Separator for non-aqueous secondary battery, and non-aqueous secondary battery

Abstract

The separator for a non-aqueous secondary battery is provided with: a porous layer containing inorganic particles and a binder resin; and an adhesive layer containing a phenyl group-containing acrylic resin and a butadiene-acrylonitrile resin, the amount of butadiene units contained in the two resins being 3-50 mol% of the total amount of acrylic units, styrene units, butadiene units, and acrylonitrile units.

Description

Technical Field

[0001] The present disclosure relates to a separator for a non-aqueous secondary battery and a non-aqueous secondary battery. Background Art

[0002] Patent Document 1 discloses an adhesive for bonding members constituting a lithium-ion secondary battery together, the adhesive containing a particulate polymer having a core-shell structure.

[0003] Patent Documents 2 and 3 disclose a non-aqueous secondary battery separator having an adhesive layer provided on one or both surfaces of a laminate of a porous substrate and a porous layer, wherein the adhesive layer is formed by adhesive resin particles attached to the laminate.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: International Publication No. 2015 / 005145

[0007] Patent Document 2: International Publication No. 2019 / 130994

[0008] Patent Document 3: International Publication No. 2020 / 246497 Summary of the Invention

[0009] Problems to be solved by the invention

[0010] From the viewpoint of preventing battery short circuits, the separator is required to have good adhesion to the electrodes.

[0011] In order to more firmly bond the separator to the electrode, an operation of laminating the separator impregnated with an electrolyte and the electrode and hot pressing the laminating electrodes (referred to as "wet hot pressing") is performed during battery production.

[0012] As batteries become larger, wet hot pressing equipment becomes larger in size. Therefore, there is a demand for developing a separator that exhibits excellent adhesion to electrodes even when wet hot pressing is performed at relatively low temperature and low pressure.

[0013] The present disclosure has been completed based on the above circumstances.

[0014] An object of the present disclosure is to provide a non-aqueous secondary battery separator that exhibits excellent adhesion to electrodes by wet hot pressing at low temperature and low pressure.

[0015] Means for solving problems

[0016] Specific means for solving the aforementioned problems include the following.

[0017] <1>

[0018] A separator for a non-aqueous secondary battery, comprising:

[0019] a porous layer containing inorganic particles and a binder resin; and

[0020] The adhesive layer contains a phenyl-containing acrylic resin and a butadiene-acrylonitrile resin, wherein the amount of butadiene units contained in the two resins accounts for 3 mol% to 50 mol% of the total amount of acrylic units, styrene units, butadiene units and acrylonitrile units.

[0021] <2>

[0022] like <1> The non-aqueous secondary battery separator further comprises a porous substrate.

[0023] The porous substrate has the porous layer on one or both sides thereof.

[0024] The adhesive layer is provided on one or both surfaces of a laminate of the porous substrate and the porous layer.

[0025] <3>

[0026] like <1> or <2> The non-aqueous secondary battery separator, wherein the adhesive layer comprises resin particles,

[0027] The resin particles include at least one of a phenyl group-containing acrylic resin and a butadiene-acrylonitrile resin.

[0028] <4>

[0029] like <3> In the non-aqueous secondary battery separator, the average primary particle size of the resin particles contained in the adhesive layer is 0.1 μm to 1.0 μm.

[0030] <5>

[0031] like <1> ~ <4> The non-aqueous secondary battery separator according to any one of the preceding claims, wherein the mass ratio of the phenyl-containing acrylic resin to the butadiene-acrylonitrile resin contained in the adhesive layer is 60:40 to 95:5.

[0032] <6>

[0033] like <1> ~ <5> The non-aqueous secondary battery separator according to any one of the preceding claims, wherein the phenyl-containing acrylic resin comprises a styrene unit and an acrylic acid unit.

[0034] The molar ratio of the styrene-based unit to the acrylic-based unit is 30:70 to 50:50.

[0035] <7>

[0036] like <1> ~ <6> The non-aqueous secondary battery separator according to any one of the preceding claims, wherein the resin contained in the adhesive layer as a whole has a glass transition temperature of 58°C to 100°C.

[0037] <8>

[0038] like <1> ~ <7> The non-aqueous secondary battery separator according to any one of the preceding claims, wherein the weight per unit area of ​​the adhesive layer is 0.05 g / m 2 ~1.0g / m 2 .

[0039] <9>

[0040] like <1> ~ <8> The non-aqueous secondary battery separator according to any one of the preceding claims, wherein the average primary particle size of the inorganic particles contained in the porous layer as a whole is 0.01 μm to 1.0 μm.

[0041] <10>

[0042] like <1> ~ <9> The non-aqueous secondary battery separator according to any one of the preceding claims, wherein the binder resin comprises at least one selected from the group consisting of polyamide resins, acrylic resins, fluorine resins, and styrene-butadiene resins.

[0043] <11>

[0044] A non-aqueous secondary battery comprising a positive electrode, a negative electrode and a <1> ~ <10> The non-aqueous secondary battery separator according to any one of the preceding claims,

[0045] The non-aqueous secondary battery generates electromotive force through doping and dedoping of lithium ions.

[0046] Effects of the Invention

[0047] According to the present disclosure, a non-aqueous secondary battery separator can be provided that exhibits excellent adhesion to an electrode by wet hot pressing at low temperature and low pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] [ Figure 1 ] is a schematic cross-sectional view of an example of a diaphragm of the present disclosure.

[0049] [ Figure 2 ] is a schematic cross-sectional view of an example of a diaphragm of the present disclosure.

[0050] [ Figure 3 ] is a schematic cross-sectional view of an example of a diaphragm of the present disclosure.

[0051] [ Figure 4] is a schematic cross-sectional view of an example of a diaphragm of the present disclosure.

[0052] [ Figure 5 ] is a schematic cross-sectional view of an example of a diaphragm of the present disclosure.

[0053] [ Figure 6 ] is a schematic cross-sectional view of an example of a diaphragm of the present disclosure.

[0054] [ Figure 7 ] is a schematic cross-sectional view of an example of a diaphragm of the present disclosure. DETAILED DESCRIPTION

[0055] Hereinafter, embodiments of the present disclosure will be described. These descriptions and examples are examples of the embodiments and do not limit the scope of the embodiments.

[0056] In the present disclosure, a numerical range expressed using “to” indicates a range including the numerical values ​​described before and after “to” as the minimum value and the maximum value, respectively.

[0057] In the numerical ranges described in stages in this disclosure, the upper limit or lower limit described in one numerical range may be replaced by the upper limit or lower limit of the numerical range described in another stage. In addition, in the numerical ranges described in this disclosure, the upper limit or lower limit of the numerical range may also be replaced by the value shown in the embodiments.

[0058] In the present disclosure, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes as long as the purpose of the process can be achieved.

[0059] In the present disclosure, when referring to the amount of each component in a composition, if there are multiple substances belonging to each component in the composition, unless otherwise specified, it refers to the total amount of the multiple substances present in the composition.

[0060] In the present disclosure, particles belonging to each component may contain multiple types. When multiple types of particles belonging to each component are present in a composition, the particle size of each component refers to the value for the mixture of the multiple types of particles present in the composition unless otherwise specified.

[0061] In this disclosure, the term "MD" (Machine Direction) refers to the longitudinal direction of a separator manufactured in an elongated shape, and the term "TD" (Transverse Direction) refers to the direction perpendicular to the MD in the plane direction of the separator. TD is also referred to as the "width direction" in this disclosure.

[0062] In this disclosure, when the stacking relationship of each layer constituting the separator is expressed as “upper” and “lower”, the layer closer to the porous substrate is referred to as “lower” and the layer farther from the porous substrate is referred to as “upper”.

[0063] In this disclosure, the volume of the porous layer excluding pores is referred to as "solid content volume."

[0064] In this disclosure, hot pressing after impregnating the separator with an electrolyte is referred to as “wet hot pressing,” and hot pressing after not impregnating the separator with an electrolyte is referred to as “dry hot pressing.”

[0065] In the present disclosure, the expression “(meth)acrylic-” means that it may be either “acrylic-” or “methacrylic-”.

[0066] In the present disclosure, the so-called "monomer unit" of a polymer or resin is a structural unit of the polymer or resin, and refers to a structural unit formed by polymerization of a monomer.

[0067] In this disclosure, the structural unit formed by polymerizing an acrylic monomer is referred to as an "acrylic unit", the structural unit formed by polymerizing a styrene monomer is referred to as a "styrene unit", the structural unit formed by polymerizing butadiene is referred to as a "butadiene unit", and the structural unit formed by polymerizing acrylonitrile is referred to as an "acrylonitrile unit".

[0068] <Separator for non-aqueous secondary batteries>

[0069] The non-aqueous secondary battery separator of the present disclosure (also referred to as "separator" in the present disclosure) comprises: a porous layer containing inorganic particles and a binder resin; and an adhesive layer containing a phenyl-containing acrylic resin and a butadiene-acrylonitrile resin, wherein the amount of butadiene units contained in these two resins in the total amount of acrylic units, styrene units, butadiene units and acrylonitrile units is 3 mol% to 50 mol%.

[0070] The phenyl-containing acrylic resin and the butadiene-acrylonitrile resin may be contained in the adhesive layer as separate molecules or in a state where the two resins are connected.

[0071] Because the separator of the present disclosure includes an adhesive layer containing a phenyl-containing acrylic resin and a butadiene-acrylonitrile resin, wherein the butadiene units contained in these two resins account for 3 to 50 mol% of the total amount of acrylic units, styrene units, butadiene units, and acrylonitrile units, excellent adhesion to the electrode is achieved by low-temperature, low-pressure wet hot pressing. The mechanism for this is presumably as follows.

[0072] Acrylic resins containing phenyl groups are resins that easily adhere to electrodes by applying heat. On the other hand, butadiene-acrylonitrile resins are resins with excellent affinity for electrolytes. Furthermore, it is speculated that since the butadiene units contained in both resins account for 3 to 50 mol% of the total amount of acrylic units, styrene units, butadiene units, and acrylonitrile units, the two resins will not separate but will be able to mix with each other. It is speculated that since the two resins are mixed and contained in the adhesive layer, the adhesive layer will adhere well to the electrodes even using low-temperature, low-pressure wet hot pressing.

[0073] If the amount of butadiene units in the phenyl-containing acrylic resin and butadiene-acrylonitrile resin relative to the total amount of acrylic units, styrene units, butadiene units, and acrylonitrile units is less than 3 mol%, the adhesive layer has low affinity for the electrolyte. To ensure sufficient impregnation of the adhesive layer with the electrolyte, the amount of butadiene units is 3 mol% or greater, preferably 3.2 mol% or greater, and more preferably 3.5 mol% or greater.

