Film for battery exterior body, battery exterior body, and secondary battery

Abstract

A film for a battery exterior body, which contains a hot-melt tetrafluoroethylene polymer that has 50 or more carbonyl group-containing groups per 106 main chain carbon atoms, has a fluorine content of 60-75 mass%, and has a thickness of 10 [mu] m or more.

Description

Technical Field

[0001] This invention relates to a thin film for battery casing, a battery casing, and a secondary battery. Background Technology

[0002] As an outer casing for batteries such as lithium-ion secondary batteries, it is known to use a combination of metal layers and resin layers, for example, requiring heat resistance to withstand mounting to the substrate during reflow soldering and water resistance to prevent the intrusion of moisture such as water vapor.

[0003] Patent Document 1 discloses an outer casing and a solid-state battery. The outer casing is made of a laminated film. The laminated film has a resin film layer containing a thermally adhesive resin with a melting point of 200°C or higher and a metal foil disposed within the resin film layer. The solid-state battery includes the outer casing. At least a portion of the aforementioned metal foil of the outer casing is exposed to form a contact portion with a positive or negative terminal, and another portion of the metal foil is exposed to form a take-out electrode portion.

[0004] On the other hand, as a heat-resistant resin layer combined with a metal layer, Patent Document 2 discloses a fluoropolymer film with an oxygen element ratio of more than a specified amount when corona discharge treatment or plasma discharge treatment is performed and the surface state after heat treatment is measured by a scanning X-ray photoelectron spectrophotometer, which is considered to have good adhesion to copper foil.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: International Publication No. 2021 / 235451

[0008] Patent Document 2: Japanese Patent Application Publication No. 2022-112028 Summary of the Invention

[0009] The problem the invention aims to solve

[0010] In Patent Document 1, polychlorotrifluoroethylene, polytetrafluoroethylene, polyphenylene sulfide, and polyamide-imide are examples of resins that constitute the resin film layer. However, it is difficult to balance the physical properties required for battery packaging materials, such as the adhesion between these resin films and the metal layer, chemical resistance, gas barrier properties, sliding properties of the resin film surface, and drawing properties.

[0011] The fluoropolymer film disclosed in Patent Document 2 exhibits adhesion to copper foil through surface modification using corona discharge or plasma discharge treatment. However, the surface modification of the fluoropolymer film by discharge treatment is also accompanied by the decomposition of the fluoropolymer near the film surface. Therefore, while there is a tendency to improve the initial adhesion (lamination characteristics) to the copper foil, its long-term sustainability and its impact on the physical properties required for the aforementioned battery packaging materials tend to increase. That is, the inventors have found that there is a so-called trade-off between the two, and when this fluoropolymer film is applied to battery components, it is easily and significantly affected by environmental changes such as temperature changes accompanying charging and discharging, and the generation of gases from the electrolyte, etc. Furthermore, the inventors have found that fluoropolymer is prone to linear expansion, so even if the fluoropolymer film becomes thicker, the impact on physical properties becomes more significant.

[0012] The inventors have discovered that when fluoropolymer films are applied to battery casings, films of a specified thickness made of fluoropolymers containing a specified amount or more of specific functional groups and a fluorine content within a specified range exhibit excellent chemical resistance and heat resistance, good adhesion to metal layers, and excellent formability such as sliding and drawing properties on the film surface, making them suitable for various battery casings.

[0013] The purpose of this invention is to provide a thin film for battery outer packaging that can form battery outer packaging components with excellent chemical resistance and gas barrier properties, good adhesion to metal layers, and excellent formability such as surface slip and drawing properties.

[0014] Another object of the present invention is to provide a battery casing having the battery casing film, and a secondary battery having the battery casing.

[0015] Solution for solving the problem

[0016] The present invention has the following aspects.

[0017] <1> A thin film for a battery casing, comprising a hot-melt tetrafluoroethylene-based polymer, wherein the hot-melt tetrafluoroethylene-based polymer is present in a proportion relative to 10 6 Each main chain carbon atom has more than 50 carbonyl groups, and the fluorine content is more than 60% by mass and less than 75% by mass, and the thickness of the thin film for the battery outer casing is more than 10 μm.

[0018] <2> according to <1> A thin film for battery casing, wherein the MFR of the hot-melt tetrafluoroethylene polymer is 10 g / 10 min or more and 60 g / 10 min or less.

[0019] <3> according to <1> or <2> A thin film for battery casing, wherein the fluorine content is 60% by mass or more and 68% by mass or less.

[0020] <4> according to <1> ~ <3> The thin film for battery casing of any one of the following, wherein the hot-melt tetrafluoroethylene polymer is a copolymer containing tetrafluoroethylene units and ethylene units.

[0021] <5> according to <1> ~ <4> A thin film for a battery casing according to any one of the following, wherein the number of carbonyl-containing groups in the hot-melt tetrafluoroethylene polymer is relative to every 10 6 Each main chain has more than 200 carbon atoms.

