JP2023135616A - Polymer membrane, film, secondary battery separator, secondary battery, vehicle, unmanned transport aircraft, electronic apparatus, and stationary power supply - Google Patents

Abstract

To provide a polymer membrane having ion conductivity and lithium dendrite resistance that is important for using a metallic lithium negative electrode.SOLUTION: A polymer membrane having a coefficient of surface elasticity of 500 MPa or more, ion conductivity of 1.0×10-5 S/cm or more, and air permeability of 5000 sec/100 mL or more after being immersed in an electrolytic solution for 19 hours. A film having the polymer membrane on at least one side of a polyolefin-based porous membrane base material. A separator for a secondary battery using the polymer membrane or the film. A secondary battery using the separator for a secondary battery, and a vehicle including the secondary battery, an unmanned transport aircraft, an electronic apparatus, a stationary power supply.SELECTED DRAWING: None

Description

The present invention relates to a polymer membrane, a film, a separator for a secondary battery, and a secondary battery.
The present invention also relates to vehicles, unmanned transportation vehicles, electronic devices, and stationary power sources that include the above-mentioned secondary battery.

Secondary batteries, such as lithium-ion secondary batteries, are used in smartphones, tablets, mobile phones, laptop computers, digital cameras, digital video cameras, portable digital devices such as portable game consoles, power tools, electric motorcycles, and electric assist bicycles. It is also widely used as a power source in automotive applications such as electric cars, hybrid cars, and plug-in hybrid cars.

In recent years, as devices have become smaller and more sophisticated, there has been a demand for higher energy density in the secondary batteries that serve as their power sources. If metallic Li can be applied to the negative electrode of secondary batteries, it is expected that the capacity will be significantly higher than that of current lithium-ion batteries. However, the metal Li negative electrode has a problem in that it forms dendrites due to repeated charging and discharging. If the dendrites grow and reach the positive electrode, there is a risk of short circuit, thermal runaway, and fire. In addition, there is a possibility that the dendrites will break, resulting in a decrease in the amount of active material, causing a decrease in capacity, and the broken dendrites may cause clogging of the separator, increasing resistance, resulting in a decrease in capacity.

That is, in realizing a secondary battery using metallic Li as a negative electrode, a separator is required to have characteristics that enable ion conduction and characteristics that suppress dendrite growth.

In general intercalation type secondary batteries, porous pores with through-holes with pore diameters of several tens of nanometers to several micrometers are used to enable ion conduction between the positive and negative electrodes while preventing short circuits due to contact between the positive and negative electrodes. Separators made of membranes or nonwoven fabrics are used. Ion conductivity is developed when the electrolytic solution permeates into the through-holes.

For example, Patent Document 1 describes a separator that has compression resistance and has a porous surface layer containing inorganic particles and a resin material containing a fluororesin, polyamide, or polyamideimide on a porous base material. is disclosed.
However, in the separator disclosed in Patent Document 1, since the base material and the surface layer are porous, there is a problem that dendrites grow along the pores.

Separators without pores have also been proposed, such as polymer electrolyte membranes made of ion-conductive polymers and without through-holes, and solid electrolyte membranes that are composites of ion-conducting polymers and particles and without through-holes. ing. However, if the strength of the polymer electrolyte membrane is low, there is a problem that dendrites may penetrate as they grow.

For example, Patent Document 2 discloses a separator that has a thermoplastic polymer layer on at least one side of a base material and has a puncture strength of 300 gf/20 μm or more.
Patent Document 3 discloses a polymer gel electrolyte having an ionic conductivity of 1×10 ⁻⁴ S/cm or more and a yield stress of more than 50 N/cm ² .

Patent No. 5994354 JP2019-179698A Patent No. 6118805

However, in the separator disclosed in Patent Document 2, the puncture strength is shown in a state where the separator is not impregnated with an electrolyte, and since the thermoplastic polymer layer is an acrylic resin, the separator shows a puncture strength in a state where the separator is impregnated with an electrolyte. In this case, the mechanical strength will be significantly reduced. The polymer gel electrolyte disclosed in Patent Document 3 shows strength not in the thickness direction, which is the growth direction of dendrites, but in the planar direction, and because it is a gel electrolyte, the strength in the thickness direction is poor.

In this way, even if a separator without through-holes is used, if the strength of the electrolyte membrane is low when it is impregnated with electrolyte, the electrolyte membrane may be pierced by the growth of dendrites, causing a short circuit between the positive and negative electrodes. However, it can be said that the problem of dendrite resistance still remains.

An object of the present invention is to provide a polymer film or the like that has ion conductivity and can suppress the growth of dendrites.

The inventors of the present invention have made extensive studies and have found that the above-mentioned problems can be solved by the following configuration, and have completed the present invention.

(1)
A polymer membrane having a surface elastic modulus of 500 MPa or more, an ionic conductivity of 1.0×10 ⁻⁵ S/cm or more, and an air permeability of 5000 seconds/100 mL or more after being immersed in an electrolytic solution for 19 hours.
(2)
The polymer membrane according to (1), wherein the change in thickness before and after the immersion in the electrolytic solution is greater than 100% and less than 450%.
(3)
The polymer film according to (1), comprising aromatic polyamide, aromatic polyimide, or aromatic polyamide-imide.
(4)
A film having a polymer membrane according to (1) on at least one side of a polyolefin porous membrane substrate.
(5)
The film according to (4), which has a peel strength of 50 gf/25 mm or more.
(6)
A separator for a secondary battery using the polymer film described in (1) or the film described in (4).
(7)
A secondary battery using the secondary battery separator described in (6).
(8)
Vehicles, unmanned transport vehicles, electronic devices, and stationary power sources that include the secondary battery described in (7).

According to the present invention, it is possible to provide a polymer membrane that has ion conductivity and can suppress the growth of dendrites, and a film having the polymer membrane. By using such a polymer membrane or a separator containing a film, dendrite growth, which is a problem with metal Li negative electrodes, can be suppressed, and a lithium secondary battery with high capacity and long life can be realized.
Further, according to the present invention, a separator for a secondary battery using the above polymer membrane or film, a secondary battery using the above separator, a vehicle, an unmanned transport vehicle, an electronic device using the above secondary battery, and Stationary power supply can be provided.

The present invention has a surface elastic modulus of 500 MPa or more, an ionic conductivity of 1.0 x 10 ^-5 S/cm or more, and an air permeability of 5000 seconds/100 mL or more after being immersed in an electrolytic solution for 19 hours. Regarding polymer membranes.
Hereinafter, the polymer membrane used in the present invention will be explained in detail.

[1] Polymer membrane (polymer)
Examples of polymers include polyamide, polyimide, polyamideimide, polyetherimide, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, polysulfone, polyethersulfone, polyphenylsulfone, polyketone, polyetherketone. , polycarbonate, polyacetal, polyphenylene sulfide, polymethylmethacrylic, polyetheretherketone, polyethersulfone, etc. These polymers may be used alone, or two or more types may be mixed or copolymerized.

