JP7782525B2 - Battery, manufacturing method thereof, metal terminal with adhesive film for metal terminal, and roll of adhesive film for metal terminal - Google Patents

Description

The present invention relates to a battery, a method for manufacturing the battery, a metal terminal with an adhesive film for a metal terminal, and a roll of the adhesive film for a metal terminal.

Many different types of batteries have been developed, and packaging materials are essential components for sealing battery elements such as electrodes and electrolytes in all batteries. Traditionally, metal packaging materials have been widely used for battery packaging, but in recent years, with the increasing performance of electric vehicles, hybrid electric vehicles, personal computers, cameras, mobile phones, and other devices, batteries are being required to come in a variety of shapes, as well as be thinner and lighter. However, the metal packaging materials that have been widely used in the past have the drawback of being difficult to adapt to the increasing variety of shapes, and there are also limitations to how light they can be made.

In recent years, a film-like laminate consisting of a base layer, a barrier layer, and a heat-sealable resin layer has been proposed as a packaging material that can be easily processed into various shapes and can be made thinner and lighter (see, for example, Patent Document 1). When using such a film-like packaging material, the battery element is sealed with the packaging material by heat-sealing the periphery of the packaging material with the innermost heat-sealable resin layers facing each other. Metal terminals protrude from the heat-sealed portion of the packaging material, and the battery element sealed with the packaging material is electrically connected to the outside through the metal terminals electrically connected to the electrodes of the battery element. That is, the heat-sealed portion of the packaging material is formed so that the metal terminals protrude outside the packaging material while being sandwiched between the heat-sealable resin layers. Because the metal terminals and the heat-sealable resin layer are made of different materials, the sealing of the battery element is likely to be poor at the interface between the metal terminals and the heat-sealable resin layer. For this reason, a known technique involves placing an adhesive film at the interface between the metal terminal and the heat-sealable resin layer to prevent a decrease in sealing performance at the interface between the metal terminal and the heat-sealable resin layer.

For example, Patent Document 2 discloses an adhesive film for sealing metal terminals in lithium batteries, which comprises a biaxially oriented polyethylene naphthalate film on both sides of which an acid-modified polyolefin layer is formed via an adhesion promoter layer made of an isocyanate component.

Japanese Patent Application Laid-Open No. 2001-202927 Patent No. 4440573

The adhesive film disclosed in Patent Document 2 uses a biaxially oriented polyethylene naphthalate film, which has high water vapor barrier properties and mechanical strength, as the substrate, with polyolefin layers laminated to both sides of the substrate via adhesion promoter layers. Therefore, by sealing the metal terminal and the heat-sealable resin layer of the packaging material via the adhesive film, the adhesion between the metal terminal and the heat-sealable resin layer is improved, and short-circuiting between the metal terminal and the barrier layer laminated to the packaging material can be prevented. The use of biaxially oriented polyethylene naphthalate film also has the advantage of excellent heat resistance.

In recent years, the uses of batteries have become more diverse. For example, batteries used in high-temperature environments or with certain types of electrolyte can cause the internal pressure of the battery's packaging to increase. For example, if a battery is exposed to high temperatures, the organic solvent used in the electrolyte can decompose, generating gas and causing the internal pressure to increase. Furthermore, charging with excessive voltage or discharging with excessive current can cause the temperature inside the battery to rise continuously, causing a runaway battery reaction and increasing the internal pressure of the packaging.

After extensive research, the inventors discovered that when the internal pressure of the battery packaging material increases, force is applied in the thickness direction of the adhesive film located between the packaging material and the metal terminal, which could cause the heat-sealed portion around the battery's periphery to open in the area where the adhesive film is located.

Under these circumstances, the primary objective of the present invention is to provide a battery in which opening of the packaging material in the area where the adhesive film is located is effectively prevented, even when the internal pressure of the battery increases. A further objective of the present invention is to provide a method for manufacturing such a battery.

The inventors conducted extensive research to solve the above-mentioned problems. As a result, they discovered that a battery having the following configuration effectively prevents the packaging material at the adhesive film location from being opened even when the internal pressure of the battery increases. The present invention was completed through further research based on this finding.

A battery comprising: a battery element including at least a positive electrode, a negative electrode, and an electrolyte; a packaging material for sealing the battery element; and metal terminals electrically connected to the positive electrode and the negative electrode, respectively, and extending outside the packaging material,
an adhesive film for a metal terminal is disposed between the metal terminal and the packaging material;
The adhesive film for a metal terminal includes a first polyolefin layer, a base film containing polyethylene naphthalate, and a second polyolefin layer in this order;
At least one of the first polyolefin layer and the second polyolefin layer contains an acid-modified polyolefin,
A battery, wherein an angle θ formed between the Y _max direction and a direction in which the metal terminal extends outside the packaging material, as measured by the following method, is 45° or more and 135° or less.

(Method of measuring in the Y _max direction)
The method for measuring the _Ymax direction of an adhesive film for metal terminals is to obtain infrared absorption spectra for the surface of the base film in 18 directions perpendicular to the thickness direction from 0° to 170° in 10° increments by polarization measurement using the single-reflection ATR method of Fourier transform infrared spectroscopy, and then calculate a value Y in each of the 18 directions by dividing the absorption peak intensity _Y765 at 765 cm ^-1 of the infrared absorption spectrum by the absorption peak intensity Y1181 at ₁₁₈₁ cm ^-1 , and the direction in which the maximum value _Ymax of all the Y values is obtained is defined as the _Ymax direction.

