Polyimide porous film, non-aqueous secondary battery separator, secondary battery, and method for manufacturing secondary battery

Abstract

To provide a porous polyimide film that has excellent adhesion to an adherend and suppresses the generation of deposits.SOLUTION: The porous polyimide film has a porous polyimide film body and at least one of resin particles and a resin porous film, adhered to one or both surfaces of the porous polyimide film body and containing a fluoropolymer resin or containing a fluoropolymer resin and an acrylic resin.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a polyimide porous membrane, a separator for a non-aqueous secondary battery, a secondary battery, and a method for manufacturing a secondary battery. [Background technology]

[0002] Patent Document 1 describes a battery separator comprising a microporous membrane and a porous layer provided on at least one surface of the microporous membrane, the porous layer containing a vinylidene fluoride-hexafluoropropylene copolymer and an acrylic resin, the vinylidene fluoride-hexafluoropropylene copolymer containing a monomer unit having a hydrophilic group and containing 0.3 mol % to 3 mol % of hexafluoropropylene monomer units, and the acrylic resin containing a butyl acrylate monomer unit. Patent Document 1 also cites a polyolefin microporous membrane as an example of the microporous membrane.

[0003] Furthermore, Patent Document 2 describes a separator material for a lithium secondary battery, which is made by dispersing and mixing polymer particles, which are fluorine-based polymer resin particles having a higher softening point than the copolymer, in the separator, which is based on a copolymer resin of vinylidene fluoride and hexafluoropropylene (VdF-HFP). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2017 / 026485 [Patent Document 2] Patent No. 3040757 Summary of the Invention [Problem to be solved by the invention]

[0005] The present disclosure aims to provide a polyimide porous membrane that has excellent adhesion to an adherend and suppresses the formation of deposits as compared to a polyolefin porous membrane provided with a porous layer containing a fluororesin on one or both sides.

Means for Solving the Problems

[0006] Specific means for solving the above problems include the following aspects.

[0007] <1> A polyimide porous membrane body, at least one of resin particles and a resin porous membrane that adheres to one or both sides of the polyimide porous membrane body and contains a fluororesin or contains a fluororesin and an acrylic resin, and having.

[0008] <2> The polyimide porous membrane according to <1>, wherein the fluororesin is a polymer containing vinylidene fluoride as a polymerization component.

[0009] <3> The polyimide porous membrane according to <1> or <2>, which satisfies the relationship of X < Y when the average pore diameter of the polyimide porous membrane body is X and the average particle diameter of the resin particles is Y. <4> The polyimide porous membrane according to <3>, wherein the ratio (Y / X) of the average particle diameter Y of the resin particles to the average pore diameter X of the polyimide porous membrane body is more than 1 and 70.0 or less. <5> The polyimide porous membrane according to <3> or <4>, wherein the average pore diameter X of the polyimide porous membrane body is 50 nm or more and 1500 nm or less. <6> The polyimide porous membrane according to any one of <3> to <5>, wherein the average particle diameter Y of the resin particles is 5 nm or more and 10 μm or less. <7> The polyimide porous membrane according to any one of <1> to <6>, wherein the porosity of the polyimide porous membrane body is 50% or more and 90% or less. <8> the fluorine atom concentration on the surface of the polyimide porous membrane body to which at least one of the resin particles and the resin porous membrane is attached is 5 atm% or more and 40 atm% or less; <1> ~ <7> 1. The polyimide porous film according to any one of the above.

[0010] <9> a polyimide porous membrane body; At least one of resin particles and a resin porous membrane adhered to one or both surfaces of the polyimide porous membrane body and containing a resin other than a polyimide resin; and A polyimide porous membrane having a surface to which at least one of the resin particles and the resin porous membrane is attached, the surface having a water contact angle of 80° or more and 120° or less.

[0011] <10> <1> ~ <9> 1. A separator for a non-aqueous secondary battery, comprising the porous polyimide film according to any one of 1 to 8. <11> An electrode; <10> and an adhesive layer formed of at least one of the resin particles and the porous resin membrane between the electrode and the porous polyimide membrane body. <12> <10> and an electrode, by using at least one of the resin particles and the porous resin membrane. [Effects of the Invention]

[0012] <1> or <9> According to the invention, it is possible to provide a polyimide porous film that has superior adhesion to an object to be adhered and suppresses the formation of deposits, compared to a polyolefin porous film having a porous layer containing a fluororesin on one or both sides.

[0013] <2> According to the present invention, it is possible to provide a polyimide porous film that has superior adhesion to a polyimide porous body and superior adhesion to an object to be adhered, compared to when the fluorine-based resin is polytetrafluoroethylene. <3> According to the invention, it is possible to provide a polyimide porous membrane that has excellent adhesion to an object to be adhered and suppresses the generation of deposits, compared to when the relationship between the average pore size X of the polyolefin porous membrane body and the average particle size Y of the resin particles is X>Y. <4> According to the invention, it is possible to provide a polyimide porous film that has excellent adhesion to an object to be adhered and that suppresses the formation of deposits, compared to when the ratio (Y / X) is 1 or less or exceeds 70.0. <5> According to the invention, it is possible to provide a polyimide porous film that has excellent adhesion to an object to be adhered and that suppresses the formation of deposits, compared to when the average pore diameter X is less than 50 nm or more than 1500 nm. <6> According to the invention, it is possible to provide a polyimide porous film that has excellent adhesion to an object to be adhered and that suppresses the formation of deposits, compared to when the average particle size Y is less than 5 nm or more than 10 μm. <7> According to the present invention, it is possible to provide a polyimide porous membrane suitable for a separator for a non-aqueous secondary battery, which can provide a secondary battery having excellent mechanical strength and high cycle characteristics, compared to polyimide porous membranes having a porosity of less than 50% or more than 90%. <8> According to the invention, it is possible to provide a polyimide porous membrane that has excellent adhesion to an object to be adhered and that suppresses the formation of deposits, compared to a case where the fluorine atom concentration on the surface of the polyimide porous membrane body to which at least one of resin particles and a resin porous membrane is attached is less than 5 atm%.

[0014] <10> According to the present invention, it is possible to provide a separator for a non-aqueous secondary battery that has excellent adhesion to electrodes and suppresses the formation of deposits, compared to a separator for a non-aqueous secondary battery made of a polyolefin porous membrane having a porous layer containing a fluororesin on one or both sides.

[0015] <11> or <12> According to the present invention, it is possible to provide a secondary battery that has excellent adhesion to electrodes and suppresses the generation of deposits, as compared with a secondary battery that includes a separator for a nonaqueous secondary battery made of a polyolefin porous membrane having a porous layer containing a fluororesin on one or both sides, or a method for manufacturing the same. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a partial cross-sectional schematic view illustrating an example of a secondary battery (lithium ion secondary battery) according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0017]

[0023] The following describes embodiments of the present disclosure. These descriptions and examples are intended to illustrate the embodiments and are not intended to limit the scope of the embodiments.

[0018] In the present disclosure, a numerical range indicated using "to" indicates a range that includes the numerical values before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in this disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples.

[0019] In the present disclosure, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes as long as the intended purpose of the process is achieved.

[0020] When embodiments of the present disclosure are described with reference to the drawings, the configuration of the embodiment is not limited to the configuration shown in the drawings. Furthermore, the sizes of the components in each drawing are conceptual, and the relative size relationships between the components are not limited to these.

[0021] In the present disclosure, each component may contain multiple corresponding substances. When referring to the amount of each component in a composition in the present disclosure, if multiple substances corresponding to each component are present in the composition, the total amount of the multiple substances present in the composition is meant unless otherwise specified.

[0022] In the present disclosure, the term "(meth)acrylic" means either "acrylic" or "methacrylic."

[0023] <Porous polyimide film> In order to improve the adhesion between a polyolefin porous membrane and another material (also called an adherend), there is a method of applying particles containing fluororesin to the interface between the polyolefin porous membrane and the other material. The polyolefin porous membrane used in this method may melt at high temperatures (e.g., 150°C or higher), and the function as a porous membrane may be impaired. On the other hand, polyimide porous films are films that are hard and have excellent heat resistance due to the polyimide resin. Therefore, unlike polyolefin porous films, they are less likely to dissolve even at the high temperatures mentioned above. However, due to their hardness, polyimide porous films have poor adhesion to other materials, and gaps may form between the polyimide porous film and other materials. Porous films have the function of allowing substances such as ions to pass through, but if gaps form between the polyimide porous film and other materials, substances that pass through the polyimide porous film may accumulate in the gaps, resulting in the formation of deposits.

[0024] A first embodiment of the polyimide porous membrane according to the present disclosure comprises a polyimide porous membrane body, and at least one of resin particles and a resin porous membrane that are adhered to one or both sides of the polyimide porous membrane body and contain a fluorine-based resin or a fluorine-based resin and an acrylic resin. Here, the "resin particles containing a fluorine-based resin, or containing a fluorine-based resin and an acrylic resin" contained in the polyimide porous film according to the present disclosure are also referred to as "fluorine-containing resin particles." Furthermore, the "resin porous film containing a fluorine-based resin, or containing a fluorine-based resin and an acrylic resin" contained in the polyimide porous film according to the present disclosure is also referred to as "fluorine-containing porous resin film."

[0025] A second embodiment of the polyimide porous membrane according to the present disclosure comprises a polyimide porous membrane body and at least one of resin particles and a resin porous membrane adhered to one or both sides of the polyimide porous membrane body and containing a resin other than polyimide resin, wherein the water contact angle of the surface of the polyimide porous membrane to which at least one of the resin particles and the resin porous membrane adheres is 80° or more and 120° or less.

[0026] In the present disclosure, unless otherwise specified, when the term "porous polyimide film according to the present disclosure" is used, it refers to both the first embodiment and the second embodiment.

[0027] As described above, the polyimide porous membrane according to the present disclosure has at least one of resin particles and a porous resin membrane provided on one or both sides of the polyimide porous membrane body. The presence of at least one of the resin particles and the porous resin membrane is thought to enhance adhesion between the polyimide porous membrane body and other materials (i.e., the object to be adhered). As a result, gaps are less likely to form between the polyimide porous membrane body and other materials, which is thought to suppress the formation of deposits of substances that pass through the polyimide porous membrane in the formed gaps. In particular, by using the polyimide porous membrane according to the present disclosure, resin particles and / or a porous resin membrane are present at the interface between the polyimide porous membrane body and other materials. As described above, the resin particles and / or porous resin membrane contain a fluorine-based resin or have a water contact angle of 80° or more and 120° or less. This is thought to suppress the formation of deposits of substances that pass through the polyimide porous membrane at the interface between the polyimide porous membrane body and other materials where the resin particles and / or porous resin membrane are present, which is thought to suppress the formation of deposits.

[0028] [Preferred Embodiment] In the polyimide porous membrane according to the present disclosure, when the average pore diameter of the polyimide porous membrane body is X and the average particle diameter of the resin particles (fluorine-containing resin particles in the case of the first embodiment) is Y, it is preferable to satisfy the relationship X < Y. In an embodiment where the average particle diameter Y of the resin particles is larger than the average pore diameter X of the polyimide porous membrane body, it is possible to suppress the burial of the resin particles in the openings of the polyimide porous membrane body. As a result, the polyimide porous membrane of this embodiment has higher adhesion to the adherend and further suppresses the formation of deposits. Here, the average particle diameter of the resin particles means the volume average particle diameter (D50v) of the resin particles.

[0029] In the polyimide porous membrane according to the present disclosure, the ratio (Y / X) of the average particle diameter Y of the resin particles (fluorine-containing resin particles in the case of the first embodiment) to the average pore diameter X of the polyimide porous membrane body is preferably more than 1 and 70.0 or less, more preferably more than 1 and 65.0 or less, still more preferably more than 1 and 60.0 or less, and particularly preferably more than 1 and 55.0 or less. By being in an embodiment where Y / X is more than 1, it is possible to more effectively suppress the burial of the resin particles in the openings of the polyimide porous membrane. Also, by being in an embodiment where Y / X is 70.0 or less, the formation of voids between the polyolefin porous membrane body and the adherend due to coarse particles is suppressed. As a result, the polyimide porous membrane of this embodiment has higher adhesion to the adherend and further suppresses the formation of deposits.

