Adhesive film, tab lead, and energy storage device

Abstract

Provided is an adhesive film formed from a first layer including a first main surface and a second layer provided on the first main surface. The first layer is a crosslinked layer having a heat collapse residual ratio of 60% or more after a load of 0.1 MPa is applied at 200°C and held for 1 minute. In a DSC curve of the first layer, a first melting peak is present between 115°C and 155°C, inclusive, and a second melting peak is present between 30°C and 70°C, inclusive. The DSC curve is obtained by measuring in the range from 0°C to 200°C at a temperature rise rate of 10°C / minute using a differential scanning calorimeter. The elastic modulus E1 of the first layer at 25°C is between 600 MPa and 1000 MPa, inclusive, the elastic modulus E1 being measured using a nanoindenter. The second layer is an acid-modified polyolefin layer.

Description

Adhesive film, tab lead, and power storage device

[0001] The present disclosure relates to an adhesive film, a tab lead, and a power storage device.

[0002] A power storage device used in a small electronic device has, for example, a structure in which a positive electrode and a negative electrode to which lead conductors are connected are sealed in an encapsulation container together with an electrolyte medium.

[0003] The surface of the encapsulation container is resin, and the lead conductor is metal, and their materials are different from each other. Therefore, the interface between the encapsulation container and the lead conductor has weak adhesion. Thus, in order to enhance the adhesive force between the encapsulation container and the lead conductor, a technique of providing an adhesive film between them has been proposed (Patent Document 1, Patent Document 2).

[0004] Japanese Patent Application Laid-Open No. 11-334389 Japanese Patent Application Laid-Open No. 2011-103245

[0005] The adhesive film of the present disclosure is an adhesive film including a first layer including a first main surface and a second layer provided on the first main surface, wherein the first layer is a crosslinked layer having a heat collapse residual rate of 60% or more after applying a load of 0.1 MPa at 200 °C and holding for 1 minute, in the DSC curve of the first layer, a first melting peak exists at 115 °C or more and 155 °C or less, and a second melting peak exists at 30 °C or more and 70 °C or less, the DSC curve is obtained by measuring in the range of 0 °C to 200 °C under the condition of a temperature increase rate of 10 °C / min using a differential scanning calorimeter, the elastic modulus E1 of the first layer at 25 °C is 600 MPa or more and 1000 MPa or less, the elastic modulus E1 is measured using a nanoindenter, and the second layer is an acid-modified polyolefin layer, and it is an adhesive film.

[0006] FIG. 1 is a cross-sectional view of the adhesive film according to Embodiment 1. FIG. 2 is a cross-sectional view of the tab lead according to Embodiment 2. FIG. 3 is a front view of the power storage device according to Embodiment 3. FIG. 4 is a partial cross-sectional view taken at the IV-IV' portion of FIG. 3.

[0007] [Problems this disclosure aims to solve] In recent years, the demand for battery reliability has been increasing, and adhesive films are required to have improved adhesion not only to lead conductors but also to encapsulation containers.

[0008] Therefore, the present disclosure aims to provide an adhesive film that has high adhesion to a sealed container when used in an energy storage device. The present disclosure also aims to provide a tabrete and an energy storage device that include the adhesive film.

[0009] [Effects of this Disclosure] According to this disclosure, it is possible to provide an adhesive film that has high adhesion to a sealed container when used in an energy storage device. Furthermore, according to this disclosure, it is possible to provide a tabrete and an energy storage device that include the adhesive film.

[0010] [Description of Embodiments of the Disclosure] Embodiments of the Disclosure will be listed and described first. (1) The adhesive film of the Disclosure is an adhesive film comprising a first layer including a first main surface and a second layer provided on the first main surface, wherein the first layer is a crosslinked layer with a thermal collapse retention rate of 60% or more after being held for 1 minute with a load of 0.1 MPa at 200°C, and in the DSC curve of the first layer, a first melting peak exists at 115°C to 155°C and a second melting peak exists at 30°C to 70°C, the DSC curve is obtained by measuring with a differential scanning calorimeter in the range of 0°C to 200°C under the condition of a heating rate of 10°C / min, the elastic modulus E1 of the first layer at 25°C is 600 MPa to 1000 MPa, the elastic modulus E1 is measured using a nanoindenter, and the second layer is an acid-modified polyolefin layer.

[0011] According to this disclosure, it is possible to provide an adhesive film that has high adhesion to a sealed container when used in an energy storage device.

[0012] (2) In (1) above, the elastic modulus E1 of the first layer at 25°C may be 700 MPa or more and 900 MPa or less. This further improves the adhesion of the adhesive film to the encapsulation container.