[0022] <6> according to <1> ~ <5> The thin film for battery casing of any one of the following, wherein the oxygen element ratio is less than 1.5 atoms when the surface state of one or both sides is measured by scanning X-ray photoelectron spectroscopy (XPS / ESCA) after heat treatment at 180°C for 3 minutes.

[0023] <7> A battery casing having a soft metal layer and <1> ~ <6> A thin film layer for the battery casing of any one of the following.

[0024] <8> according to <7> A battery casing, wherein the thickness of the thin film layer of the battery casing is greater than the thickness of the soft metal layer.

[0025] <9> according to <7> or <8> The battery casing, wherein the soft metal constituting the soft metal layer is aluminum.

[0026] <10> according to <7> ~ <9> The battery casing of any one of the above has, in sequence, the thin film layer for the battery casing, the soft metal layer, and the thin film layer for the battery casing.

[0027] <11> according to <7> ~ <10> The battery casing of any one of the following further comprises a resin film layer formed of resin, said resin being at least one resin selected from the group consisting of polyethylene, polypropylene, polyimide, polyamide, liquid crystal polymer, polyphenylene sulfide, polyethylene terephthalate, polybutylene terephthalate, cyclic olefin polymer, polystyrene, epoxy resin, bismaleimide, polyphenylene oxide, polyphenylene ether, and polybutadiene.

[0028] <12> according to <7> ~ <11> The battery casing of any one of the embodiments further comprises a resin film layer formed of a hot-melt tetrafluoroethylene polymer without carbonyl groups.

[0029] <13> according to <11> or <12> A battery casing, wherein the thin film layer of the battery casing is in contact with one side of the soft metal layer, and the resin thin film layer is in contact with the other side of the soft metal layer.

[0030] <14> according to <7> ~ <13> The battery casing of any one of the following, wherein the adhesive strength between the soft metal layer and the thin film layer of the battery casing is 100 N / m or more.

[0031] <15> A secondary battery having <7> ~ <14> The battery casing and electrolyte of any one of the following, wherein the battery casing is provided with a thin film layer at the location in contact with the electrolyte during battery fabrication.

[0032] The effects of the invention

[0033] According to the present invention, a battery outer packaging component with excellent chemical resistance and gas barrier properties, a thin film for battery outer packaging with good adhesion to the metal layer and excellent formability such as surface slip and drawing properties, a battery outer packaging, and a secondary battery having the battery outer packaging can be provided. Attached Figure Description

[0034] Figure 1 This is a perspective view showing an example of a battery casing having the thin film layer for battery casing of the present invention. Detailed Implementation

[0035] The following terms have the following meanings.

[0036] The "Mel Flow Rate (MFR) of hot-melt tetrafluoroethylene polymers" is a value determined according to ASTM D3307 at 372°C and a 5kg load.

[0037] The "melting point of a polymer" is the temperature corresponding to the maximum value of the polymer's melting peak as determined by differential scanning calorimetry (DSC).

[0038] "Glass transition temperature (Tg)" is a value determined by analyzing polymers using the dynamic viscoelasticity assay (DMA).

[0039] The thickness of the thin film and metal layer is the average value obtained by measuring five arbitrary points at 25°C using a high-precision digital micrometer "MDH-25MB" manufactured by Mitutoyo Corporation.

[0040] In polymers, a "unit" refers to a group of atoms based on a monomer formed through the polymerization of the monomer. A unit can be formed directly through a polymerization reaction, or a portion of the unit can be converted into a unit with a different structure by processing the polymer. Hereinafter, units based on monomer a will also be abbreviated as "monomer a unit".

[0041] This invention relates to a thin film for a battery casing (hereinafter also referred to as "the thin film for the battery casing"), which comprises a hot-melt tetrafluoroethylene-based polymer (hereinafter also referred to as "F polymer"), wherein the hot-melt tetrafluoroethylene-based polymer is present in a proportion relative to 10 6 Each main chain carbon atom has more than 50 carbonyl groups, and the fluorine content is more than 60% by mass and less than 75% by mass, and the thickness of the thin film for the battery outer casing is more than 10 μm.

[0042] The surface of the thin film used for the battery casing has carbonyl-containing groups derived from the molecular structure of the F polymer itself, which is believed to readily exhibit high adhesion. Furthermore, when the fluorine content of the F polymer is within a specified range, the surface tension of the thin film used for the battery casing is moderated while maintaining its chemical resistance and heat resistance, thus improving its affinity with other substrates. As a result, in the battery casing comprising the soft metal layer and the thin film used for the battery casing described later, the adhesion to the soft metal layer is excellent, and the battery casing exhibits excellent barrier properties, surface slippage, and formability such as drawing ability. This characteristic is more significantly manifested in the preferred embodiment of the thin film used for the battery casing described later.

[0043] The F polymer in this invention is a thermomeltable polymer comprising tetrafluoroethylene (hereinafter also referred to as "TFE unit")-based units (hereinafter also referred to as "TFE unit"). Here, a thermomeltable polymer refers to a polymer that exhibits a melt flow rate of 1 to 1000 g / 10 minutes under a load of 49 N.