[0030] In the polyimide porous membrane according to the present disclosure, the fluorine atom concentration on the surface of the polyimide porous membrane body to which at least one of the resin particles and the resin porous membrane is attached is preferably 5 atm% or more and 40 atm% or less, more preferably 8 atm% or more and 35 atm% or less, and still more preferably 10 atm% or more and 30 atm% or less. The fluorine atom concentration is an index of the amount of resin particles and resin porous membrane attached. A polyimide porous membrane having a fluorine atom concentration within the above range exhibits improved adhesion to an object to be adhered and further suppresses the formation of deposits.

[0031] The fluorine atom concentration on the surface of the polyimide porous membrane body to which at least one of the resin particles and the resin porous membrane is attached is measured by X-ray photoelectron spectroscopy (XPS). Specifically, an X-ray photoelectron spectrometer (JPS-9000MX manufactured by JEOL Ltd.) is used, and the surface of the polyimide porous film to be measured is analyzed using MgKα radiation as the X-ray source, with an acceleration voltage of 10 kV and an emission current of 20 mA. From the analysis results, the fluorine atomic fraction (atm%) relative to the total atomic weight of all elements is calculated, and this is taken as the fluorine atomic concentration.

[0032] The fluorine-containing resin particles and the fluorine-containing resin porous membrane in the first embodiment of the polyolefin porous membrane according to the present disclosure will be described below.

[0033] [Fluorine-containing resin particles and fluorine-containing resin porous membrane] A first embodiment of the polyolefin porous membrane according to the present disclosure comprises at least one of resin particles (i.e., fluorine-containing resin particles) and a resin porous membrane (i.e., fluorine-containing resin porous membrane) attached to one or both sides of a polyimide porous membrane body and containing a fluorine-based resin or a fluorine-based resin and an acrylic resin.

[0034] [Fluorine-containing resin particles] The fluorine-containing resin particles contain a fluorine-based resin, or contain a fluorine-based resin and an acrylic resin. The fluorine-based resin contained in the fluorine-containing resin particles is not particularly limited, but examples thereof include a polymer containing tetrafluoroethylene as a polymerization component, a polymer containing vinylidene fluoride as a polymerization component, and a polymer containing trifluorochloroethylene as a polymerization component. Examples of polymers containing tetrafluoroethylene as a polymerization component include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and tetrafluoroethylene-ethylene copolymer (ETFE). Examples of polymers containing vinylidene fluoride as a polymerization component include polyvinylidene fluoride (PVDF) and vinylidene fluoride-hexafluoropropylene copolymer (VDF-HFP). Examples of polymers containing trifluorochloroethylene as a polymer component include polytrifluorochloroethylene (PCTFE) and trifluorochloroethylene-ethylene polymer (ECTFE). Alternatively, polyvinyl fluoride (PVF) may be used.

[0035] The fluororesin is preferably a polymer containing vinylidene fluoride as a polymerization component, from the viewpoints of adhesion to the object to be adhered, suppression of deposit formation, manufacturability, and excellent adhesion to the polyimide porous body.

[0036] The weight average molecular weight of the fluororesin is preferably 10,000 or more and 200,000 or less, more preferably 20,000 or more and 140,000 or less, and even more preferably 60,000 or more and 100,000 or less, from the viewpoint of improving adhesion to the object to be adhered and suppressing the formation of deposits. The number average molecular weight of the fluororesin is preferably 5,000 or more and 180,000 or less, and more preferably 20,000 or more and 100,000 or less, from the viewpoint of improving adhesion to the object to be adhered and suppressing the formation of deposits.

[0037] In this disclosure, the weight-average molecular weight (also referred to as "Mw") of a fluororesin is measured by gel permeation chromatography (GPC). Molecular weight measurement by GPC is performed using a Tosoh HLC-8120GPC as the GPC apparatus, a Tosoh TSKgel SuperHM-M (15 cm) column, and N,N-dimethylformamide as the solvent. The weight-average molecular weight of the resin is calculated using a molecular weight calibration curve prepared using monodisperse polystyrene standard samples.

[0038] In the case of a fluororesin (such as PTFE) that is insoluble or difficult to dissolve in a solvent, the number average molecular weight can be determined by the following method. That is, the heat of crystallization (ΔHc) of the fluororesin is measured using a differential scanning calorimeter (DSC), and the value is substituted into the following formula (A) to determine the number average molecular weight. ·Formula (A) Number average molecular weight (Mn)=2.1×10 10 ×ΔHc -5.16

[0039] The acrylic resin contained in the fluorine-containing resin particles may be a polymer containing a (meth)acrylic monomer as a polymerization component, and the (meth)acrylic monomer may be at least one selected from the group consisting of (meth)acrylic acid and (meth)acrylic acid esters. The acrylic resin preferably contains 50% by mass or more, more preferably 80% by mass or more, and may contain 100% by mass of (meth)acrylic monomers relative to the total amount of polymerization components. Here, the term "acrylic resin" is a concept that encompasses both acrylic resins and methacrylic resins.

[0040] (Meth)acrylic acid, which is one of the (meth)acrylic monomers, includes not only (meth)acrylic acid but also salts thereof, such as sodium (meth)acrylate and calcium (meth)acrylate. As a (meth)acrylic acid ester, which is one of the (meth)acrylic monomers, a (meth)acrylic acid alkyl ester is preferred. Examples of (meth)acrylic acid alkyl esters include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, and isobornyl (meth)acrylate. Other examples include 2-carboxyethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 2-methoxyethyl (meth)acrylate.

[0041] The weight average molecular weight of the acrylic resin is preferably 60,000 or more and 1,000,000 or less, more preferably 50,000 or more and 300,000 or less, and even more preferably 20,000 or more and 200,000 or less, from the viewpoint of improving adhesion to the object to be adhered and suppressing the formation of deposits.

[0042] The fluorine-containing resin particles contain a fluorine-based resin or contain both a fluorine-based resin and an acrylic resin. In the fluorine-containing resin particles, the fluorine-based resin and the acrylic resin may each be used alone or in combination of two or more kinds.

[0043] When the fluorine-containing resin particles contain both a fluorine-based resin and an acrylic resin, the ratio of the fluorine-based resin to the acrylic resin is preferably 2:98 to 20:80 by mass, more preferably 5:95 to 15:85, and even more preferably 7:93 to 13:87.

[0044] The content of the fluorine-based resin and the acrylic resin in the fluorine-containing resin particles is preferably from 50% by mass to 100% by mass, more preferably from 70% by mass to 100% by mass, and even more preferably from 90% by mass to 100% by mass, based on the total mass of the fluorine-containing resin particles, from the viewpoint of improving adhesion to the object to be adhered and suppressing the formation of deposits.

[0045] (additives) The fluorine-containing resin particles may contain various additives within a range that does not impair the effects of excellent adhesion to an object to be adhered and suppression of deposit formation. The additives may include resins other than fluorine-based resins and acrylic resins, colorants (e.g., pigments, dyes), release agents (e.g., hydrocarbon waxes; natural waxes such as carnauba wax, rice wax, and candelilla wax; synthetic or mineral / petroleum waxes such as montan wax; and ester waxes such as fatty acid esters and montan acid esters), and charge control agents. The content of the additive is preferably 10% by mass or less, more preferably 5% by mass or less, based on the total mass of the fluorine-containing resin particles.

[0046] The volume average particle diameter (D50v) of the fluorine-containing resin particles, i.e., the average particle diameter Y of the fluorine-containing resin particles, is preferably 5 nm or more and 10 μm or less, more preferably 10 nm or more and 1.0 μm or less, and even more preferably 50 nm or more and 0.5 μm or less, from the viewpoints of ease of production and availability, improved adhesion to an adhered object, and suppression of deposit formation.

[0047] The volume-average particle diameter (D50v) of fluororesin particles was measured using a Coulter Multisizer II (Beckman Coulter) with a 100 μm aperture. 0.5 mg to 50 mg of fluororesin particles were dispersed in 2 mL of a 5% by mass aqueous solution of sodium alkylbenzene sulfonate. This was then mixed with 100 mL to 150 mL of electrolyte (ISOTON-II, Beckman Coulter) and dispersed for 1 minute using an ultrasonic disperser. The resulting dispersion was used as the sample. The particle diameters of 50,000 particles with diameters of 2 μm to 60 μm in the sample were measured. The volume-average particle diameter (D50v) was determined as the particle diameter at 50% cumulatively in the volume-based particle size distribution, calculated from the smallest diameter.

[0048] (Method of producing fluorine-containing resin particles) The fluorine-containing resin particles may be produced by a conventionally known method for producing resin particles. Examples of methods for producing fluorine-containing resin particles include dry production methods (such as a kneading and pulverization method) and wet production methods (such as an aggregation and coalescence method, a suspension polymerization method, a dissolution and suspension method, and an emulsion polymerization method). As the fluorine-containing resin particles, commercially available products may be used.

[0049] [Fluorine-containing resin porous membrane] The fluorine-containing porous resin membrane contains a fluorine-based resin, or contains a fluorine-based resin and an acrylic resin. The fluorine-containing resin and acrylic resin contained in the fluorine-containing resin porous membrane have the same meanings as the fluorine-containing resin and acrylic resin contained in the above-mentioned fluorine-containing resin particles, respectively, and preferred embodiments are also the same. The additives contained in the fluorine-containing resin porous membrane are also synonymous with the additives contained in the fluorine-containing resin particles described above, and the preferred embodiments are also the same.

[0050] The thickness of the fluorine-containing porous resin membrane is preferably 2 μm or more and 500 μm or less, and more preferably 5 μm or more and 100 μm or less. Here, the thickness of the fluorine-containing resin porous membrane is measured in the same manner as the average thickness of the polyimide porous membrane, which will be described later.

[0051] (Production of fluorine-containing porous resin membrane) The method for producing a fluorine-containing porous resin membrane is not particularly limited as long as it is a method capable of producing a porous membrane containing a fluorine-based resin or containing a fluorine-based resin and an acrylic resin. The fluorine-containing resin porous membrane may be formed, for example, by applying the above-mentioned fluorine-containing resin particles to the surface of a polyimide porous membrane body and heating the applied fluorine-containing resin particles to partially fuse the fluorine-containing resin particles together. In addition to heating, pressure may also be applied to fuse the fluorine-containing resin particles together.

[0052] On one or both sides of the polyimide porous membrane body, only fluorine-containing resin particles may be present, only fluorine-containing resin porous membrane may be present, or fluorine-containing resin particles and fluorine-containing resin porous membrane may be present together.

[0053] In the first embodiment of the polyimide porous membrane according to the present disclosure, the water contact angle on the surface of the polyimide porous membrane to which at least one of the fluorine-containing resin particles and the fluorine-containing resin porous membrane is attached is preferably 80° or more and 120° or less, more preferably 85° or more and 110° or less, and even more preferably 90° or more and 110° or less. Here, the water contact angle is measured in the same manner as the water contact angle in the second embodiment of the porous polyimide film according to the present disclosure, which will be described later.

[0054] Next, the resin particles and the porous resin membrane in the second embodiment of the porous polyimide membrane according to the present disclosure will be described in detail, as well as the water contact angle.

[0055] [Resin particles and porous resin membrane] A second embodiment of the polyimide porous membrane according to the present disclosure comprises at least one of resin particles and a resin porous membrane containing a resin other than polyimide resin attached to one or both surfaces of a polyimide porous membrane body, and the surface of the polyimide porous membrane body to which the at least one of the resin particles and the resin porous membrane attached has a water contact angle of 80° or more and 120° or less. That is, in the second embodiment of the polyimide porous membrane according to the present disclosure, the water contact angle of the surface of the polyimide porous membrane to which at least one of resin particles containing a resin other than polyimide resin and the resin porous membrane is attached is 80° or more and 120° or less.

