Polymer film and secondary battery

Abstract

To provide a polymer film excellent in ionic conductivity, cation transport number, and electrolyte separation property, and a secondary battery containing such a polymer film and excellent in rate characteristics.SOLUTION: A polymer film contains 35 to 99 mass% of electrolyte salt and has a haze of 0.0 to 30.0%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polymer film and a secondary battery. [Background technology]

[0002] In recent years, portable electronic devices have become smaller and more functional. This has led to a demand for higher energy density in the secondary batteries that power these devices. If metallic Li could be used for the negative electrode of secondary batteries, it is expected that the capacity would be significantly higher than that of current lithium-ion batteries.

[0003] Against this background, Patent Document 1 discloses an ion-permeable membrane that is excellent in strength, flexibility, and ion permeability. Patent Document 2 discloses an electrode composite that includes a lithium metal layer and a porous polymer layer attached to one surface of the lithium metal layer. Patent Document 3 discloses a separation membrane that is used in a lithium-ion secondary battery that contains different solvents in the positive electrode mixture layer and the negative electrode mixture layer, and that has excellent ability to separate these solvents. Patent Document 4 discloses a polymer ion-conductive membrane that combines ion conductivity and liquid separation properties. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2016 / 098660 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-134403 [Patent Document 3] International Publication No. 2022 / 107255 [Patent Document 4] International Publication No. 2023 / 068312 Summary of the Invention [Problem to be solved by the invention]

[0005] However, many challenges remain before batteries with metallic Li as the anode can be put to practical use. For example, repeated charge and discharge cycles of metallic Li anodes can lead to the formation of dendrites and the decomposition of the electrolyte due to its high reactivity. If the dendrites grow and reach the cathode, there is a risk of a short circuit and fire. Furthermore, the decomposition of the electrolyte can reduce the battery life.

[0006] To address these issues, the ion-permeable membrane of Patent Document 1 has a large free volume and excellent ionic conductivity, but cannot prevent decomposition of the electrolyte solution when operated at high current densities. Patent Document 2 suppresses decomposition of the electrolyte solution, but the polymer layer is porous and therefore does not function to suppress dendrites. The ion-conductive membranes of Patent Documents 3 and 4 require further improvements in ionic conductivity and cation transport number when considering operation at high current densities. In view of the above circumstances, the present invention aims to provide a polymer film with excellent ionic conductivity, cation transport number, and electrolyte separation properties, and a secondary battery containing such a polymer film with excellent rate characteristics. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention includes the following (1) to (21). (1) A polymer film containing 35 to 99 mass % of an electrolyte salt and having a haze of 0.0 to 30.0%. (2) A polymer film containing 35 to 99 mass % of an electrolyte salt containing an anion having an ionic radius of 0.20 nm or more and 0.60 nm or less, containing an aromatic polyamide, aromatic polyimide, or aromatic polyamideimide as a polymer constituting the polymer film, and containing 20 to 99 mol % of functional groups having a pKa of 5.0 or less or 9.0 or more in the repeating units of the polymer constituting the polymer film. (3) A polymer film having an average free volume radius of 0.26 nm or more and 0.40 nm or less, and a lithium element content of 0.7 mass % or more after immersion in an electrolyte solution for 24 hours, as measured by atomic absorption spectrometry. (4) The polymer film according to (1) or (3), wherein the repeating units of the polymer constituting the polymer film contain 20 to 99 mol % of functional groups having a pKa of 5.0 or less or 9.0 or more. (5) The polymer film according to any one of (1) to (3), which has an electrolyte content of 20.0 mass % or less when treated under the following conditions: [Processing conditions] The polymer film was washed with diethyl carbonate (DEC) and then dried at 130°C for 3 hours, after which its mass was weighed. The polymer film was then immersed in 3.0 mL of non-aqueous electrolyte (1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) ethylene carbonate (EC) / DEC = 1 / 1) for 6 hours, and the amount of electrolyte contained in the polymer film was calculated from the change in mass. Electrolyte content = (M-M0) / M0 M: Mass after immersion in electrolyte M0: Mass before immersion in electrolyte (6) The polymer film according to (2), wherein the functional group includes at least one of a sulfonic acid group, a phosphoric acid group, and a carboxylic acid group. (7) The polymer film according to (2), wherein the protons contained in the functional groups are substituted with alkali metal cations. (8) The polymer film according to (2), wherein the functional group includes an amino group. (9) The polymer film according to (1) or (3), wherein the polymer constituting the polymer film contains aromatic polyamide, aromatic polyimide, or aromatic polyamideimide. (10) The polymer film according to (1) or (2), wherein the electrolyte salt contains lithium ions. (11) The polymer film according to any one of (1) to (3), which has an electrolyte permeation rate of 0 μl / min or more and 100 μl / min or less under the following conditions: [Conditions for measuring the electrolyte permeation rate] Two dry 6 mL glass screw bottles (AS ONE Corporation, No. 2) were prepared. 2.0 mL of nonaqueous electrolyte (1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in a 1:1 ratio of ethylene carbonate (EC) to diethyl carbonate (DEC)) was added to one bottle, and a film was attached to the opening of the bottle so that there were no gaps. The other bottle was then placed on the film with its opening facing downwards and secured in place with tape. The bottle containing the electrolyte was left standing with the top facing upwards. After 3 hours, the presence or absence of permeation of the nonaqueous electrolyte into the lower bottle was confirmed, the amount of leakage was weighed, and the permeation rate was calculated. If no permeation of the nonaqueous electrolyte was observed after 3 hours, the permeation rate was recorded as 0 μl / min. (12) The polymer film according to any one of (1) to (3), wherein the thickness of the polymer film is 0.1 μm or more and 10.0 μm or less. (13) Ionic conductivity is 1.0 × 10 -6 S / cm or more 1.0×10 -1 The polymer film according to any one of (1) to (3), having a viscosity of 1000 kJ / cm or less. (14) The polymer film according to any one of (1) to (3), wherein the activation energy of ionic conduction is 1 kJ / mol or more and 25 kJ / mol or less. (15) The polymer film according to any one of (1) to (3), wherein the cationic transport number is 0.5 or more and 1.0 or less. (16) The polymer film according to (1), which contains an anion having an ionic radius of 0.20 nm or more and 0.60 nm or less. (17) The polymer film according to (1) or (2), which contains at least one of a bis(trifluoromethanesulfonyl)imide ion, a bis(fluorosulfonyl)imide ion, a trifluoromethanesulfonate ion, a hexafluorophosphate ion, and a perchlorate ion. (18) A secondary battery comprising the polymer film according to any one of (1) to (3). (19) The secondary battery according to (18), wherein the negative electrode is metallic lithium. (20) The secondary battery according to (18), which comprises a positive electrode, an electrolyte, a polymer film, an electrolyte, and a negative electrode in this order, and which is configured with electrolytes of different compositions on the positive electrode side and the negative electrode side via the polymer film. (21) The secondary battery according to (18), which comprises a positive electrode, an inorganic solid electrolyte, and a negative electrode in this order, and which contains a polymer film between the electrode and the solid electrolyte. (22) The secondary battery according to (18), comprising an electrode composite having a battery electrode on at least one surface of a polymer film. (23) A vehicle, unmanned transport aircraft, flying object, electronic device, or stationary power source including the secondary battery described in (18). [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a polymer film excellent in ionic conductivity, cation transport number and electrolyte separation property, and a secondary battery including this polymer film excellent in rate characteristics. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention will be described in detail below. One aspect of the present invention is a polymer film having excellent ionic conductivity, cation transport number, and liquid separation property, and a secondary battery having excellent rate characteristics and including the polymer film. Another aspect of the present invention is a polymer usable for the polymer film, and a solution containing the polymer.

[0010] One embodiment of the polymer film of the present invention is a polymer film in which the polymer constituting the film contains functional groups having an acid dissociation constant (pKa) of 5.0 or less or 9.0 or more in the repeating units of the polymer at 20 mol % to 99 mol %. This is preferably 40 mol % to 99 mol %, and more preferably 60 mol % to 80 mol %. The pKa of the functional groups having an acid dissociation constant (pKa) of 5.0 or less or 9.0 or more in the polymer is more preferably 4.0 or less or 9.0 or more, and particularly preferably 3.0 or less. In the present invention, the pKa is the value in water at 25°C. Functional groups having a pKa of 5.0 or less or 9.0 or more release or accept hydrogen ions, thereby interacting with cations or anions. Having functional groups having a pKa of 5.0 or less or 9.0 or more within the above ranges results in an appropriate interaction with cations or anions, and films containing such polymers exhibit excellent salt dissociation properties and good ionic conductivity and cation transport number. Specific examples of functional groups having a pKa of 5.0 or less or 9.0 or more include sulfonic acid groups, phosphoric acid groups, carboxylic acid groups, and amino groups. Polymers having functional groups having a pKa of 5.0 or less or 9.0 or more within the above range are not particularly limited, but include the polymers described below. The confirmation of each constituent component and its content in the polymer according to the embodiment of the present invention is not limited to a specific method, but each component separated by a combination of techniques such as redissolution, extraction, chromatography, distillation, liquid separation, and reprecipitation can be analyzed by a combination of nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT-IR), mass spectrometry (MS), elemental analysis, single crystal structure analysis, etc.