[0044] The melting point of polymer F is preferably above 100°C, more preferably above 180°C, and even more preferably above 200°C. The melting point of the aforementioned polymer F is preferably below 325°C, more preferably below 320°C. In this case, the heat resistance of the film used for the battery casing is readily excellent.

[0045] The glass transition temperature of polymer F is preferably 50°C or higher, more preferably 75°C or higher. The glass transition temperature of polymer F is preferably 150°C or lower, more preferably 125°C or lower.

[0046] The fluorine content of polymer F is 60% by mass or more and 75% by mass or less, preferably 60% by mass or more and 68% by mass or less. In this case, the aforementioned mechanism of action is more readily apparent. It should be noted that the fluorine content of polymer F is calculated as the proportion of fluorine atoms in all monomer units constituting polymer F.

[0047] The surface tension of polymer F is preferably 16~26 mN / m. It should be noted that the surface tension of polymer F can be determined by placing droplets of the wetting tension test mixture (manufactured by Wako Pure Chemical Industries Co., Ltd.) specified in JIS K 6768 on a plate made of polymer F.

[0048] Examples of F polymers include copolymers containing TFE units and ethylene-based units (ethylene units) [ETFE], copolymers containing TFE units and propylene-based units (propylene units), copolymers containing TFE units and perfluoro(alkyl vinyl ether) (PAVE units) (PAVE units) [PFA], copolymers containing TFE units and hexafluoropropylene (HFP)-based units (HFP units) [FEP], TFE / ethylene / HFP copolymers, copolymers containing ethylene units and trifluorochloroethylene (CTFE)-based units (CTFE units) [ECTFE], copolymers containing CTFE units and TFE units, copolymers containing TFE units and vinylidene fluoride (VdF)-based units (VdF units) [VT], copolymers containing TFE units, VdF units, and CTFE units [VTC], and copolymers containing TFE units, HFP units, and VdF units, etc.

[0049] The F polymer is preferably a copolymer containing TFE units and one or more units selected from the group consisting of PAVE units, HFP units, fluoroalkyl ethylene (FAE) units (FAE units), and ethylene units.

[0050] More specifically, the F polymer is preferably a copolymer comprising TFE and ethylene units (ETFE), a copolymer comprising TFE and HFP units (FEP), a copolymer comprising TFE and PAVE units (PFA), and more preferably ETFE. These copolymers may further comprise units based on other comonomers.

[0051] PAVE is preferably CF2=CFOCF3, CF2=CFOCF2CF3 and CF2=CFOCF2CF2CF3 (hereinafter also referred to as "PPVE"), and more preferably PPVE.

[0052] FAE preferably contains CH2=CH(CF2)2F, CH2=CH(CF2)3F, CH2=CH(CF2)4F, CH2=CF(CF2)3H, and CH2=CF(CF2)4H.

[0053] ETFE preferably comprises 35-65 mol% of TFE units and 35-65 mol% of ethylene units relative to all units. In addition, ETFE may also include other units such as PAVE units, HFP units, and FAE units.

[0054] F polymer relative to each 10 6 Each main chain carbon atom has more than 50 carbonyl-containing groups. The number of carbonyl-containing groups in the F polymer is preferably relative to the number of carbonyl-containing groups per 10... 6 Each main chain carbon atom has 100 or more, more preferably 200 or more. Furthermore, the number of carbonyl-containing groups in the F polymer is 1 × 10⁻⁶ relative to the number of carbon atoms in the main chain. 6 The number of oxygen-containing polar groups in polymer F is preferably 5,000 or less, more preferably 3,000 or less. It should be noted that the number of oxygen-containing polar groups in polymer F can be quantified by the composition of the polymer or by the method described in International Publication No. 2020 / 145133.

[0055] When polymer F has carbonyl groups within the above-mentioned range, the adhesion between the thin film for the battery casing and the soft metal layer is excellent. The battery casing having both a soft metal layer and a thin film layer exhibits excellent barrier properties, surface slippage, and drawability. Furthermore, it is easy to obtain a thin film for the battery casing that possesses excellent mechanical properties, heat resistance, surface properties, and a small dimensional change rate.

[0056] The carbonyl group is preferably a carboxyl group, alkoxycarbonyl group, amide group, isocyanate group, carbamate group (-OC(O)NH2), acid anhydride residue (-C(O)OC(O)-), imide residue (-C(O)NHC(O)-, etc.), formyl group, haloformyl group, carbamate subunit (-NHC(O)O-), carbamate group (-C(O)-NH2), urea group (-NH-C(O)-NH2), oxalamido group (-NH-C(O)-C(O)-NH2), and carbonate group (-OC(O)O-), more preferably an acid anhydride residue.

[0057] Carbonyl groups can be contained in monomer-based units of the F polymer, or they can be contained in terminal groups of the F polymer backbone. Examples of the latter include F polymers having carbonyl groups as terminal groups derived from polymerization initiators, chain transfer agents, etc.

[0058] The monomer having a carbonyl group is preferably itaconic anhydride, citraconic anhydride and 5-norbornene-2,3-dicarboxylic anhydride (hereinafter also referred to as "NAH"), and more preferably NAH.

