Exterior materials for energy storage devices

Abstract

To provide an exterior material for a power storage device capable of achieving both seal strength under high temperature and initial seal strength at a sufficiently high level.SOLUTION: A power storage device packaging material comprising a substrate layer, a barrier layer, and a sealant layer in this order, wherein the sealant layer includes a polypropylene layer P formed from a resin composition containing polypropylene and a β - crystal nucleating agent.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to an exterior material for an electricity storage device and an electricity storage device. Background Art

[0002] As electricity storage devices, for example, secondary batteries such as lithium ion batteries, nickel-metal hydride batteries, and lead-acid batteries, as well as electrochemical capacitors such as electric double layer capacitors are known. Further miniaturization of electricity storage devices is demanded due to miniaturization of portable devices or restrictions on installation space, and lithium ion batteries with high energy density have attracted attention. As an exterior material used for lithium ion batteries, metal cans have been conventionally used, but multilayer films that are lightweight, have high heat dissipation, and can be produced at low cost have come to be used.

[0003] A lithium ion battery using the above multilayer film as an exterior material is called a laminated lithium ion battery. The exterior material covers battery contents (positive electrode, separator, negative electrode, electrolytic solution, etc.) and prevents moisture from entering the interior. A laminated lithium ion battery is produced, for example, by forming a recess in a part of the exterior material by cold molding, housing the battery contents in the recess, folding back the remaining part of the exterior material, and sealing the edge portion by heat sealing (see, for example, Patent Document 1). Prior Art Literature Patent Literature

[0004] Patent Document 1 Japanese Unexamined Patent Publication No. 2013-101765 Summary of Invention Problem to be Solved by Invention

[0005] Incidentally, research and development is underway on a next-generation battery called a solid-state battery, which is considered the successor to lithium-ion batteries. Solid-state batteries are characterized by using a solid electrolyte instead of an organic electrolyte. While lithium-ion batteries cannot be used at temperatures higher than the boiling point of the electrolyte (around 80°C), solid-state batteries can be used at temperatures exceeding 100°C, and their lithium-ion conductivity can be increased by operating them at high temperatures (for example, 100-150°C).

[0006] However, when using conventional laminates as the outer casing material to manufacture laminate-type all-solid-state batteries, the insufficient heat resistance of the outer casing material may result in insufficient sealing of the all-solid-state battery package.

[0007] This disclosure aims to provide an exterior material for energy storage devices that can achieve sufficiently high levels of both seal strength at high temperatures and initial seal strength. Furthermore, this disclosure aims to provide an energy storage device using the above-mentioned exterior material. [Means for solving the problem]

[0008] An exterior material for an energy storage device according to one aspect of the present disclosure comprises a base layer, a barrier layer, and a sealant layer in that order, wherein the sealant layer includes a polypropylene layer P formed from a resin composition containing polypropylene and a β-nucleating agent.

[0009] Polypropylene is known to exist in four crystalline structures: α, β, γ, and smectic. While most structures formed under typical conditions are α-type, the inventors deliberately used an additive (crystal nucleating agent) to induce the formation of a β-type structure during heat sealing, successfully achieving both high temperature resistance and initial seal strength. The inventors speculate on the following reasons for this superior effect: Initial seal strength: Seal strength measured at room temperature (25°C). • Stress relaxation ability is important (if it is hard and brittle, it is difficult to develop strength). In the β type, stress relaxation capacity is improved, and strength is achieved. High-temperature seal strength: The seal strength measured at high temperatures (150°C). It is important that the resin is not easily heated, and that even when heated, the resin does not easily melt. The β-type melts (endothermally) at around 150°C, making it difficult to heat the resin. Also, the β-type quickly transforms into the α-type after melting, making the resin less likely to melt even when exposed to high temperatures.

[0010] In one embodiment of an exterior material for an energy storage device, the content of the β-nucleating agent may be 0.001 to 15% by mass, based on the total amount of the resin composition.

[0011] In one embodiment of the exterior material for energy storage devices, the β-nucleating agent may be an amide compound.

[0012] In one embodiment of an exterior material for an energy storage device, the sealant layer may include two or more polypropylene layers, at least one of which may be a polypropylene layer P.

[0013] In one embodiment of an exterior material for an energy storage device, the sealant layer may include two or more polypropylene layers, of which at least one layer on the barrier layer side may be a polypropylene layer P.

[0014] In one embodiment of the exterior material for an energy storage device, the polypropylene layer P may contain acid-modified polypropylene.

[0015] In one embodiment of an exterior material for an energy storage device, the sealant layer may include two or more polypropylene layers, at least one of which may include long-chain branched polypropylene.

[0016] An energy storage device relating to one aspect of this disclosure comprises an energy storage device body, terminals electrically connected to the energy storage device body, and the above-mentioned exterior material for the energy storage device that clamps the terminals and houses the energy storage device body, wherein the ends of the exterior material for the energy storage device are heat-sealed.

[0017] In one aspect of the electricity storage device, the crystallinity of β-crystals in the polypropylene layer P in the heat-sealed part of the exterior material for the electricity storage device may be 3 to 90%.

[0018] In one aspect of the electricity storage device, the crystallinity ratio (β / α) of the polypropylene layer P in the heat-sealed part of the exterior material for the electricity storage device may be 0.01 to 50.

[0019] In one aspect of the electricity storage device, when the electricity storage device is allowed to stand at 150°C for one week and then cooled to 25°C, the crystallinity of α-crystals in the polypropylene layer P in the heat-sealed part of the exterior material for the electricity storage device may be 25% or more, and the crystallinity ratio (β / α) may be 0 to 1.

Effects of the Invention

[0020] According to the present disclosure, there is provided an exterior material for an electricity storage device that can achieve both sufficiently high sealing strength at high temperatures and sufficiently high initial sealing strength at a sufficient high level. Further, according to the present disclosure, there is provided an electricity storage device using the above exterior material for an electricity storage device. Although not particularly limited, the exterior material for an electricity storage device of the present disclosure can be suitably used for all-solid-state batteries that may be exposed to high-temperature environments.