[0011] In the polymer film of the present invention, the polymer constituting the polymer film preferably has an aromatic ring on the main chain. Polymers having an aromatic ring on the main chain have excellent strength and therefore tend to maintain high strength when thinned. Examples of such polymers include aromatic polyamide (aramid), aromatic polyimide, aromatic polyamideimide, aromatic polyetherketone, aromatic polyetheretherketone, aromatic polyarylate, aromatic polysulfone, aromatic polyethersulfone, aromatic polyetherimide, and aromatic polycarbonate. A blend of multiple polymers may also be used. Among these, aromatic polyamide, aromatic polyimide, or aromatic polyamideimide is more preferred, as they tend to maintain high strength when thinned, with aromatic polyamide being particularly preferred. That is, the polymer according to the embodiment of the present invention preferably contains an aromatic polyamide.

[0012] As polymers that can be suitably used in the present invention, it is preferable that the polymer constituting the membrane contains a polymer having a structure represented by any one of the following chemical formulas (I) to (III). Examples of aromatic polyamides include those having a repeating unit represented by the following chemical formula (I), aromatic polyimides include those having a repeating unit represented by the following chemical formula (II), and aromatic polyamideimides include those having a repeating unit represented by the following chemical formula (III).

[0013] [ka]

[0014] [ka]

[0015] [ka]

[0016] The bonds constituting the main chain on the aromatic ring may be either meta-oriented or para-oriented. Furthermore, some of the hydrogen atoms on the aromatic ring may be substituted with any group. Specific examples of aromatic diamines constituting aromatic polyamides, aromatic polyimides, or aromatic polyamideimides include paraphenylenediamine, metaphenylenediamine, orthophenylenediamine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 2,2'-ditrifluoromethyl-4,4'-diaminobiphenyl, 2,2'-ditrichloromethyl-4,4'-diaminobiphenyl, 4,4'-diaminobenzophenone, 3,3'-diaminobenzophenone, 2-chloro-1,4-phenylenediamine, 2-trifluoromethyl-1,4-phenylenediamine, 5-trifluoromethyl-1,3-phenylenediamine, 4,'-oxybis(3-trifluoromethyl)aniline, 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene, 1,5'-naphthalenediamine, 9,9-bis(4-aminophenyl)fluorene, 9,9'-bis(3-methyl-4- Examples of suitable fluorenes include 9,9-bis(4-amino-3-chlorophenyl)fluorene, 4,4'-diaminodiphenyl sulfone, 1,4-phenylenediamine-4-sulfonic acid, 3,5-diamino-2,4,6-trimethylbenzenesulfonic acid, 2,2'-benzidinedisulfonic acid, and 5,5'-methylenebis(2-aminobenzoic acid). Among these, from the viewpoint of achieving both high ionic conductivity and liquid separation properties, 1,4-phenylenediamine-4-sulfonic acid, 3,5-diamino-2,4,6-trimethylbenzenesulfonic acid, 2,2'-benzidinedisulfonic acid, and 5,5'-methylenebis(2-aminobenzoic acid) are preferred because they have a functional group with a pKa of 5.0 or less. In addition, 2,2'-bis(trifluoromethyl)benzidine and 9,9-bis(4-aminophenyl)fluorene are preferred because they have a large average free volume. 2,2'-bis(trifluoromethyl)benzidine and 9,9-bis(4-aminophenyl)fluorene are preferably used as copolymerization components in an amount of 40 mol% or more and 60 mol% or less of the total diamine content.

[0017] In the polymer film of the present invention, the functional group preferably includes at least one of a sulfonic acid group, a phosphoric acid group, and a carboxylic acid group. By including the above polymer, the functional group interacts with cations, improving salt dissociation and increasing the number of carrier ions, thereby improving ionic conductivity. It is more preferable to include at least one of a sulfonic acid group and a phosphoric acid group, which have small pKa values, and it is particularly preferable to include a sulfonic acid group. The above polymer is not particularly limited, but examples include the polymers described below.

[0018] The protons of the sulfonic acid groups, phosphoric acid groups, and carboxylic acid groups contained in the polymer constituting the polymer film of the present invention are preferably substituted with alkali metal cations. By substituting the protons of the functional groups with alkali metal cations, the number of carrier ions increases and ionic conductivity is improved. As the alkali metal cation, lithium, sodium, and potassium are more preferred, and lithium is particularly preferred. The method for substituting the protons of the functional groups with alkali metal cations is not particularly limited, but examples include a method of adding a metal salt as described below.

[0019] The polymer constituting the polymer film of the present invention preferably contains an amino group among the functional groups. It is believed that the inclusion of the above polymer allows the functional group to interact with anions, trapping the anions and increasing the cation transport number. The above polymer is not particularly limited, but examples thereof include the polymers described below.

[0020] The polymer film of the present invention is preferably a film that allows ion conduction between a positive electrode and a negative electrode when used as a battery. That is, the polymer film of the present invention is preferably an ion-conductive polymer film. In the present invention, the ion-conductive polymer film has an ion conductivity of 10 -9The ionic conductivity here refers to a value measured in a 25°C environment using the measurement method described below. The upper limit of the ionic conductivity is not particularly limited, but is substantially 1.0 x 10 S / cm or less. The ionic conductivity is 1.0 x 10 -6 S / cm or more 1.0×10 -1 S / cm or less is preferable, and 5.0 × 10 -5 S / cm or more 1.0×10 -1 S / cm or less is more preferable, and 2.0×10 -4 S / cm or more 1.0×10 -1 S / cm or less is more preferable, and 4.0×10 -4 S / cm or more 1.0×10 -1 S / cm or less is more preferable, and 5.0×10 -4 S / cm or more 1.0×10 -1 S / cm or less is particularly preferred. By setting the ionic conductivity within the above range, ion permeability within the battery is high, and excellent output characteristics and cycle characteristics can be obtained. -5 By setting the ionic conductivity to 5 S / cm or more, it is possible to prevent the ion permeability from being low, the output characteristics from being reduced, and the capacity from being significantly deteriorated during repeated use. In order to set the ionic conductivity within this range, it is preferable to form a polymer film using a polymer described below.

[0021] Furthermore, the polymer film of the present invention preferably has an activation energy of ion conduction calculated from the temperature dependence of ion conductivity of 25 kJ / mol or less, more preferably 20 kJ / mol or less, even more preferably 15 kJ / mol or less, and most preferably 10 kJ / mol or less. By setting the activation energy of ion conduction within the above range, high ion conductivity can be achieved in low-temperature atmospheres, resulting in excellent output characteristics and cycle characteristics. To set the activation energy of ion conduction within this range, the content of functional groups with a pKa of 5.0 or less or 9.0 or more can be increased, or functional group-containing segments can be connected. By increasing the content of functional groups with a pKa of 5.0 or less or 9.0 or more, or by connecting functional group-containing segments, a highly ion-conductive channel can be formed in which ions are conducted via the functional groups.

[0022] The polymer film of the present invention must contain 35% to 99% by mass of electrolyte salt in order to improve ionic conductivity. By setting the electrolyte salt content within the above-mentioned range, the ionic conductivity increases as the number of carrier ions increases. The electrolyte salt content is more preferably 40% by mass or more. Furthermore, since a high content of electrolyte salt may reduce liquid separability, the content is preferably 80% by mass or less, and more preferably 60% by mass or less. Therefore, from the perspective of achieving both ionic conductivity and liquid separability, the electrolyte salt content is preferably 40% to 60% by mass. The cations constituting the electrolyte salt are preferably one or more metal element ions selected from the group consisting of lithium ions, sodium ions, magnesium ions, zinc ions, and aluminum ions. In the present invention, "a polymer film containing 35% to 99% by mass of electrolyte salt" means that the total content of all electrolyte salts, including the cations constituting the electrolyte salt, is within the above-mentioned range. While there are no particular limitations on the method for adjusting the electrolyte salt content within the above-mentioned range, examples include the addition of a metal salt, as described below.

[0023] The polymer film of the present invention preferably contains an electrolyte salt whose cation is lithium ion. The inclusion of lithium element, which has a relatively small atomic weight, in the polymer film increases ion mobility, particularly when lithium ions are used as a migration medium, resulting in practical battery performance. The lithium element content can be evaluated using known techniques such as atomic absorption spectrometry and ICP atomic emission spectrometry. From the perspective of improving ionic conductivity, the polymer film of the present invention preferably has a cation concentration of 8 mg / g or more. The cation is preferably one or more metal element ions selected from the group consisting of lithium ion, sodium ion, magnesium ion, zinc ion, and aluminum ion. The inclusion of one or more metal elements selected from the group consisting of lithium, sodium, magnesium, zinc, and aluminum in the polymer film increases ion mobility, resulting in practical battery performance. The cation concentration is more preferably 10 mg / g or more, even more preferably 12 mg / g or more, particularly preferably 13 mg / g or more, significantly more preferably 15 mg / g or more, and most preferably 20 mg / g or more. If the content of one or more metal elements selected from the group consisting of lithium, sodium, magnesium, zinc, and aluminum is less than 10 mg / g, sufficient ion conductivity may not be obtained when used in a secondary battery, resulting in poor battery performance. The above means that the polymer film contains one or more metal elements selected from the group consisting of lithium, sodium, magnesium, zinc, and aluminum, and the total content of these metal elements is sufficient as long as it is within the above range. The cation concentration can be evaluated using known techniques such as atomic absorption spectrometry and ICP atomic emission spectrometry. The method for achieving a cation concentration within the above range is not particularly limited, but examples include adding a metal salt, as described below.

