Battery

Abstract

To provide a battery that is excellent in capacity maintenance property and dendrite resistance, and that has a good heat resistance.SOLUTION: Provided is a battery that includes a positive electrode, a negative electrode, a non-aqueous electrolyte, and an ion conduction polymer film. The non-aqueous electrolyte contains a solvent with LUMO (Lowest Unoccupied Molecular Orbital) energy equal to or more than 1.9 eV. The air permeability of the ion conduction polymer film is equal to or more than 1,000 sec / 100 cc, and the ionic conductivity thereof is equal to or more than 1.0×10-5 S / cm.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This relates to a battery comprising a positive electrode, a negative electrode, a non-aqueous electrolyte, and an ion-conducting polymer membrane. [Background technology]

[0002] In recent years, research has been actively conducted on metal lithium anode batteries, batteries, and air batteries to reduce weight and increase energy output, and the design of positive electrodes, negative electrodes, separators, and electrolytes is progressing toward practical application. Among these, lithium metal is an ideal anode material because it has the highest theoretical capacity and the lowest potential among metals. However, lithium metal is highly reactive, which poses a challenge to the stable operation of the resulting batteries. Therefore, the use of ethers or high-salt concentration electrolytes as non-aqueous electrolytes has been investigated. (Patent Documents 1-2) [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2006-236809 [Patent Document 2] Special Publication No. 2018-505538 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, the batteries described in Patent Documents 1 and 2 are prone to short circuits due to the formation of needle-shaped crystals called dendrites during the charge and discharge process. Dendrites are particularly likely to form when operating at the high current densities required for electric vehicles and the like. Furthermore, it is known that when ether is included in the non-aqueous electrolyte, by-reaction products originating from the non-aqueous electrolyte that occur at the positive electrode degrade battery performance. [Means for solving the problem]

[0005] To solve the above problems, the present invention has the following features. [I] A battery comprising a positive electrode, a negative electrode, a non-aqueous electrolyte, and an ion-conducting polymer membrane, The negative electrode is metallic lithium. The above non-aqueous electrolyte contains a solvent with a Lowest Unoccupied Molecular Orbital (LUMO) energy of 1.9 eV or higher. The above solvents are 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, tetrahydrofuran (THF), alkyltetrahydrofuran, dialkylalkyltetrahydrofuran, alkoxytetrahydrofuran, dialkoxytetrahydrofuran, 1,3-dioxolane, alkyl-1,3-dioxolane, 1,4-dioxolane, 2-methyltetrahydrofuran, and derivatives or mixtures thereof. The above ion-conducting polymer film has an air permeability of 1000 seconds / 100cc or more and an ionic conductivity of 1.0 × 10⁻¹⁰ -5 S / cm or more the law of nature, The above ion-conducting polymer film has a film thickness change rate (T0 / T1) of 0.3 or more and less than 1.0, as measured under the following conditions. A battery. (Measurement conditions for film thickness change rate) The polymer film was immersed in a non-aqueous electrolyte (1M LiTFSI EC / DEC=1 / 1, manufactured by Mitsui Chemicals, Inc.) at 25°C for 24 hours. The polymer film thickness before and after immersion was measured using a high-precision digital measuring instrument (manufactured by Mitutoyo Corporation, model number: VL-50), and the values ​​were substituted into equation (1) for calculation. Film thickness change rate = (T0 / T1) (1) T0: Thickness of the polymer film before immersion in non-aqueous electrolyte (cm) T1: Thickness of the polymer film after immersion in a non-aqueous electrolyte (cm) [II] The battery according to [I], wherein the positive electrode comprises a lithium-containing olivine-type phosphate represented by the following chemical formula (1). LiM x Fe 1-x PO4(1) In the formula, M represents at least one of Mn, Cr, Co, Cu, Ni, V, Mo, Ti, Zn, Al, Ga, Mg, B, and Nb, and 0 ≤ x ≤ 1. [III] The battery according to [I] or [II], wherein the above non-aqueous electrolyte comprises an ether-based solvent. [IV] The battery according to [I] or [II], wherein the ion-conducting polymer film is a composite film having non-porous regions and microporous films. [V] The battery described in [IV], wherein the thickness of the non-porous region is 0.1 μm or more and 5 μm or less. [VI] The battery according to [I] or [II], wherein the ion-conducting polymer film has a 150°C thermal shrinkage rate of 10% or less. [VII] The battery according to [I] or [II], wherein the polymer constituting the ion-conducting polymer film is an aromatic polyamide. [VIII] At least one of the above positive electrode and the above negative electrode and an ion-conducting polymer membrane within 1 μm The battery according to [I] or [II] having the same.

Advantages of the Invention

[0006] According to the present invention, a battery excellent in capacity retention and dendrite resistance and having good heat resistance can be provided.

Embodiments for Carrying Out the Invention

[0007] The present invention will be described in detail below.

[0008] The battery of the present invention includes a positive electrode, a negative electrode, a non-aqueous electrolyte, and an ion-conducting polymer membrane, wherein the non-aqueous electrolyte contains a solvent having a LUMO energy of 1.9 eV or more, and the air permeability of the ion-conducting polymer membrane is 1000 seconds / 100 cc or more and the ion conductivity is 1.0×10 -5 S / cm or more. In order to realize the effects of the present invention, it is necessary to satisfy the above characteristics simultaneously.

[0009] The positive electrode used in the embodiment of the present invention includes a known positive electrode active material such as a lithium metal oxide containing at least one transition metal selected from manganese, cobalt, nickel, and titanium and lithium (such as lithium cobalt oxide and lithium manganese oxide) as the positive electrode active material. From the viewpoint of the capacity retention rate, it is preferable that the positive electrode is a lithium-containing olivine-type phosphate represented by the following chemical formula (1), and more preferably lithium iron phosphate. LiM x Fe 1-x PO4(1) In the formula, M represents at least one of Mn, Cr, Co, Cu, Ni, V, Mo, Ti, Zn, Al, Ga, Mg, B, and Nb, and 0≦x≦1.