Among these, polyamide, polyimide, or polyamide-imide is preferred, and aromatic polyamide, aromatic polyimide, or aromatic polyamide-imide is more preferred since the strength of the polymer film is excellent.
That is, it is preferable that the polymer film contains aromatic polyamide, aromatic polyimide, or aromatic polyamide-imide.

Among them, polyamide is preferred. More preferred is aromatic polyamide, and even more preferred is para-oriented aromatic polyamide.
A para-oriented aromatic polyamide is obtained by polymerizing a para-oriented aromatic diamine and a para-oriented aromatic dicarboxylic acid halide.

The aromatic polyamide includes a structure represented by the following chemical formula (1) and/or chemical formula (2). Ar ¹ and Ar ² in chemical formula (1) and Ar ³ in chemical formula (2) each represent an aromatic group.

In the aromatic polyamide, at least a portion of the aromatic groups Ar ¹ and Ar ² of chemical formula (1) or Ar3 of chemical formula (2) is preferably substituted with an electrically attractive group. Preferably, 30 to 100 mol% of the total of all aromatic groups are aromatic groups substituted with electron-withdrawing groups, more preferably 50 to 100 mol%. When the content is 30 mol% or more, solubility in organic solvents becomes good. Here, the electron-withdrawing group in the present invention refers to a group having an electronegativity of 2.5 or more. Examples of electron-withdrawing groups include halogen groups such as fluoro, chloro, and bromo groups, halogenated alkyl groups such as trifluoromethyl, nitro, cyano, cyanate, and phenyl groups.

Furthermore, examples of Ar ¹ , Ar ² and Ar ³ include the following chemical formulas (3) to (7). Furthermore, X and Y in chemical formulas (6) and (7) are selected from -O-, -CO-, -SO ₂ -, -CH ₂ -, -S-, -C(CH ₃ ) ₂ -, etc. However, it is not limited to this.

Specific examples of aromatic diamines include para-phenylene diamine, meta-phenylene diamine, ortho-phenylene diamine, 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, 4,4'-oxybis(3-trifluoromethyl)aniline, 1,4-bis(4-amino-2 -trifluoromethylphenoxy)benzene, 1,5'-naphthalenediamine, 4,4'-diaminodiphenylsulfone, etc., but are not limited to these.

Specific examples of aromatic dicarboxylic acid halides include terephthalic acid chloride, 2-chloroterephthalic acid chloride, 2-fluoroterephthalic acid chloride, isophthalic acid chloride, 2-chloroisophthalic acid chloride, 2-fluoroisophthalic acid chloride, , 3,5,6-tetrachloroisophthalic acid chloride, 2,3,5,6-tetrafluoroisophthalic acid chloride, 2,6'-naphthalene dicarboxylic acid chloride, trimesic acid chloride, etc., but are limited to these. It is not something that will be done.

(Membrane physical properties)
The polymer membrane of the present invention has substantially no air permeability, and has an air permeability of 5000 seconds/100 mL or more. More preferably, it is 10,000 seconds/100mL or more. When the air permeability (Gurley air permeability) is smaller than 5000 seconds/100 mL, physical through holes are often present, and the effect of blocking penetration of metal dendrites and the like may not be obtained. Furthermore, the surface elastic modulus may not be within the scope of the present invention. In order to keep the Gurley air permeability within the above range, it is preferable to set the manufacturing conditions of the polymer membrane within the range described below.

The polymer membrane of the present invention has an ionic conductivity of 1.0×10 ⁻⁵ S/cm or more after being immersed in an electrolytic solution for 19 hours, that is, when impregnated with an electrolytic solution. More preferably, it is 5.0×10 ⁻⁵ S/cm or more. By setting the ionic conductivity within the above range, excellent output characteristics and cycle characteristics can be obtained when used as a separator. If the ionic conductivity is less than 1.0 x 10 ^-5 S/cm, when used as a separator, the ion permeability will be low, resulting in a decrease in output characteristics and capacity deterioration when repeatedly charged and discharged. may become large.

The polymer membrane of the present invention has a surface elastic modulus of 500 MPa or more after being immersed in an electrolytic solution for 19 hours, that is, when impregnated with an electrolytic solution. More preferably, it is 600 MPa or more. If the surface elastic modulus is less than 500 MPa, the growth of metal dendrites cannot be suppressed when used as a separator in a metal negative electrode secondary battery, resulting in a capacity drop during repeated charging and discharging, or contact between the positive electrode and dendrites. This may cause a short circuit, resulting in smoke or fire. Furthermore, if the surface elastic modulus is less than 500 MPa, when foreign matter enters the battery, the polymer membrane may rupture and a short circuit may occur.

In the polymer membrane of the present invention, the change in thickness before and after immersion in an electrolytic solution is preferably greater than 100% and 450% or less. More preferably, it is greater than 150% and less than 400%. When the thickness change is greater than 100%, the electrolytic solution easily permeates into the polymer membrane, and the ionic conductivity can be increased. In addition, by setting it to 450% or less, it is possible to suppress the softening of the polymer film and prevent a decrease in capacity due to the growth of metal dendrites and smoke and ignition due to short circuits.

The thickness of the polymer film in the present invention is preferably 0.1 μm or more and 30 μm or less, more preferably 0.15 μm or more and 20 μm or less, and most preferably 0.2 μm or more and 15 μm or less. By setting the thickness of the polymer film to 0.1 μm or more, when used as a separator for a metal negative electrode secondary battery, it is possible to suppress the growth of dendrites and improve the safety of the battery. Further, by setting the thickness to 30 μm or less, the resistance of the polymer film can be reduced, and a decrease in battery capacity can be prevented.

The above air permeability, ionic conductivity, surface elastic modulus, and thickness change can be measured by the method described in Examples below.

[2] Method for forming polymer film (polymer synthesis)
A method for obtaining a polymer that can be used in the polymer membrane of the present invention will be explained using aromatic polyamide and aromatic polyimide as examples. Of course, the polymer that can be used in the present invention and its polymerization method are not limited thereto.

Various methods can be used to obtain aromatic polyamides. For example, when using a low temperature solution polymerization method using acid dichloride and diamine as raw materials, N-methylpyrrolidone, N,N-dimethylacetamide, dimethylformamide , synthesized in an aprotic organic polar solvent such as dimethyl sulfoxide. In the case of solution polymerization, in order to obtain a polymer with a high molecular weight, the moisture content of the solvent used for polymerization is preferably 500 ppm or less (based on mass, hereinafter the same), more preferably 200 ppm or less.

As a method for obtaining aromatic polyimide or its precursor, aromatic polyamic acid, for example, a method may be employed in which it is synthesized by solution polymerization in an aprotic organic polar solvent using tetracarboxylic acid anhydride and aromatic diamine as raw materials. I can do it. Examples of the aprotic organic polar solvent include N-methyl-2-pyrrolidone, N,N-dimethylacetamide, dimethylformamide, and dimethylsulfoxide.

