Sealing film, electrode lead wire member and battery

Abstract

To provide a sealing film, an electrode lead wire member and a battery, which enable the suppression of resin degradation, and are hard to cause delamination.SOLUTION: A sealing film 1 is arranged for sealing between a first base of metal and a second base. The sealing film 1 comprises: a first adhesive layer 2; a second adhesive layer 3; and a base material layer 4. The first adhesive layer 2 contains an acid-modified polyolefin mainly, and it adheres to the first base. The second adhesive layer 3 contains a polyolefin mainly, and it adheres to the second base. The base material layer 4 is provided between the first adhesive layer 2 and the second adhesive layer 3. To at least one of the first adhesive layer 2, the second adhesive layer 3 and the base material layer 4, at least a phenol-based antioxidant, a phosphorus-based antioxidant and a sulfur-based antioxidant are added. In the whole sealing film 1, the total addition amount of the phenol-based antioxidant, the phosphorus-based antioxidant and the sulfur-based antioxidant is 0.4 mass% or more and 0.75 mass% or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a sealing film, an electrode lead member, and a battery. [Background technology]

[0002] In recent years, secondary batteries such as lithium ion batteries and capacitors have been attracting attention as storage batteries for storing electric energy. The battery includes, for example, a battery body, a container for housing the battery body, and an electrode lead wire connected to the battery body. The container is made of a laminate for battery exterior that has excellent waterproof and light-shielding properties. The laminate for battery exterior is, for example, a laminate in which a base layer made of polyamide or the like and aluminum foil are laminated. The electrode lead wire is sealed in the container with a portion including one end pulled out from the container to the outside.

[0003] It has been proposed to interpose a sealing film between the container and the electrode lead wire in the battery (see, for example, Patent Document 1). The film (hereinafter, referred to as sealing film) seals the gap between the electrode lead wire and the container. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6596869 Summary of the Invention [Problem to be solved by the invention]

[0005] The resin of the sealing film may deteriorate (e.g., become embrittled), resulting in a decrease in adhesive strength. In addition, the sealing film is required to suppress delamination in order to prevent liquid leakage from the container.

[0006] An object of one aspect of the present invention is to provide a sealing film, an electrode lead wire member, and a battery that can suppress deterioration of a resin and are less likely to cause delamination. [Means for solving the problem]

[0007] In order to solve the above problems, one aspect of the present invention includes the following aspects.

[0008] [1] A sealing film for sealing between a first substrate and a second substrate made of metal, the sealing film comprising: a first adhesive layer mainly containing an acid-modified polyolefin and adhering to the first substrate; a second adhesive layer mainly containing a polyolefin and adhering to the second substrate; and a base layer provided between the first adhesive layer and the second adhesive layer, wherein at least a phenol-based antioxidant, a phosphorus-based antioxidant, and a sulfur-based antioxidant are added to at least one of the first adhesive layer, the second adhesive layer, and the base layer, and the total amount of the phenol-based antioxidant, the phosphorus-based antioxidant, and the sulfur-based antioxidant added to the entire sealing film is 0.4 mass% or more and 0.75 mass% or less.

[0009] [2] The sealing film according to [1], wherein the base layer mainly contains polyolefin.

[0010] [3] The sealing film described in [1] or [2], wherein the acid-modified polyolefin constituting the first adhesive layer is acid-modified polypropylene, the polyolefin constituting the second adhesive layer is polypropylene, and the base material layer mainly contains polyolefin.

[0011] [4] An electrode lead member comprising: the sealing film according to any one of [1] to [3]; and the first base which is an electrode lead extending in one direction.

[0012] [5] A battery comprising the electrode lead member according to [4], a battery body to which the electrode lead is connected, and the second base which is a container for accommodating the battery body. Effect of the Invention

[0013] According to one aspect of the present invention, it is possible to provide a sealing film, an electrode lead wire member, and a battery in which deterioration of a resin can be suppressed and delamination is unlikely to occur. [Brief description of the drawings]

[0014] [Figure 1] FIG. 2 is a schematic cross-sectional view showing a sealing film of an embodiment. [Diagram 2] FIG. 2 is a schematic perspective view showing an electrode lead wire member of the embodiment. [Diagram 3] 1 is a schematic perspective view showing a battery according to an embodiment. [Figure 4] 4 is a cross-sectional view taken along line II in FIG. 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, a sealing film, an electrode lead member, and a battery according to an embodiment will be described with reference to Figures 1 to 4. Note that in the drawings, the dimensions and ratios of components may differ from the actual ones.

[0016] <Sealing film> Fig. 1 is a schematic cross-sectional view showing a sealing film 1 of an embodiment. Fig. 2 is a schematic perspective view showing an electrode lead member 10 of an embodiment.

[0017] 2, the electrode lead member 10 includes an electrode lead 11 and a sealing film 1. The electrode lead 11 is an example of a "first base." As shown in FIG. 1, the sealing film 1 includes a first adhesive layer 2, a second adhesive layer 3, and a base layer 4.

[0018] [First adhesive layer] The first adhesive layer 2 is a layer that is fused (adhered) to the electrode lead wire 11 (see FIG. 2) by application of heat and pressure. The surface of the first adhesive layer 2 is one surface 1a of the sealing film 1. The first adhesive layer 2 is made of, for example, a resin (or a resin composition).