[0010] The negative electrode of the present invention is not particularly limited as long as it is a material capable of intercalating 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 with titanium, magnesium, or aluminum, etc.), and carbon-based materials (carbon, hard carbon, soft carbon, and graphite, etc.) can be used as appropriate. Among these, the use of metallic lithium is preferable 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 for the entire negative electrode. A lithium equivalent concentration of 1.0 mol / l or more is preferable because it allows for higher capacity. There is no particular upper limit, but it is 100 mol / l or less.

[0011] The non-aqueous electrolyte of the present invention is a mixture of a non-aqueous solvent and an electrolyte. The solvent used in the non-aqueous electrolyte is not particularly limited, and for example, organic solvents used in conventional lithium-ion batteries can be used.

[0012] The non-aqueous electrolyte of the present invention contains a solvent with a LUMO energy of 1.9 eV or higher. LUMO energy represents the energy required for a material to accept one electron; the lower the LUMO energy, the more easily the material is reduced, and the higher the LUMO energy, the better its resistance to reduction. By containing a solvent with a LUMO energy of 1.9 eV or higher, side reactions on the negative electrode surface can be suppressed, thereby improving battery performance and lifespan. This effect is particularly pronounced when using a negative electrode with high reducing properties, such as metallic lithium. Therefore, it is more preferable to contain a solvent with a LUMO energy of 2.2 eV or higher, even more preferable to 2.5 eV or higher, and particularly preferable to 2.8 eV or higher. The LUMO energy of the solvent can be determined by quantum mechanical calculations. For solvents with a LUMO energy of 1.9 eV or higher, ether-based solvents and fluorine-based solvents are used. Specifically, organic solvents such as 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, tetrahydrofuran (THF), alkyltetrahydrofuran, dialkylalkyltetrahydrofuran, alkoxytetrahydrofuran, dialkoxytetrahydrofuran, 1,3-dioxolane, alkyl-1,3-dioxolane, 1,4-dioxolane, and 2-methyltetrahydrofuran, as well as their derivatives and mixtures, are preferably used. Furthermore, it is preferable that the HOMO energy of the solvent with a LUMO energy of 2 eV or higher is -11.5 eV or lower. HOMO energy represents the energy required for a material to release one electron; the higher the HOMO energy, the more easily the material is oxidized, and the lower the HOMO energy, the better the oxidation resistance. A HOMO energy of -11.5 eV or less suppresses side reactions on the positive electrode surface, thereby improving battery performance and lifespan.

[0013] The non-aqueous electrolyte of the present invention preferably contains 20 wt% to 99% of a solvent with a LUMO energy of 1.9 eV or higher, more preferably 40 wt% to 95%, and particularly preferably 45 wt% to 90 wt%. By setting the content of the solvent with a LUMO energy of 1.9 eV or higher within the above range, it is possible to suppress the decrease in battery performance and lifespan caused by side reactions on the negative electrode surface. Furthermore, it is preferable to suppress the decrease in the ionic conductivity and battery performance of the non-aqueous electrolyte due to insufficient dissolution of the electrolyte.

[0014] Preferred electrolytes for non-aqueous electrolytes include alkali metals, particularly lithium halides, perchlorates, thiocyanates, boron fluorides, phosphorus fluorides, arsenic fluorides, aluminum fluorides, and trifluoromethyl sulfates. For example, one or more salts of lithium salts (electrolytes) such as lithium perchlorate (LiClO4), lithium hexafluoride phosphate (LiPF6), lithium tetraborate (LiBF4), lithium arsenide hexafluoride (LiAsF6), lithium trifluoromethasulfonate (LiCF3SO3), lithium bistrifluoromethylsulfonylimide [LiN(CF3SO2)2], lithium bromide (LiBr), lithium bis(oxalate) borate, lithium difluoro(oxalate) borate, lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), and lithium bis(pentafluoroethanesulfonyl)imide can be used, but lithium hexafluoride phosphate and lithium bis(fluorosulfonyl)imide are preferred.

[0015] The dissolution amount of the electrolyte in the solvent is preferably 0.5 to 7.0 mol / l, more preferably 0.8 to 5.0 mol / l, and even more preferably 1.0 to 1.5 mol / l. Further, additives may be used in the non-aqueous electrolyte as needed. Examples of the additives include vinylene carbonate, fluoroethylene carbonate, ethylene sulfite, 1,4-butane sultone, propane sultone, 2,4-difluoroanisole, biphenyl, cyclohexylbenzene, etc., and one or more of these may be used.

[0016] The ion-conductive polymer membrane (hereinafter sometimes referred to as "polymer membrane") used in the embodiments of the present invention is a membrane made of a polymer that enables ion conduction between the positive electrode and the negative electrode when used as a battery. In the embodiments of the present invention, by including this ion-conductive polymer membrane, the elution of the decomposition eluate from the positive electrode side to the negative electrode side is suppressed, and the capacity retention of the battery is increased. Further, since it is possible to prevent cracking and chipping of each layer due to the impact during battery use, which is unique to the polymer membrane, it is possible to suppress short circuits and ignition due to dendrite generation. Moreover, since the interface between the electrode mixture layer and the electrolyte layer becomes smooth and the adhesion is improved, the interface resistance value becomes small, and the battery characteristics are also improved.

[0017] The air permeability of the ion-conductive polymer membrane according to the embodiments of the present invention needs to be 1000 seconds / 100 cc or more. Preferably it is 5000 seconds / 100 cc or more, and more preferably 10000 seconds / 100 cc or more. If the air permeability is less than 1000 seconds / 100 cc, it often has physical through-holes, and the effect of blocking the penetration of dendrites and the like cannot be obtained. In order to make the air permeability within such a range, it is preferable to form the polymer membrane by the manufacturing method described later.