If equal amounts of both tetracarboxylic acid anhydride and aromatic diamine are used as raw materials, an ultra-high molecular weight polymer may be produced, so the molar ratio of one to 90.0 to 99.5 mol% of the other is adjusted. It is preferable to adjust as follows.

The intrinsic viscosity (η) of aromatic polyamide, aromatic polyimide, or aromatic polyamic acid which is a precursor thereof is preferably 3.5 dl/g or more and 5.0 dl/g or less. More preferably, it is 3.7 dl/g or more and 4.5 dl/g or less. Increasing the intrinsic viscosity means increasing the degree of polymerization, that is, the molecular weight, of the aromatic polyamide resin, which improves the strength of the polymer film when impregnated with an electrolyte. By setting the intrinsic viscosity (η) to 3.5 dl/g or more, the strength of the polymer film can be improved and dendrite growth can be suppressed. On the other hand, if the intrinsic viscosity (η) is increased too much, the coating agent supplyability during coating may be lowered. By setting the intrinsic viscosity (η) to 5.0 dl/g or less, it is possible to prevent a decrease in coating agent supply properties during coating.

(Preparation of paint)
The coating agent used in the process of manufacturing the polymer film of the present invention will be explained.
The polymer solution after polymerization may be used as a coating agent as it is, or the polymer may be isolated and then redissolved in the above-mentioned aprotic organic polar solvent or an inorganic solvent such as sulfuric acid.

The polymer concentration in the coating material is preferably 8.0% by mass or more and 12% by mass or less, more preferably 9.0% by mass or more and 11% by mass or less. By setting the polymer concentration to 8.0% by mass or more, the film formed by the manufacturing method described below is less likely to become porous and the decrease in surface elastic modulus can be suppressed, which has the effect of suppressing the growth of metal dendrites. is easy to obtain. Furthermore, by controlling the polymer concentration to 12% by mass or less, the coating material is less likely to have a high viscosity, the coating material supplyability is stabilized, and furthermore, the occurrence of streak unevenness can be suppressed when producing a polymer film.

The coating viscosity is preferably 100 Pa·s or more and 500 Pa·s or less, more preferably 200 Pa·s or more and 400 Pa·s or less. By setting the pressure to 100 Pa·s or more, dripping during coating is difficult, and non-uniformity and porosity of the polymer film can be suppressed, making it easy to obtain dendrite resistance. Furthermore, by setting the pressure to 500 Pa·s or less, it is possible to suppress a decrease in coating agent supplyability and the occurrence of streaks in the resulting polymer film.

Moreover, the coating material may contain particles. For example, inorganic oxide particles such as aluminum oxide, boehmite, silica, titanium oxide, zirconium oxide, iron oxide, magnesium oxide, inorganic nitride particles such as aluminum nitride, silicon nitride, calcium fluoride, barium fluoride, barium sulfate, etc. Preferred are hardly soluble ionic crystal particles. When particles are included, the effect of suppressing dendrite growth may increase depending on the hardness of the particles. Further, it may have the effect of suppressing shrinkage of the polymer film when heated.

Moreover, a poor solvent for the above polymer may be included. Examples include water, acetone, alcohol solvents such as ethanol and methanol, and polyhydric alcohol solvents such as ethylene glycol, propylene glycol, diethylene glycol, and tripropylene glycol.

(Formation of polymer film)
A method for forming the polymer membrane of the present invention will be explained. The coating prepared as described above can be formed into a film by a so-called solution casting method. Solution film forming methods include a wet-dry method, a dry method, a wet method, and the like, and any method may be used to form a film, but the wet-dry method will be explained here as an example.

When forming a film using the dry-wet method, the coating material is extruded from a syringe or a mouthpiece onto a support such as a glass plate, drum, endless belt, or film to form a film, and then such a film has self-retaining properties. Dry until dry. The drying conditions are preferably, for example, 50 to 200° C. for 60 minutes or less. After the dry process, the membrane is peeled off from the support and introduced into the wet process. The coagulating liquid in the wet process is not particularly limited as long as it is a poor solvent for the polymer in the coating material, but water is preferable from the viewpoint of human health and cost. The time from the end of the drying process until the membrane is immersed in the coagulation liquid is preferably within 20 seconds. More preferably, it is within 15 seconds. By setting the heating time to within 20 seconds, it is possible to suppress the formation of porosity due to partial aggregation of the polymer, the surface elastic modulus is less likely to decrease, and the growth of metal dendrites is easily suppressed. Next, drying and heat treatment are performed. The heat treatment is carried out at a temperature of 80° C. to 350° C., preferably 100° C. to 300° C., for several seconds to several tens of minutes.

[3] Film The film of the present invention preferably has the above-described polymer film on at least one side of a base material made of a porous film.

In the case of a film in which a polymer membrane is laminated on a porous membrane, the porous membrane serves as a support, so that strength can be ensured even if the polymer membrane is made thin. Further, it is also possible to reduce the resistance by making the polymer film thinner.

(porous membrane)
The porous membrane used in the present invention has a large number of micropores inside and has a structure in which these micropores are connected, allowing gas or liquid to pass from one surface to the other. Examples include a porous membrane, a nonwoven fabric, and a porous membrane sheet made of a fibrous material.

The material constituting the porous membrane is preferably made of a resin that is electrically insulating, electrically stable, and stable in electrolyte solutions. From the viewpoint of providing a shutdown function (SD function), the resin used is preferably a thermoplastic resin having a melting point of 200° C. or lower. More preferably it is 140°C or lower.

Examples of thermoplastic resins having a melting point of 200° C. or lower include polyolefin resins. The porous membrane is preferably a polyolefin porous membrane containing a polyolefin resin as a main component.
That is, the film of the present invention is a film having the above-mentioned polymer film on at least one side of a polyolefin porous film base material.

Specific examples of polyolefin resins include polyethylene, polypropylene, polybutene, polypentene, polyhexene, polymethylpentene, polyoctene, polyvinyl acetate, polymethyl methacrylate, polystyrene, and copolymers and mixtures of these. It will be done. Polyethylene, polypropylene, polybutene, polypentene, polyhexene, polymethylpentene, polyoctene, polyvinyl acetate, polymethyl methacrylate, and polystyrene are not only homopolymers but also copolymers containing other α-olefins. Good too. Furthermore, from the viewpoints of price, electrolyte resistance, and mechanical strength, polyethylene, polypropylene, and mixtures of these are more preferred.

The porous membrane may be a single-layer porous membrane containing, for example, 90% by mass or more of polyethylene, or a multi-layer porous membrane having a porous layer made of polyethylene and polypropylene.

The peel strength of the film is preferably 50 gf/25 mm or more. By setting it as 50 gf/25 mm or more, adhesiveness between the porous membrane and the polymer membrane can be obtained, and excellent thermal dimensional stability can be obtained. Furthermore, during battery production, the polymer film is difficult to peel off during film transport. Note that 1 gf=9.80665 g·m/s ² .

The peel strength of the film can be measured by the method described in Examples below.