[0059] The preferred polymer F is a copolymer containing carbonyl groups, comprising TFE units and ethylene units. Examples of such ETFEs include polymers comprising TFE units, ethylene units, and units based on carbonyl groups, wherein the total percentage of these units is 35-65 mol%, 35-65 mol%, and 0.01-5 mol% relative to all units. Specific examples of such ETFEs include polymers described in International Patent Publication No. 2006 / 134764 and Japanese Patent Application Publication No. 2012-106494.

[0060] The MFR of the F polymer contained in the film for the outer casing of this battery is preferably greater than 10 g / 10 min and less than 60 g / 10 min, more preferably greater than 15 g / 10 min and less than 50 g / 10 min. If the MFR is within the above range, the flexibility of the film for the outer casing of this battery is ensured while easily utilizing the chemical resistance, heat resistance and other properties based on the F polymer.

[0061] In the thin film used for the outer casing of this battery, one type of F polymer can be used alone, or two or more types can be used together.

[0062] The F polymer may contain other components besides the F polymer without impairing the effects of the present invention. Examples of other components include known resin additives, polyimides, polyetheretherketones, and other heat-resistant resins other than the F polymer that are hot-melt.

[0063] When the surface condition of the thin film used for the outer casing of this battery is measured using a scanning X-ray photoelectron spectroscopy (XPS / ESCA) device after heat treatment at 180°C for 3 minutes, the oxygen content is preferably less than 1.5 atomic%, more preferably less than 1.0 atomic%. This oxygen content is preferably 0.1 atomic% or higher.

[0064] In this case, the chemical resistance and gas barrier properties of the film used for the battery casing are easily improved. Furthermore, even when the oxygen ratio is within the aforementioned range, the surface properties of the F polymer contained in the film used for the battery casing are excellent, and its adhesion to the soft metal layer is readily excellent.

[0065] It should be noted that the oxygen atom ratio is obtained by placing a test piece made of a thin film for the outer casing of this battery on a metal tray, heat-treating it in an electric furnace at 180°C for 3 minutes in an air atmosphere, and then measuring the surface condition of one or both sides using XPS / ESCA.

[0066] Furthermore, the absolute value of the dimensional change rate before and after heat treatment, measured by heat-treating the film for the outer casing of this battery at 180°C for 10 minutes and then cooling it to 25°C, is preferably 2% or less, more preferably 1.8% or less. This dimensional change rate is calculated by cutting a 300mm square test piece from the film for the outer casing of this battery, marking the marks at 180mm intervals, heat-treating it at 180°C for 10 minutes in an electric furnace without applying a load in an air atmosphere, and then measuring the longitudinal and transverse intervals of the test piece after cooling to 25°C. The value is calculated from the change in the intervals of the marks before and after heat treatment.

[0067] The film for the battery casing can be formed, for example, by melt extruding an F polymer using an extrusion molding machine with a T-die. The melt extrusion of the F polymer can be performed continuously after melt mixing, or it can be performed simultaneously with melt mixing within the extrusion molding machine. Furthermore, after melt extrusion, uniaxial stretching, biaxial stretching, or no stretching can be performed. The melt extrusion conditions are generally preferably set to a temperature at least 20°C higher than the melting point of the F polymer. It should be noted that the thickness of the film for the battery casing can be controlled by appropriately adjusting the T-die gap, traction speed, and coating amount of the F polymer.

[0068] The thin film for the battery casing can also be obtained as follows: after preparing a solution or dispersion containing polymer F, it is applied to a substrate and heated, and then separated from the substrate.

[0069] The thickness of the thin film used for the battery casing is 10 μm or more. From the viewpoint of ensuring excellent chemical resistance, heat resistance, and other properties, as well as the ease of achieving excellent formability such as sliding and drawing properties of the battery casing of the present invention (described later), it is preferably 60 μm or less, more preferably 50 μm or less. Furthermore, the total thickness of the battery casing of the present invention (described later), which includes a soft metal layer and the thin film layer for the battery casing, is preferably 50 μm or more and 200 μm or less, more preferably 60 μm or more and 150 μm or less, and even more preferably 70 μm or more and 125 μm or less. According to the above-described mechanism of action, when the thickness of the thin film for the battery casing is within the above range, the chemical resistance and heat resistance of the battery casing are more excellent. In addition, in synergy with the soft metal layer, the formability such as sliding and drawing properties is easily improved.

[0070] The thin film used for the battery casing exhibits excellent barrier properties and heat resistance, making it suitable for use in casings for various batteries. Examples of batteries include, for instance, all-solid-state batteries such as sulfide-based, oxide-based, and all-resin batteries; semi-solid-state batteries such as gel polymer-type, clay-type, liquid-addition-type, and condensed matter batteries; lithium-ion batteries such as lithium-sulfur batteries (Li-S batteries), lithium manganese iron phosphate batteries (LMFP batteries), and lithium iron phosphate batteries (e.g., CATL's "M3P battery"); and solar cells.

[0071] It should be noted that the thin film used for the outer casing of this battery can also be applied to components such as tabs, leads, and separators in the various batteries mentioned above.

