Battery current collector reinforcing film and current collector

Abstract

To provide a film for reinforcing a battery current collector that has high electrolyte resistance and is less likely to cause blocking.SOLUTION: A film for reinforcing a battery current collector includes a resin film, and an adhesive layer formed on the surface of the resin film, and the adhesive layer includes an acid-modified polyolefin resin, a polyester resin, and an epoxy resin, and the adhesive layer contains 10 to 200 parts by weight of the polyester resin and 7.5 to 10 parts by weight of the epoxy resin based on 100 parts by weight of the acid-modified polyolefin resin.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a battery current collector reinforcing film and a current collector. [Background technology]

[0002] Lithium-ion batteries are known as high-capacity secondary batteries and are widely used as power sources for electronic devices. 2. Description of the Related Art In recent years, with the increasing performance of various electronic devices, development of lithium ion batteries has been ongoing to further increase their capacity, improve their safety, reduce their production costs, and so on.

[0003] In general, an electrode for a lithium ion battery comprises a current collector (metal foil) and an active material layer formed on the current collector. As an example of such an electrode for a lithium ion battery, Patent Document 1 discloses an electrode for a lithium ion battery, which includes a current collector and an active material layer formed on a surface of the current collector, the active material layer including active material particles and a binder resin, and a first xy orthogonal coordinate system is set on the surface of the active material layer, and an arithmetic mean roughness of the surface of the active material layer measured in the x-axis direction of the first xy orthogonal coordinate system is defined as R ax The arithmetic mean roughness of the surface of the active material layer measured in the y-axis direction of the first xy orthogonal coordinate system is R ay Then, R ax -R ay the absolute value of R is 0.2 μm or less, the first xy orthogonal coordinate system is rotated 45° within a plane formed by the x-axis and the y-axis to form a second xy orthogonal coordinate system, and the arithmetic average roughness of the surface of the active material layer measured in the x-axis direction of the second xy orthogonal coordinate system is defined as R ax ', and the arithmetic mean roughness of the surface of the active material layer measured in the y-axis direction of the second xy orthogonal coordinate system is R ay ', R ax '-R ay An electrode for a lithium ion battery is disclosed in which the absolute value of .lambda.' is 0.2 .mu.m or less. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2019 / 142669 Summary of the Invention [Problem to be solved by the invention]

[0005] In lithium ion batteries, the current collector (metal foil) does not directly contribute to the battery capacity, so it is preferable that it is as thin as possible. For example, Patent Document 1 describes that a current collector (metal foil) having a thickness of 1 to 500 μm can be used. However, in reality, if the thickness of the current collector (metal foil) is 10 μm or less, the current collector (metal foil) is easily damaged and no longer functions as a current collector.

[0006] In order to prevent damage to the thin current collector (metal foil), it is possible to arrange a reinforcing member on the current collector (metal foil). More specifically, it is conceivable to use a resin film as a reinforcing member and to attach the resin film to the current collector (metal foil) using an adhesive.

[0007] In lithium-ion batteries, the current collector (metal foil) is surrounded by an electrolyte, and if a resin film is placed on the current collector (metal foil), the adhesive may dissolve or swell due to the electrolyte, causing deterioration, which may lead to the resin film peeling off. For this reason, the resin film is required to be resistant to the electrolyte. Furthermore, since resin films are generally stored in a rolled state, they must not undergo blocking during storage.

[0008] The present invention has been made to solve the above problems, and an object of the present invention is to provide a film for reinforcing a battery current collector that has high electrolyte resistance and is less susceptible to blocking. [Means for solving the problem]

[0009] The battery current collector reinforcing film of the present invention is a battery current collector reinforcing film comprising a resin film and an adhesive layer formed on the surface of the resin film, wherein the adhesive layer contains an acid-modified polyolefin resin, a polyester resin, and an epoxy resin, and the adhesive layer contains 10 to 200 parts by weight of the polyester resin and 7.5 to 10 parts by weight of the epoxy resin per 100 parts by weight of the acid-modified polyolefin resin.

