydrides; rubbers such as ethylene propylene rubber, polyvinyl alcohol, and polyvinyl acetate; cellulose derivatives such as ethylcellulose, methylcellulose, hydroxyethylcellulose, and carboxymethylcellulose; resins with 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 hydroxyl groups, sulfonic acid groups, carboxyl groups, amide groups, and cyano groups can also be used as monomers when synthesizing the thermoplastic polymer.

[0054] Among these thermoplastic polymers, diene polymers, acrylic polymers, or fluorine polymers are preferred due to their excellent binding properties with electrode active materials, as well as their strength and flexibility.

[0055] (Diene polymer) Diene polymers are polymers that include monomer units obtained by polymerizing conjugated dienes having two conjugated double bonds, such as butadiene and isoprene, although these are not particularly limited. Examples of conjugated diene monomers include 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 individually or copolymerized.

[0056] The proportion of monomer units formed by polymerizing conjugated dienes in a diene polymer is not particularly limited, but for example, it is 40% by mass or more, preferably 50% by mass or more, and more preferably 60% by mass or more, of the total diene polymer.

[0057] The above-mentioned diene polymers are not particularly limited, but examples include homopolymers of conjugated dienes such as polybutadiene and polyisoprene, and copolymers of conjugated dienes with copolymerizable monomers. The copolymerizable monomers are not particularly limited, but examples include the (meth)acrylate monomers described later and the monomers listed below (hereinafter also referred to as "other monomers").

[0058] "Other monomers" are not particularly limited, but include, for example, α,β-unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile; unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, and fumaric acid; styrene 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 and ethyl vinyl ether Examples include vinyl ethers such as butyl vinyl ether; vinyl ketones such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, and isopropenyl vinyl ketone; heterocyclic vinyl compounds such as N-vinylpyrrolidone, vinylpyridine, and vinylimidazole; acrylic acid esters 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 acrylamide-2-methylpropanesulfonic acid. These may be used individually or in combination of two or more.

[0059] (Acrylic polymer) The acrylic polymer is not particularly limited, but preferably a polymer containing monomer units obtained by polymerizing (meth)acrylate monomers.

[0060] In this specification, "(meth)acrylic acid" refers to "acrylic acid or methacrylic acid," and "(meth)acrylate" refers to "acrylate or methacrylate."

[0061] (Meth)acrylate monomers are not particularly limited, but examples 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, decyl (meth)acrylate. Examples include alkyl(meth)acrylates such as acrylate, lauryl(meth)acrylate, n-tetradecyl(meth)acrylate, and stearyl(meth)acrylate; hydroxyl 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.

[0062] 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 acrylic polymers include homopolymers of (meth)acrylate monomers and copolymers of these with monomers copolymerizable therewith. Examples of copolymerizable monomers include the "other monomers" listed in the section on diene polymers above, and these may be used individually or in combination of two or more.

[0063] (Fluorine-based polymer) The fluorinated polymer is not particularly limited, but examples include homopolymers of vinylidene fluoride and copolymers of vinylidene fluoride with monomers that can copolymerize with it. Fluorinated polymers are preferred from the viewpoint of electrochemical stability.

[0064] The proportion of monomer units obtained by polymerizing vinylidene fluoride 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. Monomers copolymerizable with vinylidene fluoride are not particularly limited, but examples 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.

[0065] Among fluorinated polymers, homopolymers of vinylidene fluoride, vinylidene fluoride / tetrafluoroethylene copolymers, and vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymers are preferred. Particularly preferred fluorinated polymers are vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymers, whose monomer composition is typically 30-90% by mass of vinylidene fluoride, 9-50% by mass of tetrafluoroethylene, and 1-20% by mass of hexafluoropropylene. These fluororesin particles may be used individually or in mixtures of two or more types.

[0066] Furthermore, monomers having a hydroxyl group, carboxyl group, amino group, sulfonic acid group, amide group, or cyano group can also be used as monomers when synthesizing the above thermoplastic polymer.

[0067] The monomers having a hydroxyl group are not particularly limited, but examples include vinyl monomers such as pentenol.

[0068] The monomers having a carboxyl group are not particularly limited, but examples include unsaturated carboxylic acids having an ethylenic double bond, such as (meth)acrylic acid and itaconic acid, and vinyl monomers such as pentenoic acid.

[0069] The monomer having an amino group is not particularly limited, but examples include 2-aminoethyl methacrylate.

[0070] The monomers having a sulfonic acid group are not particularly limited, but examples include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth)alisulfonic acid, styrene sulfonic acid, ethyl (meth)acrylate-2-sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, and 3-alyloxy-2-hydroxypropanesulfonic acid.

[0071] The monomers having an amide group are not particularly limited, but examples include acrylamide, methacrylamide, N-methylolacrylamide, and N-methylolmethacrylamide.

[0072] The monomers having a cyano group are not particularly limited, but examples include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, and α-cyanoethyl acrylate.

[0073] The thermoplastic polymer used in this embodiment may be used alone or as a mixture of two or more polymers, but it is preferable to use a mixture of two or more polymers. The thermoplastic polymer may be used with a solvent, and the solvent should be one that can uniformly and stably disperse the thermoplastic polymer. Examples include N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, water, ethanol, toluene, hot xylene, methylene chloride, hexane, etc., with aqueous solvents being preferred. The thermoplastic polymer can also be used in the form of latex.

[0074] (Glass transition temperature of thermoplastic polymers) The glass transition temperature of thermoplastic polymers is not limited, but can be, for example, in the range of -30°C to 110°C.

[0075] Thermoplastic polymers have at least two glass transition temperatures, which allows them to maintain adhesion to the separator electrodes, ensure sufficient distance between the electrodes and the separator in an energy storage device, and shorten the electrolyte injection time. Preferably, thermoplastic polymers have thermal properties such that at least one of their glass transition temperatures is in the region below 20°C, and at least one of their glass transition temperatures is in the region between 40°C and 110°C.

[0076] A glass transition temperature of less than 20°C facilitates bonding between materials, preventing fracture within the thermoplastic polymer-containing layer and fracture at the interface between the substrate and the layer during the separator handling process, thereby suppressing problems such as powder shedding. Furthermore, if at least one of the glass transition temperatures of the thermoplastic polymers used is in the region below 20°C, excellent adhesion to the microporous membrane is achieved, resulting in excellent adhesion between the separator and the electrode. It is more preferable that at least one of the glass transition temperatures of the thermoplastic polymers used is in the region below 15°C, and even more preferable that it is in the region between -30°C and 15°C. Glass transition temperatures in the region below 20°C are particularly preferable to be in the region between -30°C and 15°C, in order to enhance adhesion between the thermoplastic polymer and the microporous membrane while maintaining good handling properties.

[0077] On the other hand, by including a component with a glass transition temperature of 40°C or higher in the thermoplastic polymer, adhesion between the separator and the electrode can be achieved while simultaneously suppressing the problem of blocking, which refers to the adhesion of separators to each other. Furthermore, by ensuring that at least one of the glass transition temperatures of the thermoplastic polymers used is in the range of 40°C to 110°C, excellent handling is achieved, the distance between the electrode surface and the separator substrate surface in the energy storage device can be maintained, and the electrolyte injection time can be shortened. The glass transition temperature of the component with the higher glass transition temperature is more preferably 45°C to 108°C, even more preferably 50°C to 105°C, even more preferably 60°C to less than 105°C, particularly preferably 80°C to less than 103°C, and most preferably above 90°C and below 100°C. In addition, as long as the glass transition temperature of the thermoplastic polymer does not hinder the effects of the present invention, 70°C or higher is also preferable from the viewpoint of handling.

[0078] Here, the glass transition temperature is determined from the DSC curve obtained by differential scanning calorimetry (DSC). In this specification, the glass transition temperature may also be expressed as Tg.

[0079] Specifically, it is determined by the intersection of a straight line extending the baseline on the low-temperature side of the DSC curve toward the high-temperature side, and a tangent line at the inflection point of the stepwise transition portion of the glass transition. For more details, refer to the method described in the examples.

[0080] Here, "glass transition" refers to the endothermic change in heat energy associated with the state change of the polymer specimen in DSC. Such a heat energy change is observed in the DSC curve as a step-like change or a shape that combines a step-like change with a peak.

[0081] A "step-like change" in a DSC curve refers to the portion where the curve deviates from the previous baseline and transitions to a new baseline. This also includes shapes that combine peaks and step-like changes.

[0082] An "inflection point" is the point in the stepwise transition section where the gradient of the DSC curve is at its maximum. It can also be described as the point in the stepwise transition section where an upward-convex curve changes to a downward-convex curve.

[0083] A "peak" in a DSC curve refers to the portion of the curve that moves away from the baseline and then returns to the baseline.

[0084] "Baseline" refers to the DSC curve in the temperature range where no transitions or reactions occur in the test specimen.

[0085] Having two glass transition temperatures in a thermoplastic polymer can be achieved, for example, by blending two or more thermoplastic polymers or by using a thermoplastic polymer with a core-shell structure, but is not limited to these methods. A core-shell structure is a polymer in the form of a double structure, where the polymer belonging to the central part and the polymer belonging to the outer shell have different compositions.

[0086] In particular, polymer blends or core-shell structures can control the overall glass transition temperature of a thermoplastic polymer by combining polymers with high and low glass transition temperatures. Furthermore, multiple functions can be imparted to the thermoplastic polymer as a whole. For example, in the case of blends, blending two or more polymers, particularly those with glass transition temperatures above 20°C and those with glass transition temperatures below 20°C, can achieve both resistance to stickiness and wettability to polyolefin microporous films. When blending, the mass ratio of polymers with glass transition temperatures above 20°C to polymers with glass transition temperatures below 20°C 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. In the case of a core-shell structure, the adhesion and compatibility with other materials such as polyolefin microporous membranes can be adjusted by changing the outer shell polymer, and by adjusting the polymer belonging to the central part, it is possible to create a polymer with improved adhesion to electrodes after hot pressing, for example. Furthermore, viscoelasticity can be controlled by combining a highly viscous polymer with a highly elastic polymer.

[0087] The glass transition temperature of the shell of a thermoplastic polymer having a core-shell structure is not particularly limited, but is preferably less than 20°C, more preferably 15°C or less, and even more preferably between -30°C and 15°C. The glass transition temperature of the core of a thermoplastic polymer having a core-shell structure is not particularly limited, but is preferably 20°C or higher, more preferably between 20°C and 120°C, and even more preferably between 50°C and 120°C.

[0088] In this embodiment, the glass transition temperature (Tg) of the thermoplastic polymer can be appropriately adjusted, for example, by changing the monomer components used to produce the thermoplastic polymer and the input ratio of each monomer. That is, the Tg of the homopolymer of each monomer used in the production of the thermoplastic polymer (for example, as described in "Polymer Handbook" (A WILEY-INTERSCIENCE PUBLICATION)) and the blending ratio of the monomer can be roughly estimated. For example, copolymers blended in high proportions of monomers such as styrene, methyl methacrylate, and acrylonitrile, which give polymers with a Tg of about 100°C, will have a high Tg, while copolymers blended in high proportions of monomers such as butadiene, which gives polymers with a Tg of about -80°C, and n-butyl acrylate and 2-ethylhexyl acrylate, which give polymers with a Tg of about -50°C, will have a low Tg.

[0089] Furthermore, the Tg of the polymer can be estimated using FOX's formula (Equation (1) below). The glass transition temperature of the thermoplastic polymer in this application is determined by the method using DSC described above. 1 / Tg = W1 / Tg1 + W2 / Tg2 + ... + 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 and W of the homopolymer of each monomer i. i This indicates the mass fraction of each monomer.

[0090] (Structure of the thermoplastic polymer-containing layer) In the thermoplastic polymer-containing layer, it is preferable that a thermoplastic resin having a glass transition temperature of 40°C to 110°C is present on the outermost surface side of the separator for the energy storage device, and that a thermoplastic resin having a glass transition temperature of less than 20°C 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 is in contact with the electrode when the separator for the energy storage device and the electrode are laminated. The "interface" refers to the surface of the thermoplastic polymer-containing layer that is in contact with the polyolefin microporous membrane.

[0091] In a thermoplastic polymer-containing layer, the presence of a thermoplastic polymer with a glass transition temperature of 40°C to 110°C on the outermost surface side of the separator for energy storage devices results in superior adhesion with the microporous film, and consequently, superior adhesion between the separator and the electrode. Furthermore, the presence of a thermoplastic polymer with a glass transition temperature of less than 20°C on the interface side between the polyolefin microporous film and the thermoplastic polymer-containing layer results in superior adhesion and handling between the separator and the electrode. By having such a thermoplastic polymer-containing layer, the separator tends to exhibit improved adhesion and handling between the separator and the electrode.

