Sealing film, electrode lead wire member, and battery

Abstract

The present invention provides a sealing film, an electrode lead wire member, and a battery that are less likely to form unadhered areas and can suppress spreading during heat-sealing. [Solution] The sealing film 1 seals the space between a first metal substrate and a second substrate. The sealing film 1 comprises a first adhesive layer 2, a second adhesive layer 3, and a base layer 4. The first adhesive layer 2 mainly contains acid-modified polyolefin and adheres to the first substrate. The second adhesive layer 3 mainly contains polyolefin and adheres to the second substrate. The base layer 4 is provided between the first adhesive layer 2 and the second adhesive layer 3. The total thickness of the sealing film 1 is 100, and the thickness of the base layer 4 is 5 to 25. The melting point of the resin constituting the base layer 4 is higher than the melting point of the resin constituting the first adhesive layer 2 or the second adhesive layer 3.

Description

Technical Field

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

Background Art

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

[0003] In the battery, it has been proposed to interpose a sealing film between the housing container and the electrode lead wire (see, for example, Patent Document 1). The sealing film (hereinafter referred to as the sealing film) seals between the electrode lead wire and the housing container and suppresses leakage of the content liquid in the housing container.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] For the sealing film, it is required to suppress the formation of an unbonded portion (so-called through hole) at the bonding portion and suppress the leakage of the content liquid. Further, when the sealing film softens and has high fluidity during thermocompression bonding, it may spread. For example, it is conceivable that the strip-shaped sealing film 1 spreads in the width direction beyond the range to be bonded.

[0006] One aspect of the present invention aims to provide a sealing film, an electrode lead wire member, and a battery that are less likely to form unadhered areas and can suppress spreading during heat bonding. [Means for solving the problem]

[0007] 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 metal substrate and a second substrate, 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 the thickness of the base layer is 5 to 30, with the total thickness of the sealing film being 100, and the melting point of the resin constituting the base layer is higher than the melting point of the resin constituting the first adhesive layer or the second adhesive layer.

[0009] [2] The sealing film according to [1], wherein the polyolefin constituting the second adhesive layer is an acid-modified polyolefin.

[0010] [3] The sealing film according to [1] or [2], wherein the melting point of the resin constituting the base layer is 150°C or more and 170°C or less, and the melting point of the resin constituting the second adhesive layer is 110°C or more and 150°C or less.

[0011] [4] The sealing film according to 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.

[0012] An electrode lead wire member comprising a sealing film described in any one of [5][1] to [4], and the first substrate which is an electrode lead wire extending in one direction.

[0013] A battery comprising an electrode lead wire member as described in [6][5], a battery body to which the electrode lead wire is connected, and a second base body which is a housing container for housing the battery body. [Effects of the Invention]

[0014] According to one aspect of the present invention, it is possible to provide a sealing film, an electrode lead wire member, and a battery that are less likely to form unadhered areas and can suppress spreading during thermal bonding. [Brief explanation of the drawing]

[0015] [Figure 1] This is a schematic cross-sectional view showing the sealing film of the embodiment. [Figure 2] This is a schematic perspective view showing the electrode lead wire member of the embodiment. [Figure 3] This is a schematic perspective view showing a battery according to an embodiment. [Figure 4] This is a cross-sectional view taken along line segment II in Figure 3. [Modes for carrying out the invention]

[0016] 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 those of the actual components.

[0017] <Sealing film> Figure 1 is a schematic cross-sectional view showing the sealing film 1 of the embodiment. Figure 2 is a schematic perspective view showing the electrode lead wire member 10 of the embodiment.

[0018] As shown in Figure 2, the electrode lead wire member 10 comprises an electrode lead wire 11 and a sealing film 1. The electrode lead wire 11 is an example of the "first substrate". As shown in Figure 1, the sealing film 1 comprises a first adhesive layer 2, a second adhesive layer 3, and a substrate layer 4.

[0019] [First adhesive layer] The first adhesive layer 2 is a layer that fuses (adheres) to the electrode lead wire 11 (see FIG. 2) by heating or pressurization. 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 resin composition).