[0010] The battery current collector reinforcing film of the present invention is disposed on the metal foil that constitutes the main body of the current collector. Since the metal foil is reinforced by the battery current collector reinforcing film of the present invention, the current collector is less likely to be damaged even if the metal foil is thin.

[0011] In the battery current collector reinforcing film of the present invention, the adhesive layer contains an acid-modified polyolefin resin and a polyester resin. The acid-modified polyolefin resin imparts electrolyte resistance and blocking resistance to the adhesive layer. The polyester resin imparts adhesive properties to the adhesive layer.

[0012] In the battery current collector reinforcing film of the present invention, the adhesive layer contains 10 to 200 parts by weight of polyester resin per 100 parts by weight of acid-modified polyolefin resin. If the weight ratio of the polyester resin is less than the above range, the adhesive strength of the adhesive layer decreases. If the weight ratio of the polyester resin exceeds the above range, the adhesive layer has improved adhesion but has poor electrolyte resistance, and the battery current collector reinforcing film is prone to blocking and curling.

[0013] In the battery current collector reinforcing film of the present invention, the adhesive layer contains 7.5 to 10 parts by weight of an epoxy resin per 100 parts by weight of an acid-modified polyolefin resin. When the epoxy resin is contained in the above weight ratio, the adhesive layer can be cured suitably.

[0014] In the battery current collector reinforcing film of the present invention, the acid-modified polyolefin resin preferably has a number average molecular weight (Mn) of 20,000 or more. When the acid-modified polyolefin resin has a number average molecular weight (Mn) of 20,000 or more, the adhesive layer has improved resistance to an electrolyte.

[0015] In the battery current collector reinforcing film of the present invention, the polyester resin preferably has a glass transition temperature (Tg) of -60°C or higher. When the glass transition temperature (Tg) of the polyester resin is −60° C. or higher, the adhesive strength of the adhesive layer is improved.

[0016] In the battery current collector reinforcing film of the present invention, the adhesive layer preferably has a thickness of 2 to 5 μm. When the thickness of the adhesive layer is within the above range, the overall thickness of the current collector using the battery current collector reinforcing film of the present invention can be made thin.

[0017] In the battery current collector reinforcing film of the present invention, the epoxy resin preferably functions as a curing agent. When an epoxy resin is used as a curing agent, the occurrence of blocking and curling in the battery current collector reinforcing film can be suppressed.

[0018] The current collector of the present invention is characterized by comprising the above-mentioned battery current collector reinforcing film of the present invention, and a metal foil disposed on the adhesive layer of the above-mentioned battery current collector reinforcing film.

[0019] The current collector of the present invention includes the above-mentioned battery current collector reinforcing film of the present invention. Therefore, even if the metal foil is thin, damage to the metal foil can be prevented.

[0020] In the current collector of the present invention, the metal foil is preferably made of copper or aluminum. The current collector, the metal foil of which is made of copper, functions as a negative electrode current collector. The current collector in which the metal foil is made of aluminum functions as a positive electrode current collector.

[0021] In the current collector of the present invention, the metal foil is preferably made of copper and has a thickness of 2 to 4 μm. In a typical lithium-ion battery, when the metal foil that functions as a current collector is made of copper, its thickness is about 6 μm. If the metal foil is thinner than this thickness, it becomes more susceptible to damage. However, the current collector of the present invention includes the above-mentioned battery current collector reinforcing film. Therefore, even if the metal foil is thin, damage to the metal foil can be prevented.

[0022] In the current collector of the present invention, the metal foil is preferably made of aluminum and has a thickness of 4 to 9 μm. In a typical lithium-ion battery, when the metal foil that functions as a current collector is made of aluminum, its thickness is about 12 μm. If the metal foil is thinner than this thickness, it becomes more susceptible to breakage. However, the current collector of the present invention includes the above-mentioned battery current collector reinforcing film. Therefore, even if the metal foil is thin, damage to the metal foil can be prevented. Effect of the Invention

[0023] According to the present invention, it is possible to provide a film for reinforcing a battery current collector, which has high electrolyte resistance and is less susceptible to blocking. [Brief description of the drawings]

[0024] [Figure 1] FIG. 1 is a cross-sectional view that illustrates an example of a battery current collector reinforcing film of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view that illustrates an example of the current collector of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] The battery current collector reinforcing film and current collector of the present invention will be specifically described below. However, the present invention is not limited to the following embodiments, and can be appropriately modified and applied within the scope of the present invention.