[0019] The first adhesive layer 2 mainly contains an acid-modified polyolefin. The first adhesive layer 2 "mainly contains an acid-modified polyolefin" means that the content of the acid-modified polyolefin is the highest among the resins constituting the first adhesive layer 2. The first adhesive layer 2 contains 50% by mass or more of the acid-modified polyolefin relative to the total amount of the first adhesive layer 2, preferably more than 50% by mass, and more preferably 80% by mass or more.

[0020] Examples of polyolefins constituting the first adhesive layer 2 include polypropylene, polyethylene, poly-1-butene, and polyisobutylene. Among them, polypropylene is preferable as the polyolefin constituting the first adhesive layer 2 because of its excellent flexibility. Hereinafter, polypropylene may be abbreviated as "PP".

[0021] The polyolefin may be a copolymer of propylene and ethylene (propylene-ethylene copolymer). The copolymer of propylene and ethylene may be a block copolymer or a random copolymer, but a random copolymer is preferred. The polyolefin may be a copolymer of propylene and an olefin monomer. Examples of the olefin monomer include 1-butene, isobutylene, and 1-hexene.

[0022] The acid-modified polyolefin is a polyolefin resin modified with an unsaturated carboxylic acid or a derivative of an unsaturated carboxylic acid. The acid-modified polyolefin has an acid functional group such as a carboxy group or an anhydrous carboxylic acid group in its molecular structure. The acid-modified polyolefin is obtained by graft-polymerizing an unsaturated carboxylic acid or a derivative of an unsaturated carboxylic acid to a polyolefin, or by copolymerizing an acid functional group-containing monomer with an olefin. That is, in the acid-modified polyolefin, the repeating unit having an acid group may be included in a side chain or may be included in a main chain.

[0023] Examples of the unsaturated carboxylic acid include acrylic acid and methacrylic acid. Examples of the derivatives of unsaturated carboxylic acids include unsaturated carboxylic acid esters such as ethyl acrylate, and acid anhydrides of unsaturated carboxylic acids such as maleic anhydride. The use of an acid-modified polyolefin can enhance the adhesion of the first adhesive layer 2 to the electrode lead wire 11 (see FIG. 2).

[0024] As the acid-modified polyolefin, acid-modified polypropylene (acid-modified PP) is preferable because of its excellent heat resistance. Acid-modified PP is, for example, a polymer obtained by graft-copolymerizing an unsaturated carboxylic acid or a derivative of an unsaturated carboxylic acid with polypropylene or a propylene-ethylene copolymer.

[0025] Acid-modified PP includes ionomers in which the carboxyl acid groups of an acid-modified polymer of polypropylene or an acid-modified polymer of a propylene-ethylene copolymer have been neutralized with a metal hydroxide, an alkoxide, a salt of a lower fatty acid, or the like. The acid group of the acid-modified PP is preferably a maleic anhydride group, that is, the acid-modified PP is preferably maleic anhydride-modified PP.

[0026] The melting point of the resin (or resin composition) constituting the first adhesive layer 2 is preferably 110°C or higher and 150°C or lower. If the melting point of the resin constituting the first adhesive layer 2 is 110° C. or higher, the first adhesive layer 2 is unlikely to become excessively thin during thermocompression bonding, and adhesive strength is easily ensured. If the melting point of the resin constituting the first adhesive layer 2 is 150° C. or lower, the resin is likely to flow during thermocompression bonding, so that the resin can sufficiently wrap around the electrode lead wire 11 and easily seal the entire circumference of the electrode lead wire 11.

[0027] When the "resin constituting the first adhesive layer 2" is a polymer alloy of two or more types of resin, the "melting point of the resin constituting the first adhesive layer 2" means the melting point of the polymer alloy constituting the first adhesive layer 2.

[0028] In the first adhesive layer 2, optional components other than the polyolefin include known additives such as stabilizers, antistatic agents, and colorants.

[0029] The thickness of the first adhesive layer 2 can be, for example, 25 to 70% relative to the total thickness of the sealing film 1, which is taken as 100. That is, the thickness of the first adhesive layer 2 can be 25% to 70% relative to the total thickness of the sealing film 1. The ratio of layer thicknesses when the total thickness of the sealing film 1 is taken as 100 is referred to as the "thickness ratio."

[0030] When the thickness ratio of the first adhesive layer 2 is 25 or more, the adhesive strength between the first adhesive layer 2 and the electrode lead wire 11 can be sufficiently ensured. When the thickness ratio of the first adhesive layer 2 is 70 or less, the second adhesive layer 3 and the base material layer 4 can be given a sufficient thickness. Therefore, the adhesive strength between the second adhesive layer 3 and the storage container can be increased without decreasing the electrolyte resistance of the sealing film 1. Note that "electrolyte resistance" refers to resistance to an electrolyte.

[0031] [Second adhesive layer] The second adhesive layer 3 is, for example, a layer that is fused (adhered) to a storage container by heating and pressurization. The storage container will be described later. The surface of the second adhesive layer 3 is the other surface 1b of the sealing film 1. The second adhesive layer 3 is composed of, for example, a resin (or a resin composition).

[0032] The second adhesive layer 3 mainly contains polyolefin. The second adhesive layer 3 "mainly contains polyolefin" means that the polyolefin content is the highest among the resins constituting the second adhesive layer 3. The second adhesive layer 3 contains 50 mass% or more of polyolefin relative to the total amount of the second adhesive layer 3, preferably more than 50 mass%, and more preferably 80 mass% or more.

