Slurry composition for functional layer, separator and method for producing same, and nonaqueous secondary battery

Abstract

Provided is provided a slurry composition for a functional layer containing a filler, wherein a transfer rate measured in a transfer rate measurement test is 10% to 100%.

Description

Slurry composition for functional layer, separator and method for producing the same, and non-aqueous secondary battery

[0001] The present invention relates to a slurry composition for a functional layer, a separator and a method for producing the same, and a nonaqueous secondary battery.

[0002] A non-aqueous secondary battery generally includes a separator that separates a positive electrode from a negative electrode to prevent short circuits between the positive electrode and the negative electrode. Conventionally, a separator has been used that includes a substrate (hereinafter sometimes referred to as a "separator substrate") and a functional layer formed on the separator substrate (Patent Documents 1 to 5).

[0003] JP 2015-162313 A International Publication No. WO 2015 / 068325 International Publication No. WO 2020 / 040031 International Publication No. WO 2020 / 040163 International Publication No. WO 2023 / 276738

[0004] For example, when a non-aqueous secondary battery is subjected to external pressure, the separator may be broken due to the pressure. Such separator breakage due to pressure may be referred to as "compression failure" hereinafter. When the separator is compressed and broken, the positive electrode and the negative electrode may come into contact, potentially causing an internal short circuit. Such an internal short circuit may cause heat generation in the non-aqueous secondary battery. Therefore, there is a need for the development of technology that can prevent internal short circuits when the separator is compressed and broken, thereby improving the safety of non-aqueous secondary batteries.

[0005] The present invention has been made in view of the above-mentioned problems, and aims to provide a slurry composition for a functional layer that can produce a functional layer that can suppress internal short-circuiting when the separator of a non-aqueous secondary battery is compressed and broken; a separator having a functional layer produced using the slurry composition for a functional layer and a method for producing the same; and a non-aqueous secondary battery having the separator.

[0006] The present inventors have conducted extensive research to solve the above-mentioned problems. As a result, the present inventors have found that a slurry composition containing a filler, in which a transfer rate indicating the transferability of a functional layer formed from the slurry composition to an electrode is equal to or greater than a specific threshold, can solve the above-mentioned problems, and have completed the present invention. That is, the present invention includes the following.

[0007] <1> A slurry composition for a functional layer containing a filler, the slurry composition for a functional layer having a transfer rate of 10% to 100% as measured in a transfer rate measurement test. <2> The slurry composition for a functional layer according to <1>, wherein the filler has a Mohs' hardness of 0.5 or more and 7 or less. <3> The slurry composition for a functional layer according to <1> or <2>, wherein the filler has an average particle diameter of 200 nm or more and 1,000 nm or less. <4> The slurry composition for a functional layer according to any one of <1> to <3>, wherein the filler has an envelopment index of 0.20 or more and 0.98 or less. <5> The slurry composition for a functional layer according to any one of <1> to <4>, wherein the filler has an envelopment index of 0.8 or more and 0.97 or less. <6> The slurry composition for a functional layer according to any one of <1> to <5>, wherein the filler includes one or more compounds selected from the group consisting of boehmite, barium sulfate, and a melamine compound. <7> The slurry composition for a functional layer according to any one of <1> to <6>, wherein the amount of the filler is 40% by weight or more and 98% by weight or less, based on the total solid content of the slurry composition for a functional layer. <8> The slurry composition for a functional layer according to any one of <1> to <7>, comprising a binder; the binder containing one or more functional groups selected from the group consisting of a carboxy group, a hydroxy group, an amino group, an epoxy group, an oxazoline group, a sulfo group, a nitrile group, an ester group, and an amide group. <9> A separator comprising a substrate and a functional layer formed on the substrate; the functional layer formed from the slurry composition for a functional layer according to any one of <1> to <8>. <10> A nonaqueous secondary battery comprising a positive electrode, the separator according to <9>, and a negative electrode. <11> A method for producing a separator, comprising forming a functional layer on a substrate using the slurry composition for a functional layer according to any one of <1> to <8>.

[0008] According to the present invention, it is possible to provide a slurry composition for a functional layer capable of producing a functional layer that can suppress internal short-circuiting when the separator of a non-aqueous secondary battery is compressed and broken; a separator having a functional layer produced using the slurry composition for a functional layer and a method for producing the same; and a non-aqueous secondary battery having the separator.

[0009] Fig. 1 is a cross-sectional view schematically showing a separator according to one embodiment of the present invention. Fig. 2 is a cross-sectional view schematically showing a nonaqueous secondary battery according to one embodiment of the present invention. Fig. 3 is a cross-sectional view schematically showing a pressing member being pressed against a nonaqueous secondary battery according to an example. Fig. 4 is a cross-sectional view schematically showing a nonaqueous secondary battery including a separator according to this embodiment that has been subjected to pressure from the pressing member and has been compressed to failure. Fig. 5 is a cross-sectional view schematically showing a nonaqueous secondary battery including a separator having a conventional separator substrate and a functional layer that has been subjected to pressure from the pressing member and has been compressed to failure.

[0010] The present invention will be described in detail below with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples shown below, and may be modified and implemented within the scope of the claims and their equivalents.

[0011] In the following description, unless otherwise specified, the ratio of a monomer unit formed by polymerizing a certain monomer in a polymer produced by copolymerizing multiple types of monomers usually coincides with the ratio (feed ratio) of that certain monomer to all the monomers used in the polymerization of the polymer.

[0012] In the following description, the structure of a molecule or a part thereof, such as a monomer unit, is not limited by its production method. For example, a (meth)acrylic acid alkyl ester monomer unit is a unit having a structure formed by polymerization of a (meth)acrylic acid alkyl ester monomer, but the (meth)acrylic acid alkyl ester monomer unit also includes units formed by other formation methods that have the same structure as the structure formed by polymerization of a (meth)acrylic acid alkyl ester monomer.

[0013] In the following description, unless otherwise specified, the term "(meth)acrylic acid" includes acrylic acid, methacrylic acid, and combinations thereof; the term "(meth)acrylate" includes acrylate, methacrylate, and combinations thereof; the term "(meth)acrylamide" includes acrylamide, methacrylamide, and combinations thereof; the term "(meth)acrylonitrile" includes acrylonitrile, methacrylonitrile, and combinations thereof; the term "(meth)allyl" includes allyl, methallyl, and combinations thereof; and the term "(meth)acryloyl" includes acryloyl, methacryloyl, and combinations thereof.

[0014] <Overview of Slurry Composition for Functional Layer> A slurry composition for functional layer according to one embodiment of the present invention (hereinafter sometimes simply referred to as "slurry composition") contains a filler and may further contain optional components such as a binder, a solvent, etc. as necessary. The slurry composition according to this embodiment has a transfer rate measured in a transfer rate measurement test that falls within a specific range.

[0015] The transfer rate measurement test includes the following steps in order: applying a slurry composition to a separator substrate and drying it to obtain a test separator comprising a separator substrate and a test functional layer; sandwiching the test separator between two test positive electrodes so that the positive electrode composite layer of the test positive electrode contacts the test separator to obtain a test laminate; placing the test laminate in a packaging material, adding a solvent to the packaging material, and vacuum-sealing the packaging to obtain a test sealed body; storing the test sealed body under specific conditions; and pressing the test sealed body with an indenter on a rigid flat plate. When pressed with the indenter, the test functional layer formed on the separator substrate can be transferred to the test positive electrode. The degree of transfer of this test functional layer is expressed as a transfer rate. The transfer rate is expressed as the ratio of the "diameter of the test functional layer attached to the test positive electrode" to the "diameter of the tip of the indenter."

[0016] The test separator corresponds to a separator having a functional layer formed using the functional layer slurry composition. The test sealed body corresponds to a nonaqueous secondary battery having the separator. Therefore, the transfer rate can be used as an index value representing the degree of transfer when a functional layer attached to a separator substrate is transferred to a separator electrode by pressure applied to a nonaqueous secondary battery. The slurry composition according to this embodiment has a transfer rate in a high range equal to or greater than a specific threshold value.

[0017] The slurry composition according to this embodiment can produce a functional layer that can suppress internal short circuits when a separator of a nonaqueous secondary battery is crushed under compression. The inventors speculate that the mechanism by which such excellent effects are obtained is as follows. However, the technical scope of the present invention is not limited to the mechanism described below.

[0018] Fig. 1 is a cross-sectional view schematically showing a separator 100 according to one embodiment of the present invention. Fig. 2 is a cross-sectional view schematically showing a nonaqueous secondary battery 200 according to one embodiment of the present invention. Typically, the nonaqueous secondary battery 200 includes an electrolyte and a battery container in addition to the elements shown in Fig. 2, but these electrolyte and battery container are not shown in Fig. 2.

[0019] As shown in FIG. 1 , the separator 100 includes a separator substrate 110 and a functional layer 120 formed on the separator substrate 110. The functional layer 120 is a layer formed using the slurry composition according to this embodiment. Therefore, the functional layer 120 typically contains the solids of the slurry composition, or may contain only the solids of the slurry composition. Unless otherwise specified, the "solids" of the slurry composition refers to the components of the slurry composition other than the solvent, and typically refers to the components that remain after the slurry composition has dried. In a normal state where the separator 100 is not subject to compression failure, the functional layer 120 is adhered to the separator substrate 110.

[0020] As shown in Fig. 2, a nonaqueous secondary battery 200 manufactured using this separator 100 generally includes, in this order, a negative electrode 210, the separator 100, and a positive electrode 220. The separator 100 may be provided so that the functional layer 120 faces the negative electrode 210, but is preferably provided so that the functional layer 120 faces the positive electrode 220. The example shown in Fig. 2 shows a nonaqueous secondary battery 200 that includes, in this order, the negative electrode 210, the separator substrate 110, the functional layer 120, and the positive electrode 220.

[0021] 3 is a cross-sectional view schematically illustrating a state in which a pressing member 300 is pressed against a nonaqueous secondary battery 200 according to an example. As shown in FIG. 3, it is assumed that the pressing member 300 is pressed against the nonaqueous secondary battery 200, and pressure is applied to the nonaqueous secondary battery 200. When subjected to such pressure, stress may cause the separator 100, the negative electrode 210, and the positive electrode 220 to compress and break.

[0022] FIG. 5 is a cross-sectional view schematically illustrating a state in which a nonaqueous secondary battery 930 including a separator 900 having a conventional separator substrate 910 and a functional layer 920 is subjected to compressive failure due to pressure from a pressing member 300. When compressive failure occurs as shown in FIG. 5 , the separator substrate 910 generally shrinks as indicated by arrow A1. Therefore, the functional layer 920 attached to the separator substrate 910 shrinks along with the shrinkage of the separator substrate 910. As a result, the entire separator 900 shrinks and extends inward from the negative electrode 210 and the positive electrode 220, potentially creating a portion 940 between the negative electrode 210 and the positive electrode 220 where the separator 900 is absent. When the negative electrode 210 and the positive electrode 220 come into contact with each other in this portion 940, a short circuit occurs.