[0013] (3) In (1) or (2) above, the first layer may include at least one selected from the group consisting of ethylene propylene copolymer, ethylene butene copolymer, ethylene hexene copolymer, and ethylene octene copolymer. This further improves the adhesion of the adhesive film to the encapsulating container.

[0014] (4) In any of (1) to (3) above, the first layer may contain random polypropylene with a melting point of 125°C or more and 155°C or less. This further improves the adhesion of the adhesive film to the encapsulation container.

[0015] (5) In any of (1) to (4) above, the acid-modified polyolefin layer may be an acid-modified polypropylene layer. This improves the adhesion and sealing properties of the adhesive film to the lead conductor.

[0016] (6) The tab lead of the present disclosure comprises a lead conductor and an adhesive film according to any one of (1) to (5) above attached to a part of the lead conductor, wherein the second layer of the adhesive film is disposed in contact with the lead conductor.

[0017] When the tab lead of this disclosure is used in an energy storage device, the first layer is positioned in contact with an adhesive film. In this energy storage device, the adhesive film and the encapsulation container are bonded with high adhesive strength. The tab lead is suitable for energy storage devices.

[0018] (7) The energy storage device of the present disclosure comprises a battery cell including a positive electrode, a negative electrode, and an electrolyte sandwiched between the positive electrode and the negative electrode, lead conductors electrically connected to the positive electrode and the negative electrode, and a sealed container for sealing the battery cell, wherein a portion of the lead conductors is exposed to the outside of the sealed container, and an adhesive film according to any one of (1) to (5) above is disposed between the lead conductors and the sealed container, and the first layer of the adhesive film is disposed in contact with the sealed container.

[0019] In the energy storage device of this disclosure, the adhesive film and the encapsulation container are bonded together with high adhesive strength. Therefore, the energy storage device can have excellent reliability.

[0020] (8) In (7) above, the sealing container includes a polypropylene layer in contact with the first layer, and the ratio E1 / E2 of the elastic modulus E1 of the first layer at 25°C to the elastic modulus E2 of the polypropylene layer of the sealing container at 25°C may be 0.3 or more and 1.1 or less. The elastic modulus E1 and the elastic modulus E2 are measured using a nanoindenter.

[0021] When the E1 / E2 ratio is between 0.3 and 1.1, the adhesion of the adhesive film to the encapsulation container is further improved, and the reliability of the energy storage device is further enhanced.

[0022] (9) In (7) or (8) above, the electrolyte may be a solid electrolyte. This allows the high adhesion of the adhesive film to the encapsulation container to be maintained for a long period of time, further improving the reliability of the energy storage device.

[0023] (10) In (7) or (8) above, the electrolyte may be a non-aqueous electrolyte. The energy storage device can have excellent reliability.

[0024] [Details of Embodiments of the Disclosure] Specific examples of the adhesive film, tab lead, and energy storage device of the Disclosure will be described below with reference to the drawings. In the drawings of the Disclosure, the same reference numerals indicate the same or corresponding parts. In addition, dimensional relationships such as length, width, thickness, and depth have been modified as appropriate for clarity and simplification of the drawings and do not necessarily represent actual dimensional relationships.

[0025] In this disclosure, the notation "A to B" means A or greater and B or less. If no unit is specified for A, and only a unit is specified for B, then the unit for A and the unit for B are the same.

[0026] In this disclosure, when compounds and the like are represented by chemical formulas, unless otherwise specified, the atomic ratios should include all conventionally known atomic ratios and should not necessarily be limited to those within the stoichiometric range.

[0027] In this disclosure, if one or more numerical values ​​are listed as the lower limit and upper limit of a numerical range, any combination of any one numerical value listed as the lower limit and any one numerical value listed as the upper limit shall also be disclosed.

[0028] In this disclosure, “equipment,” “includes,” “possesses,” and variations thereof are open-ended terms. Open-ended terms may or may not include additional elements in addition to the essential elements. The statement “consists of” is a closed term. However, even a configuration expressed in closed terms may include additional elements that are usually incidental or irrelevant to the subject technology.

[0029] [Embodiment 1: Adhesive Film] An adhesive film according to one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 1") will be described with reference to Figure 1. The adhesive film 1 of Embodiment 1 is an adhesive film comprising a first layer 11 including a first main surface 11a and a second layer 12 provided on the first main surface 11a. The first layer 11 is a crosslinked layer with a thermal deformation retention rate of 60% or more after applying a load of 0.1 MPa at 200°C and holding for 1 minute. In the DSC curve of the first layer 11, a first melting peak exists between 115°C and 155°C, and a second melting peak exists between 30°C and 70°C. The DSC curve is obtained by measuring with a differential scanning calorimeter in the range of 0°C to 200°C under the condition of a heating rate of 10°C / min. The elastic modulus E1 of the first layer 11 at 25°C is between 600 MPa and 1000 MPa. The elastic modulus E1 is measured using a nanoindenter. The second layer 12 is an acid-modified polyolefin layer.