[0026] FIG. 1 is a cross-sectional view that illustrates an example of a battery current collector reinforcing film of the present invention. A battery current collector reinforcing film 10 shown in FIG. 1 is composed of a resin film 11 and an adhesive layer 12 formed on the surface of the resin film 11 .

[0027] In the battery current collector reinforcing film 10, the adhesive layer 12 contains an acid-modified polyolefin resin, a polyester resin, and an epoxy resin. The adhesive layer 12 contains 100 parts by weight of the acid-modified polyolefin resin, 10 to 200 parts by weight of the polyester resin, and 7.5 to 10 parts by weight of the epoxy resin.

[0028] The battery current collector reinforcing film 10 is disposed on the metal foil that will be the main body of the current collector. The metal foil is reinforced by the battery current collector reinforcing film 10, so that even if the metal foil becomes thin, it is less likely to break.

[0029] In the battery current collector reinforcing film 10, the adhesive layer 12 contains an acid-modified polyolefin resin and a polyester resin. The acid-modified polyolefin resin imparts electrolyte resistance and blocking resistance to the adhesive layer. The polyester resin imparts adhesive properties to the adhesive layer.

[0030] In the battery current collector reinforcing film 10, the adhesive layer 12 contains 10 to 200 parts by weight of polyester resin per 100 parts by weight of acid-modified polyolefin resin. The weight ratio of polyester resin to 100 parts by weight of acid-modified polyolefin resin is preferably 40 to 150 parts by weight. If the weight ratio of the polyester resin is less than the above range, the adhesive strength of the adhesive layer 12 decreases. If the weight ratio of the polyester resin exceeds the above range, the adhesive layer 12 has improved adhesion but has poor resistance to electrolyte, and is prone to blocking and curling of the battery current collector reinforcing film 10.

[0031] In the battery current collector reinforcing film 10, the adhesive layer 12 contains 7.5 to 10 parts by weight of epoxy resin per 100 parts by weight of acid-modified polyolefin resin. The weight ratio of epoxy resin to 100 parts by weight of acid-modified polyolefin resin is preferably 7.5 to 8.5 parts by weight. When the epoxy resin is contained in the above weight ratio, the adhesive layer 12 can be cured appropriately.

[0032] Each component of the battery current collector reinforcing film of the present invention will be described in detail below.

[0033] <Resin film> The material of the resin film is not particularly limited, but is preferably made of polyimide resin, polyethylene terephthalate resin, polyphenylene sulfide resin, or the like. These resins are easy to process and have high strength, and are therefore suitable for reinforcing the metal foil that constitutes the main body of the current collector.

[0034] The thickness of the resin film is not particularly limited, but is preferably 9 μm or less, and more preferably 3 to 6 μm. If the thickness of the resin film exceeds 9 μm, the entire current collector using the battery current collector reinforcing film becomes thick. Therefore, the volume occupied by the current collector in the battery becomes large, and the amount of active material arranged on the current collector becomes relatively small. As a result, the battery capacity is likely to decrease.

[0035] <Adhesive layer> The thickness of the adhesive layer is not particularly limited, but is preferably from 2 to 5 μm, and more preferably from 3 to 4 μm. When the thickness of the adhesive layer is within the above range, the overall thickness of the current collector using the battery current collector reinforcing film of the present invention can be made thin. If the thickness of the adhesive layer is less than 2 μm, the amount of the adhesive layer is small, and therefore the adhesive strength of the adhesive layer is likely to decrease. If the thickness of the adhesive layer exceeds 5 μm, the entire current collector using the battery current collector reinforcing film becomes thick. Therefore, the volume of the current collector in the battery becomes large, and the amount of active material arranged on the current collector becomes relatively small. As a result, the battery capacity is likely to decrease.