[0033] Examples of polyolefins constituting the second adhesive layer 3 include polypropylene (PP), polyethylene, poly-1-butene, polyisobutylene, etc. Among these, PP is preferable as the polyolefin constituting the second adhesive layer 3 because of its excellent flexibility. The polyolefin may be a copolymer of propylene and ethylene (propylene-ethylene copolymer). The copolymer of propylene and ethylene may be a block copolymer or a random copolymer, with the random copolymer being preferred. The polyolefin may be a copolymer of propylene and an olefin monomer (for example, a random copolymer). Examples of the olefin monomer include 1-butene, isobutylene, and 1-hexene.

[0034] The polyolefin constituting the second adhesive layer 3 may be an acid-modified polyolefin. As the acid-modified polyolefin, acid-modified PP is preferable because it has excellent heat resistance. As the acid-modified PP, the acid-modified PP exemplified as the material of the first adhesive layer 2 is preferably used. As the acid-modified PP, a polymer obtained by acid-modifying a random copolymer of propylene and ethylene is preferable because it has excellent flexibility. By using the acid-modified polyolefin, the adhesion of the second adhesive layer 3 to the container can be increased.

[0035] The second adhesive layer 3 may contain both acid-modified PP and acid-modified polyethylene. When the second adhesive layer 3 contains both acid-modified PP and acid-modified polyethylene, the melting point of the second adhesive layer 3 can be lowered and the heating temperature when fusing the second adhesive layer 3 can be lowered, so that deterioration of the first adhesive layer 2 can be suppressed.

[0036] The melting point of the resin (or resin composition) constituting the second adhesive layer 3 is preferably 110°C or higher and 150°C or lower. If the melting point of the resin constituting the second adhesive layer 3 is 110° C. or higher, the second adhesive layer 3 is unlikely to become excessively thin during thermocompression bonding, and adhesive strength is easily ensured. If the melting point of the resin constituting the second adhesive layer 3 is 150° C. or lower, the resin is likely to flow during thermocompression bonding, making it easy to seal the gap between the container and the electrode lead wire 11.

[0037] When the "resin constituting the second adhesive layer 3" is a polymer alloy of two or more types of resin, the "melting point of the resin constituting the second adhesive layer 3" means the melting point of the polymer alloy constituting the second adhesive layer 3.

[0038] In the second adhesive layer 3, optional components other than the acid-modified polyolefin include known additives such as stabilizers, antistatic agents, and colorants.

[0039] The thickness (thickness ratio) of the second adhesive layer 3 can be, for example, 5 to 50, with the total thickness of the sealing film 1 being 100. That is, the thickness of the second adhesive layer 3 can be 5% to 50% of the total thickness of the sealing film 1.

[0040] When the thickness ratio of the second adhesive layer 3 is 5 or more, the adhesive strength between the second adhesive layer 3 and the container can be sufficiently ensured. When the thickness ratio of the second adhesive layer 3 is 50 or less, the first adhesive layer 2 and the base material layer 4 can be given a sufficient thickness. Therefore, the adhesive strength between the first adhesive layer 2 and the electrode lead wire 11 can be increased without decreasing the electrolyte resistance of the sealing film 1.

[0041] [Base material layer] The base material layer 4 is provided between the first adhesive layer 2 and the second adhesive layer 3. The base material layer 4 is made of, for example, a resin (or a resin composition).

[0042] The base layer 4 mainly contains polyolefin, for example. The base layer 4 "mainly contains polyolefin" means that the content of polyolefin is the highest among the resins constituting the base layer 4. The base layer 4 contains 50 mass % or more of polyolefin based on the total amount of the base layer 4, preferably more than 50 mass %, and more preferably 80 mass % or more.

[0043] Examples of polyolefins constituting the base layer 4 include polypropylene (PP), polyethylene, poly-1-butene, polyisobutylene, etc. Among these, PP is preferable because of its excellent flexibility.

[0044] The polyolefin constituting the base layer 4 may be a homopolymer of one type of olefin or a copolymer of two or more types of olefin. An example of the homopolymer is a homopolymer of propylene only (homo PP). An example of the copolymer is a copolymer of propylene and an olefin monomer (ethylene, 1-butene, isobutylene, 1-hexene, etc.), such as a propylene-ethylene copolymer. As the polyolefin constituting the base layer 4, the polymers exemplified as the polyolefin constituting the first adhesive layer 2 can be exemplified.

[0045] The polyolefin constituting the base layer 4 is preferably an ICP (impact copolymer). The ICP has a phase-separated structure having a first phase and a second phase, for example, an island-in-a-sea structure. The island-in-a-sea structure is a structure in which a plurality of second phases corresponding to "islands" are dispersed in the first phase corresponding to the "sea."

[0046] The first phase is composed of a homopolymer of an olefin monomer such as propylene or ethylene. The second phase is composed of a polymer different from the homopolymer that constitutes the first phase. The second phase contains a polymer of an olefin monomer such as propylene or ethylene, for example, ethylene propylene rubber (EPR). The second phase is composed of a main phase and a surface layer that covers the surface of the main phase. The main phase is composed of polyethylene, for example. The surface layer is composed of EPR, for example.

[0047] An ICP in which the homopolymer constituting the first phase is homo-PP is called a polypropylene ICP or polypropylene dispersion. An ICP in which the homopolymer constituting the first phase is homo-PP is called a block PP. ICPs are also called heterophasic copolymers or block copolymers.