[0030] <Structure of the Adhesive Film> As shown in Figure 1, the adhesive film 1 consists of a first layer 11 and a second layer 12 provided on the first main surface 11a of the first layer 11. The first layer 11 may include a first main surface 11a and a second main surface 11b opposite to the first main surface 11a. The second layer 12 may include a third main surface 12a in contact with the first main surface 11a and a fourth main surface 12b opposite to the third main surface 12a. In an energy storage device comprising the adhesive film 1, the second main surface 11b of the first layer 11 is arranged in contact with the sealing container, and the fourth main surface 12b of the second layer 12 is arranged in contact with the lead conductor.

[0031] The average thickness of the adhesive film can be set appropriately depending on the application. The average thickness of the adhesive film may be 50 μm to 250 μm, 60 μm to 210 μm, or 90 μm to 170 μm.

[0032] In this disclosure, the average thickness of the adhesive film is measured by the following procedure: The adhesive film is cut along the direction normal to the largest surface area on the outer surface of the adhesive film using a microtome or the like to expose the cross-section. The cross-section is observed at 250x magnification using a digital microscope, and the thickness of the adhesive film is measured at five locations. The average of the five thicknesses is calculated. This average corresponds to the average thickness of the adhesive film. In this disclosure, the average thicknesses of the first and second layers described later are measured in the same manner.

[0033] <First Layer> <Thermal Deformation Residual Rate> The first layer is a crosslinked layer with a thermal deformation residual rate of 60% or more after being held for 1 minute under a load of 0.1 MPa at 200°C. When the thermal deformation residual rate of the first layer is 60% or more, the first layer has excellent heat resistance, is less likely to melt during thermal fusion with the sealing container, and prevents short circuits between the metal layer of the sealing container and the lead conductor due to the melting of the adhesive film. There is no particular upper limit to the thermal deformation residual rate of the first layer, but for example, it may be 99% or less. The thermal deformation residual rate of the first layer may be 60% or more and 99% or less, or 70% or more and 95% or less. A thermal deformation residual rate of 60% or more of the first layer indicates that the first layer is a crosslinked layer.

[0034] In this disclosure, the thermal deformation retention rate of the first layer is measured by the following procedure. A sample consisting of the entire adhesive film comprising the first and second layers is prepared. Next, the sample is placed in a TMA apparatus. The probe is heated under a load of 0.1 MPa (probe diameter 0.9 mmφ), held at 200°C for 1 minute, the load is released, and the sample is removed after cooling to room temperature. In the heated and pressurized sample, the thickness Th (μm) of the first layer in the pressurized area and the thickness Tr (μm) of the first layer in the unpressurized area around the pressurized area are measured in the same manner as the method for measuring the average thickness of the adhesive film described above. (Th / Tr) × 100 is taken as the thermal deformation retention rate (%) of the first layer.

[0035] ≪DSC Curve≫ In the DSC curve of the first layer, a first melting peak exists between 115°C and 155°C, and a second melting peak exists between 30°C and 70°C. This indicates that the first layer contains two or more components. If there are two or more melting peaks between 115°C and 155°C, the first melting peak is defined as the melting peak with the largest peak height. If there are two or more melting peaks between 30°C and 70°C, the second melting peak is defined as the melting peak with the largest peak height.

[0036] In this disclosure, the DSC curve of the first layer is prepared using a differential scanning calorimeter in accordance with JIS K 7121-1987 "Method for Measuring Transition Temperature of Plastics". Specifically, the DSC curve of the first layer is obtained by removing the first layer from the adhesive film and measuring it with a differential scanning calorimeter from 0°C to 200°C at a heating rate of 10°C / min.

[0037] In the DSC curve of the first layer, the temperature of the first melting peak may be between 115°C and 150°C, between 120°C and 150°C, between 120°C and 145°C, or between 120°C and 135°C.

[0038] In the DSC curve of the first layer, the temperature of the second melting peak may be between 35°C and 66°C, between 35°C and 60°C, between 40°C and 55°C, or between 50°C and 55°C.

[0039] In the DSC curve of the first layer, the difference between the temperature of the first melting peak and the temperature of the second melting peak may be 45°C or more and 120°C or less, 49°C or more and 115°C or less, or 60°C or more and 115°C or less.