[0036] (Acid-modified polyolefin resin) As described above, the acid-modified polyolefin resin imparts electrolyte resistance and blocking resistance to the adhesive layer. This is believed to be because the acid-modified polyolefin resin has poor reactivity and is difficult to change. On the other hand, the acid-modified polyolefin resin has a low adhesive strength, and therefore, if the adhesive layer does not contain a polyester resin among the acid-modified polyolefin resin and the polyester resin, the adhesive strength of the adhesive layer will be insufficient.

[0037] The number average molecular weight (Mn) of the acid-modified polyolefin resin is preferably 20,000 or more, and more preferably 50,000 to 100,000. When the acid-modified polyolefin resin has a number average molecular weight (Mn) of 20,000 or more, the adhesive layer has improved resistance to an electrolyte.

[0038] In this specification, the number average molecular weight (Mn) of a resin can be measured by gel permeation chromatography (GPC) using tetrahydrofuran as a mobile phase and calculated using a calibration curve converted into polystyrene.

[0039] The glass transition temperature (Tg) of the acid-modified polyolefin resin is preferably 0°C or higher, and more preferably 10 to 30°C. If the glass transition temperature (Tg) of the acid-modified polyolefin resin is 30° C. or higher, the adhesive strength of the adhesive layer decreases.

[0040] In this specification, the glass transition temperature (Tg) of a resin means a value calculated by the following method. First, 5 mg of a measurement sample is placed in an aluminum pan using a differential scanning calorimeter (for example, Seiko Denshi Kogyo Co., Ltd., product name "DSC220 type") and the lid is pressed down to seal. Next, the sample is maintained at 220°C for 5 minutes to completely melt, then quenched with liquid nitrogen, and then heated from -150°C to 250°C at a heating rate of 20°C / min. The data obtained is plotted on a coordinate system with the heating time on the horizontal axis and the sample temperature on the vertical axis to draw a curve. The inflection point of the curve is taken as the glass transition point Tg.

[0041] The acid value of the acid-modified polyolefin resin is preferably 4,000 to 6,000 g / eq, and more preferably 4,200 to 5,000 g / eq. If the acid value is less than 4,000 g / eq, the reactivity with the curing agent is high and the adhesive strength is also high, but blocking is likely to occur.

[0042] (polyester resin) As mentioned above, the polyester resin imparts adhesive properties to the adhesive layer. On the other hand, polyester resins are highly reactive, and therefore, when the adhesive layer does not contain an acid-modified polyolefin resin out of the acid-modified polyolefin resin and the polyester resin, the electrolyte resistance and blocking resistance become insufficient.

[0043] The number average molecular weight (Mn) of the polyester resin is preferably from 30,000 to 120,000, and more preferably from 70,000 to 100,000. When the number average molecular weight (Mn) of the polyester resin is within the above range, the polyester resin is endowed with electrolyte resistance.

[0044] The glass transition temperature (Tg) of the polyester resin is preferably -60°C or higher, and more preferably -60 to 0°C. If the glass transition temperature (Tg) of the polyester resin is 30° C. or higher, the adhesive strength is weakened when thermal lamination is carried out.

[0045] The acid value of the polyester resin is preferably from 3,000 to 7,000 g / eq, and more preferably from 4,000 to 6,000 g / eq. If the acid value is less than 3,000 g / eq, the reactivity is high and there is a possibility that blocking may occur when the film is wound after coating.If the acid value is more than 7,000 g / eq, the reactivity is low, the crosslinking reaction does not occur, and the electrolyte resistance is poor.

[0046] (Epoxy resin) In the adhesive layer, the epoxy resin preferably functions as a curing agent. When an epoxy resin is used as a curing agent, the occurrence of blocking and curling in the battery current collector reinforcing film can be suppressed. Generally, isocyanate-based curing agents are also known as curing agents for curing adhesives. When the adhesive layer of the battery current collector reinforcing film of the present invention contains an isocyanate-based curing agent as a curing agent, the adhesive layer has improved adhesion. However, blocking and curling are more likely to occur in the battery current collector reinforcing film of the present invention. Therefore, it is preferable that the battery current collector reinforcing film of the present invention contains an epoxy resin as a curing agent rather than an isocyanate-based curing agent.