Brief Description of Drawings

[0021] [Figure 1] FIG. 1 is a perspective view showing an example of an electricity storage device. [Figure 2] FIG. 2 is a cross-sectional view taken along the line II-II shown in FIG. 1, and is a cross-sectional view schematically showing the configuration of the heat-sealed part of the exterior material for an electricity storage device. [Figure 3] FIG. 3 is a cross-sectional view schematically showing an example of an exterior material for an electricity storage device. [Figure 4] FIG. 4 is a plan view schematically showing evaluation samples produced in Examples and Comparative Examples.

Mode for Carrying Out the Invention

[0022] Embodiments of this disclosure will be described in detail below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant descriptions are omitted. Furthermore, the dimensional ratios in the drawings are not limited to those shown.

[0023] <Energy storage device> The energy storage device comprises an energy storage device body, terminals electrically connected to the energy storage device body, and an outer casing for the energy storage device that clamps the terminals and houses the energy storage device body. The terminals extend from the energy storage device body. Between the terminals and the outer casing in the energy storage device, a portion of the outer surface of the terminals is covered with a terminal resin film. The ends of the outer casing for the energy storage device are heat-sealed, and the energy storage device body is sealed by the outer casing for the energy storage device.

[0024] Figure 1 is a perspective view showing the schematic configuration of the energy storage device according to this embodiment. In Figure 1, an all-solid-state battery is shown as an example of the energy storage device 100, and the following explanation will be given. Note that the energy storage device with the configuration shown in Figure 1 is sometimes called a battery pack or battery cell.

[0025] The energy storage device 100 is an all-solid-state battery and comprises an energy storage device body 50, an outer casing material 10 for the energy storage device, a pair of metal terminals 30, and a terminal resin film 40 (tab sealant). The energy storage device body 50 is the battery body that performs charging and discharging. The outer casing material 10 covers the surface of the energy storage device body 50 and is positioned to be in contact with a part of the terminal resin film 40.

[0026] Figure 2 is a cross-sectional view taken along the line II-II shown in Figure 1, schematically illustrating the configuration of the heat-sealed portion of the exterior material for the energy storage device. As shown in the figure, the end of the exterior material 10 for the energy storage device is heat-sealed, and the symbol H indicates the heat-sealed portion.

[0027] [Exterior material for energy storage devices] The exterior material for the energy storage device comprises a base layer, a barrier layer, and a sealant layer in this order. Hereinafter, the exterior material for the energy storage device may simply be referred to as the exterior material. Figure 3 is a cross-sectional view showing an example of a cross-section of the exterior material 10. The exterior material 10 has a multilayer structure comprising, from the outside to the inside (towards the energy storage device body 50), a base layer 11, a first adhesive layer 12, a barrier layer 13, a corrosion prevention treatment layer 14, a second adhesive layer 17, and a sealant layer 16 in this order.

[0028] (Sealant layer) The sealant layer 16 is a layer that provides sealing properties to the exterior material 10 by heat sealing, and is placed on the inside and heat-sealed (heat-fused) during the assembly of the energy storage device. From the viewpoint of achieving both initial seal strength and high-temperature seal strength, heat sealing is preferably performed at 250 to 300°C, more preferably 270 to 290°C, and after heat sealing, cooling is preferably performed at a cooling rate of 1 to 100°C / min.

[0029] The sealant layer 16 includes a polypropylene layer P formed from a resin composition containing polypropylene and a β-nucleating agent. The polypropylene layer P is obtained by preparing a sealant layer forming material by adding a β-nucleating agent to a polypropylene base resin and kneading (dry blending), and then molding this material by a T-die method or an inflation method. Alternatively, a masterbatch may be prepared by kneading a nucleating agent at a high concentration into the base resin, and this may be diluted and used as a raw material for layer formation.

[0030] Polypropylene may be a homopolymer of propylene (homopolypropylene), a copolymer of ethylene, butene, octene, etc. with propylene (random polypropylene), or a polypropylene in which polyethylene (preferably polyethylene coated with ethylene propylene rubber (EPR)) is dispersed in homopolypropylene (block polypropylene). From the viewpoint of achieving both initial and high-temperature seal strength, the melting point of the base resin, polypropylene, can be 150 to 175°C, or 160 to 170°C. From this viewpoint, a homopolymer of propylene is preferably used as the polypropylene.

[0031] Polypropylene may be acid-modified polypropylene. Acid-modified polypropylene is polypropylene into which acidic groups have been introduced. Specifically, examples include polypropylene copolymerized or graft polymerized with maleic anhydride, carboxylic acid, sulfonic acid, or their derivatives. From the viewpoint of adhesion to barrier layers and terminal resin films, acid-modified polypropylene may be maleic anhydride-modified polypropylene, and from the viewpoint of adhesion and melting point, the polymerization method may be graft polymerization. In the crystallization of polypropylene, a nucleating agent acts as a starting point for the formation of crystal nuclei, and crystals grow while these form a chemical three-dimensional network. At that time, it is presumed that the acid-modified components in the polypropylene assist in network formation, thereby promoting the formation of β crystals.

[0032] Polypropylene may contain long-chain branched polypropylene. This strengthens the entanglement of the resin, further improving the seal strength (heat resistance). The content of long-chain branched polypropylene in polypropylene can be 2 to 30% by mass, or 5 to 20% by mass, from the viewpoint of flexibility and heat resistance.

[0033] Based on the total amount of the resin composition, the content of the β-nucleating agent can be 0.001 to 15% by mass, may be 0.005 to 5% by mass, may be 0.005 to 1% by mass, or may be 0.02 to 0.5% by mass. If the content of the β-nucleating agent is above the lower limit, it is easier to suppress the decrease in initial and high-temperature seal strength due to insufficient β-crystal formation, and if it is below the upper limit, it is easier to suppress the decrease in initial and high-temperature seal strength due to a decrease in cohesive force.