[0040] <<Elastic Modulus E1>> The elastic modulus E1 of the first layer at 25°C is 600 MPa or more and 1000 MPa or less. If the elastic modulus E1 is 600 MPa or more, the first layer has sufficient material strength and can obtain high adhesion to the sealed container. If the elastic modulus E1 is 1000 MPa or less, even when an external force is applied to the adhesive film, stress does not concentrate only on the resin layer (e.g., polypropylene layer) that is in contact with the first layer of the sealed container, and high adhesion to the sealed container can be obtained. The elastic modulus E1 of the first layer at 25°C may be 700 Pa or more and 990 MPa or less, 700 MPa or more and 950 MPa or less, 700 MPa or more and 900 MPa or less, or 780 MPa or more and 900 MPa or less.

[0041] In this disclosure, the modulus E1 of the first layer at 25°C is measured using a nanoindenter. The nanoindenter used is a TriboIndenterTI980 manufactured by HYSITRON. The nanoindenter uses a triangular pyramidal indenter (Berkovich indenter) with a diamond tip. Using the nanoindenter, the indenter is pressed perpendicularly to the center of the thickness direction of the cross-section of the first layer under the following measurement conditions, and the load-displacement curve is measured to calculate the modulus E1: (1) Pressing time: 3 seconds (2) Holding time: 0 seconds (3) Unloading time: 0 seconds (4) Loading rate: 8 mN / second (5) Pressing load: 0.5 mN to 5 mN (adjusted as appropriate so that the indentation size is approximately 10 μm to 20 μm) (6) Time to reach press depth: 5 seconds (7) Load holding time: 0 seconds (8) Unloading time to press depth: 5 seconds

[0042] <<Components of the first layer>>The first layer may contain at least one selected from the group consisting of an ethylene-propylene copolymer, an ethylene-butene copolymer, an ethylene-hexene copolymer, and an ethylene-octene copolymer as an elastomer component. When the first layer contains these elastomer components, in the DSC curve of the first layer, a second melting peak exists at 30°C or higher and 70°C or lower. Note that since the first layer of a conventional adhesive film does not contain an elastomer component, in the DSC curve of the first layer, a second melting peak does not exist at 30°C or higher and 70°C or lower, and the elastic modulus exceeds 1000 MPa.

[0043] The first layer may contain polypropylene. Examples of polypropylene include homopolypropylene, block polypropylene, random polypropylene, acid-modified polypropylene, and the like.

[0044] Whether the first layer contains polypropylene can be confirmed by performing imaging IR analysis using a Fourier transform infrared spectrophotometer only on the first layer of the adhesive film.

[0045] The first layer may contain polypropylene having a melting point of 115°C or higher and 155°C or lower. When the first layer contains polypropylene having a melting point of 115°C or higher and 155°C or lower, in the DSC curve of the first layer, a first melting peak exists at 115°C or higher and 155°C or lower.

[0046] The first layer may contain random polypropylene having a melting point of 125°C or higher and 155°C or lower.

[0047] The first layer may contain an elastomer component and polypropylene.

[0048] The first layer can contain various additives such as a crosslinking aid, a flame retardant, an ultraviolet absorber, a light stabilizer, a heat stabilizer, a lubricant, and a coloring agent. The types and amounts of these additives can be the same as those of conventionally known types and amounts. Examples of the crosslinking aid include trimethylolpropane methacrylate, pentaerythritol triacrylate, ethin glycol dimethacrylate, triallyl cyanurate, and triallyl isocyanurate.

[0049] ≪Average Thickness of the First Layer≫ The average thickness of the first layer may be 15 μm or more and 150 μm or less, 20 μm or more and 110 μm or less, or 30 μm or more and 60 μm or less. If the average thickness of the first layer is 15 μm or more, good adhesion to the lead conductor can be ensured. If the average thickness of the first layer is 150 μm or less, the energy storage device including the adhesive film can be made smaller.

[0050] <Second Layer> The second layer is an acid-modified polyolefin layer. Acid-modified polyolefins are polyolefins containing acid-modified groups, modified with carboxylic acids such as maleic acid, acrylic acid, methacrylic acid, and maleic anhydride. Examples of acid-modified polyolefins include maleic acid-modified polypropylene, acrylic acid-modified polypropylene, maleic anhydride-modified polypropylene, acrylic acid-modified polyethylene, maleic anhydride-modified polyethylene, and acrylic acid-modified ethylene acrylate. If the second layer is an acid-modified polypropylene layer, it has excellent adhesion and sealing properties to metals. If the second layer is a maleic anhydride-modified polypropylene layer, it has extremely excellent adhesion and sealing properties to metals. The acid-modified polyolefin layer may also contain unmodified polyolefin as a resin component, as long as it does not impair the effects of this disclosure. Hereinafter, acid-modified polyolefins and unmodified polyolefins will be collectively referred to as polyolefins.