That is, the present invention provides the following aspects.
Item 1. A battery comprising: a battery element including at least a positive electrode, a negative electrode, and an electrolyte; a packaging material that seals the battery element; and metal terminals that are electrically connected to the positive electrode and the negative electrode, respectively, and that extend outside the packaging material,
an adhesive film for a metal terminal is disposed between the metal terminal and the packaging material;
The adhesive film for a metal terminal includes a first polyolefin layer, a base film containing polyethylene naphthalate, and a second polyolefin layer in this order;
At least one of the first polyolefin layer and the second polyolefin layer contains an acid-modified polyolefin,
A battery, wherein an angle θ formed between the Y _max direction and a direction in which the metal terminal extends outside the packaging material, as measured by the following method, is 45° or more and 135° or less.
The _Ymax direction is measured by obtaining infrared absorption spectra for the surface of the base film in 18 directions perpendicular to the thickness direction from 0° to 170° at 10° intervals by polarization measurement using a single-reflection ATR method of Fourier transform infrared spectroscopy, and then calculating a value Y in each of the 18 directions by dividing the absorption peak intensity _Y765 at 765 cm ^-1 of the infrared absorption spectrum by the absorption peak intensity _Y1181 at 1181 cm ^-1 . The direction in which the maximum value _Ymax of all the Y values is obtained is defined as the _Ymax direction.
Item 2. The battery according to Item 1, wherein the thickness of the substrate film of the adhesive film for metal terminal is 10 μm or more and 50 μm or less.
Item 3. The battery according to Item 1 or 2, wherein the first polyolefin layer and the second polyolefin layer of the adhesive film for a metal terminal contain an acid-modified polyolefin.
Item 4. The battery according to any one of Items 1 to 3, wherein the thickness of the first polyolefin layer and the second polyolefin layer of the adhesive film for a metal terminal is 5 μm or more and 80 μm or less.
Item 5. The battery according to any one of Items 1 to 4, wherein the adhesive film for metal terminals has a thickness of 20 μm or more and 200 μm or less.
Item 6. The battery according to any one of Items 1 to 5, wherein the packaging material is composed of a laminate including at least a base layer, a barrier layer, and a heat-sealable resin layer in this order.
Item 7. A method for manufacturing a battery including at least a battery element including a positive electrode, a negative electrode, and an electrolyte, a packaging material that seals the battery element, and metal terminals that are electrically connected to the positive electrode and the negative electrode, respectively, and that protrude outside the packaging material,
and disposing an adhesive film for metal terminals between the metal terminals and the packaging material,
The adhesive film for a metal terminal includes a first polyolefin layer, a base film containing polyethylene naphthalate, and a second polyolefin layer in this order,
At least one of the first polyolefin layer and the second polyolefin layer contains an acid-modified polyolefin,
A method for manufacturing a battery using a packaging material in which an angle θ formed between a Y _max direction and a direction in which the metal terminal extends outward from the packaging material, as measured by the following method, is 45° or more and 135° or less.
The _Ymax direction is measured by obtaining infrared absorption spectra for the surface of the base film in 18 directions perpendicular to the thickness direction from 0° to 170° at 10° intervals by polarization measurement using a single-reflection ATR method of Fourier transform infrared spectroscopy, and then calculating a value Y in each of the 18 directions by dividing the absorption peak intensity _Y765 at 765 cm ^-1 of the infrared absorption spectrum by the absorption peak intensity _Y1181 at 1181 cm ^-1 . The direction in which the maximum value _Ymax of all the Y values is obtained is defined as the _Ymax direction.
Item 8. A metal terminal with an adhesive film for a metal terminal, in which an adhesive film for a metal terminal is attached to a metal terminal of a battery,
The adhesive film for a metal terminal includes a first polyolefin layer, a base film containing polyethylene naphthalate, and a second polyolefin layer in this order;
At least one of the first polyolefin layer and the second polyolefin layer contains an acid-modified polyolefin,
A metal terminal with an adhesive film for a metal terminal, wherein the adhesive film for a metal terminal is attached to the metal terminal such that the angle θ formed between the direction in which the metal terminal extends outward from the battery when attached to the battery and the Y _max direction of the adhesive film for a metal terminal, as measured by the method described below, is 45° or more and 135° or less.
The _Ymax direction is measured by obtaining infrared absorption spectra for the surface of the base film in 18 directions perpendicular to the thickness direction from 0° to 170° at 10° intervals by polarization measurement using a single-reflection ATR method of Fourier transform infrared spectroscopy, and then calculating a value Y in each of the 18 directions by dividing the absorption peak intensity _Y765 at 765 cm ^-1 of the infrared absorption spectrum by the absorption peak intensity _Y1181 at 1181 cm ^-1 . The direction in which the maximum value _Ymax of all the Y values is obtained is defined as the _Ymax direction.
Item 9. A roll of an adhesive film for metal terminals, which is interposed between metal terminals electrically connected to the positive and negative electrodes of a battery element including at least a positive electrode, a negative electrode, and an electrolyte, and a packaging material that seals the battery element,
The adhesive film for a metal terminal includes a first polyolefin layer, a base film containing polyethylene naphthalate, and a second polyolefin layer in this order;
At least one of the first polyolefin layer and the second polyolefin layer contains an acid-modified polyolefin,
A roll of adhesive film for metal terminal, wherein the angle θ formed by the Y _max direction and the direction perpendicular to the winding direction of the roll of adhesive film for metal terminal, as measured by the following method, is 45° or more and 135° or less.
The _Ymax direction is measured by obtaining infrared absorption spectra for the surface of the base film in 18 directions perpendicular to the thickness direction from 0° to 170° at 10° intervals by polarization measurement using a single-reflection ATR method of Fourier transform infrared spectroscopy, and then calculating a value Y in each of the 18 directions by dividing the absorption peak intensity _Y765 at 765 cm ^-1 of the infrared absorption spectrum by the absorption peak intensity _Y1181 at 1181 cm ^-1 . The direction in which the maximum value _Ymax of all the Y values is obtained is defined as the _Ymax direction.

The present invention provides a battery in which opening of the packaging material at the adhesive film location is effectively prevented even when the internal pressure of the battery increases. Furthermore, the present invention also provides a method for manufacturing such a battery, and a metal terminal with an adhesive film for metal terminals.

1 is a schematic plan view of a battery of the present invention. 2 is a schematic cross-sectional view taken along line A-A' in FIG. 1. 2 is a schematic cross-sectional view taken along line B-B' in FIG. 1. 1 is a schematic cross-sectional view of an adhesive film for a metal terminal used in a battery of the present invention. 1 is a schematic cross-sectional view of a packaging material used in a battery of the present invention. FIG. 2 is a schematic diagram illustrating the fabrication of a test battery. Schematic diagram for explaining the angle θ between the Y _max direction, which is the maximum in-plane orientation direction of naphthalene rings contained in the base film of the adhesive film for metal terminals, and the direction in which the metal terminal extends outside the packaging material. FIG. 1 is a schematic diagram for explaining an opening test of a packaging material. 1 is a schematic diagram of a metal terminal with an adhesive film for a metal terminal of the present invention.

The battery of the present invention comprises at least a battery element having a positive electrode, a negative electrode, and an electrolyte, a packaging material that seals the battery element, and metal terminals that are electrically connected to the positive electrode and the negative electrode, respectively, and extend outside the packaging material.

In the battery of the present invention, an adhesive film for metal terminals is disposed between the metal terminals and the packaging material. The adhesive film for metal terminals comprises, in this order, a first polyolefin layer, a substrate film containing polyethylene naphthalate, and a second polyolefin layer, and at least one of the first polyolefin layer and the second polyolefin layer contains an acid-modified polyolefin.

Furthermore, the battery of the present invention is characterized in that the angle θ formed by the Y _max direction of the adhesive film for metal terminals and the direction in which the metal terminals extend outward from the packaging material, as measured by the following method, is 45° or more and 135° or less.

(Method of measuring in the Y _max direction)
The method for measuring the _Ymax direction of an adhesive film for metal terminals is to obtain infrared absorption spectra for the surface of the base film in 18 directions perpendicular to the thickness direction from 0° to 170° in 10° increments by polarization measurement using the single-reflection ATR method of Fourier transform infrared spectroscopy, and then calculate a value Y in each of the 18 directions by dividing the absorption peak intensity _Y765 at 765 cm ^-1 of the infrared absorption spectrum by the absorption peak intensity Y1181 at ₁₁₈₁ cm ^-1 , and the direction in which the maximum value _Ymax of all the Y values is obtained is defined as the _Ymax direction.