[0074] If the amount of butadiene units in the phenyl-containing acrylic resin and the butadiene-acrylonitrile resin exceeds 50 mol% of the total amount of acrylic units, styrene units, butadiene units, and acrylonitrile units, the phenyl-containing acrylic resin and the butadiene-acrylonitrile resin will be difficult to mix with each other. From the perspective of ensuring good mixing of the two resins, the amount of butadiene units is 50 mol% or less, preferably 40 mol% or less, and more preferably 30 mol% or less.

[0075] The types and molar ratios of monomer units contained in the phenyl group-containing acrylic resin and the butadiene-acrylonitrile resin are determined by nuclear magnetic resonance (NMR). Specifically, the following measurements are performed.

[0076] The adhesive layer peeled from the separator or the resin material used to form the adhesive layer was used as a sample. When the resin material used to form the adhesive layer was a resin particle dispersion, the resin particle dispersion was air-dried to prepare a sample.

[0077] After the sample was swollen with deuterated chloroform, the NMR spectra were measured at room temperature at 600 MHz using an NMR apparatus (JNM-ECA600 manufactured by JEOL Ltd.) and a semi-solid probe (FGMAS probe manufactured by JEOL Ltd.). 1 H-NMR spectrum (MAS speed 6 kHz, observation width 15 ppm, number of points 32k, pulse repetition wait time 4 seconds), measured at 150 MHz 13 C-NMR spectrum. 13The C-NMR spectrum was accumulated approximately 33,000 times in quantitative mode (inverse gated decoupling method, MAS speed of 6 kHz, observation width of 250 ppm, number of points of 32k, pulse repetition wait time of 12 s).

[0078] In the above measurement, regardless of whether the acrylic unit, styrene unit, butadiene unit, or acrylonitrile unit is contained in the phenyl-containing acrylic resin or the butadiene-acrylonitrile resin, for example, if the butadiene-acrylonitrile resin contains a styrene unit, the styrene unit is also quantified.

[0079] In the above measurement, the acrylic acid-based units do not include acrylonitrile units. In other words, the acrylonitrile units are not repeatedly quantified as acrylic acid-based units.

[0080] In the above measurement, styrene units may not be detected. For example, when the phenyl-containing acrylic resin is a resin having phenyl (meth)acrylate units but no styrene units, and the butadiene-acrylonitrile resin is a resin not having styrene units, no styrene units may be detected.

[0081] The separator of the present disclosure may be in a form having only a porous layer and an adhesive layer, or may also be in a form having a porous substrate. From the perspective of improving the mechanical strength of the separator and imparting a shutdown function to the separator, the separator of the present disclosure preferably has a porous substrate. The porous substrate is a sheet material that does not contain inorganic particles and is distinguished from the porous layer in that it does not contain inorganic particles.

[0082] When the separator of the present disclosure includes a porous substrate, the separator includes a porous layer on one or both surfaces of the porous substrate, and an adhesive layer on one or both surfaces of a laminate of the porous substrate and the porous layer.

[0083] In the separator of the present disclosure, the adhesive layer preferably comprises resin particles from the perspective of ion permeability. The resin particles may be attached to the porous layer or porous substrate by utilizing their adhesive properties, or they may be contained in the adhesive layer together with a binder resin. That is, the adhesive layer may be formed by the resin particles being attached to the porous layer or porous substrate, or it may be an adhesive layer comprising resin particles and a binder resin.

[0084] When the adhesive layer includes resin particles, the resin particles preferably include at least one of a phenyl-containing acrylic resin and a butadiene-acrylonitrile resin. Specifically, the resin particles may be any of the following: phenyl-containing acrylic resin particles; butadiene-acrylonitrile resin particles; resin particles containing both a phenyl-containing acrylic resin and a butadiene-acrylonitrile resin; or a combination of two or three of these resin particles.

[0085] The layer structure of the separator of the present disclosure will be described with reference to the drawings.

[0086] Figures 1 to 7 Each of them is a schematic cross-sectional view of an embodiment of the separator of the present disclosure. Figures 1 to 7 These are schematic cross-sectional views mainly for explaining the stacking order of layers, and the structure of each layer is abstracted or simplified. Figures 1 to 7 In the description, layers having the same function are denoted by the same reference numerals.

[0087] Figure 1 The separator 101 shown is a separator in which an adhesive layer 50 is arranged on one surface of a porous layer 30 .

[0088] Figure 2 The separator 102 shown is a separator in which adhesive layers 50 are arranged on both surfaces of the porous layer 30. The adhesive layer 50 on one side and the adhesive layer 50 on the other side may be the same or different in components and / or composition.

[0089] Figure 3 The separator 103 shown is a separator having a porous layer 30 disposed on one side of a porous substrate 20 and an adhesive layer 50 disposed on one side of a laminate 40 of the porous substrate 20 and one porous layer 30. In the separator 103, the adhesive layer 50 is disposed on the surface of the porous layer 30.

[0090] Figure 4 The separator 104 shown is a separator having a porous layer 30 disposed on one side of a porous substrate 20 and an adhesive layer 50 disposed on one side of a laminate 40 of the porous substrate 20 and one porous layer 30. In the separator 104, the adhesive layer 50 is disposed on the surface of the porous substrate 20.

[0091] Figure 5 The separator 105 shown is a separator obtained by disposing a porous layer 30 on one side of a porous substrate 20, and disposing adhesive layers 50 on both sides of a laminate 40 of the porous substrate 20 and one porous layer 30. The adhesive layer 50 on one side may be the same as or different from the adhesive layer 50 on the other side in terms of components and / or composition.

[0092] Figure 6 The separator 106 shown is a separator obtained by disposing porous layers 30 on both surfaces of a porous substrate 20, and disposing an adhesive layer 50 on one surface of a laminate 40 of the porous substrate 20 and the two porous layers 30. The porous layer 30 on one side and the porous layer 30 on the other side may be the same or different in components and / or composition.

[0093] Figure 7The separator 107 shown is a separator having porous layers 30 disposed on both surfaces of a porous substrate 20, and adhesive layers 50 disposed on both surfaces of a laminate 40 of the porous substrate 20 and the two porous layers 30. The porous layer 30 on one side may be identical to or different from the porous layer 30 on the other side in terms of components and / or composition. The adhesive layer 50 on one side may be identical to or different from the adhesive layer 50 on the other side in terms of components and / or composition.

[0094] From the viewpoint of adhesion between the separator and the two opposing electrodes, it is preferable that both surfaces of the separator be formed as the adhesive layer 50. From this viewpoint, the separator 102, the separator 105, and the separator 107 are preferable.

[0095] In the separators 103 to 107, the porous layer 30 is a layer disposed on the surface of the porous substrate 20. The porous layer 30 may be present only on one side of the porous substrate 20 or on both sides of the porous substrate 20. If the porous layer 30 is present on both sides of the porous substrate 20, the heat resistance of the separator is further improved, which can further improve the safety of the battery. In addition, curling is less likely to occur in the separator, and the operability during battery manufacturing is excellent. If the porous layer 30 is present only on one side of the porous substrate 20, the ion permeability of the separator is further improved. In addition, the thickness of the entire separator can be suppressed, and a battery with a higher energy density can be manufactured.

[0096] The adhesive layer 50 is a layer disposed on the surface of the porous base material 20 or the porous layer 30 , and exists as the outermost layer of the separator.

[0097] From the perspective of ion permeability, the adhesive layer 50 is preferably a layer containing resin particles 52. From the perspective of achieving better adhesion to the electrode, the adhesive layer 50 preferably has a structure in which a large number of resin particles 52 are arranged adjacent to each other on the surface of the porous substrate 20 or the porous layer 30. From the perspective of improving the energy density of the battery, it is preferably a structure in which the resin particles 52 form a single layer in the thickness direction. However, the structure of the adhesive layer 50 is not limited to the above structure. It may also have a structure in which a large number of resin particles 52 are scattered on the surface of the porous substrate 20 or the porous layer 30, or it may have a structure in which multiple layers of resin particles 52 are stacked in the thickness direction.

[0098] In the separator bonded to the electrode, the resin particles 52 contained in the adhesive layer 50 may partially or completely melt due to the heating for bonding the separator to the electrode, and adjacent resin particles 52 may be connected to each other, and some or all of the particle shapes may not be maintained.

[0099] Hereinafter, the porous substrate, the porous layer, and the adhesive layer included in the separator of the present disclosure will be described in detail.

[0100] [Porous substrate]

[0101] In this disclosure, the so-called porous substrate refers to a substrate having pores or voids inside. Examples of such substrates include microporous membranes; porous sheets such as non-woven fabrics and paper formed from fibrous materials; composite porous sheets obtained by laminating one or more other porous layers on these microporous membranes or porous sheets; and the like. In this disclosure, from the perspective of thin film and strength of the diaphragm, a microporous membrane is preferred. The so-called microporous membrane refers to a membrane that has a large number of micropores inside to form a structure connected by micropores, and gas or liquid can pass from one side of the surface to the other side.

[0102] As a material of the porous base material, a material having electrical insulating properties is preferable.

[0103] To impart a shutdown function to the porous substrate, it is preferred that the porous substrate contain a thermoplastic resin. This shutdown function allows the constituent materials to melt when the battery temperature rises, blocking the pores of the porous substrate and thereby blocking ion migration and preventing thermal runaway. Thermoplastic resins with a melting point below 200°C are preferred. Examples of thermoplastic resins include polyesters such as polyethylene terephthalate and polyolefins such as polyethylene and polypropylene, with polyolefins being preferred.

[0104] The porous substrate is preferably a microporous membrane made of polyolefin (referred to as "polyolefin microporous membrane" in this disclosure). Examples of the polyolefin microporous membrane include polyolefin microporous membranes suitable for existing battery separators. It is preferred to select a polyolefin microporous membrane having sufficient mechanical properties and ion permeability.

[0105] From the viewpoint of exhibiting the shutdown function, the polyolefin microporous membrane is preferably a microporous membrane containing polyethylene, and the polyethylene content is preferably 95% by mass or more relative to the total mass of the polyolefin microporous membrane.

[0106] The polyolefin microporous membrane is preferably a microporous membrane made of polypropylene from the viewpoint of having heat resistance such that the membrane is less likely to be damaged when exposed to high temperatures.