[0056] [Water contact angle] In the second embodiment of the polyimide porous membrane according to the present disclosure, the water contact angle on the surface of the polyimide porous membrane body to which at least one of the resin particles and the resin porous membrane is attached is preferably 85° or more and 110° or less, and more preferably 90° or more and 110° or less. Here, the water contact angle was measured in an environment of 23°C using a contact angle meter (Kyowa Interface Science Co., Ltd., model number: CA-X type) by dropping a 1 μl water droplet with a syringe onto the surface of a polyimide porous membrane to which at least one of resin particles and a resin porous membrane was attached, and then after 1 minute, the measurement was carried out.

[0057] (resin particles) The resin contained in the resin particles can be any resin other than polyimide resin, as long as the resin can achieve the water contact angle of the surface of the polyimide porous membrane to which the resin particles are attached within the above-mentioned numerical range. The resin particles are preferably resin particles containing a fluorine-based resin or a fluorine-based resin and an acrylic resin. That is, the resin particles in the second embodiment of the polyimide porous membrane according to the present disclosure are preferably the fluorine-containing resin particles in the first embodiment of the polyimide porous membrane according to the present disclosure, and preferred aspects and production methods are also the same as those of the fluorine-containing resin particles.

[0058] (Porous resin membrane) The resin contained in the resin porous membrane is a resin other than a polyimide resin, and any resin can be used without limitation as long as the water contact angle on the surface of the polyimide porous membrane to which the resin porous membrane is attached can achieve the above-mentioned numerical range. The porous resin membrane is preferably a porous resin membrane containing a fluorine-based resin or a fluorine-based resin and an acrylic resin. That is, the porous resin membrane in the second embodiment of the porous polyimide membrane according to the present disclosure is preferably the fluorine-containing porous resin membrane in the first embodiment of the porous polyimide membrane according to the present disclosure, and preferred aspects and production methods are also similar to those of the porous fluorine-containing resin membrane.

[0059] Next, the polyimide porous membrane body in the polyimide porous membrane according to the present disclosure will be described in detail.

[0060] [Polyimide porous film body] The polyimide porous membrane according to the present disclosure has a polyimide porous membrane body. The polyimide porous membrane body preferably has a plurality of pores, many of which are interconnected, forming a state in which both surfaces of the polyimide porous membrane body are interconnected. First, preferred physical properties of the polyimide porous membrane body will be described below.

[0061] (Porosity and air permeability) In view of the permeability of substances within the porous membrane, the polyimide porous membrane body in this embodiment preferably has a porosity of 50% or more and 90% or less and an air permeability of 5 sec / 100 mL or more and 100 sec / 100 mL or less. When the polyimide porous membrane body has the above-described porosity and air permeability, the polyimide porous membrane according to the present disclosure can improve cycle characteristics when used as a separator for a non-aqueous secondary battery.

[0062] The porosity of the polyimide porous membrane body is preferably 50% or more and 90% or less, and more preferably 55% or more and 85% or less.

[0063] The porosity of the polyimide porous membrane body is determined from the apparent density and true density of the polyimide porous membrane body. The apparent density d is the mass (g) of the polyimide porous membrane body divided by the volume (cm) of the polyimide porous membrane body including pores. 3 The apparent density d is the mass per unit area of the polyimide porous membrane body (g / m 2 The true density ρ may be calculated by dividing the mass (g) of the polyimide porous membrane body by the thickness (μm) of the polyimide porous membrane body. The true density ρ is the mass (g) of the polyimide porous membrane body divided by the volume (cm) of the polyimide porous membrane body excluding pores (i.e., the volume of only the resin skeleton). 3 ) is the value divided by The porosity of the polyimide porous membrane body is calculated by the following formula (1). ·Formula (1) Porosity (%)={1-(d / ρ)}×100=[1-{(w / t) / ρ)}]×100 d: apparent density of the polyimide porous membrane body (g / cm 3 ) ρ: True density of the polyimide porous film (g / cm 3 ) w: mass per unit area of the polyimide porous membrane body (g / m 2 ) t: Thickness of the polyimide porous membrane (μm)

[0064] The air permeability of the polyimide porous membrane body is preferably 5 seconds / 100 mL or more and 100 seconds / 100 mL or less, and more preferably 5 seconds / 100 mL or more and 80 seconds / 100 mL or less. The air permeability of the polyimide porous membrane body is measured by the Gurley method (JIS P 8117:2009) air permeability test method.

[0065] (Average pore diameter) The average pore diameter X of the polyimide porous membrane body is preferably 50 nm or more and 1500 nm or less, more preferably 50 nm or more and 1000 nm or less, from the viewpoint of the permeability of substances within the porous membrane. When the polyimide porous membrane body has the above average pore diameter, the polyimide porous membrane according to the present disclosure can improve cycle characteristics when used as a separator for a non-aqueous secondary battery.

[0066] The average pore diameter in the polyimide porous membrane body is determined by observing and measuring the cross section of the polyimide porous membrane body in the thickness direction using a scanning electron microscope (SEM). Although the pores in the polyimide porous membrane body are connected to each other, the pore diameter is determined by regarding each pore as an independent pore.

[0067] Here, observation and measurement using a scanning electron microscope (SEM) will be described in detail. First, the polyimide porous membrane body is cut in the thickness direction to prepare a measurement sample with the cut surface as the measurement surface. Then, this measurement sample is observed and measured using a VE SEM manufactured by KEYENCE Corporation with the image processing software that comes standard with the measurement sample. The major and minor diameters of the pores are measured for 100 pores in the cross section of the measurement sample. Here, the major axis of a hole refers to the length of the long side of the circumscribing rectangle of the hole, and the minor axis of a hole refers to the length of the short side of the circumscribing rectangle of the hole. The average value of the major diameters of 100 pores is defined as the "average pore diameter X" in this embodiment.

[0068] (Average flatness) From the viewpoint of improving the strength of the membrane, the average flatness of the polyimide porous membrane body is preferably 0.1 or more and 0.7 or less, more preferably 0.2 or more and 0.7 or less, and further preferably 0.2 or more and 0.6 or less. The average oblateness of the polyimide porous membrane body is calculated from the major axis and minor axis values obtained by the above measurement using the following formula (2): The average value of the oblateness of 100 pores is defined as the "average oblateness" in this embodiment. Formula (2) Flattening ratio = (major axis - minor axis) / major axis

[0069] (tensile breaking strength) The tensile breaking strength of the polyimide porous membrane body is preferably 10 MPa or more, more preferably 15 MPa or more, because it is due to the strength of the polyimide resin. In particular, the above tensile breaking strength is preferably achieved in a polyimide porous membrane body having a porosity in the range of 50% to 90%.

[0070] The tensile breaking strength of the polyimide porous membrane body is measured as follows. First, a strip-shaped measurement sample having a width of 5 mm, a length of 100 mm, and a thickness of 100 μm is prepared. Using a Strograph VE-1D (Toyo Seiki Seisakusho, Ltd.), a rectangular measurement sample is pulled under the following conditions, and the tensile breaking strength is calculated from the stress (load / cross-sectional area) at the time of breakage of the measurement sample. Chuck distance: 50mm Pulling speed: 500mm / min ·Temperature 23℃ 55% relative humidity

[0071] (average film thickness) The average thickness of the polyimide porous membrane body, that is, the thickness of the polyimide porous membrane body, is not particularly limited and is selected depending on the application. The average thickness of the polyimide porous membrane body may be, for example, 10 μm or more and 1000 μm or less. The average thickness of the polyimide porous membrane body may be 20 μm or more, or 30 μm or more. The average thickness of the polyimide porous membrane body may be 500 μm or less, or 400 μm or less.

[0072] The average film thickness of the polyimide porous film body is determined by observing the cross section in the thickness direction at 10 points using a scanning electron microscope (SEM), measuring the film thickness at each observation point from 10 SEM images, and averaging the 10 measured values (film thicknesses).

[0073] (Method of manufacturing a polyimide porous film body) The polyimide porous membrane body is preferably produced, for example, through the following steps. That is, the process includes a step of applying a polyimide precursor solution containing a polyimide precursor, particles, and a solvent onto a substrate to form a coating film, and then drying the coating film to form a film containing the polyimide precursor and the resin particles (hereinafter also referred to as the first step), a step of removing the particles from the film (hereinafter also referred to as the second step), and a step of heating the film to imidize the polyimide precursor in the film (hereinafter also referred to as the third step). Each step will be described below.

[0074] [1st process] In the first step, a polyimide precursor solution containing a polyimide precursor, resin particles, and a solvent is applied onto a substrate to form a coating film, and then the coating film is dried to form a film containing the polyimide precursor and the resin particles.

[0075] [Polyimide precursor solution] (Polyimide precursor) The polyimide precursor solution used in the first step contains a polyimide precursor. The polyimide precursor is preferably a resin having a repeating unit represented by general formula (I).

[0076] [ka]

[0077] (In general formula (I), A represents a tetravalent organic group, and B represents a divalent organic group.)

[0078] Here, in the general formula (I), the tetravalent organic group represented by A is a residue obtained by removing four carboxyl groups from the starting tetracarboxylic dianhydride. On the other hand, the divalent organic group represented by B is the residue obtained by removing two amino groups from the diamine compound used as the raw material.

[0079] That is, the polyimide precursor having the repeating unit represented by general formula (I) is a polymer of a tetracarboxylic dianhydride and a diamine compound.

[0080] The tetracarboxylic acid dianhydride may be either an aromatic or aliphatic compound, but is preferably an aromatic compound, i.e., the tetravalent organic group represented by A in general formula (I) is preferably an aromatic organic group.

[0081] Examples of aromatic tetracarboxylic dianhydrides include pyromellitic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-biphenylsulfonetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 3,3',4,4'-biphenylethertetracarboxylic dianhydride, 3,3',4,4'-dimethyldiphenylsilanetetracarboxylic dianhydride, 3,3',4,4'-tetraphenylsilanetetracarboxylic dianhydride, 1,2,3,4-furantetracarboxylic dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy)diphenylsulfide dianhydride, 4,4 4,4'-bis(3,4-dicarboxyphenoxy)diphenylsulfone dianhydride, 4,4'-bis(3,4-dicarboxyphenoxy)diphenylpropane dianhydride, 3,3',4,4'-perfluoroisopropylidenediphthalic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, bis(phthalic acid)phenylphosphine oxide dianhydride, p-phenylene-bis(triphenylphthalic acid) dianhydride, m-phenylene-bis(triphenylphthalic acid) dianhydride, bis(triphenylphthalic acid)-4,4'-diphenylether dianhydride, bis(triphenylphthalic acid)-4,4'-diphenylmethane dianhydride, and the like.

[0082] Examples of aliphatic tetracarboxylic dianhydrides include butane tetracarboxylic dianhydride, 1,2,3,4-cyclobutane tetracarboxylic dianhydride, 1,3-dimethyl-1,2,3,4-cyclobutane tetracarboxylic dianhydride, 1,2,3,4-cyclopentane tetracarboxylic dianhydride, 2,3,5-tricarboxycyclopentyl acetic dianhydride, 3,5,6-tricarboxynorbornane-2-acetic dianhydride, 2,3,4,5-tetrahydrofuran tetracarboxylic dianhydride, 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic dianhydride, bicyclo[2,2,2]-oct-7-ene aliphatic or alicyclic tetracarboxylic acid dianhydrides such as 1,3,3a,4,5,9b-hexahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]furan-1,3-dione, 1,3,3a,4,5,9b-hexahydro-5-methyl-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]furan-1,3-dione, and 1,3,3a,4,5,9b-hexahydro-8-methyl-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]furan-1,3-dione.

