JP7058465B2 - Adhesive film for sealing metal terminals of power storage device - Google Patents

Description

The present invention relates to an adhesive film for sealing a metal terminal portion of a power storage device.

Lithium batteries, also called lithium secondary batteries, are batteries that are composed of solid polymers, gel-like polymers, liquids, etc. as electrolytes and are electromotive by the movement of lithium ions. Includes what is.
The composition of the lithium secondary battery consists of a positive electrode current collector (aluminum) / positive electrode active material layer (metal oxide, carbon black, metal sulfide, electrolyte, polymer positive electrode material such as polyacrylonitrile) / electrolyte (propylene carbonate, ethylene). Carbonate-based electrolytes such as carbonate, dimethyl carbonate, and ethylmethyl carbonate, inorganic solid electrolytes consisting of lithium salts, gel electrolytes) / Negative electrode active material layer (lithium metal, alloy, carbon, electrolyte, polymer negative electrode materials such as polyacrylonitrile) ) / It is composed of a lithium battery main body made of a negative electrode current collector (copper) and an exterior body for packaging them.
Applications of such a lithium secondary battery are wide-ranging, for example, a personal computer, a mobile terminal (mobile phone, PDA, etc.), a video camera, an electric vehicle, a storage battery for energy storage, a robot, a satellite, and the like. In the present specification, the positive electrode current collector and the positive electrode active material layer are also referred to as a positive electrode, and the negative electrode current collector and the negative electrode active material layer are also referred to as a negative electrode.

Conventionally, various types of batteries have been developed, but in all batteries, a packaging material is an indispensable member for encapsulating a battery element such as an electrode or an electrolyte. Conventionally, metal packaging materials have been widely used as packaging materials for batteries, but in recent years, with the increasing performance of electric vehicles, hybrid electric vehicles, personal computers, cameras, mobile phones, etc., batteries have various shapes. At the same time, there is a demand for thinner and lighter weight. However, the metal packaging material for batteries, which has been widely used in the past, has a drawback that it is difficult to keep up with the diversification of shapes and there is a limit to weight reduction.
Therefore, as a packaging material for batteries that can be easily processed into various shapes and can be made thinner and lighter, for example, a film-like laminate in which a base material layer / adhesive layer / metal layer / sealant layer is sequentially laminated. The body is proposed. In such a film-shaped packaging material for a battery, the sealant layers are opposed to each other and the peripheral edges are heat-welded by heat sealing so that the battery element can be sealed.

In such a film-shaped packaging material, the metal layer is provided mainly for the purpose of enhancing the water vapor barrier property of the packaging material. Specifically, the metal layer suppresses the generation of hydrofluoric acid when the moisture in the air reaches the inside of the battery and reacts with the electrolytic solution.
The reason why the above-mentioned film-shaped packaging material tends to be used is that when the battery is used at a high temperature and the internal pressure rises abnormally, the exterior body made of a metal can explodes and ignites. While there is a problem that the exterior body is dangerous because it can withstand, the film-shaped packaging material sealed by the heat-bonded portion peels off the heat-bonded portion and is inside when the internal pressure rises abnormally. Since it acts as a safety valve to release pressure, it loses its function as a battery, but it can reduce the risk of explosion and ignition compared to an exterior body made of a metal can.

Further, as a film-shaped packaging material used for a lithium battery, for example, as shown in FIG. 2, at least a base material layer A1 and a metal foil such as aluminum are used because of the physical properties, processability, economy, etc. required for the lithium battery. A laminated body A in which a barrier layer A2 composed of the above and a heat-adhesive resin layer A3 are laminated is used.
Then, as shown in FIG. 3A, the laminated body A is formed into a bag shape [the upper part of FIG. 3A is a pillow type packaging bag, but a three-way type, a four-sided type, or the like may be used]. After processing, the lithium battery body 30 and the metal terminals 31 connected to the positive and negative electrodes of the lithium battery body 30 are housed in a state of protruding outward, and the openings are heat-bonded and sealed, or this laminated body. As shown in FIG. 4A, A is press-molded so that the heat-adhesive resin layer A3 is located inside to form a recess, and the lithium battery main body 30 and the positive electrode and the negative electrode of the lithium battery body 30 are formed in the recess. The metal terminal 31 connected to the metal terminal 31 is housed in a state of protruding outward so that the heat-adhesive resin layer A3 of the separately prepared sheet-shaped laminated body A (not shown) is located on the recessed side. After covering the recess, the peripheral edge of the recess is heat-bonded and sealed to be used as the lithium battery 10 shown in FIG. 3 (b) or FIG. 4 (b). The reference numeral S indicates a heat-bonded portion.

In the packaging material used for such a lithium battery, the metal terminal 31 protrudes from the heat-sealed portion (heat-bonded portion S) (see FIGS. 3 (b) and 4 (b)) and is sealed by the packaging material. The lithium battery main body 30 is electrically connected to the outside by a metal terminal 31 electrically connected to the electrode of the lithium battery main body 30. That is, of the portions where the packaging material is heat-sealed, the portion where the metal terminal 31 exists is heat-sealed with the metal terminal 31 sandwiched between the heat-adhesive resin layer A3. Since the metal terminal 31 and the heat-adhesive resin layer A3 are made of different materials, the adhesiveness tends to decrease at the interface between the metal terminal 31 and the heat-adhesive resin layer A3.
Therefore, an adhesive film may be arranged between the metal terminal 31 and the heat-adhesive resin layer A3 for the purpose of enhancing their adhesiveness.