[0092] The above structure can be achieved by (a) the thermoplastic polymer consisting of a granular (particle) thermoplastic polymer and a binder polymer that adheres the granular thermoplastic polymer to the polyolefin microporous membrane with the granular thermoplastic polymer exposed on the surface, the glass transition temperature of the granular thermoplastic polymer being in the range of 40°C to 110°C, and a thermoplastic polymer with a glass transition temperature of less than 20°C being present at the interface between the polyolefin microporous membrane and the thermoplastic polymer-containing layer, and (b) the thermoplastic polymer having a laminated structure, the glass transition temperature of the thermoplastic polymer in the outermost layer when used as a separator being in the range of 40°C to 110°C, and a thermoplastic polymer with a glass transition temperature of less than 20°C being 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 with each polymer having a different Tg.

[0093] (Structure of thermoplastic polymers) Because thermoplastic polymers contain particulate polymers, they can be configured, for example, in a granular form. Having such a structure tends to result in superior adhesion between the separator and the electrode, as well as better handling of the separator. Here, "granular" refers to a state in which individual thermoplastic polymers have a contour as measured by a scanning electron microscope (SEM), and may be elongated, spherical, polygonal, or otherwise.

[0094] The average particle size of the particulate polymer is preferably 0.10 μm or more and 0.80 μm or less, more preferably 0.20 μm or more and less than 0.70 μm, and can be greater than 0.20 μm and 0.60 μm or less, from the viewpoint of being able to maintain the distance between multiple electrodes via the separator while exhibiting adhesive strength with the separator electrodes, and adjusting the ratio of the region where the particulate polymer is present and the region where the particulate polymer is layered to the above numerical range. In this specification, the average particle size of the thermoplastic polymer is the average particle size (D) of the paint containing the particulate polymer of the thermoplastic polymer. 50 ) can generally be considered as such.

[0095] From the viewpoint of maintaining the distance between multiple electrodes via the separator while exhibiting adhesive strength with the separator electrodes, and adjusting the proportion of the region where the particulate polymer exists and the region where the particulate polymer is layered to within the above numerical range, the SD value shown in the following formula is preferably 15% or less of the average particle size, more preferably 10% or less, and even more preferably 7% or less. In calculating the SD value, it is preferable to use the value of the largest single peak. SD=(D 84 -D 16 ) / 2 The particle size distribution of particulate polymers can be controlled, for example, by adjusting polymerization conditions or by classification using filtration methods.

[0096] (Degree of swelling of thermoplastic polymers in electrolyte solution) From the viewpoint of suppressing capacity reduction and energy density reduction of energy storage devices, it is preferable that the thermoplastic polymer has swelling properties in relation to the electrolyte. The degree of swelling of the thermoplastic polymer in relation to the electrolyte is preferably 2 to 15 times, more preferably 3 to 10 times, and even more preferably 4 to 8 times. The degree of swelling of the thermoplastic polymer in relation to the electrolyte can be measured by the method described later in the examples. In this embodiment, the degree of swelling of the thermoplastic polymer in relation to the electrolyte can be adjusted, for example, by changing the monomer components to be polymerized and the input ratio of each monomer.

[0097] (Basis weight per side of the thermoplastic polymer-containing layer) The basis weight of the thermoplastic polymer-containing layer formed on at least one side of the substrate surface of the separator is 0.03 g / m², from the viewpoint of adhesive strength and dot pattern formation. 2 ~0.5g / m 2 Preferably, it is 0.1 g / m 2 More than 0.4g / m 2The following is more preferable: The basis weight of the thermoplastic polymer-containing layer can be adjusted by changing the polymer concentration and amount of the coating solution.

[0098] (Coating of the substrate surface with a thermoplastic polymer-containing layer) The total coverage area ratio of the thermoplastic polymer-containing layer on at least one surface of the substrate is preferably 3% to 60%, more preferably 5% to 55%, and even more preferably 6% to 40%, from the viewpoint of suppressing separator resistance and liquid injection. The total coverage area ratio can be 7% to 35%, as long as the effects of the present invention are achieved. The total coverage area ratio S of the thermoplastic polymer-containing layer present on the substrate surface is calculated from the following formula. S(%) = Total coverage area of ​​thermoplastic polymer-containing layer ÷ Surface area of ​​substrate × 100 The total coverage area ratio of the thermoplastic polymer-containing layer can be adjusted by changing the polymer concentration of the coating solution, the amount of coating applied, the coating method, the coating conditions, etc.

[0099] [Base material] Since separators require both insulating properties and ion permeability, separator substrates are generally formed from insulating materials with a porous structure, such as paper, polyolefin nonwoven fabrics, or resin microporous membranes. In particular, for separator substrates used in energy storage devices such as non-aqueous secondary batteries, which comprise a positive electrode and a negative electrode capable of intercalating and releasing lithium, and a non-aqueous electrolyte solution obtained by dissolving an electrolyte in a non-aqueous solvent, polyolefin microporous membranes that have oxidation-reduction resistance and can construct a dense and uniform porous structure are preferred.

[0100] (Polyolefin microporous membrane) The polyolefin microporous membrane is not particularly limited, but examples include a microporous membrane composed of a polyolefin resin composition containing polyolefin, and it is preferable that the porous membrane is mainly composed of polyolefin resin. The polyolefin microporous membrane is not particularly limited in terms of the polyolefin resin content, but from the viewpoint of shutdown performance when used as a separator for energy storage devices, it is preferable that the porous membrane is composed of a polyolefin resin composition in which polyolefin resin accounts for 50% to 100% of the mass fraction of all components constituting the porous membrane. It is more preferable that the proportion of polyolefin resin is 60% to 100%, and even more preferable that it is 70% to 100%.

[0101] Polyolefin resins are not particularly limited, but refer to polyolefin resins used in ordinary extrusion, injection, inflation, and blow molding processes, and can include homopolymers and copolymers, multi-stage polymers, etc., of ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene. Furthermore, polyolefins selected from the group consisting of these homopolymers, copolymers, and multi-stage polymers can be used alone or in mixtures.

[0102] Typical examples of polyolefin resins, though not particularly limited, include polyethylene such as low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, and ultra-high molecular weight polyethylene, as well as isotactic polypropylene, atactic polypropylene, ethylene-propylene random copolymer, polybutene, and ethylene-propylene rubber.

[0103] When using a separator as a battery separator, it is preferable to use a resin mainly composed of polyethylene, which has a low melting point and high strength, and in particular, a resin mainly composed of high-density polyethylene.

[0104] Furthermore, from the viewpoint of improving the heat resistance of the porous membrane, it is more preferable to use a porous membrane made of a resin composition containing polypropylene. The resin composition may also contain polypropylene and other polyolefin resins. Here, there are no limitations on the stereostructure of the polypropylene, and any of isotactic polypropylene, syndiotactic polypropylene, and atactic polypropylene may be used.

[0105] The proportion of polypropylene to total polyolefin in the polyolefin resin composition can be 0 and is not particularly limited, but from the viewpoint of achieving both heat resistance and good shutdown function, it is preferably 35% by mass or less, more preferably 1 to 20% by mass, and even more preferably 3 to 10% by mass. In this case, there is no limitation to 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. Specifically, examples include polyethylene, polybutene, and ethylene-propylene random copolymer.

[0106] From the viewpoint of shutdown characteristics where pores are blocked by thermal melting, it is preferable to use polyethylene other than polypropylene as a polyolefin resin, such as low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, or ultra-high molecular weight polyethylene. Among these, from the viewpoint of strength, polyethylene with a density of 0.93 g / cm³ as measured according to JIS K 7112 is preferred. 3 More than 0.97g / cm 3 It is more preferable to use polyethylene, which is described below.

[0107] The viscosity-average molecular weight of the polyolefin resin constituting the polyolefin microporous membrane is not particularly limited, but is preferably 30,000 to 12,000,000, more preferably 50,000 to less than 2,000,000, even more preferably 100,000 to less than 1,200,000, and most preferably 500,000 to less than 1,000,000. A viscosity-average molecular weight of 30,000 or more is preferable because it increases the melt tension during melt molding, resulting in good moldability and a tendency for high strength due to the entanglement of polymers. On the other hand, a viscosity-average molecular weight of 12,000,000 or less is preferable because it facilitates uniform melt-kneading and tends to result in excellent sheet moldability, particularly thickness stability. Furthermore, a viscosity-average molecular weight of less than 1,000,000 is preferable because it tends to easily close the 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 1,000,000 alone, a mixture of a polyolefin with a viscosity-average molecular weight of 2,000,000 and a polyolefin with a viscosity-average molecular weight of 270,000, in which the viscosity-average molecular weight is less than 1,000,000, may be used.

[0108] Polyolefin microporous membranes may contain any additives. Such additives are not particularly limited and include, for example, polymers other than polyolefins; inorganic particles; antioxidants such as phenolic, phosphorus-based, and sulfur-based agents; metal soaps such as calcium stearate and zinc stearate; ultraviolet absorbers; light stabilizers; antistatic agents; antifogging agents; and coloring pigments. 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.

[0109] (Physical properties of polyolefin microporous membranes) Basis weight (g / m²) of polyolefin microporous membrane (hereinafter sometimes abbreviated as PO microporous membrane) 2 The puncture strength when converted to (hereinafter referred to as the basis weight equivalent puncture strength) is 50 gf / (g / m²). 2 It is preferable that it be 50 gf / (g / m³). 2PO microporous membranes having a basis weight equivalent puncture strength of 60 gf / (g / m²) or higher tend to be less prone to rupture during impact tests of energy storage devices. From the viewpoint of improving the safety of energy storage devices, such as impact resistance, while maintaining the strength of the PO microporous membrane, the basis weight equivalent puncture strength is more preferably 60 gf / (g / m²). 2 ) More preferably 70 gf / (g / m³) 2 ) or more, particularly preferably 80 gf / (g / m³) 2 ) or more. The puncture strength converted to base weight is not limited, but for example, 200 gf / (g / m 2 ) or less, 150gf / (g / m 2 ) or less, or 140 gf / (g / m³) 2 ) can be less than or equal to:

[0110] The puncture strength of the PO microporous film, which has not been converted to basis weight (hereinafter simply referred to as puncture strength), has a lower limit that 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 puncture strength of 100 gf or more is preferable from the viewpoint of suppressing the rupture of the PO microporous film in impact tests. Furthermore, the upper limit of the puncture strength of the PO microporous film is preferably 1000 gf or less, more preferably 800 gf or less, and even more preferably 700 gf or less, from the viewpoint of stability during film formation. The lower limit can be used as long as it is a value that allows for stable production in film formation and battery manufacturing. The upper limit is set in balance with other characteristics. Puncture strength can be increased by the shear force applied to the molded product during extrusion or by increasing the orientation of molecular chains due to stretching, but as strength increases, thermal stability deteriorates due to the increase in residual stress, so it is controlled according to the purpose.

[0111] The porosity of the polyolefin microporous membrane is not particularly limited, but is preferably 20% or more, more preferably 35% or more, even more preferably 40% 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 preferable from the viewpoint of ensuring the permeability of the separator. On the other hand, a porosity of 80% or less is preferable from the viewpoint of ensuring puncture strength. The porosity can be adjusted by changing the stretching ratio, etc.

[0112] The thickness of the polyolefin microporous film is not particularly limited, but is preferably 2 μm or more, more preferably 4 μm or more, even more preferably 5 μm or more, with an upper limit of preferably 30 μm or less, more preferably 20 μm or less, even more preferably 16 μm or less, and most preferably 12 μm or less. A film thickness of 2 μm or more is preferable from the viewpoint of improving mechanical strength. On the other hand, a film thickness of 30 μm or less is preferable because it tends to be advantageous in terms of increasing the capacity of the battery, as it reduces the volume occupied by the separator.

[0113] The air permeability of the polyolefin microporous membrane is preferably 10 sec / 100 cm. 3 More comfortably, 20 sec / 100 cm 3 More preferably, 30 sec / 100 cm 3 The above is the most preferable, and most preferably 40 sec / 100 cm 3 The above, and preferably 300 sec / 100 cm 3 More preferably, 200 sec / 100 cm 3 More preferably, 180 sec / 100 cm 3 The following, and particularly preferably 140 sec / 100 cm 3 The following applies: Air permeability is 10 sec / 100 cm. 3 The above is preferable from the viewpoint of suppressing self-discharge of the energy storage device. On the other hand, the air permeability is 300 sec / 100 cm. 3 The following is preferable from the viewpoint of obtaining good charge and discharge characteristics. Note that the above air permeability can be adjusted by changing the stretching temperature, stretching ratio, etc.