[0047] If it is desired to improve the adhesiveness of the adhesive layer, a small amount of an isocyanate-based hardener may be used as the hardener. In this case, the weight ratio of the isocyanate-based curing agent to the epoxy resin is preferably 1 to 10 parts by weight of the isocyanate-based curing agent per 100 parts by weight of the epoxy resin.

[0048] The acid value of the epoxy resin is preferably 150 to 350 g / eq, and more preferably 200 to 300 g / eq. If the acid value of the epoxy resin is lower than 150g / eq, the reactivity is high and the product life is short.If the acid value of the epoxy resin is higher than 350g / eq, the reactivity is low and the crosslinking reaction takes a long time, making efficient production impossible.

[0049] Such an epoxy resin is not particularly limited as long as it has a glycidyl group in the molecule, but preferably has two or more glycidyl groups in the molecule. Specifically, it is not particularly limited, but at least one selected from the group consisting of biphenyl type epoxy resin, naphthalene type epoxy resin, bisphenol A type epoxy resin, bisphenol F type epoxy resin, novolac type epoxy resin, alicyclic epoxy resin, dicyclopentadiene type epoxy resin, tetraglycidyl diaminodiphenylmethane, triglycidyl paraaminophenol, tetraglycidyl bisaminomethylcyclohexanone, and N,N,N',N'-tetraglycidyl-m-xylylenediamine can be used. Preferably, it is a biphenyl type epoxy resin, a novolac type epoxy resin, or a dicyclopentadiene type epoxy resin.

[0050] (Other additives) The adhesive layer may further contain additives such as an amine-based initiator, an imidazole-based curing agent, a phenol-based curing agent, or a cationic curing agent.

[0051] Next, a current collector using the battery current collector reinforcing film of the present invention will be described. Note that a current collector using the battery current collector reinforcing film of the present invention is also a current collector of the present invention. FIG. 2 is a cross-sectional view that illustrates an example of the current collector of the present invention. The current collector 1 shown in FIG. 2 includes the above-mentioned battery current collector reinforcing film 10 and a metal foil 20 disposed on the adhesive layer 12 of the battery current collector reinforcing film 10.

[0052] The total thickness of the current collector 1 is preferably from 10 to 23 μm, and more preferably from 10 to 18 μm. If the total thickness of the current collector is less than 10 μm, the strength tends to be insufficient. If the total thickness of the current collector exceeds 23 μm, the current collector becomes too large. Since the space inside the battery that can accommodate the current collector and active material is limited, if the current collector becomes large, the amount of active material must be reduced. Since the battery capacity depends on the amount of active material, if the current collector becomes large, the amount of active material will be reduced, and the battery capacity will decrease.

[0053] In the current collector 1, the metal foil 20 is preferably made of copper or aluminum. The current collector 1, in which the metal foil 20 is made of copper, functions as a negative electrode current collector. The current collector 1, in which the metal foil 20 is made of aluminum, functions as a positive electrode current collector.

[0054] In the current collector 1, when the metal foil 20 is made of copper, the thickness is preferably 2 to 4 μm, and more preferably 2 to 3 μm. In a typical lithium-ion battery, when the metal foil that functions as a current collector is made of copper, its thickness is about 6 μm. If the metal foil is thinner than this thickness, it becomes more susceptible to damage. However, the current collector 1 includes a film 10 for reinforcing the battery current collector. Therefore, even if the metal foil 20 is thin, damage to the metal foil 20 can be prevented.

[0055] In the current collector 1, when the metal foil 20 is made of aluminum, the thickness is preferably 4 to 9 μm, and more preferably 4 to 6 μm. In a typical lithium-ion battery, when the metal foil that functions as a current collector is made of aluminum, its thickness is about 12 μm. If the metal foil is thinner than this thickness, it becomes more susceptible to breakage. However, the current collector of the present invention includes the above-mentioned battery current collector reinforcing film. Therefore, even if the metal foil is thin, damage to the metal foil can be prevented.