However, since the metal terminal 31 as described above usually has a thickness of at least 50 μm and a width of at least 2.5 mm, a gap is provided between both side edges of the metal terminal 31 and the adhesive film by heat sealing. In order to prevent the formation of (voids) and seal the battery body with the packaging material, heat sealing at a high temperature and high pressure at which the heat-adhesive resin layer A3 melts is required. By this heat sealing at high temperature and high pressure, the thickness of the heat-adhesive resin layer A3 of the packaging material becomes thin. Further, since the thickness of the adhesive film is also reduced, the barrier layer A2 of the packaging material and the metal terminal 31 may come into contact with each other to cause a short circuit.

More specifically, as shown in FIG. 5, the lithium battery body 30 before injecting the electrolyte is a metal terminal 31 projecting from the lithium battery body 30 to the outside of the package [FIG. 3 (b), FIG. 4B] is provided. For example, the adhesive film 1'for sealing the metal terminal portion of the power storage device made of the above-mentioned acid-modified polyolefin resin single layer is fixed to both sides of the metal terminal 31 by a temporary adhesive seal. To.
Then, the lithium battery main body 30 is housed in the recess of the laminate A shown in FIG. 4A in which the recess is formed by press molding, and the recess is formed by the separately prepared sheet-shaped laminate A (not shown). Three peripheral edges including the peripheral edge provided with the metal terminal 31 of the lithium battery body 30 are heat-bonded, and then an electrolyte is injected from the peripheral edge of one unbonded portion, and then the non-bonded portion is heat-bonded. By sealing, the lithium battery 10 shown in FIG. 4 (b) is obtained.
By the way, the metal terminal 31 of the lithium battery 10 is thermally bonded in a state of being sandwiched between the above packages (laminated body A) at the portion provided with the adhesive film 1'for sealing the metal terminal portion of the power storage device. The thickness of the 31 is at least about 50 μm and the width is at least about 2.5 mm, and the gaps on both sides of the metal terminal 31 are filled with the adhesive film 1'for sealing the metal terminal portion of the power storage device and the above-mentioned package (laminated body). In order to secure the sealed state by filling with the heat-adhesive resin layer A3 of A), heat and pressure for heat-bonding are required.
However, as a result, the adhesive film 1'for sealing the metal terminal portion of the power storage device and the heat-adhesive resin layer A3 of the package (laminated body A) are extruded out of the pressurized portion, and the pressurized portion becomes thin. In general, burrs of several μm to several tens of μm are generated at both end portions of the metal terminal 31 when cutting into a small width, which causes a metal foil such as aluminum of the package (laminated body A). There is a problem that the barrier layer A2 made of the metal terminal 31 and the metal terminal 31 come into contact with each other to cause a short circuit.

Further, in order to improve this problem, as an adhesive film 1'for sealing the metal terminal portion of the power storage device used on both sides of the metal terminal 31, for example, in Patent Document 1, insulating particles are dispersed in an acid-modified polyolefin resin. An adhesive sheet for sealing a metal terminal portion having a three-layer structure in which an acid-modified polyolefin-based resin layer is formed on both sides of the insulating particle dispersion layer is described.
However, since the adhesive sheet for sealing the metal terminal portion described in Patent Document 1 is a film using an acid-modified polyolefin resin as a resin component, it becomes thin and insulated due to the heat and pressure applied during thermal bonding. In terms of properties, it may not be sufficient, and there has been a demand for an adhesive sheet for sealing a metal terminal portion with improved insulation.
It should be noted that such a problem occurs when a capacitor and an electric double layer capacitor are housed in addition to the lithium battery containing the lithium battery body.

Patent No. 5169112

In view of the above situation, it is an object of the present invention to provide an adhesive film for sealing a metal terminal portion of a power storage device having extremely excellent insulating properties.

The present invention is an adhesive film for sealing a metal terminal portion of a power storage device having at least a heat-resistant base material layer and an insulating layer, and is subjected to a nanoindentation method with respect to a cross section of the insulating layer in the thickness direction. The hardness at the time of measurement is 10 MPa or more and 300 MPa or less, and the heat-resistant base material layer is characterized by being an unstretched sheet made of a heat-resistant synthetic resin or a stretched sheet stretched in a uniaxial or biaxial direction. It is an adhesive film for sealing the metal terminal of the power storage device.

Further, the adhesive film for sealing the metal terminal portion of the power storage device of the present invention has a thickness residual ratio of 70% or more and 95% or less of the insulating layer when heat pressure is applied under the conditions of 190 ° C., 1 MPa and 3 seconds. Is preferable.
Further, it is preferable that the adhesive film for sealing the metal terminal portion of the power storage device of the present invention is provided with a modified polyolefin layer on the side opposite to the insulating layer side of the heat-resistant base material layer.
Further, it is preferable that the adhesive film for sealing the metal terminal portion of the power storage device of the present invention is provided with an insulating layer on both sides of the heat-resistant base material layer.
Further, it is preferable to provide a modified polyolefin layer on the side opposite to the heat-resistant substrate layer side of the insulating layer.
The softening temperature of the insulating layer is preferably 180 ° C. or higher and 240 ° C. or lower.
Further, the insulating layer is preferably composed of a cured product of a composition for an insulating layer containing a modified polyolefin modified with an unsaturated carboxylic acid or an acid anhydride thereof and a curing agent, and the curing agent is polyfunctional. It is preferably at least one selected from the group consisting of an isocyanate compound, a carbodiimide compound, an epoxy compound and an oxazoline compound.

Since the adhesive film for sealing the metal terminal portion of the power storage device of the present invention has the above-mentioned structure, it has extremely excellent insulating properties. Therefore, the adhesive film of the present invention can be extremely suitably used for sealing the metal terminal portion of a power storage device such as a lithium battery.