[0051] The presence of acid-modifying groups in the second layer can be confirmed by separating only the second layer from the adhesive film and performing transmitted light analysis on the second layer using a Fourier transform infrared spectrophotometer. Examples of acid-modifying groups include maleic acid, acrylic acid, methacrylic acid, and maleic anhydride. The content of acid-modifying groups in the second layer can be between 0.01% by mass and 1.0% by mass.

[0052] The presence of polyolefin in the second layer can be confirmed by removing only the second layer from the adhesive film and performing reflected light analysis on the second layer using a Fourier transform infrared spectrophotometer.

[0053] The second layer may contain various additives such as flame retardants, ultraviolet absorbers, light stabilizers, heat stabilizers, lubricants, and colorants. The types and amounts of these additives can be the same as those used in conventionally known acid-modified polyolefin layers.

[0054] ≪Average Thickness of the Second Layer≫ The average thickness of the second layer may be 35 μm or more and 200 μm or less, 40 μm or more and 160 μm or less, or 50 μm or more and 110 μm or less. If the average thickness of the second layer is 35 μm or more, good adhesion with the lead conductor can be ensured. If the average thickness of the second layer is 200 μm or less, the energy storage device including the adhesive film can be made smaller.

[0055] <Method for producing an adhesive film> The adhesive film of Embodiment 1 is produced, for example, by the following method. First, polypropylene and an elastomer component are prepared as raw materials for the first layer, and acid-modified polyolefin is prepared as raw materials for the second layer.

[0056] Specific examples of the polypropylene and elastomer components used as raw materials for the first layer are as described in Embodiment 1. The melting point of the polypropylene is 115°C to 155°C. The Shore A hardness of the elastomer component is 50 to 90. When the melting point of the polypropylene and the Shore A hardness of the elastomer component are within the above range, the elastic modulus E1 of the first layer at 25°C can be controlled to 600 MPa to 1000 MPa by adjusting the mass ratio of the polypropylene to the elastomer component. For example, when using polypropylene with a melting point of 140°C and an elastomer component with a Shore A hardness of 57 to 87, the mass ratio of the polypropylene to the elastomer component is set to polypropylene:elastomer component = 55:45 to 75:25. For example, when using polypropylene with a melting point of 152°C and an elastomer component with a Shore A hardness of 57, the mass ratio of the polypropylene to the elastomer component is set to polypropylene:elastomer component = 60:40. For example, when using polypropylene with a melting point of 129°C and an elastomer component with a Shore A hardness of 71, the mass ratio of polypropylene to elastomer component is set to polypropylene:elastomer component = 70:30.

[0057] A specific example of the acid-modified polyolefin used as the raw material for the second layer is as described in Embodiment 1.

[0058] If at least one of the first and second layers contains either an additive or a crosslinking aid, then the additive and the crosslinking aid are prepared. An example of a crosslinking aid is trimethylolpropane methacrylate.

[0059] The raw materials for the first layer and the raw materials for the second layer are mixed using known mixing equipment such as an open roll, a pressure kneader, a single-screw kneader, or a twin-screw kneader to obtain the mixed raw materials for the first layer and the mixed raw materials for the second layer.

[0060] The mixed raw materials for the first and second layers are extruded using a single-layer T-die extruder to obtain a single-layer film consisting of the first layer and a single-layer film consisting of the second layer. The single-layer film consisting of the first layer is irradiated with an electron beam at an acceleration voltage of 200 kV in an oxygen-free atmosphere to achieve an absorbed dose of 150 kGy using an electron beam irradiator to crosslink the polypropylene resin and elastomer components. Subsequently, the single-layer film consisting of the first layer is laminated with the single-layer film consisting of the second layer by thermal lamination at 180°C to obtain an adhesive film. The film formation conditions in the T-die extruder are, for example, a die lip opening of 0.3 mm thickness to 1.0 mm thickness and a take-up speed of 2 m / min to 20 m / min. The thickness of the first layer after extrusion is adjusted to 15 μm to 200 μm.

[0061] [Embodiment 2: Tab Lead] A tab lead according to one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 2") will be described with reference to Figure 2. The tab lead 20 of Embodiment 2 comprises a lead conductor 3 and an adhesive film 1 of Embodiment 1 attached to a part of the lead conductor 3. In the tab lead 20, the second layer 12 of the adhesive film 1 is arranged in contact with the lead conductor 3. In an energy storage device equipped with the tab lead 20, the second main surface 11b of the first layer 11 is arranged in contact with the sealing container, and the fourth main surface 12b of the second layer 12 is arranged in contact with the lead conductor.