[0023] FIG. 4 is a cross-sectional view schematically illustrating a state in which a nonaqueous secondary battery 200 including a separator 100 according to this embodiment is subjected to compressive failure under pressure from a pressing member 300. When compressive failure occurs as shown in FIG. 4 , the separator substrate 110 may shrink. However, the functional layer 120 formed from the slurry composition according to this embodiment can be transferred from the separator substrate 110 to the electrode opposite the functional layer 120 when pressure is applied, as represented by the transfer rate described above. Therefore, in the example shown in FIG. 4 , the functional layer 120 is transferred to the positive electrode 220 due to the pressure applied by the pressing member 300 during compressive failure. The functional layer 120 transferred to the positive electrode 220 is fixed to the positive electrode 220, and therefore can remain on the surface of the positive electrode 220 even if the separator substrate 110 shrinks. Therefore, it is possible to prevent the occurrence of a portion where the separator 100 is absent between the negative electrode 210 and the positive electrode 220 (see portion 940 in FIG. 5), and therefore it is possible to prevent an internal short circuit.

[0024] <Transfer Rate of Slurry Composition> The slurry composition according to this embodiment has a transfer rate within a specific range. The specific range of the transfer rate of the slurry composition is usually 10% or more, more preferably 20% or more, even more preferably 30% or more, even more preferably 40% or more, and particularly preferably 50% or more. The upper limit is usually 100% or less, and may be 95% or less. When the slurry composition has a transfer rate within the above range, an internal short circuit can be suppressed upon compressive failure of a separator of a nonaqueous secondary battery having a functional layer formed from this slurry composition.

[0025] The transfer rate of the slurry composition can be measured by a transfer rate measurement test, the outline of which is as described above. More specifically, the transfer rate measurement test involves: applying a slurry composition to a polyethylene separator substrate (thickness 12 μm, porosity 45%) and drying it at 50°C to form a test functional layer with a thickness of 3.0 μm, thereby obtaining a test separator including a separator substrate and a test functional layer; sandwiching a test separator between two test positive electrodes each including an aluminum foil and a positive electrode composite layer so that the positive electrode composite layer of the test positive electrode is in contact with the test separator, thereby obtaining a test laminate; placing the test laminate in a laminate pouch as a packaging material, and further adding a mixed solvent containing ethylene carbonate and ethyl methyl carbonate in a ratio of 3:7 to the laminate pouch, followed by vacuum sealing to obtain a test sealed body; storing the test sealed body at 60°C for one day and cooling it to 25°C; placing the test sealed body on a stainless steel flat plate so that the test functional layer and separator substrate are arranged in this order from the flat plate side; The test seal is pressed with a force of 500 N for 1 minute using a stainless steel indenter having a hemisphere with a diameter of 3 mm at the tip (the portion that contacts the test seal); the test positive electrode in contact with the test functional layer is removed from the test seal, washed with diethyl carbonate, and dried; the dried test positive electrode is observed with a scanning electron microscope to determine the diameter D of the test functional layer attached to the test positive electrode. ｆ and calculating the transfer rate (%) based on the following formula (M1): Transfer rate (%) = D ｆ (mm) / 3(mm)×100 (M1)

[0026] In the transfer rate measurement test, the positive electrode was LiNi ０．８ Mn ０．１ Co ０．１ O ２ A cathode mixture layer containing 96.0 parts by weight of cellulose acetate, 2.0 parts by weight of carbon black, and 2.0 parts by weight of polyvinylidene fluoride was used. The amount of the cathode mixture layer per area was 18 mg / cm. ２ ±0.5 mg / cm ２ , density is 3.30 g / cm ３ is.

[0027] In addition, in the transfer rate measurement test, the laminate pouch used in producing the test sealed body is a wrapping bag made by gluing together the edges of two rectangular films (multilayer film including a polyethylene terephthalate layer, an aluminum layer, and a polypropylene layer; thickness: 153 μm). "Vacuum sealing" of this laminate pouch means sealing the opening of the laminate pouch so that no air remains inside the laminate pouch.

[0028] The specific procedure for the transfer rate measurement test can be carried out as described in the <Method for measuring transfer rate> in the Examples section below.

[0029] The transfer rate can be adjusted, for example, by the envelopment rate of the filler contained in the slurry composition, the hardness of the filler, the particle size of the filler, and the amount of the filler. Preferred ranges for these will be described later, and it is preferable to adjust the specific values ​​within the ranges described below so as to obtain the desired transfer rate.

[0030] <Filler Contained in Slurry Composition> The slurry composition according to this embodiment contains a filler. Non-conductive particles formed of a non-conductive material can be used as the filler. This filler is contained in the functional layer, and the gaps between the filler particles can form pores in the functional layer. Therefore, in a non-aqueous secondary battery, charge can be transferred between the positive electrode and the negative electrode through the pores. Furthermore, a functional layer containing a non-conductive filler can have insulating properties. Furthermore, when the separator is compressed and broken by pressure, the insulating functional layer is transferred to the electrode, preventing contact between the positive electrode and the negative electrode, thereby preventing internal short circuits.

[0031] The filler material may be an inorganic material, an organic material, or a combination of an inorganic material and an organic material. Thus, the filler may contain particles of an inorganic material, particles of an organic material, or a combination of particles of an inorganic material and particles of an organic material. From the viewpoint of improving heat resistance, the filler preferably contains particles of an inorganic material, or may contain only particles of an inorganic material.

[0032] Examples of inorganic materials that can be included in the filler include aluminum oxide (alumina), silicon oxide, magnesium oxide (magnesia), calcium oxide, titanium oxide (titania), and BaTiO ３ Examples of suitable inorganic materials include oxides such as ZrO, hydrates such as boehmite, nitrides such as aluminum nitride and boron nitride, covalent crystalline materials such as silicon and diamond, sparingly soluble ionic crystals such as barium sulfate, calcium fluoride and barium fluoride, and clay materials such as talc and montmorillonite. Among these, hydrates and sparingly soluble ionic crystals are preferred, with boehmite and barium sulfate being more preferred. Particles of these inorganic materials may be subjected to treatments such as element substitution, surface treatment, and solid solution formation, as necessary.

[0033] Examples of organic materials that can be contained in the filler include melamine compounds and compounds containing an azo group. Among these, melamine compounds and azodicarbonamide are more preferred, and melamine compounds are even more preferred. Melamine compounds include melamine, melamine derivatives, and salts thereof. Among melamine compounds, melamine cyanurate is preferred. These preferred organic materials are foamable by heat when an internal short circuit occurs, and can therefore suppress the progression of the internal short circuit. Examples of organic materials that can be contained in the filler include those described in International Publication No. 2023 / 276738.

[0034] From the viewpoint of significantly achieving the desired effects of the present invention, the filler preferably contains one or more selected from the group consisting of boehmite, barium sulfate, and melamine compounds. Furthermore, the filler may be used alone or in combination of two or more.

[0035] The filler preferably has a Mohs hardness within a specific range. Here, the Mohs hardness of the filler refers to the Mohs hardness of the material contained in the filler. Specifically, the Mohs hardness range of the filler is preferably 0.1 or more, more preferably 0.5 or more, even more preferably 1 or more, and preferably 9 or less, more preferably 8 or less, even more preferably 7 or less, even more preferably 6 or less, and even more preferably 5 or less. Typically, when the filler particles have a low hardness, the filler particles tend to adhere to the surface of the electrode mixture layer of the electrode so as to conform to the surface irregularities. Therefore, when the Mohs hardness of the filler is below the upper limit of the range, the transfer rate can be increased and internal short circuits can be effectively suppressed. Furthermore, when the Mohs hardness of the filler is above the lower limit, deformation of the filler particles and deformation of the functional layer during the battery assembly process can be effectively suppressed.

[0036] The Mohs hardness of the filler can be measured, for example, by preparing a sample that is the same as the filler material and scratching the sample with a standard mineral that corresponds to an integer value between 1 and 10. Furthermore, when a filler made of a material with a known Mohs hardness is used, the known Mohs hardness value may be used.

[0037] The filler preferably has a degree of envelopment within a specific range. Here, the degree of envelopment of the filler refers to the degree of envelopment of the filler particles. Specifically, the range of the degree of envelopment of the filler is usually 0.20 or more, preferably 0.70 or more, more preferably 0.75 or more, even more preferably 0.80 or more, and preferably 0.98 or less, more preferably 0.97 or less, even more preferably 0.95 or less. The degree of envelopment generally represents the degree of surface roughness of the particles. Therefore, when a filler has a degree of envelopment within the above range, it indicates that the degree of surface roughness of the filler particles is within a specific range. When a filler has a degree of envelopment within the above range, the filler particles can be effectively fixed to the surface of the electrode mixture layer so that the filler particles are anchored to the surface of the electrode mixture layer. Therefore, when the degree of envelopment of the filler is within the above range, the transfer rate can be increased and internal short circuits can be effectively suppressed.

[0038] The degree of envelopment of the filler can be measured by the following measurement method. A dispersion containing the filler and having a solids concentration of 5% by weight is coated on an aluminum foil and dried to form a sample layer containing the filler. The sample layer is photographed using a field emission scanning electron microscope to obtain a secondary electron image. The observation magnification is set to a magnification that allows the entire thickness direction of the sample layer to be observed. From the obtained secondary electron image, the envelope perimeter and actual perimeter are obtained for each of 30 to 100 filler particles. The "envelopment perimeter" refers to the length of the line enveloping the outline of the filler particle in the image. In other words, the "envelopment perimeter" represents the length of the curve circumscribing the protruding portion of the particle in the image. Furthermore, the "actual perimeter" represents the perimeter of the filler particle in the image. From the obtained envelope perimeter and actual perimeter, the degree of envelopment of one particle can be calculated using the following formula (M2). The degree of envelopment of one particle is measured for each of 30 to 100 particles. The average of the envelopment degrees of 30 to 100 particles thus determined is calculated as the envelopment degree of the filler, as shown in the following formula (M3). The specific procedure for measuring the envelopment degree may be as described in <Method for measuring the envelopment degree of the filler> in the examples described later. Envelopment degree of one particle = envelopment perimeter / actual perimeter (M2) Envelopment degree of filler = average value of the envelopment degree of one particle for all measured particles (M3)

[0039] The filler preferably has an average particle size within a specific range. Here, the average particle size of the filler refers to the average particle size of the filler particles. Specifically, the average particle size of the filler is preferably 100 nm or more, more preferably 150 nm or more, even more preferably 200 nm or more, particularly preferably 250 nm or more, and preferably 1,500 nm or less, more preferably 1,000 nm or less, even more preferably 700 nm or less, particularly preferably 500 nm or less. The smaller the filler particles, the easier they are to fix to the surface of the electrode mixture layer. Therefore, when the average particle size of the filler is within the above range, the transfer rate can be increased and internal short circuits can be effectively suppressed.