[0018] The ionic conductivity of the ion-conductive polymer membrane of the present invention is -5 required to be 1.0×10 -5 S / cm or more. The ionic conductivity referred to here means the value measured by the measurement method described later in an environment of 25°C. It is preferably 5.0×10 -4It is more preferable that the ratio is S / cm or higher, 5.0 × 10 -4 It is even more preferable that the ionic conductivity is 1.0 × 10⁻⁶ or higher. By keeping the ionic conductivity within the above range, high ion permeability within the battery is achieved, resulting in excellent output characteristics and cycle characteristics. -5 If the ionic conductivity is less than S / cm, the ion permeability is low, leading to a decrease in output characteristics and significant capacity degradation with repeated use. To achieve an ionic conductivity within this range, it is preferable to form a polymer film using the polymer described later.

[0019] The ion-conducting polymer film of the present invention preferably has a non-porous region thickness of less than 20 μm. A non-porous region is defined as a region obtained by FE-SEM of a cross-sectional image of the polymer film, where a straight line perpendicular to the interface is drawn from one interface to the other interface, and the number of voids of 50 nm or more intersecting the line is determined. If there are 10 or fewer voids, it is considered a non-porous region. When the ion-conducting polymer film is a composite film consisting of a non-porous region and a microporous film, the point where the distribution and size of voids in the thickness direction begin to change is considered the interface. If the thickness of the non-porous region is 20 μm or more, the resistance of the polymer film becomes too large in terms of battery characteristics, and the weight becomes heavy when used as a battery for aerial vehicles where weight reduction is required. The thickness of the non-porous region is preferably 15 μm or less, more preferably 10 μm or less, and most preferably 5 μm or less. Furthermore, if the thickness of the non-porous region is too small, the battery cycle life decreases, so it is preferably 0.1 μm or more, more preferably 0.25 μm or more, and most preferably 0.4 μm or more.

[0020] The polymers that can be used in embodiments of the ion-conducting polymer film of the present invention are not particularly limited, but examples include polymers having aromatic rings on the main chain and fluorine-containing polymers such as polyvinylidene fluoride. Polymers having aromatic rings on the main chain are particularly suitable, and examples include aromatic polyamides (aramids), aromatic polyimides, aromatic polyamide-imides, aromatic polyether ketones, aromatic polyether ether ketones, aromatic polyarylates, aromatic polysulfones, aromatic polyethersulfones, aromatic polyetherimides, and aromatic polycarbonates. Blends of multiple polymers are also acceptable. Among these, aromatic polyamides (including aromatic polyamic acids, which are precursors of aromatic polyimides), aromatic polyimides, or aromatic polyamide-imides are more preferred, and aromatic polyamides are particularly preferred, because they tend to maintain high strength when formed into thin films.

[0021] Examples of aromatic polyamides that can be suitably used in the present invention include those having repeating units represented by the following chemical formulas (1) and / or (2).

[0022] [ka]

[0023] [ka] Ar1 and Ar2 in chemical formula (1), and Ar3 in chemical formula (2) are aromatic groups, and each may be a single group or a multi-component copolymer of multiple groups. Furthermore, the bonds constituting the main chain on the aromatic ring may be meta-oriented or para-oriented. In addition, some of the hydrogen atoms on the aromatic ring may be substituted with any group. In aromatic polyamides, it is preferable that at least a portion of the aromatic groups of chemical formula (1) Ar1 and Ar2, or chemical formula (2) Ar3, are substituted with electron-withdrawing groups. Preferably, 30 to 100 mol% of the total aromatic groups are substituted with electron-withdrawing groups, and more preferably 50 to 100 mol%. Having 30 mol% or more ensures good solubility in organic solvents. Here, an electron-withdrawing group in this invention refers to a group with an electronegativity of 2.5 or higher. Examples of electron-withdrawing groups include halogen groups such as fluoro groups, chloro groups, and bromo groups, halogenated alkyl groups such as trifluoromethyl groups, nitro groups, cyano groups, cyanate groups, and phenyl groups.

[0024] Specific examples of aromatic diamines that constitute aromatic polyamides include, but are not limited to, 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, and 4,4'-diaminodiphenylsulfone.

[0025] Specific examples of aromatic dicarboxylic acid halides include, but are not limited to, terephthalic acid chloride, 2-chloroterephthalic acid chloride, 2-fluoroterephthalic acid chloride, isophthalic acid chloride, 2-chloroisophthalic acid chloride, 2-fluoroisophthalic acid chloride, 2,3,5,6-tetrachloroisophthalic acid chloride, 2,3,5,6-tetrafluoroisophthalic acid chloride, 2,6'-naphthalenedicarboxylic acid chloride, trimesinate chloride, etc.

[0026] The confirmation of each component and its content in the ion-conducting polymer film according to the embodiment of the present invention is not limited to a specific method, but proton nuclear magnetic resonance spectroscopy ( 1 ¹H-NMR and Fourier transform infrared spectroscopy (FT-IR) can be used. Furthermore, multiple methods can be combined for verification as needed.

[0027] The electrodes in the battery according to the embodiment of the present invention may contain the same polymer as the ion-conducting polymer film. By containing the same ion-conducting polymer in the electrodes, the interlayer interfacial resistance can be reduced, and the ion conductivity and cycle characteristics can be dramatically improved, thereby enhancing the battery's performance.