[0020] The first adhesive layer 2 mainly contains an acid-modified polyolefin. That 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 with respect to the total amount of the first adhesive layer 2, preferably more than 50% by mass, and more preferably 80% by mass or more.

[0021] The first adhesive layer 2 may contain 100% by mass of the acid-modified polyolefin with respect to the total amount of the first adhesive layer 2. In one embodiment of the present invention, that the first adhesive layer 2 "mainly contains an acid-modified polyolefin" means that there is an aspect in which the first adhesive layer 2 contains 80% by mass or more and 100% by mass or less of the acid-modified polyolefin with respect to the total amount of the first adhesive layer 2.

[0022] Examples of the polyolefin constituting the first adhesive layer 2 include polypropylene, polyethylene, poly-1-butene, polyisobutylene, etc. 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".

[0023] 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 preferable. The polyolefin may be a copolymer of propylene and an olefin-based monomer. Examples of the olefin-based monomer include 1-butene, isobutylene, 1-hexene, etc.

[0024] Acid-modified polyolefins are polyolefin resins modified with unsaturated carboxylic acids or derivatives of unsaturated carboxylic acids. Acid-modified polyolefins have acidic functional groups such as carboxyl groups or carboxylic anhydride groups in their molecular structure. Acid-modified polyolefins are obtained by graft polymerization of unsaturated carboxylic acids or derivatives of unsaturated carboxylic acids onto polyolefins, or by copolymerization of acid-functional group-containing monomers with olefins. That is, in acid-modified polyolefins, the repeating units having acidic groups may be included in the side chains or in the main chain.

[0025] Examples of unsaturated carboxylic acids include acrylic acid and methacrylic acid. Examples of 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 adhesion of the first adhesive layer 2 to the electrode lead wire 11 (see Figure 2).

[0026] As an acid-modified polyolefin, acid-modified polypropylene (acid-modified PP) is preferred due to its excellent heat resistance. Acid-modified PP is, for example, a polymer obtained by graft copolymerizing polypropylene or a propylene-ethylene copolymer with an unsaturated carboxylic acid or a derivative of an unsaturated carboxylic acid.

[0027] Acid-modified PP includes ionomers obtained by neutralizing the carboxylate groups of an acid-modified polymer of polypropylene or an acid-modified polymer of propylene-ethylene copolymer with metal hydroxides, alkoxides, lower fatty acid salts, etc. The acid group in acid-modified PP is preferably a maleic anhydride group. In other words, maleic anhydride-modified PP is preferred as the acid-modified PP.

[0028] 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 heat 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 flows more easily during heat bonding, allowing the resin to sufficiently wrap around the electrode lead wire 11, making it easier to seal the entire circumference of the electrode lead wire 11.

[0029] If the "resin constituting the first adhesive layer 2" is a polymer alloy of two or more resins, then the "melting point of the resin constituting the first adhesive layer 2" refers to the melting point of the polymer alloy constituting the first adhesive layer 2.

[0030] In the first adhesive layer 2, optional components other than polyolefins include known additives such as stabilizers, antistatic agents, and colorants.

[0031] The thickness of the first adhesive layer 2 can be, for example, 5 to 90, with the total thickness of the sealing film 1 being 100. That is, the thickness of the first adhesive layer 2 can be 5% to 90% of the total thickness of the sealing film 1. Preferably, the thickness of the first adhesive layer 2 is 25 to 70, with the total thickness of the sealing film 1 being 100. The ratio of layer thicknesses when the total thickness of sealing film 1 is set to 100 is called the "thickness ratio".

[0032] If the thickness ratio of the first adhesive layer 2 is 5 or more (preferably 25 or more), sufficient adhesive strength between the first adhesive layer 2 and the electrode lead wire 11 can be ensured. If the thickness ratio of the first adhesive layer 2 is 90 or less (preferably 70 or less), sufficient thickness can be provided to the second adhesive layer 3 and the base material layer 4. Therefore, the electrolyte resistance of the sealing film 1 can not be reduced, and the adhesive strength between the second adhesive layer 3 and the containment container can be increased. Note that "electrolyte resistance" refers to resistance to electrolyte.