[0040] The average particle size of the filler can be measured using a laser diffraction method. Specifically, a dispersion containing the filler and having a solid content of 0.1 wt % is measured using a laser diffraction particle size distribution analyzer to measure the particle size distribution of the filler particles in the dispersion on a volume basis. In the measured particle size distribution, the particle diameter D50 at which the cumulative volume calculated from the smallest diameter side is 50% can be obtained as the average particle diameter. The specific procedure for measuring the average particle diameter may be as described in <Method for measuring the average particle diameter and D90 particle diameter of the filler> in the Examples described below.

[0041] The filler preferably has a D90 particle size within a specific range. Specifically, the D90 particle size range of the filler is preferably 300 nm or more, more preferably 400 nm or more, even more preferably 500 nm or more, particularly preferably 600 nm or more, and is preferably 2,500 nm or less, more preferably 2,000 nm or less, even more preferably 1,500 nm or less, particularly preferably 1,100 nm or less. When the D90 particle size of the filler is within the above range, internal short circuits can be effectively suppressed.

[0042] The D90 particle size of the filler can be measured using a laser diffraction method. In the volume-based particle size distribution of the filler particles measured by the above method, the particle size D90 at which the cumulative volume calculated from the smallest diameter side becomes 90% can be obtained as the D90 particle size.

[0043] The amount of filler is preferably 40 wt% or more, more preferably 50 wt% or more, even more preferably 60 wt% or more, and particularly preferably 70 wt% or more, based on 100 wt% of the total solids content in the slurry composition. The upper limit is preferably 98 wt% or less, and may be 97 wt% or less or 96 wt% or less. The more filler in the slurry composition, the more filler particles can adhere to the electrode. Furthermore, if the slurry composition contains a binder, the more filler, the relatively less binder there is, resulting in fewer fixing points for fixing the functional layer to the separator substrate. Therefore, the functional layer is more likely to detach from the separator substrate due to shrinkage of the separator substrate when the separator is compressed and destroyed. Therefore, the transfer rate can be increased, effectively suppressing internal short circuits.

[0044] The average particle size of the filler is represented by "D50f", the D90 particle size of the filler is represented by "D90f", the weight-based filler content relative to the total solid content contained in the slurry composition is represented by "Mf", and the filler envelopment degree is represented by "Ef". The unit of Mf is dimensionless. Therefore, for example, when the filler content relative to the total solid content (100 wt%) contained in the slurry composition is 94 wt%, the value of Mf is 0.94. In this case, the parameter "Mf × (D90f / D50f) / Ef" is preferably 1.0 or more, more preferably 2.0 or more, even more preferably 2.2 or more, and preferably 8.0 or less, more preferably 5.0 or less, and even more preferably 4.5 or less. When the parameter "Mf × (D90f / D50f) / Ef" is within the above range, internal short circuits can be effectively suppressed.

[0045] <Solvent> The slurry composition according to this embodiment typically contains a solvent. The filler described above is generally dispersed in this solvent. Either water or an organic solvent can be used as the solvent. Examples of organic solvents that can be used include acetonitrile, N-methyl-2-pyrrolidone, tetrahydrofuran, acetone, acetylpyridine, cyclopentanone, dimethylformamide, dimethyl sulfoxide, methylformamide, methyl ethyl ketone, furfural, ethylenediamine, dimethylbenzene (xylene), methylbenzene (toluene), cyclopentyl methyl ether, and isopropyl alcohol. One type of solvent may be used alone, or two or more types may be used in combination. The solvent preferably contains water, and may contain only water.

[0046] The amount of solvent contained in the slurry composition is preferably set so that the solid content of the slurry composition falls within a specific range.The specific solid content of the slurry composition is preferably 5 wt% or more, more preferably 10 wt% or more, even more preferably 15 wt% or more, and preferably 80 wt% or less, more preferably 70 wt% or less, even more preferably 60 wt% or less.When the solid content is above the lower limit of the range, the slurry composition can be smoothly dried during the production of the functional layer, thereby reducing the amount of solvent in the functional layer.On the other hand, when it is below the upper limit, the slurry composition can be smoothly applied.

[0047] <Binder> The slurry composition according to this embodiment may contain a binder as an optional component. The binder serves to bind filler particles together and to bind the filler to the separator substrate. Therefore, the binder allows the formation of a functional layer with excellent mechanical strength. Typically, a polymer having binding properties is used as the binder.

[0048] Suitable examples of polymers for use as binders include aliphatic conjugated diene / aromatic monovinyl copolymers (polymers mainly containing aliphatic conjugated diene monomer units and aromatic monovinyl monomer units), acrylic polymers (polymers mainly containing (meth)acrylic acid alkyl ester monomer units), fluorine-containing polymers (polymers mainly containing fluorine-containing monomer units), acrylic acid / acrylamide copolymers (polymers mainly containing (meth)acrylic acid units and (meth)acrylamide units), and acrylonitrile polymers (polymers mainly containing (meth)acrylonitrile units). Among these, acrylic polymers are preferred. Here, unless otherwise specified, the term "monomer unit" refers to a repeating unit having a structure formed by polymerizing a monomer. For example, a (meth)acrylic acid alkyl ester monomer unit refers to a repeating unit having a structure formed by polymerizing a (meth)acrylic acid alkyl ester monomer. Furthermore, unless otherwise specified, "mainly comprising" a certain monomer unit means that "when the total amount of all monomer units contained in the polymer is 100% by weight, the total content of the monomer unit exceeds 50% by weight."

[0049] The polymer used as a binder preferably contains a functional group. Preferably, the polymer contains one or more functional groups selected from the group consisting of a carboxy group, a hydroxy group, an amino group, an epoxy group, an oxazoline group, a sulfo group, a nitrile group, an ester group, and an amide group. Hereinafter, these carboxy groups, hydroxy groups, amino groups, epoxy groups, oxazoline groups, sulfo groups, nitrile groups, ester groups, and amide groups may be collectively referred to as "specific functional groups." Among the specific functional groups, carboxy groups, hydroxy groups, amino groups, epoxy groups, oxazoline groups, sulfo groups, nitrile groups, and amide groups are more preferred; carboxy groups, epoxy groups, and ester groups are even more preferred. The polymer may contain one type of specific functional group, or two or more types.

[0050] Polymers containing specific functional groups can have high binding strength. Therefore, when using a polymer containing specific functional groups as a binder, the amount of binder can be reduced, allowing the functional layer to be fixed to the separator substrate with a small amount of binder. Furthermore, when the amount of binder is reduced in this way, the amount of filler can be relatively increased, thereby increasing the transfer rate. Furthermore, polymers containing specific functional groups can usually improve the heat resistance of non-aqueous secondary batteries.

[0051] A polymer containing a specific functional group may be produced, for example, by a method including terminally modifying an appropriate polymer to introduce a specific functional group into the terminal of the polymer. The polymer produced by this method generally contains the specific functional group at the terminal.

[0052] The polymer containing the specific functional group is preferably produced by a method including polymerizing a monomer containing the specific functional group, and the polymer produced by this method generally contains a monomer unit containing the specific functional group. Therefore, the polymer as a binder preferably contains one or more selected from the group consisting of a carboxy group-containing monomer unit, a hydroxy group-containing monomer unit, an amino group-containing monomer unit, an epoxy group-containing monomer unit, an oxazoline group-containing monomer unit, a sulfo group-containing monomer unit, a nitrile group-containing monomer unit, an ester group-containing monomer unit, and an amide group-containing monomer unit; more preferably contains one or more selected from the group consisting of a carboxy group-containing monomer unit, a hydroxy group-containing monomer unit, an amino group-containing monomer unit, an epoxy group-containing monomer unit, an oxazoline group-containing monomer unit, a sulfo group-containing monomer unit, a nitrile group-containing monomer unit, and an amide group-containing monomer unit; and even more preferably contains one or more selected from the group consisting of a carboxy group-containing monomer unit, an epoxy group-containing monomer unit, and an ester group-containing monomer unit.

[0053] The carboxyl group-containing monomer unit refers to a repeating unit having a structure formed by polymerizing a carboxyl group-containing monomer. Monomers that can form the carboxyl group-containing monomer include monomers containing a carboxyl group (i.e., carboxyl group-containing monomers) and acid anhydride monomers that can generate a carboxyl group by hydrolysis. Examples of these include monocarboxylic acids; dicarboxylic acids and their acid anhydrides, and derivatives thereof.

[0054] Examples of monocarboxylic acids include acrylic acid, methacrylic acid, crotonic acid, 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, and α-chloro-β-E-methoxyacrylic acid. Examples of dicarboxylic acids include maleic acid, fumaric acid, itaconic acid, methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, and fluoromaleic acid. Examples of dicarboxylic acid anhydrides include maleic anhydride, acrylic anhydride, methylmaleic anhydride, and dimethylmaleic anhydride. Examples of dicarboxylic acid derivatives include maleic acid monoesters such as nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, and fluoroalkyl maleate. Among these, acrylic acid and methacrylic acid are preferred, and acrylic acid is more preferred.

[0055] The hydroxy group-containing monomer unit represents a repeating unit having a structure formed by polymerizing a hydroxy group-containing monomer. Examples of monomers that can form the hydroxy group-containing monomer unit include monomers containing a hydroxy group (i.e., hydroxy group-containing monomers). Examples of the hydroxy group-containing monomer include ethylenically unsaturated alcohols such as (meth)allyl alcohol, 3-butene-1-ol, and 5-hexene-1-ol; alkanol ester compounds of ethylenically unsaturated carboxylic acids such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, di-2-hydroxyethyl maleate, di-4-hydroxybutyl maleate, and di-2-hydroxypropyl itaconate; CH ２ =CR ａ -COO-(C ｑ H ２ｑ O) ｐ -H (wherein p represents an integer of 2 or more and 9 or less, q represents an integer of 2 or more and 4 or less, and R ａrepresents a hydrogen atom or a methyl group) and (meth)acrylic acid ester compounds; mono(meth)acrylic acid ester compounds of dihydroxy esters of dicarboxylic acids, such as 2-hydroxyethyl-2'-(meth)acryloyloxyphthalate and 2-hydroxyethyl-2'-(meth)acryloyloxysuccinate; vinyl ether compounds, such as 2-hydroxyethyl vinyl ether and 2-hydroxypropyl vinyl ether; mono(meth)allyl ether compounds of alkylene glycols, such as (meth)allyl-2-hydroxyethyl ether, (meth)allyl-2-hydroxypropyl ether, (meth)allyl-3-hydroxypropyl ether, (meth)allyl-2-hydroxybutyl ether, (meth)allyl-3-hydroxybutyl ether, (meth)allyl-4-hydroxybutyl ether, and (meth)allyl-6-hydroxyhexyl ether; diethylene glycol mono(meth)allyl ether, dipropyl ether, mono(meth)allyl ethers of halogen- and hydroxy-substituted (poly)alkylene glycols, such as glycerin mono(meth)allyl ether, (meth)allyl-2-chloro-3-hydroxypropyl ether, and (meth)allyl-2-hydroxy-3-chloropropyl ether; mono(meth)allyl ethers of polyhydric phenols, such as eugenol and isoeugenol, and halogen-substituted products thereof; (meth)allyl thioether compounds of alkylene glycols, such as (meth)allyl-2-hydroxyethyl thioether and (meth)allyl-2-hydroxypropyl thioether; and amide compounds having a hydroxy group, such as N-hydroxymethylacrylamide (N-methylolacrylamide), N-hydroxymethylmethacrylamide, N-hydroxyethylacrylamide, and N-hydroxyethylmethacrylamide.