[0024] In order to improve ionic conductivity, the polymer film according to an embodiment of the present invention preferably has a lithium ion concentration of 8 mg / g or higher. By incorporating lithium, which has a relatively small atomic weight, into the polymer film, ionic mobility is increased, particularly when lithium ions are used as a migration medium, resulting in practical battery performance. The lithium ion concentration is 10 mg / g or higher, more preferably 12 mg / g or higher, particularly preferably 13 mg / g or higher, significantly more preferably 15 mg / g or higher, and most preferably 20 mg / g or higher. If the lithium content is less than 10 mg / g, sufficient ionic conductivity may not be obtained when used in a secondary battery, resulting in poor battery performance. The lithium content can be evaluated using known techniques such as atomic absorption spectrometry and ICP atomic emission spectrometry. While there are no particular limitations on the method for achieving a lithium ion concentration within the above range, examples include the addition of a metal salt, as described below.

[0025] One embodiment of the present invention is a polymer film containing an anion having an ionic radius of 0.20 nm to 0.60 nm. The ionic radius is preferably 0.25 nm to 0.60 nm, and particularly preferably 0.30 nm to 0.60 nm. When the ionic radius of the contained anion is within the above range, the charge density of the anion decreases, weakening the electrostatic interaction between the cation and anion, thereby increasing the degree of ionic dissociation. Specific examples of anions having an ionic radius of 0.20 nm to 0.60 nm include bis(trifluoromethanesulfonylamide) ion, bis(fluorosulfonylamide) ion, trifluorosulfonate ion, hexafluorophosphate ion, and perchlorate ion. These lithium salts may be used alone or in combination of two or more. The method for incorporating an anion having an ionic radius of 0.20 nm to 0.60 nm is not particularly limited, but examples include the addition of a metal salt, as described below.

[0026] The polymer film of the present invention preferably contains at least one of bis(trifluoromethanesulfonyl)imide ions, bis(fluorosulfonyl)imide ions, trifluoromethanesulfonate ions, hexafluorophosphate ions, and perchlorate ions. By containing such ions, the number of dissociated cations in the film increases, and the polymer film exhibits good ionic conductivity.

[0027] From the viewpoint of improving the rate characteristics of a battery using the polymer film according to an embodiment of the present invention, the lithium content after 24 hours of immersion in an electrolyte solution described below, as measured by atomic absorption spectrometry, is preferably 0.7% by mass or more, more preferably 0.9% by mass or more, and particularly preferably 1.1% by mass or more. There is no particular upper limit, but it is preferably 5.0% by mass or less, more preferably 3.0% by mass or less. When the lithium content after 24 hours of immersion in an electrolyte solution is within the above range, a secondary battery containing the polymer film can suppress an increase in resistance, thereby increasing the discharge capacity at high current density and improving the rate characteristics.

[0028] In the polymer film according to the embodiment of the present invention, the mean free volume radius is preferably 0.26 nm or more and 0.4 nm or less, more preferably 0.27 nm or more and 0.4 nm or less, and even more preferably 0.30 nm or more and 0.4 nm or less. When the mean free volume radius is equal to or greater than the lower limit, the electrolyte salt can be easily dispersed uniformly, resulting in good ion conductivity. When the mean free volume radius is equal to or less than the upper limit, good electrolyte blocking performance can be achieved. While there are no particular limitations on the method for adjusting the mean free volume radius within the above range, it is preferable to form the polymer film using, for example, the polymer described below.

[0029] One embodiment of the present invention is a polymer film having a haze of 0.0% or more and 30.0% or less. A haze of 0.0% or more and 5.5% or less is more preferable, a haze of 0.0% or more and 4.5% or less is even more preferable, and a haze of 0.0% or more and 1.0% or less is particularly preferable. A haze within the above range allows a uniform film to be obtained, and good ion conductivity and electrolyte blocking performance are exhibited. While there are no particular limitations on the method for achieving a haze within the above range, it is preferable to form a polymer film using, for example, the polymer described below.

[0030] The polymer film according to the present invention preferably has a cation transference number of 0.5 to 1.0, more preferably 0.6 to 1.0, and particularly preferably 0.8 to 1.0. By ensuring that the cation transference number is within the above range, it is possible to suppress an increase in resistance due to polarization and a decrease in liquid separation, thereby achieving good battery characteristics. The cation transference number can be evaluated using known techniques that utilize AC impedance analysis and DC analysis.

[0031] The air resistance of the polymer film according to the embodiment of the present invention is 0 to 1.0 × 10 -4 (100 cc / sec) or less. -4 By making the air permeability less than 100 cc / sec, the film often has physical through-holes, which can have the effect of blocking the penetration of dendrites, etc. In order to set the air permeability resistance within this range, it is preferable to form a polymer film using a polymer described below.

[0032] The polymer film of the present invention preferably has a non-porous region. The non-porous region refers to a region having 10 or fewer voids of 50 nm or larger, as determined by drawing a line perpendicular to the interface from one interface to the other in a cross-sectional image of the polymer film obtained by field emission scanning electron microscopy (FE-SEM), as described below. In the present invention, having a non-porous region means that the thickness of the non-porous region is 0.5 μm or greater. When the polymer film is a composite membrane consisting of a non-porous region and a microporous membrane, the point where the distribution and size of the voids in the thickness direction begin to change is considered to be the interface. Having a non-porous region improves the ability to block the permeation of substances other than ions that contribute to battery operation, thereby enabling increased battery capacity and lifespan.

[0033] The polymer film of the present invention preferably has a thickness of 0.1 μm or more and less than 10 μm. By setting the thickness of the non-porous region to the aforementioned upper limit or less, the resistance of the polymer film in terms of battery characteristics can be prevented from becoming too high, and the weight can be reduced, making it suitable for use as a battery for an aerial vehicle, which requires lightweight construction. The thickness of the non-porous region is preferably 5 μm or less, particularly preferably 3 μm or less. Furthermore, if the thickness of the non-porous region is too small, the cycle life of the battery will decrease, so the thickness is preferably 0.5 μm or more, particularly preferably 1.0 μm or more. There are no particular limitations on the method for setting the thickness of the non-porous region within the above range, but this can be achieved, for example, by setting the concentration of the solution used to form the polymer film within the range described below.

[0034] The polymer film of the present invention preferably has an electrolyte content of 20.0% by mass or less, more preferably 11.0% by mass or less, more preferably 8.0% by mass or less, even more preferably 5.5% by mass or less, and particularly preferably 4.0% by mass or less, as measured by the method described below. When the electrolyte content is 20.0% by mass or less, a decrease in the strength of the polymer film inside the battery can be suppressed, and the polymer film has excellent dendrite resistance. In order to set the electrolyte content within this range, it is preferable to form the polymer film using a polymer described below.

[0035] The polymer film of the present invention preferably has an electrolyte permeation rate of 0 μl / min to 100 μl / min, more preferably 0 μl / min to 2 μl / min, more preferably 0 μl / min to 1 μl / min, and most preferably 0 μl / min. When the electrolyte permeation rate is 100 μl / min or less, the ability to block the permeation of substances other than ions that contribute to battery operation is improved, decomposition of the electrolyte on the electrode surface is suppressed, and battery capacity and lifespan can be increased. In order to achieve an electrolyte permeation rate within this range, it is preferable to form the polymer film using a polymer described below.

[0036] The polymer film of the present invention preferably has a non-porous region and a microporous membrane, and is particularly preferably a composite membrane having a non-porous region and a microporous membrane. The method for forming the composite membrane is not particularly limited, but an example is a method in which a polymer is applied to at least one side of a microporous membrane using the method described below. Examples of the microporous membrane include a porous membrane having internal pores, a nonwoven fabric, or a porous membrane sheet made of a fibrous material. The material constituting the microporous membrane is preferably made of a resin that is electrically insulating, electrically stable, and stable against nonaqueous electrolytes.

[0037] The electrodes in the secondary battery according to the embodiment of the present invention may contain the same polymer as the polymer film. By containing the same polymer in the electrodes, the interfacial resistance between the layers can be reduced, and the ionic conductivity and cycle characteristics can be dramatically improved, thereby improving the battery characteristics.

[0038] The polymer film of the present invention may contain other components that act as ion-conducting assistants, such as inorganic solid electrolytes, ionic liquids, and lithium salts, as long as the effects of the present invention are not impaired.

[0039] In the secondary battery according to the embodiment of the present invention, it is preferable that at least one of the positive electrode and the negative electrode and the polymer film are in close proximity to each other. The ion-conducting polymer of the present invention is a polymer that enables ion conduction between the positive electrode and the negative electrode. The proximity of the polymer layer to at least one of the positive electrode and the negative electrode improves ion conductivity between the layers, and the proximity to at least one of the electrodes can suppress short circuits and fires due to dendrite formation during battery use. Here, "in close proximity" means being within 1 μm, and may be in direct contact or may be via another layer.