The battery of the present invention and its manufacturing method are described in detail below.

In this specification, numerical ranges indicated with "to" mean "greater than or equal to" or "less than or equal to." For example, the expression 2 to 15 mm means 2 mm or greater and 15 mm or less.

The battery 10 of the present invention comprises at least a battery element 4 having a positive electrode, a negative electrode, and an electrolyte, a packaging material 3 that seals the battery element 4, and metal terminals 2 that are electrically connected to the positive electrode and the negative electrode, respectively, and protrude outside the packaging material 3. In the battery 10 of the present invention, an adhesive film 1 for a metal terminal, which will be described later, is disposed between the metal terminal 2 and the packaging material 3. That is, the battery 10 of the present invention can be produced by a method that includes a step of disposing the adhesive film 1 for a metal terminal between the metal terminal 2 and the packaging material 3. In producing the battery of the present invention, an adhesive film 1 for a metal terminal is used that has an angle θ, as measured by the above-mentioned method, between the Y _max direction and the direction in which the metal terminal extends outside the packaging material of 45° or more and 135° or less.

Specifically, when a battery element 4, which includes at least a positive electrode, a negative electrode, and an electrolyte, is sealed with packaging material 3, adhesive film 1 for metal terminals is interposed between metal terminal 2 and heat-sealable resin layer 35 with metal terminal 2 protruding outward. At this time, adhesive film 1 for metal terminals is positioned between metal terminal 2 and packaging material 3 so that the angle θ is between 45° and 135°. Then, flange portions of packaging material 3 (regions where heat-sealable resin layers 35 contact each other, i.e., peripheral portion 3a of the packaging material) are formed around the periphery of battery element 4, and the heat-sealable resin layers 35 of the flange portions are heat-sealed together. Finally, the battery element 4 is sealed with packaging material 3, completing the battery production process.

Furthermore, in the battery 10 of the present invention, a metal terminal 5 with an adhesive film for a metal terminal, in which an adhesive film for a metal terminal 1 has been attached to a metal terminal 2 in advance, may be placed between upper and lower packaging materials 3. In the metal terminal 5 with an adhesive film for a metal terminal, the adhesive film for a metal terminal 1 is attached to the metal terminal 2 so that the angle θ between the direction x in which the metal terminal 2 extends outward from the battery when attached to the battery (the direction x corresponding to the direction in which the metal terminal extends outward from the packaging material) and the _Ymax direction is 45° or more and 135° or less (see FIG. 9 ). The present invention can also provide such a metal terminal with an adhesive film for a metal terminal.

The battery of the present invention may be either a primary battery or a secondary battery, but is preferably a secondary battery. There are no particular limitations on the type of secondary battery, and examples include lithium ion batteries, lithium ion polymer batteries, lead acid batteries, nickel-metal hydride batteries, nickel-cadmium batteries, nickel-iron batteries, nickel-zinc batteries, silver oxide-zinc batteries, metal-air batteries, polyvalent cation batteries, condensers, and capacitors. Among these secondary batteries, lithium ion batteries and lithium ion polymer batteries are preferred.

Adhesive Film for Metal Terminal The adhesive film for metal terminal used in the battery of the present invention will be described in detail below.

The adhesive film for metal terminals is disposed between a metal terminal electrically connected to an electrode of a battery element and the packaging material that seals the battery element. Specifically, as shown in Figures 1 to 3, adhesive film for metal terminals 1 is disposed between a metal terminal 2 electrically connected to an electrode of a battery element 4 and packaging material 3 that seals the battery element 4. The metal terminal 2 protrudes outside the packaging material 3 and is sandwiched between the packaging material 3 at the peripheral edge 3a of the heat-sealed packaging material 3 via adhesive film for metal terminals 1. In the present invention, the heating temperature when heat-sealing the packaging material is typically in the range of approximately 160 to 190°C, and the pressure is typically in the range of approximately 1.0 to 2.0 MPa.

The adhesive film 1 for metal terminals is provided to improve the adhesion between the metal terminal 2 and the packaging material 3. By improving the adhesion between the metal terminal 2 and the packaging material 3, the sealing of the battery element 4 is improved. As described above, when the battery element 4 is heat-sealed, the battery element is sealed so that the metal terminal 2 electrically connected to the electrode of the battery element 4 protrudes outside the packaging material 3. Because the metal terminal 2, which is made of metal, and the heat-sealable resin layer 35 (a layer made of a heat-sealable resin such as polyolefin), which is the innermost layer of the packaging material 3, are made of different materials, the absence of such an adhesive film would likely result in poor sealing of the battery element at the interface between the metal terminal 2 and the heat-sealable resin layer 35.

In the present invention, the adhesive film 1 for metal terminals comprises, in order, a first polyolefin layer 12a, a base film 11, and a second polyolefin layer 12b, with at least one of the first polyolefin layer 12a and the second polyolefin layer 12b being formed from an acid-modified polyolefin. The first polyolefin layer 12a and the second polyolefin layer 12b are located on both surfaces of the adhesive film 1 for metal terminals. When the adhesive film 1 for metal terminals is placed between the metal terminal 2 and the packaging material 3 of the battery 10 of the present invention, the surface of the metal terminal 2, which is made of metal, and the heat-sealable resin layer 35 (a layer formed from a heat-sealable resin such as polyolefin) of the packaging material 3 are adhered via the adhesive film 1 for metal terminals.

As described below, in the battery of the present invention, as shown in the schematic diagram of FIG. 7 , the heat-sealable resin layer 35 of the packaging material 3 is heat-sealed with the adhesive film 1 for metal terminals 1 disposed between the metal terminals 2 and the packaging material 3 such that the angle θ between the Y _max direction, which is the maximum in-plane orientation direction of naphthalene rings contained in the base film 11 of the adhesive film for metal terminals 1, and the direction x in which the metal terminals 2 extend outward from the packaging material 3 is 45° or more and 135° or less. This effectively prevents opening of the heat-sealed portion of the periphery of the battery where the adhesive film for metal terminals is located, even if the internal pressure of the battery increases. That is, because the angle θ is 45° or more and 135° or less, the Y _max direction, which is the maximum in-plane orientation direction of naphthalene rings contained in the base film 11, is nearly perpendicular to the direction x in which the metal terminals 2 extend outward from the packaging material 3. This orientation of the naphthalene rings enhances the strength of the base film 11 in the direction x. Therefore, even if the internal pressure of the battery increases and a strong force is applied from inside the battery in the direction x, the base film 11 is less likely to undergo cohesive failure, and it is possible to effectively prevent the opening of the heat-sealed portion around the periphery of the battery.

[Base film 11]
In the adhesive film 1 for a metal terminal, the base film 11 is a layer that functions as a support for the adhesive film 1 for a metal terminal.

The base film 11 contains polyethylene naphthalate (PEN). As disclosed in Patent Document 2, for example, PEN has a higher melting point and glass transition point than polyethylene terephthalate (PET), polyolefin, acid-modified polyolefin, etc., and has excellent mechanical strength at high temperatures. For this reason, even when the adhesive film 1 for metal terminals is sandwiched between the metal terminal 2 and the packaging material 3 and heat-sealed, the PEN film is less likely to become thin. Furthermore, PEN has a lower water vapor permeability than PET, providing excellent water vapor barrier properties.