[0033] [Second adhesive layer] The second adhesive layer 3 is a layer that fuses (adheres) to the containment container by, for example, heating and pressurizing. The containment 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).

[0034] The second adhesive layer 3 mainly contains polyolefin. "Mainly containing polyolefin" means that polyolefin has the highest content 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.

[0035] The second adhesive layer 3 may contain 100% by mass of acid-modified polyolefin relative to the total amount of the second adhesive layer 3. In one embodiment of the present invention, the second adhesive layer 3 "mainly contains 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.

[0036] Examples of polyolefins that constitute the second adhesive layer 3 include polypropylene (PP), polyethylene, poly-1-butene, and polyisobutylene. Among these, PP is preferred as a polyolefin for the second adhesive layer 3 due to its excellent flexibility.

[0037] Polyolefins may also be copolymers of propylene and ethylene (propylene-ethylene copolymers). The copolymer of propylene and ethylene may be a block copolymer or a random copolymer, but a random copolymer is preferred. Polyolefins may also be copolymers of propylene and olefin monomers (for example, random copolymers). Examples of olefin monomers include 1-butene, isobutylene, and 1-hexene.

[0038] The polyolefin constituting the second adhesive layer 3 may be an acid-modified polyolefin. As the acid-modified polyolefin, acid-modified PP is preferred due to its excellent heat resistance. As the acid-modified PP, the acid-modified PP exemplified as the material for the first adhesive layer 2 described above is preferably used. As the acid-modified PP, a polymer obtained by acid-modifying a random copolymer of propylene and ethylene is preferred due to its excellent flexibility. By using an acid-modified polyolefin, the adhesion of the second adhesive layer 3 to the container can be improved.

[0039] 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 the deterioration of the first adhesive layer 2.

[0040] 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 heat 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 flows more easily during heat bonding, making it easier to seal the space between the containment container and the electrode lead wire 11.

[0041] If the "resin constituting the second adhesive layer 3" is a polymer alloy of two or more resins, then the "melting point of the resin constituting the second adhesive layer 3" refers to the melting point of the polymer alloy constituting the second adhesive layer 3.

[0042] In the second adhesive layer 3, optional components other than acid-modified polyolefins include known additives such as stabilizers, antistatic agents, and colorants.

[0043] The thickness (thickness ratio) of the second adhesive layer 3 can be, for example, 5 to 90, 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 90% of the total thickness of the sealing film 1. The thickness ratio of the second adhesive layer 3 is preferably 5 to 50.

[0044] If the thickness ratio of the second adhesive layer 3 is 5 or more, sufficient adhesive strength between the second adhesive layer 3 and the containment container can be ensured. If the thickness ratio of the second adhesive layer 3 is 90 or less (preferably 50 or less), sufficient thickness can be provided to the first adhesive layer 2 and the substrate layer 4. Therefore, the electrolyte resistance of the sealing film 1 can not be reduced, and the adhesive strength between the first adhesive layer 2 and the electrode lead wire 11 can be increased.

[0045] [Base material layer] The base layer 4 is interposed between the first adhesive layer 2 and the second adhesive layer 3. The base layer 4 is made of, for example, a resin (or a resin composition).

[0046] The base layer 4 mainly contains, for example, polyolefin. "Mainly containing polyolefin" means that polyolefin has the highest content among the resins constituting 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.

[0047] The base layer 4 may contain 100% by mass of acid-modified polyolefin relative to the total amount of the base layer 4. In one embodiment of the present invention, the statement that the base layer 4 "mainly contains acid-modified polyolefin" means that the base layer 4 contains 80% by mass or more and 100% by mass or less of acid-modified polyolefin relative to the total amount of the base layer 4.

[0048] Examples of polyolefins constituting the base layer 4 include polypropylene (PP), polyethylene, poly-1-butene, and polyisobutylene. Among these, PP is preferred due to its excellent flexibility.