[0048] The material of the base layer is not particularly limited, and resins other than polyolefin (for example, fluororesins such as polychlorotrifluoroethylene) may be used.

[0049] The thickness (thickness ratio) of the base material layer 4 can be, for example, 25 to 70, with the total thickness of the sealing film 1 being 100. That is, the thickness of the base material layer 4 can be 25% to 70% of the total thickness of the sealing film 1. When the thickness ratio of the base material layer 4 is 25 or more, it is possible to improve the electrolyte resistance and heat resistance of the sealing film 1. When the thickness ratio of the base material layer 4 is 25 or more, the resin does not tend to flow excessively, and tends to exhibit the necessary fluidity during compression bonding.

[0050] When the thickness ratio of the base layer 4 is 70 or less, a sufficient thickness can be imparted to the first adhesive layer 2 and the second adhesive layer 3. Therefore, it is possible to increase the adhesive strength between the first adhesive layer 2 and the electrode lead wire 11, and the adhesive strength between the second adhesive layer 3 and the container. When the thickness ratio of the base layer 4 is 70 or less, it is possible to increase the fluidity of the resin during thermocompression bonding to an appropriate range. Therefore, the resin sufficiently wraps around the electrode lead wire 11, reliably sealing the entire circumference of the electrode lead wire 11.

[0051] The melting point of the resin (or resin composition) constituting the base layer 4 is preferably 150°C or higher and 170°C or lower. When the melting point of the resin constituting the base layer 4 is 150° C. or higher, it is easy to ensure the electrolyte resistance of the sealing film 1. In addition, the sealing film 1 can be provided with heat resistance. When the melting point of the resin constituting the base layer 4 is 170° C. or lower, flexibility can be imparted to the sealing film 1. Therefore, gaps are less likely to occur between the sealing film 1 and the electrode lead wires 11 and the container.

[0052] The melting point M4 of the resin constituting the base layer 4 is preferably higher than the melting point M2 of the resin constituting the first adhesive layer 2 or the melting point M3 of the resin constituting the second adhesive layer 3. That is, the melting point M4 is preferably higher than the melting point M2 or the melting point M3. It is preferable that the melting point M4 is higher than both the melting point M2 and the melting point M3. In other words, it is preferable that the melting point M4 is higher than at least one of the melting point M2 and the melting point M3.

[0053] When the melting point M4 is higher than the melting point M2, it becomes easier to ensure the electrolyte resistance of the sealing film 1 without reducing the adhesive strength between the first adhesive layer 2 and the electrode lead wire 11. In addition, the fluidity of the resin during thermocompression bonding can be kept within an appropriate range. When the melting point M4 is higher than the melting point M3, it is easy to ensure the electrolyte resistance of the sealing film 1 without reducing the adhesive strength between the second adhesive layer 3 and the storage container. In addition, the fluidity of the resin during thermocompression bonding can be set within an appropriate range. If the melting point M4 is higher than the melting point M2 or the melting point M3, there is an advantage that the encapsulating film 1 can be easily imparted with heat resistance.

[0054] [Antioxidants] At least a phenol-based antioxidant, a phosphorus-based antioxidant, and a sulfur-based antioxidant are added to at least one of the first adhesive layer 2, the second adhesive layer 3, and the base layer 4. The layers to which these antioxidants are added may be one, two, or all of the first adhesive layer 2, the second adhesive layer 3, and the base layer 4. In particular, it is preferable that the above-mentioned three types of antioxidants are added to all of the first adhesive layer 2, the second adhesive layer 3, and the base layer 4.

[0055] In addition to the above-mentioned three types of antioxidants (phenol-based antioxidant, phosphorus-based antioxidant, and sulfur-based antioxidant), other antioxidants (for example, amine-based antioxidants) may be added to the sealing film.

[0056] Radicals can be generated in resins due to heat, light, etc., and if the generated radicals are left alone, cross-linking degradation or oxidative degradation due to autoxidation reactions can occur. For example, autoxidation reactions begin when oxygen is added to a polymer radical generated in a resin to generate a polymer peroxy radical (POO·). Autoxidation reactions proceed when hydroperoxides (POOH), generated by a hydrogen abstraction reaction from a polymer peroxy radical (POO·), decompose to generate oxy radicals (PO·) and peroxy radicals.

[0057] Phenolic antioxidants donate hydrogen to peroxy radicals and the like generated in autoxidation reactions, and at the same time, they themselves change into stable radicals, terminating the chain reaction of the autoxidation reaction. This reaction is a radical-scavenging reaction. As a result, phenolic antioxidants suppress crosslinking and oxidative degradation of resins. Because of this action, phenolic antioxidants can be called "primary antioxidants," "radical scavengers," or "radical chain inhibitors."

[0058] The phenol-based antioxidants include hindered phenol-based and semi-hindered phenol-based antioxidants, etc. Examples of the phenol-based antioxidants include monophenol-based, bisphenol-based, trisphenol-based, and tetrakisphenol-based antioxidants.

[0059] Examples of monophenol-based antioxidants include 2,6-t-butylphenol, 2-t-butyl-4-methoxyphenol, 3-t-butyl-4-methoxyphenol, 2,4-dimethyl-6-t-butylphenol, 2,6-di-t-butyl-p-cresol, 2,6-di-t-butyl-4-ethylphenol, n-octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, and methylhydroquinone.

