JP7827622B2 - 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.
This application claims priority based on Japanese Patent Application No. 2020-96744, filed on June 3, 2020, the contents of which are incorporated herein by reference.

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 with excellent waterproofing 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 storage container and the electrode lead wire (see, for example, Patent Document 1). The sealing film (hereinafter referred to as the sealing film) seals the gap between the electrode lead wire and the storage container, preventing leakage of the contents of the storage container.

Japanese Patent Application Laid-Open No. 2003-007269

Sealing films are required to prevent the formation of unbonded areas (so-called through-holes) at bonded locations and to prevent leakage of the contents. Furthermore, if the sealing film softens and becomes more fluid during thermocompression bonding, it may spread. For example, a strip-shaped sealing film 1 may spread in the width direction beyond the area that should be bonded.

One aspect of the present invention aims to provide a sealing film, electrode lead wire member, and battery that are less likely to form unbonded areas and that can suppress spreading during thermocompression bonding.

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

[1] A sealing film that seals between a first metal substrate and a second metal substrate, comprising: a first adhesive layer that primarily contains an acid-modified polyolefin and adheres to the first substrate; a second adhesive layer that primarily contains a polyolefin and adheres to the second substrate; and a base material layer that is provided between the first adhesive layer and the second adhesive layer, wherein the thickness of the base material layer is 5 to 30 times the total thickness of the sealing film (taking the thickness of the sealing film as 100); and the melting point of the resin that constitutes the base material layer is higher than the melting point of the resin that constitutes the first adhesive layer or the second adhesive layer.

[2] The sealing film described in [1], wherein the polyolefin constituting the second adhesive layer is an acid-modified polyolefin.

[3] A sealing film described in [1] or [2], wherein the melting point of the resin constituting the base material layer is 150°C or higher and 170°C or lower, and the melting point of the resin constituting the second adhesive layer is 110°C or higher and 150°C or lower.

[4] A sealing film described in any one of [1] to [3], wherein the melting point of the resin constituting the first adhesive layer is 110°C or higher and 150°C or lower.

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

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

According to one aspect of the present invention, a sealing film, electrode lead wire member, and battery can be provided that are less likely to form unbonded portions and that can suppress spreading during thermocompression bonding.

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 or 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 constituting 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.

The first adhesive layer 2 may contain 100% by mass of the acid-modified polyolefin based on the total amount of the first adhesive layer 2 .
In one embodiment of the present invention, the first adhesive layer 2 "mainly contains an acid-modified polyolefin" means that the first adhesive layer 2 contains 80% by mass or more and 100% by mass or less of acid-modified polyolefin relative to the total amount of the first adhesive layer 2.

Examples of polyolefins that may 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 may 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. In other words, 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).

As an acid-modified polyolefin, acid-modified polypropylene (acid-modified PP) is preferred 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, 5 to 90% relative to the total thickness of the sealing film 1, where the total thickness of the sealing film 1 is taken as 100. That is, the thickness of the first adhesive layer 2 can be 5 to 90% relative to the total thickness of the sealing film 1. The thickness of the first adhesive layer 2 is preferably 25 to 70% relative to the total thickness of the sealing film 1, where the total thickness of the sealing film 1 is taken as 100.
The ratio of the thickness of a layer to the total thickness of the sealing film 1, which is taken as 100, is referred to as the "thickness ratio."

When the thickness ratio of the first adhesive layer 2 is 5 or more (preferably 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 90 or less (preferably 70 or less), sufficient thickness can be imparted to the second adhesive layer 3 and the 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 second adhesive layer 3 "primarily 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% 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.

The second adhesive layer 3 may contain 100% by mass of the acid-modified polyolefin based on the total amount of the second adhesive layer 3 .
In one embodiment of the present invention, the second adhesive layer 3 "mainly contains an acid-modified polyolefin" means that the second adhesive layer 3 contains 80% by mass or more and 100% by mass or less of acid-modified polyolefin relative to the total amount of the second adhesive layer 3.

Examples of polyolefins that may be used to form the second adhesive layer 3 include polypropylene (PP), polyethylene, poly-1-butene, and polyisobutylene. Of these, PP is preferred as the polyolefin that may be used to form the second adhesive layer 3 due to 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 random copolymers being preferred. The polyolefin may also be a copolymer of propylene and an olefinic monomer (e.g., a random copolymer). Examples of olefinic monomers 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. If 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 90, 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 90% of the total thickness of the sealing film 1. The thickness ratio of the second adhesive layer 3 is preferably 5 to 50.

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 90 or less (preferably 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 the polyolefin content is the highest among the resins that make up the base layer 4. 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.