[0040] The method for producing the polymer and film of the present invention will be explained below using a wholly aromatic polyamide as an example, but the present invention is not limited thereto.

[0041] The method for producing a polymer of the present invention is characterized by adding a Brønsted base to a monomer containing a functional group and / or its conjugate base group having a pKa of 5.0 or less, followed by polycondensation of a diamine monomer and a dicarboxylic acid dichloride monomer to obtain a polymer. Adding the Brønsted base allows the functional group to remain in the state of its conjugate base during the polymerization reaction, thereby suppressing polymerization termination due to side reactions or reduced solubility and enabling the production of a high-molecular-weight polymer. While there is no limit to the amount of Brønsted base added, it is preferably 50 mol % or more, and more preferably 100 mol % or more, relative to the functional group. Furthermore, while there is no limit to the chemical species of the Brønsted base added, it is preferable to use a secondary amine and / or a tertiary amine in terms of affinity with the solvent and the polymer to be produced and removability, and it is more preferable to use a tertiary amine whose side chain is an alkyl group having from 1 to 5 carbon atoms. More specific examples include triethylamine, diisopropylethylamine, diethylamine, pyridine, 4-dimethylaminopyridine, 1,4-diazabicyclooctane, 1,8-bis(dimethylamino)naphthalene, 1,1,3,3-tetramethylguanidine, diazabicyclononene, and diazabicycloundecene.

[0042] Various known methods, such as solution polymerization and precipitation polymerization, can be used to obtain wholly aromatic polyamides. For example, when polymerizing aromatic polyamides using solution polymerization, dicarboxylic acid dichlorides and diamines can be used as raw materials and reacted at low temperatures in an aprotic solvent containing a Bronsted base. Here, the aprotic solvent is a polar solvent that does not have proton (hydrogen ion) donating properties, such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylisobutyramide, 3-methoxy-N,N-dimethylpropanamide, tetrahydrofuran, γ-butyrolactone, ethyl acetate, acetonitrile, dimethylformamide, and dimethyl sulfoxide. To prevent deactivation of the dicarboxylic acid dichlorides, the water content of the solvent used in the polymerization is preferably 500 ppm or less (by mass, hereinafter), more preferably 200 ppm or less. The polymerization reaction of wholly aromatic polyamides generates heat, so it is preferable to keep the solution temperature during polymerization at 40°C or less. If the temperature exceeds 40°C, side reactions may occur and the degree of polymerization may not be increased sufficiently. It is more preferable to keep the temperature of the solution during polymerization at 30°C or less.

[0043] When dicarboxylic acid dichlorides and diamines are used as raw materials, hydrogen chloride is produced as a by-product during the reaction, resulting in a highly acidic solution of the resulting wholly aromatic polyamide. This solution is highly corrosive, and if left untreated, it can corrode components such as metal substrates used in the production process of molded articles and films, making them unusable. Methods for removing the by-product hydrogen chloride include neutralizing the hydrogen chloride by adding a neutralizing agent during polymerization and precipitating and isolating the polymer. Neutralizing hydrogen chloride during polymerization can be achieved by neutralizing with an inorganic neutralizing agent, such as lithium carbonate, calcium carbonate, or calcium hydroxide. When neutralizing with an inorganic neutralizing agent, the solution contains inorganic salts (e.g., lithium chloride) produced by the neutralization reaction. These inorganic salts ionize in the solvent and coordinate with the amide groups of the wholly aromatic polyamide, acting as a dissolution aid in the solvent and thus improving the pot life of the solution and suppressing polymer aggregation during molding. However, because a washing step to remove the inorganic salts is required during the molding process, this method may not be usable depending on the dimensions of the molded article and / or film and the manufacturing process.

[0044] As a method for substituting the protons of the functional groups of the polymer of the present invention with alkali metal cations, a polymer containing the functional groups is polymerized by the above method, and then a basic reagent is allowed to act on the polymer to ionize the protons of the functional groups. + Here, the basic reagent is a compound in which the pKa of the conjugate acid generated from the basic reagent is smaller than the pKa of the functional group. a Preferably, the reagent has a higher basicity, such as a metal hydride and / or a metal carbonate. Specific examples include, but are not limited to, lithium hydride, sodium hydride, lithium carbonate, and sodium carbonate. When the conjugate base of the functional group is introduced into the polymer by this method, the counter ion also contains a metal cation. Therefore, when the polymer of the present invention is used as a cation-conducting material, it is particularly preferable to use a basic reagent containing the target cation, since this increases the amount of carriers contained in the film.

[0045] The viscosity ηinh of the polymer is preferably 0.3 to 7.0 dL / g. By setting the viscosity within the above range, a polymer excellent in toughness and strength and good ion conductivity can be obtained. The viscosity η can be measured, for example, by the method described below.

[0046] Next, a membrane-forming stock solution (hereinafter referred to as membrane-forming stock solution) used when producing the electrode mixture layer and the electrolyte layer according to the embodiment of the present invention will be described.

[0047] One aspect of the secondary battery according to the embodiment of the present invention is a battery in which a positive electrode current collector layer, an electrode mixture layer containing a positive electrode active material (sometimes referred to as a positive electrode layer), an electrolyte layer, an electrode mixture layer containing a negative electrode active material (sometimes referred to as a negative electrode layer), and a negative electrode current collector layer are stacked in this order or in reverse order. Also, the secondary battery can be assembled using known battery components.

[0048] The polymer film of the present invention may be used not only as an electrolyte layer in the secondary battery described above, but also as an electrode mixture layer of either the positive electrode layer or the negative electrode layer, or may be included in both layers. Furthermore, the polymer may be coated on the surface of the positive electrode layer or the negative electrode layer, so that it functions both as a protective film for the electrode surface and as an electrolyte layer.

[0049] One embodiment of the present invention is a solution containing a polymer that includes an aromatic polyamide, an aromatic polyimide, or an aromatic polyamideimide, and that has 20 to 99 mol % of functional groups with a pKa of 5.0 or less or 9.0 or more in the repeating unit of the polymer. By forming a polymer film using a polymer solution containing the above polymer, a polymer film that is excellent in dissociation of electrolyte salts, ionic conductivity, and permeation blocking performance for substances other than the ions can be obtained.

[0050] Although the polymer solution after polymerization may be used as is as the membrane-forming solution, it is preferable to add a Li salt to the polymerization solution in order to improve ionic conductivity. If the polymer contains a large amount of unnecessary substances such as neutralization salts, it is preferable to isolate the polymer and then redissolve it in an organic solvent such as the above-mentioned aprotic organic polar solvent before use. The method for isolating the polymer is not particularly limited, but examples include pouring the polymer solution after polymerization into a large amount of water or alcohol to extract the solvent and neutralization salts into water, separating the precipitated polymer, and then drying it.

[0051] In the manufacturing process of the electrode mixture layer and the electrolyte layer according to the embodiment of the present invention, it is preferable to add an active material, an inorganic solid electrolyte, a conductive additive, a lithium salt, etc. to the polymer. There is no limitation on the timing of adding these materials, and they may be added during the polymer polymerization process, the film-forming solution preparation process, or the film-forming process. However, it is preferable to add them during the film-forming solution preparation process because they can be uniformly dispersed with the polymer. They may also be added in multiple processes, or in multiple batches within the same process.

[0052] The polymer concentration in the film-forming solution is preferably 3 to 30% by mass, more preferably 4 to 20% by mass. To improve the strength, heat resistance, and ion permeability of the resulting polymer film, and to reduce the static friction coefficient, inorganic or organic particles may be added to the film-forming solution, provided that the effects of the present invention are not impaired. Examples of inorganic particles include wet and dry silica, colloidal silica, aluminum silicate, titanium oxide, calcium carbonate, calcium phosphate, barium sulfate, alumina, aluminum hydroxide, magnesium hydroxide, magnesium carbonate, zinc carbonate, titanium oxide, zinc oxide (zinc oxide), antimony oxide, cerium oxide, zirconium oxide, tin oxide, lanthanum oxide, magnesium oxide, barium carbonate, zinc carbonate, basic lead carbonate (white lead), barium sulfate, calcium sulfate, lead sulfate, zinc sulfide, mica, titanium mica, talc, clay, kaolin, lithium fluoride, and calcium fluoride. Examples of organic particles include particles crosslinked using a polymer compound as a crosslinking agent. Examples of such crosslinked particles include crosslinked particles of polymethoxysilane-based compounds, crosslinked particles of polystyrene-based compounds, crosslinked particles of acrylic-based compounds, crosslinked particles of polyurethane-based compounds, crosslinked particles of polyester-based compounds, crosslinked particles of fluorine-based compounds, and mixtures thereof.

[0053] Next, a method for producing the polymer film of the present invention will be described. The film-forming solution prepared as described above can be used to produce a film by a so-called solution film-forming method. Solution film-forming methods include a dry-wet method, a dry method, and a wet method, and any of these methods may be used to produce a film. Here, the dry-wet method will be used as an example.