[0060] Examples of bisphenol-based antioxidants include 2,2'-methylenebis(4-methyl-6-t-butylphenol), 2,2'-methylenebis(4-ethyl-6-t-butylphenol), 4,4'-thiobis(3-methyl-6-t-butylphenol), 4,4'-butylidenebis(3-methyl-6-t-butylphenol), 3,9-bis[1,1-dimethyl-2-[β-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]ethyl]2,4,8,10-tetraoxaspiro[5.5]undecane, and 2,2'-dihydroxy-3,3'-di(α-methylcyclohexyl)-5,5'-dimethyldiphenylmethane.

[0061] Examples of trisphenol-based antioxidants include 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane and 1,3,5-trimethyl-2,4,6-tris(3,5-t-butyl-4-hydroxybenzyl)benzene.

[0062] Examples of the tetrakisphenol-based antioxidant include tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane, tetrakis-[ethylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane, and pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate).

[0063] The phenol-based antioxidant is preferably a tetrakisphenol-based antioxidant. The tetrakisphenol-based antioxidant (especially pentaerythritol tetrakis [3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate]) has the effect of increasing the heat resistance of the sealing film 1. A suitable commercially available product of pentaerythritol tetrakis [3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate] is "Irganox 1010" manufactured by BASF.

[0064] Phosphorus-based antioxidants suppress the oxidation of resins by decomposing the peroxides (hydroperoxides) generated in the autoxidation reaction described above and converting them into stable alcohols. Because phosphorus-based antioxidants have this effect, they can be called "secondary antioxidants" or "peroxide decomposers."

[0065] The phosphorus-based antioxidant has, for example, a phosphate ester structure or a phosphite ester structure. Examples of phosphorus-based antioxidants include triphenyl phosphite, diphenyl isodecyl phosphite, phenyl diisodecyl phosphite, 4,4'-butylidene-bis(3-methyl-6-t-butylphenyl ditridecyl)phosphite, cyclic neopentane tetrayl bis(octadecyl phosphite), tris(nonylphenyl)phosphite, tris(2,4-di-t-butylphenyl)phosphite, cyclic neopentane tetrayl bis(2,6-di-t-butyl-4-methylphenyl)phosphite, and 2,2-methylene bis(4,6-di-t-butylphenyl)octyl phosphite.

[0066] As the phosphorus-based antioxidant, a compound having a phosphite structure, particularly tris(2,4-di-t-butylphenyl)phosphite, is preferred. Tris(2,4-di-t-butylphenyl)phosphite has excellent hydrolysis resistance. A suitable commercially available product of tris(2,4-di-t-butylphenyl)phosphite is "Irgafos168" manufactured by BASF.

[0067] Similar to phosphorus-based antioxidants, sulfur-based antioxidants act as secondary antioxidants (peroxide decomposers). Although sulfur-based antioxidants have a slower reaction rate of the above-mentioned peroxide decomposition reaction compared to phosphorus-based antioxidants, they are characterized in that they tend to accelerate the peroxide decomposition reaction when used in combination with phenol-based antioxidants. For example, sulfur-based antioxidants have a higher synergistic effect (effect obtained when used in combination with phenol-based antioxidants) in suppressing oxidation deterioration (thermooxidative deterioration) at high temperatures when used in combination with phenol-based antioxidants compared to phosphorus-based antioxidants. Since sulfur-based antioxidants differ from phosphorus-based antioxidants in this respect, they can also be called "tertiary antioxidants." Furthermore, since the sulfur-based antioxidant has a slow reaction rate of the above-mentioned peroxide decomposition reaction, the oxidation suppression effect is sustained for a long period of time even at low temperatures in the presence of a phenol-based antioxidant.

[0068] Sulfur-based antioxidants include dilauryl-3,3'-thiodipropionic acid, dimyristyl-3,3'-thiodipropionate, distearyl-3,3'-thiodipropionate, pentaerythritol-tetrakis-(β-laurylthiopropionate), bis-2-methyl-4-(3-n-alkylthiopropionyloxy)-5-tert-butylphenyl sulfide, and 2-1-mercaptobenzoimidazoline. sol, 4,6-bis(octylthiomethyl)-o-cresol, didodecyl-3,3'-thiodipropionate, 2,2-bis[[3-(dodecylthio)-1-oxopropoxy]methyl}propane-1,3-diyl bis[3-(dodecylthio)propionate], and the like.

[0069] Among them, thioether-based antioxidants, especially 2,2-bis[[3-(dodecylthio)propionic acid]2,2-bis[[3-(dodecylthio)-1-oxopropyloxy]methyl]-1,3-propanediyl, have a high synergistic effect (effect obtained when used in combination with a phenol-based antioxidant) in suppressing oxidation deterioration (thermooxidative deterioration) at high temperatures, and therefore can increase the heat resistance of the encapsulating film 1 for a long period of time.

[0070] The total amount (content) of the phenol-based antioxidant, the phosphorus-based antioxidant, and the sulfur-based antioxidant in the entire sealing film 1 is 0.4 mass % or more and 0.75 mass % or less. When the total amount is 0.4% by mass or more, it is possible to suppress deterioration (eg, embrittlement) of the resin of the sealing film 1. When the total amount is 0.75% by mass or less, it is possible to make interlayer peeling less likely to occur.