The thickness of the film of the present invention is the sum of the thickness of the laminated polymer membrane and the thickness of the porous membrane, and is preferably 1 μm or more and 50 μm or less, more preferably 2 μm or more and 40 μm or less, and more preferably 3 μm or more and 30 μm or less. It is as follows. By setting the thickness of the film to 1 μm or more, the film can be made to have excellent handling properties during film processing. Further, by setting the thickness to 50 μm or less, the resistance of the film can be reduced when used as a separator of a metal negative electrode secondary battery, and a decrease in battery capacity can be prevented.
Further, the laminated thickness of the polymer membrane in the film may be within the range of the thickness of the polymer membrane mentioned above. When polymer membranes are laminated on both sides of the porous membrane, the sum of the respective thicknesses is the laminated thickness of the polymer membranes. In order to keep the thickness of the film within this range, it may be formed by the formation method described below.

[4] Film forming method (preparation of coating material)
The film forming method of the present invention includes the step of laminating a polymer membrane on at least one surface of a porous membrane substrate. The coating agent used in the step of laminating polymer films will be explained. Note that the above-mentioned section (Polymer synthesis) can be referred to for the method of obtaining a polymer that can be used for a polymer membrane.

The polymer solution after polymerization may be used as a coating agent as it is, or the polymer may be isolated and then redissolved in the above-mentioned aprotic organic polar solvent or an inorganic solvent such as sulfuric acid.

The polymer concentration in the coating material is preferably 3.5% by mass or more and 6.0% by mass or less, more preferably 3.7% by mass or more and 5.0% by mass or less. By setting the polymer concentration to 3.5% by mass or more, the film formed by the manufacturing method described below is less likely to become porous and a decrease in surface elastic modulus can be suppressed, so that the growth of metal dendrites can be suppressed. Easy to obtain. Furthermore, by controlling the polymer concentration to 6.0% by mass or less, the coating material is less likely to have a high viscosity, the coating material supplyability is stabilized, and furthermore, the occurrence of streak unevenness can be suppressed when producing a polymer film.

The coating viscosity is preferably 2000 mPa·s or more and 5000 mPa·s or less, more preferably 2500 mPa·s or more and 4500 mPa·s or less. By setting the pressure to 2000 mPa·s or more, it is difficult to drip during coating, and it is possible to suppress non-uniformity and porosity of the polymer film, so that dendrite resistance is easily obtained. By setting the pressure to 5000 mPa·s or less, the coating agent supply property is stabilized, and furthermore, the occurrence of streak unevenness can be suppressed when producing a polymer film.

Moreover, the coating material may contain particles. For example, inorganic oxide particles such as aluminum oxide, boehmite, silica, titanium oxide, zirconium oxide, iron oxide, magnesium oxide, inorganic nitride particles such as aluminum nitride, silicon nitride, calcium fluoride, barium fluoride, barium sulfate, etc. Preferred are hardly soluble ionic crystal particles. When particles are included, the effect of suppressing dendrite growth may increase depending on the hardness of the particles. Further, it may have the effect of suppressing shrinkage of the polymer film when heated.

Moreover, a poor solvent for the above polymer may be included. Examples include water, acetone, alcohol solvents such as ethanol and methanol, and polyhydric alcohol solvents such as ethylene glycol, propylene glycol, diethylene glycol, and tripropylene glycol.

(Film formation)
A polymeric coating is applied onto at least one surface of the porous membrane. As a coating method, a known method may be used. Examples include dip coating, slit die coating, knife coating, comma coating, kiss coating, roll coating, bar coating, spray coating, dip coating, spin coating, screen printing, inkjet printing, pad printing, and other types of printing. can. The coating method is not limited to these, and the coating method may be selected depending on preferable conditions such as the polymer, particles, solvent, porous membrane, etc. used. Furthermore, in order to improve the coating properties, the coated surface of the porous membrane may be subjected to surface treatment such as corona treatment or plasma treatment.

Next, the porous membrane coated with the coating liquid is immersed in the coagulating liquid and dried. The coagulating liquid is not particularly limited as long as it is a poor solvent for the polymer in the coating material, but water is preferred from the viewpoint of its effect on the human body and cost. The time required for immersing the coated porous membrane in the coagulating liquid after coating is preferably within 20 seconds. More preferably, it is within 15 seconds. By setting the heating time to within 20 seconds, it is possible to suppress the formation of porosity due to partial aggregation of the polymer, the surface elastic modulus is less likely to decrease, and the growth of metal dendrites is easily suppressed.

[5] Secondary battery The polymer membrane and film of the present invention can be suitably used in separators for secondary batteries such as lithium ion batteries.
The present invention also relates to a separator for secondary batteries using the above-mentioned polymer membrane or film.
The present invention also relates to a secondary battery using the separator for secondary batteries.

A lithium ion battery has a structure in which a secondary battery separator and an electrolyte are interposed between a positive electrode in which a positive electrode active material is laminated on a positive electrode current collector, and a negative electrode or metal negative electrode in which a negative electrode active material is laminated on a negative electrode current collector. It becomes.

The positive electrode is made by laminating a positive electrode material consisting of an active material, a binder resin, and a conductive additive on a current collector, and the active material includes LiCoO ₂ , LiNiO ₂ , Li(NiCoMn)O ₂ , etc. Layered lithium-containing transition metal oxides, spinel- _type manganese oxides such as _LiMn2O4 , and iron-based compounds such as _LiFePO4 , elemental sulfur, solid _Li2Sn ( _n is an integer of 1 or more), organic sulfur and sulfur-based compounds such as carbon-sulfur composite polymers. As the binder resin, a resin with high oxidation resistance may be used. Specific examples include fluororesin, acrylic resin, and styrene-butadiene resin. Carbon materials such as carbon black and graphite are used as conductive aids. A metal foil is suitable as the current collector, and aluminum is often used in particular.

The negative electrode includes a metal foil such as Li, or a negative electrode material made of an active material and a binder resin, which is laminated on a current collector. Examples of active materials include metal materials such as Li, carbon materials such as artificial graphite, natural graphite, hard carbon, and soft carbon, lithium alloy materials such as tin and silicon, and lithium titanate (Li ₄ Ti ₅ O ₁₂ ). can be mentioned. As the binder resin, fluororesin, acrylic resin, styrene-butadiene resin, etc. are used. As the current collector, a metal foil is suitable, and in particular, a copper foil is often used. Further, a metal Li negative electrode can be preferably used for the purpose of producing a high energy density secondary battery.

The electrolyte serves as a field for moving ions between the positive electrode and the negative electrode in the secondary battery, and is composed of an electrolyte dissolved in an organic solvent. Examples of the electrolyte include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiFSI, LiTFSI, and the like. Examples of organic solvents include ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, gamma-butyrolactone, dimethoxyethane, diethoxyethane, and sulfolane, and two or more of these organic solvents may be mixed. You may also use it as

An example of a method for manufacturing a secondary battery will be shown. First, an active material and a conductive aid are dispersed in a binder solution to prepare an electrode coating solution, and this coating solution is applied onto a current collector and the solvent is dried to obtain a positive electrode and a negative electrode, respectively. . The thickness of the coated film after drying is preferably 50 μm or more and 500 μm or less. Metal foil such as Li may be used as the electrode. A secondary battery separator is placed between the obtained positive electrode and negative electrode so that it is in contact with the active material layer of each electrode, and is enclosed in an exterior material such as an aluminum laminate film. After injecting the electrolyte, the negative electrode lead and Install a safety valve and seal the exterior material.