[0049] 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 a homopolymer is a homopolymer of propylene alone (homoPP). An example of a 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 polyolefins constituting the base layer 4 include the polymers exemplified as polyolefins constituting the first adhesive layer 2.

[0050] As the polyolefin constituting the base layer 4, ICP (impact copolymer) is preferred. The ICP has a phase-separated structure having a first phase and a second phase, for example, a sea-island structure. The sea-island structure is a structure in which multiple second phases corresponding to "islands" are dispersed in a first phase corresponding to the "sea".

[0051] The first phase is composed of homopolymers of olefin monomers such as propylene and ethylene. The second phase is composed of polymers different from the homopolymers that make up the first phase. The second phase includes polymers of olefin monomers such as propylene and ethylene, such as ethylene-propylene rubber (EPR). The second phase is composed of a main phase and a surface layer covering the surface of the main phase. The main phase is composed of polyethylene, for example. The surface layer is composed of EPR, for example.

[0052] ICP in which the homopolymer constituting the first phase is homo-PP is called polypropylene ICP or polypropylene dispersion. ICP in which the homopolymer constituting the first phase is homo-PP is also known as block PP. ICP is also called heterophasic copolymer or block copolymer.

[0053] The constituent materials of the base layer are not particularly limited, and resins other than polyolefins (for example, fluororesins such as polychlorotrifluoroethylene) may be used.

[0054] The thickness (thickness ratio) of the base layer 4 is set to be between 5 and 30, with the total thickness of the sealing film 1 being 100. In other words, the thickness of the base layer 4 is between 5% and 30% of the total thickness of the sealing film 1. Preferably, the thickness ratio of the base layer 4 is between 25% and 30%.

[0055] When the thickness ratio of the base layer 4 is 5 or more (preferably 25 or more), the resin does not flow excessively easily, and the necessary fluidity is more readily achieved during bonding. Therefore, the spreading of the sealing film 1 can be suppressed. For example, it is possible to prevent a strip-shaped sealing film 1 from spreading in the width direction beyond the area to be bonded. In addition, when the thickness ratio of the base layer 4 is 5 or more (preferably 25 or more), there is also the advantage of improving the electrolyte resistance and heat resistance of the sealing film 1.

[0056] When the thickness ratio of the base layer 4 is 30 or less, the fluidity of the resin during heat sealing can be increased to an appropriate range. In other words, if the thickness ratio of the base layer 4 is too high, the fluidity (or flexibility) of the resin during heat sealing may be low, but when the thickness ratio of the base layer 4 is 30 or less, the fluidity (or flexibility) of the resin during heat sealing can be optimized. Therefore, even if the heat sealing time is short, the resin will sufficiently flow around the electrode lead wire 11, and the entire circumference of the electrode lead wire 11 will be reliably sealed. Consequently, it is less likely that unbonded areas (so-called through-holes) will occur at the bonding site (especially at the interface between the sealing film 1 and the electrode lead wire 11).

[0057] If the thickness ratio of the base layer 4 is 30 or less, sufficient thickness can be provided to the first adhesive layer 2 and the second adhesive layer 3. As a result, 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 containment container can both be increased.

[0058] 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. If the melting point of the resin constituting the base layer 4 is 150°C or higher, it is easier to ensure the electrolyte resistance of the sealing film 1. Furthermore, heat resistance can be imparted to the sealing film 1.

[0059] If the melting point of the resin constituting the base layer 4 is 170°C or lower, flexibility can be given to the sealing film 1. As a result, gaps are less likely to form between the electrode lead wires 11 and the containment container and the sealing film 1.

[0060] 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. That is, 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 is higher than either the melting point M2 or the melting point M3. In one embodiment of the present invention, it is desirable that the melting point M4 is higher than at least one of the melting points M2 and the melting point M3.

[0061] If the melting point M4 is higher than the melting point M2, the fluidity of the resin will not become too low, and the fluidity of the resin during thermocompression bonding can be kept within an appropriate range. In addition, 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.