[0062] In Embodiment 2, metals such as aluminum, nickel, copper, and nickel-plated copper are used as lead conductors. Aluminum is often used for the positive electrode, and aluminum, nickel, or nickel-plated copper is often used for the negative electrode. The shape of the lead conductor is not particularly limited, but a flat metal plate with a thickness of 50 μm to 2 mm, a width of 1 mm to 200 mm, and a length of 20 mm to 200 mm is preferably used.

[0063] [Embodiment 3: Energy Storage Device] An energy storage device according to one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 3") will be described with reference to Figures 3 and 4. Figure 3 is a schematic front view showing one embodiment of the energy storage device 30 of Embodiment 3. Figure 4 is a partial cross-sectional view taken along section IV-IV' of Figure 3. The energy storage device 30 of Embodiment 3 includes a battery cell 15 comprising a positive electrode 10, a negative electrode 14, and an electrolyte 13 sandwiched between the positive electrode 10 and the negative electrode 14, lead conductors 3 electrically connected to the positive electrode 10 and the negative electrode 14, and a sealed container 2 that seals the battery cell 15. A portion of the lead conductors 3 is exposed to the outside of the sealed container 2, and the adhesive film 1 of Embodiment 1 is placed between the lead conductors 3 and the sealed container 2. The first layer 11 of the adhesive film is placed in contact with the sealed container 2.

[0064] As shown in Figure 4, the sealing container 2 consists of a three-layer laminate film 8 comprising a metal layer 5 and a first resin layer 6 and a second resin layer 7 covering the metal layer 5. The metal layer 5 is formed from a metal such as aluminum foil. As the first resin layer 6 located on the outside of the sealing container 2, polyamide resins such as 6,6-nylon, 6-nylon, polyester resins, polyimide resins, etc., can be used. Furthermore, it is preferable to use an insulating resin that does not dissolve in a non-aqueous electrolyte and melts when heated for the second resin layer 7 located on the inside of the sealing container 2 and in contact with the first layer 11 of the adhesive film 1. Examples of such insulating resins include polyolefin resins, acid-modified polyolefin resins, and acid-modified styrene elastomers. The sealing container may also include a polypropylene layer as the second resin layer 7 in contact with the first layer 11. The polypropylene layer may be an acid-modified polypropylene layer. Examples of acid-modified polypropylene layers include maleic acid-modified polypropylene layers, acrylic acid-modified polypropylene layers, and maleic anhydride-modified polypropylene layers.

[0065] The sealing container 2 is made by overlapping two laminate films 8 and heat-sealing three sides other than the side through which the lead conductor 3 passes. At the outer circumference of the sealing container 2, the two metal layers 5 are bonded together via a second resin layer 7.

[0066] The lead conductor 3 is bonded (heat-sealed) to the sealing container (laminate film) via the adhesive film 1 at the sealing portion 9. Inside the energy storage device 30, a positive electrode 10, a negative electrode 14, and an electrolyte 13 are further sealed. Figure 4 shows a lead conductor connected to the negative electrode 14. A lead conductor connected to the positive electrode 10 also exists, but is not shown in Figure 4. In Embodiment 3, the electrolyte 13 may be a solid electrolyte. In Embodiment 3, the electrolyte 13 may be a non-aqueous electrolyte. For example, LiPF ６ LiBF ４ Examples include lithium salts containing fluorine, dissolved in diethyl carbonate (DEC), dimethyl carbonate (DMC), propylene carbonate (PC), etc.

[0067] The sealed container includes a polypropylene layer in contact with the first layer, and the ratio E1 / E2 of the elastic modulus E1 of the first layer at 25°C to the elastic modulus E2 of the polypropylene layer of the sealed container at 25°C may be 0.3 or more and 1.1 or less, 0.25 or more and 1.0 or less, or 0.60 or more and 0.90 or less. The elastic modulus E2 of the polypropylene layer of the sealed container at 25°C is measured in the same manner as the elastic modulus E1 of the first layer at 25°C.

[0068] This embodiment will be described in more detail by reference to examples. However, this embodiment is not limited by these examples.

[0069] [Preparation of Adhesive Film] As the raw materials for the first layer, polypropylene (PP) and elastomer components were prepared in the mass ratios shown in Tables 1 and 2, and 5 parts by weight of trimethylolpropane methacrylate was also prepared. These raw materials were mixed using a twin-screw kneader to obtain the raw materials for the first layer. In all samples, the polypropylene was random polypropylene. The melting points of the polypropylene used in each sample are shown in Tables 1 and 2. The component names, Shore A hardness, and melting points of the elastomer components used in each sample are shown in Tables 1 and 2.