[0056] The amino group-containing monomer unit refers to a repeating unit having a structure formed by polymerizing an amino group-containing monomer. Examples of monomers that can form the amino group-containing monomer unit include monomers containing an amino group (i.e., amino group-containing monomers). Examples of amino group-containing monomers include dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, aminoethyl vinyl ether, and dimethylaminoethyl vinyl ether.

[0057] The epoxy group-containing monomer unit represents a repeating unit having a structure formed by polymerizing an epoxy group-containing monomer. Monomers capable of forming the epoxy group-containing monomer unit include monomers containing an epoxy group (i.e., epoxy group-containing monomers). Epoxy group-containing monomers include monomers containing a non-aromatic carbon-carbon double bond and an epoxy group. Examples of monomers containing a non-aromatic carbon-carbon double bond and an epoxy group include unsaturated glycidyl ethers such as vinyl glycidyl ether, allyl glycidyl ether, butenyl glycidyl ether, and o-allylphenyl glycidyl ether; diene or polyene monoepoxides such as butadiene monoepoxide, chloroprene monoepoxide, 4,5-epoxy-2-pentene, 3,4-epoxy-1-vinylcyclohexene, and 1,2-epoxy-5,9-cyclododecadiene; and 3,4-epoxy-1- Examples of the glycidyl ester include alkenyl epoxides such as butene, 1,2-epoxy-5-hexene, and 1,2-epoxy-9-decene; and glycidyl ester compounds of unsaturated carboxylic acids such as glycidyl acrylate, glycidyl methacrylate, glycidyl crotonate, glycidyl 4-heptenoate, glycidyl sorbate, glycidyl linoleate, glycidyl 4-methyl-3-pentenoate, glycidyl ester of 3-cyclohexenecarboxylic acid, and glycidyl ester of 4-methyl-3-cyclohexenecarboxylic acid. Of these, allyl glycidyl ether is preferred.

[0058] The oxazoline group-containing monomer unit refers to a repeating unit having a structure formed by polymerizing an oxazoline group-containing monomer. Monomers capable of forming the oxazoline group-containing monomer unit include monomers containing an oxazoline group (i.e., oxazoline group-containing monomers). Examples of oxazoline group-containing monomers include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline.

[0059] The sulfo group-containing monomer unit refers to a repeating unit having a structure formed by polymerizing a sulfo group-containing monomer. Examples of monomers that can form the sulfo group-containing monomer unit include monomers containing a sulfo group (i.e., sulfo group-containing monomers). Examples of sulfo group-containing monomers include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth)allyl sulfonic acid, styrene sulfonic acid, (meth)acrylic acid-2-ethyl sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, and 3-allyloxy-2-hydroxypropanesulfonic acid.

[0060] The nitrile group-containing monomer unit refers to a repeating unit having a structure formed by polymerizing a nitrile group-containing monomer. Monomers capable of forming the nitrile group-containing monomer unit include monomers containing a nitrile group (i.e., nitrile group-containing monomers). Examples of the nitrile group-containing monomer include α,β-ethylenically unsaturated nitrile monomers. Examples of the α,β-ethylenically unsaturated nitrile monomer include acrylonitrile; α-halogenoacrylonitriles such as α-chloroacrylonitrile and α-bromoacrylonitrile; and α-alkylacrylonitriles such as methacrylonitrile and α-ethylacrylonitrile. Among these, acrylonitrile is preferred.

[0061] The ester group-containing monomer unit refers to a repeating unit having a structure formed by polymerizing an ester group-containing monomer. Monomers capable of forming the ester group-containing monomer unit include monomers containing an ester group (i.e., ester group-containing monomers). Examples of the ester group-containing monomer include (meth)acrylic acid alkyl ester monomers. Examples of the (meth)acrylic acid alkyl ester monomer include acrylic acid alkyl esters such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, butyl acrylate (e.g., n-butyl acrylate and t-butyl acrylate), pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate (e.g., 2-ethylhexyl acrylate), nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, and stearyl acrylate; and Examples of the methacrylic acid alkyl esters include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, butyl methacrylate (e.g., n-butyl methacrylate and t-butyl methacrylate), pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate (e.g., 2-ethylhexyl methacrylate), nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, and stearyl methacrylate. Among these, 2-ethylhexyl acrylate and n-butyl acrylate are preferred, with 2-ethylhexyl acrylate being more preferred.

[0062] The amide group-containing monomer unit refers to a repeating unit having a structure formed by polymerizing an amide group-containing monomer. Examples of monomers that can form the amide group-containing monomer unit include monomers containing an amide group (i.e., amide group-containing monomers). Examples of amide group-containing monomers include acrylamide and methacrylamide.

[0063] The amount of monomer units containing a specific functional group contained in the polymer as a binder is preferably 10 wt% or more, more preferably 20 wt% or more, even more preferably 30 wt% or more, and preferably 70 wt% or less, more preferably 60 wt% or less, and even more preferably 50 wt% or less, relative to 100 wt% of all monomer units contained in the polymer. When the amount of monomer units containing a specific functional group is equal to or greater than the lower limit of the above range, the heat resistance of the non-aqueous secondary battery can be improved and heat generation during an internal short circuit can be suppressed. When the amount of monomer units containing a specific functional group is equal to or less than the upper limit of the above range, the adhesion of the functional layer to the separator substrate in the battery can be reduced, thereby increasing the transfer rate. The amount of monomer units in the polymer is １ H-NMR, １３ It can be measured using a nuclear magnetic resonance (NMR) method such as C-NMR.

[0064] The polymer serving as a binder may contain any monomer unit other than the monomer unit containing the specific functional group described above. Examples of the optional monomer unit include an aromatic monovinyl monomer unit, an aliphatic conjugated diene monomer unit which may be hydrogenated, and a crosslinkable monomer unit.

[0065] The aromatic monovinyl monomer unit refers to a repeating unit having a structure formed by polymerizing an aromatic monovinyl monomer. Examples of aromatic monovinyl monomers include styrene, α-methylstyrene, pt-butylstyrene, butoxystyrene, vinyltoluene, chlorostyrene, and vinylnaphthalene. Among these, styrene is preferred.

[0066] The optionally hydrogenated aliphatic conjugated diene monomer unit represents a repeating unit having a structure formed by polymerizing an aliphatic conjugated diene monomer, and a repeating unit having a structure formed by polymerizing and hydrogenating an aliphatic conjugated diene monomer. Examples of the aliphatic conjugated diene monomer include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, and 2-chloro-1,3-butadiene. Among these, 1,3-butadiene is preferred.

[0067] The crosslinkable monomer unit represents a repeating unit having a structure formed by polymerizing a crosslinkable monomer. Examples of the crosslinkable monomer include polyfunctional (meth)acrylate compounds such as allyl (meth)acrylate, ethylene di(meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, and trimethylolpropane tri(meth)acrylate. Among these, allyl methacrylate is preferred.

[0068] The monomer unit contained in the polymer as a binder may be one type or two or more types. In addition, the binder may be used alone or in combination of two or more types.

[0069] The polymer used as the binder preferably has a glass transition temperature Tg within a specific range. Specifically, the range of the glass transition temperature Tg of the polymer is preferably −50°C or higher, more preferably −45°C or higher, even more preferably −40°C or higher, and preferably 100°C or lower, more preferably 80°C or lower, and even more preferably 60°C or lower. When the glass transition temperature Tg of the polymer is within this range, the functional layer is easily peeled off from the separator substrate when the separator is compressed and broken, thereby effectively increasing the transfer rate and effectively suppressing internal short circuits. The glass transition temperature Tg of the polymer can be measured by differential scanning calorimetry (DSC) at a heating rate of 5°C / min.

[0070] When the slurry composition contains a solvent, the binder may be dissolved in the solvent, or may be dispersed in the slurry composition without dissolving in the solvent. Typically, when 0.5 g of a soluble binder is dissolved in 100 g of solvent at 25° C., the amount of insoluble matter in the solvent is less than 50 mass %. Furthermore, when 0.5 g of a non-soluble binder is dissolved in 100 g of solvent at 25° C., the amount of insoluble matter in the solvent is 50 mass % or more. In particular, it is preferable that the binder is not dissolved in the solvent but dispersed as particles. When a particulate binder is used in this way, the flexibility of the functional layer can be increased, thereby improving the handleability of the separator.

[0071] When the binder is particulate, the average particle diameter of the binder particles is preferably 30 nm or more, more preferably 50 nm or more, even more preferably 70 nm or more, and preferably 300 nm or less, more preferably less than 200 nm, and even more preferably 150 nm or less. When the average particle diameter of the binder is within this range, the functional layer is easily peeled off from the separator substrate when the separator is compressed and broken, effectively increasing the transfer rate and effectively suppressing internal short circuits. Furthermore, the internal resistance of the nonaqueous secondary battery is usually reduced. The average particle diameter of the binder particles refers to the particle diameter at which the cumulative volume calculated from the smallest diameter side in the particle size distribution measured by laser diffraction is 50%.

[0072] The binder may be configured to swell to an appropriate degree in the presence of the electrolyte of the nonaqueous secondary battery. Generally, the more the binder swells in the presence of the electrolyte, the lower the binding strength of the binder tends to be. Therefore, the binder may be swelled to the extent that the functional layer can be fixed to the separator substrate when the separator is not crushed by compression. If the binder's adhesiveness is reduced by swelling, the functional layer will be more likely to peel off from the separator substrate when the separator is crushed by compression, which can contribute to an increase in the transfer rate.

[0073] The polymer as a binder may be produced by, for example, the method described in WO 2020 / 040031, WO 2020 / 040163, or WO 2023 / 276738.

[0074] The amount of binder is preferably 1.0 part by weight or more, more preferably 1.5 parts by weight or more, and even more preferably 2.0 parts by weight or more, and preferably 10 parts by weight or less, more preferably 8 parts by weight or less, and even more preferably 5 parts by weight or less, per 100 parts by weight of filler. When the amount of binder is equal to or greater than the lower limit of the above range, the adhesion of the functional layer to the separator substrate can be improved when the separator is not crushed by compression. When the amount of binder is equal to or less than the upper limit, the number of adhesion points to the separator substrate by the binder is reduced, making it easier for the functional layer to peel from the separator substrate when the separator is crushed by compression, thereby improving the transfer rate and effectively suppressing internal short circuits. Furthermore, the heat resistance of nonaqueous secondary batteries can usually be improved.