[0107] From the viewpoint of having a shutdown function and heat resistance that is not easily damaged when exposed to high temperatures, the polyolefin microporous membrane is preferably a polyolefin microporous membrane comprising polyethylene and polypropylene. As the polyolefin microporous membrane comprising polyethylene and polypropylene, a microporous membrane in which polyethylene and polypropylene are mixed in one layer can be cited. In the microporous membrane, from the viewpoint of simultaneously achieving the shutdown function and heat resistance, it is preferred to include polyethylene of 95% by mass or more and polypropylene of 5% by mass or less. In addition, from the viewpoint of simultaneously achieving the shutdown function and heat resistance, a polyolefin microporous membrane of the following structure is also preferred, which has a laminated structure of more than two layers, at least one layer comprising polyethylene, and at least one layer comprising polypropylene.

[0108] The polyolefin contained in the polyolefin microporous membrane preferably has a weight-average molecular weight (Mw) of 100,000 to 5,000,000. A polyolefin with an Mw of 100,000 or greater can impart sufficient mechanical properties to the microporous membrane. On the other hand, a polyolefin with an Mw of 5,000,000 or less can provide excellent shutdown properties of the microporous membrane, making it easier to form the microporous membrane.

[0109] As methods for producing polyolefin microporous membranes, the following methods can be cited: a method in which a molten polyolefin resin is extruded from a T-die to form a sheet, the sheet is crystallized, then stretched, and then heat-treated to form a microporous membrane; a method in which a molten polyolefin resin is extruded from a T-die together with a plasticizer such as liquid paraffin, the sheet is cooled to form a sheet, the sheet is stretched, the plasticizer is extracted, and the sheet is heat-treated to form a microporous membrane; and the like.

[0110] Examples of porous sheets formed from fibrous materials include non-woven fabrics, paper, and other porous sheets formed from fibrous materials of the following substances: polyesters such as polyethylene terephthalate; polyolefins such as polyethylene and polypropylene; heat-resistant resins such as wholly aromatic polyamides, polyamide-imides, polyimides, polyethersulfones, polysulfones, polyetherketones, and polyetherimides; cellulose; and the like.

[0111] In this disclosure, a heat-resistant resin refers to a resin having a melting point of 200°C or higher, or a resin having no melting point but a decomposition temperature of 200°C or higher. In other words, a heat-resistant resin in this disclosure is a resin that does not melt or decompose in a temperature range below 200°C.

[0112] As composite porous sheets, sheets obtained by laminating a functional layer on a microporous membrane or a porous sheet formed of a fibrous material can be cited. Such composite porous sheets are preferred from the viewpoint of being able to further add functions through the functional layer. As the functional layer, for example, from the viewpoint of imparting heat resistance, a porous layer formed of a heat-resistant resin can be cited. As heat-resistant resins, one or more heat-resistant resins selected from wholly aromatic polyamides, polyamide-imides, polyimides, polyethersulfones, polysulfones, polyetherketones, and polyetherimides can be cited. As composite methods, there can be cited: a method of coating a functional layer on a microporous membrane or a porous sheet; a method of bonding a microporous membrane or a porous sheet to a functional layer with an adhesive; a method of thermocompression bonding a microporous membrane or a porous sheet to a functional layer; and the like.

[0113] In order to improve the wettability with the coating liquid for forming the porous layer, various surface treatments can be applied to the surface of the porous substrate within the range that does not damage the properties of the porous substrate. Examples of surface treatments include corona treatment, plasma treatment, flame treatment, and ultraviolet irradiation treatment.

[0114] - Characteristics of porous substrates -

[0115] As for the thickness of the porous substrate, from the perspective of improving the energy density of the battery, it is preferably less than 15 μm, more preferably less than 12 μm, and further preferably less than 10 μm. From the perspective of the manufacturing yield of the diaphragm and the manufacturing yield of the battery, it is preferably more than 3 μm, more preferably more than 5 μm, and further preferably more than 7 μm.

[0116] The thickness of the porous substrate was determined by measuring 20 points within a 10 cm square using a contact thickness gauge and averaging the measured values.

[0117] From the viewpoint of suppressing battery short circuit, the air permeability of the porous substrate is preferably 30 sec / 100 mL or more, more preferably 50 sec / 100 mL or more, and even more preferably 70 sec / 100 mL or more.

[0118] From the perspective of ion permeability and the perspective of suppressing clogging of the porous structure at the boundary between the porous substrate and the porous layer or the adhesive layer when exposed to high temperatures, the air permeability of the porous substrate is preferably 200 seconds / 100 mL or less, more preferably 180 seconds / 100 mL or less, and even more preferably 160 seconds / 100 mL or less.

[0119] The air permeability (seconds / 100 mL) of the porous substrate was measured using a digital Oken-type air permeability tester in accordance with JIS P8117:2009.

[0120] [Porous layer]

[0121] The porous layer is a layer having a large number of micropores inside and forming a structure in which the micropores are connected, and gas or liquid can pass from one surface to the other surface.

[0122] When the separator of the present disclosure is provided with a porous substrate, the porous layer may be present only on one side of the porous substrate or on both sides of the porous substrate. If the porous layer is present on both sides of the porous substrate, curling is less likely to occur in the separator, and the operability during battery manufacturing is excellent. If the porous layer is present only on one side of the porous substrate, the ion permeability of the separator is further improved. In addition, the thickness of the entire separator can be suppressed, and a battery with a higher energy density can be manufactured.

[0123] The porous layer included in the separator of the present disclosure contains at least inorganic particles and a binder resin.

[0124] -Inorganic particles-

[0125] Examples of the inorganic particles include metal hydroxide particles, metal oxide particles, metal sulfate particles, metal carbonate particles, metal nitride particles, and clay mineral particles.

[0126] Examples of the metal hydroxide constituting the metal hydroxide particles include magnesium hydroxide, aluminum hydroxide, calcium hydroxide, chromium hydroxide, zirconium hydroxide, cerium hydroxide, nickel hydroxide, and boron hydroxide, with magnesium hydroxide being preferred.

[0127] Examples of the metal oxide constituting the metal oxide particles include silica, alumina, boehmite (alumina monohydrate), titania, zirconia, magnesia, and barium oxide, with alumina being preferred.

[0128] Examples of the metal sulfate constituting the metal sulfate particles include barium sulfate and calcium sulfate, with barium sulfate being preferred.

[0129] Examples of the metal carbonate constituting the metal carbonate particles include calcium carbonate, magnesium carbonate, and barium carbonate.

[0130] Examples of the metal nitride constituting the metal nitride particles include boron nitride and aluminum nitride.

[0131] Examples of the clay mineral particles include calcium silicate and talc.

[0132] The inorganic particles may be those whose surfaces are modified with a silane coupling agent or the like.

[0133] The inorganic particles may be used alone or in combination of two or more.

[0134] The inorganic particles are preferably at least one selected from the group consisting of metal hydroxide particles, metal oxide particles, and metal sulfate particles from the viewpoint of stability in an electrolyte solution and electrochemical stability.

[0135] The shape of the inorganic particles is not limited and may be any of spherical, elliptical, plate-like, needle-like, and irregular shapes. From the perspective of suppressing battery short circuits, the inorganic particles contained in the porous layer are preferably plate-like particles or unaggregated primary particles.

[0136] From the viewpoint of ion permeability of the porous layer, the average primary particle size of the entire inorganic particles contained in the porous layer is preferably 0.01 μm or more, more preferably 0.02 μm or more, and even more preferably 0.03 μm or more.

[0137] From the viewpoint of suppressing interlayer delamination between the porous layer and the porous substrate or the adhesive layer and maintaining adhesion between the separator and the electrode, the average primary particle size of the inorganic particles contained in the porous layer is preferably 1.0 μm or less, more preferably 0.9 μm or less, and further preferably 0.8 μm or less.

[0138] The average primary particle size of the inorganic particles is determined by measuring the major diameters of 100 randomly selected inorganic particles during observation using a scanning electron microscope (SEM), and averaging the major diameters of the 100 particles. The sample for SEM observation is an inorganic particle that is a material for forming a porous layer, or an inorganic particle taken out from a porous layer. There is no limitation on the method for taking out the inorganic particles from the porous layer. Examples of the method include: immersing the porous layer peeled off from the diaphragm in an organic solvent that can dissolve the binder resin, dissolving the binder resin with the organic solvent, and taking out the inorganic particles; heating the porous layer peeled off from the diaphragm to about 800°C, causing the binder resin to disappear, and taking out the inorganic particles; and the like.

[0139] From the viewpoint of achieving well-balanced heat resistance and ion permeability of the porous layer, adhesion of the porous layer to the porous substrate, etc., the content of the inorganic particles is preferably 60% by mass to 99% by mass, more preferably 65% ​​by mass to 98% by mass, and still more preferably 68% by mass to 96% by mass relative to the total mass of the porous layer.

[0140] When the porous layer exists on both sides of the porous substrate, the type or amount of inorganic particles contained in one porous layer may be the same as or different from the type or amount of inorganic particles contained in the other porous layer.

[0141] -Organic particles-

[0142] The porous layer may also contain organic particles. Examples of organic particles include particles formed from crosslinked polymers such as crosslinked poly(meth)acrylic acid, crosslinked poly(meth)acrylate, crosslinked polysiloxane, crosslinked polystyrene, crosslinked polydivinylbenzene, styrene-divinylbenzene copolymer crosslinked products, melamine resins, phenolic resins, and benzoguanamine-formaldehyde condensates; and particles formed from heat-resistant polymers such as polysulfone, polyacrylonitrile, aromatic polyamide, and polyacetal.

[0143] The resin constituting the organic particles may be a mixture, modified product, derivative, copolymer (random copolymer, alternating copolymer, block copolymer, graft copolymer), or crosslinked product of the above-mentioned exemplary materials.

[0144] The organic particles may be used alone or in combination of two or more.

[0145] -Binding resin-

[0146] The binder resin contained in the porous layer not only has the function of bonding the inorganic particles contained in the porous layer to each other, but also has the function of bonding the porous layer to the porous substrate, bonding the porous layer to the electrode, and improving the heat resistance of the porous layer.

[0147] When the porous layer exists on both sides of the porous substrate, the type or amount of the binder resin contained in one porous layer may be the same as or different from the type or amount of the binder resin contained in the other porous layer.

[0148] Examples of the binder resin include polyamide resins, acrylic resins, fluorine resins, styrene-butadiene resins, homopolymers or copolymers of vinyl nitrile compounds (acrylonitrile, methacrylonitrile, etc.), carboxymethyl cellulose, hydroxyalkyl cellulose, polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, polyethers (polyethylene oxide, polypropylene oxide, etc.), polysulfones, polyketones, polyetherketones, polyethersulfones, and mixtures thereof.