[0056] The current collector 1 can be produced by thermocompression bonding a battery current collector reinforcing film 10 to a metal foil 20. The conditions for the thermocompression bonding are not particularly limited, but may be, for example, 0.1 to 1 MPa, 80 to 100° C., and 0.5 to 5 seconds.

[0057] Next, a lithium ion battery electrode using the current collector of the present invention and a lithium ion battery using the lithium ion battery electrode will be described.

[0058] First, the negative electrode of a lithium ion battery will be described. As the current collector of the present invention used for the negative electrode of a lithium ion battery, it is preferable to use one in which the metal foil is made of copper. In the negative electrode of a lithium ion battery, in the current collector of the present invention, a negative electrode active material layer is formed on the surface of the metal foil on the side where the battery current collector reinforcing film is not disposed.

[0059] The negative electrode active material layer contains negative electrode active material particles, and may contain a binder resin and a conductive assistant as necessary.

[0060] The negative electrode active material particles are not particularly limited as long as they can absorb and release lithium ions, and examples thereof include graphite, amorphous carbon, silicon, silicon oxide, metallic lithium, and the like.

[0061] The binder resin is not particularly limited, but may be, for example, a commonly used one such as polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (PVDF).

[0062] The conductive assistant is not particularly limited, but for example, commonly used ones such as carbon black, ketjen black, acetylene black, natural graphite, artificial graphite, and carbon fiber can be used.

[0063] The mixing ratio of the negative electrode active material particles, the binder resin, and the conductive assistant is preferably set appropriately depending on the type of negative electrode active material particles, the desired battery capacity, and the size of the battery to be manufactured.

[0064] Next, the positive electrode of the lithium ion battery will be described. As the current collector of the present invention used for the positive electrode of a lithium ion battery, it is preferable to use one in which the metal foil is made of aluminum. In a positive electrode for a lithium ion battery, in the current collector of the present invention, a positive electrode active material layer is formed on the surface of the metal foil on the side where the battery current collector reinforcing film is not disposed.

[0065] The positive electrode active material layer contains positive electrode active material particles, and may contain a binder resin and a conductive assistant as necessary.

[0066] As the positive electrode active material particles, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium iron phosphate, or the like can be used.

[0067] The binder resin and conductive assistant used in the positive electrode active material layer may be the same as the binder resin and conductive assistant used in the negative electrode active material layer.

[0068] The mixing ratio of the positive electrode active material particles, the binder resin, and the conductive assistant is preferably set appropriately depending on the type of positive electrode active material particles, the desired battery capacity, and the size of the battery to be manufactured.

[0069] Next, a lithium ion battery using a lithium ion battery negative electrode and a lithium ion battery positive electrode will be described. A lithium ion battery comprises an outer container, a separator disposed within the outer container, a negative electrode and a positive electrode disposed on either side of the separator, and an electrolyte injected into the outer container. The electrolyte is not limited to being poured into the outer container as described above, but may be present in a state in which it has soaked into the negative electrode and the positive electrode, for example.

[0070] The outer container may be made of a conventionally known material, and is preferably made of a flexible film from the viewpoint of reducing the weight of the battery. The flexible film may be a metal layer having a resin layer on both sides of the metal layer, which serves as a base material. The metal layer may be selected from those having barrier properties to prevent leakage of the electrolyte or intrusion of moisture from the outside, and may be made of aluminum, stainless steel, or the like.

[0071] As the separator, for example, a resin porous film, a woven fabric, a nonwoven fabric, or the like can be used. The resin component may be a polyolefin resin such as polypropylene or polyethylene, a polyester resin, an acrylic resin, a styrene resin, or a nylon resin. In particular, a polyolefin-based microporous membrane is preferred because of its excellent ion permeability and ability to physically isolate the positive electrode and the negative electrode.

