JP7794557B2 - Sealing film, electrode lead wire member and battery - Google Patents

Description

The present invention relates to a sealing film, an electrode lead wire member, and a battery.

In recent years, secondary batteries such as lithium-ion batteries and capacitors have been attracting attention as storage batteries for storing electrical energy. The battery comprises, 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 using a battery exterior laminate that has excellent waterproof and light-blocking properties. The battery exterior laminate is, for example, a laminate formed by laminating a substrate layer made of polyamide or the like and aluminum foil. The electrode lead wire is sealed in the container with one end of the electrode lead wire extended to the outside.

In the battery, it has been proposed to interpose a sealing film between the housing and the electrode lead wire (see, for example, Patent Document 1). The film (hereinafter referred to as the sealing film) seals the gap between the electrode lead wire and the housing.

Patent No. 6596869

The resin in the sealing film may deteriorate (e.g., become embrittled), reducing the adhesive strength. Furthermore, sealing films are required to suppress delamination to prevent liquid leakage from the container.

One aspect of the present invention aims to provide a sealing film, electrode lead wire member, and battery that can suppress resin deterioration and are less likely to cause delamination.

To solve the above problems, one aspect of the present invention includes the following:

[1] A sealing film that seals between a first substrate and a second substrate made of metal, comprising: a first adhesive layer that mainly contains an acid-modified polyolefin and adheres to the first substrate; a second adhesive layer that mainly contains a polyolefin and adheres to the second substrate; and a base layer provided between the first adhesive layer and the second adhesive layer; at least a phenolic 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 phenolic antioxidant, the phosphorus-based antioxidant, and the sulfur-based antioxidant added to the entire sealing film is 0.4% by mass or more and 0.75% by mass or less.

[2] The sealing film according to [1], wherein the substrate layer primarily contains polyolefin.

[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 layer mainly contains polyolefin.

[4] An electrode lead wire member comprising the sealing film described in any one of [1] to [3] and the first base, which is an electrode lead wire extending in one direction.

[5] A battery comprising the electrode lead wire member described in [4], a battery body to which the electrode lead wire is connected, and the second base which is a container for housing the battery body.

One aspect of the present invention provides a sealing film, electrode lead wire member, and battery that can suppress resin deterioration and are less likely to cause delamination.

1 is a schematic cross-sectional view showing a sealing film of an embodiment. FIG. 2 is a schematic perspective view showing an electrode lead wire member according to the embodiment. 1 is a schematic perspective view showing a battery according to an embodiment. 4 is a cross-sectional view taken along line II in FIG. 3.

The sealing film, electrode lead wire member, and battery according to the embodiment will be described below with reference to Figures 1 to 4. Note that the dimensions and proportions of the components in the drawings may differ from the actual dimensions and proportions.

<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.

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 .

[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 heating and pressurizing. 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).

The first adhesive layer 2 primarily contains an acid-modified polyolefin. The fact that the first adhesive layer 2 "primarily contains an acid-modified polyolefin" means that the acid-modified polyolefin content is the highest among the resins that make up the first adhesive layer 2. The first adhesive layer 2 contains 50% by mass or more of 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.

Examples of polyolefins that can be used to form the first adhesive layer 2 include polypropylene, polyethylene, poly-1-butene, and polyisobutylene. Among these, polypropylene is preferred as the polyolefin that can be used to form the first adhesive layer 2 due to its excellent flexibility. Hereinafter, polypropylene may be abbreviated as "PP."

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 random copolymers being preferred. The polyolefin may also be a copolymer of propylene and an olefin-based monomer. Examples of olefin-based monomers include 1-butene, isobutylene, and 1-hexene.

Acid-modified polyolefins are polyolefin resins modified with unsaturated carboxylic acids or derivatives of unsaturated carboxylic acids. Acid-modified polyolefins have acid functional groups, such as carboxy groups or carboxylic anhydride groups, in their molecular structure. Acid-modified polyolefins are obtained by graft polymerizing unsaturated carboxylic acids or derivatives of unsaturated carboxylic acids onto polyolefins, or by copolymerizing acid functional group-containing monomers with olefins. That is, in acid-modified polyolefins, the repeating units containing acid groups may be contained in either side chains or the main chain.