[6] Applications The secondary battery of the present invention can be suitably used as a power source for vehicles, unmanned transportation vehicles, electronic devices, stationary power sources, and the like.
The present invention also relates to a vehicle, an unmanned transport vehicle, an electronic device, and a stationary power source including the above-described secondary battery.

As explained above, the following matters are disclosed in this specification.
(1)
A polymer membrane having a surface elastic modulus of 500 MPa or more, an ionic conductivity of 1.0×10 ⁻⁵ S/cm or more, and an air permeability of 5000 seconds/100 mL or more after being immersed in an electrolytic solution for 19 hours.
(2)
The polymer membrane according to (1), wherein the change in thickness before and after the immersion in the electrolytic solution is greater than 100% and less than 450%.
(3)
The polymer film according to (1) or (2), containing aromatic polyamide, aromatic polyimide, or aromatic polyamide-imide.
(4)
A film having a polymer membrane according to any one of (1) to (3) on at least one side of a polyolefin porous membrane base material.
(5)
The film according to (4), which has a peel strength of 50 gf/25 mm or more.
(6)
A separator for a secondary battery using the polymer film according to any one of (1) to (3) or the film according to (4) or (5).
(7)
A secondary battery using the secondary battery separator described in (6).
(8)
Vehicles, unmanned transport vehicles, electronic devices, and stationary power sources that include the secondary battery described in (7).

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited thereto in any way. The measurement method used in this example is shown below.

[1] Measurement method 1. Intrinsic viscosity (η)
The polymer was dissolved in N-methyl-2-pyrrolidone (NMP) containing 2.5% by mass of lithium bromide (LiBr) at a concentration of 0.5 g/dl and heated to 30°C using an Ubbelohde viscometer. The flow time was measured. The flow time of blank NMP in which no polymer was dissolved was measured in the same manner, and the intrinsic viscosity (η) (dl/g) was calculated using equation (1).

Intrinsic viscosity (η) (dl/g) = [ln(t/t0)]/0.5 (1)
t0: Blank flow time (seconds)
t: Sample flow time (seconds).

2. Paint viscosity 2 mL of the paint was filled into the sample adapter of an RB80 viscometer (manufactured by Toki Sangyo Co., Ltd.), and the temperature was controlled at 30°C. An adapter was set in the viscometer, and measurement was performed at a rotation speed of 50 rpm using a 17 mmΦ rotor.

3. Air Permeability Measurement was performed using an Oken air permeability meter (manufactured by Asahi Seiko Co., Ltd., EGO-1T) at an air volume of 100 mL. The upper measurement limit of the device is 10000s/100mL. The polymer film was fixed to avoid wrinkles and measured according to JIS P8117. Three measurement points were set at equal intervals in the TD direction, and the average value was used as the air permeability (s/100mL).
The air permeability of the porous membrane of Comparative Example 7 was measured in accordance with JIS P8117 similarly to the polymer membrane.
For Examples 2, 4, 6, 8, 10, 12, 14, 16, 17 and Comparative Examples 4 to 6 and 9, the air permeability of the films was measured in accordance with JIS P8117 in the same manner as the polymer membrane. The value obtained by subtracting the air permeability of the porous membrane from the air permeability of the film was used as the air permeability of the polymer membrane (s/100 mL).

4. Thickness of polymer membrane, thickness of porous membrane, and thickness of film The cross section of the polymer membrane and film was cut using a cross-section polisher (SM-9010 manufactured by JEOL Ltd.), and the cross section in the thickness direction in the width direction was coated with platinum. It was used as an observation sample. Next, a cross section of the sample was photographed at an arbitrary magnification using a field emission scanning electron microscope (JSM 6701F manufactured by JEOL Ltd.), and the thickness of the polymer film and the thickness of the porous film were determined. The acceleration voltage during observation was 2.0 kV. The interface between the polymer membrane layer and the porous membrane layer in the film was judged from the difference in cross-sectional structure or image contrast. In addition, the thickness of the film was the sum of the thickness of the laminated polymer membrane and the thickness of the porous membrane, and when polymer membranes were laminated on both sides of the porous membrane, the thickness of each layer was determined.

5. Surface elastic modulus After immersing the polymer membrane in an electrolyte solution (1M LiTFSI ethylene carbonate (EC)/diethyl carbonate (DEC) = 1/1, manufactured by Mitsui Chemicals) for 19 hours, it was immersed in Ar at room temperature (25 °C). Evaluation was performed using the nanoindentation method in an atmosphere. The device was an ultra-microhardness meter Nano Indenter G200X (Inforce 50) manufactured by KLA Tencor, the indenter was a diamond triangular pyramid indenter, and the indentation amount was the same as the thickness of the polymer film determined in [1] Measurement Method 4 above. It was set to 10% or less. In addition, in the case of a film in which a polymer membrane and a porous membrane were laminated, measurements were made from the polymer membrane layer side of the surface facing the metal negative electrode. In Comparative Example 7, a porous membrane was used as an evaluation sample and evaluated in the same manner as the polymer membrane.

The surface elastic modulus E/(1−ν ² ) of the sample is calculated from equation (2).

E ^* : Composite elastic modulus including the contribution of elastic deformation of the indenter ν _i : Poisson's ratio of the indenter E _i : Elastic modulus of the indenter

The composite elastic modulus E ^* , which includes the contribution of the elastic deformation of the indenter, is expressed as in equation (3),

β: Constant determined from the shape of the indenter (1.034 for a diamond triangular pyramid indenter)

After the sample is pushed in with a load P, the elastic deformation recovers and the projected area of the remaining indentation is A, which is expressed as in equation (4).

η: Correction coefficient for the shape of the indenter tip k: Constant determined from the shape of the indenter (24.56 for a diamond triangular pyramid indenter)
h: Total measured displacement dP/dh: Initial slope at unloading in the obtained load-indentation depth diagram ε: Constant determined from the shape of the indenter (0.75 for a diamond triangular pyramid indenter)

Equations (3) and (4) were substituted into equation (2) to determine the surface elastic modulus.

6. Ionic conductivity After immersing the polymer membrane in an electrolytic solution (1M LiTFSI ethylene carbonate (EC)/diethyl carbonate (DEC) = 1/1, manufactured by Mitsui Chemicals) for 19 hours, it was placed on a SUS304 electrode to cover the electrode part. After dropping the electrolyte, it was sandwiched between another SUS electrode to produce a laminate of electrode/polymer membrane/electrode. An evaluation cell was prepared by fixing the laminate with a silicon plate to prevent it from shifting.