[0072] In addition, the present invention is a battery casing (hereinafter also referred to as "the battery casing") having a soft metal layer and a thin film layer for the battery casing.

[0073] Because the battery casing has a soft metal layer, it has excellent barrier properties. The battery casing has a thin film layer with excellent adhesion to the soft metal layer, and it has excellent heat resistance. Even when the laminate is heated, the fluoropolymer-containing layer can be prevented from peeling off from the metal layer.

[0074] This battery casing has such characteristics that, if used as a casing for various secondary batteries, it exhibits excellent barrier properties and heat resistance even under repeated charge and discharge conditions, and tends to maintain battery characteristics such as charge and discharge capacity.

[0075] In the outer casing of this battery, the soft metal layer can be a foil-shaped or plate-shaped soft metal, more preferably a soft metal foil.

[0076] As the soft metal constituting the soft metal support, at least one can be selected from the group consisting of aluminum, stainless steel, and copper. From the viewpoint of further improving the mechanical properties, barrier properties, and chemical resistance (corrosion resistance) of the film for this oscillating member, aluminum is preferred as the soft metal. Aluminum can be a pure metal or an alloy. In the latter case, an aluminum alloy with an aluminum content of 80% by mass or more is preferred. In other words, the soft metal support is further preferably aluminum foil.

[0077] The adhesion strength between the soft metal layer and the thin film layer of the battery casing is preferably 100 N / m or higher. The upper limit of the adhesion strength is 1000 N / m. When the adhesion strength is within the above range, the heat resistance, surface slippage, and deep drawing properties of the battery casing can be further improved.

[0078] It should be noted that the adhesive strength between the soft metal layer and the thin film layer used for the outer casing of this battery is a value obtained by measuring the peel strength as described in the embodiments described later.

[0079] The water vapor transmission rate of the soft metal layer is preferably 1 g / m 2 For temperatures below 1 day, 0.1 g / m² is preferred. 2 For temperatures below 1 day, a further preferred value is 0.01 g / m³. 2 • Less than 1 day. It should be noted that the water vapor transmission rate is based on JIS K7129-1:2019 and is measured using a differential pressure gas / water vapor transmission tester (GC method) at 40℃ and RH90%.

[0080] The preferred oxygen permeability of the soft metal layer is 1 g·ml / m³. 2 Less than 1 day atm, preferably 0.1 g / ml / m 2 Less than 1 day atm, further preferably 0.01 g / ml / m 2 • Days • below atm. It should be noted that the oxygen permeability is based on JIS K7126-2:2006 and was measured at 23°C using a differential pressure gas / water vapor permeation tester (GC method).

[0081] The surface of a soft metal layer can also be surface treated.

[0082] From the viewpoint of improving the mechanical properties of the battery casing and further enhancing its formability, such as barrier properties, chemical resistance (corrosion resistance), sliding properties, and drawing properties, the thickness of the soft metal layer is preferably 10 μm or more and 60 μm or less, more preferably 15 μm or more and 50 μm or less.

[0083] Furthermore, from the viewpoint of improving the chemical resistance and heat resistance of the battery casing, and further enhancing its formability such as sliding and drawing properties, the thickness of the soft metal layer is preferably in the range of more than 25% and less than 200% of the thickness of the thin film layer for the battery casing, and more preferably, the thickness of the thin film layer for the battery casing is thicker than the thickness of the soft metal layer. More preferably, the thickness of the soft metal layer is more than 40% and less than 150% of the thickness of the thin film layer for the battery casing. It should be noted that when the battery casing has a structure comprising multiple thin film layers for the battery casing, their total thickness is used as the thickness of the thin film layer for the battery casing.

[0084] The battery casing may further include a resin film layer formed of resin (hereinafter also referred to as "resin film layer A"), wherein the resin is at least one resin selected from the group consisting of polyethylene, polypropylene, polyimide, polyamide, liquid crystal polymer, polyphenylene sulfide, polyethylene terephthalate, polybutylene terephthalate, cyclic olefin polymer, polystyrene, epoxy resin, bismaleimide, polyphenylene oxide, polyphenylene ether, and polybutadiene.

[0085] The battery casing may further have a resin film layer (hereinafter also referred to as "resin film layer B") formed of a hot-melt tetrafluoroethylene polymer without carbonyl groups. Examples of hot-melt tetrafluoroethylene polymers without carbonyl groups include those with a carbonyl group content relative to 10 6 Copolymers with fewer than 50 carbon atoms in the main chain and containing ethylene and TFE units [ETFE], copolymers containing TFE and PAVE units [PFA], polymers containing vinylidene fluoride units [PVDF], polymers containing vinyl fluoride units [PVF], etc.

[0086] When the battery casing has either or both of the above-mentioned resin film layer A and resin film layer B, the thickness of resin film A and resin film layer B is not limited as long as it does not impair the effect of the present invention, and is generally preferably in the range of 1 to 50 μm.