FIG. 1A is a diagram illustrating a typical layer structure of the adhesive film of the present invention. FIG. 1B is a schematic diagram illustrating a method for measuring the hardness (indentation hardness) of the insulating layer. FIG. 2 is a diagram illustrating a basic layer structure of a package used for a power storage device. FIG. 3 is a diagram illustrating an embodiment of a package used for a power storage device. FIG. 4 is a diagram illustrating another embodiment of the package used for the power storage device. FIG. 5 is a diagram illustrating an example of how to provide an adhesive film for sealing a metal terminal portion of a power storage device.

Hereinafter, the present invention will be described in detail.
As a result of diligent studies, the present inventors have laminated a heat-resistant base material layer and an insulating layer having a predetermined hardness as an adhesive film for sealing a metal terminal portion of a power storage device (hereinafter, also simply referred to as an adhesive film). It has been found that the insulating property can be extremely improved by adopting the above-mentioned structure, and the present invention has been completed.

First, a package of a power storage device used for the adhesive film of the present invention will be described.
The package A has a structure in which at least a base material layer A1, a barrier layer A2 made of a metal foil such as aluminum, and a heat-adhesive resin layer A3 made of a polyolefin resin are laminated, as shown in FIG. Used.
Examples of the base material layer A1 include a biaxially stretched polyester film, a biaxially stretched nylon film, and a laminate thereof, and the thickness thereof is about 6 to 30 μm.
Further, as the barrier layer A2, for example, a metal foil such as aluminum, nickel, or stainless steel can be mentioned, and the thickness thereof is about 15 μm or more and 80 μm or less.
Examples of the polyolefin resin forming the heat-adhesive resin layer A3 include low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, ethylene-based resins such as ethylene-butene copolymers, and homopolypropylene. Examples thereof include a single substance or a mixture of propylene-based resins such as an ethylene-propylene copolymer and an ethylene-propylene-butene copolymer, and the thickness thereof is approximately 20 μm or more and 100 μm or less.

Next, the adhesive film of the present invention will be described in detail below with reference to drawings and the like, but the form and the like of the power storage device are the same as those described in the background technique, and the drawings described in the background technique are used. Will be explained.
Note that FIG. 1A is a diagram schematically showing a typical layer structure of the adhesive film of the present invention, and FIG. 1B is a method for measuring the hardness (indentation hardness) of the insulating layer. 2 is a schematic diagram illustrating the basic layer structure of a package used for a power storage device, and FIG. 3 is a diagram illustrating an embodiment of a package used for a power storage device. FIG. 4 is a diagram illustrating another embodiment of the package used for the energy storage device, and FIG. 5 is a diagram illustrating an example of how to provide an adhesive film for sealing the metal terminal portion of the energy storage device. , 1'is an adhesive film for sealing the metal terminal of the power storage device, 2 is a heat-resistant base material layer, 3 is an insulating layer, 10 is a lithium battery, 30 is a lithium battery body, 31 is a metal terminal, A is a laminate, and A1 is. A base material layer, A2 is a barrier layer made of a metal foil, and A3 is a heat-adhesive resin layer.

FIG. 1A is a diagram illustrating a typical layer structure of the adhesive film of the present invention, and as shown in FIG. 1A, the adhesive film 1 of the present invention is a heat-resistant substrate. It has a structure in which the insulating layer 3 is laminated on the layer 2.
The heat-resistant base material layer 2 is a layer that guarantees the heat resistance of the adhesive film of the present invention. Due to heat shrinkage of the adhesive film causing warpage and heat wrinkles, the metal terminal 31 and the end portion of the barrier layer A2 of the laminate A are likely to be short-circuited, and the insulating property of the obtained lithium battery is lowered. Sometimes.

As a material constituting such a heat-resistant base material layer 2, heat resistance that is not melted and crushed by heat and pressure during heat bonding is required, and therefore polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyamides, and polyimides are required. , Polymethylpentene, polyphenylene oxide, polysulfone, polyether ether ketone, polyphenylene sulfide, fluororesin, polyarylate, polymethylpentene, polyolefins such as polypropylene, unstretched sheets made of heat-resistant synthetic resins such as polyetherimide, or Examples thereof include a stretched sheet stretched in a uniaxial or biaxial direction, a non-woven fabric, a mesh, a laminated cloth, and the like.

Further, the material constituting the heat-resistant base material layer 2 preferably has a melting point of 180 ° C. or higher. If the melting point is less than 180 ° C., the adhesive film of the present invention may be melted or softened during the thermal bonding, and the insulating property of the adhesive film of the present invention may be deteriorated.
Further, the heat-resistant substrate layer 2 preferably has a heat shrinkage rate (temperature: 210 ° C., pressure: 1 MPa, 3 seconds) of 10% or less. If the heat shrinkage rate exceeds 10%, the adhesive film of the present invention may shrink during the heat bonding, and the insulating property may deteriorate.

The insulating layer 3 is required to have heat resistance and resistance to an electrolytic solution, which are melted and not crushed by the heat (160 to 190 ° C.) and pressure (1.0 to 2.0 MPa) at the time of thermal adhesion described above.
In such an adhesive film of the present invention, as shown in FIG. 1A, it is preferable that the insulating layer 3 is laminated on both side surfaces of the heat-resistant base material layer 2.
Since the insulating layer 3 is laminated on both sides of the heat-resistant base material layer 2, the adhesive film of the present invention has heat resistance and electrolysis that is not melted and crushed by the heat and pressure at the time of heat bonding described above. The resistance to the liquid is improved, and the adhesive strength between the constituent layers is also excellent.