The AC impedance of the fabricated cell was measured at 25°C using an electrochemical test device (manufactured by Biologic, model number: SP-150) under the conditions of an amplitude of 10 mV and a frequency of 1 MHz to 10 mHz, and the resistance was determined from a graph plotted on a complex plane. The value was read and substituted into equation (5) to calculate the ionic conductivity. The measurement was performed five times, and the calculated average value was taken as the ionic conductivity.

σ=d/AR (5)
σ: Ionic conductivity (S/cm)
d: Thickness of polymer membrane (cm) (before immersion in electrolyte)
A: Area of electrode (cm ² )
R: resistance value (Ω)

The ionic conductivity of the porous membrane of Comparative Example 7 was measured in the same manner as the polymer membrane, and the ionic conductivity value was obtained. For Examples 2, 4, 6, 8, 10, 12, 14, 16, 17 and Comparative Examples 4 to 6 and 9, which produced films, the resistance values were obtained by measuring in the same manner as the polymer film, (6) By substituting it into the equation, the ionic conductivity was calculated.

σ=d/{A(R1-R0)} (6)
σ: Ionic conductivity (S/cm)
d: Thickness of polymer membrane (cm) (before immersion in electrolyte)
A: Area of electrode (cm ² )
R0: Resistance value of porous membrane (Ω)
R1: Film resistance value (Ω)

7. Change in thickness before and after immersion in electrolyte The polymer membrane was immersed in an electrolyte (1M LiTFSI EC/DEC=1/1, manufactured by Mitsui Chemicals) for 19 hours, and the thickness of the polymer membrane before and after immersion was measured using a high-precision digital length measuring device ( It was measured using a Mitutoyo Co., Ltd. model number: VL-50) and calculated by substituting it into equation (7).

Thickness change (%) = (d2/d1) x 100 (7)
d1: Thickness of polymer membrane (cm) (before immersion in electrolyte)
d2: Thickness of polymer membrane (cm) (after immersion in electrolyte)

Films of Examples 2, 4, 6, 8, 10, 12, 14, 16, 17, and Comparative Examples 4 to 6, and 9 were immersed in an electrolytic solution in the same way as the polymer membrane, and the thickness before and after immersion was measured. It was measured. The thickness of the porous membrane was also measured and calculated by substituting it into equation (8). Note that the porous membrane used was made of polyethylene whose thickness did not change before and after being immersed in the electrolytic solution.

Thickness change (%) = ((d4-d0)/(d3-d0)) x 100 (8)
d0: Thickness of porous membrane (cm)
d3: Film thickness (cm) (before electrolyte immersion)
d4: Film thickness (cm) (after immersion in electrolyte)

8. Peel Strength A transparent double-sided tape (manufactured by 3M Company, product number 665) cut to a width of 18 mm and a length of 100 mm was attached to an acrylic plate with a thickness of 2 mm. Next, films cut into lengths of 25 mm and 200 mm were attached to cover the entire surface of the transparent double-sided tape. In Example 17, the film was attached so that the polymer membrane side of the film was on the transparent double-sided tape side.
Thereafter, the peel strength by 180 degree peeling was measured using a rheometer (manufactured by Sun Science Co., Ltd., model number: CR-3000EX) at a peeling rate of 300 mm/min.

9. Dendrite resistance evaluation Dendrite resistance against metal Li was evaluated. In a metal Li negative electrode, Li ions in the electrolyte are deposited on the metal surface during charging and are dissolved during discharge. Li dendrites are formed when the reaction on the metal Li surface is non-uniform, and Li precipitation progresses quickly in areas with low resistance. If the dendrite penetrates the separator, unstable voltage behavior is observed. In the present invention, the dendrite resistance of polymer membranes or films was evaluated by the following method.

In a glove box with an argon atmosphere, the separator was a polymer membrane or film, the working electrode and counter electrode were metal Li (manufactured by Honjo Metals), and the electrolyte was 1M LiTFSI EC/DEC=1/1 (manufactured by Mitsui Chemicals). A battery for evaluation was produced using an HS cell (manufactured by Hosensha). The above evaluation battery was set in a charging/discharging device (manufactured by Hokuto Denko Co., Ltd.), and a cycle test was conducted at a current density of 4 mA/cm ² and a current application period of 62 minutes. Dendrite resistance was determined based on the following criteria.

Stable voltage behavior for 100 cycles or more: 〇 Unstable voltage behavior within 99 cycles after 21 cycles: △
Unstable voltage behavior within 20 cycles: ×

10. Battery performance evaluation The positive electrode sheet contained 92 parts by mass of Li(Ni _5/10 Mn _2/10 Co _3/10 )O ₂ as a positive electrode active material, 2.5 parts by mass of each of acetylene black and graphite as positive electrode conductive additives. A positive electrode slurry in which 3 parts by mass of polyvinylidene fluoride as a positive electrode binder was dispersed in N-methyl-2-pyrrolidone using a planetary mixer was applied onto aluminum foil, dried, and rolled to prepare a positive electrode slurry (coating). Fabric weight: 9.5 mg/cm ² ). This positive electrode sheet was cut out to a size of 15 mmΦ.

The negative electrode sheet was made by dispersing 98 parts by mass of natural graphite as a negative electrode active material, 1 part by mass of carboxymethyl cellulose as a thickener, and 1 part by mass of styrene-butadiene copolymer as a negative electrode binder in water using a planetary mixer. The resulting negative electrode slurry was applied onto a copper foil, dried, and rolled to produce a negative electrode slurry (coating weight: 5.5 mg/cm ² ). This negative electrode sheet was cut into a size of 15 mmΦ.

In a glove box with an argon atmosphere, the separator is a polymer membrane or film, the electrolyte is 1M LiTFSI EC/DEC=1/1 (manufactured by Mitsui Chemicals), and an evaluation battery is constructed using an HS cell (manufactured by Hosensha). Created. The above evaluation battery was set in a charging/discharging device (manufactured by Hokuto Denko Co., Ltd.), and the charging conditions were constant current charging with a rate of 0.2C and a cutoff voltage of 4.1V, and the discharging conditions were a rate of 0.5C and a cutoff voltage of 2. Constant current discharge of 7V was performed 100 times.

<Calculation of discharge capacity maintenance rate>
Discharge capacity maintenance rate (%) = ((discharge capacity after 100 times)/(first discharge capacity)) x 100
The discharge capacity maintenance rate was calculated. Five of the above laminated batteries were produced, and the average value was taken as the discharge capacity retention rate.
○: Discharge capacity retention rate is 90% or more △: Discharge capacity retention rate is 80% or more and less than 90% ×: Discharge capacity retention rate is less than 80%

[2] Preparation of polymer membrane and film [Example 1]
2,2'-ditrifluoromethyl-4,4'-diaminobiphenyl was dissolved in dehydrated N-methyl-2-pyrrolidone. 2-fluoroterephthalic acid chloride corresponding to 98.5 mol % based on the total amount of diamine was added as an acid dichloride and stirred to polymerize an aromatic polyamide. The obtained polymerization solution was neutralized with 96.5 mol% lithium carbonate based on the total amount of acid dichloride, and further neutralized with 11 mol% diethanolamine, so that the aromatic polyamide concentration was 9.5% by mass and the viscosity was An aromatic polyamide solution having a pressure of 223 Pa·s was obtained. The aromatic polyamide resin had an intrinsic viscosity (η) of 4 dl/g.