[0072] The electrolyte may be a non-aqueous electrolyte containing a lithium salt. Examples of lithium salts include LiClO4, LiBF6, LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiB 10 Cl 10 , LiAlCl4, LiCl, LiBr, LiB(C2H5)4, CF3SO3Li, CH3SO3Li, LiC4F9SO3, Li(CF3SO2)2N, lithium lower fatty acid carboxylates, etc.

[0073] Examples of the solvent for dissolving the lithium salt include carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), and vinylene carbonate (VC); lactones such as γ-butyrolactone and γ-valerolactone; ethers such as trimethoxymethane, 1,2-dimethoxyethane, diethyl ether, tetrahydrofuran, and 2-methyltetrahydrofuran; sulfoxides such as dimethyl sulfoxide; Examples of solvents that can be used include oxolanes such as 3-dioxolane and 4-methyl-1,3-dioxolane; nitrogen-containing solvents such as acetonitrile, nitromethane, formamide, and dimethylformamide; organic acid esters such as methyl formate, methyl acetate, ethyl acetate, butyl acetate, methyl propionate, and ethyl propionate; phosphate triesters and diglymes; triglymes; sulfolanes such as sulfolane and methylsulfolane; oxazolidinones such as 3-methyl-2-oxazolidinone; and sultones such as 1,3-propane sultone, 1,4-butane sultone, and naphtha sultone. EXAMPLES

[0074] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0075] Example 1 A resin film made of polyethylene terephthalate and having a thickness of 6 μm was prepared. Next, 100 parts by weight of acid-modified polyolefin resin (number average molecular weight: 53,000, Tg: 20°C, acid value: 4460 g / eq), 45 parts by weight of polyester resin (number average molecular weight: 88,000, Tg: -56°C, acid value: 5400 g / eq), and 10 parts by weight of epoxy resin (equivalent weight: 238 g / eq) (manufactured by Nippon Kayaku Co., Ltd.: product name "NC-3000") were mixed to prepare an adhesive composition. Next, the adhesive composition was applied onto the resin film to a thickness of 3 μm to form an adhesive layer. Through the above steps, a battery current collector reinforcing film according to Example 1 was produced.

[0076] (Example 2) to (Example 3) and (Comparative Example 1) to (Comparative Example 11) Except for changing the composition of the adhesive layer as shown in Table 1, battery current collector reinforcing films according to Examples 2 and 3 and Comparative Examples 1 to 11 were produced in the same manner as in Example 1. In Table 1, the isocyanate-based curing agent is a product name "Coronate L" (manufacturer: Tosoh Corporation). In addition, in Table 1, the numerical values ​​for "mixing ratio" refer to "parts by weight."

[0077] [Table 1]

[0078] (Blocking evaluation) The battery current collector reinforcing film according to each Example and Comparative Example was placed on a PET film with the adhesive surface facing the PET film, and after storing the film at a temperature of 40° C. for 3 days with a load of 1 kg on the current collector reinforcing film, the film was visually observed to see if blocking had occurred. The results are shown in Table 1. The evaluation criteria are as follows: 〇: Peeling is possible without any resistance △: Peeling is possible with some noise ×: Cannot be peeled off

[0079] (Appearance evaluation) The battery current collector reinforcing films according to the respective Examples and Comparative Examples were visually evaluated for curling and tackiness immediately after production. The evaluation results are shown in Table 1. The evaluation criteria are as follows: [Criteria for evaluating curl] 〇: Film warpage height is less than 10 mm ×: Film warpage height is 10mm or more [Evaluation criteria for tackiness] The reinforcing film was placed on the PET film with the adhesive side in contact, and a 2 kg roller was passed back and forth over the reinforcing film once. The PET film was then shaken to evaluate whether the reinforcing film peeled off. None: Not attached to the PET film Slightly sticky: Sticks to PET film but can be shaken off Yes: Cannot be shaken off

[0080] (Electrolyte resistance test) A LiPF6 solution was prepared by dissolving LiPF6 in a 1:1:1 mixture of ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate to a concentration of 1 mol / L. Next, the battery current collector reinforcing film according to each of the Examples and Comparative Examples was immersed in a LiPF6 solution at 60° C. for 168 hours. After immersion, the LiPF6 solution was wiped off from the battery current collector reinforcing film according to each Example and Comparative Example, and the weights of the films were measured. The change in weight from before immersion was calculated, and the results are shown in Table 1. In addition, a negative weight change shown in Table 1 means that the adhesive layer was dissolved. Moreover, a weight change of more than 10% means that the adhesive layer absorbed too much LiPF6 solution and swelled.