Further, in the adhesive film of the present invention, the insulating layer 3 has a hardness of 10 MPa or more and 300 MPa or less as measured by the nanoindentation method with respect to the cross section of the insulating layer 3 in the thickness direction. More specifically, as shown in FIG. 1 (b), a nanoindenter (TriboIndenter TI950 manufactured by HYSITRON) is used at the center (line AA) of the cross section 3a of the insulating layer 3 with respect to the cross section 3a. The hardness (indentation hardness) calculated by pushing the indenter 12 made of a diamond tip having a triangular pyramid (Berkovich indenter) from the vertical direction to form a depression 13 and measuring the load-displacement curve. ..
When the hardness of the insulating layer 3 is within the above range, the adhesive film of the present invention is extremely excellent in insulating performance. This is because the insulating layer 3 having such hardness is not crushed during the heat bonding, the pressurized portion is not thinned, and minute foreign substances such as electrode active material and electrode tab debris are present. Even when it is present in a heat-sealed portion such as between the electrode tab and the heat-adhesive resin layer A3, it is considered that excellent insulation performance is exhibited because it is not easily crushed by foreign matter.
Further, in the adhesive film of the present invention, the insulating layer may have a multilayer structure of two or more layers. As a result, even when a thin-walled portion or a through hole is formed in the first insulating layer, the second and third insulating layers can maintain the insulating property.
The preferable lower limit of the hardness of the insulating layer 3 is 15 MPa, the preferable upper limit is 250 MPa, the more preferable lower limit is 20 MPa, and the more preferable upper limit is 220 MPa.

In the adhesive film of the present invention, the softening temperature of the insulating layer 3 is preferably 180 ° C. or higher and 240 ° C. or lower. If the softening temperature is less than 180 ° C, the heat resistance may be insufficient and a short circuit may easily occur during heat sealing, and if it exceeds 240 ° C, the insulating layer 3 may become hard and crack during processing to impair the insulating property. be.

In the adhesive film of the present invention, the insulating layer 3 is preferably a cured product of a composition for an insulating layer containing a modified polyolefin modified with an unsaturated carboxylic acid or an acid anhydride thereof and a curing agent.
Since the adhesive film of the present invention is used by interposing it between the laminate A and the metal terminal 31, metal adhesiveness is required on at least one side, and metal adhesiveness is imparted by using a modified polyolefin. Can be done. Further, by modifying the olefin, a reaction point with the curing agent is generated, and the insulating layer 3 having an appropriate hardness can be formed.

The modified polyolefin modified with the unsaturated carboxylic acid or its acid anhydride may be further modified with a (meth) acrylic acid ester. The modified polyolefin further modified with the (meth) acrylic acid ester can be obtained, for example, by acid-modifying the polyolefin with an unsaturated carboxylic acid or an acid anhydride thereof in combination with the (meth) acrylic acid ester. It is a thing.
In the present invention, "(meth) acrylic acid ester" means "acrylic acid ester" or "methacryl acid ester".
The modified polyolefin may be used alone or in combination of two or more.

The modified polyolefin is not particularly limited as long as it is a resin containing at least an olefin as a monomer unit.
Examples of the resin containing the olefin include those made of at least one of polyethylene and polypropylene, and those made of polypropylene are preferable.

Examples of the polyethylene include those composed of at least one of homopolyethylene and an ethylene copolymer.
Further, examples of polypropylene include those composed of at least one of homopolypropylene and propylene copolymer.
Examples of the propylene copolymer include copolymers of propylene such as ethylene-propylene copolymer, propylene-butene copolymer, and ethylene-propylene-butene copolymer with other olefins.

The ratio of the propylene unit contained in the polypropylene is preferably about 50 mol% to 100 mol%, preferably about 80 mol% to 100 mol%, from the viewpoint of further enhancing the insulating property and durability of the battery packaging material. It is more preferable to do so.
The proportion of ethylene units contained in the polyethylene is preferably about 50 mol% to 100 mol%, preferably 80 mol% to 100 mol%, from the viewpoint of further enhancing the insulating property and durability of the battery packaging material. It is more preferable to set the degree.
Further, the ethylene copolymer and the propylene copolymer may be either a random copolymer or a block copolymer, respectively.
Further, the ethylene copolymer and the propylene copolymer may be either crystalline or amorphous, and may be a copolymer or a mixture thereof.
Further, the polyolefin may be formed of one kind of homopolymer or copolymer, or may be formed of two or more kinds of homopolymers or copolymers.

Examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, maleic acid, itaconic acid, fumaric acid, and crotonic acid.
Further, as the acid anhydride, the acid anhydride of the unsaturated carboxylic acid exemplified above is preferable, and maleic anhydride and itaconic anhydride are more preferable.

The modified polyolefin may be modified with one kind of unsaturated carboxylic acid or its acid anhydride, or may be modified with two or more kinds of unsaturated carboxylic acid or its acid anhydride. May be good.

The (meth) acrylic acid ester is, for example, an esterified product of (meth) acrylic acid and an alcohol having 1 to 30 carbon atoms, preferably an ester of (meth) acrylic acid and an alcohol having 1 to 20 carbon atoms. Examples include compounds.
Specific examples of the above (meth) acrylic acid ester include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, and hexyl (meth) acrylate. Examples thereof include octyl (meth) acrylate, decyl (meth) acrylate, lauryl (meth) acrylate, and stearyl (meth) acrylate.
In the modification of the polyolefin, only one type (meth) acrylic acid ester may be used, or two or more types may be used.

The ratio of the unsaturated carboxylic acid or the acid anhydride thereof in the modified polyolefin is preferably about 0.1% by mass or more and about 30% by mass or less, and is about 0.1% by mass or more and about 20% by mass or less, respectively. Is more preferable. Within such a range, the insulation and durability of the battery packaging material can be further enhanced.

The proportion of the (meth) acrylic acid ester in the modified polyolefin is preferably 0.1% by mass or more and 40% by mass or less, and more preferably 0.1% by mass or more and 30% by mass or less. preferable. Within such a range, the insulation and durability of the battery packaging material can be further enhanced.