[0062] If the melting point M4 is higher than the melting point M3, the fluidity of the resin will not become too low, and the fluidity of the resin during heat-press bonding can be kept within an appropriate range. In addition, it becomes easier to ensure the electrolyte resistance of the sealing film 1 without reducing the adhesive strength between the second adhesive layer 3 and the containment container. If the melting point M4 is higher than either or both of the melting points M2 or M3, there is also the advantage that it is easier to impart heat resistance to the sealing film 1.

[0063] <Electrode lead wire component> As shown in Figure 2, the electrode lead wire member 10 has an electrode lead wire 11 and a pair of sealing films 1. The pair of sealing films 1 are arranged with their first adhesive layers 2 facing each other. The pair of sealing films 1 sandwich the electrode lead wire 11. Each of the pair of sealing films 1 contacts a region corresponding to one side and the other side of the electrode lead wire 11. Therefore, the pair of sealing films 1 as a whole are in contact with the entire circumference of the electrode lead wire 11.

[0064] 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.

[0065] The electrode lead wire 11 is conductive. The electrode lead wire 11 is electrically connected to the lithium-ion battery 30 (see Figure 3). The electrode lead wire 11 conducts power between the lithium-ion battery 30 and external devices. As the material for the lead wire body 111, known metals such as aluminum, copper, nickel, iron, gold, platinum, and various alloys can be used. Among these, aluminum or copper are preferred because they have excellent conductivity and are cost-effective.

[0066] The lead wire body 111 may have a nickel-plated surface. The nickel plating of the lead wire body 111 may be formed by electroplating using a Watt bath mainly composed of nickel sulfate, nickel chloride, boric acid, etc. It is preferable to perform the nickel plating of the lead wire body 111 using a nickel sulfamate plating bath mainly composed of nickel sulfamate and boric acid. The plating film formed by this method has excellent flexibility, making the plating film less prone to cracking. The lead wire body 111 is preferably made of an aluminum plate or a nickel-plated copper plate.

[0067] 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 resistant to corrosion caused by the electrolyte inside the battery. Examples of the surface treatment layer 112 include acid-resistant coatings made from phosphates, chromates, fluorides, or triazinethiol compounds. The acid-resistant coating can be formed by applying a chemical conversion treatment to the lead wire body 111.

[0068] 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 over the entire surface of the lead wire body 111. Note that the electrode lead wire does not necessarily need to have a surface treatment layer formed on it.

[0069] Because the thickness ratio of the substrate layer 4 in the sealing film 1 is within the aforementioned range, the resin flows appropriately during heat sealing. Therefore, even with a short heat sealing time, the resin sufficiently flows around the electrode lead wires 11, ensuring complete sealing of the entire circumference of the electrode lead wires 11. Consequently, no unbonded areas (through-holes) are created at the bonding points (especially at the interface between the sealing film 1 and the electrode lead wires 11), preventing the electrolyte from leaking out of the container. Thus, a highly reliable battery 100 (see Figure 3) can be realized. The sealing film 1 enables highly reliable sealing with a short heat sealing time, thereby increasing the productivity of the battery 100 (see Figure 3).

[0070] Because the thickness ratio of the substrate layer 4 of the sealing film 1 is within the aforementioned range, it exhibits good adhesive strength to the electrode lead wires 11 and the housing container, and also possesses resistance to the electrolyte. Thus, a battery 100 that is less prone to degradation is obtained.

[0071] 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. Therefore, during thermocompression bonding, the fluidity of the resin constituting the base layer 4 is within an appropriate range, and the space between the electrode lead wire 11 and the containment container can be reliably sealed. Consequently, leakage of the electrolyte from the containment container to the outside can be suppressed.

[0072] The sealing film 1 contains an acid-modified polyolefin as the material for forming the first adhesive layer 2. Therefore, the first adhesive layer 2 readily heat-fusses to the electrode lead wire 11, and the interface between the electrode lead wire 11 and the sealing film 1 can be sealed. Thus, leakage of the electrolyte from the containment container to the outside can be suppressed.

[0073] When the forming material for the second adhesive layer 3 includes an acid-modified polyolefin, the second adhesive layer 3 readily heat-seals with the resin material constituting the battery housing, and readily seals the interface between the housing and the sealing film 1.