[0034] Examples of β-crystal nucleating agents from the viewpoint of β-crystal formation include amide compounds, tetraoxaspiro compounds, and quinacridone compounds. The amide compound may be an amide compound having a naphthalene skeleton, a compound having a naphthalene skeleton and two amide bonds, or an amide compound having a cyclohexyl group and a naphthalene skeleton. The amide compound may be N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide or a derivative thereof, or N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide. The above β-crystal nucleating agents may be used individually or as a blend of two or more.

[0035] The β-nucleating agent can be analyzed using known analytical methods such as IR, NMR, various mass (mass) spectroscopy methods, X-ray analysis, and Raman spectroscopy.

[0036] The sealant layer 16 may include two or more polypropylene layers from the viewpoint of easily adjusting the physical properties of the film. The number of polypropylene layers can be 2 to 10, or 2 to 3, from the viewpoint of processability. However, at least one of these layers is the polypropylene layer P. The polypropylene layers other than polypropylene layer P are formed from a resin composition containing polypropylene. The polypropylene used as the base resin for each layer may be the same or different.

[0037] If the sealant layer 16 includes two or more polypropylene layers, at least one of them on the barrier layer side may be a polypropylene layer P. In the sealant layer 16, the layer that is most susceptible to load (and therefore most prone to cracking), and is in contact with the barrier layer, greatly affects the seal strength. Therefore, by arranging the polypropylene layer P to be in contact with at least the barrier layer, it is easier to improve the seal strength both initially and at high temperatures.

[0038] If the sealant layer 16 includes two or more polypropylene layers, from the viewpoint of adhesion to the barrier layer and cost, at least one of the layers on the barrier layer side may be acid-modified polypropylene, but all of the layers may be acid-modified polypropylene.

[0039] If the sealant layer 16 includes two or more polypropylene layers, from the viewpoint of flexibility and heat resistance, at least one of the layers on the barrier layer side may contain long-chain branched polypropylene, but all of the layers may contain long-chain branched polypropylene.

[0040] The resin composition forming the polypropylene layer may contain other components such as antioxidants, slip agents, flame retardants, antiblocking agents, light stabilizers, dehydrating agents, hydrogen sulfide adsorbents, and tackifiers. The resin composition forming the polypropylene layer may also contain, for example, zinc oxide or cupric oxide to provide hydrogen sulfide resistance, and zeolites to provide moisture barrier properties.

[0041] The thickness of the sealant layer 16 can be 5 μm or more from the viewpoint of sealing performance, and 300 μm or less from the viewpoint of cell volume. From this viewpoint, the thickness of the sealant layer 16 may be 25 to 200 μm or 50 to 150 μm.

[0042] When the sealant layer includes two or more polypropylene layers, the thickness ratio of each layer can be, for example, 1:2, 1:1, 2:1, etc. for two layers, and 1:2:1, 2:4:4, 2:3:5, 4:4:2, 5:3:2, etc. for three layers.

[0043] When the sealant layer 16 includes two polypropylene layers, multiple resin compositions may be prepared and laminated by the T-die method or the inflation method, or one layer may be formed and then another layer may be extruded onto it, or each layer may be made by the T-die method or the inflation method and then bonded together with an adhesive. As for the adhesive to be used, an agent containing acid-modified polypropylene and a curing agent (e.g., isocyanate) can be used from the viewpoint of interfacial adhesion.

[0044] The lamination of the sealant layer 16 onto the barrier layer 13 can be performed by dry lamination using the second adhesive layer 17 after preparing the sealant layer in advance as described above, but it may also be performed by thermal lamination without using the second adhesive layer 17. Alternatively, the sealant layer may be directly laminated onto the barrier layer 13 by thermal lamination using the T-die method after heating the sealant layer forming material.

[0045] The degree of crystallinity of the β-crystals in the polypropylene layer P (polypropylene layer P after heat sealing) at room temperature (25°C) in the heat-sealed portion of the exterior material can be 3 to 90%, may be 15 to 80%, or 30 to 70%. A degree of crystallinity of β-crystals above the lower limit makes it easier to ensure initial seal strength. A degree of crystallinity of β-crystals below the upper limit makes it easier to ensure seal strength at high temperatures (seal strength at high temperatures tends to decrease if a large amount of β-crystals remain). The degree of crystallinity and the degree of crystallinity ratio can be measured by wide-angle X-ray diffraction.

[0046] The crystallinity ratio (β / α: ratio of β crystals to α crystals) of the polypropylene layer P at room temperature (25°C) in the heat-sealed portion of the exterior material formed by heat sealing can be 0.01 to 50, may be 0.5 to 30, or 1 to 25. A crystallinity ratio above the lower limit makes it easier to ensure initial seal strength. A crystallinity ratio below the upper limit makes it easier to ensure seal strength at high temperatures (high-temperature seal strength tends to decrease if a large amount of β crystals remain).

[0047] When the energy storage device is left standing at 150°C for one week and then cooled to 25°C, the degree of crystallinity of the α-crystals in the polypropylene layer P at room temperature (25°C) in the heat-sealed portion of the exterior material can be 25% or more, and the degree of crystallinity ratio (β / α) can be 0 to 1. The degree of crystallinity and the degree of crystallinity ratio (β / α) may be 35% or more and 0 to 0.8, respectively, and 50% or more and 0 to 0.5. A sufficiently high proportion of α-crystals (low proportion of β-crystals) after standing at 150°C for one week means that sufficient transition from β-crystals to α-crystals has occurred, which means that the seal strength at high temperatures is excellent.

[0048] Whether the polypropylene layer can be suitably used as the sealant layer 16 can be determined by the following method. For the polypropylene layer, DSC measurements are performed under the following conditions to confirm whether the layer has a melting main peak at 160-170°C in the 1st run and a melting main peak at 140-160°C in the 2nd run. Such a layer (polypropylene layer P) can be determined to be suitable for use as the sealant layer 16 described above. The 1st run profile is intended to form an α-crystal by gradually heating and then transition to a β-crystal by gradually cooling. The 2nd run profile is intended to prevent the transition to an α-crystal by rapidly heating. <Measurement conditions> 1st run: Heating from 25℃ to 290℃ (rate: 1.5℃ / min, hold: 290℃-10min), cooling from 290℃ to 25℃ (1.5℃ / min, 25℃-10min) 2nd run: Heating from 25℃ to 290℃ (150℃ / min, 290℃-10min)

[0049] The melting peak temperature of the sealant layer 16 varies depending on the application, but for exterior materials for all-solid-state batteries, it is preferably 160 to 280°C because it improves heat resistance.