The weight average molecular weight of the modified polyolefin is preferably about 6000 or more and 200,000 or less. When the weight average molecular weight is in the range, the affinity of the insulating layer 3 with respect to the metal terminal 31 and the heat-adhesive resin layer A3 can be stabilized, so that the adhesion can be stabilized for a long period of time.
The weight average molecular weight of the modified polyolefin is more preferably about 8,000 or more and 150,000 or less. In the present invention, the weight average molecular weight of the modified polyolefin is a value measured by gel permeation chromatography (GPC) measured under the condition of using polystyrene as a standard sample.

The melting point of the modified polyolefin is preferably about 50 ° C. or higher and 120 ° C. or lower. When the melting point is in the range, the affinity of the insulating layer 3 with respect to the metal terminal 31 and the heat-adhesive resin layer A3 can be stabilized, so that the adhesion can be stabilized for a long period of time.
The melting point of the modified polyolefin is more preferably about 50 ° C. or higher and 100 ° C. or lower. In the present invention, the melting point of the modified polyolefin means the endothermic peak temperature in the differential scanning calorimetry.

In the modified polyolefin, the method for modifying the polyolefin is not particularly limited, and for example, an unsaturated carboxylic acid or an acid anhydride thereof or a (meth) acrylic acid ester may be copolymerized with the polyolefin.
Examples of such copolymerization include random copolymerization, block copolymerization, graft copolymerization (graft modification) and the like, and preferred examples include graft copolymerization.

Examples of the curing agent in the composition for the insulating layer include polyfunctional isocyanate compounds, carbodiimide compounds, epoxy compounds, oxazoline compounds and the like.

The polyfunctional isocyanate compound is not particularly limited as long as it is a compound having two or more isocyanate groups.
Specific examples of the above-mentioned polyfunctional isocyanate compound include isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), and polymers or nurates thereof. Examples thereof include a mixture of the above and a copolymer with another polymer.

［一般式（１）において、ｎは２以上の整数である。］
で表される繰り返し単位を有するポリカルボジイミド化合物、
下記一般式（２）：

［一般式（２）において、ｎは２以上の整数である。］
で表される繰り返し単位を有するポリカルボジイミド化合物、
及び下記一般式（３）：

［一般式（３）において、ｎは２以上の整数である。］
で表されるポリカルボジイミド化合物が挙げられる。一般式（１）～（３）において、ｎは、通常３０以下の整数であり、好ましくは３～２０の整数である。 The carbodiimide compound is not particularly limited as long as it is a compound having at least one carbodiimide group (-N = C = N-).
Among them, as the carbodiimide compound, a polycarbodiimide compound having at least two carbodiimide groups is preferable.
As a specific example of a particularly preferable carbodiimide compound, the following general formula (1):

[In the general formula (1), n is an integer of 2 or more. ]
Polycarbodiimide compound having a repeating unit represented by,
The following general formula (2):

[In the general formula (2), n is an integer of 2 or more. ]
Polycarbodiimide compound having a repeating unit represented by,
And the following general formula (3):

[In the general formula (3), n is an integer of 2 or more. ]
Examples thereof include a polycarbodiimide compound represented by. In the general formulas (1) to (3), n is usually an integer of 30 or less, preferably an integer of 3 to 20.

The epoxy compound is not particularly limited as long as it is a compound having at least one epoxy group.
Examples of the epoxy compound include bisphenol A diglycidyl ether, modified bisphenol A diglycidyl ether, novolak glycidyl ether, glycerin polyglycidyl ether, polyglycerin polyglycidyl ether and the like.
The above epoxy compounds may be used alone or in combination of two or more.
The epoxy compound is not particularly limited as long as it is a resin capable of forming a crosslinked structure by an epoxy group existing in the molecule, and a known epoxy resin can be used.
The weight average molecular weight of the epoxy resin is preferably in the range of 50 to 2000. From the viewpoint of further enhancing the insulating property and durability of the battery packaging material, the weight average molecular weight of the epoxy resin is preferably about 100 to 1000, more preferably about 200 to 800. In the present invention, the weight average molecular weight of the epoxy resin is a value measured by gel permeation chromatography (GPC) measured under the condition of using polystyrene as a standard sample.

The oxazoline compound is not particularly limited as long as it is a compound having an oxazoline skeleton.
Specific examples of the oxazoline compound include the Epocross series manufactured by Nippon Shokubai Co., Ltd.

In the adhesive film of the present invention, the curing agent may be composed of two or more kinds of compounds from the viewpoint of increasing the mechanical strength of the insulating layer 3.
In the composition for an insulating layer, the content of the curing agent is preferably in the range of 0.1 parts by mass or more and 50 parts by mass or less, and 0.1 parts by mass or more and 30 parts by mass with respect to 100 parts by mass of the modified polyolefin. It is more preferably in the range of parts by mass or less.
Further, in the composition for an insulating layer, the content of the curing agent is preferably in the range of 1 equivalent or more and 30 equivalents or less as the reactive group in the curing agent with respect to 1 equivalent of the carboxyl group in the modified polyolefin. It is more preferable that the amount is in the range of 1 equivalent or more and 20 equivalents or less. Thereby, insulation and durability can be further improved.

The softening temperature of the insulating layer 3 is preferably 180 ° C. or higher and 240 ° C. or lower, and more preferably 200 ° C. or higher and 240 ° C. or lower.
The softening temperature of the modified polyolefin is a value measured by a method according to JIS K7196: 2012, and specifically, a value measured by a method described in Examples described later.

In the adhesive film of the present invention, it is preferable that the modified polyolefin layer is laminated directly or via another insulating layer on the side opposite to the insulating layer 3 side of the heat-resistant substrate layer 2. That is, as a preferable structure of the adhesive film of the present invention, for example, an insulating layer / a heat-resistant base material layer / a modified polyolefin layer can be mentioned.
By having the modified polyolefin layer, the adhesiveness of the adhesive film of the present invention to the metal terminal 31 of the power storage device and the above-mentioned packaging material is extremely excellent.