[0074] Since the electrode lead wire member 10 is equipped with a sealing film 1, no unadhesive parts (through holes) are created, and leakage of the electrolyte solution inside the containment container to the outside can be suppressed.

[0075] <Battery> Figure 3 is a schematic perspective view showing the battery 100 of the embodiment. As shown in Figure 3, the battery 100 comprises the electrode lead wire member 10 described above, a housing container 20, and a lithium-ion battery 30 (battery body).

[0076] The containment container 20 has a container body 21 and a lid 22. The containment container 20 is an example of the "second substrate". The container body 21 has a molded portion 21a that forms a recess for housing the lithium-ion battery 30. The container body 21 is obtained by drawing a laminate for battery casing. The lid 22 is made of a laminate for battery casing and has the same planar area as the container body 21. The laminate for battery casing will be described later. The container 20 is formed by overlapping the container body 21 and the lid 22 and heat-sealing the peripheral edge 25.

[0077] Figure 4 is a cross-sectional view taken along line segment II in Figure 3. As shown in Figure 4, the laminate for the battery casing, 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.

[0078] The resins constituting the first film substrate 201 and the second film substrate 202 are not particularly limited, but polyamide, polyethylene terephthalate (PET), phenolic resin, polypropylene, etc. are preferred. As the metal foil 203, aluminum foil, stainless steel foil, copper foil, iron foil, etc. are preferred.

[0079] The sealant layer 204 is heat-fused to the second adhesive layer 3 of the sealing film 1. The resin constituting the sealant layer 204 is selected to be fused to the sealing film 1. Examples of resins constituting the sealant layer 204 include polypropylene resins and polyethylene resins. As polypropylene resins, polypropylene homopolymers, copolymers of propylene and ethylene, etc., can be used. As polyethylene resins, low-density polyethylene, linear low-density polyethylene, etc., may be used.

[0080] As shown in Figures 3 and 4, in the battery 100, the electrode lead wires 11 are drawn out from the lithium-ion battery 30 inside the housing 20 (inside the molded part 21a) to the outside of the housing 20. The electrode lead wires 11 are fused to the sealant layer 204 of the housing 20 via the sealing film 1.

[0081] In the battery 100, since the electrode lead wire member 10 has the aforementioned sealing film 1, no unadhesive parts (through holes) are created, and leakage of the electrolyte from the housing to the outside can be suppressed. Therefore, a highly reliable battery 100 can be realized.

[0082] Preferred embodiments of the present invention have been described above with reference to the attached drawings, but the present invention is not limited to these examples. The shapes and combinations of the constituent members shown in the above examples are just examples, and can be modified in various ways 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 resins other than polyolefin. Also, the sealing film may contain layers other than the first adhesive layer, the base layer, and the second adhesive layer. [Examples]

[0083] The present invention will be described below with reference to Reference Example 1, Examples 2-4, and Comparative Examples 1-6, but the present invention is not limited to these examples.

[0084] <Preparation of sealing film> A sealing film was prepared in which a first adhesive layer, a substrate layer, and a second adhesive layer were laminated in this order as follows: The resins that would be the raw materials for each layer were heated and melted separately, and a laminate was obtained by simultaneously forming a multilayer film using an extruder capable of simultaneous multilayer extrusion molding. By cutting this laminate into strips (width 15 mm, thickness 100 μm), the sealing films of each example and comparative example were obtained.

[0085] The constituent materials of the first adhesive layer, the substrate 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℃) Second adhesive layer: Random copolymer of propylene and ethylene (melting point 140°C)

[0086] The melting point M4 of polypropylene ICP, which is the resin constituting the base layer, is higher than the melting point M2 of the resin constituting the first adhesive layer and the melting point M3 of the resin constituting the second adhesive layer.

[0087] Maleic anhydride-modified polypropylene is a polymer obtained by graft polymerization of maleic anhydride onto a random copolymer of propylene and ethylene. Polypropylene ICP has a structure in which the second phase is dispersed within 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.