[0075] The amount of binder is preferably 1 wt% or more, more preferably 1.4 wt% or more, even more preferably 1.9 wt% or more, and preferably 9 wt% or less, more preferably 7 wt% or less, and even more preferably 4.6 wt% or less, based on 100 wt% of the total solids content in the slurry composition. When the amount of binder is equal to or greater than the lower limit of the above range, the adhesion of the functional layer to the separator substrate can be improved when the separator is not crushed by compression. When the amount of binder is equal to or less than the upper limit, the number of adhesion points to the separator substrate by the binder is reduced, making it easier for the functional layer to peel from the separator substrate when the separator is crushed by compression, thereby improving the transfer rate and effectively suppressing internal short circuits. Furthermore, the heat resistance of nonaqueous secondary batteries can usually be improved.

[0076] <Viscosity modifier> The slurry composition according to the present embodiment may contain a viscosity modifier as an optional component. The viscosity modifier serves to adjust the viscosity of the slurry composition. Typically, a soluble polymer that can be dissolved in a solvent is used as the viscosity modifier.

[0077] Preferred viscosity modifiers include, for example, cellulose derivatives, polyacrylic acid compounds such as polyacrylic acid and its salts (e.g., sodium salts), and polyvinyl alcohol. Among these, cellulose derivatives and polyacrylic acid compounds are more preferred, and cellulose derivatives are even more preferred.

[0078] Examples of cellulose derivatives include nonionic cellulose derivatives, anionic cellulose derivatives, and cationic cellulose derivatives.

[0079] Examples of nonionic cellulose derivatives include alkyl celluloses such as methyl cellulose, methyl ethyl cellulose, ethyl cellulose, and microcrystalline cellulose; and hydroxyalkyl celluloses such as hydroxyethyl cellulose, hydroxybutyl methyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose stearoxy ether, carboxymethyl hydroxyethyl cellulose, alkyl hydroxyethyl cellulose, and nonoxynyl hydroxyethyl cellulose.

[0080] Examples of anionic cellulose derivatives include derivatives of the above-mentioned nonionic cellulose derivatives substituted with various derivative groups and salts thereof. Examples of salts include sodium salts and ammonium salts. Specific examples of anionic cellulose derivatives include sodium cellulose sulfate, carboxymethyl cellulose (CMC), and salts thereof.

[0081] Examples of cationic cellulose derivatives include low-nitrogen hydroxyethyl cellulose dimethyl diallyl ammonium chloride (polyquaternium-4), O-[2-hydroxy-3-(trimethylammonio)propyl]hydroxyethyl cellulose chloride (polyquaternium-10), and O-[2-hydroxy-3-(lauryldimethylammonio)propyl]hydroxyethyl cellulose chloride (polyquaternium-24).

[0082] Among the above, carboxymethyl cellulose and its salts are preferred.

[0083] The viscosity modifier may be used alone or in combination of two or more.

[0084] The amount of the viscosity modifier is preferably 0.01 parts by weight or more, more preferably 0.1 parts by weight or more, even more preferably 0.5 parts by weight or more, and is preferably 10 parts by weight or less, more preferably 8 parts by weight or less, even more preferably 5 parts by weight or less, relative to 100 parts by weight of the filler.

[0085] <Wetting Agent> The slurry composition according to the present embodiment may contain a wetting agent as an optional component. The wetting agent serves to improve the coatability of the slurry composition. As the wetting agent, for example, a surfactant can be used. Preferred examples of the surfactant include polyether surfactants, sulfonic acid surfactants, fluorine surfactants, silicon surfactants, and acetylene surfactants.

[0086] Specific examples of polyether surfactants include "NOPTEX ED052" manufactured by San Nopco Ltd. Specific examples of sulfonic acid surfactants include dioctyl sulfosuccinic acid or its salts. Specific examples of fluorine-based surfactants include the Megafac (registered trademark) series manufactured by DIC Corporation, the Futergent (registered trademark) series manufactured by Neos Corporation, and the Surflon (registered trademark) series manufactured by AGC. Specific examples of silicone-based surfactants include dimethylpolysiloxane. Specific examples of acetylene-based surfactants include the Surfynol (registered trademark) series and Dynol series manufactured by Air Products and Chemicals Co., Ltd. Among these, polyether-based surfactants are preferred from the viewpoint of improving the stability of the slurry composition.

[0087] The wetting agent may be used alone or in combination of two or more.

[0088] The amount of wetting agent is preferably 0.1 parts by weight or more, more preferably 0.5 parts by weight or more, even more preferably 1 part by weight or more, and preferably 10 parts by weight or less, more preferably 5 parts by weight or less, even more preferably 3 parts by weight or less, relative to 100 parts by weight of the filler.

[0089] <Dispersant> The slurry composition according to this embodiment may contain a dispersant as an optional component. The dispersant serves to suppress the aggregation of filler particles contained in the slurry composition. Examples of dispersants include polycarboxylic acids, polysulfonic acids, polystyrene sulfonic acids, naphthalene sulfonic acid-formalin condensates, and polyethylene glycols. Among these, polycarboxylic acids are preferred, and poly(meth)acrylic acids are more preferred. The polycarboxylic acids are preferably salts such as sodium salts and ammonium salts. One type of dispersant may be used alone, or two or more types may be used in combination.

[0090] The amount of dispersant is preferably 0.01 parts by weight or more, more preferably 0.1 parts by weight or more, even more preferably 0.5 parts by weight or more, and is preferably 10 parts by weight or less, more preferably 5 parts by weight or less, even more preferably 3 parts by weight or less, relative to 100 parts by weight of the filler.

[0091] <Optional Additives> The slurry composition according to the present embodiment may further contain optional additives as needed. Examples of optional additives include any polymer other than the above-described polymers, antioxidants, antifoaming agents, wetting agents, and electrolyte additives that inhibit electrolyte decomposition. One type of optional additive may be used alone, or two or more types may be used in combination.

[0092] <Characteristics of Slurry Composition> The slurry composition according to this embodiment is preferably a liquid composition having a viscosity suitable for coating. The viscosity of the slurry composition at 25°C is preferably 5 mPa·s or more, more preferably 10 mPa·s or more, even more preferably 15 mPa·s or more, and preferably 200 mPa·s or less, more preferably 100 mPa·s or less, even more preferably 70 mPa·s or less. The viscosity of the slurry composition can be measured using a Brookfield viscometer at a rotation speed of 60 rpm.

[0093] The slurry composition according to the present embodiment can be used to form a functional layer of a separator for a nonaqueous secondary battery. The functional layer thus formed can suppress an internal short circuit when the separator of the nonaqueous secondary battery is crushed by compression. In one example, a nonaqueous secondary battery having a functional layer formed using the slurry composition can suppress an internal short circuit when subjected to a crash test using the method described in the "Crash Test" section of the Examples section below, thereby suppressing explosion and fire caused by the internal short circuit.

[0094] In addition, a functional layer formed from the slurry composition according to the present embodiment can generally improve the heat resistance of a nonaqueous secondary battery. In one example, a nonaqueous secondary battery having a functional layer formed using the slurry composition can suppress explosion and fire due to an internal short circuit when subjected to a hot box test described in the "Hot Box Test" section of the Examples below.

[0095] <Method for Producing Slurry Composition> The slurry composition according to this embodiment can be produced, for example, by a production method including mixing the above-described components. Preferable specific examples include a step of producing a binder composition containing a solvent and a binder, a step of producing a filler dispersion containing a filler, a solvent, and a dispersant, and a step of mixing the binder composition, the filler dispersion, and, if necessary, optional components (such as a viscosity modifier or a wetting agent). Mixing may be performed using a mixer such as a ball mill, a sand mill, a bead mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, a planetary mixer, or a Filmix.

[0096] <Separator> A separator according to one embodiment of the present invention includes a separator substrate and a functional layer formed on the separator substrate. The functional layer may be formed on one side or both sides of the separator substrate. In a preferred embodiment, the functional layer is formed on the positive electrode side of the separator substrate. The functional layer of the separator according to this embodiment is formed from the above-described slurry composition.

[0097] Since the functional layer of the separator according to this embodiment is formed from the above-described slurry composition, a high transfer rate can usually be obtained when the separator is used in place of a test separator to perform a transfer rate measurement test. In this case, the functional layer of the separator corresponds to the test functional layer in the transfer rate measurement test, and the obtained transfer rate represents the degree of transfer of the functional layer from the separator substrate to the test positive electrode. Specifically, the range of transfer rates obtained in the transfer rate measurement test using the separator in place of the test separator is preferably the same as the range of transfer rates described in the section on the slurry composition above.

[0098] The separator according to the present embodiment can suppress an internal short circuit when the separator of a nonaqueous secondary battery is crushed by compression. In one example, a nonaqueous secondary battery including the separator according to the present embodiment can suppress an internal short circuit when subjected to a crash test described in the <Crash Test> section of the Examples section described later, thereby suppressing explosion and fire caused by the internal short circuit.

[0099] Furthermore, the separator according to the present embodiment can generally improve the heat resistance of a nonaqueous secondary battery. In one example, a nonaqueous secondary battery including the separator according to the present embodiment can suppress explosion and fire due to an internal short circuit when subjected to a hot box test described in the "Hot Box Test" section of the Examples below.

[0100] The separator substrate is typically a porous material such as a microporous membrane or nonwoven fabric. This separator substrate may also be an organic separator substrate made of an organic material. Preferred examples of organic materials for forming the separator substrate include polyolefin resins such as polyethylene and polypropylene, polyethylene terephthalate (PET) resins, and aromatic polyamide resins, from the viewpoints of improving the cycle characteristics and reducing the internal resistance of the secondary battery. The thickness of the separator substrate is preferably 0.5 μm or more, more preferably 1 μm or more, and preferably 40 μm or less, more preferably 30 μm or less.

[0101] Since the functional layer of the separator is formed from the above-mentioned slurry composition, it typically contains the solids of the slurry composition, or may contain only the solids of the slurry composition. For example, the functional layer may be formed from a dried product of the slurry composition. Thus, the functional layer contains a filler and may further contain optional components such as a binder, a viscosity modifier, a wetting agent, a dispersant, and optional additives. Typically, the components contained in the functional layer are those contained in the slurry composition, and therefore the ratio of the amounts of these components is the same as the ratio of the amounts of the components in the slurry composition. Furthermore, if a polymer such as a binder contained in the slurry composition contains a crosslinkable functional group, the polymer may be crosslinked in the functional layer.

[0102] The functional layer may contain a solvent such as water derived from the slurry composition. However, the amount of solvent in the functional layer is preferably small from the viewpoint of improving the battery characteristics such as the rate characteristics of the secondary battery. Specifically, the amount of solvent in the functional layer is preferably 3 wt% or less, more preferably 1 wt% or less, and even more preferably 0.1 wt% or less, relative to 100 wt% of the functional layer. In particular, it is particularly preferable that the functional layer does not contain a solvent.