[0028] The ion-conducting polymer film of the present invention may contain other components that act as ion conduction aids, as long as they do not hinder the effects of the present invention. Examples include inorganic solid electrolytes, ionic liquids, and lithium salts. In particular, the addition of lithium salts is a preferred method from the viewpoint of ionic conductivity, ion migration rate at the interfaces of each layer, thermal and electrochemical stability, discharge capacity, and cycle characteristics. There are no specific restrictions on lithium salts, but LiPF6, LiAsF6, LiClO4, LiBF4, LiBr, lithium bis(oxalate) borate, lithium difluoro(oxalate) borate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, and lithium bis(pentafluoroethanesulfonyl)imide are preferred. These lithium salts may be used alone or in combination of two or more. There are no specific restrictions on the content of lithium salts and other components, but it is preferable that it be 50% by mass or less of the total ion-conducting polymer film.

[0029] The ion-conducting polymer film of the present invention preferably has a film thickness change rate (T0 / T1) of 0.3 or more and less than 1.0, as measured under the conditions described later. (Measurement conditions for film thickness change rate) The polymer film was immersed in a non-aqueous electrolyte (1M LiTFSI EC / DEC=1 / 1, manufactured by Mitsui Chemicals, Inc.) at 25°C for 24 hours. The thickness of the polymer film before and after immersion was measured using a high-precision digital measuring instrument (manufactured by Mitutoyo Corporation, model number: VL-50), and the values ​​were substituted into equation (1) for calculation. Film thickness change rate = (T0 / T1) (1) T0: Thickness of the polymer film before immersion in non-aqueous electrolyte (cm) T1: Thickness of the polymer film after immersion in a non-aqueous electrolyte (cm).

[0030] When the film thickness change rate is 0.3 or higher, the decrease in the strength of the polymer film inside the battery can be suppressed, resulting in excellent dendrite resistance. Furthermore, when it is less than 1.0, the ion conductivity of the polymer film inside the battery is excellent. More preferably, it is between 0.3 and 0.9. To achieve this range for the film thickness change rate, the polymers described later can be used as the polymers constituting the ion-conducting polymer film.

[0031] The ion-conducting polymer film of the present invention preferably has non-porous regions and porous regions, and is particularly preferably a composite film having non-porous regions and a microporous film. The method for forming the composite film is not particularly limited, but one example is a method of coating at least one side of a microporous film with an ion-conducting polymer using the method described later. Furthermore, examples of microporous membranes include porous membranes having voids inside, nonwoven fabrics, or porous membrane sheets made of fibrous materials. The material constituting the microporous membrane is preferably made of a resin that is electrically insulating, electrically stable, and stable in non-aqueous electrolytes. In addition, from the viewpoint of providing a shutdown function, the resin used is preferably a thermoplastic resin with a melting point of 200°C or lower. The shutdown function here refers to the function that, when a lithium-ion battery overheats abnormally, melts with heat to close the porous structure, stops ion movement, and stops power generation.

[0032] Examples of thermoplastic resins include polyolefin resins, and the microporous membrane is preferably a polyolefin microporous membrane, and more preferably has a melting point of 200°C or lower. Specific examples of polyolefin resins used for the microporous membrane include polyethylene, polypropylene, copolymers thereof, and mixtures combining these. Examples include a single-layer microporous membrane containing 90% by mass or more of polyethylene, and a multilayer microporous membrane made of polyethylene and polypropylene.

[0033] The ion-conducting polymer film of the present invention preferably has a 150°C heat shrinkage rate of 10% or less, determined by the method described later. Furthermore, it is preferable that both the longitudinal direction (MD) and the width direction (TD) of the polymer film have a heat shrinkage rate of 10% or less, more preferably 8% or less, and most preferably 5% or less. The lower limit is not particularly limited, but it is -1% or more. By having the heat shrinkage rate of either MD or TD within the above range, it is possible to suppress short circuits at the battery ends due to dimensional changes in the polymer film when the battery generates heat, resulting in a battery with excellent heat resistance. In order to achieve the heat shrinkage rate within the above range, it is preferable to use a polymer having the molecular structure described above and to set the manufacturing conditions of the polymer film within the range described later.

[0034] It is preferable that at least one of the positive electrode and the negative electrode of the present invention is located in close proximity to the ion-conducting polymer film. The ion-conducting polymer of the present invention is a polymer that enables ion conduction between the positive electrode and the negative electrode. By having the polymer layer in close proximity to at least one of the positive electrode and the negative electrode, the ion conductivity between each layer is improved, and by being located in close proximity to at least one of the electrodes, short circuits and ignition due to dendrite formation during battery use can be suppressed. Here, "located in close proximity" means being within 1 μm, and they may be in direct contact or connected via other layers.

[0035] Next, a method for manufacturing a battery according to an embodiment of the present invention will be described below. One embodiment of the battery according to the present invention is one in which a current collector layer on the positive electrode side, an electrode mixture layer containing a positive electrode active material (sometimes referred to as the positive electrode layer), an electrolyte layer, an electrode mixture layer containing a negative electrode active material (sometimes referred to as the negative electrode layer), and a current collector layer on the negative electrode side are stacked in this order or the reverse order. Furthermore, the battery can be assembled using known battery components.

[0036] The ion-conducting polymer of the present invention may be used not only as a polymer film and as an electrolyte layer in the battery described above, but may also be included in either the positive electrode layer or the negative electrode electrode mixture layer, or in both layers. Furthermore, the ion-conducting polymer may be applied to the surface of the positive electrode layer or the negative electrode layer to serve as both a protective film for the electrode surface and an electrolyte layer.

[0037] The material used as the current collector layer in the battery according to the embodiment of the present invention is not particularly limited, but for example, metal foil made of gold, silver, aluminum, copper, stainless steel, nickel, titanium, alloys thereof, carbon-based materials, etc. can be used.