[0054] When forming a film by the dry / wet method, the film-forming solution is extruded from a die onto a support such as a drum, an endless belt, or a film to form a film, which is then dried until it becomes self-supporting. Drying conditions can be, for example, 60 to 220°C for 60 minutes or less. However, after the dry process, the film is peeled off from the support and introduced into the wet process, where it is subjected to desalting, desolvation, etc., and is stretched, dried, and heat-treated as necessary.

[0055] When stretching, the areal stretching ratio is preferably within the range of 0.8 to 8.0 times (area ratio is defined as the value obtained by dividing the area of the film after stretching by the area of the film before stretching; a ratio of 1 or less means relaxation), and more preferably 1.0 to 5.0 times. When heat-treating, the heat treatment is carried out at a temperature of 80°C to 500°C, preferably 130°C to 400°C, for several seconds to several tens of minutes. The polymer film of the present invention obtained by the above-mentioned production method can be used as an electrolyte membrane by being inserted directly between positive and negative electrodes.

[0056] When the polymer film of the present invention is formed into a composite membrane having a nonporous region and a microporous membrane, the polymer film and the microporous membrane obtained by the above-mentioned membrane-forming method may be used by being stacked or bonded together. A method of applying the above-mentioned polymerized membrane-forming solution to a microporous membrane and laminating them is also preferred, and the solution can be applied to the microporous membrane using any coating method such as a roll coater, a slit coater, or a dip coater.

[0057] The thickness of the polymer film according to the embodiment of the present invention is not particularly limited, but is preferably 0.03 to 30 μm, more preferably 0.10 to 20 μm, even more preferably 0.20 to 15 μm, and particularly preferably 0.20 to 10 μm. Furthermore, when the polymer film of the present invention is a composite membrane of a polymer film and a microporous membrane, the thickness ratio of the polymer film to the microporous membrane is preferably 0.001 to 5, more preferably 0.01 to 1. By setting the thickness within the above range, the polymer film has sufficient strength and is suitable for use without an increase in resistance due to the membrane thickness. The thickness of the polymer film can be controlled by various conditions, such as the concentration of the membrane-forming solution, the viscosity of the membrane-forming solution, the type and concentration of additives in the membrane-forming solution, the casting thickness of the polymer film, the heat treatment temperature, and the stretching conditions.

[0058] One embodiment of the present invention is a secondary battery containing the polymer film of the present invention. One embodiment of the secondary battery of the present invention is a secondary battery in which the above-described polymer film is disposed between a positive electrode and a negative electrode. Any method can be used to manufacture the battery. By including the polymer film, crossover between electrodes of by-products generated at the electrodes and the formation of dendrites at the negative electrode are suppressed, thereby improving the life and capacity of the battery.

[0059] From the viewpoint of energy density, the secondary battery according to the embodiment of the present invention is preferably a metal Li negative electrode battery, a silicon negative electrode battery, a clay battery, or a sulfur battery. Among sulfur batteries, a lithium-sulfur battery is more preferable.

[0060] The battery according to the embodiment of the present invention preferably comprises a positive electrode, an electrolyte, a polymer film, an electrolyte, and a negative electrode in this order, with the positive electrode and the negative electrode preferably having electrolytes with different compositions separated by a polymer film. It is also preferable that the battery comprises a positive electrode, an inorganic solid electrolyte, and a negative electrode in this order, with a polymer film between the electrode and the solid electrolyte. This configuration can suppress electrolyte decomposition, leading to increased capacity and longer battery life.

[0061] The positive electrode of the battery according to the embodiment of the present invention contains a known positive electrode active material, such as a lithium metal oxide (such as lithium cobalt oxide or lithium manganese oxide) containing lithium and at least one transition metal selected from manganese, cobalt, nickel, and titanium.

[0062] The negative electrode of the present invention is not particularly limited as long as it is a material capable of absorbing and releasing metal ions as an active material. For example, known negative electrode active materials such as Li, Sn, Si, In, lithium alloy particles (lithium alloy particles of lithium and titanium, magnesium, aluminum, etc.), and carbonaceous materials (carbon, hard carbon, soft carbon, graphite, etc.) can be appropriately used. Among these, the use of metallic lithium is preferred from the viewpoint of increasing the energy of the battery. Furthermore, the lithium equivalent concentration of the negative electrode is preferably 1.0 mol / L or more in the entire negative electrode. A lithium equivalent concentration of 1.0 mol / L or more can increase the capacity. The upper limit is not particularly limited, but is substantially 100 mol / L or less.

[0063] The nonaqueous electrolyte of the present invention is not particularly limited and may be any organic solvent used in conventional lithium ion batteries. The electrolyte to which the present invention is applied may be solid or liquid, but it is preferable to use an electrolytic solution in order to increase the contact area with the electrode. As the solvent for the electrolyte, cyclic esters, chain esters, cyclic ethers, chain ethers, etc. are used, and specifically, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), γ-butyrolactone (γBL), 2-methyl-γ-butyrolactone, acetyl-γ-butyrolactone, γ-valerolactone, 1,2-dimethoxyethane (DME), 1,2-ethoxyethane, diethyl ether, ethylene glycol dialkyl ether, diethylene glycol dialkyl ether, triethylene glycol dialkyl ether, tetraethylene glycol dialkyl ether, dipropyl carbonate, methyl butyl carbonate, methyl propyl carbonate, Preferred solvents include organic solvents such as methyl acrylate, ethyl butyl carbonate, ethyl propyl carbonate, butyl propyl carbonate, alkyl propionate, dialkyl malonate, alkyl acetate, tetrahydrofuran (THF), alkyl tetrahydrofuran, dialkyl alkyl tetrahydrofuran, alkoxy tetrahydrofuran, dialkoxy tetrahydrofuran, 1,3-dioxolane, alkyl-1,3-dioxolane, 1,4-dioxolane, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, methyl propionate, ethyl propionate, phosphate triester, N-methyl-2-pyrrolidone, and sulfolane; and water, derivatives, and mixtures thereof.

[0064] As the electrolyte contained in the non-aqueous electrolyte solution, alkali metal halides, particularly lithium halides, perchlorates, thiocyanates, boron fluorides, phosphorus fluorides, arsenic fluorides, aluminum fluorides, trifluoromethyl sulfates, etc. are preferably used. For example, one or more salts such as lithium salts (electrolytes) can be used, including lithium perchlorate (LiClO), lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium hexafluoroarsenic (LiAsF), lithium trifluoromethanesulfonate (LiCFSO), lithium bis(trifluoromethanesulfonyl)imide [LiN(CFSO)], lithium bromide (LiBr), lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(pentafluoroethanesulfonyl)imide, with lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) being preferred.

[0065] The non-aqueous electrolyte of the secondary battery according to the embodiment of the present invention preferably contains at least one type of metal ion, and the metal ion concentration is preferably 0.5 mol / L or more and 7.0 mol / L or less. The metal ion is preferably a metal ion that migrates between the positive and negative electrodes during charging and discharging of the battery. Specifically, in the case of a lithium-ion battery, it is lithium ion, and in the case of a sodium battery, it is sodium ion. The metal ion concentration is preferably 0.5 mol / L or more and 5.0 mol / L or less, and more preferably 1.0 mol / L or more and 5.0 mol / L or less. When the metal ion concentration is within the above range, the battery exhibits good battery characteristics. From the viewpoint of battery operability, the metal ion is preferably lithium ion, sodium ion, magnesium ion, potassium ion, or calcium ion, more preferably lithium ion, sodium ion, or magnesium ion, and particularly preferably lithium ion. Furthermore, an additive may be used in the non-aqueous electrolyte as needed. Examples of the additive include vinylene carbonate, fluoroethylene carbonate, ethylene sulfite, 1,4-butane sultone, propane sultone, 2,4-difluoroanisole, biphenyl, cyclohexylbenzene, and the like, and one or more of these may be used.

[0066] Next, a method for manufacturing a secondary battery according to an embodiment of the present invention will be described below.

[0067] The material used as the current collector layer in the secondary battery according to the embodiment of the present invention is not particularly limited, but for example, metal foils made of gold, silver, aluminum, copper, stainless steel, nickel, titanium, alloys thereof, carbon-based materials, etc. can be used.

[0068] The electrode mixture layer of the positive electrode of the secondary battery according to the embodiment of the present invention may be a single component or may contain other components. Examples of such other components include known positive electrode active materials, such as lithium metal oxides (e.g., lithium cobaltate and lithium manganese oxide) containing lithium and at least one transition metal selected from manganese, cobalt, nickel, and titanium. The active material of the negative electrode electrode mixture layer is not particularly limited, but any material capable of absorbing and releasing metal ions may be used. Examples of known negative electrode active materials include Li, Sn, Si, In, lithium alloy particles (e.g., lithium alloy particles of lithium and titanium, magnesium, aluminum, etc.), and carbon-based materials (e.g., carbon, hard carbon, soft carbon, and graphite).