[0083] Among these, the tetracarboxylic acid dianhydride is preferably an aromatic tetracarboxylic acid dianhydride, specifically, for example, pyromellitic acid dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, 2,3,3',4'-biphenyltetracarboxylic acid dianhydride, 3,3',4,4'-biphenylethertetracarboxylic acid dianhydride, 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride, further, pyromellitic acid dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride is more preferable, and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride is particularly preferable.

[0084] The tetracarboxylic dianhydrides may be used alone or in combination of two or more. When two or more kinds are used in combination, aromatic tetracarboxylic dianhydrides or aliphatic tetracarboxylic acids may be used in combination, or an aromatic tetracarboxylic dianhydride and an aliphatic tetracarboxylic dianhydride may be used in combination.

[0085] On the other hand, a diamine compound is a diamine compound having two amino groups in its molecular structure. The diamine compound may be either an aromatic or aliphatic compound, but an aromatic compound is preferable. In other words, the divalent organic group represented by B in the general formula (I) is preferably an aromatic organic group.

[0086] Examples of the diamine compound include p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylethane, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone, 1,5-diaminonaphthalene, 3,3-dimethyl-4,4'-diaminobiphenyl, 5-amino-1-(4'-aminophenyl)-1,3,3-trimethylindane, 6-amino-1-(4'-aminophenyl)-1,3 ,3-Trimethylindane, 4,4'-diaminobenzanilide, 3,5-diamino-3'-trifluoromethylbenzanilide, 3,5-diamino-4'-trifluoromethylbenzanilide, 3,4'-diaminodiphenyl ether, 2,7-diaminofluorene, 2,2-bis(4-aminophenyl)hexafluoropropane, 4,4'-methylene-bis(2-chloroaniline), 2,2',5,5'-tetrachloro-4,4'-diaminobiphenyl, 2,2'-dichloro-4,4'-diamino-5,5'-dimethicone 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, 1,4-bis(4-aminophenoxy)benzene, 4,4'-bis(4-aminophenoxy)-biphenyl, 1,3'-bis(4-aminophenoxy)benzene, 9,9-bis(4-aminophenyl)fluorene aromatic diamines such as 4,4'-(p-phenyleneisopropylidene)bisaniline, 4,4'-(m-phenyleneisopropylidene)bisaniline, 2,2'-bis[4-(4-amino-2-trifluoromethylphenoxy)phenyl]hexafluoropropane, and 4,4'-bis[4-(4-amino-2-trifluoromethyl)phenoxy]-octafluorobiphenyl; aromatic diamines having two amino groups bonded to an aromatic ring and a heteroatom other than the nitrogen atom of the amino groups, such as diaminotetraphenylthiophene;1,1-meta-xylylenediamine, 1,3-propanediamine, tetramethylenediamine, pentamethylenediamine, octamethylenediamine, nonamethylenediamine, 4,4-diaminoheptamethylenediamine, 1,4-diaminocyclohexane, isophoronediamine, tetrahydrodicyclopentadienylenediamine, hexahydro-4,7-methanoindanidinediamine, tricyclo[6,2,1,0; 2.7 ]-undecylenedimethyldiamine, 4,4'-methylenebis(cyclohexylamine), and other aliphatic diamines and alicyclic diamines.

[0087] Among these, the diamine compound is preferably an aromatic diamine compound, specifically, for example, p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone, and particularly, 4,4'-diaminodiphenyl ether and p-phenylenediamine are preferred.

[0088] The diamine compounds may be used singly or in combination of two or more. When two or more diamine compounds are used in combination, aromatic diamine compounds or aliphatic diamine compounds may be used in combination, or an aromatic diamine compound and an aliphatic diamine compound may be used in combination.

[0089] The weight average molecular weight of the polyimide precursor used in this embodiment is preferably 5,000 or more and 300,000 or less, and more preferably 10,000 or more and 150,000 or less.

[0090] The weight-average molecular weight of the polyimide precursor is measured by gel permeation chromatography (GPC) under the following measurement conditions. Column: Tosoh TSKgel α-M (7.8 mm ID x 30 cm) Eluent: DMF (dimethylformamide) / 30mM LiBr / 60mM phosphoric acid ·Flow rate: 0.6mL / min ·Injection volume: 60μL Detector: RI (Differential Refractive Index Detector)

[0091] In this embodiment, the content of the polyimide precursor may be 0.1% by mass or more and 40% by mass or less, and preferably 1% by mass or more and 25% by mass or less, based on the total mass of the polyimide precursor solution.

[0092] (particle) The polyimide precursor solution used in the first step contains particles. From the viewpoint of forming pores, it is preferable that the particles are not dissolved but are dispersed in the polyimide precursor solution. The material of the particles is not particularly limited as long as the particles are not dissolved in the polyimide precursor solution. In this embodiment, "the particles are not soluble" means that the particles are not soluble in the target liquid (specifically, the solvent contained in the polyimide precursor solution) at 25°C, and also means that the particles are soluble in the target liquid within a range of 3% by mass or less.

[0093] The particles are roughly classified into resin particles and inorganic particles, and either of these may be used, but resin particles are preferred from the viewpoint of excellent particle removability in the second step described below.

[0094] -Resin particles- The resin particles are not particularly limited as long as they are not dissolved in the polyimide precursor solution (specifically, the solvent contained in the polyimide precursor solution). In consideration of the removability of the particles in the second step described below, resin particles made of a resin other than polyimide are preferred. Examples of the resin particles include resin particles obtained by polycondensation of polymerizable monomers such as polyester resins and urethane resins, and resin particles obtained by addition polymerization (specifically, radical addition polymerization) of polymerizable monomers such as vinyl resins, olefin resins, and fluororesins. Among these, vinyl resin is preferred as the resin particles, and specifically, at least one selected from the group consisting of (meth)acrylic resin, (meth)acrylic acid ester resin, styrene-(meth)acrylic resin, and polystyrene resin is preferred.

[0095] The resin particles may be crosslinked or may not be crosslinked. In addition, the resin particles are preferably used as a resin particle dispersion containing resin particles obtained by, for example, emulsion polymerization, in order to simplify the process of producing a polyimide precursor solution.

[0096] When the resin particles are made of a vinyl resin, examples of the monomers used to obtain the vinyl resin include the following monomers. Monomers used to obtain vinyl resins include, for example, styrene, alkyl-substituted styrenes (e.g., α-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, 4-ethylstyrene, etc.), halogen-substituted styrenes (e.g., 2-chlorostyrene, 3-chlorostyrene, 4-chlorostyrene, etc.), styrenes having a styrene skeleton such as vinylnaphthalene; methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, etc. vinyl nitriles such as acrylonitrile and methacrylonitrile; vinyl ethers such as vinyl methyl ether and vinyl isobutyl ether; vinyl ketones such as vinyl methyl ketone, vinyl ethyl ketone and vinyl isopropenyl ketone; acids such as (meth)acrylic acid, maleic acid, cinnamic acid, fumaric acid and vinyl sulfonic acid; bases such as ethyleneimine, vinylpyridine and vinylamine; and the like. In addition to the above-mentioned monomers, other monomers may be used in combination, such as monofunctional monomers such as vinyl acetate, bifunctional monomers such as ethylene glycol dimethacrylate, nonane diacrylate, and decanediol diacrylate, and polyfunctional monomers such as trimethylolpropane triacrylate and trimethylolpropane trimethacrylate. The vinyl resin may be a resin using one of these monomers alone, or may be a resin that is a copolymer using two or more types of monomers.

[0097] When the resin particles are made of a vinyl resin, the vinyl resin is preferably obtained using styrene as a monomer. In the vinyl resin obtained using styrene, the proportion of styrene in the total monomer components is preferably 20% by mass or more and 100% by mass or less, more preferably 40% by mass or more and 100% by mass or less. That is, the vinyl resin preferably contains styrene-derived structural units in an amount of 20% by mass or more and 100% by mass or less, and more preferably 40% by mass or more and 100% by mass or less, based on the mass of the vinyl resin.

[0098] The average particle size, shape, etc. of the resin particles are not particularly limited and may be appropriately determined depending on the desired size and / or shape of the pores. The volume average particle diameter of the resin particles is, for example, in the range of 0.03 μm to 3.0 μm. The volume average particle diameter of the resin particles is preferably 0.04 μm or more, more preferably 0.05 μm or more, and even more preferably 0.07 μm or more. The volume average particle diameter of the resin particles is preferably 2.50 μm or less, more preferably 2.45 μm or less, and even more preferably 2.40 μm or less.

[0099] The average particle diameter of resin particles is determined by using the particle size distribution obtained by measurement with a laser diffraction particle size analyzer (e.g., Coulter Counter LS13, Beckman Coulter), subtracting the cumulative distribution for volume from the small particle size side for each divided particle size range (channel), and measuring the particle diameter at which the cumulative 50% of all particles is the volume average particle diameter D50v.

[0100] -Inorganic particles- Specific examples of inorganic particles include silica (silicon dioxide) particles, magnesium oxide particles, alumina particles, zirconia particles, calcium carbonate particles, calcium oxide particles, titanium dioxide particles, zinc oxide particles, and cerium oxide particles. As described above, the particle shape is preferably close to spherical. From this perspective, preferred inorganic particles include silica particles, magnesium oxide particles, calcium carbonate particles, magnesium oxide particles, and alumina particles, more preferred inorganic particles include silica particles, titanium oxide particles, and alumina particles, and even more preferred inorganic particles include silica particles. These inorganic particles may be used alone or in combination of two or more kinds.

[0101] If the inorganic particles have insufficient wettability and dispersibility in the solvent of the polyimide precursor solution, the surfaces of the inorganic particles may be modified as necessary. Examples of methods for surface modification of inorganic particles include a method of treating with an alkoxysilane having an organic group, such as a silane coupling agent; and a method of coating with an organic acid such as oxalic acid, citric acid, or lactic acid.

[0102] The average particle size and shape of the inorganic particles are not particularly limited, and may be appropriately determined depending on the desired size and shape of the pores.

[0103] The content of particles contained in the polyimide precursor solution used in the first step may be 0.1% by mass or more and 40% by mass or less, preferably 0.5% by mass or more and 30% by mass or less, more preferably 1% by mass or more and 25% by mass or less, and even more preferably 1% by mass or more and 20% by mass or less, based on the total mass of the polyimide precursor solution.

[0104] (solvent) The polyimide precursor solution used in the first step contains a solvent. The solvent is preferably one that dissolves the polyimide precursor and does not dissolve or hardly dissolves the particles. The solvent is not particularly limited as long as it has the above properties, but is preferably a water-soluble organic solvent, water, or a mixed solvent thereof, and more preferably a mixed solvent of a water-soluble organic solvent and water (also referred to as an aqueous solvent).

[0105] -Water-soluble organic solvent- The term "water-soluble" in the context of a water-soluble organic solvent means that the target substance dissolves in water at 25°C in an amount of 1% by mass or more. Examples of the water-soluble organic solvent include aprotic polar solvents, water-soluble ether solvents, water-soluble ketone solvents, and water-soluble alcohol solvents.

[0106] Specific examples of the aprotic polar solvent include at least one selected from the group consisting of N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-1,3-dimethyl-2-imidazolidinone (DMI), N,N-dimethylacetamide (DMAc), N,N-diethylacetamide (DEAc), dimethyl sulfoxide (DMSO), hexamethylene phosphoramide (HMPA), N-methylcaprolactam, N-acetyl-2-pyrrolidone, 1,3-dimethyl-imidazolidone, etc. Among these, N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-1,3-dimethyl-2-imidazolidinone (DMI), and N,N-dimethylacetamide (DMAc) are preferred as the aprotic polar solvent.

[0107] A water-soluble ether solvent is a water-soluble solvent having an ether bond in one molecule. Examples of water-soluble ether solvents include tetrahydrofuran (THF), dioxane, trioxane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, and diethylene glycol diethyl ether. Among these, tetrahydrofuran and dioxane are preferred as water-soluble ether solvents.