Examples of the polyolefin-based resin constituting the modified polyolefin layer include polypropylene-based resins (homotype, ethylene-propylene copolymer, ethylene-propylene-butene copolymer), and polyethylene-based resins (low-density polyethylene, Medium density polyethylene, high density polyethylene, linear low density polyethylene, copolymer of ethylene and butene, polymer of ethylene and acrylic acid or methacrylic acid derivative, copolymer of ethylene and vinyl acetate, Metal ion-containing polyethylene and polyethylene grafted with unsaturated carboxylic acid), or a blend thereof, and the like can be mentioned.

The modified polyolefin layer is a layer that thermally adheres to the metal terminal 31, and as the polyolefin-based resin, a polyolefin resin graft-modified with unsaturated carboxylic acid, a copolymer of ethylene or propylene and acrylic acid, or methacrylic acid. Alternatively, a metal-crosslinked polyolefin resin or the like can be exemplified, and if necessary, a butene component, an ethylene-propylene-butene copolymer, an amorphous ethylene-propylene copolymer, a propylene-α-olefin copolymer, an olefin, etc. 5% or more of the system elastomer or the like may be added.
In consideration of moisture resistance and heat resistance, a polyolefin resin graft-modified with an unsaturated carboxylic acid, particularly a polypropylene resin graft-modified with an unsaturated carboxylic acid is preferable.

Such a modified polyolefin layer may be laminated, for example, directly on the side surface opposite to the heat-resistant base material layer 2 side of the above-mentioned insulating layer 3 or via another insulating layer, and further, the above-mentioned heat-resistant group. In addition to the modified polyolefin layer laminated on the side opposite to the insulating layer 3 side of the material layer 2, the modified polyolefin layer may be laminated on the side surface opposite to the heat-resistant substrate layer 2 side of the insulating layer 3. ..
That is, as a preferable configuration of the adhesive film of the present invention, for example, a modified polyolefin layer / insulating layer / heat-resistant substrate layer / insulating layer, an insulating layer / heat-resistant substrate layer / insulating layer / modified polyolefin layer, modified polyolefin layer / Examples thereof include an insulating layer / heat-resistant base material layer / insulating layer / modified polyolefin layer, a heat-resistant base material layer / insulating layer / modified polyolefin layer, a modified polyolefin layer / heat-resistant base material layer / insulating layer / modified polyolefin layer, and the like.

In the adhesive film of the present invention having the above-mentioned structure, it is preferable that the thickness residual ratio of the insulating layer 3 is 70% or more and 95% or less when heat pressure is applied under the conditions of 190 ° C., 1 MPa and 3 seconds. If it is less than 70%, the insulating property of the adhesive film of the present invention may be insufficient, and if it exceeds 95%, the adhesiveness between the adhesive film and the metal terminal 31 or the packaging bag (laminate A) May be inadequate.
The more preferable lower limit of the thickness residual ratio is 75%, and the more preferable upper limit is 90%.

The method for producing the adhesive film of the present invention is not particularly limited, and a conventionally known method, for example, extruding the resin material of the heat-resistant substrate layer 2 onto one surface of a PEN (biaxially stretched polyethylene naphthalate) film. The heat-resistant base material layer 2 is formed, the composition for the insulating layer is applied onto the heat-resistant base material layer 2, the formed coating film is dried and then cured to form the insulating layer 3, and the PEN film is peeled off. How to do it, etc.

Since the adhesive film of the present invention has a structure in which the heat-resistant base material layer 2 and the insulating layer 3 described above are laminated, the adhesive film has extremely excellent insulating properties.
Such an adhesive film of the present invention is extremely preferably used for sealing the metal terminal 31 of the above-mentioned power storage device.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples and Comparative Examples.
In the text, "part" or "%" is based on mass unless otherwise specified.

<Manufacturing of laminates for packaging energy storage devices>
One side of an aluminum foil (40 μm thick) that has been chemically treated (phosphate chromate-treated) on both sides with a chemical treatment liquid consisting of a phenol resin, a chromium fluoride (trivalent) compound, and a phosphoric acid in advance, and 25 μm. A biaxially stretched nylon film having a thickness is laminated via a urethane adhesive, and the other surface of the aluminum foil and an unstretched polypropylene film having a thickness of 30 μm are laminated with an acid-modified polypropylene resin (grafted with an unsaturated carboxylic acid). The laminate was laminated with polypropylene) and heated to a temperature equal to or higher than the softening point of the acid-modified polypropylene resin with hot air to prepare a laminate to be used in Examples.

(Examples 1 to 3)
A modified polypropylene resin (maleic anhydride-modified ethylene-propylene copolymer, weight average molecular weight 100,000, melting point 100 ° C., in polypropylene main skeleton) as a main agent on both sides of a PEN (biaxially stretched polyethylene naphthalate) film (12 μm). A composition for an insulating layer containing a prepolymer type diphenylmethane diisocyanate (NCO content, 31% by weight) with an ethylene content of 2.1 mol% and a maleic anhydride modification degree of 3.0% by weight) as a curing agent is 10 μm. And dried at 80 ° C. for 60 seconds to form an insulating layer.
The content of the curing agent is 10 equivalents in Example 1, 1 equivalent in Example 2, and 30 equivalents in Example 3 as reactive groups in the curing agent with respect to 1 equivalent of the carboxyl group in the modified polypropylene resin. Equivalent.
Next, the acid-modified polypropylene resin was sequentially extruded onto each insulating layer to a thickness of 30 μm with a T-die extruder, and then aged at 70 ° C. for 24 hours to obtain the adhesive films of Examples 1 to 3. rice field.