As long as the base film 11 contains polyethylene naphthalate (PEN), it may also contain other resins. Examples of other resins include polyesters other than PEN, epoxy resins, acrylic resins, fluororesins, silicone resins, phenolic resins, polyetherimide resins, polyimide resins, polycarbonates, and mixtures or copolymers of these.

Specific examples of polyester resins other than PEN include polyethylene terephthalate, polybutylene terephthalate, polybutylene naphthalate, polyethylene isophthalate, copolymer polyesters whose repeating units are primarily ethylene terephthalate, and copolymer polyesters whose repeating units are primarily butylene terephthalate. Specific examples of copolymer polyesters whose repeating units are primarily ethylene terephthalate include copolymer polyesters in which ethylene terephthalate is the main repeating unit and is polymerized with ethylene isophthalate (hereinafter abbreviated as polyethylene (terephthalate/isophthalate)), polyethylene (terephthalate/isophthalate), polyethylene (terephthalate/adipate), polyethylene (terephthalate/sodium sulfoisophthalate), polyethylene (terephthalate/sodium isophthalate), polyethylene (terephthalate/phenyl-dicarboxylate), and polyethylene (terephthalate/decanedicarboxylate). Specific examples of copolymer polyesters containing butylene terephthalate as the main repeating unit include copolymer polyesters in which butylene terephthalate is the main repeating unit and is polymerized with butylene isophthalate (hereinafter abbreviated as polybutylene (terephthalate/isophthalate)), polybutylene (terephthalate/adipate), polybutylene (terephthalate/sebacate), polybutylene (terephthalate/decanedicarboxylate), and polybutylene naphthalate. The polyesters other than PEN may be used alone or in combination of two or more.

In the present invention, from the viewpoint of providing excellent sealing properties (water vapor barrier properties) between the packaging material and the metal terminal, it is preferable that the base film 11 be made of a polyethylene naphthalate (PEN) film.

The base film 11 is uniaxially or biaxially stretched. Biaxially stretched base film 11 has improved heat resistance due to oriented crystallization, making it suitable for use as the base film 11.

Furthermore, in the battery of the present invention, the Y _max direction, which is the maximum in-plane orientation direction of the naphthalene rings contained in the base film 11 of the adhesive film for metal terminal 1, and the Y max direction, which is the maximum in-plane orientation direction of the naphthalene rings contained in the base film 11 of the adhesive film for metal terminal 1, are aligned with each other.
The adhesive film 1 for a metal terminal is arranged so that the angle θ between the direction x in which the adhesive film 1 for a metal terminal extends outward is 45° or more and 135° or less, and the strength of the base film 11 of the adhesive film 1 for a metal terminal in the direction x is increased against the force applied when the internal pressure of the battery increases. Therefore, even when the internal pressure of the battery increases and a strong force is applied from inside the battery in the direction x, the base film 11 is less likely to undergo cohesive failure, making it possible to suitably prevent the packaging material from being opened. The measurement method for the _{Y max} direction is as follows.

<Measurement of maximum in-plane orientation direction of naphthalene rings (Y _max direction)>
Using polarization measurement by single-reflection ATR in Fourier transform infrared spectroscopy (FT-IR), infrared absorption spectra are obtained for the surface of the substrate film in 18 directions perpendicular to the thickness direction, from 0° (an arbitrary reference direction perpendicular to the thickness direction) to 170° in 10° increments. Here, the surface of the substrate film is the surface on which either the first polyolefin layer or the second polyolefin layer is laminated. Next, for each of the 18 directions, the absorption peak intensity Y ₇₆₅ at 765 cm ⁻¹ of the infrared absorption spectrum is divided by the absorption peak intensity Y ₁₁₈₁ at 1181 cm ⁻¹ to calculate a value Y . Next, the direction in which the maximum value Y _max of the obtained values Y (18 values) is obtained is designated as the Y _max direction. The following conditions can be used, for example, to measure the infrared absorption spectrum. When measuring the maximum in-plane orientation direction ( _Ymax direction) of the naphthalene rings on the surface of the substrate film of an adhesive film for metal terminals obtained from a battery, first, the peripheral heat-sealed portion interposing the metal terminal is cut off, the battery packaging material is removed, and the adhesive film for metal terminals is separated from the battery. Next, the first polyolefin layer or the second polyolefin layer is peeled off, and the measurement can be performed in the state where the substrate film is exposed. Furthermore, when measuring the maximum in-plane orientation direction ( _Ymax direction) of the naphthalene rings on the surface of the substrate film of an adhesive film for metal terminals obtained from a film heat-sealed to a metal terminal, the adhesive film for metal terminals is physically separated from the metal terminal, and the first polyolefin layer or the second polyolefin layer is peeled off, and the measurement can be performed in the state where the substrate film is exposed. When peeling off the first polyolefin layer or the second polyolefin layer from the substrate film in the state of an adhesive film for metal terminals, for example, the first polyolefin or the second polyolefin can be dissolved using a solvent such as heated xylene to expose the substrate film. The degree of surface orientation of the substrate film is an index showing the stretched state of the substrate film, and therefore the measured value will not change whether it is measured after obtaining the substrate film or after the first polyolefin layer or the second polyolefin layer is peeled off and removed from the adhesive film for metal terminal obtained from a battery to expose the substrate film. The degree of surface orientation of the substrate film may be measured after obtaining the substrate film.

(Measurement conditions for infrared absorption spectrum)
Spectrometer: IS10 manufactured by Thermo
Attachment: Single reflection ATR attachment (Seagull)
Detector: MCT (Hg Cd Te)
Resolution: 8cm ^-1
IRE: Ge
Incident angle: 30°
Polarizer: wire grid, S-polarized light Baseline: average value of intensity in the range from 1800 cm ⁻¹ to 2000 cm ⁻¹ Absorption peak intensity Y ₇₆₅ : value obtained by subtracting the baseline value from the maximum peak intensity in the range from 760 ^{cm −1} to 770 cm −1 Absorption peak intensity Y ₁₁₈₁ : value obtained by subtracting the baseline value from the maximum peak intensity in the range from 1176 cm ⁻¹ to 1186 cm ⁻¹

In the battery of the present invention, the angle θ between the Y _max direction, which is the maximum in-plane orientation direction of naphthalene rings contained in the base film 11 of the adhesive film for metal terminal 1, and the direction x in which the metal terminal 2 extends outward from the packaging material 3 is 45° or more and 135° or less, thereby suitably preventing opening of the packaging material in the portion where the adhesive film is located, even when the internal pressure of the battery increases. The mechanism behind this can be considered as follows: That is, as described above, when the internal pressure of the packaging material for the battery increases, a large force is applied from the inside to the outside of the battery. At this time, there is a risk that the packaging material will open in the portion where the adhesive film for metal terminal is located between the metal terminal and the packaging material. Further investigation into this point revealed that, when the base film of the adhesive film for metal terminal contains polyethylene naphthalate, when force is applied in the direction x in which the metal terminal 2 extends outward from the packaging material 3, the base film of the adhesive film for metal terminal is likely to peel off in layers, causing the base film of the adhesive film for metal terminal to break and resulting in opening of the battery. This is thought to be because the naphthalene rings contained in the base film are oriented in the stretching direction (i.e., perpendicular to the thickness direction) due to the stretching during the production of the base film, resulting in directions of high strength and directions of low strength in the base film, and when the direction of low strength of the base film approaches the direction x, the base film becomes more likely to peel off in layers.