The base layer 4 may contain 100% by mass of the acid-modified polyolefin based on the total amount of the base layer 4 .
In one embodiment of the present invention, the base layer 4 "mainly contains an acid-modified polyolefin" means that the base layer 4 contains 80% by mass or more and 100% by mass or less of the acid-modified polyolefin relative to the total amount of the base layer 4.

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 constituting 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 a polymer of an olefin-based monomer, such as propylene or ethylene, for example, 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 constituting the substrate layer is not particularly limited, and resins other than polyolefins (e.g., fluororesins such as polychlorotrifluoroethylene) may also be used.

The thickness (thickness ratio) of the base material layer 4 is 5 to 30, with the total thickness of the sealing film 1 being 100. In other words, the thickness of the base material layer 4 is 5 to 30% of the total thickness of the sealing film 1. The thickness ratio of the base material layer 4 is preferably 25 to 30.

When the thickness ratio of the base layer 4 is 5 or more (preferably 25 or more), the resin does not flow excessively and is more likely to exhibit the necessary fluidity during crimping. This prevents the sealing film 1 from spreading. For example, it prevents the strip-shaped sealing film 1 from spreading in the width direction beyond the area to be adhered. Furthermore, when the thickness ratio of the base layer 4 is 5 or more (preferably 25 or more), there is also the advantage that the electrolyte resistance and heat resistance of the sealing film 1 can be improved.

When the thickness ratio of the base material layer 4 is 30 or less, the fluidity of the resin during thermocompression bonding can be increased to an appropriate range. In other words, if the thickness ratio of the base material layer 4 is too high, the fluidity (or flexibility) of the resin during thermocompression bonding may be reduced, but when the thickness ratio of the base material layer 4 is 30 or less, the fluidity (or flexibility) of the resin during thermocompression bonding can be optimized. Therefore, even with a short heat sealing time, the resin sufficiently wraps around the electrode lead wire 11, reliably sealing the entire circumference of the electrode lead wire 11. Therefore, unbonded areas (so-called through holes) are less likely to occur at the bonding points (especially the interface between the sealing film 1 and the electrode lead wire 11).

When the thickness ratio of the base layer 4 is 30 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 storage container.

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 layer 4 is 170°C or lower, flexibility can be imparted to the sealing film 1. As a result, gaps are less likely to form between the electrode lead wire 11 and the container and the sealing film 1.

The melting point M4 of the resin constituting the base layer 4 is 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 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 one aspect of the present invention, 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, the resin fluidity does not decrease too much, and the resin fluidity during thermocompression bonding can be kept within an appropriate range. Furthermore, 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.

When the melting point M4 is higher than the melting point M3, the fluidity of the resin does not become too low, and the fluidity of the resin during thermocompression bonding can be kept within an appropriate range. In addition, the electrolyte resistance of the sealing film 1 can be easily ensured without reducing the adhesive strength between the second adhesive layer 3 and the storage container.
If the melting point M4 is higher than either or both of the melting point M2 and the melting point M3, there is also an advantage that the sealing film 1 can be easily provided with heat resistance.

<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 of the lead wire body 111. Among these, aluminum or copper is preferred because of its 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 therefore 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 Figure 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 thereon.

Since the thickness ratio of the base material layer 4 of the sealing film 1 is within the aforementioned range, the resin easily flows appropriately during thermocompression bonding. Therefore, even if the heat sealing time is short, the resin sufficiently wraps around the electrode lead wire 11, reliably sealing the entire circumference of the electrode lead wire 11. Therefore, no unbonded portions (through holes) are formed at the bonded locations (particularly the interface between the sealing film 1 and the electrode lead wire 11), and leakage of the electrolyte solution in the container to the outside can be suppressed. This makes it possible to realize a highly reliable battery 100 (see FIG. 3 ).
The sealing film 1 enables highly reliable sealing in a short heat sealing time, and therefore can increase the productivity of the battery 100 (see FIG. 3).

Because the thickness ratio of the base material layer 4 of the sealing film 1 is within the aforementioned range, the sealing film 1 has good adhesive strength to the electrode lead wire 11 and the container, and is resistant to the electrolyte. This results in a battery 100 that is resistant to deterioration.

The melting point M4 of the resin that makes up the base layer 4 is higher than the melting point M2 of the resin that makes up the first adhesive layer 2 or the melting point M3 of the resin that makes up the second adhesive layer 3. Therefore, during thermocompression bonding, the fluidity of the resin that makes up the base layer 4 is within an appropriate range, ensuring a reliable seal between the electrode lead wire 11 and the container. This prevents the electrolyte in the container from leaking to the outside.

The sealing film 1 contains acid-modified polyolefin as the material for 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. This prevents the electrolyte solution in the container from leaking to the outside.