[0038] The electrode mixture layer of the positive electrode according to the embodiment of the present invention may be a single element or may contain other components. As other components, known positive electrode active materials such as lithium metal oxides (such as lithium cobaltate or lithium manganate) containing at least one transition metal selected from manganese, cobalt, nickel, and titanium, and lithium, can be used as appropriate. Furthermore, the active material of the negative electrode electrode mixture layer is not particularly limited, but any material that can intercept and release metal ions, etc., is acceptable. For example, known negative electrode active materials such as Li, Sn, Si, In, lithium alloy particles (lithium alloy particles of lithium with titanium, magnesium, or aluminum, etc.), and carbon-based materials (carbon, hard carbon, soft carbon, and graphite, etc.) can be used as appropriate.

[0039] A method for obtaining a polymer that can be used as an ion-conducting polymer according to an embodiment of the present invention will be described using aromatic polyamides, aromatic polyimides, or their precursors such as polyamic acid as examples, but the polymers that can be used and the polymerization methods thereof are not limited thereto.

[0040] Various methods are available for obtaining aromatic polyamides. For example, when using a low-temperature solution polymerization method with acid dichloride and diamine as raw materials, the synthesis is carried out in aprotic organic polar solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, dimethylformamide, and dimethyl sulfoxide. In solution polymerization, in order to obtain polymers with high molecular weight, it is preferable to keep the water content of the solvent used for polymerization at 500 ppm or less (by mass, the same applies hereinafter), and more preferably at 200 ppm or less. Furthermore, a metal salt may be added to promote the dissolution of the polymer. As this metal salt, alkali metal or alkaline earth metal halides that dissolve in aprotic organic polar solvents are preferred, such as lithium chloride, lithium bromide, sodium chloride, sodium bromide, potassium chloride, and potassium bromide. Since using equal amounts of both the acid dichloride and diamine may result in the formation of ultra-high molecular weight polymers, it is preferable to adjust the molar ratio so that one is 95.0 to 99.95 mol% of the other. Furthermore, although the polymerization reaction of aromatic polyamides is exothermic, if the temperature of the polymerization system rises, side reactions may occur and the degree of polymerization may not reach a sufficient level. Therefore, it is preferable to cool the temperature of the solution during polymerization to 40°C or below. In addition, when using acid dichloride and diamine as raw materials, hydrogen chloride is produced as a by-product during the polymerization reaction. To neutralize this, it is preferable to use inorganic neutralizing agents such as lithium carbonate, calcium carbonate, or calcium hydroxide, or organic neutralizing agents such as ethylene oxide, propylene oxide, ammonia, triethylamine, triethanolamine, or diethanolamine.

[0041] On the other hand, when polymerizing the aromatic polyimide or its precursor, polyamic acid, that can be used in the present invention, for example, using tetracarboxylic anhydride and aromatic diamine as raw materials, a method such as solution polymerization in an aprotic organic polar solvent such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, dimethylformamide, or dimethyl sulfoxide can be employed. Since using equal amounts of both the tetracarboxylic anhydride and aromatic diamine as raw materials may result in the formation of a supermolecular-weight polymer, it is preferable to adjust the molar ratio so that one is 90.0 to 99.5 mol% of the other. Furthermore, although the polymerization reaction is exothermic, precipitation may occur due to the imidation reaction if the temperature of the polymerization system rises, so it is preferable to keep the temperature of the solution during polymerization below 70°C. Methods for obtaining aromatic polyimide by imidizing the aromatic polyamic acid synthesized in this way include heat treatment, chemical treatment, or a combination thereof. The heat treatment method generally involves imidizing the polyamic acid by heating it to about 100 to 500°C. On the other hand, chemical treatments include methods using tertiary amines such as triethylamine as catalysts and dehydrating agents such as aliphatic acid anhydrides and aromatic acid anhydrides, as well as methods using imidizing agents such as pyridine.

[0042] The viscosity ηinh of aromatic polyamides and aromatic polyimides, or their precursor polyamic acids, is preferably 0.5 to 7.0 dl / g. By setting the viscosity within this range, polymers with excellent toughness, strength, and good ionic conductivity can be obtained. The viscosity η can be measured, for example, by the method described later.

[0043] Next, the film-forming stock solution (hereinafter referred to as the film-forming stock solution) used in manufacturing the electrode mixture layer and electrolyte layer according to the embodiment of the present invention will be described.

[0044] The polymer solution after polymerization may be used as the film-forming stock solution. However, if the solution contains a large amount of unwanted substances such as neutralization salts, it is preferable to isolate the polymer first and then redissolve it in the aforementioned aprotic organic polar solvent or an organic solvent such as sulfuric acid before use. The method for isolating the polymer is not particularly limited, but one method is to immerse the polymer solution after polymerization in a large amount of water to extract the solvent and neutralization salts into the water, separate only the precipitated polymer, and then dry it.

[0045] In the manufacturing process of the electrode mixture layer and 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 ion-conducting polymer. There are no limitations on the timing of adding these materials; they may be added in the polymer polymerization step, the film-forming stock solution preparation step, or the film-forming step. However, it is preferable to add them in the film-forming stock solution preparation step because they can be uniformly dispersed with the polymer. Furthermore, they can be added in multiple steps, or added in multiple stages within the same step.

[0046] The concentration of the ion-conducting polymer in the film-forming stock solution is preferably 3 to 30% by mass, and more preferably 4 to 20% by mass. Inorganic or organic particles may be added to the film-forming stock solution to improve the strength, heat resistance, ion permeability, and static friction coefficient of the resulting polymer film, as long as they do not hinder the effects of the present invention. 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 (lead white), 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 compounds, crosslinked particles of polystyrene compounds, crosslinked particles of acrylic compounds, crosslinked particles of polyurethane compounds, crosslinked particles of polyester compounds, crosslinked particles of fluorine compounds, or mixtures thereof.