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 acid-modified polyolefin can improve the adhesiveness of the first adhesive layer 2 to the electrode lead wire 11 (see FIG. 2).

A preferred acid-modified polyolefin is acid-modified polypropylene (acid-modified PP) due to its excellent heat resistance. Acid-modified PP is a polymer obtained by graft-copolymerizing, for example, polypropylene or a propylene-ethylene copolymer with an unsaturated carboxylic acid or a derivative of an unsaturated carboxylic acid.

Acid-modified PP includes ionomers in which the carboxylic acid groups of an acid-modified polymer of polypropylene or an acid-modified polymer of propylene-ethylene copolymer are neutralized with metal hydroxides, alkoxides, salts of lower fatty acids, or the like.
The acid group of the acid-modified PP is preferably a maleic anhydride group, i.e., the acid-modified PP is preferably maleic anhydride-modified PP.

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 less likely to become excessively thin during thermocompression bonding, making it easier to ensure adhesive strength. If the melting point of the resin constituting the first adhesive layer 2 is 150°C or lower, the resin is more likely to flow during thermocompression bonding, making it easier for the resin to wrap sufficiently around the electrode lead wire 11 and seal the entire periphery of the electrode lead wire 11.

If 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.

Optional components other than polyolefin in the first adhesive layer 2 include known additives such as stabilizers, antistatic agents, and colorants.

The thickness of the first adhesive layer 2 can be, for example, 25 to 70% of the total thickness of the sealing film 1, where 100 is the total thickness of the sealing film 1. In other words, the thickness of the first adhesive layer 2 can be 25% to 70% of the total thickness of the sealing film 1. The ratio of the layer thickness to the total thickness of the sealing film 1, which is 100, is called the "thickness ratio."

When the thickness ratio of the first adhesive layer 2 is 25 or more, sufficient adhesive strength can be ensured between the first adhesive layer 2 and the electrode lead wire 11. When the thickness ratio of the first adhesive layer 2 is 70 or less, sufficient thickness can be imparted to the second adhesive layer 3 and base material layer 4. This makes it possible to increase the adhesive strength between the second adhesive layer 3 and the storage container without reducing the electrolyte resistance of the sealing film 1. Note that "electrolyte resistance" refers to resistance to electrolyte.

[Second adhesive layer]
The second adhesive layer 3 is a layer that is fused (adhered) to the storage container by, for example, heating and pressurizing. 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 made of, for example, a resin (or a resin composition).

The second adhesive layer 3 primarily contains polyolefin. The fact that the second adhesive layer 3 "primarily contains polyolefin" means that the polyolefin content is the highest among the resins that make up the second adhesive layer 3. The second adhesive layer 3 contains 50% by mass or more of polyolefin relative to the total amount of the second adhesive layer 3, preferably more than 50% by mass, and more preferably 80% by mass or more.

Examples of polyolefins constituting the second adhesive layer 3 include polypropylene (PP), polyethylene, poly-1-butene, and polyisobutylene. Of these, PP is preferred 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 a random copolymer being preferred. The polyolefin may be a copolymer of propylene and an olefinic monomer (for example, a random copolymer). Examples of the olefinic monomer include 1-butene, isobutylene, and 1-hexene.

The polyolefin constituting the second adhesive layer 3 may be an acid-modified polyolefin. Acid-modified PP is preferred as an acid-modified polyolefin due to its excellent heat resistance. The acid-modified PP exemplified above as a material for 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 preferred as the acid-modified PP due to its excellent flexibility. The use of acid-modified polyolefin can enhance the adhesion of the second adhesive layer 3 to the container.

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 reduced, thereby suppressing deterioration of the first adhesive layer 2.

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 less likely to become excessively thin during thermocompression bonding, making it easier to ensure adhesive strength. If the melting point of the resin constituting the second adhesive layer 3 is 150°C or lower, the resin is more likely to flow during thermocompression bonding, making it easier to seal the gap between the container and the electrode lead wire 11.

If 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.

Optional components in the second adhesive layer 3 other than the acid-modified polyolefin include known additives such as stabilizers, antistatic agents, and colorants.