[0108] A water-soluble ketone solvent is a water-soluble solvent having a ketone group in one molecule. Examples of the water-soluble ketone solvent include acetone, methyl ethyl ketone, and cyclohexanone. Among these, acetone is preferred as the water-soluble ketone solvent.

[0109] The water-soluble alcoholic solvent is a water-soluble solvent having an alcoholic hydroxyl group in one molecule. Examples of the water-soluble alcoholic solvent include methanol, ethanol, 1-propanol, 2-propanol, tert-butyl alcohol, ethylene glycol, monoalkyl ethers of ethylene glycol, propylene glycol, monoalkyl ethers of propylene glycol, diethylene glycol, monoalkyl ethers of diethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, 2-butene-1,4-diol, 2-methyl-2,4-pentanediol, glycerin, 2-ethyl-2-hydroxymethyl-1,3-propanediol, and 1,2,6-hexanetriol. Among these, preferred water-soluble alcohol solvents are methanol, ethanol, 2-propanol, ethylene glycol, monoalkyl ethers of ethylene glycol, propylene glycol, monoalkyl ethers of propylene glycol, diethylene glycol, and monoalkyl ethers of diethylene glycol.

[0110] The water-soluble organic solvent preferably contains an organic amine compound. The organic amine compound will be described below.

[0111] Organic amine compounds The organic amine compound converts the polyimide precursor (its carboxyl group) into an amine salt, thereby increasing its solubility in aqueous solvents and also functioning as an imidization accelerator. Specifically, the organic amine compound is preferably an amine compound having a molecular weight of 170 or less. The organic amine compound is preferably a compound other than the diamine compounds that are raw materials for polyimide precursors. The organic amine compound is preferably a water-soluble compound, which means that the target substance dissolves in water at 25°C in an amount of 1% by mass or more.

[0112] The organic amine compound includes a primary amine compound, a secondary amine compound, and a tertiary amine compound. Among these, the organic amine compound is preferably at least one selected from secondary amine compounds and tertiary amine compounds (particularly, tertiary amine compounds). When a tertiary amine compound or a secondary amine compound (particularly, a tertiary amine compound) is used as the organic amine compound, the solubility of the polyimide precursor in a solvent tends to increase, film-forming properties tend to improve, and the storage stability of the polyimide precursor solution tends to improve.

[0113] In addition to monovalent amine compounds, examples of the organic amine compound include divalent or higher polyvalent amine compounds. The use of divalent or higher polyvalent amine compounds facilitates the formation of a pseudo-crosslinked structure between polyimide precursor molecules and also facilitates the improvement of the storage stability of the polyimide precursor solution.

[0114] Examples of primary amine compounds include methylamine, ethylamine, n-propylamine, isopropylamine, 2-ethanolamine, and 2-amino-2-methyl-1-propanol. Examples of secondary amine compounds include dimethylamine, 2-(methylamino)ethanol, 2-(ethylamino)ethanol, and morpholine. Examples of tertiary amine compounds include 2-dimethylaminoethanol, 2-diethylaminoethanol, 2-dimethylaminopropanol, pyridine, triethylamine, picoline, N-methylmorpholine, N-ethylmorpholine, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, and N-alkylpiperidines (e.g., N-methylpiperidine, N-ethylpiperidine, etc.). The organic amine compound is preferably a tertiary amine compound from the viewpoint of obtaining a high-strength film. In this respect, it is more preferably at least one selected from the group consisting of 2-dimethylaminoethanol, 2-diethylaminoethanol, 2-dimethylaminopropanol, pyridine, triethylamine, picoline, N-methylmorpholine, N-ethylmorpholine, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, N-methylpiperidine, and N-ethylpiperidine. In particular, N-alkylmorpholine is preferably used.

[0115] Here, as the organic amine compound, from the viewpoint of obtaining a film with high strength, an amine compound having an aliphatic cyclic structure or an aromatic cyclic structure having a nitrogen-containing heterocyclic structure (hereinafter referred to as "nitrogen-containing heterocyclic amine compound") is also preferred. As the nitrogen-containing heterocyclic amine compound, a tertiary amine compound is more preferred. That is, a tertiary cyclic amine compound is more preferred. Examples of tertiary cyclic amine compounds include isoquinolines (amine compounds having an isoquinoline skeleton), pyridines (amine compounds having a pyridine skeleton), pyrimidines (amine compounds having a pyrimidine skeleton), pyrazines (amine compounds having a pyrazine skeleton), piperazines (amine compounds having a piperazine skeleton), triazines (amine compounds having a triazine skeleton), imidazoles (amine compounds having an imidazole skeleton), morpholines (amine compounds having a morpholine skeleton), polyaniline, and polypyridine.

[0116] From the viewpoint of obtaining a polyimide film with reduced thickness variation, the tertiary cyclic amine compound is preferably at least one selected from the group consisting of morpholines, pyridines, piperidines, and imidazoles, and more preferably a morpholine (an amine compound having a morpholine skeleton) (i.e., a morpholine-based compound). Among these, at least one selected from the group consisting of N-methylmorpholine, N-methylpiperidine, pyridine, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, and picoline is more preferred, and N-methylmorpholine is more preferred.

[0117] The organic amine compounds may be used alone or in combination of two or more.

[0118] The content of the organic amine compound used in this embodiment is preferably 30% or less, more preferably 15% or less, based on the total mass of the polyimide precursor solution. The lower limit of the content of the organic amine compound is not particularly limited, but may be, for example, 1% or more based on the total mass of the polyimide precursor solution.

[0119] The water-soluble organic solvents may be used alone or in combination of two or more. In addition, from the viewpoint of preventing the water-soluble organic solvent from remaining in the polyimide porous membrane body and obtaining a polyimide porous membrane body with high mechanical strength, the boiling point of the water-soluble organic solvent is preferably 270°C or less, more preferably 60°C or more and 250°C or less, and even more preferably 80°C or more and 230°C or less.

[0120] The content of the water-soluble organic solvent used in this embodiment is preferably 30% by mass or less, and more preferably 20% by mass or less, based on the total mass of the aqueous solvent contained in the polyimide precursor solution. The lower limit of the content of the water-soluble organic solvent is not particularly limited, but may be, for example, 1% by mass relative to the total mass of the polyimide precursor solution.

[0121] -water- Examples of water include distilled water, ion-exchanged water, ultrafiltered water, and pure water.

[0122] The content of water used in this embodiment is preferably 50% by mass or more and 90% by mass or less, more preferably 60% by mass or more and 90% by mass or less, and even more preferably 60% by mass or more and 80% by mass or less, based on the total mass of the aqueous solvent contained in the polyimide precursor solution.

[0123] The content of the aqueous solvent in the polyimide precursor solution used in the first step may be 50% by mass or more and 99% by mass or less, and preferably 40% by mass or more and 99% by mass or less, based on the total mass of the polyimide precursor solution.

[0124] (Other additives) The polyimide precursor solution used in the first step may contain a catalyst for accelerating the imidization reaction, a leveling material for improving the quality of the film formation, and the like. As a catalyst for promoting the imidization reaction, a dehydrating agent such as an acid anhydride, or an acid catalyst such as a phenol derivative, a sulfonic acid derivative, or a benzoic acid derivative may be used.

[0125] The polyimide precursor solution may contain a conductive agent (e.g., a polyimide precursor having a volume resistivity of 100%) to impart conductivity to the polyimide film, depending on the intended use of the polyimide film. 7 Ω·cm) or semiconductive materials (e.g., conductive materials with a volume resistivity of 10 7 Ω cm or more 10 13 It may contain (or less than Ω·cm). Examples of conductive agents include carbon black (e.g., acidic carbon black having a pH of 5.0 or less); metals (e.g., aluminum, nickel, etc.); metal oxides (e.g., yttrium oxide, tin oxide, etc.); ion-conductive substances (e.g., potassium titanate, LiCl, etc.); and the like. These conductive agents may be used alone or in combination of two or more.

[0126] The polyimide precursor solution may also contain inorganic particles added to improve the mechanical strength of the polyimide film depending on the intended use of the polyimide film. Examples of inorganic particles include particulate materials such as silica powder, alumina powder, barium sulfate powder, titanium oxide powder, mica, and talc. It may also contain LiCoO2, LiMn2O, etc., which are used as electrodes in lithium ion batteries.

[0127] [Preparation of polyimide precursor solution] The method for preparing the polyimide precursor solution used in the first step is not particularly limited. From the viewpoint of process simplification, a method of preparing a polyimide precursor solution by synthesizing a polyimide precursor in a dispersion liquid obtained by dispersing particles in an aqueous solvent is preferred. When the particles are resin particles, the dispersion liquid may be obtained by granulating the resin particles in an aqueous solvent. A specific example of a method for preparing the polyimide precursor solution is as follows. First, resin particles are granulated in an aqueous solvent to obtain a resin particle dispersion, and then, in the resin particle dispersion, a tetracarboxylic dianhydride and a diamine compound are polymerized in the presence of an organic amine compound to produce a resin (polyimide precursor), thereby obtaining a polyimide precursor solution.

[0128] Other examples of the method for preparing the polyimide precursor solution include a method of mixing a solution in which a polyimide precursor is dissolved in an aqueous solvent with dry resin particles, and a method of mixing a solution in which a polyimide precursor is dissolved in an aqueous solvent with a dispersion in which resin particles are previously dispersed in an aqueous solvent.

[0129] [Application and drying of polyimide precursor solution] In the first step, the polyimide precursor solution obtained by the above-described method is applied to a substrate to form a coating film. This coating film contains a solution containing polyimide precursors and particles. The particles in this coating film are distributed in a state where aggregation is suppressed. Thereafter, the coating film formed on the substrate is dried to form a film containing the polyimide precursor and the particles.

[0130] The substrate onto which the polyimide precursor solution is applied is not particularly limited. Examples of substrates include resin substrates such as polystyrene and polyethylene terephthalate; glass substrates; ceramic substrates; metal substrates such as iron and stainless steel (SUS); and composite material substrates that combine these materials. Furthermore, if necessary, the substrate may be provided with a release layer by performing a release treatment using, for example, a silicone-based or fluorine-based release agent, etc. It is also effective to roughen the surface of the substrate to a size approximately equal to the particle diameter of the particles, thereby facilitating exposure of the particles at the surface that contacts the substrate.

[0131] The method for applying the polyimide precursor solution onto the substrate is not particularly limited, and examples thereof include various methods such as spray coating, spin coating, roll coating, bar coating, slit die coating, and inkjet coating.

[0132] The method for drying the coating film formed on the substrate is not particularly limited, and examples thereof include various methods such as heat drying, natural drying, and vacuum drying. More specifically, it is preferable to form the coating by drying the coating so that the amount of solvent remaining in the coating is 50% or less (preferably 30% or less) relative to the solid content of the coating. Since the dispersion state of the particles changes depending on the drying rate, the irregularity of the dispersion state of the pores in the produced polyimide porous membrane body is controlled by the drying rate. Specifically, when the drying speed is slowed, particles tend to move more easily in the coating film, which increases the dispersibility of particles in the coating film and tends to reduce the irregularity of the pore dispersion state in the polyimide porous membrane body.On the other hand, when the drying speed is increased, particles tend to be fixed in a biased state in the coating film, which tends to increase the irregularity of the pore dispersion state in the polyimide porous membrane body. The drying speed can be controlled by adjusting the drying temperature, drying time, or the like.

[0133] In the first step, after obtaining the coating film, a treatment for exposing the particles may be carried out during the process of drying to form a film. By carrying out this treatment for exposing the particles, the porosity of the polyimide porous membrane body can be increased. Specific examples of the treatment for exposing particles include the following methods. After obtaining a coating film containing a polyimide precursor and particles, the coating film is dried to form a film containing the polyimide precursor and particles. In this process, the polyimide precursor in the formed film is in a water-soluble state, as described above. Therefore, the particles can be exposed from the film by, for example, wiping the film with water or immersing it in water. Specifically, for example, by wiping the film surface with water to expose the particles, the polyimide precursor (and solvent) covering the particles is removed. As a result, the particles are exposed on the surface of the treated film. In particular, when a coating with embedded particles is formed, it is preferable to employ the above-described treatment as a treatment for exposing the particles embedded in the coating.