[0047] Next, a method for forming the ion-conducting polymer film of the present invention will be described. The film-forming stock solution prepared as described above can be used to form a film using a so-called solution film-forming method. Solution film-forming methods include the dry-wet method, the dry method, and the wet method, and any of these methods can be used to form the film, but here we will explain using the dry-wet method as an example.

[0048] In the wet-dry method for film formation, the film-forming solution is extruded from a die onto a support such as a drum, endless belt, or film to form a film, which is then dried until it becomes self-retaining. The drying conditions can be, for example, 60 to 220°C for 60 minutes or less. However, if a polyamic acid polymer is used and a film made of polyamic acid is to be obtained without imidization, the drying temperature is preferably 60 to 150°C. More preferably, it is 60 to 130°C. After the dry process, the film is peeled from the support and introduced into the wet process, where desalting, desolvation, etc., are performed, and stretching, drying, and heat treatment are carried out as needed.

[0049] When stretching, the stretching ratio is preferably in the range of 0.8 to 8.0 times in terms of surface magnification (surface magnification is defined as the value obtained by dividing the area of ​​the stretched film by the area of ​​the film before stretching; a value of 1 or less means relaxed), and more preferably in the range of 1.0 to 5.0 times. When heat treatment is performed, 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 ion-conducting polymer film of the present invention obtained by the above manufacturing method can be used as an electrolyte film by inserting it directly between the positive and negative electrodes.

[0050] When the ion-conducting polymer film of the present invention is a composite film having non-porous regions and microporous films, the polymer film and microporous film obtained by the above-described film-forming method may be used in layers or bonded together. Alternatively, a method of applying the polymerized film-forming solution described above onto the microporous film and laminating it is also preferred, and any coating method such as a roll coater, slit coater, or dip coater can be used to apply the solution onto the microporous film.

[0051] The thickness of the ion-conducting 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, and even more preferably 0.20 to 15 μm. Furthermore, when the ion-conducting polymer film of the present invention is a composite film, the thickness ratio of the polymer film to the microporous film is preferably 0.001 to 5, and more preferably 0.01 to 1. By keeping the thickness within the above range, the strength of the polymer film is sufficient, there is no increase in resistance due to the film thickness, and it can be used suitably. The thickness of the ion-conducting polymer film can be controlled by various conditions such as the concentration of the film-forming solution, the viscosity of the film-forming solution, the type and concentration of additives in the film-forming solution, the casting thickness of the polymer film, the heat treatment temperature, and the stretching conditions.

[0052] The battery of the present invention is formed by placing an ion-conducting polymer film obtained by the above-described film-forming method between the positive electrode and the negative electrode. Furthermore, any method can be used to manufacture the battery.

[0053] The battery according to the embodiment of the present invention can be suitably used as a power source for small electronic devices, transportation vehicles such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), and large industrial equipment such as industrial cranes. It can also be suitably used as an energy storage device for power leveling in solar cells and wind power generation equipment, and for smart grids. Furthermore, it can be suitably used as a battery for use in special environments such as space. [Examples]

[0054] The present invention will be described in more detail below with reference to the following examples. The physical properties of the examples were measured by the following method.

[0055] (1) Logarithmic viscosity ηinh The polymer is dissolved at a concentration of 0.5 g / dl in N-methylpyrrolidone (NMP) with 2.5 mass% lithium bromide (LiBr) added, and the flow time is measured at 30°C using an Ubbelohde viscometer. The flow time of a blank LiBr 2.5 mass% / NMP without dissolving the polymer is measured in the same way, and the logarithmic viscosity ηinh (dl / g) can be calculated using the following formula.

[0056] Logarithmic viscosity ηinh(dl / g)=[ln(t / t0)] / 0.5 t0: Blank flow time (seconds) t: Sample flow time (seconds).

[0057] (2) Air permeability Measurements were performed using an Ogane-type air permeability meter (EGO-1T, manufactured by Asahi Seiko Co., Ltd.) with an air flow rate set to 100cc. The upper limit of the device's measurement capacity is 10,000 seconds / 100cc. The polymer film was fixed in place to prevent wrinkles, and measurements were taken according to JIS P8117. Three measurement points were set at equal intervals from TD, and the average value was used as the air permeability (seconds / 100cc).

[0058] (3) Cross-sectional structure (thickness of polymer film, thickness of non-porous region) The polymer films obtained in the examples were cross-sectioned using a cross-section polisher (JEOL SM-9010), and the cross-sections in the thickness direction in the width direction were coated with platinum to prepare observation samples. Next, the cross-sections of the samples were photographed at arbitrary magnifications using a field emission scanning electron microscope (JEOL JSM-6701F) to determine the thickness of the polymer films. The acceleration voltage during observation was 2.0 kV. If 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 layer was determined. Next, the thickness of the non-porous region was determined from images taken at 10,000x magnification using the following method: A straight line perpendicular to the interface was drawn from one interface of the polymer film to the other interface, and the number of voids of 50 nm or more intersecting the line was determined. If there were 10 or fewer voids, it was determined to be a non-porous region, and its thickness was calculated. In the case of a composite film consisting of a non-porous region and a microporous film, the point where the distribution and size of voids in the thickness direction began to change was considered the interface.

[0059] (4) Film thickness change rate (T0 / T1) The polymer film was immersed in a non-aqueous electrolyte (1M LiTFSI EC / DEC=1 / 1, manufactured by Mitsui Chemicals, Inc.) at 25°C for 24 hours. The polymer film thickness before and after immersion was measured using a high-precision digital measuring instrument (manufactured by Mitutoyo Corporation, model number: VL-50), and the values ​​were substituted into equation (1) for calculation. Film thickness change rate = (T0 / T1) (1) T0: Thickness of the polymer film before immersion in non-aqueous electrolyte (cm) T1: Thickness of the polymer film after immersion in a non-aqueous electrolyte (cm).