[0149] From the viewpoint of suppressing interlayer delamination between the porous layer and the adhesive layer, the binder resin is preferably a resin having excellent affinity with the adhesive layer, and specifically, at least one selected from the group consisting of polyamide resins, acrylic resins, fluorine resins, and styrene-butadiene resins.

[0150] As the binder resin, from the viewpoint of the heat resistance of the porous layer, a polyamide resin is preferably used. As the polyamide resin, for example, wholly aromatic polyamide, polyamide-imide, poly-N-vinylacetamide, polyacrylamide, copolyether polyamide, polyimide, polyetherimide can be mentioned. These resins can be used alone or in combination of two or more.

[0151] Among polyamide resins, fully aromatic polyamides are preferred from the perspective of durability. A fully aromatic polyamide is a polyamide whose main chain consists solely of benzene rings and amide bonds. A small amount of aliphatic monomers may also be copolymerized in a fully aromatic polyamide. Fully aromatic polyamides are also referred to as aramids.

[0152] The wholly aromatic polyamide may be of meta or para type. Among the wholly aromatic polyamides, meta-type wholly aromatic polyamide (also known as meta-type aromatic polyamide) is preferred from the viewpoint of easy formation of a porous layer and excellent redox resistance in electrode reactions. Specifically, the wholly aromatic polyamide is preferably poly(m-phenylene isophthalamide) or poly(p-phenylene terephthalamide), and more preferably poly(m-phenylene isophthalamide).

[0153] When the porous layer contains wholly aromatic polyamide, the content of the wholly aromatic polyamide is preferably 85% by mass to 100% by mass, more preferably 90% by mass to 100% by mass, and even more preferably 95% by mass to 99% by mass, relative to the total amount of all resins contained in the porous layer.

[0154] Examples of the acrylic resin include homopolymers or copolymers of acrylic monomers and copolymers of acrylic monomers and styrene monomers. These resins may be used alone or in combination of two or more.

[0155] Examples of acrylic monomers for acrylic resins include (meth)acrylic acid, methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, isobornyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate. Preferred acrylic monomers are alkyl (meth)acrylates. The alkyl group in the ester portion of the alkyl (meth)acrylate is preferably an alkyl group having 1 to 10 carbon atoms, more preferably an alkyl group having 1 to 8 carbon atoms. One acrylic monomer may be used alone or in combination of two or more.

[0156] Examples of styrene monomers for acrylic resins include styrene, α-methylstyrene; alkyl-substituted styrenes such as 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, and 4-ethylstyrene; halogenated styrenes such as 2-chlorostyrene, 3-chlorostyrene, and 4-chlorostyrene; and fluorostyrenes such as 4-fluorostyrene and 2,5-difluorostyrene. Styrene monomers are preferably styrene and α-methylstyrene, with styrene being more preferred. Styrene monomers may be used alone or in combination of two or more.

[0157] Examples of fluorine-based resins include polyvinylidene fluoride resins. Examples of polyvinylidene fluoride resins include homopolymers of vinylidene fluoride (i.e., polyvinylidene fluoride); copolymers of vinylidene fluoride with halogen-containing monomers such as hexafluoropropylene, tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, vinyl fluoride, and trichloroethylene; copolymers of vinylidene fluoride with monomers other than halogen-containing monomers; copolymers of vinylidene fluoride, a halogen-containing monomer, and monomers other than halogen-containing monomers; and mixtures thereof. These resins may be used alone or in combination of two or more.

[0158] Styrene-butadiene resins are copolymers of styrene monomers and butadiene. Examples of styrene monomers include styrene, α-methylstyrene; alkyl-substituted styrenes such as 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, and 4-ethylstyrene; halogenated styrenes such as 2-chlorostyrene, 3-chlorostyrene, and 4-chlorostyrene; and fluorostyrenes such as 4-fluorostyrene and 2,5-difluorostyrene. Styrene monomers are preferably styrene and α-methylstyrene, with styrene being more preferred. Styrene monomers may be used alone or in combination of two or more.

[0159] A small amount of acrylic monomers may also be copolymerized in the styrene-butadiene resin. As the acrylic monomer, an alkyl (meth)acrylate is preferred. The alkyl group in the ester portion of the alkyl (meth)acrylate is preferably an alkyl group having 1 to 10 carbon atoms, more preferably an alkyl group having 1 to 8 carbon atoms. Specific examples of acrylic monomers include methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and the like. One acrylic monomer may be used alone, or two or more may be used in combination.

[0160] From the viewpoint of achieving well-balanced heat resistance and ion permeability of the porous layer, adhesion of the porous layer to the porous substrate, etc., the content of the binder resin is preferably 1 mass % to 40 mass %, more preferably 2 mass % to 35 mass %, and further preferably 4 mass % to 32 mass % relative to the total mass of the porous layer.

[0161] -Other ingredients-

[0162] The porous layer may contain additives such as dispersants such as surfactants, wetting agents, defoaming agents, and pH adjusters. Dispersants are added to the coating liquid used to form the porous layer to improve dispersibility, coating properties, or storage stability. Wetting agents, defoaming agents, and pH adjusters are added to the coating liquid used to form the porous layer, for example, to improve affinity with the porous substrate, to suppress air ingestion into the coating liquid, or to adjust the pH.

[0163] - Characteristics of the porous layer -

[0164] As for the thickness of each porous layer, from the viewpoint of heat resistance, it is preferably 0.5 μm or more, more preferably 1.0 μm or more, and further preferably 1.5 μm or more. From the viewpoint of ion permeability and battery energy density, it is preferably 5.0 μm or less, more preferably 4.0 μm or less, and further preferably 3.5 μm or less.

[0165] As for the thickness of the porous layer, when the porous layer exists on both sides of the porous substrate, the total thickness of the two sides is preferably 1.0 μm or more, more preferably 2.0 μm or more, further preferably 2.5 μm or more, preferably 10.0 μm or less, more preferably 8.0 μm or less, further preferably 6.0 μm or less.

[0166] The thickness of the porous layer is the value obtained by subtracting the thickness of the porous substrate from the thickness of the flat film after removing the adhesive layer from the separator. The thickness of the flat film after peeling the adhesive layer from the separator is measured at 20 points within a 10 cm square using a contact thickness gauge and the average of the measured values ​​is used to determine the thickness.

[0167] [Adhesive layer]

[0168] The adhesive layer is a layer disposed on the surface of the porous layer or porous substrate and exists as the outermost layer of the separator. The adhesive layer has a large number of gaps or micropores, allowing gas or liquid to pass from one surface to the other.

[0169] From the perspective of ion permeability, the adhesive layer is preferably an adhesive layer containing resin particles. An adhesive layer containing resin particles has excellent ion permeability due to the gaps between the resin particles. The resin particles preferably maintain their shape in the electrolyte and are electrochemically stable.

[0170] The resin particles preferably contain at least one of a phenyl group-containing acrylic resin and a butadiene-acrylonitrile resin. Specifically, the resin particles may be any of the following: phenyl group-containing acrylic resin particles; butadiene-acrylonitrile resin particles; resin particles containing a phenyl group-containing acrylic resin and a butadiene-acrylonitrile resin; or a combination of two or three of these resin particles.

[0171] When the adhesive layer contains resin particles, it may further contain a non-granular resin. This resin functions as, for example, a binding resin between the resin particles or a binding resin between the resin particles and the porous layer or porous substrate. This resin is preferably at least one of a phenyl-containing acrylic resin and a butadiene-acrylonitrile resin.

[0172] When the adhesive layer contains resin particles, the average primary particle size of the resin particles contained in the adhesive layer as a whole is preferably 0.1 μm or more, more preferably 0.2 μm or more, and even more preferably 0.3 μm or more, from the viewpoint of ion permeability of the adhesive layer.

[0173] From the viewpoint of preventing the resin particles from falling off, the average primary particle size of the entire resin particles contained in the adhesive layer is preferably 1.0 μm or less, more preferably 0.9 μm or less, and even more preferably 0.8 μm or less.

[0174] The average primary particle size of the resin particles was determined by measuring the major diameters of 100 randomly selected resin particles observed using a scanning electron microscope (SEM) and averaging the major diameters of the 100 particles. The sample used for SEM observation was the resin particles used as the material for forming the adhesive layer or the resin particles removed from the adhesive layer.

[0175] The adhesive layer contains a phenyl-containing acrylic resin and a butadiene-acrylonitrile resin. The phenyl-containing acrylic resin and the butadiene-acrylonitrile resin contained in the adhesive layer may be separate molecules, molecules formed by connecting the two resins, or a mixture thereof.

[0176] With respect to the phenyl-containing acrylic resin and butadiene-acrylonitrile resin contained in the adhesive layer, the amount of butadiene units contained in the two resins in the total amount of acrylic units, styrene units, butadiene units and acrylonitrile units is 3 mol% to 50 mol%, preferably 3.2 mol% to 40 mol%, and more preferably 3.5 mol% to 30 mol%.

[0177] From the perspective of facilitating adhesion of the adhesive layer to the electrode by wet hot pressing, the mass ratio of the phenyl-containing acrylic resin to the butadiene-acrylonitrile resin contained in the adhesive layer (phenyl-containing acrylic resin: butadiene-acrylonitrile resin) is preferably 60:40 to 95:5, more preferably 55:45 to 92:8, and even more preferably 51:49 to 90:10.

[0178] - Phenyl-containing acrylic resin -

[0179] The polymerization component that provides the phenyl group to the phenyl-containing acrylic resin is not limited. Examples of the polymerization component that provides the phenyl group include phenyl (meth)acrylate and styrene-based monomers.

[0180] The phenyl group-containing acrylic resin preferably has a styrene unit from the viewpoint that the resin can be easily bonded to the electrode by wet hot pressing. That is, the phenyl group-containing acrylic resin preferably contains at least an acrylic monomer and a styrene monomer as polymerization components.

[0181] When the phenyl-containing acrylic resin comprises an acrylic monomer and a styrene monomer as polymer components, the phenyl-containing acrylic resin may be a random copolymer, an alternating copolymer, a block copolymer, or a graft copolymer of the two monomers. For example, the phenyl-containing acrylic resin may be a block copolymer or a graft copolymer of an acrylic monomer and a styrene monomer, with the acrylic units being arranged in the core of the phenyl-containing acrylic resin particles and the styrene units being arranged in the shell.