The aromatic polyamide solution was cast onto a PET film as a support, and dried with hot air at a temperature of 130° C. until the polymer film had self-supporting properties. Next, it was introduced into a water bath and the support was peeled off under water. The time from the end of the drying process to the start of the wet process was 15 seconds. Subsequently, after wiping off the water on the surface of the obtained water-containing polymer film, heat treatment was performed for 1 minute in a hot air oven at a temperature of 280° C. to obtain a polymer film. Table 1 shows the evaluation results of the obtained polymer film.

[Example 2]
An aromatic polyamide resin was polymerized and neutralized in the same manner as in Example 1, and the resulting aromatic polyamide solution was diluted with N-methyl-2-pyrrolidone to give an aromatic polyamide concentration of 4% by mass and a viscosity of 4100 mPa·s. A coating material was obtained.

The coating solution was applied by dip coating to both sides of a polyethylene porous membrane substrate (thickness: 12 μm, air permeability: 164 seconds/100 mL). It was immersed in a water tank 11 seconds after coating, and after being taken out from the water tank, it was dried until the solvent contained therein volatilized, thereby forming a polymer film on the porous membrane base material to obtain a film. Table 1 shows the measurement results of the properties of the obtained film.

[Example 3]
An aromatic polyamide resin was polymerized and neutralized in the same manner as in Example 1, and the resulting aromatic polyamide solution was diluted with N-methyl-2-pyrrolidone to give an aromatic polyamide concentration of 8.5% by mass and a viscosity of 150 Pa.・A coating material of s was obtained.
Film formation was performed in the same manner as in Example 1 using the obtained coating material. Table 1 shows the evaluation results of the obtained polymer film.

[Example 4]
An aromatic polyamide resin was polymerized and neutralized in the same manner as in Example 1, and the resulting aromatic polyamide solution was diluted with N-methyl-2-pyrrolidone to give an aromatic polyamide concentration of 3.5% by mass and a viscosity of 2200 mPa.・A coating material of s was obtained. Using the obtained coating material, coating was performed on a porous membrane substrate in the same manner as in Example 2. Table 1 shows the evaluation results of the obtained film.

[Example 5]
An aromatic polyamide resin was polymerized and neutralized in the same manner as in Example 1, except that the amount of 2-fluoroterephthalic acid chloride added was 97.0 mol%. An aromatic polyamide solution (coating) having an aromatic polyamide concentration of 9.5% by mass and a viscosity of 150 Pa·s was obtained. The aromatic polyamide resin had an intrinsic viscosity (η) of 3.6 dl/g. Film formation was performed in the same manner as in Example 1 using the obtained coating material. Table 1 shows the evaluation results of the obtained polymer film.

[Example 6]
The aromatic polyamide resin was polymerized and neutralized in the same manner as in Example 5, and the resulting aromatic polyamide solution was diluted with N-methyl-2-pyrrolidone to give an aromatic polyamide concentration of 4% by mass and a viscosity of 2400 mPa·s. A coating material was obtained. Using the obtained coating material, coating was performed on a porous membrane substrate in the same manner as in Example 2. Table 1 shows the evaluation results of the obtained film.

[Example 7]
A polymer film was obtained in the same manner as in Example 1, except that during film formation, the time from completion of the drying process to transition to the wet process was 20 seconds. Table 1 shows the evaluation results of the obtained polymer film.

[Example 8]
A film was obtained in the same manner as in Example 2, except that the film was immersed in a water tank for 17 seconds after the coating was applied by dip coating. Table 1 shows the evaluation results of the obtained film.

[Example 9]
2,2'-ditrifluoromethyl-4,4'-diaminobiphenyl was dissolved in dehydrated N-methyl-2-pyrrolidone. 2-fluoroterephthalic acid chloride corresponding to 98.0 mol % based on the total amount of diamine was added thereto as acid dichloride and stirred to polymerize aromatic polyamide. The obtained polymerization solution was neutralized with 96.5 mol% lithium carbonate based on the total amount of acid dichloride, and further neutralized with 11 mol% diethanolamine, resulting in an aromatic polyamide concentration of 11.5% by mass and a viscosity. An aromatic polyamide solution (coating material) having a pressure of 450 Pa·s was obtained. The aromatic polyamide resin had an intrinsic viscosity (η) of 4 dl/g.
Film formation was performed in the same manner as in Example 1 using the obtained coating material. Table 1 shows the evaluation results of the obtained polymer film.

[Example 10]
An aromatic polyamide resin was polymerized and neutralized in the same manner as in Example 1, and the resulting aromatic polyamide solution was diluted with N-methyl-2-pyrrolidone to give an aromatic polyamide concentration of 5.5% by mass and a viscosity of 4700 mPa.・A coating material of s was obtained. Using the obtained coating material, coating was performed on a porous membrane substrate in the same manner as in Example 2. Table 1 shows the evaluation results of the obtained film.

[Example 11]
An aromatic polyamide resin was polymerized and neutralized in the same manner as in Example 1, except that the amount of 2-fluoroterephthalic acid chloride added was 99.5 mol%. An aromatic polyamide solution (coating) having an aromatic polyamide concentration of 9.5% by mass and a viscosity of 420 Pa·s was obtained. The aromatic polyamide resin had an intrinsic viscosity (η) of 4.7 dl/g. Film formation was performed in the same manner as in Example 1 using the obtained coating material. Table 1 shows the evaluation results of the obtained polymer film.

[Example 12]
The aromatic polyamide resin was polymerized and neutralized in the same manner as in Example 11, and the resulting aromatic polyamide solution was diluted with N-methyl-2-pyrrolidone to give an aromatic polyamide concentration of 4% by mass and a viscosity of 4800 mPa·s. A coating material was obtained. Using the obtained coating material, coating was performed on a porous membrane substrate in the same manner as in Example 2. Table 1 shows the evaluation results of the obtained film.

[Example 13]
An aromatic polyamide resin was polymerized and neutralized in the same manner as in Example 1, except that the amount of 2-fluoroterephthalic acid chloride added was 96.5 mol%. An aromatic polyamide solution (coating) having an aromatic polyamide concentration of 9.5% by mass and a viscosity of 85 Pa·s was obtained. The aromatic polyamide resin had an intrinsic viscosity (η) of 3.0 dl/g. Film formation was performed in the same manner as in Example 1 using the obtained coating material. Table 1 shows the evaluation results of the obtained polymer film.

[Example 14]
An aromatic polyamide resin was polymerized and neutralized in the same manner as in Example 13, and the resulting aromatic polyamide solution was diluted with N-methyl-2-pyrrolidone to give an aromatic polyamide concentration of 4% by mass and a viscosity of 2000 mPa·s. A coating material was obtained. Using the obtained coating material, coating was performed on a porous membrane substrate in the same manner as in Example 2. Table 1 shows the evaluation results of the obtained film.