When the material forming the second adhesive layer 3 contains acid-modified polyolefin, the second adhesive layer 3 is easily heat-sealed with the resin material that constitutes the battery container, making it easy to seal the interface between the container and the sealing film 1.

The electrode lead wire member 10 is provided with a sealing film 1, which prevents unbonded areas (through holes) from occurring and prevents the electrolyte in the storage container from leaking to the outside.

<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, so no unbonded areas (through holes) are formed, and leakage of the electrolyte solution inside the container to the outside can be suppressed. 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 100 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)

The melting point M4 of polypropylene ICP, the resin that constitutes the base layer, is higher than the melting point M2 of the resin that constitutes the first adhesive layer and the melting point M3 of the resin that constitutes the second adhesive layer.

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.

<Preparation of electrode lead wire>
An electrode lead wire was fabricated having a lead wire body and a surface treatment layer formed on the surface of the lead wire body. The lead wire body was made of a rectangular nickel-plated copper foil measuring 45 mm wide and 52 mm long.

<Presence or absence of unbonded parts (through holes)>
The presence or absence of unbonded portions (through holes) at the interface between the electrode lead wire and the sealing film was evaluated as follows.
The sealing film and the electrode lead wire were overlapped and heat-sealed to obtain a measurement specimen. The heat-sealing temperature was 180°C and the pressure was 0.5 MPa. The heat-sealing time (takt time) was 2.4 seconds, 2.7 seconds, or 3.0 seconds.

Colored water was added to the bonded area between the sealing film and the electrode lead wire, and it was checked whether the colored water penetrated along the length of the sealing film. If there was an unbonded area (through hole), the colored water would flow through the unbonded area along the length of the sealing film. If there was no unbonded area, no penetration of the colored water was observed.

If no penetration of the colored water was observed, it was judged as "no penetration" (OK), and it was evaluated that no unbonded areas had formed. If penetration of the colored water was observed, it was judged as "penetration" (NG), and it was evaluated that an unbonded area had formed. The results are shown in Table 1.

<Expansion of sealing films>
The spreading of the sealing film after heat sealing was evaluated as follows.
The sealing film and the electrode lead wire were overlapped and heat-sealed at a temperature of 180° C. and a pressure of 0.5 MPa for a heat-sealing time (takt time) of 3.0 seconds.

When the heat during heat sealing increases the fluidity of the resin, the width of the strip-shaped sealing film (15 mm wide) expands.

If the width of the strip-shaped sealing film after thermocompression bonding (heat sealing) was 15.0 mm or more but less than 16.0 mm, the film was judged to have small spread (OK). If the width of the strip-shaped sealing film after thermocompression bonding was 16.0 mm or more, the film was judged to have large spread (NG). The results are shown in Table 1.

As shown in Table 1, in comparative examples where the thickness ratio of the substrate layer was outside the range of 5 or more and 30 or less, penetration of colored water was observed when the takt time (heat sealing time) was short, and unbonded areas were formed.

In contrast, in Examples 1 to 4, where the thickness ratio of the base layer was in the range of 5 to 30, no penetration of the colored water was observed. This shows that in Examples 1 to 4, unbonded areas were less likely to form even with a short takt time.

Furthermore, in Comparative Examples 5 and 6, where the thickness ratio of the base layer was 0, the width of the sealing film increased significantly due to heat sealing. In contrast, in Examples 1 to 4, the increase in the width of the sealing film was kept small.

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 (9)

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,
The thickness of the base material layer is 5 or more and 30 or less, and the thickness of the first adhesive layer is 55 or more and 70 or less, where the total thickness of the sealing film is 100,
A sealing film, wherein the melting point of the resin constituting the base material layer is higher than the melting point of the resin constituting the first adhesive layer or the second adhesive layer. The sealing film according to claim 1, wherein the polyolefin constituting the second adhesive layer is an acid-modified polyolefin. the melting point of the resin constituting the base layer is 150°C or higher and 170°C or lower;
The sealing film according to claim 1 or 2, wherein the melting point of the resin constituting the second adhesive layer is 110°C or higher and 150°C or lower. The sealing film according to any one of claims 1 to 3, wherein the melting point of the resin constituting the first adhesive layer is 110°C or higher and 150°C or lower. The sealing film according to any one of claims 1 to 4, wherein the thickness of the second adhesive layer is 15 to 25, where the total thickness of the sealing film is 100. The seal film according to any one of claims 1 to 5, wherein the base layer comprises an acid-modified polyolefin. The seal film according to any one of claims 1 to 6, wherein the base layer contains a copolymer of propylene and ethylene. The sealing film according to any one of claims 1 to 7 ,
the first base being an electrode lead wire extending in one direction. The electrode lead wire member according to claim 8 ;
a battery body to which the electrode lead wires are connected;
The second base is a container that houses the battery body.