[0182] The acrylic monomer is preferably at least one selected from the group consisting of (meth)acrylic acid, (meth)acrylate salts, and (meth)acrylate esters. The acrylic monomer may be used alone or in combination of two or more.

[0183] Examples of the (meth)acrylate include sodium (meth)acrylate, potassium (meth)acrylate, magnesium (meth)acrylate, and zinc (meth)acrylate.

[0184] Examples of the (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, isobornyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-(diethylamino)ethyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, and phenyl (meth)acrylate.

[0185] The acrylic monomer is preferably an alkyl (meth)acrylate. The alkyl group in the ester portion of the alkyl (meth)acrylate is preferably an alkyl group having 1 to 10 carbon atoms, more preferably an alkyl group having 1 to 8 carbon atoms.

[0186] Specifically, preferred acrylic monomers include methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. These acrylic monomers may be used alone or in combination of two or more.

[0187] Examples of styrene-based monomers include styrene, α-methylstyrene; alkyl-substituted styrenes such as 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, and 4-ethylstyrene; halogenated styrenes such as 2-chlorostyrene, 3-chlorostyrene, and 4-chlorostyrene; and fluorostyrenes such as 4-fluorostyrene and 2,5-difluorostyrene. Styrene-based monomers may be used alone or in combination of two or more.

[0188] As the styrene-based monomer, styrene and α-methylstyrene are preferred, and styrene is more preferred.

[0189] Phenyl-containing acrylic resins preferably contain styrene units and acrylic units, with a molar ratio (styrene units:acrylic units) of 30:70 to 50:50, more preferably 35:65 to 45:55, and even more preferably 37:63 to 43:57, from the perspective of easy adhesion to electrodes by wet hot pressing. This molar ratio is determined by nuclear magnetic resonance (NMR). Details of NMR are described above.

[0190] The phenyl-containing acrylic resin may also contain monomers other than acrylic monomers and styrene monomers as polymerization components. As such monomers, for example, monomers containing acid groups may be cited. As monomers containing acid groups, monomers having carboxyl groups such as crotonic acid, maleic acid, fumaric acid, and itaconic acid may be cited; monomers having sulfonic acid groups such as vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth)allyl sulfonic acid, (meth)acrylic acid-2-sulfonic acid ethyl ester, 2-acrylamido-2-methylpropanesulfonic acid, and 3-allyloxy-2-hydroxypropanesulfonic acid; monomers having phosphate groups such as 2-(meth)acryloyloxyethyl phosphate, methyl-2-(meth)acryloyloxyethyl phosphate, and ethyl-(meth)acryloyloxyethyl phosphate; monomers having hydroxyl groups such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; and the like. Monomers containing acid groups may be used alone or in combination of two or more.

[0191] The phenyl-containing acrylic resin may also contain a crosslinking monomer as a polymerizable component. Examples of the crosslinking monomer include multifunctional monomers having two or more polymerizable groups. Examples of the multifunctional monomer include divinyl compounds such as divinylbenzene; di(meth)acrylate compounds such as diethylene glycol dimethacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, and 1,3-butanediol diacrylate; tri(meth)acrylate compounds such as trimethylolpropane trimethacrylate and trimethylolpropane triacrylate; ethylenically unsaturated monomers containing epoxy groups such as allyl glycidyl ether and glycidyl methacrylate; and the like. The multifunctional monomers may be used alone or in combination of two or more.

[0192] -Butadiene-acrylonitrile resin-

[0193] The butadiene-acrylonitrile resin may be composed solely of butadiene units and acrylonitrile units, or may be composed of butadiene units, acrylonitrile units, and other monomer units. Specifically, the butadiene-acrylonitrile resin may be a binary copolymer of butadiene and acrylonitrile, or a copolymer of butadiene, acrylonitrile, and other monomers. Examples of other monomers include styrene monomers and acrylic monomers.

[0194] Examples of styrene-based monomers include styrene, α-methylstyrene; alkyl-substituted styrenes such as 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, and 4-ethylstyrene; halogenated styrenes such as 2-chlorostyrene, 3-chlorostyrene, and 4-chlorostyrene; and fluorostyrenes such as 4-fluorostyrene and 2,5-difluorostyrene. Styrene-based monomers are preferably styrene and α-methylstyrene, with styrene being more preferred. Styrene-based monomers may be used alone or in combination of two or more.

[0195] Examples of acrylic monomers include (meth)acrylic acid, methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, isobornyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate. Preferred acrylic monomers are alkyl (meth)acrylates. The alkyl group in the ester portion of the alkyl (meth)acrylate is preferably an alkyl group having 1 to 10 carbon atoms, more preferably an alkyl group having 1 to 8 carbon atoms. One acrylic monomer may be used alone, or two or more may be used in combination.

[0196] From the perspective of excellent affinity with phenyl-containing acrylic resins, the molar ratio of butadiene units to acrylonitrile units (butadiene units:acrylonitrile units) in the butadiene-acrylonitrile resin is preferably 60:40 to 1:99, and more preferably 50:50 to 10:90. This molar ratio is determined using nuclear magnetic resonance (NMR). Details of NMR are described above.

[0197] -Other resins-

[0198] Adhesive layer can also comprise other resins except the acrylic resin containing phenyl and butadiene-acrylonitrile resin.As other resins, for example, homopolymer or copolymer, carboxymethyl cellulose, hydroxyalkyl cellulose, polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, polyether (polyethylene oxide, polypropylene oxide etc.) or the mixture of two or more thereof can be enumerated, for example, polyvinylidene fluoride resin, fluorine-based rubber, vinyl nitrile compound (acrylonitrile, methacrylonitrile etc.).These resins can be included with the form of resin particles, and can also be included as the binding resin of resin particles.

[0199] The mass ratio of other resins in the total resins of the adhesive layer is preferably 10 mass % or less, more preferably 5 mass % or less, further preferably 1 mass % or less, and particularly preferably substantially not contained.

[0200] The total mass ratio of the phenyl-containing acrylic resin and the butadiene-acrylonitrile resin in the total resin of the adhesive layer is preferably 90 mass % or more, more preferably 95 mass % or more, further preferably 99 mass % or more, and particularly preferably 100 mass %.

[0201] The glass transition temperature of the entire resin contained in the adhesive layer is preferably 58° C. or higher, more preferably 58.5° C. or higher, and even more preferably 59° C. or higher from the viewpoint of excellent adhesion to the electrode, although the detailed mechanism is unclear.

[0202] The upper limit of the glass transition temperature of the entire resin contained in the adhesive layer is not limited, but is preferably 100° C. or lower, more preferably 95° C. or lower, and even more preferably 94° C. or lower.

[0203] The glass transition temperature of the resin can be controlled by adjusting the types and copolymerization ratio of the monomers used as polymerization components according to the FOX equation.

[0204] The glass transition temperature of a resin is determined from a differential scanning calorimetry (DSC) curve obtained by differential scanning calorimetry (DSC). In the DSC curve, the intersection of the baseline on the low temperature side and the tangent line of the curve in the step-like change portion is defined as intersection point (1), and the intersection of the baseline on the high temperature side and the tangent line of the curve in the step-like change portion is defined as intersection point (2). The temperature at the center between intersection points (1) and (2) is defined as the glass transition temperature.

[0205] -Other ingredients-

[0206] The adhesive layer may contain additives such as dispersants such as surfactants, wetting agents, defoaming agents, and pH adjusters. For example, a dispersant may be added to the resin particle dispersion used to form the adhesive layer to improve dispersibility, coating properties, or storage stability. For example, a wetting agent, defoaming agent, or pH adjuster may be added to the resin particle dispersion used to form the adhesive layer to improve affinity with the porous layer or porous substrate, to suppress air ingestion into the resin particle dispersion, or to adjust the pH.

[0207] -Adhesive layer characteristics-

[0208] From the viewpoint of adhesion to the electrode, the basis weight (mass per unit area) of the adhesive layer is preferably 0.05 g / m 2 More than 0.07 g / m 2 More preferably, 0.1 g / m 2 above.

[0209] From the viewpoint of ion permeability, the weight per unit area of ​​the adhesive layer is preferably 1.0 g / m 2 Below, more preferably 0.8g / m 2 Below, more preferably 0.6g / m 2 the following.

[0210] When the adhesive layer exists on both sides of the separator, the total weight per unit area of ​​the adhesive layer on both sides is preferably 0.1 g / m 2 ~2.0g / m 2 , more preferably 0.14 g / m 2 ~1.6g / m 2 , more preferably 0.2g / m 2 ~1.2g / m 2 .

[0211] Regarding the weight per unit area of ​​the adhesive layer, the separator was cut into 20 cm × 20 cm pieces, the mass of the layer corresponding to the adhesive layer was measured, and the mass was divided by the area to obtain the total weight of both sides. When the same amount of adhesive layer was formed on both sides of the separator, 1 / 2 of the total of the two sides was taken as the weight per unit area of ​​one side (g / m 2 ).

[0212] [Characteristics of diaphragm]

[0213] As for the thickness of the separator, from the perspective of the mechanical strength of the separator, it is preferably 5 μm or more, more preferably 7 μm or more, and further preferably 9 μm or more. From the perspective of the energy density of the battery, it is preferably 22 μm or less, more preferably 20 μm or less, and further preferably 18 μm or less.

[0214] The thickness of the separator was determined by measuring 20 points within a 10 cm square using a contact thickness gauge and averaging the measured values.

[0215] From the viewpoint of suppressing battery short circuit, the air permeability of the separator is preferably 60 sec / 100 mL or more, more preferably 70 sec / 100 mL or more, and even more preferably 80 sec / 100 mL or more.

[0216] From the viewpoint of ion permeability, the air permeability of the separator is preferably 260 sec / 100 mL or less, more preferably 250 sec / 100 mL or less, and even more preferably 240 sec / 100 mL or less.

[0217] The air permeability (seconds / 100 mL) of the separator was measured using a digital Oken-type air permeability tester in accordance with JIS P8117:2009.

[0218] [Method for manufacturing diaphragm]

[0219] The separator of the present disclosure can be produced, for example, using the following manufacturing method A or manufacturing method B. Manufacturing methods A and B are methods for producing separators having a porous substrate. By replacing the porous substrate in manufacturing methods A and B with a release sheet and removing the release sheet at an appropriate time, a separator having only a porous layer and an adhesive layer can be produced.

[0220] In Manufacturing Methods A and B, the porous layer is formed on the porous substrate by wet coating. In this disclosure, wet coating refers to a method in which the coating layer is solidified in a solidifying solution, while dry coating refers to a method in which the coating layer is dried and solidified.