[0114] The average pore size of the polyolefin microporous film is preferably 0.15 μm or less, more preferably 0.1 μm or less, and preferably 0.01 μm or more as the lower limit. Setting the average pore size to 0.15 μm or less is preferable when used as a separator for energy storage devices, from the viewpoint of suppressing self-discharge of the energy storage device and suppressing capacity reduction. The average pore size can be adjusted by changing the stretching ratio when manufacturing the polyolefin microporous film.

[0115] The short-circuit temperature, an indicator of the heat resistance of the polyolefin microporous membrane, is preferably 140°C or higher, more preferably 150°C or higher, and even more preferably 160°C or higher. Setting the short-circuit temperature to 140°C or higher is preferable from the viewpoint of safety of the energy storage device when used as a separator for energy storage devices.

[0116] The viscosity-average molecular weight of the polyolefin microporous membrane is not particularly limited, but is preferably between 100,000 and 5,000,000, more preferably between 300,000 and 1,500,000, and even more preferably between 500,000 and 1,000,000. A viscosity-average molecular weight of 100,000 to 5,000,000 is preferable in terms of puncture strength, permeability, thermal shrinkage, and shutdown function of the polyolefin microporous membrane.

[0117] (Method for manufacturing polyolefin microporous membranes) The method for producing a polyolefin microporous membrane is not particularly limited, and known production methods can be employed. For example, a method in which a polyolefin resin composition and a plasticizer are melt-kneaded together to form a sheet, which is then optionally stretched, and the plasticizer is extracted to create porosity; a method in which a polyolefin resin composition is melt-kneaded together and extruded at a high draw ratio, and then the polyolefin crystal interface is peeled off by heat treatment and stretching to create porosity; a method in which a polyolefin resin composition and an inorganic filler are melt-kneaded together to form a sheet, which is then peeled off by stretching to create porosity; and a method in which a polyolefin resin composition is dissolved, immersed in a poor solvent for polyolefin, and the polyolefin is solidified while the solvent is removed to create porosity. Below, as an example of a method for producing a porous membrane, a method in which a polyolefin resin composition and a plasticizer are melt-kneaded together to form a sheet, and then the plasticizer is extracted will be described.

[0118] First, the polyolefin resin composition and the plasticizer are melt-kneaded. A melt-kneading method involves, for example, introducing the polyolefin resin and, if necessary, other additives into a resin mixing device such as an extruder, kneader, laboplast mill, kneading roll, or Banbury mixer, and mixing the resin components while introducing the plasticizer in a desired ratio. In this case, it is preferable to pre-mix the polyolefin resin, other additives, and plasticizer in a predetermined ratio using a Henschel mixer or the like before introducing them into the resin mixing device. More preferably, only a portion of the plasticizer is introduced during the pre-kneading, and the remaining plasticizer is mixed while feeding it to the side of the resin mixing device. This improves the dispersibility of the plasticizer, allowing the sheet-like molded product of the melt-kneaded resin composition and plasticizer to be stretched at a high magnification without film breakage during subsequent stretching processes.

[0119] As a plasticizer, a non-volatile solvent capable of forming a uniform solution 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 interfacial delamination between the resin and plasticizer is less likely to occur even when the molten mixture is stretched, thus facilitating uniform stretching.

[0120] The ratio of polyolefin resin composition to plasticizer is not particularly limited as long as they can be uniformly melt-mixed and molded into a sheet. For example, the mass fraction of plasticizer in a composition consisting of polyolefin resin composition and plasticizer is preferably 30 to 80% by mass, more preferably 40 to 70% by mass. When the mass fraction of plasticizer is 80% by mass or less, the melt tension during melt molding is less likely to be insufficient, and moldability tends to improve. On the other hand, when the mass fraction of plasticizer is 30% by mass or more, even if the mixture of polyolefin resin composition and plasticizer is stretched at a high magnification, the polyolefin chains do not break, forming a uniform and fine pore structure and easily increasing strength.

[0121] Next, the molten mixture is formed into a sheet. One method for producing a sheet-shaped molded product is to extrude the molten mixture into a sheet through a T-die or the like, and then cool and solidify it by contacting it with a heat conductor to a temperature sufficiently lower than the crystallization temperature of the resin components. As the heat conductor used for cooling and solidification, metal, water, air, or the plasticizer itself can be used, but a metal roll is preferred because it has high heat conduction efficiency. In this case, when contacting the metal roll, sandwiching the mixture between the rolls is even more preferable because it further increases the efficiency of heat conduction, orients the sheet, increases film strength, and improves the surface smoothness of the sheet. The die lip spacing when extruding the mixture into a sheet from the T-die is preferably 400 μm to 3000 μm, and more preferably 500 μm to 2500 μm. When the die lip spacing is 400 μm or more, die residue is reduced, the impact on film quality such as streaks or defects is less, and film breakage in the subsequent stretching process tends to be prevented. On the other hand, when the die lip spacing is 3000 μm or less, the cooling rate is faster, uneven cooling can be prevented, and the sheet thickness stability tends to be maintained.

[0122] It is preferable to stretch the sheet-like molded article obtained in this manner. While either uniaxial stretching or biaxial stretching can be suitably used for the stretching process, biaxial stretching is preferred from the viewpoint of the strength of the resulting porous film. When the sheet-like molded article is stretched at high magnification in the biaxial direction, the molecules become oriented in the planar direction, resulting in a porous film that is less prone to tearing and possesses high puncture strength. Examples of stretching methods include simultaneous biaxial stretching, sequential biaxial stretching, multi-stage stretching, and multiple-pass stretching. Simultaneous biaxial stretching is preferred from the viewpoint of improving puncture strength, stretching uniformity, and shutdown properties.

[0123] Here, simultaneous biaxial stretching refers to a stretching method in which stretching in the MD direction and stretching in the TD direction 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 when stretching is being performed in the MD direction or the TD direction, the other direction is in an unconstrained state or fixed to a fixed length.

[0124] The stretching ratio is preferably in the range of 20 to 100 times in terms of surface magnification, and more preferably in the range of 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, and more preferably in the range of 5 to 8 times in the MD direction and 5 to 8 times in the TD direction. When the total area magnification is 20 times or more, the resulting porous film tends to be given sufficient strength, while when the total area magnification is 100 times or less, film breakage during the stretching process is prevented, and high productivity tends to be obtained.

[0125] The sheet-like molded body may also be rolled. Rolling can be carried out, for example, by a pressing method using a double-belt press. Rolling can particularly increase the orientation of the surface layer. The rolling surface ratio is preferably greater than 1 and 3 or less, and more preferably greater than 1 and 2 or less. When the rolling surface ratio is greater than 1, the surface orientation increases and the film strength of the resulting porous film tends to increase. On the other hand, when the rolling surface ratio is 3 or less, the difference in orientation between the surface layer and the central interior is small, and it tends to form a uniform porous structure in the thickness direction of the film, which is preferable.

[0126] Next, the plasticizer is removed from the sheet-like molded body to form a porous film. Methods for removing the plasticizer include, for example, immersing the sheet-like molded body in an extraction solvent to extract the plasticizer and then thoroughly drying it. The extraction method can be either batch or continuous. To suppress shrinkage of the porous film, it is preferable to restrain the edges of the sheet-like molded body during the immersion and drying process. Furthermore, it is preferable that the amount of plasticizer remaining in the porous film be less than 1% by mass.

[0127] It is preferable to use an extraction solvent that is a poor solvent for polyolefin resins and a good solvent for plasticizers, and whose boiling point is 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-chlorinated 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 and reused by operations such as distillation.

[0128] To suppress shrinkage of the porous membrane, heat treatment such as thermal fixation or thermal relaxation can be performed after the stretching process or after the formation of the porous membrane. Furthermore, post-treatment such as hydrophilization with surfactants or crosslinking with ionizing radiation may be performed on the porous membrane.

[0129] [Porous layer] Optionally, the separator for the energy storage device may include a porous layer containing an inorganic filler and a resin binder. The porous layer may be located on at least a portion of the surface of a substrate such as a polyolefin microporous film, and / or between the substrate and the thermoplastic polymer-containing layer. The porous layer may be present on one side or both sides of the substrate.

[0130] (Inorganic filler) The inorganic filler used in the porous layer described above is not particularly limited, but it is preferable to have a melting point of 200°C or higher, high electrical insulation properties, and electrochemical stability within the operating range of lithium-ion secondary batteries.

[0131] 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 hydroxide oxide or boehmite, potassium titanate, talc, kaolinite, decite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amethyst, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; and glass fibers. 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, as boehmite, synthetic boehmite that can reduce ionic impurities that adversely affect the properties of electrochemical elements is preferred.

[0132] Examples of inorganic filler shapes include plate-like, flaky, polyhedral, needle-like, columnar, granular, spherical, spindle-shaped, and block-like shapes, and multiple types of inorganic fillers having the above shapes may be used in combination. Among these, block-like shapes are preferred from the viewpoint of balancing permeability and heat resistance.

[0133] The aspect ratio of the inorganic filler is preferably 1.0 to 5.0, and more preferably 1.1 to 3.0. An aspect ratio of 5.0 or less is preferable from the viewpoint of suppressing the amount of moisture adsorption of the multilayer porous membrane and suppressing capacity degradation when repeated cycles are performed, and from the viewpoint of suppressing deformation of the polyolefin microporous membrane at temperatures exceeding its melting point.

[0134] The specific surface area of ​​the inorganic filler is 3.0 m². 2 / g or more 17m 2 It is preferable that it be less than or equal to / g, and more preferably 5.0m 2 / g or more 15m 2 It is less than or equal to / g, and more preferably 6.5m2 13 m or more per g 2 It is 17 m or less per g. The specific surface area is 17 m 2 By being 17 m or less per g, it is preferable from the viewpoint of suppressing the water adsorption amount of the multilayer porous membrane and suppressing the capacity deterioration when cycles are repeated. The specific surface area is 3.0 m 2 By being 3.0 m or more per g, it is preferable from the viewpoint of suppressing the 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.

[0135] In the particle size distribution of the slurry containing the inorganic filler, the average particle size D of the inorganic particles 50 is preferably 0.10 μm or more and 1.40 μm or less, more preferably 0.20 μm or more and 0.80 μm or less, and still more preferably 0.25 μm or more and 0.50 μm or less. D 50 By being 0.10 μm or more, it is preferable from the viewpoint of suppressing the water adsorption amount of the multilayer porous membrane and suppressing the capacity deterioration when cycles are repeated. D 50 By being 1.40 μm or less, it is preferable from the viewpoint of suppressing the deformation at a temperature exceeding the melting point of the polyolefin microporous membrane.

[0136] Also, in the particle size distribution of the slurry containing the inorganic filler, the D of the inorganic particles 10 is 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 still more preferably 0.10 μm or more and 0.35 μm or less. D 10 By being 0.08 μm or more, it is preferable from the viewpoint of suppressing the water adsorption amount of the multilayer porous membrane and suppressing the capacity deterioration when cycles are repeated. D 10 By being 0.80 μm or less, it is preferable from the viewpoint of suppressing the deformation at a temperature exceeding the melting point of the polyolefin microporous membrane.

[0137] As a method for adjusting the particle size distribution of the inorganic filler as described above, for example, a method of pulverizing the inorganic filler using a ball mill, a bead mill, a jet mill, etc. to obtain a desired particle size distribution, a method of blending after preparing fillers with a plurality of particle size distributions, etc. can be mentioned.

[0138] The proportion of inorganic filler in the porous layer can be appropriately determined from the viewpoint of the binding properties of the inorganic filler, the permeability and heat resistance of the multilayer porous film, and 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.

[0139] (Resin binder) While there are no particular limitations on the type of resin binder, when using the multilayer porous membrane in this embodiment as a separator for lithium-ion secondary batteries, it is preferable to use one that is insoluble in the electrolyte of the lithium-ion secondary battery and electrochemically stable within the operating range of the lithium-ion secondary battery.

[0140] Specific examples of resin binders are listed below (1) to (7). 1) Polyolefins: for example, polyethylene, polypropylene, ethylene propylene rubber, and modified versions thereof; 2) Conjugated diene polymers: for example, styrene-butadiene copolymers and their hydrides, acrylonitrile-butadiene copolymers and their hydrides, acrylonitrile-butadiene-styrene copolymers and their hydrides; 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-based resins: for example, polyvinyl alcohol, polyvinyl acetate; 5) Fluorine-containing resins: for example, polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer; 6) Cellulose derivatives: for example, ethylcellulose, methylcellulose, hydroxyethylcellulose, carboxymethylcellulose; 7) Resins with a melting point and / or glass transition temperature of 180°C or higher, or polymers that do not have a melting point but have a decomposition temperature of 200°C or higher: for example, polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, polyester.