[0134] [Second and third steps] In the second step, particles are removed from the film obtained in the first step. By removing the particles from the film, a porous film is formed. In the third step, the film is heated to imidize the polyimide precursor in the film. A polyimide porous membrane body is produced through the second and third steps.

[0135] [Particle Removal] The method for removing the particles from the film in the second step may be determined appropriately depending on the particles in the film. Methods for removing particles from a coating include, for example, a method in which the particles (preferably resin particles) are decomposed and removed by heating, a method in which the particles are removed by dissolving them in an organic solvent, and a method in which the resin particles are removed by decomposition using a laser or the like. These methods may be used alone or in combination of two or more. Two or more methods for removing particles from the coating may be used in combination to adjust the particle removal rate, thereby controlling the shape of the pores (specifically, the oblateness).

[0136] When using a method of decomposing and removing particles by heating, this method can also serve as the third step described below. However, from the viewpoint of ease of control of the shape of the pores (specifically, the oblateness), it is preferable to perform the third step (imidization) after removing the particles from the coating in the second step. In the second step, when the resin particles are decomposed and removed by heating, the heating conditions include the following. The heating temperature is, for example, preferably 150°C or higher and 350°C or lower, more preferably 170°C or higher and 350°C or lower, and even more preferably 200°C or higher and 350°C or lower. The heating time is, for example, preferably from 1 minute to 60 minutes, more preferably from 1 minute to 45 minutes, and even more preferably from 1 minute to 30 minutes.

[0137] When using a method of dissolving and removing the resin particles with an organic solvent, a specific example is a method of bringing the film into contact with an organic solvent to dissolve and remove the resin particles in the organic solvent. Examples of methods for contacting the film with an organic solvent include immersing the film in the organic solvent, applying the organic solvent to the film, and contacting the film with organic solvent vapor.

[0138] The organic solvent used to dissolve the resin particles is not particularly limited as long as it does not dissolve the polyimide precursor and polyimide and can dissolve the resin particles. When the particles are resin particles, examples of the organic solvent that can be used include ethers such as tetrahydrofuran and 1,4-dioxane; aromatics such as benzene and toluene; ketones such as acetone; and esters such as ethyl acetate. Among these, ethers such as tetrahydrofuran and 1,4-dioxane; or aromatics such as benzene and toluene are preferred, and it is more preferred to use tetrahydrofuran or toluene.

[0139] When using a method of dissolving and removing particles with an organic solvent, it is preferable to perform this method when the imidization rate of the polyimide precursor in the coating is 10% or more, from the viewpoints of particle removability and preventing the coating itself from dissolving in the organic solvent. As a method for achieving an imidization rate of 10% or more, for example, the heating conditions in the first stage described below can be mentioned. That is, after the first stage of heating described below, it is preferable to dissolve and remove the particles in the coating with an organic solvent.

[0140] [Imidization] In the third step, heating for imidizing the polyimide precursor in the coating is preferably performed in multiple stages, for example, two or more stages. For example, when the particles are resin particles and are heated in two stages, the heating conditions shown below are specifically employed. The shape of the pores (specifically, the oblateness) is controlled by the heating conditions when the polyimide precursor is imidized. By appropriately controlling the heating conditions (i.e., the heating temperature and heating time), the shrinkage rate of the coating (particularly in the thickness direction) changes, and thus the shape of the pores (specifically, the oblateness) is controlled.

[0141] The heating conditions for the first stage are preferably a temperature at which the shape of the resin particles is maintained. Specifically, for example, the temperature is preferably in the range of 50°C or higher but lower than 250°C, and more preferably in the range of 100°C or higher but 230°C or lower. The heating time is preferably in the range of 10 minutes or higher but 120 minutes or lower. The higher the heating temperature, the shorter the heating time can be. In the heating conditions for the first stage, the heating temperature is also referred to as the preimidization temperature, and the heating time is also referred to as the preimidization time.

[0142] The heating conditions for the second stage include, for example, heating at 250°C to 500°C (preferably 300°C to 450°C) for 20 minutes to 120 minutes. Heating conditions within this range allow the imidization reaction to proceed further. During the heating reaction, it is advisable to gradually increase the temperature stepwise or at a constant rate before reaching the final heating temperature. In the heating conditions for the second stage, the heating temperature and the heating time are also referred to as the firing temperature and firing time, respectively.

[0143] The heating conditions are not limited to the two-stage heating method described above, and a one-stage heating method may also be used. In the case of a one-stage heating method, the imidization may be completed only under the heating conditions shown in the second stage above.

[0144] Here, the imidization rate of the polyimide precursor will be described. Examples of the partially imidized polyimide precursor include precursors having a structure having repeating units represented by the following general formula (I-1), (I-2), and (I-3).

[0145] [ka]

[0146] In general formulas (I-1), (I-2), and (I-3), A represents a tetravalent organic group, B represents a divalent organic group, l represents an integer of 1 or more, and m and n each independently represent an integer of 0 or 1 or more.

[0147] A and B have the same meanings as A and B in general formula (I) described below.

[0148] The imidization ratio of a polyimide precursor represents the ratio of the number of imide ring-closed bonds (2n+m) to the total number of bonds (2l+2m+2n) in the bonds of the polyimide precursor (reaction sites between tetracarboxylic dianhydride and diamine compound). In other words, the imidization ratio of a polyimide precursor is expressed as "(2n+m) / (2l+2m+2n)".

[0149] The imidization rate of the polyimide precursor (the value of "(2n+m) / (2l+2m+2n)") is measured by the following method.

[0150] -Measurement of imidization rate of polyimide precursor- Preparation of polyimide precursor samples (i) The polyimide precursor solution to be measured is applied to a silicon wafer to a film thickness of 1 μm to 10 μm to prepare a coating sample. (ii) The coating sample is immersed in tetrahydrofuran (THF) for 20 minutes to replace the solvent in the coating sample with tetrahydrofuran (THF). The solvent for immersion is not limited to THF, but can be selected from solvents that do not dissolve the polyimide precursor and are miscible with the solvent components contained in the polyimide precursor solution. Specifically, alcohol solvents such as methanol and ethanol, and ether compounds such as dioxane are used. (iii) The coating sample is removed from the THF, and the THF adhering to the surface of the coating sample is removed by blowing N2 gas. The coating sample is then dried under a reduced pressure of 10 mmHg or less at a temperature of 5 to 25°C for 12 hours or more to prepare a polyimide precursor sample.

[0151] Preparation of 100% imidized standard sample (iv) In the same manner as in (i) above, a polyimide precursor solution to be measured is applied to a silicon wafer to prepare a coating sample. (v) The coating sample is heated at 380°C for 60 minutes to carry out an imidization reaction, and a 100% imidized standard sample is prepared.

[0152] Measurement and analysis (vi) Using a Fourier transform infrared spectrophotometer (FT-730, manufactured by Horiba, Ltd.), the infrared absorption spectra of the 100% imidized standard sample and the polyimide precursor sample are measured. -1 The absorption peak (Ab') derived from the aromatic ring near 1500 cm -1 )) for 1780cm -1 The absorption peak (Ab') (1780 cm) derived from the imide bond -1 )) to find the ratio I'(100). (vii) Similarly, the polyimide precursor sample was measured, and the -1 The absorption peak (Ab) derived from the aromatic ring near 1500 cm -1 )) for 1780cm -1 The absorption peak (Ab (1780 cm)) derived from the imide bond near -1 )) to find the ratio I(x).

[0153] Then, the imidization rate of the polyimide precursor is calculated using the measured absorption peaks I'(100) and I(x) based on the following formula. Formula: Imidization rate of polyimide precursor = I(x) / I'(100) ·Formula: I'(100)=(Ab'(1780cm -1 )) / (Ab'(1500cm -1 )) ·Formula: I(x)=(Ab(1780cm -1 )) / (Ab(1500cm -1 ))

[0154] This measurement of the imidization rate of a polyimide precursor is also applicable to the measurement of the imidization rate of an aromatic polyimide precursor. When measuring the imidization rate of an aliphatic polyimide precursor, a peak derived from a structure that remains unchanged before and after the imidization reaction is used as an internal standard peak instead of the absorption peak of the aromatic ring.

[0155] The substrate used in the first step may be peeled off from the film after the first step, may be peeled off from the film after the second step, or may be peeled off from the polyimide porous film body obtained after the third step.

[0156] The polyimide porous film body may have a single-layer structure or a multi-layer structure.

[0157] [Application of resin particles to the surface of a polyimide porous membrane body and formation of a resin porous membrane on the surface of a polyimide porous membrane body] The resin particles can be applied to the surface of the polyimide porous membrane body by the following method. Examples of methods for applying the resin particles include spraying, bar coating, die coating, knife coating, roll coating, reverse roll coating, gravure coating, screen printing, inkjet printing, lamination, electrophotography, etc. Alternatively, the resin particles may be dispersed in a dispersion medium to prepare a liquid composition, and the liquid composition may be applied to the surface of the polyimide porous membrane body, followed by removing the dispersion medium. The amount of resin particles attached to the surface of the polyimide porous membrane body may be controlled by the amount of resin particles applied by the above-mentioned application means, or the amount of resin particles applied to the surface of the polyimide porous membrane body may be adjusted using an applicator or the like.

[0158] The resin porous membrane can be formed on the surface of the polyimide porous membrane body by the following method. For example, resin particles are applied to the surface of a polyimide porous membrane body using the above-mentioned application method, and the applied resin particles are heated to partially fuse the resin particles together, thereby forming a resin porous membrane. Here, in addition to heating, pressure may be applied to fuse the resin particles together. The heating conditions are preferably, for example, at or above the glass transition point of the resin contained in the resin particles. Furthermore, the pressure conditions are preferably, for example, 3 MPa or more and 300 MPa or less.

[0159] The polyimide porous membrane according to the present disclosure preferably has at least one of resin particles (fluorine-containing resin particles in the first embodiment) and a resin porous membrane (fluorine-containing resin porous membrane in the first embodiment) on two surfaces of the polyimide porous membrane body, but also includes an embodiment in which at least one of resin particles and a resin porous membrane is present on only one surface of the polyimide porous membrane body.

[0160] <Separator for non-aqueous secondary batteries> The separator for a nonaqueous secondary battery according to the present disclosure (hereinafter also simply referred to as "separator") comprises the porous polyimide film according to the present disclosure as described above. The separator according to the present disclosure is made of the polyimide porous film according to the present disclosure, which enhances adhesion to the electrode and suppresses the formation of deposits due to ion accumulation. In particular, when the separator according to the present disclosure is applied to a lithium-ion secondary battery, the formation of deposits due to ion accumulation is suppressed at the interface between the separator and the electrode, which can also suppress lithium dendrites.

[0161] <Secondary battery and method for manufacturing the secondary battery> A secondary battery according to the present disclosure and a method for manufacturing a secondary battery according to the present disclosure will be described. The secondary battery according to the present disclosure includes the above-described electrode and the above-described separator according to the present disclosure, and has an adhesive layer made of at least one of resin particles and a resin porous membrane between the electrode and the polyimide porous membrane body. The secondary battery according to the present disclosure has the above-described configuration, which improves adhesion with the electrode and suppresses the formation of deposits due to the accumulation of ions. In particular, if the secondary battery according to the present disclosure is a lithium-ion secondary battery, the formation of deposits due to the accumulation of lithium ions is suppressed, which can also suppress the formation of lithium dendrites. Furthermore, since the secondary battery according to the present disclosure has the above-described configuration, the adhesion between the polyimide porous membrane body and the electrodes is high, and the formation of gaps between the polyimide porous membrane body and the electrodes during charging and discharging can be suppressed. In a secondary battery, if gaps are formed between the separator and the electrodes, ions become less likely to move, resulting in a deterioration in cycle performance. However, as described above, the secondary battery according to the present disclosure is less likely to form gaps between the polyimide porous membrane body and the electrodes, and therefore it is presumed that excellent cycle performance can be obtained.