(Example 4)
An adhesive film was obtained in the same manner as in Example 1 except that a carbodiimide compound (weight average molecular weight 2000, carbodiimide equivalent 200) was used as a curing agent.

(Example 5)
An adhesive film was obtained in the same manner as in Example 1 except that an epoxy compound (jER828, manufactured by Mitsubishi Chemical Corporation) was used as a curing agent.

(Example 6)
An adhesive film was obtained in the same manner as in Example 1 except that an oxazoline compound (Epocross WS-500, manufactured by Nippon Shokubai) was used as a curing agent.

(Example 7)
A modified polypropylene resin (maleic anhydride-modified ethylene-propylene copolymer, weight average molecular weight 100,000, melting point 100 ° C., in polypropylene main skeleton) as a main agent on both sides of a PEN (biaxially stretched polyethylene naphthalate) film (12 μm). A composition for an insulating layer containing a prepolymer type diphenylmethane diisocyanate (NCO content, 31% by weight) with an ethylene content of 2.1 mol% and a maleic anhydride modification degree of 3.0% by weight) as a curing agent is 10 μm. And dried at 80 ° C. for 60 seconds to form an insulating layer. Next, the acid-modified polypropylene resin was extruded onto the insulating layer to a thickness of 50 μm on only one side with a T-die extruder, and then aged at 70 ° C. for 24 hours to obtain the adhesive film of Example 7.

(Example 8)
A modified polypropylene resin (maleic anhydride-modified ethylene-propylene copolymer, weight average molecular weight 100,000, melting point 100 ° C., in polypropylene main skeleton) as a main agent on both sides of a PEN (biaxially stretched polyethylene naphthalate) film (12 μm). A composition for an insulating layer containing a prepolymer type diphenylmethane diisocyanate (NCO content, 31% by weight) with an ethylene content of 2.1 mol% and a maleic anhydride modification degree of 3.0% by weight) as a curing agent is 10 μm. And dried at 80 ° C. for 60 seconds to form an insulating layer. Then, it was aged at 70 ° C. for 24 hours to obtain an adhesive film of Example 8.

(Example 9)
A modified polypropylene resin (maleic anhydride-modified ethylene-propylene copolymer, maleic anhydride-modified ethylene-propylene copolymer, weight average molecular weight 100,000, melting point 100 ° C., in polypropylene main skeleton) as a main agent on one side of a PEN (biaxially stretched polyethylene naphthalate) film (12 μm). A composition for an insulating layer containing a prepolymer type diphenylmethane diisocyanate (NCO content, 31% by weight) with an ethylene content of 2.1 mol% and a maleic anhydride modification degree of 3.0% by weight) as a curing agent is 10 μm. And dried at 80 ° C. for 60 seconds to form an insulating layer. Next, 50 mg / m ² of an isocyanate-based adhesive accelerator was applied to the opposite surface coated with the insulating layer, and the acid-modified polypropylene resin was extruded to a thickness of 50 μm with a T-die extruder on only one side, and then at 70 ° C. 24. Time aging was performed to obtain the adhesive film of Example 9.

(Comparative Example 1)
50 mg / m ² of an isocyanate-based adhesive accelerator is applied to one side of a PEN (biaxially stretched polyethylene naphthalate) film (12 μm), and an acid-modified polypropylene resin is extruded to a thickness of 40 μm with a T-die extruder. 50 mg / m ² of an isocyanate-based adhesive accelerator was applied to the other surface, and the acid-modified polypropylene resin was extruded to a thickness of 40 μm with a T-die extruder and aged at 45 ° C. for 72 hours. An adhesive film was obtained.

(Comparative Example 2)
An adhesive film was obtained in the same manner as in Example 1 except that no curing agent was added.

(Comparative Example 3)
An acid-modified polypropylene film having a thickness of 100 μm was used as the adhesive film of Comparative Example 3.

The adhesive films according to Examples and Comparative Examples were evaluated as follows. The results are shown in Table 1.

(Evaluation methods)
-The softening temperature was measured using EXSTAR6000 manufactured by Seiko Instruments Inc. in accordance with the regulations of JIS K7196: 2012.

-Cut the laminate for packaging the insulating power storage device into 60 mm x 60 mm (2 sheets) and the adhesive film into 60 mm x 60 mm (2 sheets).
Next, the laminated bodies are laminated so that the unstretched propylene films face each other, an adhesive film is sandwiched between them, and a nickel foil having a width of 4 mm, a length of 80 mm, and a thickness of 100 μm is sandwiched between the adhesive films.
The terminal of the tester was connected to the nickel foil and the aluminum foil of the laminated film, and in that state, the nickel foil was sealed with a hot plate having a width of 7 mm in the direction orthogonal to the length direction of the nickel foil (sealing condition: 190 ° C., 1 MPa). At this time, the time until the nickel foil and the aluminum foil were short-circuited was measured, and the insulating property was evaluated according to the following criteria.
◯: 150 seconds or more Δ: 120 seconds or more and less than 150 seconds ×: less than 120 seconds

A heat-resistant shrinkable adhesive film is cut into a width of 15 × 70 mm, and a biaxially stretched polyethylene terephthalate film having a thickness of 12 μm is cut into a width of 20 × 70 mm, and the adhesive film is sandwiched between two biaxially stretched polyethylene films. In this state, the shrinkage rate of the film after applying thermal pressure under the conditions of 190 ° C., 1 MPa, and 3 seconds was measured, and the heat-resistant shrinkage property was evaluated according to the following criteria.
◯: Shrinkage rate is 10% or less ×: Shrinkage rate is greater than 10%