[0069] A secondary battery according to an embodiment of the present invention preferably includes an electrode composite having a battery electrode on at least one side of a polymer film. The electrode composite preferably has the polymer film and electrode in close proximity. The polymer film of the present invention is a polymer film that enables ion conduction between a positive electrode and a negative electrode. The proximity of the polymer film to at least one of the positive electrode and the negative electrode reduces the interfacial resistance between the layers, and the proximity of the polymer film to at least one of the electrodes can suppress short circuits and fires due to dendrite formation during battery use. Here, "close proximity" refers to being within 1 μm, and may be in direct contact or may be via another layer. Methods for bringing the electrode and polymer film into close proximity include a roll press method and a method in which a solution containing the polymer film is applied to the electrode and dried.

[0070] The secondary battery according to the embodiment of the present invention can be suitably used as a power source for electronic devices such as mobile phones and watches, vehicles such as electric vehicles (EVs), hybrid vehicles (HEVs), plug-in hybrid vehicles (PHEVs), airplanes, and UAMs, unmanned transport vehicles such as drones, flying objects such as HAPS (High Altitude Platform Stations), and large industrial equipment such as industrial cranes. It can also be suitably used as a power storage device for leveling power in solar cells, wind power generation equipment, and the like, or for smart grids, or as a stationary power source. Furthermore, it can also be suitably used as a battery for use in special environments such as space. [Example]

[0071] The present invention will be described in more detail below with reference to examples. The physical properties of the examples were measured by the following methods.

[0072] (1) Logarithmic viscosity ηinh A polymer is dissolved at a concentration of 0.5 g / dL in N-methylpyrrolidone (NMP) containing 2.5 mass% lithium bromide (LiBr), and the flow time is measured at 30° C. using an Ubbelohde viscometer. The flow time of a blank LiBr 2.5 mass% / NMP solution in which no polymer is dissolved is also measured in the same manner, and the logarithmic viscosity ηinh (dL / g) can be calculated using the following formula.

[0073] Logarithmic viscosity ηinh(dl / g)=[ln(t / t0)] / 0.5 t0: Blank flow time (seconds) t: sample flow time (seconds).

[0074] (2) Air resistance Measurements were carried out using an Oken air permeability meter (EGO-1T, manufactured by Asahi Seiko Co., Ltd.) with an air volume set to 100cc. The device's upper measurement limit is 10,000 seconds / 100cc. The polymer film was fixed to prevent wrinkles, and measurements were taken in accordance with JIS P8117:2009. Three measurement points were measured at equal intervals in the TD direction, and the reciprocal of the average air permeability was used as the air permeability resistance (100cc / sec).

[0075] (3) Cross-sectional structure (thickness of polymer film, thickness of non-porous region) The polymer films obtained in the examples were cross-section-cut using a cross-section polisher (SM-9010 manufactured by JEOL Ltd.), and the cross sections in the thickness direction in the width direction were platinum-coated to prepare observation samples. Next, the cross sections of the samples were photographed at an arbitrary magnification using a field emission scanning electron microscope (FE-SEM) (JSM 6701F manufactured by JEOL Ltd.), and the thickness of the polymer film was determined. The accelerating voltage during observation was 2.0 kV. When the polymer film was a composite film, the interface between the non-porous layer and the microporous layer was determined from the difference in cross-sectional structure or image contrast, and the thickness of each was determined. Next, the thickness of the non-porous region was determined from the image taken at 10,000x magnification using the following method: A line perpendicular to the interface was drawn from one interface of the polymer film to the other, and the number of voids of 50 nm or larger that intersected the line was counted. If there were 10 or fewer voids, the region was determined to be non-porous, and the thickness was calculated. If the polymer film was a composite membrane consisting of a non-porous region and a microporous membrane, the point where the distribution and size of the voids in the thickness direction began to change was considered to be the interface.

[0076] (4) Ionic conductivity A polymer film punched to a diameter of 22 mm was immersed in a non-aqueous electrolyte (1M LiTFSI ethylene carbonate (EC) / diethyl carbonate (DEC) = 1 / 1) for 24 hours, then placed on a SUS304 electrode with a diameter of 15.5 mm and a thickness of 0.5 mm so as to cover the electrode portion. Non-aqueous electrolyte was then dripped onto the film, and the film was sandwiched between another SUS304 electrode with a diameter of 15.5 mm and a thickness of 0.5 mm to produce an electrode / polymer film / electrode laminate. The laminate was fixed with a silicon plate to prevent it from shifting, and an evaluation cell was produced.

[0077] The AC impedance of the prepared cell was measured at 25°C using an electrochemical tester (Biologic, model number: SP-150) under conditions of an amplitude of 10 mV and a frequency of 1 MHz to 10 mHz. The resistance value was read from a graph plotted on a complex plane and substituted into equation (1) to calculate the ionic conductivity. Five measurements were taken, and the calculated average value was used as the ionic conductivity. σ=T0 / AR (1) σ: Ionic conductivity (S / cm) T0: Thickness of polymer film (cm) A: electrode area (cm 2 ) R: Resistance value (Ω).

[0078] (5) Activation energy of ionic conduction A polymer film punched to a diameter of 22 mm was immersed in a non-aqueous electrolyte (1 M LiTFSI, ethylene carbonate (EC) / diethyl carbonate (DEC) = 1 / 1) for 24 hours, and then, using an HS cell (manufactured by Hosen Co., Ltd.), it was placed on a SUS306 electrode with a diameter of 15.5 mm and a thickness of 0.5 mm so as to cover the electrode portion. After non-aqueous electrolyte was added dropwise, the film was sandwiched between another SUS306 electrode with a diameter of 15.5 mm and a thickness of 0.5 mm to produce an electrode / polymer film / electrode laminate. The AC impedance of the prepared cell was measured using an electrochemical tester under conditions of an amplitude of 10 mV and a frequency of 1 MHz-10 mHz in an atmosphere of 0°C, 20°C, 40°C, and 60°C, and the resistance value was read from a graph plotted on a complex plane and substituted into equation (1) to calculate the ionic conductivity. The activation energy of ionic conduction was calculated from the measurement temperature and the Arrhenius plot for each temperature.

[0079] (6) Cation transference number Using an HS cell, a 15 mm diameter, 0.2 mm thick Li metal film, a polymer film to be tested, and another 15 mm diameter, 0.2 mm thick Li metal film were stacked in an argon atmosphere (oxygen concentration ≤ 0.1 ppm, dew point ≤ -75°C). 300 μL of 1M LiTFSI EC / DEC = 1 / 1 (volume ratio) was injected and sealed. The AC impedance of the fabricated cell was measured at 25°C using an electrochemical tester under conditions of 10 mV amplitude and 1 MHz-100 mHz frequency. The interfacial resistance (R0) was calculated from the second arc of the Cole plot. Next, the electrode interface DC resistance was measured by applying a DC voltage (V) and measuring the initial current (I0) and steady-state current (I1). Finally, the AC impedance was measured at 25°C using an electrochemical tester under conditions of 10 mV amplitude and 1 MHz-100 mHz frequency. The interfacial resistance (R1) was calculated from the second arc of the Cole plot. The lithium transference number (τ) was calculated from the obtained values using the following formula.

[0080]

number

[0081] (7) Hayes Measurement was carried out using the following measuring instrument.

[0082] Equipment: Direct-reading haze meter HGM-2DP (for light source C) (manufactured by Suga Test Instruments Co., Ltd.) Light source: Halogen lamp 12V, 50W Light receiving characteristics: 395~745nm Optical conditions: Compliant with JIS-K7105-1981.

[0083] (8) Electrolyte content The polymer film was washed with dimethyl carbonate (DMC) for 10 seconds, the surface was wiped with Kimwipes, and then dried at 130°C for 3 hours. The mass was then weighed, and the polymer film was then immersed in 3.0 mL of non-aqueous electrolyte (1 M LiTFSI EC / DEC = 1 / 1) for 6 hours. The amount of electrolyte contained in the polymer film was calculated from the change in mass. Electrolyte content = (M-M0) / M0 M: Mass after immersion in electrolyte M0: Mass before immersion in electrolyte (9) Electrolyte permeation rate Two dry 6 mL glass screw bottles (As One Corporation, No. 2) were prepared. 2.0 mL of nonaqueous electrolyte (1 M LiTFSI EC / DEC = 1 / 1) was added to one bottle, and a film was attached to the mouth of the bottle so that there were no gaps. The other bottle was then placed on the film with its mouth facing downwards and secured with tape. The bottle containing the electrolyte was left standing with the top facing upwards. After 3 hours, the presence or absence of permeation of the nonaqueous electrolyte into the lower bottle was confirmed, the amount of outflow was weighed, and the permeation rate was calculated. If no permeation of the nonaqueous electrolyte was confirmed after 3 hours, the permeation rate was recorded as 0 μl / min.

[0084] (10)Liquid separation property In a dry room, a film was placed on a sample mount and fixed with tape. 10 μL of a non-aqueous electrolyte (1 M LiPF6EC / PC=1 / 1) was dropped onto the film, and the time until a stain appeared on the sample mount was measured.

[0085] ◎: 3 hours or more, ○: 3 hours or less, 1 hour or more, ×: 1 hour or less.

[0086] (11) Mean free volume radius Positron annihilation lifetime measurements were carried out under the following conditions.