[0071] The addition amount of the antioxidant in each layer (the first adhesive layer 2, the second adhesive layer 3, and the base material layer 4) constituting the sealing film 1 is not particularly limited as long as the addition amount of the antioxidant in the entire sealing film 1 is within the aforementioned range (0.4% by mass or more and 0.75% by mass or less). The addition amount of the antioxidant in the first adhesive layer 2 may be, for example, 0.25% by mass or more and 1.0% by mass or less. The addition amount of the antioxidant in the second adhesive layer 3 may be, for example, 0.25% by mass or more and 1.0% by mass or less. The addition amount of the antioxidant in the base material layer 4 may be, for example, 0.25% by mass or more and 1.0% by mass or less.

[0072] The total addition amount of the three types of antioxidants in the base material layer 4 may be set lower than the total addition amount of the three types of antioxidants in the first adhesive layer 2 or the second adhesive layer 3. For example, the total addition amount A4 of the antioxidant in the base material layer 4 may be 0.25% by mass or more and 0.5% by mass or less. The total addition amount A2 of the antioxidant in the first adhesive layer 2 may be 0.5% by mass or more and 0.75% by mass or less. The total addition amount A3 of the antioxidant in the second adhesive layer 3 may be 0.5% by mass or more and 0.75% by mass or less. The total addition amounts A2 to A4 may be in a relationship that satisfies, for example, A4 < A2 and A4 < A3. According to this configuration, the interlayer peeling strength between the base material layer 4 and the first adhesive layer 2, and the interlayer peeling strength between the base material layer 4 and the second adhesive layer 3 can be increased.

[0073] <Electrode lead wire member> As shown in FIG. 2, the electrode lead wire member 10 has an electrode lead wire 11 and a pair of sealing films 1. In the pair of sealing films 1, the first adhesive layers 2 are arranged facing each other. The pair of sealing films 1 sandwich the electrode lead wire 11. The pair of sealing films 1 are in contact with regions corresponding to one surface and the other surface of the electrode lead wire 11, respectively. Therefore, the pair of sealing films 1 are in contact with the entire circumference of the electrode lead wire 11 as a whole.

[0074] The electrode lead wire 11 has a lead wire body 111 and a surface treatment layer 112. The electrode lead wire 11 extends linearly in one direction. The electrode lead wire 11 is made of metal.

[0075] The electrode lead wire 11 has electrical conductivity. The electrode lead wire 11 is electrically connected to the lithium ion battery 30 (see FIG. 3). The electrode lead wire 11 provides electrical continuity between the lithium ion battery 30 and an external device. Known metals such as aluminum, copper, nickel, iron, gold, platinum, various alloys, etc., can be used as the material of the lead wire body 111. Among them, aluminum and copper are preferable because they have excellent conductivity and are advantageous in terms of cost.

[0076] The surface of the lead wire body 111 may be nickel plated. The nickel plating of the lead wire body 111 may be formed by electroplating using a Watts bath containing nickel sulfate, nickel chloride, boric acid, or the like as main components. The nickel plating of the lead wire body 111 is preferably performed using a nickel sulfamate plating bath containing nickel sulfamate and boric acid as main components. The plating film formed by this method has excellent flexibility and is less likely to crack. The lead body 111 is preferably an aluminum plate or a nickel-plated copper plate.

[0077] The surface treatment layer 112 is formed on the surface of the lead wire body 111. The surface treatment layer 112 has corrosion resistance. "Corrosion resistance" refers to the property of being less susceptible to corrosion by the electrolyte inside the battery. The surface treatment layer 112 may be, for example, an acid-resistant coating made of a phosphate, a chromate, a fluoride, a triazine thiol compound, or the like. The acid-resistant coating can be formed by subjecting the lead wire body 111 to a chemical conversion treatment.

[0078] 2, the surface treatment layer 112 is formed on a part of the surface of the lead body 111, but the surface treatment layer 112 may be formed on the entire surface of the lead body 111. Note that the electrode lead wire does not necessarily need to have a surface treatment layer formed thereon.

[0079] The sealing film 1 contains the above-mentioned three types of antioxidants (phenol-based antioxidant, phosphorus-based antioxidant, and sulfur-based antioxidant), and thus can suppress embrittlement of the resin due to oxidation. The phenol-based antioxidant has the effect of terminating the chain reaction of autoxidation by capturing radicals. The phosphorus-based antioxidant terminates the chain reaction of autoxidation by decomposing peroxides (hydroperoxides). Therefore, by using the phenol-based antioxidant and the phosphorus-based antioxidant in combination, it is possible to effectively suppress oxidative deterioration (e.g., embrittlement) of the resin.

[0080] A sulfur-based antioxidant is further added to the sealing film 1. When used in combination with a phenol-based antioxidant, the sulfur-based antioxidant has a high synergistic effect on suppressing oxidative degradation (thermo-oxidative degradation) at high temperatures, and furthermore, due to its low reaction rate, the oxidative suppression effect can be maintained for a long period of time even at low temperatures. Therefore, oxidative degradation (e.g., embrittlement) can be suppressed over a wide temperature range. Furthermore, in the sealing film 1, since the amount of the antioxidant added is within the above-mentioned range (0.4 mass % or more and 0.75 mass % or less), delamination is unlikely to occur.

[0081] The sealing film 1 contains acid-modified polyolefin as a material for forming the first adhesive layer 2. Therefore, the first adhesive layer 2 is easily heat-sealed to the electrode lead wire 11, and the interface between the electrode lead wire 11 and the sealing film 1 can be sealed.