[0141] From the viewpoint of further improving safety during short circuits, 3) acrylic polymers, 5) fluororesins, and 7) polyamides as polymers are preferred. As for polyamides, all aromatic polyamides, particularly polymetaphenylene isophthalamide, are preferred from the viewpoint of durability.

[0142] From the viewpoint of compatibility between the resin binder and the electrode, 2) conjugated diene polymers are preferred, and from the viewpoint of voltage resistance, 3) acrylic polymers and 5) fluororesins are preferred.

[0143] The above 2) Conjugated diene polymers are polymers that contain conjugated diene compounds as monomer units.

[0144] Examples of the above-mentioned conjugated diene compounds include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chlor-1,3-butadiene, substituted linear-conjugated pentadienes, substituted and side-conjugated hexadienes, etc. These may be used individually or in combination of two or more. Among these, 1,3-butadiene is particularly preferred.

[0145] The above 3) Acrylic polymer is a polymer that contains a (meth)acrylic compound as a monomer unit. The above (meth)acrylic compound refers to at least one selected from the group consisting of (meth)acrylic acid and (meth)acrylic acid esters.

[0146] Examples of (meth)acrylic acid esters used in the acrylic polymers described in 3) above include alkyl (meth)acrylic acid 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 individually or in combination of two or more. Among these, 2-ethylhexyl acrylate (EHA) and butyl acrylate (BA) are particularly preferred.

[0147] From the viewpoint of safety in impact tests, acrylic polymers are preferably polymers that contain EHA or BA as the main constituent units. The main constituent units refer to monomers and corresponding polymer portions that account for 40 mol% or more of the total raw materials for forming the polymer.

[0148] The above 2) conjugated diene polymers and 3) acrylic polymers may also be obtained by copolymerizing them with other monomers that can copolymerize with them. Examples of other copolymerizable monomers that can be used include unsaturated alkyl carboxylates, aromatic vinyl monomers, vinyl cyanide monomers, unsaturated monomers containing hydroxyalkyl groups, unsaturated carboxylic acid amide monomers, crotonic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, etc. These may be used individually or in combination of two or more. Among the above, unsaturated alkyl carboxylate monomers are particularly preferred. Examples of unsaturated alkyl carboxylate monomers include dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, dimethyl itaconate, monomethyl fumarate, monoethyl fumarate, etc. These may be used individually or in combination of two or more.

[0149] Furthermore, the conjugated diene polymer described in 2) above may be obtained by copolymerizing the above (meth)acrylic compound as another monomer.

[0150] The resin binder is preferably in the form of latex, and more preferably an acrylic polymer latex, from the viewpoint of having strong binding force between multiple inorganic particles even at high temperatures exceeding room temperature, and suppressing thermal shrinkage.

[0151] The average particle size of the resin binder is preferably 50 nm to 500 nm, more preferably 60 nm to 460 nm, and even more preferably 80 nm to 250 nm. When the average particle size of the resin binder is 50 nm or more, when a porous layer containing inorganic filler and binder is laminated on at least one side of a polyolefin porous film, ion permeability is less likely to decrease, and high power characteristics are easily obtained. In addition, even when the temperature rises rapidly during abnormal heat generation, it exhibits smooth shutdown characteristics, and high safety is easily obtained. When the average particle size of the resin binder is 500 nm or less, good binding properties are exhibited, and when a multilayer porous film is formed, thermal shrinkage is good, and safety tends to be superior.

[0152] The average particle size of resin binders can be controlled by adjusting the polymerization time, polymerization temperature, raw material composition ratio, raw material input order, pH, and other factors.

[0153] Dispersants such as surfactants may be added to the coating solution to stabilize dispersion or improve coating properties. Dispersants are substances that adsorb to the surface of inorganic particles in the slurry and stabilize the inorganic particles by electrostatic repulsion, etc. Examples include polycarboxylates, sulfonates, and polyoxyethers. The amount of dispersant to be added is preferably 0.2 parts by weight or more and 5.0 parts by weight or less in terms of solid content, and more preferably 0.3 parts by weight or more and 1.0 part by weight or less, per 100 parts by weight of inorganic filler.

[0154] (Physical properties, composition, and formation methods of porous layers) From the perspective of suppressing the coffee-ring phenomenon by suppressing the penetration of the thermoplastic polymer-containing coating liquid into the porous layer or the migration of the thermoplastic polymer into the porous layer, the pore diameter of the porous layer is preferably 0.03 μm or more and 0.40 μm or less, more preferably 0.05 μm or more and 0.25 μm or less, and even more preferably 0.08 μm or more and 0.20 μm or less.

[0155] The thickness of the porous layer is preferably 0.5 μm or more and 5.0 μm or less, more preferably 0.7 μm or more and 4.0 μm or less, even more preferably 1.0 μm or more and 3.0 μm or less, and particularly preferably 1.5 μm or more and 2.0 μm or less. That the thickness of the porous layer is 0.5 μm or more is preferable from the perspective of suppressing deformation at a temperature exceeding the melting point of the porous membrane. That the thickness of the porous layer is 5.0 μm or less is preferable from the perspective of improving the battery capacity or suppressing the moisture adsorption amount of the multilayer porous membrane.

[0156] The layer density in the porous layer is preferably 1.10 g / (m 2 ·μm) or more and 3.00 g / (m 2 ·μm) or less, more preferably 1.20 g / (m 2 ·μm) or more and 2.90 g / (m 2 ·μm) or less, even more preferably 1.40 g / (m 2 ·μm) or more and 2.70 g / (m 2 ·μm) or less, and particularly preferably 1.50 g / (m 2 ·μm) or more and 2.50 g / (m 2 ·μm) or less. That the layer density in the porous layer is 1.10 g / (m 2 ·μm) or more is preferable from the perspective of suppressing deformation at a temperature exceeding the melting point of the PO microporous membrane. That the layer density in the porous layer is 3.00 g / (m 2 ·μm) or less is preferable from the perspective of maintaining the ion permeability of the porous layer and suppressing capacity deterioration during repeated cycles.

[0157] One method for forming a porous layer is to apply a coating solution containing an inorganic filler and a resin binder to at least one side of a porous film mainly composed of a polyolefin resin to form a porous layer.

[0158] The solvent for the coating solution is preferably one that can uniformly and stably disperse the inorganic filler and resin binder, and examples include N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, water, ethanol, toluene, hot xylene, methylene chloride, hexane, etc.

[0159] Various additives such as dispersants including surfactants, thickeners, wetting agents, defoamers, and pH adjusters containing acids and alkalis may be added to the coating solution to improve dispersion stabilization and coating properties. These additives are preferably those that can be removed during solvent removal, but they may remain in the porous layer if they are electrochemically stable within the operating range of lithium-ion secondary batteries, do not inhibit the battery reaction, and are stable up to about 200°C.

[0160] The method for dispersing the inorganic filler and resin binder in the solvent of the coating solution is not particularly limited as long as it can achieve the dispersion characteristics of the coating solution required for the coating process. Examples include ball mills, bead mills, planetary ball mills, vibrating ball mills, sand mills, colloid mills, attritors, roll mills, high-speed impeller dispersion, dispersers, homogenizers, high-speed impact mills, ultrasonic dispersion, and mechanical stirring using stirring blades, etc.

[0161] Regarding the method of applying the coating solution to a microporous film, there are no particular limitations as long as the method can achieve the required layer thickness and coating area. Examples include gravure coater, small-diameter gravure coater, reverse roll coater, transfer roll coater, kiss coater, dip coater, knife coater, air doctor coater, blade coater, rod coater, squeeze coater, cast coater, die coater, screen printing, and spray coating.

[0162] Furthermore, it is preferable to apply a surface treatment to the surface of the microporous membrane, which serves as the separator substrate, prior to applying the coating solution, as this facilitates the application of the coating solution and improves the adhesion between the inorganic filler-containing porous layer and the microporous membrane surface after coating. 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 roughening, solvent treatment, acid treatment, and ultraviolet oxidation.

[0163] Regarding the method for removing the solvent from the coated film after coating, there are no particular limitations as long as it does not adversely affect the microporous film. Examples include drying the film at a temperature below its melting point while fixing the film, or drying it under reduced pressure at a low temperature. From the viewpoint of controlling the shrinkage stress in the MD direction of the porous film and multilayer porous film, it is preferable to adjust the drying temperature, winding tension, etc., as appropriate.

[0164] [Physical properties and composition of separators] From the viewpoint of further suppressing the increase in separator resistance or film thickness, improving liquid injection properties, and thereby improving the performance of the energy storage device, the ratio of the thickness of the thermoplastic polymer-containing layer to the thickness of the substrate, or the ratio of the thickness of the thermoplastic polymer-containing layer to the thickness of the substrate and porous layer, is preferably 0.05 or more and 0.40 or less, more preferably 0.10 or more and 0.40 or less, and even more preferably 0.10 or more and 0.30 or less.

[0165] From the viewpoint of excellent electrolyte pouring performance, resistance to air pockets, and short pouring time, the separator preferably has an electrolyte contact angle of 0° to 20°, more preferably 2° to 18°, and even more preferably 4° to 16°. The electrolyte contact angle is more preferably measured on the surface in which the thermoplastic polymer-containing layer in the separator is formed in a dot-like pattern.

[0166] The lower limit of the thickness of the separator for energy storage devices is preferably 5 μm or more, more preferably 6 μm or more, and the upper limit is preferably 25 μm or less, more preferably 18 μm or less, even more preferably 14 μm or less, and most preferably 13 μm or less. A separator thickness of 5 μm or more is preferable from the viewpoint of ensuring the strength of the separator for energy storage devices. On the other hand, a separator thickness of 25 μm or less is preferable from the viewpoint of obtaining good charge and discharge characteristics.

[0167] The lower limit of the air permeability of the separator for energy storage devices is preferably 10 sec / 100 cm. 3 More comfortably, 20 sec / 100 cm 3 More preferably, 30 sec / 100 cm 3 Most preferably 40 sec / 100 cm 3 The upper limit is preferably 500 sec / 100 cm. 3 More preferably, 300 sec / 100 cm 3 More preferably, 200 sec / 100 cm 3 The following applies: The air permeability of the separator is set to 10 sec / 100 cm. 3 The above is preferable when used as a separator for energy storage devices, from the viewpoint of further suppressing the self-discharge of the energy storage device. On the other hand, the air permeability of the separator is 500 sec / 100 cm. 3 The following is preferable from the viewpoint of obtaining good charge and discharge characteristics. The air permeability of the separator for energy storage devices can be adjusted by changing the stretching temperature and stretching ratio when manufacturing the polyolefin microporous film, the area ratio of the thermoplastic polymer, its form, etc.

[0168] The separator for energy storage devices has a shutdown temperature, which is an indicator of the safety of the energy storage device, preferably 160°C or lower, more preferably 155°C or lower, and even more preferably 150°C or lower. Furthermore, by controlling the composition and structure of the substrate, the shutdown temperature can be reduced to 145°C or lower.

[0169] The separator for energy storage devices preferably has a short-circuit temperature of 140°C or higher, more preferably 150°C or higher, and even more preferably 160°C or higher, which is an indicator of heat resistance. A short-circuit temperature of 140°C or higher is preferable from the viewpoint of safety of the energy storage device when used as a separator for energy storage devices. Furthermore, by controlling the composition and structure of the base material, the short-circuit temperature can be increased to 190°C or higher.

[0170] The lower limit of the basis weight of the separator for energy storage devices is preferably 3.5 g / m². 2 More preferably, 4.5 g / m 2 The above limits apply, with the upper limit preferably being 18 g / m². 2 More preferably, 14 g / m 2 More preferably, 12 g / m 2 The following is most preferably 11 g / m² 2 The following applies: The basis weight of the separator is 3.5 g / m². 2 The above is preferable from the viewpoint of ensuring the strength of the separator for energy storage devices. On the other hand, the basis weight of the separator is 18 g / m 2 The following is preferable from the viewpoint of obtaining good charge and discharge characteristics.

[0171] The lower limit of the puncture strength of the separator for energy storage devices is preferably 200 gf or more, more preferably 300 gf or more, even more preferably 400 gf or more, and most preferably 500 gf or more. A puncture strength of 200 gf or more is preferable from the viewpoint of safety of the energy storage device when used as a separator for energy storage devices. There is no upper limit to the puncture strength, but it can be 800 gf or less from the viewpoint of suppressing shrinkage at high temperatures.