[0162] The method for producing a secondary battery according to the present disclosure includes a step of bonding the separator according to the present disclosure and an electrode with at least one of resin particles and a porous resin membrane (hereinafter also referred to as a bonding step). In the bonding step, it is preferable to apply at least one of heat and pressure to the laminate of the separator and electrode according to the present disclosure.

[0163] Hereinafter, with reference to FIG. 1, a secondary battery according to the present disclosure and a method for manufacturing a secondary battery according to the present disclosure will be described using a lithium ion secondary battery as an example.

[0164] FIG. 1 is a partial cross-sectional schematic diagram illustrating an example of a secondary battery (lithium ion secondary battery) according to the present disclosure. As shown in FIG. 1 , the lithium-ion secondary battery 100 includes a positive electrode active material layer 110, an adhesive layer 410, a separator layer 510, an adhesive layer 420, and a negative electrode active material layer 310, all of which are housed inside an exterior member (not shown). The positive electrode active material layer 110 is provided on a positive electrode current collector 130, and the negative electrode active material layer 310 is provided on a negative electrode current collector 330. The separator layer 510 is provided to separate the positive electrode active material layer 110 and the negative electrode active material layer 310, and is disposed between the positive electrode active material layer 110 and the negative electrode active material layer 310 so that the positive electrode active material layer 110 and the negative electrode active material layer 310 face each other. The separator layer 510 includes a separator 511 and an electrolyte solution 513 filled in the pores of the separator 511. Here, the separator 511 is the polyimide porous film body of the separator according to the present disclosure (or the polyimide porous film according to the present disclosure) described above, and the adhesive layers 410 and 420 represent adhesive layers made of at least one of the resin particles and the resin porous film in the separator according to the present disclosure (or the polyimide porous film according to the present disclosure). More specifically, the adhesive layer 410 is formed at the interface between the non-opening portion of the separator 511 and the positive electrode active material layer 110, and the adhesive layer 420 is formed at the interface between the non-opening portion of the separator 511 and the negative electrode active material layer 310. The positive electrode current collector 130 and the negative electrode current collector 330 are members that are provided as needed.

[0165] (Positive electrode current collector 130 and negative electrode current collector 330) There are no particular limitations on the material used for the positive electrode current collector 130 and the negative electrode current collector 330, and any known conductive material may be used. For example, metals such as aluminum, copper, nickel, and titanium may be used.

[0166] (Cathode active material layer 110) The positive electrode active material layer 110 is a layer containing a positive electrode active material. It may contain known additives such as a conductive additive and a binder resin, as needed. The positive electrode active material is not particularly limited, and known positive electrode active materials can be used. Examples include lithium-containing composite oxides (LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiFeMnO4, LiV2O5, etc.), lithium-containing phosphates (LiFePO4, LiCoPO4, LiMnPO4, LiNiPO4, etc.), and conductive polymers (polyacetylene, polyaniline, polypyrrole, polythiophene, etc.). One type of positive electrode active material may be used alone, or two or more types may be used in combination.

[0167] (Negative electrode active material layer 310) The negative electrode active material layer 310 is a layer containing a negative electrode active material. If necessary, it may contain known additives such as a binder resin. The negative electrode active material is not particularly limited, and known positive electrode active materials can be used. Examples include carbon materials (graphite (natural graphite, artificial graphite), carbon nanotubes, graphitized carbon, low-temperature fired carbon, etc.), metals (aluminum, silicon, zirconium, titanium, etc.), metal oxides (tin dioxide, lithium titanate, etc.), etc. One type of negative electrode active material may be used alone, or two or more types may be used in combination.

[0168] (Electrolyte 513) The electrolytic solution 513 may be, for example, a non-aqueous electrolytic solution containing an electrolyte and a non-aqueous solvent. Examples of the electrolyte include lithium salt electrolytes (LiPF, LiBF, LiSbF, LiAsF, LiClO, LiN(FSO), LiN(CFSO), LiN(CFS0), LiC(CFSO), etc.) One type of electrolyte may be used alone, or two or more types may be used in combination. Examples of non-aqueous solvents include cyclic carbonates (ethylene carbonate, propylene carbonate, butylene carbonate, etc.), chain carbonates (diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, etc.), etc. One type of non-aqueous solvent may be used alone, or two or more types may be used in combination.

[0169] (Manufacturing Method of Secondary Battery 100) An example of a method for manufacturing the secondary battery 100 will be described. A coating liquid for forming the positive electrode active material layer 110 containing the positive electrode active material is applied to the positive electrode current collector 130 and dried to obtain a positive electrode having the positive electrode active material layer 110 provided on the positive electrode current collector 130. Similarly, a coating solution for forming the negative electrode active material layer 310 containing the negative electrode active material is applied to the negative electrode current collector 330 and dried to obtain a negative electrode including the negative electrode active material layer 310 provided on the negative electrode current collector 330. The positive electrode and the negative electrode may each be subjected to compression processing as necessary. Next, a separator 511 is disposed between the positive electrode active material layer 110 of the positive electrode and the negative electrode active material layer 310 of the negative electrode so that the positive electrode active material layer 110 and the negative electrode active material layer 310 face each other, thereby obtaining a laminate structure. The laminate structure has a positive electrode (positive electrode current collector 130, positive electrode active material layer 110), a separator layer 510, and a negative electrode (negative electrode active material layer 310, negative electrode current collector 330) laminated in this order. Then, at least one of pressure and heat is applied to the laminate structure to bond the positive electrode and the separator 511, and the separator 511 and the negative electrode (bonding process). The laminate structure may be subjected to compression processing as necessary. Next, after the laminated structure is housed in an exterior member, electrolyte solution 513 is poured into the interior of the laminated structure. The poured electrolyte solution 513 also permeates the pores of separator 511. In this way, the lithium ion secondary battery 100 is obtained.

[0170] In the bonding step, the heat and pressure used for bonding between the positive electrode and the separator 511 and between the separator 511 and the negative electrode may be determined depending on the type of resin particles contained in the separator 511 and / or the type of resin contained in the resin porous membrane. In addition, in the bonding step, the conditions for applying the heat and pressure used for bonding may also be determined depending on the type of resin particles contained in the separator 511 and / or the type of resin contained in the resin porous membrane.

[0171] The bonding step when the resin particles are fluorine-containing resin particles will be described below. At least one of heat and pressure is applied in the thickness direction to a laminated structure including a separator 511 having fluorine-containing resin particles attached to its surface, thereby bonding between the positive electrode and the separator 511, and between the separator 511 and the negative electrode. When pressure is applied in the thickness direction of the laminated structure, the fluorine-containing resin particles become fluidized by the pressure and exhibit adhesive properties, thereby bonding the positive electrode and separator 511, and the separator 511 and negative electrode together.

[0172] A known pressure device is used as a means for applying pressure to the laminated structure. Examples of a pair of pressure members included in the pressure device include a combination of a pressure roll and a pressure roll, a combination of a pressure roll and a pressure belt, and a combination of a pressure belt and a pressure belt. The pressure applied to the laminated structure varies depending on the type of fluorine-containing resin particles, but is preferably from 3 MPa to 300 MPa, more preferably from 10 MPa to 200 MPa, and even more preferably from 30 MPa to 150 MPa. When applying pressure to the laminated structure, heat may be applied to the laminated structure.

[0173] While the lithium ion secondary battery according to the present disclosure has been described above with reference to Fig. 1, the lithium ion secondary battery according to the present disclosure is not limited thereto. As long as the separator according to the present disclosure is applied, the form of the battery is not particularly limited. [Example]

[0174] Hereinafter, embodiments of the present invention will be described in detail with reference to examples, but the embodiments of the present invention are not limited to these examples. In the following description, unless otherwise specified, "parts" and "%" are by mass.

[0175] <Preparation of fluorine-containing resin particles> Fluorine-containing resin particles were prepared as follows.

[0176] [PVDF particle dispersion 1] 7.8 g of PVDF (manufactured by Sigma-Aldrich) was dissolved in 534 g of NMP (manufactured by Mitsubishi Chemical Corporation) at 85°C, and 66 g of water was added to the solution to prepare a PVDF solution. This 85°C solution was continuously added to a water tank containing 600 g of water at 85°C. 7.8 g of a 10% by mass aqueous magnesium acetate solution was added to the mixture to aggregate the PVDF particles, which was then filtered through a membrane filter to obtain PVDF particle dispersion 1 (referred to as "PVDF1" in the tables) with an average particle size of 100 nm.

[0177] [PTFE particle dispersion 1] Lubron LDW-410 (average particle size 0.20 μm, manufactured by Daikin Industries, Ltd.) was used to prepare PTFE particle dispersion 1 (referred to as "PTFE1" in the table).

[0178] [PTFE particle dispersion 2] 15 g of Lubron L-5F (average particle diameter 5 μm, manufactured by Daikin Industries, Ltd.) was added to a tank containing 185 g of toluene, and the mixture was thoroughly stirred and subjected to ultrasonic dispersion for 30 minutes to obtain PTFE particle dispersion 2 (referred to as "PTFE2" in the table).

[0179] [PTFE particle dispersion 3] PTFE particle dispersion 3 (referred to as "PTFE3" in the table) was obtained in the same manner as PTFE particle dispersion 2, except that Microdispers-8000 (average particle diameter 8 μm, manufactured by Techno Chemical Co., Ltd.) was used.

[0180] <Preparation of the polyimide porous membrane> A polyimide porous membrane body was prepared as follows.

[0181] <Particle preparation> -Resin particle dispersion (1)- 110 parts by weight of styrene, 5 parts by weight of surfactant Dowfax 2A1 (47% solution, Dow Chemical Company), and 220 parts by weight of deionized water were mixed and emulsified using a dissolver at 1,500 rpm for 30 minutes to produce a monomer emulsion. Next, 20 parts by weight of Dowfax 2A1 (47% solution, Dow Chemical Company) and 446.8 parts by weight of deionized water were added to a reaction vessel. After heating to 75°C under a nitrogen stream, 90 parts by weight of the monomer emulsion was added. A polymerization initiator solution consisting of 5.4 parts by weight of ammonium persulfate dissolved in 25 parts by weight of deionized water was then added dropwise over 10 minutes. After reacting for 50 minutes, the remaining monomer emulsion was added dropwise over 30 minutes, and the mixture was allowed to react for an additional 180 minutes before cooling to obtain resin particle dispersion (1). The solid content of the resin particle dispersion (1) was 36.0% by mass, and the average particle size of the resin particles was 0.05 μm.

[0182] -Resin particle dispersion (2)- Resin particle dispersion (2) containing resin particles with an average particle size of 0.40 μm was obtained in the same manner as in resin particle dispersion (1), except that the amount of Dowfax 2A1 added to the reactor was 1.0 part by mass.

[0183] -Resin particle dispersion (3)- Resin particle dispersion (3) containing resin particles with an average particle size of 0.11 μm was obtained in the same manner as in resin particle dispersion (1), except that the amount of Dowfax 2A1 charged into the reactor was 14 parts by mass.

[0184] -Resin particle dispersion (4)- Resin particle dispersion (4) containing resin particles with an average particle size of 0.10 μm was obtained in the same manner as in resin particle dispersion (1), except that the amount of Dowfax 2A1 added to the reactor was 18 parts by mass.