[0103] The thickness of the functional layer is preferably 0.1 μm or more, more preferably 0.5 μm or more, even more preferably 1 μm or more, and preferably 20 μm or less, more preferably 10 μm or less, even more preferably 5 μm or less. When the thickness of the functional layer is equal to or greater than the lower limit of the above range, the mechanical strength of the functional layer can be increased, and internal short circuits can be effectively suppressed. When the thickness of the functional layer is equal to or less than the upper limit of the above range, the internal resistance of the secondary battery can be reduced.

[0104] The separator may include any layer other than the separator substrate and the functional layer. For example, the separator may include an adhesive layer that improves adhesion between the separator and the electrode. Typically, the adhesive layer is formed as the outermost layer of the separator. Therefore, the adhesive layer may be provided between the functional layer and the electrode. Generally, the adhesive layer is thin, so that the filler in the functional layer can break through the adhesive layer upon compressive failure. Therefore, even if the separator includes an adhesive layer, the functional layer can be transferred to the electrode.

[0105] The separator according to this embodiment can be manufactured by a manufacturing method that includes forming a functional layer on a separator substrate using the above-described slurry composition. The formation of the functional layer on the separator substrate may be performed, for example, by the following methods: (1) A method in which the slurry composition is supplied to the surface of the separator substrate and then dried; or (2) A method in which the slurry composition is supplied to a release support and dried to form a functional layer, and the resulting functional layer is transferred to the surface of the separator substrate.

[0106] Among these, the method (1) is preferred because it is easy to control the thickness of the functional layer. The method (1) typically includes a supplying step of supplying the slurry composition onto the separator substrate and a drying step of drying the slurry composition supplied onto the separator substrate.

[0107] Examples of methods for supplying the slurry composition onto the separator substrate include a method of coating the surface of the separator substrate with the slurry composition and a method of immersing the separator substrate in the slurry composition. Specific examples of methods for coating the slurry composition include the doctor blade method, reverse roll method, direct roll method, gravure method, extrusion method, brush coating method, dip coating method, spray coating method, and vacuum impregnation method. Among these, when the slurry composition is to be impregnated into the inside of the separator substrate, the dip coating method, spray coating method, vacuum impregnation method, and gravure method are preferred.

[0108] Examples of methods for drying the slurry composition on the separator substrate include warm air drying, hot air drying, low-humidity air drying, vacuum drying, and drying by irradiation with energy rays such as infrared rays and electron beams. The drying temperature is preferably less than 80°C, and more preferably less than 60°C, from the viewpoint of avoiding thermal shrinkage of the separator substrate and thermal decomposition or sublimation of the polymer in the slurry composition.

[0109] The method for producing a separator may further include any step in combination with the steps described above. For example, when a polymer such as a binder has crosslinkability, the method for producing a separator may include a step of crosslinking the polymer.

[0110] <Non-aqueous secondary battery> A non-aqueous secondary battery according to one embodiment of the present invention comprises a positive electrode, the separator described above, and a negative electrode. In addition, non-aqueous secondary batteries typically further contain an electrolyte solution.

[0111] Since the nonaqueous secondary battery according to this embodiment includes the separator described above, a high transfer rate can usually be obtained when a transfer rate measurement test is performed using the nonaqueous secondary battery instead of a test sealed body. In this transfer rate measurement test, the functional layer of the separator corresponds to the test functional layer in the transfer rate measurement test, and the obtained transfer rate represents the degree of transfer of the functional layer from the separator substrate to an electrode such as a positive electrode. Specifically, the range of transfer rates obtained in a transfer rate measurement test using a nonaqueous secondary battery instead of a test sealed body is preferably the same as the range of transfer rates described in the section on the slurry composition above.

[0112] The nonaqueous secondary battery according to this embodiment can suppress an internal short circuit when the separator is crushed by compression. In one example, the nonaqueous secondary battery according to this embodiment can suppress an internal short circuit when a crash test described in the <Crash Test> section of the Examples to be described later is performed, thereby suppressing rupture and fire due to the internal short circuit.

[0113] In addition, the nonaqueous secondary battery according to this embodiment can generally improve the heat resistance of the nonaqueous secondary battery. In one example, the nonaqueous secondary battery according to this embodiment can suppress explosion and fire due to an internal short circuit when subjected to a hot box test described in the "Hot Box Test" section of Examples below.

[0114] The electrodes, such as the positive electrode and the negative electrode, are not particularly limited, and any known positive electrode and negative electrode that can be used in a non-aqueous secondary battery may be used. The electrodes typically include a current collector and an electrode composite layer containing an electrode active material. Thus, the positive electrode typically includes a current collector for the positive electrode and a positive electrode composite layer containing a positive electrode active material. Furthermore, the negative electrode typically includes a current collector for the negative electrode and a negative electrode composite layer containing a negative electrode active material. Generally, an electrode is provided such that its electrode composite layer faces the separator, and therefore a non-aqueous battery may include a negative electrode current collector, a negative electrode composite layer, a separator, a positive electrode composite layer, and a positive electrode current collector, in this order in the thickness direction.

[0115] Typically, the positive electrode composite layer has a higher hardness than the negative electrode composite layer. Furthermore, a functional layer containing a filler generally tends to adhere to a layer having a high hardness. Therefore, from the viewpoint of promoting the transfer of the functional layer and effectively suppressing internal short circuits, it is preferable that the separator be provided so that the functional layer faces the positive electrode. There is no limitation on the positive electrode active material contained in the positive electrode composite layer of this positive electrode. However, from the viewpoint of increasing the capacity of the secondary battery, Li ｘ Ni ｙ Mn ｚ Co （１－ｙ－ｚ） O ２ (wherein x, y, and z represent numbers satisfying 0.95≦x≦1.2, 0.70≦y≦0.95, z>0, and 1−y−z>0.) A specific example of the lithium metal composite oxide represented by the above composition formula is LiNi ０．８ Mn ０．１ Co ０．１ O ２ (NMC811) is preferred.

[0116] As the electrolyte, an organic electrolyte solution in which a supporting electrolyte is dissolved in an organic solvent is usually used. For example, in a lithium ion secondary battery, a lithium salt is used as the supporting electrolyte. For example, LiPF ６ , LiAsF ６ , LiBF ４ , LiSbF ６ , LiAlCl ４ , LiClO ４ , C.F. ３ SO ３ Li, C ４ F ９ SO ３ Li, CF ３ COOLi, (CF ３ CO) ２ NLi, (CF ３ SO ２ ) ２ NLi, (C ２ F ５ SO ２ Among them, LiPF is the most popular because it is easily soluble in solvents and shows a high degree of dissociation. ６ , LiClO ４ , C.F.３ SO ３ Li is preferred. The electrolyte may be used alone or in combination of two or more. Generally, the higher the degree of dissociation of the supporting electrolyte, the higher the lithium ion conductivity tends to be.

[0117] As the organic solvent for the electrolyte, a solvent capable of dissolving the supporting electrolyte can be used. For example, preferred organic solvents for the electrolyte of a lithium ion secondary battery include carbonate solvents such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), ethyl methyl carbonate (EMC), and vinylene carbonate (VC); ester solvents such as γ-butyrolactone and methyl formate; ether solvents such as 1,2-dimethoxyethane and tetrahydrofuran; and sulfur-containing compound solvents such as sulfolane and dimethyl sulfoxide. These solvents may be used alone or in combination of two or more. The concentration of the electrolyte in the electrolyte may be appropriately adjusted. Furthermore, the electrolyte may contain any additive.

[0118] A nonaqueous secondary battery can be produced, for example, by stacking a positive electrode and a negative electrode with a separator interposed therebetween, rolling or folding the resulting assembly as necessary according to the battery shape, placing the assembly in a battery container, injecting an electrolyte into the battery container, and sealing the container. To prevent internal pressure rise, overcharge / discharge, and other problems from occurring in the secondary battery, a fuse, an overcurrent prevention element such as a PTC element, an expanded metal, a lead plate, or the like may be provided as necessary. The secondary battery may have any shape, such as a coin type, a button type, a sheet type, a cylindrical type, a rectangular type, or a flat type.

[0119] The present invention will be specifically described below with reference to examples. The present invention is not limited to the following examples. In the following description, "%" and "parts" representing amounts are by weight unless otherwise specified. Furthermore, unless otherwise specified, the operations described below were carried out in air at room temperature and normal pressure (23°C, 1 atm).

[0120] In a polymer produced by polymerizing a plurality of types of monomers, the ratio of a monomer unit formed by polymerizing a certain monomer in the polymer usually coincides with the ratio (feed ratio) of that monomer to all the monomers used in the polymerization of the polymer, unless otherwise specified.

[0121] <Method for measuring average particle size and D90 particle size of filler> The average particle size of the filler was measured using a laser diffraction method as follows. Each filler dispersion prepared in the Examples and Comparative Examples was adjusted to a solids concentration of 0.1 wt % using purified water to prepare a measurement sample. The particle size distribution (volume basis) of the filler in the measurement sample was measured using a laser diffraction particle size distribution analyzer ("LS-13 320" manufactured by Beckman Coulter, Inc.). In the measured particle size distribution, the 50% particle size D50, at which the cumulative volume calculated from the smallest diameter side was 50%, was taken as the average particle size. In addition, the D90 particle size, at which the cumulative volume calculated from the smallest diameter side was 90% in the particle size distribution, was obtained.

[0122] <Method for Measuring Filler Envelopment Degree> Each filler dispersion prepared in the Examples and Comparative Examples was adjusted to a solids concentration of 5 wt% using purified water. The filler dispersion was then coated on aluminum foil and dried to form a sample layer containing the filler. Next, the sample layer was photographed using a field-emission scanning electron microscope ("Regulus 8230" manufactured by Hitachi High-Technologies) to obtain a secondary electron image. The observation magnification was 20,000x (a magnification that allows the entire thickness direction of the sample layer to be observed) and the irradiation voltage was 1 keV. The obtained secondary electron image was used to obtain the envelope perimeter and actual perimeter for 30 to 100 filler particles using image processing software ("WINROOF" manufactured by Mitani Shoji Co., Ltd.). The perimeter was calculated in the perimeter I mode. From the obtained envelope perimeter and actual perimeter, the envelopment degree of each particle was calculated for each of the 30 to 100 particles using the following formula (M2): The average of the envelopment degrees of 30 to 100 particles thus determined was calculated as the envelopment degree of the filler, as shown in formula (M3): Envelopment degree of one particle = envelopment perimeter / actual perimeter (M2) Envelopment degree of filler = average value of the envelopment degree of one particle for all measured particles (M3)

[0123] <Transfer Rate Measurement Method> The transfer rate was measured by the following transfer rate measurement test. A positive electrode manufactured in the same manner as in the Examples and Comparative Examples described below was cut into a size of 3.0 cm x 4.0 cm. A separator was also manufactured in the same manner as in the Examples and Comparative Examples to obtain a test separator for measuring the transfer rate. The test separator was sandwiched between the two cut-out positive electrodes and fixed with polyimide tape to prevent misalignment, thereby obtaining a test laminate. In this case, the positive electrode was arranged so that the positive electrode composite layer faced the separator.