Further investigations by the present inventors have confirmed that, when an adhesive film for a metal terminal is disposed between the metal terminal and the packaging material, by using a base film in which the angle θ is 45° or more and 135° or less, the Y _max direction, which is the maximum in-plane orientation direction of naphthalene rings, and the x direction in which the metal terminal 2 extends outward from the packaging material 3 become nearly perpendicular, thereby effectively preventing the base film from being destroyed in the x direction. Here, the absorption peak intensity Y ₇₆₅ at 765 cm ⁻¹ in the infrared absorption spectrum is due to the out-of-plane vibration of the group CH, and the absorption peak intensity Y ₁₁₈₁ at 1181 cm ⁻¹ in the infrared absorption spectrum is due to the vibration of the naphthalene ring.

From the viewpoint of more effectively preventing opening of the packaging material at the portion where the adhesive film is located, in the battery of the present invention, the lower limit of the angle θ between the Y _max direction and the direction x is preferably about 50° or more, and the upper limit is preferably about 130° or less, more preferably about 120° or less, and even more preferably about 90° or less. Preferred ranges of the angle θ between the Y _max direction and the direction x include about 50 to 130°, about 50 to 120°, about 50 to 90°, about 60 to 130°, about 60 to 120°, and about 60 to 90°. The direction x in which the metal terminal extends outward from the packaging material is usually the length direction of the metal terminal.

If necessary, the surface of the base film 11 may be subjected to known adhesion-enhancing treatments such as corona discharge treatment, ozone treatment, and plasma treatment.

The thickness of the base film 11 is not particularly limited, but is preferably approximately 10 to 50 μm, more preferably approximately 10 to 30 μm, from the standpoint of preventing short circuits while providing excellent sealing between the packaging material and the metal terminal.

[First and second polyolefin layers 12a, 12b]
In the adhesive film for metal terminals 1, at least one of the first and second polyolefin layers 12a, 12b is formed from an acid-modified polyolefin. That is, in the present invention, one of the first and second polyolefin layers 12a, 12b may be formed from an acid-modified polyolefin and the other from a polyolefin, or both the first and second polyolefin layers 12a, 12b may be formed from an acid-modified polyolefin. Acid-modified polyolefins have a high affinity with metals and heat-sealable resins such as polyolefins. Furthermore, polyolefins have a high affinity with heat-sealable resins such as polyolefins. Therefore, by disposing the layer formed from the acid-modified polyolefin on the metal terminal 2 side, excellent adhesion can be achieved at the interface between the adhesive film for metal terminals 1 and the metal terminal 2 and the heat-sealable resin layer 35.

The adhesive film 1 for metal terminals may be a laminate having a first polyolefin layer 12a, a base film 11, and a second polyolefin layer 12b in that order. For example, as shown in Figure 4, it has a laminate structure in which the first polyolefin layer 12a, base film 11, and second polyolefin layer 12b are laminated in that order.

In the first and second polyolefin layers 12a and 12b, the acid-modified polyolefin is not particularly limited as long as it is an acid-modified polyolefin, but preferred examples include polyolefins graft-modified with an unsaturated carboxylic acid or its anhydride.

Specific examples of acid-modified polyolefins include polyethylenes such as low-density polyethylene, medium-density polyethylene, high-density polyethylene, and linear low-density polyethylene; crystalline or amorphous polypropylenes such as homopolypropylene, polypropylene block copolymers (e.g., propylene and ethylene block copolymers), and polypropylene random copolymers (e.g., propylene and ethylene random copolymers); and ethylene-butene-propylene terpolymers. Of these polyolefins, polyethylene and polypropylene are preferred.

The acid-modified polyolefin may also be a cyclic polyolefin. For example, a carboxylic acid-modified cyclic polyolefin is a polymer obtained by copolymerizing a cyclic polyolefin by replacing some of the monomers constituting the cyclic polyolefin with an α,β-unsaturated carboxylic acid or its anhydride, or by block polymerizing or graft polymerizing a cyclic polyolefin with an α,β-unsaturated carboxylic acid or its anhydride.

The acid-modified cyclic polyolefin is a copolymer of an olefin and a cyclic monomer. Examples of the olefin that constitutes the cyclic polyolefin include ethylene, propylene, 4-methyl-1-pentene, butadiene, and isoprene. Examples of the cyclic monomer that constitutes the cyclic polyolefin include cyclic alkenes such as norbornene; specifically, cyclic dienes such as cyclopentadiene, dicyclopentadiene, cyclohexadiene, and norbornadiene. Among these polyolefins, cyclic alkenes are preferred, and norbornene is even more preferred. Another example of a constituent monomer is styrene.

Examples of carboxylic acids or anhydrides thereof used for acid modification include maleic acid, acrylic acid, itaconic acid, crotonic acid, maleic anhydride, and itaconic anhydride.

When either the first or second polyolefin layer 12a, 12b is formed from a polyolefin, examples of the polyolefin include the same polyolefins as those exemplified above as acid-modified polyolefins or acid-modified cyclic polyolefins.

The first and second polyolefin layers 12a, 12b may each be formed from a single resin component, or from a blend polymer of two or more resin components. Furthermore, the first and second polyolefin layers 12a, 12b may each be formed from a single layer, or from two or more layers of the same or different resin components.

Furthermore, the first and second polyolefin layers 12a and 12b may each contain a filler, if necessary. By including a filler in the first and second polyolefin layers 12a and 12b, the filler functions as a spacer, effectively preventing short circuits between the metal terminal 2 and the barrier layer 33 of the packaging material 3. The particle size of the filler is approximately 0.1 to 35 μm, preferably approximately 5.0 to 30 μm, and more preferably approximately 10 to 25 μm. The filler content is approximately 5 to 30 parts by weight, preferably approximately 10 to 20 parts by weight, per 100 parts by weight of the resin components forming the first and second polyolefin layers 12a and 12b, respectively.