[0172] The upper limit of the thermal shrinkage rate of a separator for energy storage devices at 150°C is preferably 10% or less, more preferably 5% or less, even more preferably 3% or less, and most preferably 2% or less. The lower limit can be 0% if the presence of a porous layer can suppress deformation of the polyolefin microporous film due to heating. A thermal shrinkage rate of 10% or less at 150°C is preferable from the viewpoint of safety of the energy storage device when used as a separator for energy storage devices.

[0173] From the viewpoint of efficiently exhibiting the effects of the present invention, the separator preferably has a multilayer structure in which thermoplastic polymer-containing layers are formed on both sides of the substrate, and more preferably a porous layer containing an inorganic filler and a resin binder is formed between at least one side of the substrate and the thermoplastic polymer-containing layer.

[0174] [Method for manufacturing separators] The method for manufacturing the separator is not particularly limited, and one example is to apply a coating solution containing a thermoplastic polymer onto at least one surface of a substrate such as a polyolefin microporous membrane.

[0175] In another aspect of the present invention, a method for manufacturing a separator, comprising the following steps: The process of preparing the base material, A step of forming a thermoplastic polymer-containing layer by applying a coating solution containing a thermoplastic polymer to at least one surface of the substrate, A method for manufacturing a separator is provided, comprising the above, wherein the coating liquid has a solid content of 6% to 35% by mass of the total coating liquid, preferably 10% to 30% by mass, a viscosity of 10 mPa·s to 100 mPa·s, preferably 25 mPa·s to 80 mPa·s, a surface tension of 10 mN / m to 45 mN / m, preferably 20 mN / m to 40 mN / m, more preferably 25 mN / m to 35 mN / m, and a pH of 6 to 10, preferably 7 to 9.

[0176] The substrates described above may be prepared, and it is preferable to use the polyolefin microporous membrane described above as the substrate. From the viewpoint of controlling the ratio of the region where particulate polymers exist and the region where particulate polymers are stacked in a cross-section passing through the center of the dot-like pattern of the thermoplastic polymer-containing layer described above, and from the viewpoint of controlling the liquid penetration of the thermoplastic polymer-containing coating solution into the substrate, it is preferable to prepare a substrate with an average pore size of 0.15 μm or less.

[0177] The method for applying a coating solution containing a thermoplastic polymer to a porous film is not particularly limited as long as it can achieve the required layer thickness and coating area. Examples include gravure coater, small-diameter gravure coater, reverse roll coater, transfer roll coater, kiss coater, dip coater, knife coater, air doctor coater, blade coater, rod coater, squeeze coater, cast coater, die coater, screen printing, spray coating, spray coater coating, and inkjet coating. Of these, the gravure coater or spray coating method is preferred from the viewpoint of having a high degree of freedom in the coating shape of the thermoplastic polymer and being able to easily obtain a desirable area ratio. Furthermore, from the viewpoint of adjusting the dot-like pattern of the thermoplastic polymer-containing layer as described above, the gravure coater, inkjet coating, and coating methods that allow for easy adjustment of the printing plate are preferred.

[0178] The components of the thermoplastic polymer-containing coating solution may be the components of the thermoplastic polymer-containing layer described above.

[0179] When applying a thermoplastic polymer-containing coating solution to a substrate such as a polyolefin microporous film, from the viewpoint of controlling the ratio of the region where particulate polymers exist and the region where particulate polymers are stacked in a cross-section passing through the center of the dot-like pattern of the thermoplastic polymer-containing layer described above, and from the viewpoint of suppressing coffee ring formation, the number of binder particles per unit volume of the coating droplet should be 5 × 10 8 pcs / μL or more 5×10 9It is preferable to adjust the concentration to less than or equal to 1 / μL.

[0180] If the coating solution penetrates deep into the microporous membrane, the adhesive resin will fill the surface and interior of the pores, reducing permeability. Therefore, a poor solvent such as a thermoplastic polymer is preferred as the medium for the coating solution.

[0181] When a poor solvent of a thermoplastic polymer is used as the medium for the coating solution, the coating solution does not penetrate into the interior of the microporous film, and the adhesive polymer mainly exists on the surface of the microporous film, which is preferable from the viewpoint of suppressing a decrease in permeability. Water is preferred as such a medium. In addition, there are no particular limitations on the medium that can be used in combination with water, but examples include ethanol and methanol.

[0182] From the viewpoint of adjusting the dot-like pattern of the thermoplastic polymer-containing layer as described above, it is preferable to optimize the thermoplastic polymer-containing coating solution (also simply called paint) using the thermoplastic polymer, poor solvent, etc., described above.

[0183] The solid content of the coating is preferably 6% to 35% by mass of the total coating liquid, more preferably 10% to 33% by mass, more preferably 15% to 31% by mass, and even more preferably 30% by mass or less, from the viewpoint of controlling the proportion of the region where particulate polymers exist and the region where particulate polymers are stacked in a cross-section passing through the center of the dot-shaped pattern of the thermoplastic polymer-containing layer described above, and from the viewpoint of suppressing a decrease in the capacity and energy density of the energy storage device including the separator. Furthermore, from the viewpoint of suppressing the coating liquid from flowing and losing its ability to maintain the dot shape, the solid content of the coating is preferably 6% by mass or more.

[0184] The viscosity of the paint at 20°C is 10 mPa·s to 100 mPa·s, preferably 25 mPa·s to 80 mPa·s, from the viewpoint of controlling the proportion of the region where the particulate polymer described above exists and the region where the particulate polymer is layered, as well as from the viewpoint of suppressing the formation of coffee rings.

[0185] The surface tension of the paint is preferably 10 mN / m to 45 mN / m, more preferably 20 mN / m to 40 mN / m, and more preferably 25 mN / m to 35 mN / m, from the viewpoint of controlling the ratio of the region where particulate polymers exist and the region where particulate polymers are stacked in a cross-section passing through the center of the dot-shaped pattern of the thermoplastic polymer-containing layer described above, and from the viewpoint of suppressing the formation of coffee rings. From the viewpoint of suppressing the coating liquid from flowing and losing its ability to maintain the dot shape, the surface tension of the paint is preferably 10 mN / m or more.

[0186] The pH of the paint is 6 to 10, preferably 7 to 9, from the viewpoint of controlling the ratio of the region where the particulate polymer described above is present and the region where the particulate polymer is layered, as well as from the viewpoint of suppressing the formation of a coffee ring.

[0187] Paints are prepared by first creating thermoplastic polymer particles using methods such as emulsion polymerization or suspension polymerization, and then adding thickeners or preservatives. The solid content of the paint is adjusted to the desired concentration by adding a solvent. The viscosity of the paint is adjusted by adding polymers such as xanthan gum, carboxymethylcellulose, or polyacrylamide. The surface tension of the paint can be adjusted by adding cationic, anionic, or nonionic surfactants, for example.

[0188] Average particle size (D) of paint containing particulate polymers of thermoplastic polymers 50 From the viewpoint of controlling the ratio of the region where the particulate polymer described above is present and the region where the particulate polymer is stacked, as well as from the viewpoint of suppressing coffee ring formation, it is preferable that the diameter be adjusted to within the range of 0.10 μm to 0.80 μm.

[0189] Furthermore, surface treatment of the microporous film as a separator substrate prior to coating is preferable because it facilitates the application of the coating solution and improves the adhesion between the microporous film or porous layer and the thermoplastic polymer. The surface treatment method is not particularly limited as long as it does not significantly impair the porous structure of the microporous film, and examples include corona discharge treatment, plasma treatment, mechanical roughening, solvent treatment, acid treatment, and ultraviolet oxidation.

[0190] In the case of corona discharge treatment, the corona treatment intensity of the substrate surface is 1 W / (m²). 2 / min) or more 40W / (m 2 It is preferable that the range is 3W / (m²) or less, and 2 / min) or more 32W / (m 2 It is more preferable that the range be less than or equal to 5W / (m 2 / min) or more 25W / (m 2 It is even more preferable that the corona treatment intensity is within the range of ( / min) or less. Corona treatment intensities within the above range are preferable because they tend to improve the affinity with the electrolyte and improve wettability by introducing hydrophilic groups to the hydrophobic surface, and also allow control of the spread of the coating solution during dot formation. Furthermore, it is also preferable to perform corona discharge treatment after the dot-like pattern of the thermoplastic polymer-containing layer has been formed by coating.

[0191] Regarding the method for removing the solvent from the coated film after coating, there are no particular limitations as long as it does not adversely affect the porous film. For example, methods include drying at a temperature below the melting point while fixing the porous film, drying under reduced pressure at low temperatures, and immersing the adhesive polymer in a poor solvent to solidify the adhesive polymer while simultaneously extracting the solvent.

[0192] The drying rate of the coating film is 0.06 g / (m²). 2 ·s) or more 4.0g / (m 2 It is preferable that it be within the range of 0.10 g / (m 2 ·s) or more 4.0g / (m 2 It is more preferable that it be within the following range: 0.20 g / (m 2·s) or less, more preferably within the range of from 3.0 g / (m 2 ·s) or less. When the drying rate is within the above range, an appropriate drying rate suppresses leveling and can appropriately control the uneven structure of the thermoplastic polymer particles on the dot surface. From the same viewpoint, in drying the coating film, it is also preferable to raise the temperature by heating or the like so as not to impair the particle shape of the thermoplastic polymer-containing layer.

[0193] From the viewpoint of controlling the ratio of the region where the particulate polymer exists and the region where the particulate polymer is laminated as described above, the coating process is such that the basis weight of the thermoplastic polymer-containing layer on at least one side of the substrate is 0.03 g / m 2 ~0.5 g / m 2 It is preferably carried out so as to be.

[0194] The method for producing the separator may further include a step of forming an inorganic particle-containing layer by applying a coating solution containing inorganic particles to the surface of the substrate between the step of preparing the substrate and the step of forming the thermoplastic polymer-containing layer, if desired.

[0195] Since the formed inorganic particle-containing layer can be regarded as the porous layer described above, the components contained in the coating solution containing inorganic particles may be the components of the porous layer described above. Further, as the inorganic particles, the inorganic fillers described above may be used.

[0196] The application of the coating liquid containing inorganic particles onto the surface of the substrate can be carried out in the same manner as the method for forming the porous layer described above. From the perspective of controlling the ratio of the region where the particulate polymer exists and the region where the particulate polymers are laminated in the cross-section passing through the center of the dot pattern of the thermoplastic polymer-containing layer described above, and from the perspective of controlling the liquid penetration of the thermoplastic polymer-containing coating liquid into the inorganic particle-containing layer, the pore diameter of the inorganic particle-containing layer is preferably adjusted to be 0.03 μm or more and 0.4 μm or less, more preferably 0.05 μm or more and 0.25 μm or less, and still more preferably 0.08 μm or more and 0.20 μm or less. Considering the pore diameter of the inorganic particle-containing layer, by adjusting the solid content concentration, viscosity, surface tension, and particulate polymer of the paint containing the particulate polymer of the thermoplastic polymer, the ratio of the region where the particulate polymers are laminated can be controlled.

[0197] In order to uniformly control the height of the region where the particulate polymers are laminated to be more than 1 layer and not more than 3 layers, for example, in addition to adjusting the pore diameter of the inorganic particle-containing layer to be 0.03 μm or more and 0.4 μm or less as described above, for the paint, it is preferable to adjust the physical properties such that the solid content concentration is 9% by mass or more and 30% by mass or less, the viscosity is 25 mPa·s or more and 60 mPa·s or less, the surface tension is 25 mN / m or more and 39 mN / m or less, and the average particle diameter of the particulate polymer is 0.50 μm or more and 0.80 μm or less.

[0198] 〔Laminated body〕 The laminated body provided as another aspect of the present invention is one in which a separator and an electrode are laminated. The separator according to the first and / or second embodiment can be used as a laminated body by adhering to the electrode. The laminated body has excellent handling properties during winding and rate characteristics of the power storage device, and furthermore, also has excellent adhesiveness and permeability between the thermoplastic polymer and the polyolefin microporous membrane. Therefore, the use of the laminated body is not particularly limited, but for example, it can be suitably used for power storage devices such as batteries such as non-aqueous electrolyte secondary batteries, capacitors, and capacitors.

[0199] The electrodes used in the laminate can be those described in the section on energy storage devices below. The method for manufacturing the laminate using separators is not particularly limited, but for example, it can be manufactured by stacking the separator and electrodes and heating and / or pressing as needed. Heating and / or pressing can be done when stacking the electrodes and separators. Alternatively, it can be manufactured by heating and / or pressing a wound body obtained by winding the electrodes and separators into a circular or flat spiral shape after stacking them.