[0050] (base material layer) The base layer 11 provides heat resistance during the sealing process when manufacturing energy storage devices and plays a role in suppressing the occurrence of pinholes that may occur during molding and distribution. In particular, for exterior materials of large-scale energy storage devices, it can also provide scratch resistance, chemical resistance, and insulation.

[0051] The base layer 11 is preferably a layer made of a resin film formed from an insulating resin. Examples of resin films include stretched or unstretched films such as polyester film, polyamide film, polypropylene film, and polyphenylene sulfide film. The base layer 11 may be a single-layer film made of any of these resin films, or it may be a laminated film made of two or more of these resin films.

[0052] Among these, polyester film and polyamide film are preferred as the base layer 11 due to their excellent moldability, and polyamide film is more preferred. These films are preferably biaxially oriented films. Examples of polyester resins constituting the polyester film include polyethylene terephthalate. Examples of polyamide resins constituting the polyamide film include nylon 6, nylon 6,6, copolymers of nylon 6 and nylon 6,6, nylon 6,10, polymetaxylylene adipamide (MXD6), nylon 11, nylon 12, etc. Among these, nylon 6 (ONy) is preferred from the viewpoint of excellent heat resistance, puncture strength, and impact strength.

[0053] Examples of stretching methods for biaxially oriented films include sequential biaxial stretching, tubular biaxial stretching, and simultaneous biaxial stretching. From the viewpoint of obtaining better deep-drawing properties, it is preferable that the biaxially oriented film is stretched by the tubular biaxial stretching method.

[0054] The thickness of the base layer 11 is preferably 6 to 40 μm, and more preferably 10 to 30 μm. A base layer thickness of 6 μm or more tends to improve the pinhole resistance and insulation properties of the exterior material 10. When the thickness of the base layer 11 exceeds 40 μm, the total thickness of the exterior material 10 tends to increase.

[0055] (First adhesive layer) The first adhesive layer 12 is a layer that adheres the base layer 11 and the barrier layer 13. Specific examples of materials constituting the first adhesive layer 12 include polyurethane resins obtained by reacting a bifunctional or more isocyanate compound with a main component such as polyester polyol, polyether polyol, acrylic polyol, or carbonate polyol. The various polyols mentioned above can be used individually or in combination of two or more, depending on the functions and performance required for the exterior material. In addition, various other additives and stabilizers may be added to the polyurethane resin, depending on the performance required for the adhesive.

[0056] The thickness of the first adhesive layer 12 is not particularly limited, but from the viewpoint of obtaining desired adhesive strength, conformability, and processability, for example, 1 to 10 μm is preferred, and 3 to 7 μm is more preferred.

[0057] (Barrier layer) The barrier layer 13 has water vapor barrier properties that prevent moisture from entering the inside of the energy storage device. Furthermore, the barrier layer 13 is ductile for deep drawing. As the barrier layer 13, various metal foils such as aluminum, stainless steel, and copper, as well as metal vapor-deposited films, inorganic oxide vapor-deposited films, carbon-containing inorganic oxide vapor-deposited films, and films with these vapor-deposited films can be used. From the viewpoints of mass (specific gravity), moisture resistance, processability, and cost, metal foil is preferred, and aluminum foil is more preferred.

[0058] As for the aluminum foil, soft aluminum foil that has undergone annealing treatment is particularly preferred because it can provide the desired ductility during molding. However, it is even more preferable to use aluminum foil containing iron in order to provide further pinhole resistance and ductility during molding. The iron content in the aluminum foil is preferably 0.1 to 9.0% by mass, and more preferably 0.5 to 2.0% by mass, of 100% by mass of aluminum foil. By having an iron content of 0.1% by mass or more, an exterior material 10 with better pinhole resistance and ductility can be obtained. By having an iron content of 9.0% by mass or less, an exterior material 10 with better flexibility can be obtained. Untreated aluminum foil may be used, but it is preferable to use degreased aluminum foil. When degreasing the aluminum foil, the degreasing treatment may be applied to only one side of the aluminum foil, or to both sides.

[0059] The thickness of the barrier layer 13 is not particularly limited, but it is preferably 9 to 200 μm, and more preferably 15 to 100 μm, considering barrier properties, pinhole resistance, and processability.

[0060] (Corrosion-resistant treatment layer) The corrosion-preventive treatment layer 14 is a layer provided to prevent corrosion of the barrier layer 13. The corrosion-preventive treatment layer 14 can be formed, for example, by degreasing, hot water modification, anodizing, chemical conversion, or a combination of these treatments.

[0061] Degreasing methods include acid degreasing and alkaline degreasing. Acid degreasing methods include using inorganic acids such as sulfuric acid, nitric acid, hydrochloric acid, and hydrofluoric acid individually, or mixtures thereof. Alkaline degreasing methods include using sodium hydroxide, etc.

[0062] Examples of hydrothermal alteration treatments include the boehmite treatment, which involves immersing aluminum foil in boiling water to which triethanolamine has been added. Examples of anodizing treatments include the anodizing treatment.

[0063] Chemical treatments can be immersion-type or coating-type. Immersion-type chemical treatments include, for example, chromate treatment, zirconium treatment, titanium treatment, vanadium treatment, molybdenum treatment, calcium phosphate treatment, strontium hydroxide treatment, cerium treatment, ruthenium treatment, or various chemical treatments consisting of mixed phases of these. On the other hand, a coating-type chemical treatment is a method of applying a coating agent having corrosion-preventive properties onto the barrier layer 13.