The thickness (thickness ratio) of the second adhesive layer 3 can be, for example, 5 to 50, where the total thickness of the sealing film 1 is 100. In other words, the thickness of the second adhesive layer 3 can be 5 to 50% of the total thickness of the sealing film 1.

When the thickness ratio of the second adhesive layer 3 is 5 or more, sufficient adhesive strength can be ensured between the second adhesive layer 3 and the storage container. When the thickness ratio of the second adhesive layer 3 is 50 or less, sufficient thickness can be imparted to the first adhesive layer 2 and the base material layer 4. As a result, the electrolyte resistance of the sealing film 1 is not reduced, and the adhesive strength between the first adhesive layer 2 and the electrode lead wire 11 can be increased.

[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).

The base layer 4 primarily contains, for example, polyolefin. The fact that the base layer 4 "primarily contains polyolefin" means that among the resins that make up the base layer 4, the polyolefin content is the highest. The base layer 4 contains 50% by mass or more of polyolefin relative to the total amount of the base layer 4, preferably more than 50% by mass, and more preferably 80% by mass or more.

Examples of polyolefins that make up the base layer 4 include polypropylene (PP), polyethylene, poly-1-butene, and polyisobutylene. Of these, PP is preferred due to its excellent flexibility.

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 olefins. An example of the homopolymer is a homopolymer of propylene only (homoPP). 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.
Examples of the polyolefin constituting the base material layer 4 include the polymers exemplified as the polyolefin constituting the first adhesive layer 2 .

ICP (impact copolymer) is preferred as the polyolefin that constitutes the base layer 4. ICP has a phase-separated structure with a first phase and a second phase, such as an island-sea structure. An island-sea structure is a structure in which multiple islands, representing the second phase, are dispersed within the first phase, representing the "sea."

The first phase is composed of a homopolymer of an olefin-based 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, for example, a polymer of an olefin-based monomer, such as propylene or ethylene, such as ethylene propylene rubber (EPR). The second phase is composed of, for example, a main phase and a surface layer that covers the surface of the main phase. The main phase is composed of, for example, polyethylene. The surface layer is composed of, for example, EPR.

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 a so-called block PP. ICPs are also called heterophasic copolymers or block copolymers.

The material of the substrate layer is not particularly limited, and resins other than polyolefins (for example, fluororesins such as polychlorotrifluoroethylene) may also be used.

The thickness (thickness ratio) of the base material layer 4 can be, for example, 25 to 70% relative to the total thickness of the sealing film 1, where 100 is the total thickness of the sealing film 1. That is, the thickness of the base material layer 4 can be 25% to 70% relative to 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 the necessary fluidity is easily exhibited during pressure bonding.

When the thickness ratio of the base layer 4 is 70 or less, sufficient thickness can be imparted to the first adhesive layer 2 and the second adhesive layer 3. This increases 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, the fluidity of the resin during thermocompression bonding can be increased to an appropriate range. This allows the resin to adequately wrap around the electrode lead wire 11, reliably sealing the entire circumference of the electrode lead wire 11.

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 material layer 4 is 150° C. or higher, it is easy to ensure the electrolyte resistance of the sealing film 1. In addition, heat resistance can be imparted to the sealing film 1.
When the melting point of the resin constituting the base material layer 4 is 170°C or less, 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 wire 11 and the container.

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. In other words, the melting point M4 is preferably higher than either the melting point M2 or the melting point M3. It is desirable that the melting point M4 be higher than both the melting point M2 and the melting point M3. In other words, it is desirable that the melting point M4 be higher than at least one of the melting points M2 and M3.

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 set 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 also an advantage that the sealing film 1 can be easily imparted with heat resistance.

[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 substrate layer 4. These antioxidants may be added to one, two, or all of the first adhesive layer 2, the second adhesive layer 3, and the substrate 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 substrate layer 4.

In addition to the three types of antioxidants mentioned above (phenol-based antioxidants, phosphorus-based antioxidants, and sulfur-based antioxidants), other antioxidants (e.g., amine-based antioxidants) may also be added to the sealing film.