[0200] Furthermore, the laminate can also be manufactured by laminating the positive electrode-separator-negative electrode-separator or negative electrode-separator-positive electrode-separator in a flat plate shape, and heating and / or pressing as necessary. In lamination, from the viewpoint of efficiently exhibiting the effects of the present invention, it is preferable that the side of the separator having the porous layer described above and the positive electrode face each other with respect to the substrate of the separator.

[0201] More specifically, the separator described above can be prepared as a vertically elongated separator with a width of 10 to 500 mm (preferably 80 to 500 mm) and a length of 200 to 4000 m (preferably 1000 to 4000 m), and the separator can be 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 manufacture the product.

[0202] The heating temperature is preferably 40 to 120°C. The heating time is preferably 5 seconds to 30 minutes. The pressing pressure is preferably 1 to 30 MPa. The pressing time is preferably 5 seconds to 30 minutes. The order of heating and pressing is also flexible; heating can be done before pressing, after pressing, or simultaneously. Of these, heating and pressing simultaneously is preferred.

[0203] <Energy storage devices> Separators can be used for separating materials in batteries, capacitors, and other devices. In particular, when used as separators for energy storage devices, they can provide excellent adhesion to electrodes and superior battery performance. The following describes preferred embodiments when the energy storage device is a non-aqueous electrolyte secondary battery.

[0204] When manufacturing a non-aqueous electrolyte secondary battery using the separator according to the first and / or second embodiment, there are no limitations on the positive electrode, negative electrode, or non-aqueous electrolyte; known ones can be used.

[0205] The cathode material is not particularly limited, but examples include lithium-containing composite oxides such as LiCoO2, LiNiO2, spinel-type LiMnO4, and olivine-type LiFePO4.

[0206] The negative electrode material is not particularly limited, but examples include carbon materials such as graphite, non-graphitizable carbon, easily graphitizable carbon, and composite carbon bodies; silicon, tin, metallic lithium, and various alloy materials.

[0207] The non-aqueous electrolyte is not particularly limited, but an electrolyte in which the electrolyte is dissolved in an organic solvent can be used. Examples of organic solvents include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, and examples of electrolytes include lithium salts such as LiClO4, LiBF4, and LiPF6.

[0208] The method for manufacturing an energy storage device using the separator according to the first and / or second embodiment is not particularly limited, but in the case of a secondary battery, for example, the separator described above may be prepared as a vertically elongated separator with a width of 10 to 500 mm (preferably 80 to 500 mm) and a length of 200 to 4000 m (preferably 1000 to 4000 m), the separator may be stacked in the order of positive electrode-separator-negative electrode-separator or negative electrode-separator-positive electrode-separator, wound into a circular or flat spiral to obtain a wound body, the wound body may be placed in a battery case, and then an electrolyte may be injected to manufacture the device.

[0209] In this case, the laminate described above may be formed by heating and / or pressing the wound body. Alternatively, the laminate described above may be wound in a circular or flat spiral shape as the wound body. Furthermore, the energy storage device may be manufactured by laminating a positive electrode-separator-negative electrode-separator or negative electrode-separator-positive electrode-separator in a flat plate shape, or by laminating the above laminate with a bag-shaped film, injecting an electrolyte, and optionally performing a heating and / or pressing step. The heating and / or pressing step described above can be performed before and / or after the electrolyte injection step.

[0210] In an energy storage device comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, it is preferable that the separator be arranged such that the side having the porous layer described above faces the positive electrode, with respect to the substrate, in order to efficiently exert the effects of the present invention.

[0211] Unless otherwise specified, the measured values ​​of the various parameters mentioned above are those measured in accordance with the measurement methods described in the examples below. [Examples]

[0212] Hereinafter, the present invention will be described in detail based on examples and comparative examples, but the present invention is not limited to the examples. The measurement methods and evaluation methods for various physical properties used in the following production examples, examples, and comparative examples are as follows. Unless otherwise specified, various measurements and evaluations were carried out under the conditions of room temperature of 23°C, 1 atmospheric pressure, and relative humidity of 50%.

[0213] [Measurement method] <Viscosity average molecular weight (hereinafter also referred to as "Mv")> Based on ASRM-D4020, the intrinsic viscosity [η] at 135°C in a decalin solvent was determined, and the Mv of polyethylene was calculated by the following formula. [η]=0.00068×Mv 0.67 Also, the Mv of polypropylene was calculated from the following formula. [η]=1.10×10 -4 Mv 0.80

[0214] <Average particle size of thermoplastic polymer> The average particle size of the thermoplastic polymer was measured using a particle size measuring device (Microtrac MT3300EXII, manufactured by Nikkiso Co., Ltd.). An aqueous dispersion of thermoplastic polymer particles was prepared (solid content concentration: 25 to 30%). As the measurement conditions, the loading index = 0.15 to 0.3 and the measurement time = 300 seconds. In the obtained data, the numerical value of the particle size at which the cumulative frequency is 50% was taken as the average particle size (μm) and is described in Tables 1-1 to 1-3 below. In addition, the average particle size of the thermoplastic polymer may be calculated by measuring the particle sizes of 100 different thermoplastic polymer particles when observed at a magnification at which the diameter of one particle can be measured (for example, 10,000 times when the thermoplastic polymer is about 0.5 μm) using a scanning electron microscope (SEM) (model: S-4800, manufactured by HITACHI).

[0215] <Areal density of polyolefin microporous membrane and areal density per side of thermoplastic polymer-containing layer> A 10cm x 10cm square sample was cut from the substrate (polyolefin porous substrate or polyolefin porous substrate + inorganic filler porous layer), and its weight was measured using an electronic balance AEL-200 manufactured by Shimadzu Corporation. Multiplying the obtained weight by 100 gives 1 m 2 Weight of film per unit (g / m²) 2 ) was calculated. A 10cm x 10cm square sample was cut from a separator with a thermoplastic polymer-containing layer formed on the base material, and its weight was measured using an electronic balance AEL-200. Multiplying the obtained weight by 100 gives 1 m 2 Weight per separator (g / m²) 2 ) was calculated. The basis weight per side of the thermoplastic polymer-containing layer was calculated from the difference in basis weight between the substrate and the separator. When forming a porous layer between the substrate surface and the thermoplastic polymer-containing layer, the weight before and after the formation of the porous layer can be measured in the manner described above, and the basis weight of the porous layer can be calculated from the weight difference before and after. Furthermore, the basis weight of the thermoplastic polymer-containing layer can be calculated from the weight measurements before and after the formation of the thermoplastic polymer-containing layer. Alternatively, the basis weight per side of the thermoplastic polymer-containing layer may be calculated by peeling the layer off a 10cm x 10cm square sample surface and determining the weight loss rate using a thermogravimetric differential thermal analyzer (NEXTA STA 200RV, Hitachi High-Tech Science Corporation). The workability of peeling off the thermoplastic polymer-containing layer can be improved by pre-treating it with a solvent such as acetone or ethanol to induce swelling.

[0216] <Porosity (%) of polyolefin microporous membranes> A 10cm x 10cm square sample is cut from the polyolefin microporous membrane, its volume (cm³) and mass (g) are determined, and the membrane density is calculated to be 0.95 (g / cm³). 3 The calculation was performed using the following formula. Porosity = (Volume - Mass / Membrane Density) / Volume × 100

[0217] <Film thickness (μm)> Using the "KBM™" microthickness gauge manufactured by Toyo Seiki Co., Ltd., the thickness of polyolefin microporous films, films coated with porous layers on both sides, and films coated with a porous layer on only one side were measured at room temperature (23±2℃), and the thickness of the porous layer was calculated from these thicknesses. In addition, for films containing thermoplastic polymer layers, the thickness of each layer was measured using cross-sectional SEM images.

[0218] <Air permeability (sec / 100cm 3 )> In accordance with JIS P-8117, the air permeability was defined as the air permeability resistance measured using a Gurley-type air permeability meter G-B2 (trademark) manufactured by Toyo Seiki Co., Ltd.

[0219] <Puncture strength (gf) of polyolefin microporous membranes> A polyolefin microporous membrane was fixed using a Kato Tech KES-G5 (trademark) handy compression tester with a sample holder having an opening diameter of 11.3 mm. Next, a puncture test was performed on the central part of the fixed polyolefin microporous membrane at a 25°C atmosphere with a needle tip radius of curvature of 0.5 mm and a puncture speed of 2 mm / sec, to obtain the puncture strength (gf) as the maximum puncture load. Furthermore, the puncture strength converted to basis weight can also be calculated from the puncture strength and basis weight.

[0220] <Glass transition temperature of thermoplastic polymers (°C)> A suitable amount of thermoplastic polymer coating solution (non-volatile content = 30%) was placed in an aluminum dish and dried in a hot air dryer at 130°C for 30 minutes. Approximately 5 mg of the dried film was placed in an aluminum container for measurement, and DSC and DDSC curves under a nitrogen atmosphere were obtained using a DSC analyzer (TA Instruments, DSC Q2000). The measurement conditions were as follows. (First stage heating program) Start at 40°C and increase the temperature at a rate of 50°C per minute. Once it reaches 200°C, maintain that temperature for 5 minutes. (Second stage cooling program) The temperature is reduced from 200°C at a rate of 20°C per minute. After reaching -50°C, it is maintained at that temperature for 5 minutes. (3rd stage heating program) The temperature was increased from -50°C to 200°C at a rate of 20°C per minute. DSC and DDSC data were acquired during this third stage of temperature increase. According to the method described in JIS-K7121, the glass transition temperature (Tg) was defined as the intersection point of the baseline (a straight line extending the baseline in the obtained DSC curve toward the higher temperature side) and the tangent line at the inflection point (the point where the curve, which is convex upwards, changes to a curve, which is convex downwards).

[0221] <Total coverage area ratio of thermoplastic polymer-containing layer relative to the substrate surface (%)> The total coverage area ratio of the thermoplastic polymer-containing layer coating pattern on the substrate surface was measured using a microscope (model: VHX-7000, manufactured by Keyence Corporation). The separator sample was photographed using coaxial reflected light at a magnification that allowed for simultaneous observation of 10 or more dots (for example, 100x magnification for dots with a diameter of approximately 200 μm). From the command "Measurement / Scale," select "Automatic Area Measurement (Particle Count)," "Extraction Method Brightness (Standard)," and "Fill Holes." Select an appropriate brightness (preferably between -10 and 10) to binarize the covered and uncoated areas of the thermoplastic polymer-containing layer, and measure the total coverage area ratio of the thermoplastic polymer-containing layer. If the contrast is unclear, another light source (model: PD2-1024, manufactured by CCS Corporation) may be used.

[0222] <Cross-sectional observation> The separator sample is cross-sectionally processed using a broad ion beam (BIB). The cross-sectional processing is performed using a Hitachi High-Tech IM4000 with argon beam, an acceleration voltage of 3kV, and a beam current of 25-35μA. To suppress thermal damage during processing, the multilayer porous film is cooled as needed until immediately before processing. Specifically, the multilayer porous film is left overnight in a -40°C cooling device. This results in a smooth cross-section of the separator.

[0223] (Measurement of the layering ratio of thermoplastic polymer-containing layers) The stacking ratio of the thermoplastic polymer-containing layer was measured using a scanning electron microscope (SEM) (model: S-4800, manufactured by Hitachi). A smooth separator cross-section was vapor-deposited with osmium, and under conditions of an acceleration voltage of 1.0 kV and 5000x magnification, the cross-section of one dot was observed over the entire diameter of the dot, and the ratio of the region where n (n≧1) layers of particulate polymer of the thermoplastic polymer were stacked to the region where one or more thermoplastic polymer-containing layers were present was calculated.

[0224] (Height measurement of the thermoplastic polymer-containing layer) The height of the thermoplastic polymer-containing layer was measured using a scanning electron microscope (SEM) (model: S-4800, manufactured by Hitachi). A smooth separator cross-section was coated with osmium vapor deposition and observed under conditions of an acceleration voltage of 1.0 kV and 5000x magnification. The maximum thickness of the thermoplastic polymer-containing layer was measured at five points, and the average of these measurements was calculated as the height.

[0225] (Other observations and measurements) Similarly to the above, the presence or absence of an inorganic porous layer containing inorganic filler and resin binder may be observed in a smooth separator cross-section, and the average or maximum thickness (i.e., average or maximum height) of the substrate, the average or maximum thickness (i.e., average or maximum height) of the inorganic porous layer, the maximum height of the dots on one side of the separator, and the sum or difference of the maximum heights of the dots on both sides of the separator may be calculated. In the case of average thickness, the thickness was observed randomly in 3 to 5 fields of view of the smooth separator cross-section, and the average value of these was calculated as the average height. In the case of a dot pattern, the distance from the substrate surface to the top of the dot along the thickness direction of the thermoplastic polymer-containing layer was taken as the maximum dot thickness, and the average dot height was calculated in the same way as above.