Both inorganic and organic fillers can be used. Examples of inorganic fillers include carbon (carbon, graphite), silica, aluminum oxide, barium titanate, iron oxide, silicon carbide, zirconium oxide, zirconium silicate, magnesium oxide, titanium oxide, calcium aluminate, calcium hydroxide, aluminum hydroxide, magnesium hydroxide, and calcium carbonate. Examples of organic fillers include fluororesin, phenolic resin, urea resin, epoxy resin, acrylic resin, benzoguanamine-formaldehyde condensate, melamine-formaldehyde condensate, cross-linked polymethyl methacrylate, and cross-linked polyethylene. From the standpoints of shape stability, rigidity, and content resistance, aluminum oxide, silica, fluororesin, acrylic resin, and benzoguanamine-formaldehyde condensate are preferred, with spherical aluminum oxide and silica being particularly preferred. Methods for mixing the filler into the resin component that forms the polyolefin layer 12 include melt-blending the two in advance using a Banbury mixer or the like to create a masterbatch and then mixing it in a predetermined ratio, or directly mixing it with the resin component.

The first and second polyolefin layers 12a and 12b may each contain a pigment, if necessary. Various inorganic pigments can be used as the pigment. A specific example of a pigment is carbon (carbon, graphite), which was exemplified above as a filler. Carbon (carbon, graphite) is a material commonly used inside batteries and is unlikely to leach into the electrolyte. Furthermore, it provides a significant coloring effect, and sufficient coloring can be achieved with an amount that does not impair adhesion. It also does not melt due to heat, and can increase the apparent melt viscosity of the added resin. Furthermore, it prevents the pressurized portion from becoming thin during thermal bonding (heat sealing), providing excellent sealing between the packaging material and the metal terminal.

When adding a pigment to the first and second polyolefin layers 12a and 12b, the amount of pigment added is, for example, approximately 0.05 to 0.3 parts by mass, preferably approximately 0.1 to 0.2 parts by mass, per 100 parts by mass of the resin components forming the first and second polyolefin layers 12a and 12b when carbon black with a particle size of approximately 0.03 μm is used. Adding a pigment to the first and second polyolefin layers 12a and 12b makes it possible to detect the presence or absence of the adhesive film 1 for metal terminals using a sensor or to visually inspect the film. When adding a filler and a pigment to the first and second polyolefin layers 12a and 12b, the filler and pigment may be added to the same first and second polyolefin layers 12a and 12b. However, to avoid impairing the thermal adhesiveness of the adhesive film 1 for metal terminals, it is preferable to add the filler and pigment separately to the first and second polyolefin layers 12a and 12b.

The first and second polyolefin layers 12a, 12b can each be composed of a resin film. When the first and second polyolefin layers 12a, 12b are composed of a resin film, an adhesive film for metal terminals can be suitably produced by laminating a resin film formed from the above-mentioned polyolefin or acid-modified polyolefin onto the base film 11 using, for example, a dry lamination method. Alternatively, an adhesive film for metal terminals can be suitably produced by extruding the resin that constitutes the first and second polyolefin layers 12a, 12b onto the base film 11.

When the first and second polyolefin layers 12a, 12b, each made of a resin film, are laminated onto the surface of the base film 11, the surfaces of the first and second polyolefin layers 12a, 12b facing the base film 11 may be subjected to a known adhesion-enhancing treatment, such as corona discharge treatment, ozone treatment, or plasma treatment, as necessary. In particular, corona discharge treatment enhances adhesion between the base film 11 and the first and second polyolefin layers 12a, 12b, providing excellent sealing between the packaging material and the metal terminal.

The thickness of the first and second polyolefin layers 12a, 12b can be selected appropriately depending on the layer structure of the adhesive film for metal terminals 1. Taking into consideration the filling of resin and pinholes after heat sealing, the lower limit is preferably approximately 5 μm or more, more preferably approximately 20 μm or more, and the upper limit is preferably approximately 80 μm or less, more preferably approximately 50 μm or less. Furthermore, the thickness ranges of the first and second polyolefin layers 12a, 12b are preferably approximately 5 to 80 μm, approximately 5 to 50 μm, approximately 20 to 80 μm, and approximately 20 to 50 μm, respectively.

[Adhesion promoter layer]
The adhesion promoter layer (not shown) is a layer that is provided as needed for the purpose of firmly adhering the base film 11 to the first and second polyolefin layers 12 a, 12 b. The adhesion promoter layer may be provided on only one side between the base film 11 and the first and second polyolefin layers 12 a, 12 b, or on both sides.

The adhesion promoter layer can be formed using known adhesion promoters, such as isocyanate-based, polyethyleneimine-based, polyester-based, polyurethane-based, and polybutadiene-based. From the perspective of further improving electrolyte resistance, it is preferable to form the layer using an isocyanate-based adhesion promoter. Isocyanate-based adhesion promoters containing an isocyanate component selected from triisocyanate monomer and polymeric MDI provide excellent laminate strength and minimize loss of laminate strength after immersion in electrolyte. It is particularly preferable to form the adhesive using an adhesion promoter made from the triisocyanate monomer triphenylmethane-4,4',4"-triisocyanate or the polymeric MDI polymethylene polyphenyl polyisocyanate (NCO content approximately 30%, viscosity 200-700 mPa·s). It is also preferable to form the adhesive using the triisocyanate monomer tris(p-isocyanatephenyl)thiophosphate or a two-component curing adhesion promoter that uses a polyethyleneimine-based compound as the main component and polycarbodiimide as the crosslinking agent.

The adhesion promoter layer can be formed by coating and drying using known coating methods such as bar coating, roll coating, and gravure coating. The coating amount of the adhesion promoter is approximately 20 to 100 mg/ ^m² , preferably approximately 40 to 60 mg/ ^m² , for adhesion promoters made from triisocyanate; approximately 40 to 150 mg/ ^m² , preferably approximately 60 to 100 mg/ ^m² , for adhesion promoters made from polymeric MDI; and approximately 5 to 50 mg/ ^m² , preferably approximately 10 to 30 mg/m², for ^two -component curing adhesion promoters that contain polyethyleneimine as the base component and polycarbodiimide as the crosslinking agent. The triisocyanate monomer is a monomer having three isocyanate groups per molecule, and the polymeric MDI is a mixture of MDI and MDI oligomers formed by polymerization of MDI, as shown in the following formula:

The adhesive film 1 for metal terminals can be manufactured by laminating first and second polyolefin layers 12a, 12b, respectively, on both surfaces of the base film 11. The base film 11 and the first and second polyolefin layers 12a, 12b can be laminated using known methods such as extrusion lamination or thermal lamination. Furthermore, when laminating the base film 11 and the first and second polyolefin layers 12a, 12b via an adhesion promoter layer, for example, the adhesion promoter that constitutes the adhesion promoter layer can be applied and dried on the base film 11 using the method described above, and the first and second polyolefin layers 12a, 12b can then be laminated on top of the adhesion promoter layer.

The thickness (total thickness) of the adhesive film 1 for metal terminals is not particularly limited, but the lower limit is preferably at least about 20 μm, more preferably at least about 50 μm, and the upper limit is preferably no more than about 200 μm, more preferably no more than about 150 μm. Furthermore, the thickness range is preferably about 20 to 200 μm, about 20 to 150 μm, about 50 to 200 μm, or about 50 to 150 μm.