[0060] When removing the polymer film from inside the battery, if it was already immersed in a non-aqueous electrolyte, that state was defined as T1. Subsequently, the polymer film was washed with dimethyl carbonate and dried at 60°C for 24 hours, and the state after that was defined as T0.

[0061] (5) Ionic conductivity After immersing the polymer film in a non-aqueous electrolyte (1M LiTFSI ethylene carbonate (EC) / diethyl carbonate (DEC) = 1 / 1) for 24 hours, it was placed on a SUS304 electrode so as to cover the electrode portion, and after dropping the non-aqueous electrolyte, it was sandwiched between another SUS electrode to create a laminate of electrode / polymer film / electrode. The laminate was then fixed with a silicon plate to prevent shifting and an evaluation cell was created.

[0062] For the fabricated cells, the AC impedance was measured at 25°C using an electrochemical test apparatus (Biologic, model number: SP-150) under the conditions of an amplitude of 10mV and a frequency of 1MHz-10mHz. The resistance value was read from the graph plotted on the complex plane and substituted into equation (2) to calculate the ionic conductivity. Five measurements were taken, and the average value was used as the ionic conductivity. σ = T0 / AR (2) σ: Ionic conductivity (S / cm) T0: Thickness of the polymer film (cm) A: Electrode area (cm²) 2 ) R: Resistance value (Ω).

[0063] (6) Heat shrinkage rate at 150°C (heat resistance) The polymer film was cut into pieces measuring 50 mm in the longitudinal direction (MD) and 50 mm in the width direction (TD), with the longitudinal length denoted as LMD1 (50 mm) and the width direction as LTD1 (50 mm). Next, the samples were heat-treated by standing them in a 150°C hot air oven for 30 minutes, and then removed from the oven and allowed to cool. The dimensions of the shortest points in both the longitudinal and width directions of the samples removed from the oven were measured, with the longitudinal length denoted as LMD2 (mm) and the width direction as LTD2 (mm). The thermal shrinkage rate in each direction was calculated based on equations (3) and (4), and the value in the direction with the larger shrinkage rate in either MD or TD was used as the thermal shrinkage rate value. Measurements were performed five times for each sample and the average was calculated.

[0064] MD thermal shrinkage rate (%) = [(LMD1 - LMD2) / LMD1] × 100 (3) TD thermal shrinkage rate (%) = [(LTD1 - LTD2) / LTD1] × 100 (4) In the above evaluation, if the MD and TD directions were unknown, the thermal shrinkage rate at 150°C was measured for all directions, and the value of the direction with the largest thermal shrinkage rate was taken as the 150°C thermal shrinkage rate.

[0065] (7) Battery characteristics The fabricated batteries were placed in a charge / discharge device (manufactured by Hokuto Denko Co., Ltd.). When the positive electrode was NCM, the charging conditions were constant current charging at a rate of 0.1C and a cutoff voltage of 4.1V, and the discharging conditions were constant current discharging at a rate of 0.3C and a cutoff voltage of 2.7V, and these cycles were performed 50 times. When the positive electrode was LFP, the charging conditions were constant current charging at a rate of 0.1C and a cutoff voltage of 3.8V, and the discharging conditions were constant current discharging at a rate of 0.3C and a cutoff voltage of 2.7V, and these cycles were performed 50 times. The discharge capacity at the end of the first cycle was taken as E1 (mAh), and the discharge capacity at the end of the 50th cycle was taken as E50 (mAh). The discharge capacity retention rate was calculated based on equation (5). The calculated values ​​were judged according to the following criteria.

[0066] Discharge capacity maintenance rate (%)=[E50(mAh) / E1(mAh)]×100 (5) Discharge capacity maintenance rate 80% or more:◎ Discharge capacity maintenance rate 50% or more but less than 80%: ○ Discharge capacity maintenance rate 40% or more but less than 50%: △ Discharge capacity retention rate less than 40%: ×.

[0067] (8) LUMO energy, HOMO energy The LUMO and HOMO energies of organic solvents contained in non-aqueous electrolytes were calculated using the quantum chemistry calculation program Gaussian16 (Gaussian, Inc.) with the semi-empirical molecular orbital method PM3 and the basis set STO-3G.

[0068] (Reference Example 1) Ion-conducting polymer film F1 2,2'-ditrifluoromethyl-4,4'-diaminobiphenyl was dissolved in dehydrated N-methyl-2-pyrrolidone. 2-fluoroterephthalic acid chloride, equivalent to 98.5 mol% of the total diamine, was added as an acid dichloride, and the mixture was stirred to polymerize the aromatic polyamide. The resulting polymerization solution was neutralized with 96.5 mol% lithium carbonate relative to the total acid dichloride, and then further neutralized with 11 mol% diethanolamine to obtain an aromatic polyamide solution with an aromatic polyamide concentration of 9.5% by mass. The intrinsic viscosity (η) of the aromatic polyamide resin was 4 dl / g. The obtained aromatic polyamide solution was diluted with N-methyl-2-pyrrolidone to obtain a solution with an aromatic polyamide concentration of 6% by mass.

[0069] A 6% by mass aromatic polyamide solution was cast onto a PET film support and dried at a hot air temperature of 130°C until the polymer film became self-supporting. Next, the support was immersed in a 25°C water bath for 10 minutes and peeled off in water. Subsequently, the water on the surface of the resulting hydrated polymer film was wiped off, and then the film was heat-treated in a hot air oven at 280°C for 1 minute to obtain the polymer film.

[0070] (Reference Example 2) Ion-conducting polymer film F2 Similar to Reference Example 1, an aromatic polyamide resin was polymerized, and the resulting aromatic polyamide solution was diluted with N-methyl-2-pyrrolidone to obtain a coating agent with an aromatic polyamide concentration of 4% by mass.