[0226] <Average pore size of porous layer> After obtaining a smooth separator cross-section using the above cross-sectional observation method, the mode diameter obtained by image processing using the method described in International Publication No. 2021 / 006357 was taken as the average pore diameter of the porous layer.

[0227] <Characteristics of coating solutions containing thermoplastic polymers> For the thermoplastic polymer-containing coating solution, the viscosity was measured at 20°C using a B-type viscometer, and the pH was measured using a pH meter.

[0228] <Adhesion to electrodes> The separators for energy storage devices obtained in each example and comparative example, and the positive electrode used as the substrate (manufactured by enertech, positive electrode material: LiCoO2, conductive additive: acetylene black, L / W: 36 mg / cm² on both sides) 2 The aluminum current collector (thickness: 15 μm) and the positive electrode (thickness after pressing: 120 μm) were cut into rectangular shapes with a width of 15 mm and a length of 60 mm, respectively. A laminate was obtained by stacking these pieces so that the thermoplastic polymer-containing layer of the separator and the positive electrode active material were facing each other, and then the laminate was pressed under the following conditions. Press pressure: 1 MPa Temperature: 100℃ Press time: 30 seconds For the pressed laminate, a 90° peel test was performed at a peeling speed of 50 mm / min using force gauges ZP5N and MX2-500N (product name) manufactured by IMADA Corporation. The electrodes were fixed, and the separator was gripped and pulled to measure the peel strength. At this time, the average value of the peel strength in the peel test over a length of 40 mm performed under the above conditions was adopted as the adhesive strength to the electrode. When a separator achieving an adhesive strength of 1.0 N / m or more and 10.0 N / m or less obtained by this method is used in an energy storage device, the adhesive strength to the opposing positive and negative electrodes will be good. A porous layer may or may not exist between the thermoplastic polymer layer and the polyolefin microporous membrane facing the positive electrode. In the examples and comparative examples, measurements were taken by stacking the materials so that the side with a porous layer between the thermoplastic polymer layer and the polyolefin microporous membrane faced the positive electrode. It is preferable that the adhesive strength between at least one surface of the separator and the positive electrode satisfies the above value, and it is more preferable that the adhesive strength between the other surface and the positive electrode also satisfies the above range.

[0229] <Pouring properties of electrolyte> The separators for energy storage devices obtained in each example and comparative example, and the negative electrode as the substrate (manufactured by enertech, negative electrode material: graphite, conductive additive: acetylene black, L / W: 20 mg / cm³ on both sides) 2 A rectangular shape with a width of 15 mm and a length of 60 mm was cut from the Cu current collector (thickness: 10 μm, thickness of the negative electrode after pressing: 140 μm), and a laminate was obtained by stacking them so that the thermoplastic polymer-containing layer of the separator and the negative electrode active material faced each other. The laminate was sandwiched between two glass plates (Matsunami Glass Co., Ltd., S1214, size: 76 × 26 mm, thickness: 1.2~1.5 mm), and fixed in three places (both sides and the top) with clips (KOKUYO Co., Ltd., JB34c, double clip (medium), silver, jaw width 25 mm), and immersed in an electrolyte (Kishida Chemical Co., Ltd., LBG-00307, ​​ethylene carbonate (EC): diethyl carbonate (DEC) = (2:3 volume / volume %)). The parts of the separator and electrode surface where the electrolyte had penetrated were visually observed, and the time required for the electrolyte to penetrate the entire surface was adopted as the time required for the electrolyte to be completed. Energy storage devices using separators obtained by this method that achieve a penetration completion time of 8 minutes or less, preferably 6 minutes or less, exhibit good electrolyte penetration at the interfaces with opposing positive and negative electrodes, improving the overall liquid injection performance of the cell. Therefore, the liquid injection performance was evaluated according to the following criteria. [Evaluation Criteria] A (Excellent): Infusion completion time is 6 minutes or less. B (Good): Injection completion time is more than 6 minutes and less than 8 minutes. C (Poor): Injection completion time is more than 8 minutes but less than 10 minutes. D (Severely Poor): Injection completion time is 10 minutes or more.

[0230] <Cycle Characteristics> a. Fabrication of the positive electrode A slurry is prepared by dispersing 91% by mass of lithium-nickel-cobalt-manganese composite oxide (NCM111) as the positive electrode active material, 2.5% by mass each of flake graphite and carbon black as conductive additives, and 4% by mass of polyvinylidene fluoride (PVDF) as a binder in N-methylpyrrolidone (NMP). This slurry is applied to one side of a 15 μm thick aluminum foil, which will serve as the positive electrode current collector, using a die coater. After drying at 120°C for approximately 4 minutes, it is compressed and molded using a roll press. At this time, the amount of active material applied to one side of the positive electrode is 15.9 mg / cm². 2 The electrode density is approximately 2.4 g / cm³. 3 Ensure that the positive electrode has an area of ​​2.00 cm². 2 It was punched out in a circular shape.

[0231] b. Fabrication of the negative electrode A slurry is prepared by dispersing 96.4% by mass of artificial graphite as the negative electrode active material and 1.7% by mass of carboxymethylcellulose and 1.9% by mass of styrene-butadiene copolymer latex as binders in purified water. This slurry is applied to one side of a 10 μm thick copper foil, which will serve as the negative electrode current collector, using a die coater. After drying at 90°C for approximately 4 minutes, it is compressed and molded using a roll press. At this time, the amount of active material applied to the negative electrode is 8.3 mg / cm². 2 The electrode density is 1.25 g / cm³. 3 The fabricated negative electrode has an area of ​​2.05 cm². 2 It was punched out in a circular shape.

[0232] c. Non-aqueous electrolyte A mixture of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1:2 was used to dissolve LiPF6 as a solute to a concentration of 1.0 mol / L, and 1% by mass of vinylene carbonate was added as an additive to prepare the solution.

[0233] d. Battery assembly and evaluation The positive and negative electrodes are stacked vertically from bottom to top in the order of negative electrode, separator, and positive electrode, with the active material surfaces of the positive and negative electrodes facing each other, and placed in a stainless steel container with a lid. The container and lid are insulated from each other, 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. The non-aqueous electrolyte prepared in c. above is poured into this container and sealed.

[0234] The simple battery assembled as described above was charged to a voltage of 4.2V at a current of 0.24mA (approximately 0.05C) in a 25°C atmosphere. Then, while maintaining the voltage at 4.2V, the current was gradually reduced from 0.24mA until it reached 0.03mA, at which point charging was considered complete, thus completing the first charge after the battery was made. The battery was then discharged to a voltage of 3.0V at a current of 0.96mA (approximately 0.2C) to perform the initial charge and discharge.

[0235] Next, under a 45°C atmosphere, the battery was charged to a voltage of 4.2V with a current of 4.8mA (approximately 1.0C), and then the current was gradually reduced from 4.8mA to maintain the voltage at 4.2V. Charging was considered complete when the current was reduced to 0.03mA, and then the battery was discharged to a voltage of 3.0V with a current of 4.8mA. This cycle was repeated. This constituted one cycle, and the charge and discharge of the simple battery was repeated. The cycle characteristics were then evaluated using the capacity retention rate after 300 cycles relative to the initial capacity of the simple battery (capacity in the first cycle), according to the following criteria. [Evaluation Criteria] A (Excellent): Volume retention rate of 65% or more B (Good): Volume retention rate of 60% or more but less than 65% C (Poor): Volume retention rate between 55% and less than 60% D (Severely Poor): Volume retention rate less than 55%

[0236] <Measuring the contact angle of the electrolyte> A glass plate (Matsunami Glass Co., Ltd., S1214, size: 76 x 26 mm, thickness: 1.2-1.5 mm) was attached to the opposite side of the separator for energy storage devices obtained in each example and comparative example using double-sided tape (Nichiban Co., Ltd., Nicetack, NW-15) to prepare a sample for measurement. Using a dynamic contact angle meter (Kyowa Interface Science Co., Ltd., model DCA-VM), an electrolyte (Kishida Chemical Co., Ltd., LBG-00307, ​​EC / DEC (2:3 v / v %)) was applied, and the contact angle was taken at 6000 ms from the liquid separation point. The contact angle was measured in a constant temperature room under conditions of 23°C and 42% humidity.

[0237] <Measurement of swelling degree> The material used for the uniform diffusion layer was vacuum-dried at a temperature below its melting point for 12 hours to completely remove the solvent and obtain a dried uniform diffusion layer material. Approximately 0.5 g of the obtained dried material was weighed, and the mass before immersion (W) was determined. A The dried material was placed in a 50 mL vial with 10 g of an electrolyte solution containing 1 mol / L LiPF6 at 25°C in a ratio of ethylene carbonate (EC):diethyl carbonate (DEC) = 1:2 (volume ratio), and immersed for 72 hours. After that, the sample was removed, wiped with a paper towel, and its mass was measured immediately. The mass after immersion (W) was then measured. B ) The degree of electrolyte swelling in the uniform diffusion layer was calculated using the following formula. Swelling degree (%) = W B / W A ×100 In the above formula, if the material of the uniform diffusion layer neither swells nor dissolves in the electrolyte, the degree of swelling is 100%.

[0238] <Measuring surface tension> Using a bubble pressure dynamic surface tensimeter (KRUSS BP100), the surface tension of the paint was measured using a 0.300-0.380 mm diameter capillary after filling a dedicated glass cell with paint. The surface tension was calculated using the maximum bubble pressure method. The surface tension value measured 10 seconds (s) after the start of measurement was defined as the surface tension value.

[0239] <Heat shrinkage rate at 150℃ (%)> As a sample, a porous membrane or multilayer porous membrane was cut to a length of 100 mm in the MD direction and 100 mm in the TD direction, and left standing in a 150°C oven for 1 hour. During this time, the sample was sandwiched between 10 sheets of paper to prevent direct contact with the hot air. After removing the sample from the oven and allowing it to cool, its length (mm) was measured, and the thermal shrinkage rate was calculated using the following formula. Measurements were taken in both the MD and TD directions, and the larger value was used as the thermal shrinkage rate. Thermal shrinkage rate (%) = {(100 - length after heating) / 100} × 100

[0240] <Thermoplastic polymer> The following thermoplastic polymers were prepared. • Acrylic 1 A latex blend (acrylic 1, average particle size: 0.55 μm, 6x swelling) was formed by blending high Tg (Tg=95℃) acrylic latex with low Tg (Tg<20℃) acrylic latex. • Acrylic 2 A latex blend (acrylic 2, average particle size: 0.50 μm, swelling degree 8 times) was formed by blending high Tg (Tg=67℃) acrylic latex with low Tg (Tg<20℃) acrylic latex. • Acrylic 3 A latex blend (acrylic 3, average particle size: 0.50 μm, 6x swelling) was formed by blending high-Tg (Tg=95℃) acrylic latex with low-Tg (Tg<20℃) acrylic latex. • Acrylic 4 A latex blend (acrylic 4, average particle size: 0.40 μm, 6x swelling) was formed by blending high Tg (Tg=95℃) acrylic latex with low Tg (Tg<20℃) acrylic latex. PVDF We prepared commercially available polyvinylidene fluoride (PVDF-HFP copolymer, Tm=150℃, average particle size: 0.20 μm).

[0241] <Example 1> (Manufacturing of polyolefin microporous membrane 1A) 47 parts by mass of homopolymer high-density polyethylene with an Mv of 700,000, 46 parts by mass of homopolymer high-density polyethylene with an Mv of 300,000, and 7 parts by mass of homopolymer polypropylene with 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 was added to 99 parts by mass of the resulting polyolefin mixture as an antioxidant, and the mixture was dry-blended again using a tumbler blender to obtain the final mixture. The resulting mixture was fed to a twin-screw extruder via a feeder under a nitrogen atmosphere. Furthermore, liquid paraffin (kinematic viscosity at 37.78°C: 7.59 × 10⁻⁶) was used. -5 m 2 The mixture ( / s) was injected into the extruder cylinder using a plunger pump. The operating conditions of the feeder and pump were adjusted so that the proportion of liquid paraffin in the total mixture extruded was 68 parts by mass, i.e., the polymer concentration was 32 parts by mass.