[0124] The test laminate was placed in a laminate pouch (DNP's "D-EL408PH-3"; a pouch made by bonding two multilayer films including a polyethylene terephthalate layer, an aluminum layer, and a polypropylene layer; the thickness of each sheet forming the pouch was 153 μm) as a packaging material. Furthermore, a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (EC / EMC=3 / 7; volume ratio) was added to the laminate pouch, and the laminate pouch was vacuum-sealed to obtain a sealed test body.

[0125] The test sealed body was stored at 60° C. for 1 day and then cooled to 25° C. Thereafter, the test sealed body was placed on a 3 mm thick SUS plate such that the functional layer was closer to the SUS plate than the separator substrate.

[0126] The test seal placed on the SUS plate was pressed with a force of 500 N for 1 minute using a stainless steel indenter with a 3 mm diameter hemisphere at the tip. The laminate pouch was then disassembled to remove the positive electrode in contact with the functional layer. The removed positive electrode was washed with diethyl carbonate (DEC) and dried. The dried positive electrode was observed with a scanning electron microscope (SEM) to measure the diameter of the functional layer attached to the positive electrode. The diameter D of the functional layer attached to the positive electrode was ｆ The transfer rate was calculated from [mm] based on the following formula (M1): Transfer rate (%) = D ｆ / 3×100 (M1)

[0127] <Crash Test> The secondary battery into which the electrolyte was injected was left standing at 25°C for 5 hours. Next, it was charged to a cell voltage of 3.65 V using a constant current method at 0.2 C at 25°C, and then aged for 12 hours at 60°C. Then, it was discharged to a cell voltage of 3.00 V using a constant current method at 0.2 C at 25°C. Then, it was subjected to CC-CV charging (upper limit cell voltage 4.25 V) using a constant current method at 0.2 C, and CC discharge to 3.00 V using a constant current method at 0.2 C. This charge-discharge cycle at 0.2 C was repeated three times. Then, it was charged to 4.25 V (cutoff condition: 0.02 C) using a constant voltage-constant current (CC-CV) method at a charge rate of 0.2 C in an atmosphere at 25°C. Then, a crash test was conducted based on the UL1642 standard.

[0128] The above test was carried out on five lithium ion secondary batteries (test specimens) each manufactured by the same method, and evaluation was carried out according to the following criteria based on the number of test specimens that did not burst or catch fire. The greater the number of test specimens that did not burst or catch fire, the better the lithium ion secondary battery's ability to suppress internal short circuits. A: The number of test specimens that did not burst or catch fire was 4 or 5. B: The number of test specimens that did not burst or catch fire was 3. C: The number of test specimens that did not burst or catch fire was 2. D: The number of test specimens that did not burst or catch fire was 1 or 0.

[0129] <Hot Box Test> The secondary battery into which the electrolyte was injected was left standing at 25°C for 5 hours. Next, it was charged to a cell voltage of 3.65 V using a constant current method at 0.2 C at 25°C, and then aged for 12 hours at 60°C. Then, it was discharged to a cell voltage of 3.00 V using a constant current method at 0.2 C at 25°C. Then, it was CC-CV charged (upper limit cell voltage 4.25 V) using a constant current method at 0.2 C, and CC discharged to 3.00 V using a constant current method at 0.2 C. This charge-discharge cycle at 0.2 C was repeated three times. Then, it was charged to 4.25 V (cutoff condition: 0.02 C) using a constant voltage-constant current (CC-CV) method at a charge rate of 0.2 C in an atmosphere of 25°C. Then, it was heated to 150°C at a rate of 5°C / min, and the presence or absence of ignition was measured.

[0130] The above test was carried out on five lithium ion secondary batteries (test specimens) each manufactured by the same method, and evaluation was carried out according to the following criteria based on the number of test specimens that did not burst or catch fire. The greater the number of test specimens that did not burst or catch fire, the better the lithium ion secondary battery's ability to suppress heat generation during an internal short circuit. A: The number of test specimens that did not burst or catch fire was 4 or 5. B: The number of test specimens that did not burst or catch fire was 3. C: The number of test specimens that did not burst or catch fire was 2. D: The number of test specimens that did not burst or catch fire was 1 or 0.

[0131] Production Example 1 Production of Binder (Polymer A) A 10-liter reactor was charged with 100 parts of ion-exchanged water, as well as 35 parts by weight of acrylonitrile, 62 parts by weight of 1,3-butadiene, and 3 parts by weight of methacrylic acid as monomers. Furthermore, 2 parts of potassium oleate as an emulsifier, 0.1 part of potassium phosphate as a stabilizer, and 0.5 parts of 2,2',4,6,6'-pentamethylheptane-4-thiol (TIBM) as a molecular weight modifier, and emulsion polymerization was carried out at 30°C in the presence of 0.35 parts of potassium persulfate as a polymerization initiator.

[0132] When the polymerization conversion rate reached 90%, 0.2 parts of hydroxylamine sulfate per 100 parts of monomer was added to the reactor to terminate the polymerization. Subsequently, the mixture was heated and subjected to steam distillation under reduced pressure at about 70°C to recover the residual monomer. Then, 2 parts of alkylated phenol were added to the reactor as an antioxidant to obtain an aqueous dispersion of the polymer.

[0133] Next, 400 mL of the obtained aqueous dispersion of the polymer (total solid content: 48 g) was placed in a 1-liter autoclave equipped with a stirrer, and nitrogen gas was passed through for 10 minutes to remove dissolved oxygen in the aqueous dispersion. A catalyst solution was prepared by mixing 50 mg of palladium acetate as a hydrogenation catalyst with 180 mL of water containing 4 times the molar amount of nitric acid relative to Pd, and this catalyst solution was added to the aqueous dispersion of the polymer. After the system was purged with hydrogen gas twice, the contents of the autoclave were heated to 50 ° C. while pressurized with hydrogen gas to 3 MPa, and the polymer was hydrogenated for 6 hours.

[0134] The contents of the autoclave were then returned to room temperature, and a nitrogen atmosphere was created inside the system. The aqueous polymer dispersion was concentrated using an evaporator to a solids concentration of 40%, to obtain an aqueous dispersion containing polymer A as a binder. The obtained polymer A was a particulate polymer dispersed in water, and the average particle size of the polymer A particles was 0.10 μm, and the glass transition temperature Tg of polymer A was −35° C.

[0135] Example 1 (Preparation of Slurry Composition) 98 parts of barium sulfate particles (average particle size 0.35 μm, Mohs hardness 3) as a filler, 2 parts of a carboxylic acid polymer (sodium polyacrylate, "GL366" manufactured by Nippon Shokubai Co., Ltd.) as a dispersant, and purified water were mixed to obtain a filler dispersion containing a filler with a solid content of 40%. 1 liter of this filler dispersion was subjected to a dispersion treatment using a bead mill ("Star Mill" manufactured by Ajisawa Fine Tech Co., Ltd.) with zirconia balls having a diameter of 0.5 mm at a speed of 8 m / s for a treatment time of 120 minutes. After the dispersion treatment, the average particle size of the filler in the filler dispersion was 0.3 μm, the D90 particle size was 0.8 μm, and the envelopment ratio was 0.93.

[0136] 100 parts of the filler dispersion were weighed out in terms of filler content. To this filler dispersion, 1.0 part (solid content equivalent) of carboxymethyl cellulose (Daicel Corporation's "1220") as a viscosity modifier, 3.0 parts (solid content equivalent) of an aqueous dispersion of polymer A as a binder, and 0.2 parts (solid content equivalent) of a polyether surfactant (San Nopco's "Noptex ED052") as a wetting agent were added. Ion-exchanged water as a solvent was further added to this dispersion, and the mixture was stirred for 30 minutes using a three-one motor to obtain a slurry composition 1 having a slurry solid content of 20%.

[0137] (Production of separator with functional layer) A polyethylene separator substrate (manufactured by Asahi Kasei Corporation, product name "ND412", thickness: 12 μm, porosity: 45%, produced by a wet method) was prepared. The slurry composition 1 obtained above was applied to the separator substrate using a gravure coater. The applied slurry composition 1 was then dried at a temperature of 50°C using a safety oven to form a functional layer (functional layer thickness: 3.0 μm) on one side of the separator substrate. This operation resulted in a separator including a separator substrate and a functional layer.

[0138] (Production of Negative Electrode) 63 parts of styrene as monomers, 34 parts of 1,3-butadiene, 2 parts of itaconic acid, and 1 part of 2-hydroxyethyl acrylate; 0.3 parts of t-dodecyl mercaptan as a molecular weight modifier; 5 parts of sodium dodecylbenzenesulfonate as an emulsifier; 150 parts of ion-exchanged water; and 1 part of potassium persulfate as a polymerization initiator were charged into a 5 MPa pressure vessel equipped with a stirrer and thoroughly stirred. The heat-resistant vessel was then heated to 55°C to initiate polymerization. When the monomer consumption reached 95.0%, the vessel was cooled to terminate the reaction, yielding an aqueous dispersion containing a polymer. A 5% aqueous sodium hydroxide solution was added to the resulting aqueous dispersion, and the pH was adjusted to 8. Unreacted monomers were then removed by heated, reduced-pressure distillation. The mixture was then cooled to a temperature of 30°C or below to yield an aqueous dispersion containing a negative electrode binder (negative electrode binder composition).

[0139] 48.75 parts of artificial graphite (theoretical capacity 360 mAh / g) as a negative electrode active material, 48.75 parts of natural graphite (theoretical capacity 360 mAh / g), and 1 part of carboxymethyl cellulose (solid content equivalent) were added to a planetary mixer. The mixture was then diluted with ion-exchanged water to a solid content of 60% and kneaded for 60 minutes at a rotation speed of 45 rpm. Then, 1.5 parts of the negative electrode binder composition (solid content equivalent) were added and kneaded for 40 minutes at a rotation speed of 40 rpm. Then, ion-exchanged water was added to the mixture to obtain a viscosity of 3000 ± 500 mPa s (measured at 25 ° C. and 60 rpm), thereby preparing a negative electrode slurry composition.

[0140] The negative electrode slurry composition was applied to the surface of a 15 μm thick copper foil current collector using a comma coater in an amount of 11±0.5 mg / cm after drying. ２ The copper foil coated with the negative electrode slurry composition was then transported at a speed of 400 mm / min through an oven at 80°C for 2 minutes and then through an oven at 110°C for 2 minutes, thereby drying the negative electrode slurry composition on the copper foil and obtaining a negative electrode blank having a current collector and a negative electrode composite layer. The negative electrode composite layer side of the prepared negative electrode blank was then roll-pressed under a temperature of 25±3°C and a pressure of 11 t (tons), until the density of the negative electrode composite layer reached 1.60 g / cm. ３ A negative electrode of 1000 .mu.m was obtained.