[0221] Production Method A (Discontinuous Production Method): A porous layer is formed on a porous substrate unwound from a reel to obtain a laminate of the porous substrate and the porous layer. The laminate is then temporarily wound onto another reel. An adhesive layer is then formed on the laminate unwound from the reel to obtain a separator, which is then wound onto yet another reel.

[0222] Production method B (continuous production method): A porous layer and an adhesive layer are formed continuously or simultaneously on a porous substrate unwound from a reel, and the resulting separator is wound onto another reel.

[0223] The production method B may be any one of the following aspects B-1 to B-4.

[0224] Mode B-1: A porous layer-forming coating liquid is applied to a porous substrate, which is then immersed in a coagulation liquid to solidify the coating layer. The substrate is then pulled out of the coagulation liquid, washed with water, and dried. Subsequently, a resin particle dispersion is applied and the substrate is dried.

[0225] Mode B-2: A porous layer-forming coating liquid is applied to a porous substrate, which is then immersed in a coagulation liquid to solidify the coating layer. The substrate is then pulled out of the coagulation liquid and washed with water. Subsequently, a resin particle dispersion is applied and the substrate is dried.

[0226] Mode B-3: The porous layer-forming coating liquid and the resin particle dispersion are simultaneously applied to the porous substrate in two layers, which is then immersed in a coagulation liquid to solidify the former coating layer, which is then pulled out of the coagulation liquid, washed with water, and dried.

[0227] Method B-4: A porous substrate is coated with a coating liquid for forming a porous layer, immersed in a coagulation liquid to solidify the coating layer, pulled out of the coagulation liquid, and transported in a water bath containing resin particles to perform water washing and adhesion of resin particles, pulled out of the water bath, and dried.

[0228] Hereinafter, the details of the steps included in the manufacturing method will be described by taking the manufacturing method B of embodiment B-1 as an example.

[0229] In the manufacturing method B of embodiment B-1, a porous layer is formed on at least one surface of a porous substrate by a wet coating method to obtain a laminate of the porous substrate and the porous layer. Subsequently, an adhesive layer is formed on at least one surface of the laminate by a dry coating method. The manufacturing method B of embodiment B-1 includes the following steps (1) to (7), and steps (1) to (7) are performed in sequence.

[0230] Step (1): Preparation of a coating liquid for forming a porous layer

[0231] The coating liquid for forming the porous layer (hereinafter referred to as the "coating liquid" in the description of the production method) is prepared by dissolving or dispersing the binder resin and inorganic particles of the porous layer in a solvent. Other components besides the binder resin and inorganic particles are dissolved or dispersed in the coating liquid as needed.

[0232] The solvent used to prepare the coating solution includes a solvent that dissolves the binder resin of the porous layer (hereinafter also referred to as a "good solvent"). Examples of the good solvent include polar amide solvents such as N-methylpyrrolidone, dimethylacetamide, dimethylformamide, and dimethylformamide.

[0233] From the perspective of forming a porous layer with a good porous structure, the solvent used to prepare the coating liquid preferably contains a phase separation agent that induces phase separation. Therefore, the solvent used to prepare the coating liquid is preferably a mixed solvent of a good solvent and a phase separation agent. The phase separation agent is preferably mixed with the good solvent in an amount that ensures a viscosity within a range suitable for coating. Examples of the phase separation agent include water, methanol, ethanol, propanol, butanol, butanediol, ethylene glycol, propylene glycol, and tripropylene glycol.

[0234] From the viewpoint of forming a good porous structure, the solvent used for preparing the coating liquid is preferably a mixed solvent of a good solvent and a phase separation agent, wherein the mixed solvent contains 60% by mass or more of the good solvent and 5% to 40% by mass of the phase separation agent.

[0235] From the viewpoint of forming a good porous structure, the resin concentration of the coating liquid is preferably 1% to 20% by mass. From the viewpoint of forming a good porous structure, the inorganic particle concentration of the coating liquid is preferably 0.5% to 50% by mass.

[0236] Step (2): Preparation of resin particle dispersion

[0237] The resin particle dispersion is prepared by dispersing the resin particles in a suitable dispersion medium (e.g., water). A surfactant may be added to the resin particle dispersion to improve the dispersibility of the resin particles in the dispersion medium. The resin particle dispersion may also be a commercially available product or a dilution of a commercially available product.

[0238] From the viewpoint of coating suitability, the concentration of the resin particles in the resin particle dispersion is preferably 1% by mass to 60% by mass.

[0239] Step (3): Applying the coating liquid

[0240] A coating liquid is applied to at least one surface of a porous substrate to form a coating layer on the porous substrate. Examples of methods for applying the coating liquid to the porous substrate include knife coating, Meyer rod coating, die coating, reverse roll coating, roller coating, gravure coating, screen printing, inkjet coating, and spray coating. In the case of forming porous layers on both sides of a porous substrate, it is preferred to apply the coating liquid to both sides of the porous substrate simultaneously from the perspective of productivity.

[0241] Step (4): Curing of the coating layer

[0242] The porous substrate with the coating layer formed thereon is immersed in a coagulation solution to induce phase separation in the coating layer while simultaneously solidifying the binder resin, thereby forming a porous layer containing the binder resin and inorganic particles. Thus, a laminate consisting of the porous substrate and the porous layer is obtained.

[0243] The coagulation solution typically contains a good solvent and a phase separation agent used to prepare the coating solution, and water. From a production perspective, the mixing ratio of the good solvent and the phase separation agent is preferably consistent with the mixing ratio of the mixed solvent used to prepare the coating solution. To achieve porous structure formation and productivity, the water content in the coagulation solution is preferably 40% to 90% by mass. The temperature of the coagulation solution is, for example, 20°C to 50°C.

[0244] Step (5): Washing and drying of the coating layer

[0245] The laminate is lifted out of the coagulation liquid and washed with water. The coagulation liquid is removed from the laminate by washing with water. The laminate is then dried to remove water from the laminate. Washing can be performed, for example, by transporting the laminate in a water bath. Drying can be performed, for example, by transporting the laminate in a high-temperature environment, blowing air on the laminate, or contacting the laminate with heated rollers. The drying temperature is preferably 40°C to 80°C.

[0246] Step (6): Application of resin particle dispersion

[0247] A resin particle dispersion is applied to at least one surface of the laminate. Examples of methods for applying the resin particle dispersion include knife coating, gravure coating, Meyer bar coating, die coating, reverse roll coating, roller coating, screen printing, inkjet coating, and spray coating.

[0248] Step (7): Drying of the resin particle dispersion

[0249] The resin particle dispersion on the laminate is dried to adhere the resin particles to the surface of the laminate. Drying is performed, for example, by conveying the laminate in a high-temperature environment or blowing air on the laminate. The drying temperature is preferably 40°C to 100°C.

[0250] Production method A or production method B of embodiment B-2 to embodiment B-4 can be implemented by partially omitting or modifying the above-mentioned steps (1) to (7).

[0251] <Non-aqueous Secondary Battery>

[0252] The non-aqueous secondary battery disclosed herein generates electromotive force through the doping and dedoping of lithium ions. The battery comprises a positive electrode, a negative electrode, and a separator disclosed herein. Doping refers to the absorption, loading, adsorption, or insertion of lithium ions into the active material of an electrode, such as a positive electrode.

[0253] The non-aqueous secondary battery disclosed herein has a structure in which a battery element (composed of a negative electrode and a positive electrode facing each other with a separator interposed therebetween) is enclosed in an outer packaging material along with an electrolyte solution. The non-aqueous secondary battery disclosed herein is suitable for non-aqueous electrolyte secondary batteries, particularly lithium-ion secondary batteries.

[0254] The non-aqueous secondary battery of the present disclosure has excellent battery productivity because the separator of the present disclosure can be well bonded to the electrodes by wet hot pressing at low temperature and low pressure.

[0255] Hereinafter, examples of the positive electrode, negative electrode, electrolyte solution, and outer casing material included in the non-aqueous secondary battery of the present disclosure will be described.

[0256] As an embodiment of the positive electrode, an active material layer containing a positive electrode active material and a binder resin is formed on a current collector. The active material layer may further contain a conductive additive. Examples of the positive electrode active material include transition metal oxides containing lithium, specifically LiCoO2, LiNiO2, LiMn 1 / 2 Ni 1 / 2 O2、LiCo 1 / 3 Mn 1 / 3Ni 1 / 3 O2, LiMn2O4, LiFePO4, LiCo 1 / 2 Ni 1 / 2 O2、LiAl 1 / 4 Ni 3 / 4 O2, etc. Examples of binder resins include polyvinylidene fluoride resins and styrene-butadiene copolymers. Examples of conductive additives include carbon materials such as acetylene black, Ketjen black, and graphite powder. Examples of current collectors include aluminum foil, titanium foil, and stainless steel foil with a thickness of 5 to 20 μm.

[0257] As an embodiment of the negative electrode, there can be mentioned a structure in which an active material layer containing a negative electrode active material and a binder resin is formed on a current collector. The active material layer may further contain a conductive additive. As the negative electrode active material, there can be mentioned materials that can electrochemically absorb lithium ions, specifically, for example, carbon materials; alloys of silicon, tin, aluminum, etc. with lithium; Wood's metal; etc. As the binder resin, there can be mentioned, for example, polyvinylidene fluoride resins, styrene-butadiene copolymers, etc. As the conductive additive, there can be mentioned, for example, carbon materials such as acetylene black, Ketjen black, graphite powder, and ultrafine carbon fibers. As the current collector, there can be mentioned, for example, copper foil, nickel foil, stainless steel foil, etc. with a thickness of 5μm to 20μm. In addition, metal lithium foil can also be used as the negative electrode instead of the above-mentioned negative electrode.

[0258] The electrolyte is a solution obtained by dissolving a lithium salt in a non-aqueous solvent. Examples of lithium salts include LiPF6, LiBF4, and LiClO4. Examples of non-aqueous solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and their fluorinated derivatives; and cyclic esters such as γ-butyrolactone and γ-valerolactone. These can be used alone or in combination. A suitable electrolyte solution is one in which a cyclic carbonate and a chain carbonate are mixed at a mass ratio of 20:80 to 40:60 (cyclic carbonate:chain carbonate), and a lithium salt is dissolved in a range of 0.5 mol / L to 1.5 mol / L.

[0259] Examples of the outer packaging material include aluminum laminated film packaging, metal cases, etc. The shape of the battery includes rectangular, cylindrical, button-shaped, etc. The separator of the present disclosure is suitable for any shape.