[0064] Of these corrosion prevention treatments, if at least a portion of the corrosion prevention treatment layer is formed by hot water modification, anodizing, or chemical conversion, it is preferable to perform the degreasing treatment described above beforehand. Furthermore, if a degreased metal foil, such as a metal foil that has undergone an annealing process, is used as the barrier layer 13, it is not necessary to perform degreasing treatment again when forming the corrosion prevention treatment layer 14.

[0065] The coating agent used in the coating-type chemical conversion treatment preferably contains trivalent chromium. The coating agent may also contain at least one polymer selected from the group consisting of cationic polymers and anionic polymers, as described later.

[0066] In particular, in the hydrothermal alteration treatment and anodic oxidation treatment described above, the surface of the aluminum foil is dissolved by the treatment agent, forming aluminum compounds (boehmite, anodized aluminum) with excellent corrosion resistance. As a result, a co-continuous structure is formed from the barrier layer 13 using aluminum foil to the corrosion-preventive treatment layer 14, and therefore the above treatment is included in the definition of chemical conversion treatment. On the other hand, as will be described later, it is also possible to form the corrosion-preventive treatment layer 14 using only a pure coating method, which is not included in the definition of chemical conversion treatment. One example of this method is to use a sol of a rare earth element oxide such as cerium oxide with an average particle size of 100 nm or less, as it has a corrosion-preventive effect on aluminum (inhibitor effect) and is also environmentally suitable. By using this method, it is possible to impart a corrosion-preventive effect to metal foils such as aluminum foil even with a general coating method.

[0067] Examples of sols for the rare earth element oxides mentioned above include sols using various solvents such as aqueous, alcohol, hydrocarbon, ketone, ester, and ether systems. Among these, aqueous sols are preferred. In order to stabilize the dispersion of the rare earth element oxide sols, inorganic acids or their salts, such as nitric acid, hydrochloric acid, and phosphoric acid, or organic acids such as acetic acid, malic acid, ascorbic acid, and lactic acid are usually used as dispersion stabilizers. Of these dispersion stabilizers, phosphoric acid in particular is expected to provide the following benefits in the exterior material 10: (1) stabilization of sol dispersion, (2) improved adhesion with the barrier layer 13 by utilizing the aluminum chelating ability of phosphoric acid, and (3) improved cohesive force of the corrosion prevention treatment layer 14 (oxide layer) due to the ease with which dehydration condensation of phosphoric acid occurs even at low temperatures.

[0068] The corrosion-preventive treatment layer 14 formed by the above-mentioned rare earth element oxide sol is an aggregate of inorganic particles, and therefore, even after the drying and curing process, the cohesive force of the layer itself may decrease. Therefore, in this case, it is preferable that the corrosion-preventive treatment layer is compounded with the following anionic polymer or cationic polymer to compensate for the cohesive force.

[0069] The corrosion-preventive treatment layer is not limited to the layer described above. For example, it may be formed using a treatment agent that combines a resin binder (such as aminophenol) with phosphoric acid and a chromium compound, as is known from the application of chromate coatings. Using this treatment agent, a layer can be formed that possesses both corrosion-preventive properties and adhesion. Furthermore, although it is necessary to consider the stability of the coating liquid, a layer can be formed that possesses both corrosion-preventive properties and adhesion by using a coating agent that pre-mixes a rare earth element oxide sol with a cationic polymer or anionic polymer into a single liquefaction.

[0070] The mass per unit area of ​​the corrosion-preventive treatment layer is 0.005 to 0.200 g / m², regardless of whether it is a multilayer or single-layer structure. 2 Preferably, 0.010 to 0.100 g / m 2 A more preferable mass per unit area is 0.005 g / m². 2If the above is true, it is easier to impart corrosion prevention functionality to the barrier layer 13. Also, the above mass per unit area is 0.200 g / m². 2 Even if the thickness exceeds a certain limit, the corrosion prevention function does not change significantly. On the other hand, when using rare earth element oxide sols, if the coating film is thick, the heat during drying may result in insufficient curing, potentially leading to a decrease in cohesive force. The thickness of the corrosion prevention treatment layer 14 can be calculated from its specific gravity.

[0071] The corrosion-preventive treatment layer may, from the viewpoint of adhesion between the sealant layer and the barrier layer, for example, contain cerium oxide, 1 to 100 parts by mass of phosphoric acid or phosphate per 100 parts by mass of cerium oxide, and a cationic polymer; it may be formed by applying a chemical conversion treatment to the barrier layer 13; or it may be formed by applying a chemical conversion treatment to the barrier layer and also contain a cationic polymer.

[0072] (Second adhesive layer) The second adhesive layer 17 is a layer that bonds the barrier layer 13, on which the corrosion-preventive treatment layer 14 is formed, to the sealant layer 16. A general adhesive for bonding the barrier layer 13 and the sealant layer 16 can be used for the second adhesive layer 17.

[0073] If the corrosion-preventive treatment layer 14 has a layer containing at least one polymer selected from the group consisting of cationic polymers and anionic polymers described above, it is preferable that the second adhesive layer 17 is a layer containing a compound that is reactive with the polymer contained in the corrosion-preventive treatment layer 14 (hereinafter also referred to as "reactive compound").

[0074] For example, if the corrosion-preventive treatment layer 14 contains a cationic polymer, the second adhesive layer 17 contains a compound that is reactive with the cationic polymer. If the corrosion-preventive treatment layer 14 contains an anionic polymer, the second adhesive layer 17 contains a compound that is reactive with the anionic polymer. Furthermore, if the corrosion-preventive treatment layer 14 contains both a cationic polymer and an anionic polymer, the second adhesive layer 17 contains a compound that is reactive with the cationic polymer and a compound that is reactive with the anionic polymer. However, the second adhesive layer 17 does not necessarily have to contain the above two types of compounds, and may contain a compound that is reactive with both the cationic polymer and the anionic polymer. Here, "reactive" means forming a covalent bond with the cationic polymer or the anionic polymer. The second adhesive layer 17 may further contain an acid-modified polyolefin resin.