[0082] When the base layer 4 mainly contains polyolefin, the fluidity of the resin during thermocompression bonding can be increased to an appropriate range, and therefore the resin can sufficiently flow around the electrode lead wire 11 during thermocompression bonding, ensuring the entire periphery of the electrode lead wire 11 is sealed.

[0083] The electrode lead member 10 includes the sealing film 1, and therefore can suppress oxidation deterioration (eg, embrittlement) over a wide temperature range, and can also make interlayer peeling less likely to occur.

[0084] <Battery> FIG. 3 is a schematic perspective view showing the battery 100 of the embodiment. As shown in FIG. 3, the battery 100 includes the above-mentioned electrode lead member 10, a container 20, and a lithium ion battery 30 (battery body).

[0085] The storage container 20 has a container body 21 and a lid 22. The storage container 20 is an example of a "second base." The container body 21 has a molded portion 21a that forms a recess for accommodating the lithium ion battery 30. The container body 21 is obtained by drawing a laminate for battery exterior packaging. The lid 22 is made of the laminate for battery exterior packaging and has the same planar area as the container body 21. The laminate for battery exterior packaging will be described later. The storage container 20 is formed by overlapping a container body 21 and a lid 22 and heat sealing a peripheral portion 25.

[0086] FIG. 4 is a cross-sectional view taken along line II in FIG. As shown in FIG. 4, the laminate for battery exterior use, which is the constituent material of the container body 21 and the lid 22, is a laminate in which a first film substrate 201, a second film substrate 202, a metal foil 203, and a sealant layer 204 are laminated in this order.

[0087] The resin constituting the first film substrate 201 and the second film substrate 202 is not particularly limited, but polyamide, polyethylene terephthalate (PET), phenolic resin, polypropylene, etc. are suitable. The metal foil 203 is preferably an aluminum foil, a stainless steel foil, a copper foil, an iron foil, or the like.

[0088] The sealant layer 204 is in contact with the second adhesive layer 3 of the sealing film 1 and is heat-sealed. A resin capable of being fused to the sealing film 1 is selected as the resin constituting the sealant layer 204. Examples of the resin constituting the sealant layer 204 include polypropylene-based resins and polyethylene-based resins. As the polypropylene-based resin, a homopolymer of polypropylene, a copolymer of propylene and ethylene, etc. may be used. As the polyethylene-based resin, low-density polyethylene, linear low-density polyethylene, etc. may be used.

[0089] 3 and 4, in the battery 100, the electrode lead wire 11 is drawn from the lithium ion battery 30 inside the container 20 (inside the molded portion 21a) to the outside of the container 20. The electrode lead wire 11 is fused to the sealant layer 204 of the container 20 via the sealing film 1.

[0090] According to the battery 100, since the electrode lead member 10 has the above-mentioned sealing film 1, it is possible to suppress oxidation deterioration (e.g., embrittlement) over a wide temperature range and to make interlayer peeling less likely to occur, thereby achieving a highly reliable battery 100.

[0091] Although the preferred embodiment of the present invention has been described above with reference to the attached drawings, the present invention is not limited to the above embodiment. The shapes and combinations of the components shown in the above embodiment are merely examples, and can be modified based on design requirements and the like without departing from the spirit of the present invention. For example, the first adhesive layer and the second adhesive layer may contain a resin other than polyolefin. The sealing film may also contain layers other than the first adhesive layer, the base layer, and the second adhesive layer. EXAMPLES

[0092] The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

[0093] <Preparation of sealing film> A sealing film in which the first adhesive layer, the base material layer, and the second adhesive layer were laminated in this order was produced as follows. The resins that were the raw materials for each layer were separately heated and melted, and a laminate was obtained by simultaneous multilayer film formation using an extruder capable of simultaneous multilayer extrusion molding. The laminate was cut into a strip shape (width 15 mm, thickness 105 μm) to obtain the sealing film of each example and comparative example.

[0094] The constituent materials of the first adhesive layer, the base material layer, and the second adhesive layer are as follows: First adhesive layer: Maleic anhydride modified polypropylene (melting point 140°C) Base layer: Polypropylene ICP (melting point 161°C) Second adhesive layer: Random copolymer of propylene and ethylene (melting point 140°C)

[0095] Maleic anhydride modified polypropylene is a polymer obtained by graft polymerizing maleic anhydride onto a random copolymer of propylene and ethylene. Polypropylene ICP has a structure in which the second phase is dispersed in the first phase (sea-island structure). The first phase is composed of homo-PP. The second phase contains ethylene propylene rubber and polyethylene. Polypropylene ICP is a mixture containing PP, ethylene propylene rubber, and polyethylene. The first adhesive layer has a thickness of 35 μm. The base layer has a thickness of 40 μm. The second adhesive layer has a thickness of 30 μm.

[0096] A phenol-based antioxidant, a phosphorus-based antioxidant, and a sulfur-based antioxidant were added to the first adhesive layer, the base layer, and the second adhesive layer at a ratio (by mass) of the phenol-based antioxidant, the phosphorus-based antioxidant, and the sulfur-based antioxidant to each other of 1:1:3.

[0097] The phenol-based antioxidant used was pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate). As the phosphorus-based antioxidant, tris(2,4-ditert-butylphenyl)phosphite was used. The sulfur-based antioxidant used was 2,2-Bis{[3-(dodecylthio)-1-oxopropoxy]methyl}propane-1,3-diyl bis[3-(dodecylthio)propionate].