Radicals can be generated in resins due to heat, light, etc., but if these radicals are left unattended, they can lead to cross-linking and oxidative degradation due to autoxidation. For example, an autoxidation reaction begins when oxygen is added to a polymer radical generated in the resin to generate a polymer peroxy radical (POO.). The autoxidation reaction proceeds when hydroperoxide (POOH), generated by a hydrogen abstraction reaction from the polymer peroxy radical (POO.), decomposes to generate an oxy radical (PO.) or peroxy radical.

Phenol-based antioxidants donate hydrogen to peroxy radicals and other radicals produced in autoxidation reactions, while also converting themselves into stable radicals, thereby terminating the autoxidation chain reaction. This reaction is a radical-scavenging reaction. As a result, phenol-based antioxidants suppress crosslinking and oxidative degradation of resins. Because of their effects, phenol-based antioxidants can be called "primary antioxidants," "radical scavengers," or "radical chain inhibitors."

Phenol-based antioxidants include hindered phenols and semi-hindered phenols. Examples of phenol-based antioxidants include monophenols, bisphenols, trisphenols, and tetrakisphenols.

Examples of monophenolic 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.

Examples of bisphenol 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.

Trisphenol 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.

Tetrakisphenol antioxidants 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-t-butyl-4-hydroxyphenyl)propionate].

As a phenol-based antioxidant, a tetrakisphenol-based antioxidant is preferred. Tetrakisphenol-based antioxidants (especially pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]) are effective in improving 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.

Phosphorus-based antioxidants inhibit resin oxidation by decomposing the peroxides (hydroperoxides) produced in the autoxidation reaction described above and converting them into stable alcohols. Because of this effect, phosphorus-based antioxidants can be called "secondary antioxidants" or "peroxide decomposers."

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-butylphenylditridecyl)phosphite, cyclic neopentane tetrayl bis(octadecyl phosphite), tris(nonylphenyl)phosphite, tris(2,4-ditert-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.

As phosphorus-based antioxidants, compounds with a phosphite ester structure, particularly tris(2,4-di-t-butylphenyl) phosphite, are preferred. Tris(2,4-di-t-butylphenyl) phosphite has excellent hydrolysis resistance. A suitable commercially available tris(2,4-di-t-butylphenyl) phosphite product is "Irgafos 168" manufactured by BASF.

Similar to phosphorus-based antioxidants, sulfur-based antioxidants function as secondary antioxidants (peroxide decomposers). Although sulfur-based antioxidants have a slower reaction rate for the aforementioned peroxide decomposition reaction than phosphorus-based antioxidants, they are characterized by the fact that, when used in combination with phenolic antioxidants, they tend to accelerate the peroxide decomposition reaction. For example, sulfur-based antioxidants have a stronger synergistic effect (the effect obtained when used in combination with phenolic antioxidants) in inhibiting oxidative degradation (thermo-oxidative degradation) at high temperatures when used in combination with phenolic antioxidants than phosphorus-based antioxidants. Because 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 for the above-mentioned peroxide decomposition reaction, the oxidation suppression effect is maintained for a long period of time even at low temperatures in the presence of a phenol-based antioxidant.

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-mercaptobenzimida Examples include 4,6-bis(octylthiomethyl)-o-cresol, didodecyl-3,3'-thiodipropionate, and 2,2-Bis{[3-(dodecylthio)-1-oxopropoxy]methyl}propane-1,3-diyl bis[3-(dodecylthio)propionate].

Among these, thioether-based antioxidants, particularly 2,2-bis[[3-(dodecylthio)propionic acid]3-(dodecylthio)-1-oxopropyloxy]methyl]-1,3-propanediyl bis[3-(dodecylthio)propionic acid], have a high synergistic effect (an effect obtained when used in combination with a phenol-based antioxidant) in suppressing oxidative degradation (thermooxidative degradation) at high temperatures. Therefore, the heat resistance of the sealing film 1 can be improved over a long period of time.

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 added is 0.4% by mass or more, it is possible to suppress deterioration (e.g., embrittlement) of the resin of the sealing film 1. When the total amount added is 0.75% by mass or less, it is possible to make interlayer delamination less likely to occur.