[0075] Compounds that react with cationic polymers include at least one compound selected from the group consisting of polyfunctional isocyanate compounds, glycidyl compounds, compounds having a carboxyl group, and compounds having an oxazoline group.

[0076] Examples of these polyfunctional isocyanate compounds, glycidyl compounds, compounds having a carboxyl group, and compounds having an oxazoline group include the polyfunctional isocyanate compounds, glycidyl compounds, compounds having a carboxyl group, and compounds having an oxazoline group that were previously exemplified as crosslinking agents for creating a crosslinked structure of cationic polymers. Among these, polyfunctional isocyanate compounds are preferred because they have high reactivity with cationic polymers and readily form crosslinked structures.

[0077] Compounds that react with anionic polymers include at least one compound selected from the group consisting of glycidyl compounds and compounds having an oxazoline group. Examples of these glycidyl compounds and compounds having an oxazoline group include the glycidyl compounds and compounds having an oxazoline group that were previously exemplified as crosslinking agents for creating a crosslinked structure of cationic polymers. Among these, glycidyl compounds are preferred due to their high reactivity with anionic polymers.

[0078] When the second adhesive layer 17 contains an acid-modified polyolefin resin, it is preferable that the reactive compound is also reactive with the acidic groups in the acid-modified polyolefin resin (i.e., forms a covalent bond with the acidic groups). This further improves adhesion to the corrosion-preventive treatment layer 14. In addition, the acid-modified polyolefin resin becomes a cross-linked structure, further improving the solvent resistance of the exterior material 10.

[0079] The content of the reactive compound is preferably equal to or 10 times the amount of the acidic groups in the acid-modified polyolefin resin. If the amount is equal to or greater than the amount, the reactive compound will react sufficiently with the acidic groups in the acid-modified polyolefin resin. On the other hand, if the amount exceeds 10 times the amount, the crosslinking reaction with the acid-modified polyolefin resin will be sufficiently saturated, and unreacted material will be present, raising concerns about a decrease in various performance characteristics. Therefore, for example, the content of the reactive compound is preferably 5 to 20 parts by mass (solid content ratio) per 100 parts by mass of the acid-modified polyolefin resin.

[0080] Acid-modified polyolefin resins are polyolefin resins into which acidic groups have been introduced. Examples of acidic groups include carboxyl groups, sulfonic acid groups, and acid anhydride groups, with maleic anhydride groups and (meth)acrylic acid groups being particularly preferred. As an acid-modified polyolefin resin, for example, the same type as the modified polyolefin resin used in the sealant layer 16 can be used.

[0081] The second adhesive layer 17 may contain various additives such as flame retardants, slip agents, antiblocking agents, antioxidants, light stabilizers, and tackifiers.

[0082] Examples of adhesives that form the second adhesive layer 17 include polyurethane resins obtained by reacting a difunctional or more isocyanate compound with a main component such as polyester polyol, polyether polyol, acrylic polyol, or carbonate polyol, and epoxy resins obtained by reacting an amine compound with a main component having epoxy groups, which are preferred from the viewpoint of heat resistance.

[0083] The thickness of the second adhesive layer 17 is not particularly limited, but from the viewpoint of obtaining the desired adhesive strength and processability, it is preferably 1 to 10 μm, and more preferably 2 to 7 μm.

[0084] [Metal terminal (terminal)] Of the pair of metal terminals 30, 30, one metal terminal 30 is electrically connected to the positive terminal of the energy storage device body 50, and the other metal terminal 30 is electrically connected to the negative terminal of the energy storage device body 50. The pair of metal terminals 30, 30 extend from the energy storage device body 50 to the outside of the exterior material 10. The shape of the pair of metal terminals 30, 30 can be, for example, a flat plate shape.

[0085] The material for the metal terminal 30 can be any metal. The metal used for the metal terminal 30 should be determined by considering the structure of the energy storage device body 50 and the materials of its components. For example, if the energy storage device 100 is an all-solid-state battery, aluminum can be used as the material for the metal terminal 30 connected to the positive electrode of the energy storage device body 50. For the metal terminal 30 connected to the negative electrode of the energy storage device body 50, copper with a nickel plating layer formed on its surface, or nickel can be used.

[0086] The thickness of the metal terminals 30 depends on the size and capacity of the battery. For small batteries, the thickness of the metal terminals 30 can be, for example, 50 μm or more. For large batteries such as those used for energy storage and automotive applications, the thickness of the metal terminals 30 can be appropriately set within a range of, for example, 100 to 500 μm.

[0087] [Resin film for terminals] The terminal resin film is a film used to cover a portion of the outer surface of a terminal in a power storage device that comprises a power storage device body and terminals electrically connected to the power storage device body.

[0088] The terminal resin film 40 is positioned to cover a portion of the outer surface of the metal terminal 30. Specifically, between the metal terminal 30 and the outer casing material 10, a portion of the outer surface of the metal terminal 30 is covered with the terminal resin film 40 by heat sealing. By positioning the terminal resin film 40 between the metal terminal 30 and the outer casing material 10, the sealing and insulating properties of the energy storage device 100 can be further enhanced. The terminal resin film 40 has heat resistance equivalent to or exceeding that of the sealant layer 16 and the base material layer 11 described above.

[0089] As the terminal resin film 40, for example, thermoplastic resins such as polyolefin, polyamide, polyester, polycarbonate, polyphenylene ether, polyacetal, polystyrene, polyvinyl chloride, and polyvinyl acetate can be used, and from the viewpoint of heat resistance and sealing suitability, polyolefin, polyamide, and polyester can be used.

[0090] Examples of polyolefin resins include low-density, medium-density, and high-density polyethylene; ethylene-α-olefin copolymers; polypropylene; and propylene-α-olefin copolymers. When polyolefin resins are copolymers, they may be block copolymers or random copolymers.

[0091] Examples of polyester resins include polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). These polyester resins may be used individually or in combination of two or more. Alternatively, a copolymer of any acid and glycol may be used.

[0092] Examples of polyamide resins include nylon 6 and nylon 6,6.