[0087] Equipment: Fuji Invac small positron beam generator PALS-200A Positron source: 22Na-based positron beam Gamma-ray detector: BaF2 scintillator and photomultiplier tube Device constants: 234~246ps, 24.55ps / ch Beam intensity: 3 keV Measurement temperature: 23℃ Measurement atmosphere (decompression degree): 1 x 10 -6 ~1×10 -8 Pa Total count: Approximately 5,000,000 counts Sample size and pretreatment: The sample was attached to a 15 mm square Si wafer and degassed in vacuum. The third component of the obtained positron annihilation lifetime curve was analyzed by the nonlinear least-squares program POSITRONFIT to calculate the mean free volume radius (nm).

[0088] (12) Amount of lithium element in the polymer film The polymer film was washed with dimethyl carbonate (DMC) for 10 seconds, wiped with Kimwipes, and vacuum-dried at room temperature for 1 hour. The dried polymer film was immersed in a nonaqueous electrolyte (1M LiTFSI EC / DEC = 1 / 1) with a mass 1500 times that of the polymer film for 24 hours, then washed again with DMC for 10 seconds, wiped with Kimwipes, and vacuum-dried at room temperature for 1 hour. The polymer film was heated and carbonized with sulfuric acid, followed by thermal ashing. The ash was thermally decomposed with sulfuric acid and nitric acid, dissolved in dilute nitric acid, and adjusted to a constant volume. The solution was measured by atomic absorption spectrometry using a ZA3300 atomic absorption spectrometer (Hitachi High-Tech Science).

[0089] (13) Dendrite resistance 30 ml of non-aqueous electrolyte (1 M LiTFSI EC / DEC = 1 / 1) was dropped onto a metal Li of φ15 mm and thickness 0.2 mm placed in a CR2032 coin battery container, and then a polymer film for secondary batteries obtained in the examples was punched out to φ19 mm and placed so as to cover the electrode part. 30 ml of non-aqueous electrolyte (1 M LiTFSI EC / DEC = 1 / 1) was dropped onto the film, and the film was sandwiched between another metal Li of φ15 mm and thickness 0.2 mm, a spring was inserted, the lid was closed, and the battery was crimped to prepare a coin battery for measuring dendrite resistance. The obtained coin battery was charged and discharged at 0.2 mA / cm using a battery charge / discharge device (Meiden Hokuto Co., Ltd., Model HJ1005SM8A). 2 A charge-discharge cycle test was carried out with current application for 60 minutes under the conditions shown above. Dendrite resistance was evaluated according to the following criteria. Stable voltage behavior and no short circuit for over 30 cycles: Yes Unstable voltage behavior within 30 cycles or short circuit and inability to charge / discharge: ×

[0090] (14) Rate characteristics The positive electrode sheet contains Li(Ni 5 / 10 Mn 2 / 10 Co 3 / 10 ) O2 (Hosensha, coating weight: 9.5 mg / cm 2 ) was used. This positive electrode sheet was punched out to a diameter of 15 mm. A lithium metal foil (thickness: 200 μm) having a diameter of 16 mm was used as the negative electrode. Next, the polymer film for secondary batteries obtained in the example was punched out to a diameter of 19 mm, and the above-mentioned positive electrode and negative electrode were stacked on both sides of the sample so that the active material layer separated the samples. The positive electrode coated portion was arranged so that the entire negative electrode coated portion faced the positive electrode coated portion, and the resultant was introduced into a coin battery container. After injecting an electrolyte (1M LiPF6EC / DEC=1 / 1), a spring was inserted, the lid was closed, and the resultant was crimped to obtain a coin battery. The rate characteristics of the prepared coin batteries were evaluated using a battery charge / discharge device according to the following procedure, and the charge conditions were a current density of 0.2 mA / cm. 2 The upper voltage was 4.2 V, and the discharge conditions were a constant current charge and discharge density of 1.0 mA / cm. 2 The battery was discharged once at a constant current with a lower limit of 2.5 V, and then charged at a current density of 0.2 mA / cm 2 The upper limit voltage was 4.2 V, and the discharge conditions were a constant current charge and discharge density of 4.0 mA / cm. 2 The battery was subjected to one constant current discharge at a lower limit voltage of 2.5V.

[0091] <Calculation of discharge capacity retention rate> (Current density 4.0mA / cm 2 Discharge capacity) / (current density 1.0mA / cm 2 The discharge capacity retention rate was calculated by multiplying the discharge capacity of the battery by 100. Five coin batteries were fabricated, and the average value was taken as the discharge capacity retention rate. ◯: 70% or more, △: 60% or more but less than 70%, ×: less than 60%.

[0092] (Reference Example 1) Polymer solution P1 Dehydrated NMP (N-methyl-2-pyrrolidone, Mitsubishi Chemical Corporation) was dissolved in 60 mol % of the total diamines (PDSA, 1,4-phenylenediamine-4-sulfonic acid, Sigma-Aldrich), 40 mol % of TFMB (2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, Tokyo Chemical Industry Co., Ltd.), and 200 mol % of triethylamine (Fujifil Wako Pure Chemical Industries, Ltd.) in an amount equivalent to PDSA. The solution was cooled to 5°C in an ice-water bath. While maintaining the system in an ice-water bath under nitrogen, 99 mol % of CTPC (2-chloroterephthaloyl chloride, Nippon Light Metal Co., Ltd.) was added over 30 minutes. After the complete addition, the mixture was stirred for approximately 1 hour to polymerize an aromatic polyamide. The resulting polymerization solution was neutralized with 97 mol% lithium carbonate (Honjo Chemical Co., Ltd.) based on the total amount of acid chloride to obtain a polymer solution. The resulting polymer solution was added to a large amount of t-butanol with stirring to solidify the polymer into fibers. The precipitated polymer was separated, pulverized in a mixer for 5 minutes, and dried in a hot air oven at 80°C for 3 hours and a vacuum oven at 130°C for 8 hours to obtain aromatic polyamide p-1 (logarithmic viscosity 1.4 dl / g) containing sulfonic acid groups (-SO3H) in the repeating unit as a powder. The polymer powder was then redissolved in dehydrated NMP at a 45:55 mass ratio of lithium salt LiTFSI (lithium bis(trifluoromethanesulfonyl)imide, Fujifil Wako Pure Chemical Industries) to a polymer concentration of 10 mass%, obtaining polymer solution P1.

[0093] (Reference Example 2) Polymer solution P2 A polymer solution P2 was obtained in the same manner as in Reference Example 1, except that the mass ratio of polymer powder p-1 to LiTFSI was 40:60.

[0094] (Reference Example 3) Polymer solution P3 A polymer solution P3 was obtained in the same manner as in Reference Example 2, except that LiFSI (lithium bis(fluorosulfonyl)imide, manufactured by Fujifilm Wako Co., Ltd.) was used instead of LiTFSI as the lithium salt.

[0095] (Reference Example 4) Polymer solution P4 Aromatic polyamide p-2 (logarithmic viscosity 1.2 dL / g) was obtained as a powder in the same manner as in Reference Example 1, except that PDSA equivalent to 80 mol % and TFMB equivalent to 20 mol % were added relative to the total amount of diamines. Then, polymer solution P4 was obtained in the same manner as in Reference Example 1, except that aromatic polyamide p-2 was used as the polymer powder.

[0096] (Reference Example 5) Polymer solution P5 A polymer solution P5 was obtained in the same manner as in Reference Example 4, except that the mass ratio of polymer powder p-2 to LiTFSI was 60:40.

[0097] (Reference Example 6) Polymer solution P6 Aromatic polyamide p-3 (logarithmic viscosity 0.8 dl / g) was obtained as a powder in the same manner as in Reference Example 1, except that FDA (9,9-bis(4-aminophenyl)fluorene, manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of TFMB as the diamine, and PDSA and FDA were added in an amount of 60 mol % and 40 mol %, respectively, based on the total amount of diamine. Polymer solution P6 was then obtained in the same manner as in Example 1, except that the mass ratio of polymer powder p-3 to LiTFSI was 55:45.

[0098] (Reference Example 7) Polymer solution P7 Aromatic polyamide p-4 (logarithmic viscosity 1.6 dL / g) was obtained as a powder in the same manner as in Reference Example 1, except that MBAA (5,5'-methylenebis(2-aminobenzoic acid), manufactured by Seika Corporation) was used instead of PDSA as the diamine. Thereafter, polymer solution P7 was obtained in the same manner as in Example 1, except that the mass ratio of polymer powder p-3 to LiTFSI was 55:45.

[0099] (Reference Example 8) Polymer solution P8 0.048 mol / L PDSA and 200 mol% triethylamine (Fujifil Wako Pure Chemical Industries, Ltd.) were dissolved in dehydrated NMP under a nitrogen stream and cooled to 5°C in an ice-water bath. While maintaining the system in an ice-water bath under a nitrogen stream, 100 mol% CTPC relative to PDSA was added over 30 minutes. After the entire amount was added, the mixture was stirred for approximately 1 hour to polymerize aromatic polyamide. 0.032 mol / L TFMB and 100 mol% CTPC relative to TFMB were then added over 30 minutes. After the entire amount was added, the mixture was stirred for approximately 1 hour to polymerize. The resulting polymerization solution was neutralized with 97 mol% lithium carbonate (Honjo Chemical Co., Ltd.) relative to the total amount of acid chloride to obtain a polymer solution. The resulting polymerization solution was neutralized with 97 mol% lithium carbonate relative to the total amount of acid chloride to obtain a polymer solution. The resulting polymer solution was added to a large amount of t-butanol with stirring to solidify the polymer into a fibrous form, and the precipitated polymer was separated and then pulverized in a mixer for 5 minutes, followed by drying in a hot air oven at 80°C for 3 hours and in a vacuum oven at 130°C for 8 hours to obtain aromatic polyamide p-5 (logarithmic viscosity 2.2 dl / g) as a powder. Polymer solution P8 was then obtained in the same manner as in Reference Example 2, except that aromatic polyamide p-5 was used as the polymer powder.