[0141] (Production of Positive Electrode) NMC811 (LiNi) as a positive electrode active material was added to a planetary mixer. ０．８ Mn ０．１ Co ０．１ O ２ 96.0 parts of ethylenediamine fluoride (E2), 2.0 parts of carbon black (Li-100 manufactured by Denka Co., Ltd.) as a conductive material, equivalent to the solid content, and 2.0 parts of polyvinylidene fluoride (Solef (registered trademark) 5130 manufactured by Solvay) were added and mixed. Furthermore, N-methylpyrrolidone (NMP) was gradually added to the planetary mixer, and the mixture was stirred and mixed at a temperature of 25±3°C and a rotation speed of 60 rpm to obtain a positive electrode slurry composition having a viscosity of 3,600 mPa s (measured with a Brookfield viscometer at 25±3°C and 60 rpm (rotor M4)).

[0142] The positive electrode slurry composition was applied to a 20 μm thick aluminum foil current collector using a comma coater in an amount of 18±0.5 mg / cm after drying. ２ The aluminum foil coated with the positive electrode slurry composition was then transported at a speed of 0.5 m / min through an oven at 90°C for 2 minutes, and then through an oven at 120°C for 2 minutes, thereby drying the positive electrode slurry composition on the aluminum foil and obtaining a positive electrode raw sheet comprising a current collector and a positive electrode composite layer. Thereafter, the positive electrode composite layer side of the prepared positive electrode raw sheet was roll-pressed under a temperature of 25±3°C and a load of 14 t (tons), and the density of the positive electrode composite layer was measured to be 3.30 g / cm. ３ A positive electrode of 1000 .mu.m was obtained.

[0143] (Manufacture of secondary battery) The negative electrode, separator, and positive electrode obtained above were stacked in this order to prepare a laminate cell (equivalent to an initial design discharge capacity of 3 Ah). At this time, the functional layer of the separator was arranged to face the positive electrode composite layer of the positive electrode. The obtained laminate was placed in an aluminum package and vacuum dried at 60°C for 10 hours. Then, LiPF 5 with a concentration of 1.0 M was added as an electrolyte. ６ A solution (solvent: a mixed solvent of ethylene carbonate (EC) / diethyl carbonate (DEC) = 3 / 7 (volume ratio), additive: containing 2 volume % vinylene carbonate (solvent ratio)) was filled into the aluminum packaging. Furthermore, in order to seal the opening of the aluminum packaging, the aluminum packaging was closed by heat sealing at a temperature of 150°C, thereby producing a lithium ion secondary battery. This lithium ion secondary battery was evaluated by a collision test and a hot box test.

[0144] Example 2 A slurry composition 2, a separator, and a lithium ion secondary battery were produced and evaluated in the same manner as in Example 1, except that in the step (production of a slurry composition), the amount of the aqueous dispersion of polymer A to be mixed with the filler dispersion was changed to 8 parts (corresponding to the solid content) per 100 parts of the filler.

[0145] Example 3 In the step (production of a slurry composition), the amount of the aqueous dispersion of polymer A mixed with the filler dispersion was changed to 1 part (solid content equivalent) per 100 parts of filler. In addition, the amount of carboxymethyl cellulose mixed with the filler dispersion was changed to 0.5 parts (solid content equivalent) per 100 parts of filler. Except for the above, slurry composition 3, a separator, and a lithium ion secondary battery were produced and evaluated in the same manner as in Example 1.

[0146] Example 4 A resin composition 4, a separator, and a lithium ion secondary battery were produced and evaluated in the same manner as in Example 1, except that in the step (production of a slurry composition), the amount of the aqueous dispersion of polymer A to be mixed with the filler dispersion was changed to 97 parts (corresponding to the solid content) per 100 parts of the filler.

[0147] Example 5 A slurry composition 5, a separator, and a lithium ion secondary battery were produced and evaluated in the same manner as in Example 1, except that in the step (production of a slurry composition), the conditions for the dispersion treatment using a bead mill when preparing a filler dispersion were changed to a speed of 8 m / sec and a treatment time of 60 minutes. The average particle size of the filler in the filler dispersion after the dispersion treatment was 0.32 μm, the D90 particle size was 1.1 μm, and the degree of envelopment was 0.8.

[0148] Example 6 A slurry composition 6, a separator, and a lithium ion secondary battery were produced and evaluated in the same manner as in Example 1, except that in the step (production of a slurry composition), the conditions for the dispersion treatment using a bead mill when preparing a filler dispersion were changed to a speed of 8 m / sec and a treatment time of 240 minutes. The average particle size of the filler in the filler dispersion after the dispersion treatment was 0.28 μm, the D90 particle size was 0.7 μm, and the degree of envelopment was 0.97.

[0149] Example 7 A slurry composition 7, a separator, and a lithium-ion secondary battery were produced and evaluated in the same manner as in Example 1, except that in the step (production of a slurry composition), the type of filler was changed from the barium sulfate particles used in Example 1 to other barium sulfate particles (average particle diameter 0.6 μm, Mohs hardness 3). After the dispersion treatment, the average particle diameter of the filler in the filler dispersion was 0.32 μm, the D90 particle diameter was 1.3 μm, and the envelopment degree was 0.7.

[0150] Example 8 A slurry composition 8, a separator, and a lithium ion secondary battery were produced and evaluated in the same manner as in Example 1, except that in the step (production of a slurry composition), the conditions for the dispersion treatment using a bead mill when preparing a filler dispersion were changed to a speed of 8 m / sec and a treatment time of 360 minutes. The average particle size of the filler in the filler dispersion after the dispersion treatment was 0.26 μm, the D90 particle size was 0.5 μm, and the degree of envelopment was 0.98.

[0151] Example 9 A slurry composition 9, a separator, and a lithium-ion secondary battery were produced and evaluated in the same manner as in Example 1, except that in the step (production of a slurry composition), the type of filler was changed from the barium sulfate particles used in Example 1 to other barium sulfate particles (average particle diameter 1.5 μm, Mohs hardness 3). The average particle diameter of the filler in the filler dispersion after the dispersion treatment was 1.2 μm, the D90 particle diameter was 2.0 μm, and the envelopment degree was 0.92.

[0152] Example 10 A slurry composition 10, a separator, and a lithium-ion secondary battery were produced and evaluated in the same manner as in Example 1, except that in the step (production of a slurry composition), the type of filler was changed from the barium sulfate particles used in Example 1 to boehmite particles (average particle size 0.4 μm, Mohs hardness 4). The average particle size of the filler in the filler dispersion after the dispersion treatment was 0.3 μm, the D90 particle size was 0.9 μm, and the envelopment degree was 0.91.

[0153] Example 11 A slurry composition 11, a separator, and a lithium-ion secondary battery were produced and evaluated in the same manner as in Example 1, except that in the step (production of a slurry composition), the type of filler was changed from the barium sulfate particles used in Example 1 to alumina particles (average particle diameter 0.4 μm, Mohs hardness 9). The average particle diameter of the filler in the filler dispersion after the dispersion treatment was 0.3 μm, the D90 particle diameter was 0.6 μm, and the degree of envelopment was 0.95.

[0154] Example 12 In the step (production of a slurry composition), the type of filler was changed from the barium sulfate particles used in Example 1 to melamine cyanurate (average particle size 1.5 μm). The type of dispersant was changed from the carboxylic acid polymer used in Example 1 to carboxymethyl cellulose (Daicel Corporation's "1220"). Furthermore, the amount of purified water was changed so that the solids concentration of the filler dispersion was 25%. Except for the above, a slurry composition 12, a separator, and a lithium-ion secondary battery were produced and evaluated in the same manner as in Example 1. After the dispersion treatment, the filler in the filler dispersion had an average particle size of 0.3 μm, a D90 particle size of 0.7 μm, and an envelopment ratio of 0.94.

[0155] <Comparative Example 1> A resin composition 13, a separator, and a lithium ion secondary battery were produced and evaluated in the same manner as in Example 1, except that in the step (production of a slurry composition), the amount of the aqueous dispersion of polymer A to be mixed with the filler dispersion was changed to 150 parts (corresponding to the solid content) per 100 parts of the filler.

[0156] <Comparative Example 2> In the step (production of a slurry composition), the type of filler was changed from the barium sulfate particles used in Example 1 to other barium sulfate particles (average particle diameter 1.5 μm, Mohs hardness 3). Furthermore, the amount of aqueous dispersion of polymer A mixed with the filler dispersion was changed to 8 parts (solid content equivalent) per 100 parts of filler. Except for the above, a resin composition 14, a separator, and a lithium-ion secondary battery were produced and evaluated in the same manner as in Example 1. After the dispersion treatment, the average particle diameter of the filler in the filler dispersion was 1.2 μm, the D90 particle diameter was 2.0 μm, and the envelopment degree was 0.92.

[0157] <Results> The results of the above-mentioned Examples and Comparative Examples are shown in the table below. In the table below, the meanings of the abbreviations are as follows: D50: average particle size of the filler Filler amount: amount of filler relative to 100% by weight of the total solid content of the slurry composition HNBR: hydrogenated nitrile rubber CMC: carboxymethyl cellulose

[0158]

[0159]

[0160] REFERENCE SIGNS LIST 100 Separator 110 Separator substrate 120 Functional layer 200 Non-aqueous secondary battery 210 Negative electrode 220 Positive electrode 300 Pressing member

Claims

1. A slurry composition for a functional layer containing a filler, the slurry composition for a functional layer having a transfer rate of 10% to 100% as measured in a transfer rate measurement test.

2. The slurry composition for a functional layer according to claim 1, wherein the filler has a Mohs hardness of 0.5 or more and 7 or less.

3. The slurry composition for a functional layer according to claim 1, wherein the filler has an average particle size of 200 nm or more and 1000 nm or less.

4. The slurry composition for a functional layer according to claim 1, wherein the filler has an envelopment degree of 0.20 or more and 0.98 or less.

5. The slurry composition for a functional layer according to claim 2, wherein the filler has an envelopment degree of 0.8 or more and 0.97 or less.

6. The slurry composition for a functional layer according to claim 1, wherein the filler comprises one or more selected from the group consisting of boehmite, barium sulfate, and a melamine compound.

7. A slurry composition for a functional layer according to claim 1, wherein the amount of the filler is 40% by weight or more and 98% by weight or less based on the total solid content contained in the slurry composition for a functional layer.

8. A slurry composition for a functional layer according to claim 1, comprising a binder; the binder containing one or more functional groups selected from the group consisting of a carboxy group, a hydroxy group, an amino group, an epoxy group, an oxazoline group, a sulfo group, a nitrile group, an ester group, and an amide group.

9. A separator comprising a substrate and a functional layer formed on the substrate; the functional layer being formed from the functional layer slurry composition according to any one of claims 1 to 8.

10. A non-aqueous secondary battery comprising a positive electrode, the separator according to claim 9, and a negative electrode.

11. A method for producing a separator, comprising forming a functional layer on a substrate using the functional layer slurry composition according to any one of claims 1 to 8.

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