[0087] The aforementioned resin film layer A and resin film layer B may further contain various additives, inorganic fillers, and other components without impairing the effects of the present invention. Furthermore, each resin film layer may be bonded to the soft metal layer via an adhesive layer.

[0088] The battery casing is preferably configured such that one side of the thin film layer and the soft metal layer of the battery casing are in contact.

[0089] The battery casing is more preferably configured to have a thin film layer for the battery casing, a flexible metal layer, and another thin film layer for the battery casing in sequence, and even more preferably configured to have the two surfaces of the thin film layer for the battery casing in contact with the flexible metal layer. In this case, the thin film layer for the battery casing in contact with the two surfaces of the flexible metal layer can be a thin film for the battery casing containing the same type of F polymer, or it can be two types of thin films for the battery casing containing different types of F polymer.

[0090] When the battery casing also includes either or both of the aforementioned resin film layer A and resin film layer B, it is preferable that the resin film layer is in contact with one side of the soft metal layer, or that the resin film layer is in contact with one or both sides of the soft metal layer, and that the opposite side of the battery casing film layer is in contact with the soft metal layer. When the battery casing film layer is in contact with both sides of the soft metal layer, the resin film layer may be present on one outer side of the battery casing film layer in contact with the soft metal layer, or the resin film layer may be present on both outer sides of the battery casing film layer. When the resin film layers are multiple, they may be of the same or different types.

[0091] More preferably, the battery casing is configured such that one side of the battery casing film layer is in contact with the soft metal layer, and the other side of the resin film layer (resin film layer A or resin film layer B) is in contact with the soft metal layer. In this case, from the viewpoint of maximizing the chemical resistance, heat resistance, and barrier properties of the battery casing, it is preferable that the battery casing film layer side of the battery casing is the position in contact with the electrolyte.

[0092] The battery casing can be obtained, for example, by hot-pressing a soft metal layer and a thin film onto the battery casing, and further hot-pressing a resin film layer as needed (hot lamination).

[0093] Alternatively, a soft metal layer can be obtained by pre-fabricating a laminate consisting of a thin film for the outer casing of the battery and a resin film (resin film A or resin film B) using a hot lamination method, and then hot-pressing a soft metal layer onto the surface of the laminate on the side of the thin film for the outer casing of the battery.

[0094] This battery casing can be used without particular restriction for the purpose of packaging batteries, for example, it can be a bag-shaped battery casing (hereinafter also referred to as "battery bag").

[0095] A battery bag using this battery casing can be made into a bag shape by heat-sealing a portion of the periphery of one or more battery casings.

[0096] Examples of battery bag forms include: a three-sided sealed bag formed by folding one battery casing back halfway and overlapping it, then heat-sealing the first layer of the overlapping three sides together; and a four-sided sealed bag formed by overlapping two battery casings and heat-sealing the first layer of the overlapping four sides together. This type of battery bag exhibits excellent barrier properties and heat resistance, suppressing interfacial delamination between the sealing portion and the layers of the battery bag even at high temperatures.

[0097] These battery pouches can be used for all types of batteries mentioned above. In addition to laminated and pouch types, they can also be applied to battery cells of various shapes, such as cylindrical and square.

[0098] Figure 1 This illustrates an example of an all-solid-state battery in which the outer casing forms the outer packaging of an all-solid-state battery cell. The all-solid-state battery 40 has an all-solid-state battery cell 42 and an outer casing 10 that encloses the all-solid-state battery cell 42. The bag 30 is a bag with a three-sided seal formed by folding the outer casing 10 back midway and heat-sealing the periphery of the overlapping three sides to create a three-sided sealing portion 32. The positive terminal 44 and negative terminal 46 protruding from the outer casing formed by the outer casing 10 are sealed while being held between two outer casings 10.

[0099] This type of all-solid-state battery, with its external casing, exhibits excellent barrier properties and heat resistance. When exposed to high temperatures, delamination is less likely to occur at the sealing portions of the laminated structure serving as the external casing and at the interfaces between the layers of the laminate. Therefore, compared to previous designs, it is possible to suppress the decrease in charge / discharge capacity when exposed to high temperatures.

[0100] The present invention also relates to a secondary battery having a battery casing and an electrolyte, wherein a thin film layer of the battery casing exists in the position that contacts the electrolyte during battery manufacturing. With this configuration, the battery casing exhibits excellent chemical resistance and heat resistance to the electrolyte, as well as excellent barrier properties.

[0101] As secondary batteries, the various batteries mentioned above can be cited, and their electrolytes can be either liquid or solid.

[0102] The thin film for the battery casing and the battery casing formed from the thin film for the battery casing have been described above, but the present invention is not limited to the configuration of the above embodiments.

[0103] For example, the battery casing formed by the battery casing film and the battery casing film can be modified by adding any other configuration to the above-described embodiment, or it can be replaced by any configuration that performs the same function.

[0104] Example

[0105] The present invention will be described in detail below through embodiments, but the present invention is not limited thereto.