There are no particular limitations on the method for interposing the adhesive film 1 for metal terminals between the metal terminal 2 and the packaging material 3. For example, as shown in Figures 1 to 3, the adhesive film 1 for metal terminals may be wrapped around the metal terminal 2 in the area where the metal terminal 2 is sandwiched between the packaging material 3. Furthermore, although not shown, the adhesive film 1 for metal terminals may be arranged on both sides of the metal terminal 2 so that it crosses the two metal terminals 2 in the area where the metal terminal 2 is sandwiched between the packaging material 3.

The adhesive film 1 for metal terminals of the present invention may also be in the form of a roll of adhesive film for metal terminals, interposed between metal terminals electrically connected to the positive and negative electrodes of a battery element including at least a positive electrode, a negative electrode, and an electrolyte, and a packaging material that seals the battery element. When in the form of a roll, the length of the adhesive film 1 for metal terminals in the roll-up direction is, for example, approximately 50 to 500 m.

[Metal terminal 2]
The metal terminal 2 (tab) is a conductive member electrically connected to an electrode (positive electrode or negative electrode) of the battery element 4, and is made of a metal material. The metal material constituting the metal terminal 2 is not particularly limited, and examples thereof include aluminum, nickel, and copper. For example, the metal terminal 2 connected to the positive electrode of a lithium ion battery is usually made of aluminum or the like. Furthermore, the metal terminal connected to the negative electrode of a lithium ion battery is usually made of copper, nickel, or the like.

The surface of the metal terminal 2 is preferably subjected to a chemical conversion treatment to enhance electrolyte resistance. For example, when the metal terminal 2 is made of aluminum, specific examples of chemical conversion treatment include known methods for forming an acid-resistant coating using phosphates, chromates, fluorides, triazine thiol compounds, etc. Among the methods for forming acid-resistant coatings, phosphate chromate treatment, which uses a three-component solution consisting of phenolic resin, chromium (III) fluoride compound, and phosphoric acid, is preferred.

The size of the metal terminal 2 may be set appropriately depending on the size of the battery being used, etc. The thickness of the metal terminal 2 is preferably about 50 to 1000 μm, more preferably about 70 to 800 μm. The length of the metal terminal 2 is preferably about 1 to 200 mm, more preferably about 3 to 150 mm. The width of the metal terminal 2 is preferably about 1 to 200 mm, more preferably about 3 to 150 mm.

[Packaging material 3]
The packaging material 3 may have a laminated structure including at least a base material layer 31, a barrier layer 33, and a heat-sealable resin layer 35 in this order. FIG. 5 shows an example of a cross-sectional structure of the packaging material 3, in which the base material layer 31, an optional adhesive layer 32, a barrier layer 33, an optional adhesive layer 34, and a heat-sealable resin layer 35 are laminated in this order. In the packaging material 3, the base material layer 31 is the outermost layer, and the heat-sealable resin layer 35 is the innermost layer. During battery assembly, the heat-sealable resin layers 35 located on the periphery of the battery element 4 are brought into contact with each other and heat-sealed to seal the battery element 4. While FIGS. 1 to 3 illustrate the battery 10 using an embossed-type packaging material 3 formed by embossing or the like, the packaging material 3 may also be an unformed pouch-type. Pouch-type packaging includes three-sided seal, four-sided seal, and pillow-type packaging, and any of these types may be used.

(Base material layer 31)
In the packaging material 3, the base layer 31 is a layer that functions as a base material for the packaging material and forms the outermost layer side.

The material from which the base layer 31 is formed is not particularly limited, as long as it is insulating. Examples of materials that can be used to form the base layer 31 include polyester, polyamide, epoxy, acrylic, fluororesin, polyurethane, silicone resin, phenol, polyetherimide, polyimide, and mixtures or copolymers thereof. Polyesters such as polyethylene terephthalate and polybutylene terephthalate have the advantage of being highly resistant to electrolyte and less susceptible to whitening due to adhesion of electrolyte, making them ideal for use as a material to form the base layer 31. Furthermore, polyamide film has excellent stretchability and can prevent whitening due to cracking of the resin in the base layer 31 during molding, making it ideal for use as a material to form the base layer 31.

The base layer 31 may be formed from a uniaxially or biaxially stretched resin film, or from an unstretched resin film. Among these, uniaxially or biaxially stretched resin films, especially biaxially stretched resin films, are preferably used as the base layer 31 because they have improved heat resistance due to oriented crystallization.

Among these, nylon and polyester are preferred as the resin film forming the base layer 31, and biaxially oriented nylon and biaxially oriented polyester are more preferred.

The base material layer 31 can also be made by laminating resin films made of different materials to improve pinhole resistance and insulation when used as a battery package. Specific examples include a multilayer structure in which polyester film and nylon film are laminated together, or a multilayer structure in which biaxially oriented polyester and biaxially oriented nylon are laminated together. When the base material layer 31 has a multilayer structure, the resin films may be bonded together using an adhesive, or they may be laminated directly without an adhesive. When bonding without an adhesive, examples include methods in which the films are bonded in a hot-melt state, such as co-extrusion, sand lamination, and thermal lamination.

The base layer 31 may also be made low-friction to improve formability. When making the base layer 31 low-friction, there are no particular restrictions on the coefficient of friction of its surface, but examples include a coefficient of friction of 1.0 or less. Methods for making the base layer 31 low-friction include matte treatment, forming a thin layer of slip agent, or a combination of these.

The thickness of the substrate layer 31 is, for example, approximately 10 to 50 μm, and preferably approximately 15 to 30 μm.

(Adhesive layer 32)
In the packaging material 3, the adhesive layer 32 is a layer that is disposed on the base material layer 31 as needed to impart adhesion to the base material layer 31. That is, the adhesive layer 32 is provided between the base material layer 31 and the barrier layer 33.

The adhesive layer 32 is formed from an adhesive capable of bonding the base layer 31 and the barrier layer 33. The adhesive used to form the adhesive layer 32 may be a two-component curing adhesive or a one-component curing adhesive. Furthermore, the adhesive mechanism used to form the adhesive layer 32 is not particularly limited, and may be any of a chemical reaction type, solvent evaporation type, thermal melting type, thermal pressure type, etc.

The resin components of the adhesive that can be used to form the adhesive layer 32 are preferably polyurethane-based two-component curing adhesives; polyamide, polyester, or blends of these with modified polyolefins, from the viewpoints of excellent ductility, durability and resistance to deformation under high humidity conditions, and resistance to thermal degradation during heat sealing, as well as effectively preventing a decrease in the laminate strength between the base layer 31 and the barrier layer 33 and preventing delamination.

The adhesive layer 32 may also be multi-layered with different adhesive components. When the adhesive layer 32 is multi-layered with different adhesive components, from the viewpoint of improving the laminate strength between the base material layer 31 and the barrier layer 33, it is preferable to select a resin with excellent adhesion to the base material layer 31 for the adhesive component disposed on the base material layer 31 side, and an adhesive component with excellent adhesion to the barrier layer 33 for the adhesive component disposed on the barrier layer 33 side. When the adhesive layer 32 is multi-layered with different adhesive components, specific examples of the adhesive component disposed on the barrier layer 33 side include acid-modified polyolefin, metal-modified polyolefin, a mixed resin of polyester and acid-modified polyolefin, and a resin containing copolymer polyester.