[0070]

[0071]

[0072] As the raw material for the second layer, maleic anhydride-modified random polypropylene with a melting point of 140°C and an acid modification rate of 1.2% by mass was prepared. The raw material for the second layer was also kneaded using a twin-screw kneader.

[0073] The raw materials for the first and second layers were extruded using a single-layer T-die extruder to obtain single-layer films consisting of the first and second layers, respectively. For samples other than samples 1-5, the single-layer films consisting of the first layer were irradiated with an electron beam at an acceleration voltage of 200 kV in an oxygen-free atmosphere to achieve an absorbed dose of 150 kGy using an electron beam irradiator to crosslink the polypropylene resin and elastomer components.

[0074] Next, a single-layer film consisting of the first layer was laminated with a single-layer film consisting of the second layer by heat lamination at 180°C to obtain an adhesive film. This resulted in obtaining adhesive films for each sample with the first and second layers laminated. For all samples, the take-up speed was 8 m / min and the die lip opening was 0.4 mm. The average thicknesses of the first and second layers, respectively, in the obtained adhesive films are shown in Tables 1 and 2.

[0075] [Measurement of Adhesive Film] <Heat Deformation Remaining Rate> For the first layer of adhesive film of each sample, the heat deformation remaining rate was measured after applying a load of 0.1 MPa at 200°C and holding for 1 minute. The specific measurement method is as described in Embodiment 1. The results are shown in Tables 1 and 2.

[0076] ≪DSC Curves≫ DSC curves were created for the first layer of adhesive film for each sample, and the first melting peak temperature and the second melting peak temperature were measured. The specific measurement method is as described in Embodiment 1. The results are shown in Tables 1 and 2. "None" in the "Second Melting Peak" column for Sample 1-1 indicates that there was no second melting peak. "None (105)" in the "Second Melting Peak" column for Sample 1-4 indicates that there was no second melting peak, but there was a melting peak with a peak temperature of 105°C.

[0077] <<Elastic Modulus E1>> The elastic modulus E1 of the first layer of the adhesive film of each sample was measured at 25°C. The specific measurement method is as described in Embodiment 1. The results are shown in Tables 1 and 2.

[0078] [Adhesion Test between Adhesive Film and Encapsulation Container] A three-layer sheet was prepared as the encapsulation container, consisting of a polyamide layer (33 μm thick, corresponding to the first resin layer), a metal layer made of aluminum foil (40 μm thick), and a maleic acid-modified polypropylene layer (80 μm thick, corresponding to the second resin layer), laminated in the order described above. The size of the encapsulation container was 100 mm in length and 200 mm in width. The first layer of each sample's adhesive film (10 mm in length, 55 mm in width) was placed in contact with the maleic acid-modified polypropylene layer of the encapsulation container and pressed to bond, thereby preparing the first test sample. The pressing conditions were as described in Press Condition 1 and Press Condition 2 below. Press Condition 1: 200°C, surface pressure 2.0 MPa, 5 seconds Press Condition 2: 200°C, surface pressure 2.0 MPa, 3 seconds

[0079] For the first test sample of each specimen, the adhesive film was pulled away from the encapsulation container at a 180° angle, and the 180° peel strength was measured. The tensile speed was 50 mm / min. The results are shown in the "Adhesion to Encapsulation Container" column, "Press Condition 1" and "Press Condition 2" in Tables 1 and 2. In Tables 1 and 2, "A" is indicated if the peel strength is 60 N / cm or higher, and "B" is indicated if the peel strength is less than 60 N / cm. In the above adhesion test, if the results for both "Press Condition 1" and "Press Condition 2" are "A", the adhesive film is judged to have high adhesion to the encapsulation container.

[0080] [E1 / E2] The elastic modulus E2 of the maleic acid-modified polypropylene layer of the sealing container used for each sample was measured at 25°C. The specific measurement method is as described in Embodiment 1. E1 / E2 was calculated based on the elastic modulus E1 and E2. The results are shown in Tables 1 and 2.