[0098] The amount of each antioxidant added is shown in Table 1. Table 1 also shows the amount of antioxidant added for each layer and the total amount of antioxidants added. The "total amount added" is the total amount of the three types of antioxidants added in the entire sealing film 1.

[0099] <Whether or not the resin has deteriorated> A laminate obtained by attaching the sealing film to a polyimide base film was used as a measurement specimen. The measurement specimen was placed in a metal container. The container was a non-sealed container with an air vent. The container containing the measurement specimen was placed in a hot air drying oven and stored under heating at 150°C for a specified period of time. The measurement specimen was removed from the hot air drying oven and cooled to room temperature.

[0100] The presence or absence of deterioration of the resin constituting the sealing film was evaluated as follows. If no yellowing of the resin was observed after heating for 30 days or more, it was judged as "no deterioration" (OK). If yellowing of the resin occurred within 30 days, it was judged as "deterioration" (NG). Yellowing of the resin is considered to indicate embrittlement. The results are shown in Table 1.

[0101] <Interlaminar peel strength> The 180-degree peel strength of the measurement specimen was measured using a tester (Shimadzu Corporation's tabletop precision universal testing machine: Autograph AGS-500NX) as follows. A cut (half cut) of several tens of μm in depth was made in the film thickness direction of the measurement specimen. A cutter blade was inserted between the layers of the measurement specimen, which was a laminate of a sealing film and a base film, and a part of the layer was peeled off. The end of the sealing film and the end of the base film were held by the gripping part of the tester, and the sealing film and the base film were peeled off so that the peeled layer was peeled off at 180 degrees. The peeling speed was 50 mm / min.

[0102] A peel strength of 25N / 15mm or more was judged as "good" (OK). A peel strength of less than 25N / 15mm was judged as "weak" (NG). The results are shown in Table 1.

[0103] [Table 1]

[0104] As shown in Table 1, in Examples 1 to 4 in which the phenol-based antioxidant, phosphorus-based antioxidant, and sulfur-based antioxidant were added in the prescribed amounts (0.4% by mass or more and 0.75% by mass or less), no deterioration of the resin was observed. Furthermore, in Examples 1 to 4, the peel strength was high. In contrast, resin deterioration was observed in Comparative Example 3, in which no antioxidant was added, and Comparative Example 2, in which a small amount of antioxidant was added. Also, it was found that Comparative Example 1, in which the amount of antioxidant added exceeded the above range, had low peel strength and was prone to interlayer delamination. [Explanation of symbols]

[0105] 1...sealing film, 2...first adhesive layer, 3...second adhesive layer, 4...base material layer, 10...electrode lead wire member, 11...electrode lead wire (first substrate), 20...container (second substrate), 30...lithium ion battery (battery body), 100...battery.

Claims

1. A sealing film that seals between a first base body and a second base body made of metal, a first adhesive layer that mainly contains an acid-modified polyolefin and adheres to the first substrate; a second adhesive layer primarily comprising a polyolefin and adhering to the second substrate; A base layer provided between the first adhesive layer and the second adhesive layer, At least one of the first adhesive layer, the second adhesive layer, and the base material layer is added with at least a phenol-based antioxidant, a phosphorus-based antioxidant, and a sulfur-based antioxidant, the total amount of the phenol-based antioxidant, the phosphorus-based antioxidant, and the sulfur-based antioxidant added in the entire sealing film is 0.4 mass% or more and 0.75 mass% or less, and the sealing film satisfies the following requirement (a) or (b): (a) the substrate layer contains a polyolefin, and the polyolefin constituting the substrate layer consists of one kind of polyolefin, or (b) the resin constituting the base layer is a resin other than polyolefin; Meet the sealing film.

2. In the first adhesive layer, a total amount of the phenol-based antioxidant, the phosphorus-based antioxidant, and the sulfur-based antioxidant is 0.75 mass% or less, In the second adhesive layer, a total amount of the phenol-based antioxidant, the phosphorus-based antioxidant, and the sulfur-based antioxidant is 0.75 mass% or less; The sealing film according to claim 1 , wherein a total amount of the phenol-based antioxidant, the phosphorus-based antioxidant, and the sulfur-based antioxidant added to the base layer is 0.75 mass % or less.

3. The requirement (a) is satisfied, The seal film according to claim 1 or 2, wherein the base layer mainly contains the polyolefin.

4. The acid-modified polyolefin constituting the first adhesive layer is an acid-modified polypropylene, The polyolefin constituting the second adhesive layer is polypropylene. The seal film according to any one of claims 1 to 3.

5. The sealing film according to any one of claims 1 to 4, wherein the phenol-based antioxidant, the phosphorus-based antioxidant, and the sulfur-based antioxidant are added to the first adhesive layer, the second adhesive layer, and the base material layer, respectively.

6. The sealing film according to any one of claims 1 to 5, wherein the total amount of the phenol-based antioxidant, the phosphorus-based antioxidant, and the sulfur-based antioxidant added to each of the first adhesive layer, the second adhesive layer, and the base material layer is 0.25 to 0.75 mass%.

7. The sealing film according to any one of claims 1 to 6, the first base being an electrode lead wire extending in one direction.

8. The electrode lead member according to claim 7 , a battery body to which the electrode lead wires are connected; The second base is a container that houses the battery body.

Images