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

The total amount of the three antioxidants added in the base layer 4 may be set to be lower than the total amount of the three antioxidants added in the first adhesive layer 2 or the second adhesive layer 3.
For example, the total amount A4 of antioxidants added in the base layer 4 may be 0.25% by mass or more and 0.5% by mass or less. The total amount A2 of antioxidants added in the first adhesive layer 2 may be 0.5% by mass or more and 0.75% by mass or less. The total amount A3 of antioxidants added in the second adhesive layer 3 may be 0.5% by mass or more and 0.75% by mass or less. The total amounts A2 to A4 may satisfy the relationships A4<A2 and A4<A3, for example.
According to this configuration, the interlayer peel strength between the base material layer 4 and the first adhesive layer 2, and the interlayer peel strength between the base material layer 4 and the second adhesive layer 3 can be increased.

<Electrode lead wire member>
As shown in FIG. 2 , the electrode lead member 10 includes an electrode lead 11 and a pair of sealing films 1 .
The pair of sealing films 1 are disposed with the first adhesive layers 2 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 periphery of the electrode lead wire 11 as a whole.

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.

The electrode lead wire 11 is conductive. The electrode lead wire 11 is electrically connected to the lithium ion battery 30 (see FIG. 3 ). The electrode lead wire 11 conducts electricity between the lithium ion battery 30 and an external device.
Known metals such as aluminum, copper, nickel, iron, gold, platinum, and various alloys can be used as the material for the lead wire body 111. Among these, aluminum and copper are preferred because of their excellent conductivity and cost advantage.

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 its 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 its main components. The plating film formed by this method has excellent flexibility and is less likely to crack.
The lead wire body 111 is preferably an aluminum plate or a nickel-plated copper plate.

The surface treatment layer 112 is formed on the surface of the lead wire body 111. The surface treatment layer 112 is corrosion-resistant. "Corrosion resistance" refers to the property of being less susceptible to corrosion by the electrolyte inside the battery. Examples of the surface treatment layer 112 include an acid-resistant coating made from materials such as phosphate, chromate, fluoride, or triazine thiol compounds. The acid-resistant coating can be formed by applying a chemical conversion treatment to the lead wire body 111.

In FIG. 2, the surface treatment layer 112 is formed on a portion of the surface of the lead wire body 111, but the surface treatment layer 112 may be formed on the entire surface area of the lead wire body 111. Note that the electrode lead wire does not necessarily need to have a surface treatment layer formed.

The sealing film 1 contains the three types of antioxidants mentioned above (phenolic antioxidant, phosphorus-based antioxidant, and sulfur-based antioxidant), which can prevent embrittlement of the resin due to oxidation. The phenolic 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, the combined use of a phenolic antioxidant and a phosphorus-based antioxidant can effectively prevent oxidative degradation (e.g., embrittlement) of the resin.

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 in suppressing oxidative degradation (thermo-oxidative degradation) at high temperatures, and furthermore, due to its slow reaction rate, the oxidation-suppressing 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, the amount of the antioxidant added is in the above-mentioned range (0.4 mass % or more and 0.75 mass % or less), so that delamination is unlikely to occur.

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

When the base layer 4 primarily contains polyolefin, the fluidity of the resin during thermocompression bonding can be increased to an appropriate range. As a result, the resin can sufficiently wrap around the electrode lead wire 11 during thermocompression bonding, ensuring a reliable seal around the entire circumference of the electrode lead wire 11.

The electrode lead wire member 10 includes a sealing film 1, which helps prevent oxidation degradation (e.g., embrittlement) over a wide temperature range and makes delamination less likely to occur.

<Battery>
FIG. 3 is a schematic perspective view showing the battery 100 according to the embodiment.
As shown in FIG. 3, the battery 100 includes the electrode lead wire member 10 described above, a container 20, and a lithium ion battery 30 (battery body).

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 use. The lid 22 is made of the laminate for battery exterior use and has the same area in plan view as the container body 21. The laminate for battery exterior use 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 edge 25 .

FIG. 4 is a cross-sectional view taken along line II in FIG.
As shown in Figure 4, the battery exterior laminate, 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.