[0106] Preparation of each component

[0107] [Films of thermomeltable tetrafluoroethylene-based polymers (F polymers)]

[0108] • Film F1: Contains, sequentially, 58.0 mol%, 38.6 mol%, 3.1 mol%, and 0.3 mol% of TFE units, ethylene units, CH2=CH(CF2)2F-based units, and NAH units, and relative to each 10 6 A thin film (thickness: 25 μm, oxygen atom ratio: 0.8 atom%) of ETFE (fluorine content: 64% by mass, MFR: 27.0 g / 10 min, melting point: 237 °C) with 3000 carbonyl-containing groups per main chain carbon atom.

[0109] Film F2: Contains, sequentially, 97.9 mol%, 2.0 mol%, and 0.1 mol% TFE, PPVE, and NAH units, and relative to each 1 × 10 6 A thin film (thickness: 25 μm, oxygen atom ratio: 0.5 atom%) of PFA (fluorine content: 75% by mass, MFR: 11.0 g / 10 min, melt temperature: 300 °C) with 1000 carbonyl-containing groups per main chain carbon atom.

[0110] • F film 3: Contains TFE units and PPVE units, and relative to each 1×10 6 A thin film of PFA (fluorine content: 75% by mass, melting temperature: 305℃) with less than 10 carbonyl groups per main chain carbon atom (thickness: 25μm, oxygen atom ratio: less than 0.1 atoms).

[0111] • F film 4: While circulating nitrogen gas containing 0.50 vol% vinyl acetate near the discharge electrode and the roller grounding electrode of the corona discharge device, F film 3 is continuously passed along the roller grounding electrode at a discharge rate of 1000 W·min / m 2 The above-mentioned F-film (thickness: 25 μm, oxygen atom ratio: 10 atoms) underwent corona discharge treatment.

[0112] • F film 5: A PVDF (fluorine content: 59% by mass) homopolymer film (thickness: 25 μm) as a homopolymer of vinylidene fluoride.

[0113] In addition, F film 1 and F film 2 are equivalent to the battery outer casing film of the present invention.

[0114] [Soft metal layer]

[0115] Metal layer 1: Aluminum alloy foil (based on JIS H 4160:1994 aluminum alloy foil, alloy type 8079, thickness: 40μm, length: 30cm, width: 30cm)

[0116] 2. Fabrication of the battery casing

[0117] Example 1

[0118] F film 1 is laminated on both sides of metal layer 1, and then a release film (Toray DuPont polyimide film "Kapton (registered trademark) 200H / V", thickness 50μm) is laminated on the outer sides of both sides. The laminate is pressed using a vacuum pressing device at 240°C, 15 minutes, and 10MPa, then removed and cooled at 25°C for 5 minutes. After cooling, the release films on both sides are peeled off to obtain battery outer casing 1.

[0119] Example 2

[0120] F-film 2 is laminated on both sides of metal layer 1, and then a release film of the same type as in Example 1 is laminated on the outer sides of both sides. The laminate is pressed using a vacuum pressing device at 305°C for 15 minutes and 1 MPa, then removed and cooled at 25°C for 5 minutes. After cooling, the release films on both sides are peeled off to obtain battery outer casing 2.

[0121] Example 3

[0122] F-films 3 are laminated on both sides of the metal layer 1, and then release films, similar to those in Example 1, are placed and laminated on the outer sides of both sides. The laminate is pressed under the same conditions as in Example 2, removed, and placed in a 25°C atmosphere for 5 minutes to cool. After cooling, the release films on both sides are peeled off to obtain the battery outer casing 3.

[0123] Example 4

[0124] F-film 4 is laminated on both sides of metal layer 1, and then a release film, the same as in Example 1, is placed and laminated on the outer sides of both sides. The laminate is pressed under the same conditions as in Example 2, removed, and placed in a 25°C atmosphere for 5 minutes to cool. After cooling, the release films on both sides are peeled off to obtain the battery outer casing 4.

[0125] Example 5

[0126] F-films 5 are laminated on both sides of the metal layer 1, and then release films, similar to those in Example 1, are placed and laminated on the outer sides of both sides. The laminate is pressed under the same conditions as in Example 1, removed, and placed in a 25°C atmosphere for 5 minutes to cool. After cooling, the release films on both sides are peeled off to obtain the battery outer casing 5.

[0127] 3. Evaluation of the battery casing

[0128] 3-1. Adhesion (Durability to hydrogen sulfide gas)

[0129] The battery casings fabricated in each example were placed between the upper and lower parts of a detachable flask with vents at the top and bottom, respectively. Nitrogen gas was introduced at 50 ml / min through the upper vent and nitrogen gas with a hydrogen sulfide concentration of 20 ± 5 ppm was introduced at 50 ml / min through the lower vent. The mixture was then left to stand for 48 hours.

[0130] Then, the battery casing was removed and cut into 1cm wide sections. The side of the battery casing exposed to nitrogen gas containing hydrogen sulfide was peeled from one end along the length to a position of 50mm between the thin film layer and the aluminum layer. Then, a tensile testing machine was used to peel the casing at 25°C and a tensile speed of 100mm / min at a 90° angle. The average load measured over a distance of 20mm to 80mm was taken as the peel strength (N / cm). When the peel strength of battery casing 1 exposed to nitrogen gas containing hydrogen sulfide was set to 100, the relative values ​​of the peel strength of battery casings 2 to 4 exposed to hydrogen sulfide were set as follows: 0 for those with a relative value of 100 or higher, △ for those with a relative value of 75 or higher but less than 100, and × for those with a relative value of less than 75. The adhesion was then evaluated.