-Measurement of Hardness of Insulating Layer by Nano Indentation Method The hardness of the insulating layer was measured using a nano indenter (TriboIndenter TI950 manufactured by HYSITRON). In the nano indenter, a regular triangular pyramid indenter (Berkovich indenter) having a diamond tip at the tip was used. The adhesive films obtained in Examples and Comparative Examples were cut in the laminating direction to expose the cross section of the insulating layer.
Next, using a nano indenter, the indenter was pushed in the direction perpendicular to the locations (5 locations) approximately at the center of the cross section of the insulating layer under the following conditions, and the load-displacement curve was measured to calculate the hardness. The hardness of the insulating layer in Table 1 is an average value of values measured five times.
Measurement conditions / measurement temperature 23 ° C
・ Relative humidity 70%
・ Pushing depth 150 nm
・ Pushing depth arrival time 10 sec
・ Load holding time 5 sec
・ Pushing depth unloading time 10 sec

-Thickness residual ratio The adhesive films obtained in Examples and Comparative Examples were measured for the thickness of the insulating layer from the cross sections cut in the stacking direction before and after applying heat pressure at 190 ° C. for 1 MPa for 3 seconds, respectively. The survival rate was calculated by the formula.
Residual rate (%) = Insulation layer thickness after heat pressure applied / Insulation layer thickness before heat pressure applied x 100

-Initial laminate strength The adhesive film is cut to a width of 15 x 70 mm, and after partial peeling from the end face while applying ethyl acetate to the adhesive interface, acid is used with a tensile tester (manufactured by Shimadzu Corporation, trade name: AGS-50D). The peel strength between the modified polypropylene / PEN layers was measured, and the average strength was used as the measured value (tensile speed: 50 mm / min).

・ Electrolyte-resistant laminating strength adhesive film was cut into 30 × 70 mm, soaked in electrolytic solution for 7 days, then taken out, and both ends were trimmed by 7.5 mm to prepare a sample for measurement of 15 × 70 mm. .. Using the prepared measurement sample, the laminate strength was measured in the same manner as the initial laminate strength.
The electrolytic solution was obtained by mixing lithium hexafluorophosphate with a solution prepared by mixing ethylene carbonate: diethyl carbonate: dimethyl carbonate = 1: 1: 1.

As shown in Table 1, the adhesive film according to the examples had a high softening temperature and was excellent in heat resistance, and was excellent in all of insulating property, heat shrinkage property, initial laminating strength and electrolytic solution laminating strength. The laminate strength was measured between the acid-modified polypropylene / PEN in Examples 1 to 7 and 9 and Comparative Examples 1 and 2.
Further, the adhesive film according to Example 2 in which the content of the curing agent in the composition for the insulating layer was small was lower in softening temperature and slightly inferior in insulating property as compared with other examples, and the insulating layer. The adhesive film of Example 9 in which is laminated only on one surface side of the heat-resistant substrate layer tends to have a slightly inferior insulating property at around 150 seconds as compared with the adhesive film according to the other examples. In addition, the electrolytic solution laminating strength was inferior to that of the adhesive film according to the other examples.
Since the adhesive film of Comparative Example 1 did not have an insulating layer laminated, it was inferior in the evaluation of the insulating property and the electrolytic solution laminating strength, and the adhesive film of Comparative Example 2 had a low residual thickness of the insulating layer. The adhesive film according to Comparative Example 3 which was inferior in insulating property and used only the acid-modified polyolefin layer was inferior in insulating property and heat shrinkage property.

The adhesive film for sealing the metal terminal portion of the power storage device of the present invention can be extremely suitably used for sealing the metal terminal portion of the power storage device such as a lithium battery.

1,1'Power storage device Adhesive film for sealing metal terminals 2 Heat-resistant base material layer 3 Insulation layer 3a Cross section 10 Lithium battery 12 Indenter 13 Indentation 30 Lithium battery body 31 Metal terminal A Laminated body A1 Base material layer A2 Made of metal foil Barrier layer A3 Thermal adhesive resin layer

Claims (8)

An adhesive film for sealing a metal terminal portion of a power storage device having a structure including at least a heat-resistant base material layer and an insulating layer.
The hardness as measured by the nanoindentation method with respect to the cross section in the thickness direction of the insulating layer is 10 MPa or more and 300 MPa or less.
The heat-resistant base material layer is an unstretched sheet made of a heat-resistant synthetic resin or a stretched sheet stretched in a uniaxial or biaxial direction (except when it is a fibrous sheet or a porous sheet).
An adhesive film for sealing the metal terminal of a power storage device. The adhesive film for sealing a metal terminal portion of a power storage device according to claim 1, wherein the residual thickness of the insulating layer is 70% or more and 95% or less when heat pressure is applied under the conditions of 190 ° C., 1 MPa, and 3 seconds. The adhesive film for sealing a metal terminal portion of a power storage device according to claim 1 or 2, wherein a modified polyolefin layer is provided on the side opposite to the insulating layer side of the heat-resistant base material layer. The adhesive film for sealing a metal terminal portion of a power storage device according to claim 1 or 2, wherein an insulating layer is provided on both sides of the heat-resistant base material layer. The adhesive film for sealing a metal terminal portion of a power storage device according to claim 4, wherein a modified polyolefin layer is provided on the side opposite to the heat-resistant substrate layer side of the insulating layer. The adhesive film for sealing a metal terminal portion of a power storage device according to claim 1, 2, 3, 4 or 5, wherein the softening temperature of the insulating layer is 180 ° C. or higher and 240 ° C. or lower. The first, second, third, fourth, fifth or sixth claim, wherein the insulating layer is a cured product of a composition for an insulating layer containing a modified polyolefin modified with an unsaturated carboxylic acid or an acid anhydride thereof and a curing agent. Energy storage device Adhesive film for sealing metal terminals. The adhesive film for sealing a metal terminal of a power storage device according to claim 7, wherein the curing agent is at least one selected from the group consisting of a polyfunctional isocyanate compound, a carbodiimide compound, an epoxy compound, and an oxazoline compound.

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