[Example 15]
A polyvinylidene fluoride resin was dissolved and diluted with N-methyl-2-pyrrolidone to obtain a coating material having a polyvinylidene fluoride concentration of 15% by mass and a viscosity of 2000 mPa·s. The obtained coating material was cast onto a PET film as a support and dried with hot air at a temperature of 130° C. until the polymer film had self-supporting properties. Next, it was introduced into a water bath and the support was peeled off under water. The time from the end of the drying process to the start of the wet process was 15 seconds. Subsequently, after wiping off the water on the surface of the obtained water-containing polymer film, heat treatment was performed for 1 minute in a hot air oven at a temperature of 130° C. to obtain a polymer film. Table 1 shows the evaluation results of the obtained polymer film.

[Example 16]
Using the polyvinylidene fluoride coating used in Example 15, coating was performed on a porous membrane substrate in the same manner as in Example 2. Table 1 shows the evaluation results of the obtained film.

[Example 17]
An aromatic polyamide resin was polymerized and neutralized in the same manner as in Example 1, and the resulting aromatic polyamide solution was diluted with N-methyl-2-pyrrolidone to give an aromatic polyamide concentration of 4% by mass and a viscosity of 4100 mPa·s. A coating material was obtained.
The coating solution was applied by die coating to one side of a polyethylene porous membrane substrate (thickness: 12 μm, air permeability: 164 seconds/100 mL). It was immersed in a water tank 11 seconds after coating, and after being taken out from the water tank, it was dried until the solvent contained therein volatilized, thereby forming a polymer film on the porous membrane base material to obtain a film. Table 1 shows the measurement results of the properties of the obtained film.

[Comparative example 1]
An aromatic polyamide was polymerized in the same manner as in Example 1, except that the amount of polymerization solvent used was changed so that the polymer concentration in the resulting aromatic polyamide solution was 20% by mass. The obtained aromatic polyamide solution had a viscosity of 760 Pa·s and an intrinsic viscosity (η) of 8 dl/g, and was used as it was as a coating material.

Film formation was carried out in the same manner as in Example 1, except that the time from completion of the drying process to transition to the wet process was 9 seconds. Table 2 shows the evaluation results of the obtained polymer membrane.

[Comparative example 2]
An aromatic polyamide was polymerized and neutralized in the same manner as in Example 1, except that the amount of polymerization solvent used was changed so that the polymer concentration in the resulting aromatic polyamide solution was 3% by mass. The obtained aromatic polyamide solution had a viscosity of 1 Pa·s and an intrinsic viscosity (η) of 0.6 dl/g.
Film formation was performed in the same manner as in Example 1, except that the time from completion of the drying process to transition to the wet process was 25 seconds. Table 2 shows the evaluation results of the obtained polymer membrane.

[Comparative example 3]
2-chloro-1,4-phenylenediamine was dissolved in dehydrated N-methyl-2-pyrrolidone. 2-chloroterephthalic acid chloride corresponding to 98.5 mol % based on the total amount of diamine was added thereto as acid dichloride and stirred to polymerize aromatic polyamide. The obtained polymerization solution was neutralized with 96.5 mol% lithium carbonate based on the total amount of acid dichloride, and further neutralized with 11 mol% diethanolamine, so that the aromatic polyamide concentration was 9.5% by mass and the viscosity was An aromatic polyamide solution having a pressure of 260 Pa·s was obtained. The aromatic polyamide resin had an intrinsic viscosity (η) of 4 dl/g.
Film formation was performed in the same manner as in Example 1 using the obtained polymer solution. Table 2 shows the evaluation results of the obtained polymer membrane.

[Comparative example 4]
The coating material obtained in Comparative Example 1 was applied to both sides of a porous membrane substrate by dip coating. Coating was carried out in the same manner as in Example 2 except that the film was immersed in a water tank 9 seconds after coating to obtain a film. Table 2 shows the measurement results of the properties of the obtained film.

[Comparative example 5]
Using the coating material obtained in Comparative Example 2, it was coated on both sides of a porous membrane substrate by dip coating. Coating was carried out in the same manner as in Example 2 except that the film was immersed in a water tank 25 seconds after coating to obtain a film. Table 2 shows the measurement results of the properties of the obtained film.

[Comparative example 6]
The polymer solution obtained in Comparative Example 3 was diluted with N-methyl-2-pyrrolidone to obtain a coating material with an aromatic polyamide concentration of 4% by mass and a viscosity of 5 Pa·s. Coating was carried out in the same manner as in Example 2 using this coating agent. Table 2 shows the measurement results of the properties of the obtained film.

[Comparative Example 7]
The polyethylene porous membrane substrate used in Example 2 was used as a sample. The measurement results are shown in Table 2.

[Comparative example 8]
An aromatic polyamide resin was polymerized and neutralized in the same manner as in Example 1, except that the amount of 2-fluoroterephthalic acid chloride added was 96 mol%. An aromatic polyamide solution (coating) having an aromatic polyamide concentration of 9.5% by mass and a viscosity of 10 Pa·s was obtained. The aromatic polyamide resin had an intrinsic viscosity (η) of 2.0 dl/g. Film formation was performed in the same manner as in Example 1 using the obtained coating material. Table 2 shows the evaluation results of the obtained polymer membrane.

[Comparative Example 9]
An aromatic polyamide resin was polymerized and neutralized in the same manner as in Comparative Example 8, and the resulting aromatic polyamide solution was diluted with N-methyl-2-pyrrolidone to give an aromatic polyamide concentration of 6% by mass and a viscosity of 3000 mPa·s. A coating material was obtained. Using the obtained coating material, coating was performed on a porous membrane substrate in the same manner as in Example 2. Table 2 shows the evaluation results of the obtained film.

In Tables 1 and 2 below, when the thickness (μm) of the polymer membrane is “1+1”, it means that the porous membrane has a polymer membrane of 1 μm on both sides.

Claims (8)

A polymer membrane having a surface elastic modulus of 500 MPa or more, an ionic conductivity of 1.0×10 ⁻⁵ S/cm or more, and an air permeability of 5000 seconds/100 mL or more after being immersed in an electrolytic solution for 19 hours. The polymer membrane according to claim 1, wherein the change in thickness before and after the immersion in the electrolytic solution is greater than 100% and less than 450%. The polymer membrane according to claim 1, comprising aromatic polyamide, aromatic polyimide or aromatic polyamideimide. A film having the polymer membrane according to claim 1 on at least one side of a polyolefin porous membrane substrate. The film according to claim 4, which has a peel strength of 50 gf/25 mm or more. A separator for a secondary battery using the polymer film according to claim 1 or the film according to claim 4. A secondary battery using the secondary battery separator according to claim 6. A vehicle, an unmanned transport vehicle, an electronic device, or a stationary power supply comprising the secondary battery according to claim 7.