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.

The sealant layer 204 is in contact with and heat-sealed to the second adhesive layer 3 of the sealing film 1. A resin that can be fused to the sealing film 1 is selected as the resin that constitutes the sealant layer 204. Examples of resins that constitute the sealant layer 204 include polypropylene-based resins and polyethylene-based resins. Examples of polypropylene-based resins that can be used include polypropylene homopolymers and copolymers of propylene and ethylene. Examples of polyethylene-based resins that can be used include low-density polyethylene and linear low-density polyethylene.

As shown in Figures 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.

In the battery 100, the electrode lead wire member 10 has the above-mentioned sealing film 1, which suppresses oxidation degradation (e.g., embrittlement) over a wide temperature range and makes delamination less likely to occur. This makes it possible to realize a highly reliable battery 100.

The above describes preferred embodiments of the present invention with reference to the accompanying drawings, but the present invention is not limited to these examples. The shapes and combinations of the components shown in the above examples are merely examples, and various modifications can be made based on design requirements, etc., 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. Furthermore, the sealing film may include layers other than the first adhesive layer, base layer, and second adhesive layer.

The present invention will be described below using examples, but the present invention is not limited to these examples.

<Preparation of sealing film>
A sealing film having a first adhesive layer, a base material layer, and a second adhesive layer laminated in this order was produced as follows. The resins used as 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. This laminate was cut into strips (width 15 mm, thickness 105 μm) to obtain the sealing films of each example and comparative example.

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)

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 a second phase is dispersed within a 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 thickness of the first adhesive layer is 35 μm, the thickness of the base material layer is 40 μm, and the thickness of the second adhesive layer is 30 μm.

A phenolic 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. The addition ratio (by mass) of the phenolic antioxidant, the phosphorus-based antioxidant, and the sulfur-based antioxidant was 1:1:3.

The phenolic 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].

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 antioxidants added to the entire sealing film 1.

<Whether or not the resin has deteriorated>
A laminate obtained by attaching a 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 at 150°C for a predetermined period of time. The measurement specimen was removed from the hot air drying oven and cooled to room temperature.

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 in less than 30 days, it was judged as "deterioration" (NG). Yellowing of the resin is considered to indicate embrittlement. The results are shown in Table 1.

<Interlayer peel strength>
The 180-degree peel strength of the measurement specimen was measured using a testing machine (a tabletop precision universal testing machine: Autograph AGS-500NX manufactured by Shimadzu Corporation) 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 portion of the layer was peeled off. The end of the sealing film and the end of the base film were gripped with the gripping parts of the testing machine, and the sealing film and the base film were peeled off so that the peeled layers were peeled off at 180 degrees. The peeling speed was 50 mm/min.

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

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.

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...Storage container (second substrate), 30...Lithium ion battery (battery body), 100...Battery.

Claims (7)

A sealing film that seals between a first substrate and a second substrate 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;
a 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;
the total amount of the phenol-based antioxidant, the phosphorus-based antioxidant, and the sulfur-based antioxidant added to the first adhesive layer is 0.75 mass% or less;
the total amount of the phenol-based antioxidant, the phosphorus-based antioxidant, and the sulfur-based antioxidant added to the second adhesive layer is 0.75 mass% or less;
a total amount of the phenol-based antioxidant, the phosphorus-based antioxidant, and the sulfur-based antioxidant added to the base layer being 0.75 mass % or less; The sealing film according to claim 1, wherein the substrate layer primarily contains polyolefin. the acid-modified polyolefin constituting the first adhesive layer is acid-modified polypropylene,
the polyolefin constituting the second adhesive layer is polypropylene;
The seal film according to claim 1 or 2, wherein the base layer mainly contains polyolefin. The sealing film according to any one of claims 1 to 3, 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. 5. 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 each of the first adhesive layer, the second adhesive layer, and the base material layer is 0.25 to 0.75 mass%. The sealing film according to any one of claims 1 to 5 ,
the first base being an electrode lead wire extending in one direction. The electrode lead wire member according to claim 6 ;
a battery body to which the electrode lead wires are connected;
The second base is a container that houses the battery body.