[0081] [Adhesion Test between Adhesive Film and Lead Conductor] A flat conductor made of aluminum plate with a length of 100 mm, a width of 45 mm, and an average thickness of 0.4 mm was used as the base material for the lead conductor. Chromium chloride hexahydrate (5.0 g / L) and potassium formate (170 g / L) were mixed in pure water to obtain a surface treatment solution. The lead conductor was immersed in the surface treatment solution at 45°C, and the current density was 10 A / dm². ２Cathodic electrolysis was performed for 10 seconds. This yielded a lead conductor with a conductive coating. A second layer of adhesive film (10 mm long, 55 mm wide) for each sample was placed in contact with one main surface of the lead conductor, and pressed at 210°C for 10 seconds to bond, thereby preparing a second test sample. For each second test sample, the conductor was cut 10 mm from the end in the width direction, leaving the insulating film on the surface, and the conductor was bent. The adhesive film was then pulled 180° away from the lead conductor to peel it off, and the 180° peel strength was measured. The tensile speed was 100 mm / min. The measurement was performed 1 hour after bonding. The results are shown in the "Adhesion to Lead Conductor" column of Tables 1 and 2. In Tables 1 and 2, "A" is written if the peel strength is 15 N / cm or more, and "B" is written if the peel strength is less than 15 N / cm. In the adhesion test described above, if the result is "A", the adhesive film is judged to have high adhesion to the lead conductor.

[0082] The adhesive films of Samples 1 to 6 correspond to the examples. It was confirmed that the adhesive films of these samples have high adhesion to the encapsulation container and lead conductor.

[0083] The adhesive films of samples 1-1 to 1-5 correspond to the examples. It was confirmed that the adhesive films of these samples had insufficient adhesion to the encapsulation container.

[0084] While embodiments and examples of this disclosure have been described above, it is intended from the outset that the configurations of each of the embodiments and examples described above may be combined or modified in various ways as appropriate. The embodiments and examples disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than the embodiments and examples described above, and all modifications within the scope of the claims are intended to be included in the meaning of equivalences.

[0085] 1 Adhesive film, 2 Encapsulation container, 3 Lead conductor, 5 Metal layer, 6 First resin layer, 7 Second resin layer, 8 Laminate film, 9 Sealing portion, 10 Positive electrode, 11 First layer, 11a First main surface, 11b Second main surface, 12 Second layer, 12a Third main surface, 12b Fourth main surface, 13 Electrolyte, 14 Negative electrode, 15 Battery cell, 30 Energy storage device.

Claims

1. An adhesive film comprising a first layer including a first main surface and a second layer provided on the first main surface, wherein the first layer is a crosslinked layer with a thermal deformation retention rate of 60% or more after being held for 1 minute with a load of 0.1 MPa at 200°C, the DSC curve of the first layer shows a first melting peak at 115°C to 155°C and a second melting peak at 30°C to 70°C, the DSC curve is obtained by measuring with a differential scanning calorimeter in the range of 0°C to 200°C under the condition of a heating rate of 10°C / min, the elastic modulus E1 of the first layer at 25°C is 600 MPa to 1000 MPa, the elastic modulus E1 is measured using a nanoindenter, and the second layer is an acid-modified polyolefin layer.

2. The adhesive film according to claim 1, wherein the elastic modulus E1 of the first layer at 25°C is 700 MPa or more and 900 MPa or less.

3. The adhesive film according to claim 1 or 2, wherein the layer comprises at least one selected from the group consisting of ethylene propylene copolymer, ethylene butene copolymer, ethylene hexene copolymer, and ethylene octene copolymer.

4. The adhesive film according to any one of claims 1 to 3, wherein the first layer comprises random polypropylene with a melting point of 125°C or higher and 155°C or lower.

5. The adhesive film according to any one of claims 1 to 4, wherein the acid-modified polyolefin layer is an acid-modified polypropylene layer.

6. A tab lead comprising a lead conductor and an adhesive film according to any one of claims 1 to 5 attached to a part of the lead conductor, wherein the second layer of the adhesive film is disposed in contact with the lead conductor.

7. An energy storage device comprising: a battery cell including a positive electrode, a negative electrode, and an electrolyte sandwiched between the positive electrode and the negative electrode; lead conductors electrically connected to the positive electrode and the negative electrode, respectively; and a sealing container for sealing the battery cell, wherein a portion of the lead conductors is exposed to the outside of the sealing container, and an adhesive film according to any one of claims 1 to 5 is disposed between the lead conductors and the sealing container, and the first layer of the adhesive film is disposed in contact with the sealing container.

8. The energy storage device according to claim 7, wherein the encapsulating container includes a polypropylene layer in contact with the first layer, the ratio E1 / E2 of the elastic modulus E1 of the first layer at 25°C to the elastic modulus E2 of the polypropylene layer of the encapsulating container at 25°C is 0.3 or more and 1.1 or less, and the elastic modulus E1 and the elastic modulus E2 are measured using a nanoindenter.

9. The energy storage device according to claim 7 or claim 8, wherein the electrolyte is a solid electrolyte.

10. The energy storage device according to claim 7 or claim 8, wherein the electrolyte is a non-aqueous electrolyte.

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