[0260] The nonaqueous secondary battery of the present disclosure can be produced by, for example, the following Production Method 1 or Production Method 2 using a laminated product in which the separator of the present disclosure is disposed between a positive electrode and a negative electrode.

[0261] Manufacturing Method 1: After temporarily bonding the electrodes and separator by dry hot pressing, the stack is placed in an outer packaging material (e.g., aluminum laminate, similarly hereinafter), and the electrolyte is injected. The stack is then wet hot pressed from above the outer packaging material to bond the electrodes and separator and seal the outer packaging material.

[0262] Manufacturing method 2: The laminate is placed in an outer packaging material, and the electrolyte is injected therein. The laminate is then wet-hot pressed from above the outer packaging material to bond the electrodes and separators and seal the outer packaging material.

[0263] In Production Methods 1 and 2, the wet hot pressing temperature is preferably 50°C to 80°C, more preferably 60°C to 70°C. The wet hot pressing pressure is preferably 40 kPa to 200 kPa, more preferably 50 kPa to 100 kPa. The wet hot pressing time is preferably adjusted according to the pressing temperature and pressure, for example, within the range of 8 to 20 hours.

[0264] When manufacturing a laminated product in which a separator is arranged between a positive electrode and a negative electrode, the method of arranging the separator between the positive electrode and the negative electrode can be a method in which the positive electrode, the separator, and the negative electrode are stacked in sequence in at least one layer (the so-called stacking method), or a method in which the positive electrode, the separator, the negative electrode, and the separator are overlapped in sequence and wound along the length direction.

[0265] Example

[0266] The following examples provide a more detailed description of the separator and non-aqueous secondary battery of the present disclosure. The materials, amounts, ratios, and processing steps shown in the following examples may be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the separator and non-aqueous secondary battery of the present disclosure should not be construed as being limited based on the specific examples shown below.

[0267] In the following description, unless otherwise specified, synthesis, treatment, production, etc. are performed at room temperature (25°C ± 3°C).

[0268] <Measurement Method, Evaluation Method>

[0269] The measurement methods and evaluation methods used in Examples and Comparative Examples are as follows.

[0270] [Air permeability of separator and porous substrate]

[0271] The air permeability (sec / 100 mL) of the separator and the porous substrate was measured using a digital Oken-type air permeability tester (Asahi Seiko Co., Ltd., EGO1-55-1MR) in accordance with JIS P8117:2009.

[0272] [Thickness of separator and porous substrate]

[0273] The thickness of the separator and porous substrate was measured using a contact thickness gauge (Mitutoyo Co., Ltd., LITEMATIC VL-50S) at 20 points within a 10 cm square and the averaged results were calculated. A spherical probe with a 10 mm radius (Mitutoyo Co., Ltd.) was used as the measuring terminal, and a load of 0.19 N was applied during the measurement.

[0274] [Thickness of porous layer]

[0275] The thickness of the porous substrate was subtracted from the thickness of the flat film after removing the adhesive layer from the separator. The thickness of the flat film was measured at 20 points within a 10 cm square using a contact thickness gauge (Mitutoyo Co., Ltd., LITEMATIC VL-50S) and the averaged results were used to determine the thickness. A spherical probe with a 10 mm radius (Mitutoyo Co., Ltd.) was used as the measuring terminal, and a load of 0.19 N was applied during the measurement.

[0276] [Weight per unit area of ​​adhesive layer]

[0277] The separator was cut into 20 cm × 20 cm pieces, and the mass of the layer portion corresponding to the adhesive layer was measured. The mass was divided by the area to obtain the total weight per unit area of ​​both sides (g / m2). 2 In all the embodiments and comparative examples, an equal amount of adhesive layer is formed on both sides of the separator. Therefore, the unit area weight calculated on one side is half of the total unit area weight of the two sides (g / m2). 2 ).

[0278] [Average primary particle size of inorganic particles]

[0279] The inorganic particles used to form the porous layer were used as samples and observed using a scanning electron microscope (SEM) to determine the average primary particle size. Specifically, the major diameters of 100 randomly selected inorganic particles were measured during the SEM observation, and the average of the 100 major diameters was taken as the average primary particle size (μm).

[0280] [Average primary particle size of resin particles]

[0281] The dried product of the resin particle dispersion used to form the adhesive layer was used as a sample and observed using a SEM to determine the average primary particle size. Specifically, the major diameters of 100 randomly selected resin particles were measured during the SEM observation, and the average of the 100 major diameters was taken as the average primary particle size (μm).

[0282] [Glass transition temperature of resin]

[0283] The dried product of the resin particle dispersion used to form the adhesive layer was used as a sample for differential scanning calorimetry (DSC). As the DSC apparatus, a Q200 Differential Scanning Calorimeter (TA Instruments) was used, and the weight of the sample was 5 mg. After heating from -65°C to 150°C at a heating rate of 10°C / min, quenching was performed, and the temperature was raised again at the same heating rate to obtain a DSC curve. In the obtained DSC curve, the intersection point (1) of the baseline on the low temperature side and the tangent line of the curve of the step-shaped change part, and the intersection point (2) of the baseline on the high temperature side and the tangent line of the curve of the step-shaped change part were determined, and the temperature at the center of the intersection point (1) and the intersection point (2) was taken as the glass transition temperature (Tg, °C).

[0284] [Resin composition]

[0285] The monomer units contained in the resin constituting the adhesive layer were quantified using NMR.

[0286] The dried product of the resin particle dispersion used to form the adhesive layer was used as a sample. After the sample was swollen with deuterated chloroform, the NMR device (JNM-ECA600 manufactured by JEOL Ltd.) and a semi-solid probe (FGMAS probe manufactured by JEOL Ltd.) were used to measure the NMR at 600 MHz at room temperature. 1 H-NMR spectrum (MAS speed 6 kHz, observation width 15 ppm, number of points 32k, pulse repetition wait time 4 seconds), measured at 150 MHz 13 C-NMR spectrum. 13The C-NMR spectrum was accumulated approximately 33,000 times in quantitative mode (inverse gated decoupling method, MAS speed of 6 kHz, observation width of 250 ppm, number of points of 32k, pulse repetition wait time of 12 s).

[0287] [Adhesive strength]

[0288] Prepare a secondary battery for the test described later. A compression bending test (three-point bending test) was performed on the battery. The measurement was carried out by installing a compression bending test fixture on Tensilon (A&D company, STB-1225S). The distance between the support platforms was set to 4 cm, and the battery was placed on the support platform in such a way that the short side direction of the battery was parallel to the long side direction of the indenter and the compression position during the measurement was the center of the long side direction of the electrode in the battery. The displacement when the indenter was lowered to apply a load of 0.1N was recorded as 0, and the measurement was started. The compression speed during the measurement was set to 2 mm / min, and the measurement was performed until the displacement was 2 mm. The yield point load (N) in the load-displacement curve obtained from the result was used as the bonding strength. In the case where the yield point load could not be observed, the maximum load (N) was used as the bonding strength. The results are shown in Table 3.

[0289] [Heat resistance]

[0290] Prepare the secondary battery for the test described below. At room temperature, charge the battery at a constant current and constant voltage of 0.2C and 4.2V. Next, place the battery in an oven at a temperature of 150°C and place a weight of about 500g on the battery. After 60 minutes, take the battery out of the oven and cool it to room temperature. Measure the battery voltage. If it is below 3.5V, it is determined that a short circuit has occurred. The number of short circuits in the 5 batteries is classified as follows. The results are shown in Table 3.

[0291] A: 0

[0292] B: 1~2

[0293] C: 3 to 5

[0294] <Production of diaphragms and batteries>

[0295] [Example 1]

[0296] - Diaphragm production -

[0297] A mixed solvent of dimethylacetamide (DMAc) and tripropylene glycol (TPG) (DMAc:TPG = 80:20 [mass ratio]) was prepared. Meta-aramid (poly(m-phenylene isophthalamide, Teijin, CONEX)) was dissolved in the mixed solvent to a resin concentration of 4 mass %, thereby obtaining a resin solution. Magnesium hydroxide particles (average primary particle size 0.8 μm) were added to the resin solution at a ratio of magnesium hydroxide particles:meta-aramid = 70:30 [mass ratio], and the mixture was stirred and mixed to obtain a coating solution (1).

[0298] A resin particle dispersion (1) (dispersion medium: water, solid content concentration: 7% by mass) was prepared. The dried product of the resin particle dispersion (1) was used as a sample and subjected to the aforementioned SEM observation, DSC, and NMR analysis to analyze the particle size of the resin particles, the Tg of the resin, and the composition of the resin. The results are shown in Table 2.

[0299] A suitable amount of coating liquid (1) was loaded onto a pair of Meyer rods, and a polyethylene microporous membrane (thickness 9 μm, air permeability 95 sec / 100 mL) was passed between the Meyer rods, and the coating liquid (1) was applied equally to both surfaces. The membrane was immersed in a coagulation liquid (DMAc:TPG:water = 30:8:62 [mass ratio], liquid temperature 40°C) to solidify the coating layer, and then washed in a water washing tank at a water temperature of 40°C and dried. Next, the membrane was passed between a pair of rod coaters loaded with a suitable amount of resin particle dispersion (1), and the resin particle dispersion (1) was applied equally to both surfaces, and dried. As described above, a diaphragm having a porous layer and an adhesive layer formed on both surfaces of the polyethylene microporous membrane was obtained.

[0300] Observation of the obtained separator using a SEM revealed that the porous layer had a large number of micropores inside and formed a structure in which the micropores were connected, allowing gas or liquid to pass from one surface to the other surface.

[0301] -Making the positive electrode-

[0302] A double-arm mixer was used to stir and mix 89.5 parts by mass of lithium cobalt oxide powder (positive electrode active material), 4.5 parts by mass of acetylene black (conductive aid), 6 parts by mass of polyvinylidene fluoride (PVDF) (binding resin), and an appropriate amount of N-methyl-2-pyrrolidone to prepare a positive electrode slurry. The positive electrode slurry was applied to both sides or one side of a 20 μm thick aluminum foil, dried, and then pressed to obtain a positive electrode having a positive electrode active material layer on both sides or one side.