[0185] -Resin particle dispersion (5)- Five parts by mass of surfactant Dowfax 2A1 and 195 parts by mass of deionized water were mixed in a water tank, and while stirring the mixture, 115 parts by mass of Eposter S12 (particle diameter 1.2 μm, manufactured by Nippon Shokubai Co., Ltd.) was added, and the mixture was further dispersed using an ultrasonic vibrator to obtain resin particle dispersion (5).

[0186] -Resin particle dispersion (6)- Five parts by mass of surfactant Dowfax 2A1 and 195 parts by mass of deionized water were mixed in a water tank, and while stirring the mixture, 115 parts by mass of Eposter MA1002 (particle diameter 2.0 μm, manufactured by Nippon Shokubai Co., Ltd.) was added, and the mixture was further dispersed using an ultrasonic vibrator to obtain resin particle dispersion (6).

[0187] <Preparation of Polyimide Precursor-Containing Liquid> -Preparation of polyimide precursor-containing liquid (A)- 560.0 parts by mass of ion-exchanged water was heated to 50°C under a nitrogen stream, and 53.75 parts by mass of p-phenylenediamine and 146.25 parts by mass of 3,3',4,4'-biphenyltetracarboxylic dianhydride were added with stirring. A mixture of 150.84 parts by mass of N-methylmorpholine (hereinafter also referred to as "MMO") and 89.16 parts by mass of ion-exchanged water was added over 20 minutes with stirring at 50°C under a nitrogen stream. The reaction was carried out at 50°C for 15 hours to obtain a polyimide precursor-containing solution (A) containing the polyimide precursor (A) at a solids concentration of 20% by mass.

[0188] <Polyimide porous membrane body (1)> 169.85 parts of the polyimide precursor-containing liquid (A), 238.97 parts of the resin particle dispersion (1), and 191.18 parts of an aqueous solvent (a mixed solution of NMP and water, mass ratio=17.83:173.35) were mixed. The mixture was ultrasonically dispersed at 50° C. for 30 minutes to obtain a polyimide precursor solution in which resin particles were dispersed. The obtained polyimide precursor solution was used to obtain a polyimide porous film as follows.

[0189] A 1.0 mm thick stainless steel substrate was prepared for forming a coating film of the polyimide precursor solution. The polyimide precursor solution was applied to the stainless steel substrate using an applicator over an area of 10 cm x 10 cm, resulting in a coating film with a thickness of 400 μm after drying. The resulting coating film was then dried at 50°C for 120 minutes (first step). Thereafter, the temperature was increased at a rate of 10°C / min, and after being maintained at 200°C for 60 minutes, the material was cooled to room temperature and immersed in tetrahydrofuran for 30 minutes to remove the resin particles (second step). Subsequently, the temperature was increased from room temperature (25°C, the same applies below) at a rate of 10°C / min, and when it reached 350°C, it was maintained at that temperature for 60 minutes (third step). Thereafter, it was cooled to room temperature to obtain a polyimide porous membrane body (1) having a membrane thickness of 20 μm.

[0190] <Polyimide porous membrane body (2) to (6)> Polyimide porous membranes (2) to (6) were obtained in the same manner as for the polyimide porous membrane body (1), except that resin particle dispersions (2) to (6) were used.

[0191] <Polyimide porous membrane body (7)> A polyimide precursor solution in which resin particles were dispersed was obtained in the same manner as in the polyimide porous membrane body (1), except that 389.65 parts of the polyimide precursor-containing liquid (A), 128.5 parts of the resin particle dispersion liquid (1), and 137.94 parts of an aqueous solvent (a mixed solution of NMP and water, mass ratio = 30.41:107.53) were mixed. Furthermore, a polyimide porous membrane body (7) was obtained in the same manner as in the polyimide porous membrane body (1), except that the obtained polyimide precursor solution in which resin particles were dispersed was heated and dried at 80 ° C. in the first step, held at 200 ° C. for 60 minutes in the second step, and then held at 350 ° C. for 60 minutes to heat-remove the particles, and the temperature reached 400 ° C. in the third step and held for 60 minutes.

[0192] <Polyimide porous membrane body (8)> A polyimide precursor solution in which resin particles were dispersed was obtained in the same manner as in the polyimide porous membrane (1), except that 289.65 parts of the polyimide precursor-containing liquid (A), 172.41 parts of the resin particle dispersion liquid (1), and 137.94 parts of an aqueous solvent (a mixed solution of NMP and water, mass ratio = 30.41:107.53) were mixed. Furthermore, a polyimide porous membrane body (8) was obtained in the same manner as in the polyimide porous membrane body (1), except that the obtained polyimide precursor solution in which resin particles were dispersed was heated and dried at 80 ° C. in the first step, held at 200 ° C. for 60 minutes in the second step, and then held at 350 ° C. for 60 minutes to heat-remove the particles, and the temperature reached 400 ° C. in the third step and held for 60 minutes.

[0193] [Measurements and calculations] The porosity and average pore diameter of the obtained polyimide porous membrane body were determined by the methods described above. Regarding the air permeability, a sample for measuring the air permeability was prepared from the obtained polyimide porous membrane body in accordance with the air permeability test method of the Gurley method (JIS P 8117:2009), and the obtained measurement sample was used to measure the air permeability by the method described above. The results are shown in Table 1.

[0194] [Examples 1 to 12] The fluorine-containing resin particles shown in Table 1 below were applied to both surfaces of a polyimide porous membrane body shown in Table 1 below in an amount shown in Table 1 below to obtain a separator.

[0195] [Comparative Example 1] A separator was obtained in the same manner as in Example 1, except that the polyolefin porous membrane body (9) shown below was used instead of the polyimide porous membrane body.

[0196] <Polyolefin porous membrane body (9)> A polyolefin microporous membrane produced by the same method as in Comparative Example 2 of WO 2017 / 170288 was used as the polyolefin porous membrane body (9). Specifically, the weight average molecular weight (Mw) is 5.6 × 10 570 parts by weight of high density polyethylene having a molecular weight distribution (MWD) of 4.05 and Mw of 1.9 × 10 6 A polyethylene resin composition was obtained by adding 0.08 parts by weight of a phenolic antioxidant and 0.08 parts by weight of a phosphorus-based antioxidant per 100 parts by weight of polyethylene resin to a polyethylene resin (melting point 135°C, crystal dispersion temperature 90°C) composed of 30 parts by weight of ultra-high molecular weight polyethylene having a molecular weight of 1.09 and an MWD of 5.09. 28.5 parts by weight of the obtained polyethylene resin composition was charged into a twin-screw extruder (strong mixing type segment), and 71.5 parts by weight of liquid paraffin was fed from a side feeder of the twin-screw extruder. The mixture was melt-kneaded at 190°C and 300 rpm to prepare a polyethylene resin composition solution in the extruder. The polyethylene resin composition solution thus prepared was extruded at 240°C through a T-die attached to the tip of an extruder and formed into a gel-like sheet (800 mm wide) with a thickness of 800 μm while being taken up by a cooling roll. The resulting gel-like sheet was then introduced into a stretching machine as shown in Figure 1 of International Publication No. 2017 / 170288, and the resulting gel-like sheet was heated to a first oven temperature of 125°C. The sheet was then simultaneously biaxially stretched 5x5 times at a conveying speed of 45 m / min and a temperature of 115°C to obtain a stretched gel-like sheet. The stretched gel-like sheet was then immersed in a bath of methylene chloride adjusted to 25°C, and the liquid paraffin present in the gel-like sheet was removed until the amount of liquid paraffin present in the gel-like sheet was 1% or less by volume. The sheet was then dried in an air stream at room temperature. The dried film was heat-set in an oven at 120°C for 10 minutes. In this way, a polyolefin porous membrane body (9) with a thickness of 20 μm was obtained.

[0197] Comparative Example 2 A separator was obtained in the same manner as in Example 2, except that the polyolefin porous membrane body (9) was used instead of the polyimide porous membrane body.

[0198] [evaluation] (Adhesive strength) The separator obtained as described above and the negative electrode active material layer of the negative electrode (a laminate of a negative electrode current collector and a negative electrode active material layer) were stacked so as to be in contact with each other to produce a laminate structure, and the resulting laminate structure was hot-pressed in its thickness direction at 1 MPa and 80°C for 20 seconds. The separator and the positive electrode were then manually peeled off using tweezers, and the adhesive strength was evaluated using the following three-level scale. The results are shown in Table 1. -Evaluation criteria- A: The positive electrode and separator were separated due to strong force. B: The positive electrode and separator were separated with a fairly strong force. C: The positive electrode and separator were separated with a weak force.

[0199] (Lithium dendrites and cycle characteristics) Using the separator obtained as described above, a lithium ion secondary battery having the configuration shown in FIG. 1 was fabricated. The separator was bonded to the positive electrode and negative electrode by heat pressing a laminated structure in which the positive electrode, separator, and negative electrode were laminated in this order in the thickness direction at 5 MPa and 80°C for 20 seconds. The obtained secondary battery was subjected to 600 repeated charge / discharge cycles (1 C charge and 1 C discharge at 25° C.), and the state of lithium deposition on the electrode surface and the rate of decrease in battery capacity were examined. It can be said that the less lithium precipitates on the electrode surface, the better the lithium dendrites are, and the smaller the rate of decrease in battery capacity, the better the cycle characteristics are. The results are shown in Table 1.

[0200] -Lithium dendrite evaluation criteria- A: There is almost no lithium deposition on the electrode surface and it remains in good condition. B: Lithium deposition is observed on the electrode surface, but it is minor. C: A large amount of lithium deposition is observed on the electrode surface.

[0201] -Cycle evaluation criteria- A: The reduction rate of battery capacity is less than 20%. B: The reduction rate of battery capacity is 20% or more and less than 40%. C: The battery capacity reduction rate is 40% or more.

[0202] [Table 1]

[0203] Table 1 also reveals that the polyolefin porous membranes (separators) of the examples have high adhesion to the electrodes, which are the objects to be adhered, and suppress the formation of lithium dendrites. [Explanation of symbols]

[0204] 100 Lithium-ion secondary battery 110 Cathode active material layer 130 Positive electrode current collector 310 Negative electrode active material layer 330 Negative electrode current collector 410 Adhesive layer 420 Adhesive layer 510 Separator layer 511 Separator

Claims

1. a polyimide porous membrane body; Resin particles attached to one or both surfaces of the polyimide porous membrane body and containing a fluorine-based resin or a fluorine-based resin and an acrylic resin; and When the average pore diameter of the polyimide porous membrane body is X and the average particle diameter of the resin particles is Y, the ratio (Y / X) of the average particle diameter Y of the resin particles to the average pore diameter X of the polyimide porous membrane body is greater than 1 and is not greater than 70.0, the fluorine atom concentration on the surface of the polyimide porous membrane body to which the resin particles are attached is 18 atm % or more and 40 atm % or less; Polyimide porous membrane.

2. 2. The polyimide porous film according to claim 1, wherein the fluorine-based resin is a polymer containing vinylidene fluoride as a polymerization component.

3. 3. The polyimide porous membrane according to claim 1, wherein the average pore diameter X of the polyimide porous membrane body is 50 nm or more and 1500 nm or less.

4. The polyimide porous film according to any one of claims 1 to 3, wherein the resin particles have an average particle diameter Y of 5 nm or more and 10 µm or less.

5. The polyimide porous film according to any one of claims 1 to 4, wherein the porosity of the polyimide porous film body is 50% or more and 90% or less.

6. A polyimide porous membrane described in any one of claims 1 to 5, wherein the water contact angle of the surface of the polyimide porous membrane body to which the resin particles are attached is 80° or more and 120° or less.

7. A separator for a non-aqueous secondary battery, comprising the polyimide porous membrane according to any one of claims 1 to 6.

8. A secondary battery comprising an electrode and the non-aqueous secondary battery separator according to claim 7, wherein an adhesive layer made of the resin particles is formed between the electrode and the polyimide porous membrane body.

9. A method for manufacturing a secondary battery, comprising a step of bonding the separator for a non-aqueous secondary battery according to claim 7 and an electrode with the resin particles.

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