[0093] To impart sealing properties, heat resistance, and other functionalities, for example, antioxidants, slip agents, flame retardants, antiblocking agents, light stabilizers, dehydrating agents, tackifiers, nucleating agents, plasticizers, etc., may be added to the terminal resin film 40. For example, zinc oxide or cupric oxide may be added to the terminal resin film to impart hydrogen sulfide resistance, and zeolites may be added to impart moisture barrier properties.

[0094] The thickness of the terminal resin film 40 can be 25 μm or more from the viewpoint of sealing performance, and 500 μm or less from the viewpoint of productivity. From this viewpoint, the thickness of the terminal resin film 40 may be 50 to 300 μm, or 80 to 200 μm.

[0095] Although embodiments of this disclosure have been described in detail above, this disclosure is not limited to the embodiments described above, and various modifications and changes are possible within the scope of the gist of this disclosure as described in the claims. In the above embodiment, an example was given in which the corrosion-preventive treatment layer 14 is provided only on one surface of the barrier layer 13 (the side with the second adhesive layer 17). However, the corrosion-preventive treatment layer 14 may also be provided on the other surface of the barrier layer 13 (the side with the first adhesive layer 12). If the sealant layer 16 is attached to the barrier layer 13 by thermal lamination instead of dry lamination, the second adhesive layer 17 does not need to be provided. If the base material layer 11 is provided by coating, the first adhesive layer 12 does not need to be provided. In the above embodiment, a solid-state battery was exemplified as the energy storage device to which the exterior material 10 is applied, but the exterior material 10 may also be applied to other energy storage devices (for example, lithium-ion batteries). [Examples]

[0096] The present disclosure will be described in more detail below based on examples, but the present disclosure is not limited to the following examples.

[0097] [Materials used] • Substrate layer (thickness 25 μm): A polyethylene terephthalate film with corona treatment applied to one side was used. • First adhesive layer (thickness 4 μm): A polyurethane adhesive (manufactured by Toyo Ink Co., Ltd.) was used, which was a polyester polyol-based main component combined with a tolylene diisocyanate adduct-type curing agent. • Corrosion prevention treatment layer: The following solution was used. (CL-1): A "sodium polyphosphate stabilized cerium oxide sol" was used, which was prepared by adjusting the solid content to 10% by mass using distilled water as the solvent. The sodium polyphosphate stabilized cerium oxide sol was obtained by mixing 10 parts by mass of sodium phosphoric acid with 100 parts by mass of cerium oxide. (CL-2): A composition consisting of 90% by mass of "polyallylamine (manufactured by Nitto Boseki Co., Ltd.)" and 10% by mass of "polyglycerol polyglycidyl ether (manufactured by Nagase ChemteX Corporation)" was used, adjusted to a solid content concentration of 5% by mass using distilled water as a solvent. • Barrier layer (40 μm thick): Made of annealed and degreased soft aluminum foil (Toyo Aluminum Co., Ltd., "8079 material"). • The second adhesive layer (thickness 3 μm) used an epoxy adhesive prepared by diluting a mixture of 100 parts by mass of epoxy resin (Adeka Corporation, product name: EP4100) and 25 parts by mass of polyamidoamine-based curing agent (Adeka Corporation, product name: EH4602) with ethyl acetate to a solid content of 30% by mass. • Sealant layer (thickness of layer (1) 53.3 μm, thickness of layer (2) 26.7 μm, total thickness 80 μm): The base resin and nucleating agent shown in Table 1 were prepared. The nucleating agent was added to the base resin according to Tables 2 and 3 and mixed by dry blending (the mixing ratios in the tables are in "mass %"). A sealant layer was formed using this mixture (sealant layer forming material). The layer (2) side was designated as the barrier layer side.

[0098] [Table 1]

[0099] [Manufacturing of exterior materials] (Example 1) Apply (CL-1) to both surfaces of the barrier layer at a dry application rate of 70 mg / m². 2 The material was coated using microgravure coating and then baked in a drying unit at 200°C. Next, (CL-2) was applied to the resulting layer at a dry coating rate of 20 mg / m². 2 By applying a microgravure coating in this manner, a composite layer consisting of (CL-1) and (CL-2) was formed as a corrosion-preventive treatment layer. This composite layer exhibits corrosion-preventive performance by combining the two types, (CL-1) and (CL-2). A barrier layer with a corrosion-preventive treatment layer was bonded to a substrate layer using a polyurethane adhesive (first adhesive layer) via a dry lamination method. The lamination of the barrier layer and the substrate layer was performed by applying a polyurethane adhesive to one surface of the barrier layer to a cured thickness of 4 μm, drying it at 80°C for 1 minute, laminating it with the substrate layer, and aging it at 60°C for 5 days. The sealant layer was laminated on the opposite side of the barrier layer from the substrate layer by thermal lamination using a T-die method while applying a temperature of 270°C to the sealant layer forming material. Using the method described above, an exterior material (a laminate consisting of a base layer, a first adhesive layer, a corrosion-preventive treatment layer, a barrier layer, a corrosion-preventive treatment layer, and a sealant layer) was fabricated.

[0100] (Examples 2-9) Except for changing the layer structure of the sealant layer as shown in Table 2, the exterior material was manufactured in the same manner as in Example 1.

[0101] (Example 10) Except for changing the method of laminating the sealant layer from heat lamination to dry lamination, the exterior material was manufactured in the same manner as in Example 1. Specifically, the side of the barrier layer opposite the substrate layer was bonded to the sealant layer using an epoxy adhesive (second adhesive layer) via a dry lamination method. The sealant layer was prepared in advance using the T-die method as shown in Table 2. Lamination of the barrier layer and the sealant layer was performed by applying epoxy adhesive to the side of the barrier layer opposite the substrate layer so that the cured thickness would be 3 μm, drying at 80°C for 1 minute, laminating with the sealant layer, and aging at 120°C for 3 hours. Using the method described above, an exterior material (a laminate consisting of a base layer, a first adhesive layer, a corrosion-preventive treatment layer, a barrier layer, a corrosion-preventive treatment layer, a second adhesive layer, and a sealant layer) was fabricated.