[0303] - Fabrication of the negative electrode -

[0304] A double-arm mixer was used to stir and mix 300 parts by mass of artificial graphite as the negative electrode active material, 7.5 parts by mass of an aqueous dispersion containing 40% by mass of a modified styrene-butadiene copolymer as a binder resin, 3 parts by mass of carboxymethyl cellulose as a thickener, and an appropriate amount of water to prepare a negative electrode slurry. The negative electrode slurry was applied to both sides or one side of a 10 μm thick copper foil, dried, and then pressed to produce a negative electrode having a negative electrode active material layer on both sides or one side.

[0305] -Preparation of a battery for evaluating bonding strength-

[0306] Cut the double-sided positive electrode and double-sided negative electrode into 30mm×70mm rectangles respectively.

[0307] The diaphragm was cut into a rectangle with a TD of 35 mm and a MD of 75 mm.

[0308] They are overlapped in a manner that the positive electrode and the negative electrode are alternately stacked and a separator is sandwiched between the positive electrode and the negative electrode to make a stack consisting of 3 positive electrodes, 3 negative electrodes, and 5 separators. The stack is inserted into a package made of aluminum laminate film, and an electrolyte (1 mol / LLiPF6-ethylene carbonate: ethyl methyl carbonate [mass ratio 3:7]) is injected into the package to allow the electrolyte to penetrate into the stack. Then, a hot press is used to perform hot pressing (wet hot pressing) along the stacking direction of the stack together with the package to bond the electrode to the separator. The hot pressing conditions are set to a pressing temperature of 60 ° C, a pressing pressure of 50 kPa, and a pressing time of 17 hours. The secondary battery for the test obtained as described above is provided for the aforementioned bonding strength.

[0309] -Preparation of a battery for heat resistance evaluation-

[0310] The single-sided positive electrode and the single-sided negative electrode were cut into rectangles of 14 mm × 20 mm.

[0311] The separator was cut into a rectangle of TD 20 mm x MD 26 mm.

[0312] They are overlapped in a manner such that the positive electrode active material layer is opposite to the negative electrode active material layer and in a manner such that a separator is sandwiched between the positive electrode and the negative electrode to produce a stack consisting of one positive electrode, one negative electrode, and one separator. The stack is inserted into a package made of aluminum laminate film, and an electrolyte (1 mol / L LiPF6-ethylene carbonate: ethyl methyl carbonate [mass ratio 3:7]) is injected into the package to allow the electrolyte to penetrate into the stack. Next, a hot press is used to perform hot pressing (wet hot pressing) along the stacking direction of the stack together with the package to bond the electrode to the separator. The hot pressing conditions are set to a pressing temperature of 60°C, a pressing pressure of 50kPa, and a pressing time of 17 hours. The test secondary battery obtained as described above is subjected to the aforementioned evaluation of heat resistance.

[0313] [Example 2]

[0314] A resin particle dispersion (2) (dispersion medium: water, solid content concentration: 7% by mass) was prepared. The dried product of the resin particle dispersion (2) was used as a sample and subjected to the aforementioned SEM observation, DSC, and NMR analysis to analyze the particle size of the resin particles, the Tg of the resin, and the composition of the resin. The results are shown in Table 2.

[0315] A separator was produced in the same manner as in Example 1 except that the resin particle dispersion (1) was replaced with the resin particle dispersion (2). The basis weight of the adhesive layer was as shown in Table 2.

[0316] Observation of the obtained separator using a SEM revealed that the porous layer had a large number of micropores inside and formed a structure in which the micropores were connected, allowing gas or liquid to pass from one surface to the other surface.

[0317] [Comparative Example 1]

[0318] A resin particle dispersion (3) (dispersion medium: water, solid content concentration: 7% by mass) was prepared. The dried product of the resin particle dispersion (3) was used as a sample and subjected to the aforementioned SEM observation, DSC, and NMR analysis to analyze the particle size of the resin particles, the Tg of the resin, and the composition of the resin. The results are shown in Table 2.

[0319] A separator was produced in the same manner as in Example 1 except that the resin particle dispersion (1) was replaced with the resin particle dispersion (3). The basis weight of the adhesive layer was as shown in Table 2.

[0320] [Comparative Example 2]

[0321] A separator was produced in the same manner as in Example 1 except that the resin particle dispersion (1) was replaced with a liquid butadiene-acrylonitrile copolymer (hereinafter referred to as liquid NBR). The basis weight of the adhesive layer was as shown in Table 2.

[0322] [Comparative Example 3]

[0323] The same procedures as in Example 1 were followed, but the resin particle dispersion (1) was replaced with a mixture of the resin particle dispersion (1) and liquid NBR, and a diaphragm was attempted. The mixing ratio was set to 15:85 (mass ratio) of solid content of the resin particle dispersion (1): liquid NBR. The resin particles in the resin particle dispersion (1) separated from the liquid NBR, and an adhesive layer could not be formed. The glass transition temperature was not measured in this example.

[0324] The particle sizes of the resin particles listed in Table 2 are values ​​measured for the resin particle dispersion (1). The types and amounts of monomer units listed in Table 2 are based on the measurement results of the resin particle dispersion (1) and the measurement results of liquid NBR.

[0325] [Example 3]

[0326] A separator was produced in the same manner as in Example 1 except that the magnesium hydroxide particles were replaced with barium sulfate particles (average primary particle size: 0.03 μm). The composition of the porous layer and the weight per unit area of ​​the adhesive layer are as shown in Tables 1 and 2.

[0327] Observation of the obtained separator using a SEM revealed that the porous layer had a large number of micropores inside and formed a structure in which the micropores were connected, allowing gas or liquid to pass from one surface to the other surface.

[0328] [Comparative Example 4]

[0329] A separator was produced in the same manner as in Example 3 except that the resin particle dispersion (1) was replaced with the resin particle dispersion (3). The composition of the porous layer and the basis weight of the adhesive layer are as shown in Tables 1 and 2.

[0330] [Example 4]

[0331] A separator was produced in the same manner as in Example 1, except that the meta-aramid was replaced with an acrylic resin and the magnesium hydroxide particles were replaced with alumina particles (average primary particle size 1.0 μm). The composition of the porous layer and the weight per unit area of ​​the adhesive layer are shown in Tables 1 and 2.

[0332] Observation of the obtained separator using a SEM revealed that the porous layer had a large number of micropores inside and formed a structure in which the micropores were connected, allowing gas or liquid to pass from one surface to the other surface.

[0333] [Comparative Example 5]

[0334] A separator was produced in the same manner as in Example 4 except that the resin particle dispersion (1) was replaced with the resin particle dispersion (3). The composition of the porous layer and the weight per unit area of ​​the adhesive layer are as shown in Tables 1 and 2.

[0335] [Example 5]

[0336] A separator was produced in the same manner as in Example 1, except that the meta-aramid was replaced with an acrylic resin and the magnesium hydroxide particles were replaced with boehmite particles (average primary particle size 1.0 μm). The composition of the porous layer and the weight per unit area of ​​the adhesive layer are shown in Tables 1 and 2.

[0337] Observation of the obtained separator using a SEM revealed that the porous layer had a large number of micropores inside and formed a structure in which the micropores were connected, allowing gas or liquid to pass from one surface to the other surface.

[0338] The acrylic resin used to form the porous layer in Example 4, Comparative Example 5, and Example 5 was n-butyl methacrylate / acrylonitrile copolymer.

[0339] The abbreviations in Tables 1 and 2 have the following meanings.

[0340] PE: Polyethylene

[0341] St:Styrene

[0342] MMA: methyl methacrylate

[0343] BMA: n-butyl methacrylate

[0344] EHMA: 2-ethylhexyl methacrylate

[0345] Bt: Butadiene

[0346] AN: Acrylonitrile

[0347] [Table 1]

[0348]

[0349] [Table 2]

[0350]

[0351] [Table 3]

[0352]

[0353] All documents, patent applications, and technical standards described in this specification are incorporated herein by reference to the same extent as if each document, patent application, and technical standard were specifically and individually indicated.

[0354] The entire disclosure of Japanese application No. 2023-028672 filed on February 27, 2023 is incorporated into this specification by reference.

[0355] Description of Reference Numerals

[0356] 101, 102, 103, 104, 105, 106, 107 diaphragms

[0357] 20 Porous substrate

[0358] 30 porous layer

[0359] 40 laminates

[0360] 50 adhesive layer

[0361] 52 resin particles

Claims

1. A separator for a non-aqueous secondary battery, comprising: a porous layer containing inorganic particles and a binder resin; and The adhesive layer contains a phenyl-containing acrylic resin and a butadiene-acrylonitrile resin, wherein the amount of butadiene units contained in the two resins accounts for 3 mol% to 50 mol% of the total amount of acrylic units, styrene units, butadiene units and acrylonitrile units.

2. The non-aqueous secondary battery separator according to claim 1, further comprising a porous substrate. The porous substrate has the porous layer on one or both sides. The adhesive layer is provided on one or both surfaces of a laminate of the porous substrate and the porous layer.

3. The non-aqueous secondary battery separator according to claim 1, wherein The adhesive layer includes resin particles, The resin particles include at least one of a phenyl group-containing acrylic resin and a butadiene-acrylonitrile resin.

4. The non-aqueous secondary battery separator according to claim 3, wherein The average primary particle size of the entire resin particles contained in the adhesive layer is 0.1 μm to 1.0 μm.

5. The non-aqueous secondary battery separator according to claim 1, wherein The mass ratio of the phenyl-containing acrylic resin to the butadiene-acrylonitrile resin contained in the adhesive layer is 60:40 to 95:

5.

6. The non-aqueous secondary battery separator according to claim 1, wherein The phenyl-containing acrylic resin has a styrene unit and an acrylic unit. The molar ratio of the styrene-based unit to the acrylic-based unit is 30:70 to 50:

50.

7. The non-aqueous secondary battery separator according to claim 1, wherein The glass transition temperature of the entire resin contained in the adhesive layer is 58°C to 100°C.

8. The non-aqueous secondary battery separator according to claim 1, wherein The weight per unit area of ​​the adhesive layer is 0.05 g / m 2 ~1.0g / m 2 .

9. The non-aqueous secondary battery separator according to claim 1, wherein The average primary particle size of the entire inorganic particles contained in the porous layer is 0.01 μm to 1.0 μm.

10. The non-aqueous secondary battery separator according to claim 1, wherein The binder resin includes at least one selected from the group consisting of polyamide resins, acrylic resins, fluorine resins, and styrene-butadiene resins.

11. A non-aqueous secondary battery comprising a positive electrode, a negative electrode, and the non-aqueous secondary battery separator according to any one of claims 1 to 10 disposed between the positive electrode and the negative electrode. The non-aqueous secondary battery generates electromotive force through doping and dedoping of lithium ions.

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