[0242] Next, these materials were melt-kneaded in a twin-screw extruder while being heated to 160°C. The resulting molten mixture was extruded through a T-die onto a cooling roll with a controlled surface temperature of 80°C. The extruded material was then brought into contact with the cooling roll for molding (casting) and cooled and solidified to obtain a sheet-like molded product. This sheet was stretched in a simultaneous twin-screw stretcher at a magnification of 7 × 6.4 times and a temperature of 122°C. After immersion in methylene chloride to extract and remove liquid paraffin, it was dried and stretched 1.85 times in the transverse direction at a temperature of 132°C in a tenter stretcher. Subsequently, this stretched sheet was relaxed by approximately 10% in the width direction and heat-treated to obtain a polyolefin microporous membrane 1A.

[0243] The physical properties (basis weight, film thickness, porosity, air permeability, puncture strength, etc.) of the obtained polyolefin microporous membrane 1A were measured as needed using the method described above. The physical properties of the polyolefin microporous membrane 1A that can be used as a substrate are shown in Table 2.

[0244] (Manufacturing of polyolefin microporous membrane 2A) 65 parts by mass of homopolymer high-density polyethylene with an Mv of 900,000 and 35 parts by mass of homopolymer high-density polyethylene with an Mv of 300,000 were dry-blended using a tumbler blender. 1 part by mass of tetrakis-[methylene-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane was added to 99 parts by mass of the resulting polyolefin mixture as an antioxidant, and the mixture was dry-blended again using a tumbler blender to obtain the final mixture. The resulting mixture was fed to a twin-screw extruder via a feeder under a nitrogen atmosphere. Furthermore, liquid paraffin (kinematic viscosity at 37.78°C: 7.59 × 10⁻⁶) was used. -5 m 2 The mixture ( / s) was injected into the extruder cylinder using a plunger pump. The operating conditions of the feeder and pump were adjusted so that the proportion of liquid paraffin in the total mixture extruded was 70 parts by mass, i.e., the polymer concentration was 30 parts by mass.

[0245] Next, these materials were melt-kneaded in a twin-screw extruder while being heated to 160°C. The resulting molten mixture was extruded through a T-die onto a cooling roll with a surface temperature controlled to 80°C. The extruded material was then brought into contact with the cooling roll for molding (casting) and cooled and solidified to obtain a sheet-like molded product. This sheet was stretched in a simultaneous twin-screw stretcher at a magnification of 7 × 6.4 times and a temperature of 120°C. After that, it was immersed in methylene chloride to extract and remove the liquid paraffin, dried, and then stretched 2.0 times in the transverse direction at a temperature of 132°C in a tenter stretcher. Subsequently, this stretched sheet was relaxed by approximately 15% in the width direction and heat-treated to obtain a polyolefin microporous membrane 2A.

[0246] The physical properties (basis weight, film thickness, porosity, air permeability, puncture resistance, etc.) of the obtained polyolefin microporous membrane 2A were measured as needed using the method described above. The physical properties of the polyolefin microporous membrane 2A that can be used as a substrate are shown in Table 2.

[0247] Formation of a porous layer As a coating solution for forming a porous layer on the surface of polyolefin microporous film 1A, aluminum hydroxide oxide (boehmite, block-shaped; D) is used as an inorganic filler. 50 100 parts by mass of (0.4 μm), 100 parts by mass of water, and 0.5 parts by mass of dispersant 1 (sodium polyacrylate; weight-average molecular weight 6,000; less than 1.0% by mass of insoluble matter when 1.0 g is dissolved in 100 g of water) were mixed and subjected to bead milling. The bead milling was performed under the conditions of a bead diameter of 0.1 mm and a rotation speed of 2000 rpm in the mill. Acrylic latex 1 (a copolymer having 80% by mass of units derived from butyl acrylate, 16% by mass of units derived from methyl methacrylate, 3% by mass of units derived from acrylic acid, and 1% by mass of units derived from acrylamide; D) was added to the mixed solution as a non-water-soluble binder. 50 A coating solution was prepared by mixing 4 parts by mass of (150 nm, Tg=-28℃), 0.5 parts by mass of water-soluble binder 1 (carboxymethylcellulose sodium; weight-average molecular weight 360,000; degree of etherification = 0.9; insoluble matter less than 1.0% by mass when 1.0 g is dissolved in 100 g of water), and 0.1 parts by mass of additive 1 (polyoxyethylene alkylene alkyl ether (Emulgen LS-110 manufactured by Kao Corporation)).

[0248] On one surface of the polyolefin microporous membrane 1A, a treatment intensity of 15 W / (m²) was applied. 2 Corona discharge treatment was performed at 1 / min. A coating solution was applied to the treated surface using a gravure coater. Subsequently, the coating solution on the polyolefin microporous film 1A was dried at 60°C to remove water, forming a porous layer with a thickness of 1.5 μm on one side of the polyolefin microporous film 1A, obtaining a separator with a porous layer on one side. If necessary, a similar layer was also formed on the other side to obtain a separator with porous layers on both sides. Furthermore, a porous layer can be formed on one or both sides of the polyolefin microporous membrane 2A using the same method as described above.

[0249] (Dot coating of thermoplastic polymer-containing layers onto polyolefin microporous films) Under the conditions of the inorganic filler-containing coating solution shown in Table 1, porous layers were formed on both sides of a polyolefin microporous film (2A). Acrylic 1 was then dot-coated onto one or both surfaces of the film under the conditions of the dot pattern, coverage area ratio, basis weight, layering ratio, and maximum height shown in Table 1. The film was dried at 40°C to remove water from the coating solution, yielding a separator for energy storage devices having a thermoplastic polymer-containing layer in a dot pattern on one or both sides. The dot diameter of the dot pattern was 220 μm, and the dot-to-dot distance was 180 μm. The obtained separator and a simple battery containing it were evaluated using the method described above. Physical properties (basis weight, film thickness, air permeability, puncture strength, etc.) were also measured using the method described above as needed. The results are also shown in Table 1.

[0250] <Examples 2-13, Comparative Examples 1-6> As shown in Table 1, separators for energy storage devices having a thermoplastic polymer-containing layer on one or both sides of a polyolefin microporous film were obtained in the same manner as in Example 1, except that conditions such as the substrate type, the presence or absence of a porous layer on one or both sides of the substrate, the inorganic filler-containing coating solution, the thickness of the porous layer, the thermoplastic polymer type, the presence or absence of dot coating, the dot pattern, the coverage area ratio, the basis weight, the lamination ratio, and the maximum height were changed. The obtained separators and simple batteries containing them were evaluated using the method described above. The results obtained are also shown in Table 1. In Example 12, there was a portion of the thermoplastic polymer-containing layer on the separator surface that was partially continuous in the MD direction, but the liquid pouring properties were good.

[0251] In Examples 2, 8, and 10, a porous layer containing inorganic particles and a resin binder was formed on one side of a polyolefin microporous film (2A, 1A, and 1A, respectively), and thermoplastic polymer-containing layers were coated on both sides of it in a dot pattern under the conditions shown in Table 1 to obtain a separator having an asymmetrical multilayer structure relative to the microporous film.

[0252] [Table 1-1]

[0253] [Table 1-2]

[0254] [Table 1-3]

[0255] [Table 2] [Explanation of Symbols]

[0256] 1 Separator 2 Particulate polymer 3 Base material 4 Particle scattering section L Observation length X Number of layers of particulate polymer a. Dot diameter b. Distance between dots

Claims

1. A separator for an energy storage device comprising a base material and a thermoplastic polymer-containing layer formed on at least one surface of the base material and containing a thermoplastic polymer, The thermoplastic polymer includes particulate polymer, The thermoplastic polymer-containing layer has a dot-like pattern, In a cross-section passing through the center of the dot-shaped pattern, the ratio of the region where the particulate polymer is stacked in five or more layers to the region where the particulate polymer is stacked in one or more layers (R Ｘ＞５／Ｘ≧１ A separator for energy storage devices, in which the ratio is 30% or less.

2. A separator for an energy storage device comprising a base material and a thermoplastic polymer-containing layer formed on at least one surface of the base material and containing a thermoplastic polymer, The thermoplastic polymer includes particulate polymer, The thermoplastic polymer-containing layer has a dot-like pattern, In a cross-section passing through the center of the dot-shaped pattern, the ratio (R) of the region where the particulate polymer is stacked in layers greater than one and three or fewer layers to the region where one or more layers of the particulate polymer are present. １＜Ｘ≦３／Ｘ≧１ A separator for energy storage devices, wherein the ratio is between 40% and 100%.

3. In a cross-section passing through the center of the dot-shaped pattern, the ratio of the region where one layer of particulate polymer is stacked to the region where one or more layers of particulate polymer are present (R ０＜Ｘ≦１（Ｘ＝１）／Ｘ≧１ A separator for an energy storage device according to claim 1 or 2, wherein the ratio of ) is 50% or less.

4. In a cross-section passing through the center of the dot-shaped pattern, the ratio (R) of the region where the particulate polymer is stacked in layers higher than one and two or fewer layers to the region where one or more layers of the particulate polymer are present. １＜Ｘ≦２／Ｘ≧１ Let A be the region where one or more layers of particulate polymer are present, and the ratio of the region where one layer of particulate polymer is stacked to the region where one or more layers of particulate polymer are present (R ０＜Ｘ≦１（Ｘ＝１）／Ｘ≧１ When B is the ratio of A to B, (R ０＜Ｘ≦１（Ｘ＝１）／Ｘ≧１ / R １＜Ｘ≦２／Ｘ≧１ A separator for an energy storage device according to claim 1 or 2, wherein the value of ) is 0 or more and 1 or less.

5. In a cross-section passing through the center of the dot-shaped pattern, the ratio (R) of the region where the particulate polymer is stacked in layers higher than n layers (n+1) or less to the region where one or more layers of the particulate polymer exist is ｎ＜Ｘ≦ｎ＋１／Ｘ≧１ Regarding ), see the following formula: (R １＜Ｘ≦２／Ｘ≧１ )≧(R ０＜Ｘ≦１（ｘ＝１）／Ｘ≧１ )≧(R ２＜Ｘ≦３／Ｘ≧１ )≧(R ｎ＜Ｘ≦ｎ＋１／Ｘ≧１ ) {In the formula, n is an integer greater than or equal to 3} A separator for an energy storage device according to claim 1 or 2, wherein the above holds true.

6. The separator for an energy storage device according to claim 1 or 2, wherein the average particle size of the particulate polymer is 0.10 μm or more and 0.80 μm or less.

7. The separator for an energy storage device according to claim 1 or 2, wherein the thermoplastic polymer has at least two glass transition temperatures, at least one of which is in the region of less than 20°C, and at least one of which is in the region of 40°C or more and 110°C or less.

8. The separator for an energy storage device according to claim 1 or 2, wherein the total coverage area ratio of the thermoplastic polymer to the surface of the substrate on at least one side is 3% or more and 60% or less.

9. The basis weight of the thermoplastic polymer-containing layer on at least one side is 0.03 g / m². ２ ~0.5 g / m ２ A separator for an energy storage device according to claim 1 or 2.

10. A separator for an energy storage device according to claim 1 or 2, wherein a porous layer containing an inorganic filler and a resin binder is formed between at least one side of the substrate and the thermoplastic polymer-containing layer.

11. The separator for an energy storage device according to claim 10, wherein the pore diameter of the porous layer is 0.03 μm or more and 0.40 μm or less.

12. The separator for an energy storage device according to claim 10, wherein the thickness of the substrate or the ratio of the thickness of the thermoplastic polymer-containing layer to the thickness of the substrate and the porous layer is 0.10 or more and 0.40 or less.

13. A separator for an energy storage device according to claim 10, wherein the thermoplastic polymer-containing layer is provided on both sides of the substrate, the sum of the maximum heights of the dots on both sides is 0.2 μm or more and 4.5 μm or less, and the difference in the maximum heights of the dots on both sides is greater than 0.0 μm and 1.0 μm or less.

14. A method for manufacturing a separator for an energy storage device according to claim 1 or 2, The process of preparing the base material, The process includes the step of forming a thermoplastic polymer-containing layer by applying a coating solution containing a thermoplastic polymer to at least one surface of the substrate. The coating liquid has a solid content of 6% to 35% by mass of the total coating liquid, a viscosity of 10 mPa·s to 100 mPa·s, a surface tension of 20 mN / m to 45 mN / m, and a pH of 6 to 10. A method for manufacturing separators for energy storage devices.

15. Between the step of preparing the substrate and the step of forming the thermoplastic polymer-containing layer, The invention further comprises the step of forming an inorganic particle-containing layer by applying a coating solution containing inorganic particles to the surface of the substrate. A method for manufacturing a separator for an energy storage device according to claim 14.

16. An energy storage device comprising a positive electrode, a negative electrode, a separator for an energy storage device according to claim 10, and a non-aqueous electrolyte, wherein the separator for the energy storage device is arranged such that the side having the porous layer and the positive electrode face each other with respect to the substrate.

Images