[0081] After immersion, the appearance of the battery current collector reinforcing film according to each of the Examples and Comparative Examples was visually observed, and the electrolyte resistance was evaluated. The results are shown in Table 1. The evaluation criteria are as follows: No change: The appearance of the battery current collector reinforcing film was almost unchanged before and after immersion. Peeling: The adhesive layer was peeled off from the resin film. Fusion: The adhesive layer melted and fused to the resin film.

[0082] (Peel test) A 2 μm thick copper foil or a 4 μm thick aluminum foil was placed on the adhesive layer of the battery current collector reinforcing film of each Example and Comparative Example, and thermocompression bonded under conditions of 0.5 MPa and 0.1 seconds to produce a current collector. Thereafter, using the current collector immediately after production, a T-peel test was carried out in accordance with JIS K 6854-3: 1999 to peel the interface between the adhesive layer and the copper foil or aluminum foil. In addition, the current collector after production was left to stand at 23° C. for one month, and then the same peel test was carried out. In addition, the manufactured current collector was immersed in a LiPF6 solution prepared by dissolving LiPF6 at 1 mol / L in a solution of ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate in a 1:1:1 ratio at 60°C for 168 hours, and then a similar peel test was performed. The results are shown in Table 1. The evaluation criteria for the peel test are as follows. [Evaluation criteria when using copper foil] ◎: The copper foil was broken. ○: Peel strength is 1.5N / 25mm or more. △: The peel strength is 0.1 N / 25 mm or more and less than 1.5 N / 25 mm. ×: The peel strength is less than 0.1 N / 25 mm. [Evaluation criteria when using aluminum foil] ○: Peel strength is 1.5N / 25mm or more. △: The peel strength is 0.1 N / 25 mm or more and less than 1.5 N / 25 mm. ×: The peel strength is less than 0.1 N / 25 mm.

[0083] As shown in Table 1, it was found that the battery current collector reinforcing films according to the respective Examples had high electrolyte resistance, were less susceptible to blocking, and had sufficiently high adhesion. [Explanation of symbols]

[0084] 1 Current collector 10. Battery collector reinforcing film 11 Resin film 12 Adhesive layer 20 Metal foil

Claims

1. A battery current collector reinforcing film comprising a resin film and an adhesive layer formed on a surface of the resin film, The adhesive layer contains an acid-modified polyolefin resin, a polyester resin, and an epoxy resin, The adhesive layer contains 10 to 100 parts by weight of the polyester resin and 7.5 to 10 parts by weight of the epoxy resin, relative to 100 parts by weight of the acid-modified polyolefin resin.

2. 2 . The battery current collector reinforcing film according to claim 1 , wherein the acid-modified polyolefin resin has a number average molecular weight (Mn) of 20,000 or more.

3. 3. The battery current collector reinforcing film according to claim 1, wherein the polyester resin has a glass transition temperature (Tg) of −60° C. or higher.

4. 4. The battery current collector reinforcing film according to claim 1, wherein the adhesive layer has a thickness of 2 to 5 μm.

5. 5. The battery current collector reinforcing film according to claim 1, wherein the epoxy resin functions as a hardener.

6. A battery current collector reinforcing film according to any one of claims 1 to 5, a metal foil disposed on the adhesive layer of the battery current collector reinforcing film.

7. The current collector according to claim 6 , wherein the metal foil is made of copper or aluminum.

8. 8. The current collector according to claim 7, wherein the metal foil is made of copper and has a thickness of 2 to 4 μm.

9. 8. The current collector according to claim 7, wherein the metal foil is made of aluminum and has a thickness of 4 to 9 μm.

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