[0131] It should be noted that for the battery casing 3, the peel strength measured using a tensile testing machine before exposure to nitrogen gas containing hydrogen sulfide was used as the range of the above relative value of "×", therefore no adhesiveness evaluation was performed.

[0132] 3-2. Sliding and drawing properties

[0133] For the battery casing used for the evaluation of "3-1. Adhesion", a straight forming die with a forming depth of 5mm [made of carbon steel (only the punch R is chrome plated), punch: 33.3mm × 53.9mm, die: 80mm × 120mm, corner R: 2mm, punch R: 1.3mm, die R: 1mm] was used to perform deep drawing in one stage under anti-wrinkle pressure (calculated value) of 0.7MPa. The formed body was visually observed for whitening and cracks.

[0134] The case where neither whitening nor cracking was observed during molding was rated as "0", the case where whitening was observed in the molded body was rated as "△", and the case where cracking was observed in the molded body was rated as "×". It should be noted that for the battery outer casing 5, the above-mentioned adhesion evaluation did not yield sufficient results, therefore the evaluation of sliding and drawing properties was not performed.

[0135] The evaluation results are shown in Table 1.

[0136] [Table 1]

[0137]

[0138] The publications of Japanese Patent Applications Nos. 2023-120103, 2023-194606 and 2024-034259 are incorporated herein by reference in their entirety.

[0139] All documents, patent applications and technical standards described herein are incorporated herein by reference to the same extent as the specific and separately recorded documents, patent applications and technical standards.

[0140] Explanation of reference numerals in the attached figures

[0141] 10 Battery casing

[0142] 30 bags

[0143] 32 Sealing part

[0144] 40 All-Solid-State Battery

[0145] 42 all-solid-state battery cells

[0146] 44 Positive extremes

[0147] 46 Negative extremes

Claims

1. A thin film for a battery casing comprising a hot-melt tetrafluoroethylene-based polymer, wherein the hot-melt tetrafluoroethylene-based polymer is present in a proportion relative to 10 6 Each main chain carbon atom has more than 50 carbonyl groups, and the fluorine content is more than 60% by mass and less than 75% by mass, and the thickness of the thin film for the battery outer casing is more than 10 μm.

2. The thin film for battery casing according to claim 1, wherein, The MFR of the hot-melt tetrafluoroethylene polymer is greater than 10 g / 10 min and less than 60 g / 10 min.

3. The thin film for battery casing according to claim 1, wherein, The fluorine content is 60% by mass or more and 68% by mass or less.

4. The thin film for battery casing according to claim 1, wherein, The hot-melt tetrafluoroethylene polymer is a copolymer containing tetrafluoroethylene units and ethylene units.

5. The thin film for battery casing according to claim 1, wherein, The number of carbonyl-containing groups in the hot-melt tetrafluoroethylene polymer relative to 10 6 Each main chain has more than 200 carbon atoms.

6. The thin film for battery casing according to claim 1, wherein, The oxygen ratio was less than 1.5 atoms when the surface condition of one or both sides of the sample was measured using a scanning X-ray photoelectron spectroscopy (XPS / ESCA) device after heat treatment at 180℃ for 3 minutes.

7. A battery casing comprising a soft metal layer and a thin film layer for a battery casing according to any one of claims 1 to 6.

8. The battery casing according to claim 7, wherein, The thickness of the thin film layer used for the battery casing is greater than the thickness of the soft metal layer.

9. The battery casing according to claim 7, wherein, The soft metal is aluminum.

10. The battery casing according to claim 7, wherein the battery casing thin film layer, the soft metal layer and the battery casing thin film layer are sequentially formed.

11. The battery casing according to claim 7, further comprising a resin film layer formed of resin, said resin being at least one resin selected from the group consisting of polyethylene, polypropylene, polyimide, polyamide, liquid crystal polymer, polyphenylene sulfide, polyethylene terephthalate, polybutylene terephthalate, cyclic olefin polymer, polystyrene, epoxy resin, bismaleimide, polyphenylene oxide, polyphenylene ether, and polybutadiene.

12. The battery casing according to claim 7, further comprising a resin film layer, said resin film layer being formed of a hot-melt tetrafluoroethylene polymer without carbonyl groups.

13. The battery casing according to claim 11 or 12, wherein, The outer thin film layer of the battery casing is in contact with one side of the soft metal layer, and the resin thin film layer is in contact with the other side of the soft metal layer.

14. The battery casing according to claim 7, wherein, The bonding strength between the soft metal layer and the thin film layer used for the battery casing is above 100 N / m.

15. A secondary battery having a battery casing and an electrolyte as described in claim 12, wherein the battery casing is provided with a thin film layer at a location in contact with the electrolyte during battery fabrication.

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