[0102] (Examples 11-12) Except for changing the layer structure of the sealant layer as shown in Table 2, the exterior material was manufactured in the same manner as in Example 10.

[0103] (Comparative Examples 1-4) Except for changing the layer structure of the sealant layer as shown in Table 3, the exterior material was manufactured in the same manner as in Example 1.

[0104] (Comparative Example 5) Except for changing the layer structure of the sealant layer as shown in Table 3, the exterior material was manufactured in the same manner as in Example 10.

[0105] [Measurement of crystallinity after heat sealing] Two exterior materials were prepared and stacked so that the sealant layers faced each other. They were then heat-sealed at 290°C, 0.5 MPa for 15 seconds with a seal width of 5 mm. After that, they were cooled to 25°C at a rate of 50°C / min. A cross-section of the heat-sealed area was cut out, and the degree of crystallinity of each layer in the sealant was measured using wide-angle X-ray diffraction. The conditions for wide-angle X-ray diffraction were as follows: Filter: Ni (under Cu-Kα line) Output: 40kV, 40mA Analysis: Calculated from diffraction peaks on the α-crystal (040, 060, 110, 130) plane and the β-crystal (300) plane. The measurement conditions for each degree of crystallinity in the table were as follows. • β-crystallinity: Measured at 25°C after heat sealing. • β / α: Measured at 25°C after heat sealing. • α-crystallinity, β / α: Measured at 25°C after being left to stand for one week in a 150°C environment after heat sealing.

[0106] [Table 2]

[0107] [Table 3]

[0108] [Measurement of heat seal strength at room temperature] A sample of the exterior material, cut to 60mm x 120mm, was folded in half, and one side was heat-sealed with a 10mm wide sealing bar at 290°C, 0.5MPa, and for 15 seconds. After heat sealing, the exterior material was aged at 150°C for 60 minutes, then cooled to room temperature. The heat-sealed area was cut to a width of 15mm (see Figure 4), and the seal strength (T-type peel strength) was measured using a testing machine (INSTRON). The test was conducted in accordance with JIS K6854, at 25°C, 50%RH atmosphere, and a peeling speed of 50mm / min. Based on the measured seal strength (burst strength) value, it was evaluated according to the following criteria. A result of C or higher was considered a pass. A: Seal strength of 90N / 15mm or more B: Seal strength of 80N / 15mm or more, and less than 90N / 15mm C: Seal strength of 70N / 15mm or more, and less than 80N / 15mm D: Seal strength less than 70N / 15mm

[0109] [Measurement of high-temperature heat seal strength] A sample of the exterior material, cut to 60mm x 120mm, was folded in half, and one side was heat-sealed with a 10mm wide sealing bar at 290°C, 0.5MPa, and for 15 seconds. The heat-sealed area was then cut to a width of 15mm (see Figure 4), left to stand for 5 minutes at 150°C, and the seal strength (T-type peel strength) was measured at 150°C with a peeling speed of 50mm / min using a testing machine (INSTRON). The measured seal strength (burst strength) was evaluated based on the following criteria. A result of C or higher was considered acceptable. A: Seal strength of 35N / 15mm or more B: Seal strength of 30N / 15mm or more, and less than 35N / 15mm C: Seal strength of 20N / 15mm or more, and less than 30N / 15mm. D: Seal strength less than 20N / 15mm

[0110] [Table 4]

[0111] [Determining the suitability of the polypropylene layer] DSC measurements were performed on some sealant layers under the following conditions to confirm whether the layers had a melting main peak at 160-170°C in the first run and a melting main peak at 140-160°C in the second run. The melting main peaks are shown in Table 5. In light of the results in Table 4, it can be seen that such polypropylene layers can be suitably used as sealant layers. <Measurement conditions> 1st run: Heating from 25℃ to 290℃ (rate: 1.5℃ / min, hold: 290℃-10min), cooling from 290℃ to 25℃ (1.5℃ / min, 25℃-10min) 2nd run: Heating from 25℃ to 290℃ (150℃ / min, 290℃-10min)

[0112] [Table 5] [Explanation of symbols]

[0113] 10...Exterior material for energy storage device, 11...Base material layer, 12...First adhesive layer, 13...Barrier layer, 14...Corrosion prevention treatment layer, 16...Sealant layer, 17...Second adhesive layer, 30...Metal terminal, 40...Resin film for terminal, 50...Energy storage device body, 100...Energy storage device, H...Heat seal section.

Claims

1. The substrate layer, barrier layer, and sealant layer are provided in this order. The sealant layer includes a polypropylene layer P formed from a resin composition containing polypropylene and a β-nucleating agent. An exterior material for an energy storage device having a heat-sealed portion obtained by heat-sealing the end of the exterior material for the energy storage device, which is left standing at 150°C for one week and then cooled to 25°C, wherein the crystallinity of the α crystal of the polypropylene layer P in the heat-sealed portion is 25% or more, and the crystallinity ratio (β / α) is 0 to 1.

2. The exterior material for an energy storage device according to claim 1, wherein the content of the β-nucleating agent is 0.001 to 15% by mass, based on the total amount of the resin composition.

3. The exterior material for an energy storage device according to claim 1 or 2, wherein the β-nucleating agent is an amide compound.

4. The exterior material for an energy storage device according to any one of claims 1 to 3, wherein the sealant layer comprises two or more polypropylene layers, and at least one of them is the polypropylene layer P.

5. The exterior material for an energy storage device according to any one of claims 1 to 4, wherein the sealant layer comprises two or more polypropylene layers, and at least one of these layers on the barrier layer side is the polypropylene layer P.

6. The exterior material for an energy storage device according to any one of claims 1 to 5, wherein the polypropylene layer P includes acid-modified polypropylene.

7. The exterior material for an energy storage device according to any one of claims 1 to 6, wherein the sealant layer comprises two or more polypropylene layers, and at least one of these layers comprises long-chain branched polypropylene.

8. An exterior material for an energy storage device according to any one of claims 1 to 7, which is for an all-solid-state battery.

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