[0071] A polymer film was formed on a porous polyethylene membrane substrate (thickness 12 μm, air permeability 160 seconds / 100 cc) by gravure coating, thereby obtaining a film. The coating conditions are shown in Table 2.

[0072] (Reference Example 3) Ion-conducting polymer film F3 Similar to Reference Example 1, an aromatic polyamide resin was polymerized, and the resulting aromatic polyamide solution was diluted with N-methyl-2-pyrrolidone to obtain a coating agent with an aromatic polyamide concentration of 3% by mass.

[0073] A polymer film was formed on a porous polyethylene membrane substrate (thickness 12 μm, air permeability 160 seconds / 100 cc) by gravure coating, thereby obtaining a film. The coating conditions are shown in Table 2.

[0074] (Example 1) A battery was fabricated using an HS cell (manufactured by Hosen Co., Ltd.) by placing the following components into the cell in the following order: 15mmΦ metallic lithium (manufactured by Honjo Metal Co., Ltd., thickness: 0.2mm), 200μL of 1M LiFSI DME (manufactured by Mitsui Chemicals, Inc.), the ion-conducting polymer film F1 obtained in Reference Example 1, 200μL of 1M LiFSI DME (manufactured by Mitsui Chemicals, Inc.), and a 15mmΦ cut LFP cathode sheet (Hosen Co., Ltd. HS-LIB-P-LFP-001, cathode active material: LiFePO4). The battery was fabricated in a glove box under an argon atmosphere.

[0075] (Example 2) A battery was fabricated in the same manner as in Example 1, except that an ion-conducting polymer film F2 was used as the ion-conducting polymer film.

[0076] (Example 3) As the positive electrode, an NCM positive electrode sheet (manufactured by Hachiyama Co., Ltd., positive electrode active material: Li(Ni) 5 / 10 Mn 2 / 10 Co 3 / 10 ) O2, application amount: 9.5 mg / cm² 2 Except for using ), the battery was prepared in the same manner as in Example 1.

[0077] (Comparative Example 1) A battery was fabricated in the same manner as in Example 1, except that a polyethylene porous membrane substrate (thickness 12 μm, air permeability 160 seconds / 100 cc) was used as the ion-conducting polymer membrane.

[0078] (Comparative Example 2) A battery was fabricated in the same manner as in Example 2, except that ion-conducting polymer film F3 was used as the ion-conducting polymer film.

[0079] Examples 1-3, which had an air permeability of 1000 seconds / 100cc or higher, showed better discharge capacity retention rates than Comparative Examples 1 and 2. This is thought to be because Examples 1-3, having a non-porous structure, suppressed short circuits caused by dendrites. Furthermore, Examples 2 and 3, which had a smaller thickness of the non-porous region, showed higher discharge capacity retention rates than Example 1. This suggests that a smaller thickness of the non-porous region allows for good battery characteristics while maintaining dendrite resistance. In particular, Example 2, which used LFP in the positive electrode, showed the highest discharge capacity retention rate.

[0080] [Table 1]

[0081] [Table 2]

Claims

1. A battery comprising a positive electrode, a negative electrode, a non-aqueous electrolyte, and an ion-conducting polymer membrane, The negative electrode is metallic lithium. The above non-aqueous electrolyte contains a solvent with a Lowest Unoccupied Molecular Orbital (LUMO) energy of 1.9 eV or higher. The above solvent is 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, tetrahydrofuran (THF), alkyltetrahydrofuran, dialkylalkyltetrahydrofuran, alkoxytetrahydrofuran, dialkoxytetrahydrofuran, 1,3-dioxolane, alkyl-1,3-dioxolane, 1,4-dioxolane, 2-methyltetrahydrofuran, and derivatives or mixtures thereof. The above ion-conducting polymer film has an air permeability of 1000 seconds / 100cc or more and an ionic conductivity of 1.0 × 10⁻¹⁰ －５ It is S / cm or higher, A battery in which the above-mentioned ion-conducting polymer film has a film thickness change rate (T0 / T1) of 0.3 or more and less than 1.0, as measured under the following conditions. (Measurement conditions for film thickness change rate) The polymer film was immersed in a non-aqueous electrolyte (1M LiTFSI EC / DEC = 1 / 1, manufactured by Mitsui Chemicals, Inc.) at 25°C for 24 hours. The polymer film thickness before and after immersion was measured using a high-precision digital measuring instrument (manufactured by Mitutoyo Corporation, model number: VL-50), and the values ​​were substituted into equation (1) for calculation. Film thickness change rate = (T0 / T1) (1) T0: Thickness of the polymer film before immersion in non-aqueous electrolyte (cm) T1: Thickness of the polymer film after immersion in a non-aqueous electrolyte (cm)

2. The battery according to claim 1, wherein the positive electrode comprises a lithium-containing olivine-type phosphate represented by the following chemical formula (1). LiM ｘ Fe １－ｘ PO ４ (1) In the formula, M represents at least one of Mn, Cr, Co, Cu, Ni, V, Mo, Ti, Zn, Al, Ga, Mg, B, and Nb, and 0 ≤ x ≤ 1.

3. The battery according to claim 1 or 2, wherein the non-aqueous electrolyte contains an ether-based solvent.

4. The battery according to claim 1 or 2, wherein the ion-conducting polymer film is a composite film having a non-porous region and a microporous film.

5. The battery according to claim 4, wherein the thickness of the non-porous region is 0.1 μm or more and 5 μm or less.

6. The battery according to claim 1 or 2, wherein the ion-conducting polymer film has a 150°C thermal shrinkage rate of 10% or less.

7. The battery according to claim 1 or 2, wherein the polymer constituting the ion-conducting polymer film is an aromatic polyamide.

8. The battery according to claim 1 or 2, wherein at least one of the positive electrode and the negative electrode has an ion-conducting polymer film with a thickness of 1 μm or less.

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