[0088] <Fabrication of electrode lead wires> An electrode lead wire was fabricated, comprising a lead wire body and a surface treatment layer formed on the surface of the lead wire body. A rectangular nickel-plated copper foil measuring 45 mm in width and 52 mm in length was used as the lead wire body.

[0089] <Presence or absence of unbonded areas (through-holes)> The presence or absence of unadhered areas (through-holes) at the interface between the electrode lead wire and the sealing film was evaluated as follows. The sealing film and electrode lead wires were overlapped and bonded by heat sealing to obtain the sample for measurement. The heat sealing temperature was 180°C and the pressure was 0.5 MPa. The heat sealing time (cycle time) was 2.4 seconds, 2.7 seconds, or 3.0 seconds.

[0090] Colored water was added to the bonding area between the sealing film and the electrode lead wire, and it was examined whether the colored water penetrated along the length of the sealing film. If there was an unbonded area (through-hole), the colored water flowed 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.

[0091] If no penetration of the colored water was observed, it was judged as "no penetration" (OK), and it was evaluated that no unadhered areas were formed. If penetration of the colored water was observed, it was judged as "penetration present" (NG), and it was evaluated that unadhered areas were formed. The results are shown in Table 1.

[0092] <Expansion of sealing film> The expansion of the sealing film after heat sealing was evaluated as follows. The sealing film and electrode lead wires were overlapped and bonded by heat sealing. The heat sealing temperature was 180°C and the pressure was 0.5 MPa. The heat sealing time (cycle time) was 3.0 seconds.

[0093] When the heat generated during heat sealing increases the fluidity of the resin, the strip-shaped (15mm wide) sealing film expands in width.

[0094] If the width of the strip-shaped sealing film after heat sealing was 15.0 mm or more but less than 16.0 mm, it was judged as small film spreading (OK). If the width of the strip-shaped sealing film after heat sealing was 16.0 mm or more, it was judged as large film spreading (NG). The results are shown in Table 1.

[0095] [Table 1]

[0096] As shown in Table 1, in Comparative Examples 1 to 4, where the thickness ratio of the substrate layer fell outside the range of 5 to 25, penetration of colored water was observed during short cycle times (heat sealing time), and unadhered areas were formed.

[0097] In contrast, in Examples 2-4, where the substrate layer thickness ratio was in the range of 5 to 25, no penetration of colored water was observed. This indicates that in Examples 2-4, unadhered areas were less likely to form even with short cycle times.

[0098] Furthermore, in Comparative Examples 5 and 6, where the thickness ratio of the base layer was 0, the width of the sealing film expanded significantly due to heat sealing. In contrast, in Examples 2 to 4, the expansion of the sealing film width was kept to a minimum. [Explanation of symbols]

[0099] 1...Sealing film, 2...First adhesive layer, 3...Second adhesive layer, 4...Base layer, 10...Electrode lead wire component, 11...Electrode lead wire (first base), 20...Housing container (second base), 30...Lithium-ion battery (battery body), 100...Battery.

Claims

1. A sealing film that seals the space between a first metal substrate and a second substrate, A first adhesive layer mainly comprising an acid-modified polyolefin, which adheres to the first substrate, A second adhesive layer mainly comprising polyolefin and adhering to the second substrate, A substrate layer provided between the first adhesive layer and the second adhesive layer, The thickness of the substrate layer is 5 to 25, with the total thickness of the sealing film being 100. The melting point of the resin constituting the base layer is higher than the melting point of the resin constituting the first adhesive layer or the second adhesive layer. The substrate layer is a sealing film containing a propylene-based resin having a sea-island structure in which a dispersed phase containing ethylene-propylene rubber is dispersed in a continuous phase of propylene polymer.

2. The sealing film according to claim 1, wherein the polyolefin constituting the second adhesive layer is an acid-modified polyolefin.

3. 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.

4. 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.

5. A sealing film according to any one of claims 1 to 4, An electrode lead wire member comprising: a first substrate which is an electrode lead wire extending in one direction;

6. The electrode lead wire member according to claim 5, The battery body to which the electrode lead wires are connected, A battery comprising: a second base which is a housing container for housing the battery body.

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