[0100] (Reference Example 9) Polymer solution P9 Aromatic polyamide p-6 (logarithmic viscosity 1.8 dL / g) was obtained as a powder in the same manner as in Reference Example 8, except that the amount of PDSA added was 0.064 mol / L and the amount of TFMB added was 0.016 mol / L. Then, polymer solution P9 was obtained in the same manner as in Reference Example 1, except that aromatic polyamide p-6 was used as the polymer powder.

[0101] (Reference Example 10) Polymer solution P10 A polymer solution P10 was obtained in the same manner as in Reference Example 1, except that the mass ratio of polymer powder p-1 to LiTFSI was 78:32.

[0102] (Reference Example 11) Polymer Solution P11 Aromatic polyamide p-7 (logarithmic viscosity 1.4 dL / g) was obtained as a powder in the same manner as in Reference Example 1, except that PDSA was used in an amount corresponding to 100 mol % of the total amount of diamine. Then, polymer solution P11 was obtained in the same manner as in Reference Example 1, except that the mass ratio of polymer powder p-7 to LiTFSI was 50:50.

[0103] (Reference Example 12) Polymer solution P12 TFMB (100 mol % based on the total amount of diamines) was dissolved in dehydrated NMP under a nitrogen stream and cooled to 5°C in an ice-water bath. CTPC (99 mol % based on the total amount of diamines) was added over 30 minutes while the system was maintained in the ice-water bath under a nitrogen stream. After the entire addition, the mixture was stirred for approximately 1 hour to polymerize aromatic polyamide. The resulting polymerization solution was neutralized with 97 mol % lithium carbonate based on the total amount of acid chlorides to obtain a polymer solution. The resulting polymer solution was added to a large amount of water with stirring to solidify the polymer into a fibrous form. The precipitated polymer was separated, crushed in a mixer for 5 minutes, and dried in a hot air oven at 80°C for 3 hours and in a vacuum oven at 130°C for 8 hours to obtain aromatic polyamide polymer p-8 (logarithmic viscosity 2.8 dl / g) as a powder. Thereafter, the polymer powder p5 and the lithium salt LiTFSI were redissolved in dehydrated NMP at a mass ratio of 78:32, so that the polymer concentration was 10 mass %, to obtain a polymer solution P12.

[0104] (Reference Example 13) Polymer solution P13 Aromatic polyamide p-9 (logarithmic viscosity 2.5 dL / g) was obtained as a powder in the same manner as in Reference Example 1, except that DPE (4,4'-diaminodiphenyl ether, manufactured by Tokyo Chemical Industry Co., Ltd.) was used as the diamine in an amount equivalent to 100 mol% of the total amount of diamine. Then, polymer solution P13 was obtained in the same manner as in Reference Example 12, except that the ratio of polymer powder p-6 to LiTFSI was 50:50 by mass.

[0105] (Example 1) Polymer film F1 Polymer solution P1 was applied to a PET film support in the form of a film, and then dried in a hot air oven at 130°C for 5 minutes to make the film self-supporting. The film was then peeled off from the PET. It was then vacuum dried at 130°C for 1 hour to obtain polymer film F1. The evaluation results of the obtained sample are shown in Table 2.

[0106] (Examples 2 to 9, Comparative Examples 1 to 4) Polymer films F2 to F13 were obtained in the same manner as in Example 1, except that the polymer solutions shown in the table were used instead of polymer solution P1. Table 2 shows the evaluation results of the obtained samples.

[0107] [Table 1]

[0108] [Table 2]

Claims

1. A polymer film containing 35 to 99% by mass of an electrolyte salt and having a haze of 0.0 to 30.0%.

2. A polymer film containing 35 to 99 mass % of an electrolyte salt containing an anion having an ionic radius of 0.20 nm or more and 0.60 nm or less, and containing an aromatic polyamide, aromatic polyimide, or aromatic polyamideimide as a polymer constituting the polymer film, and having 20 to 99 mol % of functional groups having a pKa of 5.0 or less or 9.0 or more in the repeating units of the polymer constituting the polymer film.

3. A polymer film having an average free volume radius of 0.26 nm or more and 0.40 nm or less, and a lithium element content of 0.7 mass % or more after immersion in an electrolyte solution for 24 hours, as measured by atomic absorption spectrometry.

4. 4. The polymer film according to claim 1, wherein the repeating units of the polymer constituting the polymer film contain functional groups having a pKa of 5.0 or less or 9.0 or more in an amount of 20 to 99 mol %.

5. 4. The polymer film according to claim 1, wherein the electrolyte content is 20.0 mass % or less when treated under the following conditions: [Processing conditions] The polymer film was washed with diethyl carbonate (DEC) and then dried at 130°C for 3 hours, after which the mass was weighed. The polymer film was then immersed in 3.0 mL of a nonaqueous electrolyte (1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) ethylene carbonate (EC) / DEC=1 / 1) for 6 hours, and the amount of electrolyte contained in the polymer film was calculated from the change in mass. Electrolyte content = (M-M0) / M0 M: Mass after immersion in electrolyte M0: Mass before immersion in electrolyte

6. 3. The polymer film of claim 2, wherein the functional group comprises at least one of a sulfonic acid group, a phosphoric acid group, and a carboxylic acid group.

7. 3. The polymer film according to claim 2, wherein the protons contained in the functional groups are substituted with cations of alkali metals.

8. The polymer film of claim 2 , wherein the functional group comprises an amino group.

9. 4. The polymer film according to claim 1, wherein the polymer constituting the polymer film contains an aromatic polyamide, an aromatic polyimide, or an aromatic polyamideimide.

10. 3. The polymer film according to claim 1, wherein the electrolyte salt contains lithium ions.

11. 4. The polymer film according to claim 1, wherein the permeation rate of an electrolyte solution is 0 μl / min or more and 100 μl / min or less under the following conditions: [Conditions for measuring the permeation rate of the electrolyte] Two dry 6 mL glass screw bottles (No. 2, manufactured by AS ONE Corporation) were prepared, and 2.0 mL of nonaqueous electrolyte (1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) ethylene carbonate (EC) / diethyl carbonate (DEC) = 1 / 1) was added to one bottle, and a film was attached to the mouth of the bottle so that there were no gaps. Furthermore, the other bottle was placed on the film with its mouth facing downwards and secured in place with tape. The bottle containing the electrolyte was left standing with the top facing up, and after 3 hours, it was confirmed whether or not the non-aqueous electrolyte had permeated into the lower bottle, and the amount of the outflow was weighed to calculate the permeation rate. If no permeation of the non-aqueous electrolyte was confirmed after 3 hours, the permeation rate was recorded as 0 μl / min.

12. 4. The polymer film according to claim 1, wherein the thickness of the polymer film is 0.1 μm or more and 10.0 μm or less.

13. Ion conductivity is 1.0 x 10 －６ S / cm or more 1.0×10 －１ 4. The polymer film according to claim 1, wherein the viscosity is 0.5 S / cm or less.

14. 4. The polymer film according to claim 1, wherein the activation energy of ionic conduction is 1 kJ / mol or more and 25 kJ / mol or less.

15. 4. The polymer film according to claim 1, wherein the cationic transport number is 0.5 or more and 1.0 or less.

16. 2. The polymer film according to claim 1, comprising an anion having an ionic radius of 0.20 nm or more and 0.60 nm or less.

17. 3. The polymer film according to claim 1, which contains at least one of a bis(trifluoromethanesulfonyl)imide ion, a bis(fluorosulfonyl)imide ion, a trifluoromethanesulfonate ion, a hexafluorophosphate ion, and a perchlorate ion.

18. A secondary battery comprising the polymer film according to any one of claims 1 to 3.

19. 19. The secondary battery according to claim 18, wherein the negative electrode is metallic lithium.

20. 20. The secondary battery according to claim 18, comprising a positive electrode, an electrolyte, a polymer film, an electrolyte, and a negative electrode in this order, with the electrolytes on the positive electrode side and the negative electrode side having different compositions separated by the polymer film.

21. 19. The secondary battery according to claim 18, comprising a positive electrode, an inorganic solid electrolyte, and a negative electrode in this order, and a polymer membrane between the electrode and the solid electrolyte.

22. 20. The secondary battery of claim 18, comprising an electrode composite having a battery electrode on at least one side of a polymer membrane.

23. A vehicle, an unmanned transport aircraft, an air vehicle, an electronic device, or a stationary power source comprising the secondary battery according to claim 18.

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