The thickness of the adhesive layer 32 is, for example, approximately 2 to 50 μm, and preferably approximately 3 to 25 μm.

(Barrier layer 33)
In the packaging material, the barrier layer 3 is a layer that not only improves the strength of the packaging material but also has the function of preventing water vapor, oxygen, light, and the like from penetrating into the battery. Specific examples of metals that constitute the barrier layer 3 include aluminum, stainless steel, and titanium, with aluminum being preferred. The barrier layer 3 can be formed, for example, from a metal foil, a metal vapor-deposited film, an inorganic oxide vapor-deposited film, a carbon-containing inorganic oxide vapor-deposited film, or a film provided with any of these vapor-deposited films. It is preferably formed from a metal foil, and more preferably from an aluminum foil. From the viewpoint of preventing the occurrence of wrinkles or pinholes in the barrier layer 3 during the production of the packaging material, it is more preferable that the barrier layer be formed from a soft aluminum foil such as annealed aluminum (JIS H4160:1994 A8021H-O, JIS H4160:1994 A8079H-O, JIS H4000:2014 A8021P-O, JIS H4000:2014 A8079P-O).

The thickness of the barrier layer 33 is preferably approximately 10 to 200 μm, and more preferably approximately 20 to 100 μm, from the viewpoint of making the packaging material thinner while also making it less susceptible to pinholes during molding.

It is also preferable that at least one surface, and preferably both surfaces, of the barrier layer 3 be chemically treated to stabilize adhesion and prevent dissolution and corrosion. Here, chemical treatment refers to a process that forms an acid-resistant coating on the surface of the barrier layer.

[Adhesive layer 34]
In the packaging material 3, the adhesive layer 34 is a layer that is provided as needed between the barrier layer 33 and the heat-sealable resin layer 35 in order to firmly bond the heat-sealable resin layer 35.

The adhesive layer 34 is formed from an adhesive capable of bonding the barrier layer 33 and the heat-sealable resin layer 35. The composition of the adhesive used to form the adhesive layer is not particularly limited, but examples include resin compositions containing acid-modified polyolefins. Examples of acid-modified polyolefins include the same ones exemplified for the first and second polyolefin layers 12a and 12b.

The thickness of the adhesive layer 34 is, for example, approximately 1 to 40 μm, preferably approximately 2 to 30 μm.

[Thermofusible resin layer 35]
In the packaging material 3, the heat-sealable resin layer 35 corresponds to the innermost layer, and is a layer that seals the battery element by heat-sealing the heat-sealable resin layers together when the battery is assembled.

The resin components used in the heat-sealable resin layer 35 are not particularly limited, as long as they are heat-sealable, but examples include polyolefins and cyclic polyolefins.

Specific examples of the polyolefin include polyethylenes such as low-density polyethylene, medium-density polyethylene, high-density polyethylene, and linear low-density polyethylene; crystalline or amorphous polypropylenes such as homopolypropylene, polypropylene block copolymers (e.g., propylene and ethylene block copolymers), and polypropylene random copolymers (e.g., propylene and ethylene random copolymers); and ethylene-butene-propylene terpolymers. Of these polyolefins, polyethylene and polypropylene are preferred.

The cyclic polyolefin is a copolymer of an olefin and a cyclic monomer. Examples of the olefin that constitutes the cyclic polyolefin include ethylene, propylene, 4-methyl-1-pentene, butadiene, and isoprene. Examples of the cyclic monomer that constitutes the cyclic polyolefin include cyclic alkenes such as norbornene; specifically, cyclic dienes such as cyclopentadiene, dicyclopentadiene, cyclohexadiene, and norbornadiene. Among these polyolefins, cyclic alkenes are preferred, and norbornene is even more preferred. Another example of a constituent monomer is styrene.

Among these resin components, preferred are crystalline or amorphous polyolefins, cyclic polyolefins, and blend polymers thereof; more preferred are polyethylene, polypropylene, ethylene-norbornene copolymers, and blend polymers of two or more of these.

The heat-sealable resin layer 35 may be formed from a single resin component, or from a blend polymer of two or more resin components. Furthermore, the heat-sealable resin layer 35 may be formed from only one layer, or may be formed from two or more layers of the same or different resin components.

The thickness of the heat-sealable resin layer 35 is not particularly limited, but may be approximately 2 to 2000 μm, preferably approximately 5 to 1000 μm, and more preferably approximately 10 to 500 μm.

The present invention will be explained in detail below using examples and comparative examples. However, the present invention is not limited to these examples.

<Measurement of maximum in-plane orientation direction of naphthalene rings (Y _max direction)>
The _Ymax direction, which is the maximum in-plane orientation direction of naphthalene rings contained in each substrate film (polyethylene naphthalate (PEN) film) used in the following Examples and Comparative Examples, was measured by the following method. First, infrared absorption spectra were obtained for the surface of the substrate film in 18 directions perpendicular to the thickness direction from 0° to 170° at 10° increments by polarization measurement using single-reflection ATR Fourier transform infrared spectroscopy. Here, this surface of the substrate film is the surface on which the acid-modified polyolefin layer is laminated. Next, for each of the 18 directions, the absorption peak intensity _Y765 at 765 cm ^-1 of the infrared absorption spectrum was divided by the absorption peak intensity _Y1181 at 1181 cm ^-1 to calculate the value Y. Next, the direction in which the maximum _Ymax of the obtained values Y (18 values) was obtained was determined as the _Ymax direction. The results are shown in Table 1. Specific measurement conditions for the infrared absorption spectrum are as follows.

(Measurement conditions for infrared absorption spectrum)
Spectrometer: IS10 manufactured by Thermo
Attachment: Single reflection ATR attachment (Seagull)
Detector: MCT (Hg Cd Te)
Resolution: 8cm ^-1
IRE: Ge
Incident angle: 30°
Polarizer: wire grid, S-polarized light Baseline: average value of intensity in the range from 1800 cm ⁻¹ to 2000 cm ⁻¹ Absorption peak intensity Y ₇₆₅ : value obtained by subtracting the baseline value from the maximum peak intensity in the range from 760 ^{cm −1} to 770 cm −1 Absorption peak intensity Y ₁₁₈₁ : value obtained by subtracting the baseline value from the maximum peak intensity in the range from 1176 cm ⁻¹ to 1186 cm ⁻¹

Examples 1-3 and Comparative Examples 1-2
<Preparation of adhesive film for metal terminals>
The substrate film used was a sequentially biaxially stretched PEN film (thickness 12 μm) that had been subjected to corona discharge treatment on both sides. An adhesion promoter of triphenylmethane-4,4',4"-triisocyanate was applied to one side of the PEN film by gravure printing at 50 mg/ ^m2 (solid content) and dried. Then, maleic acid-modified polypropylene (hereinafter referred to as PPa) containing 0.15 parts by weight of carbon black was extrusion-coated to a thickness of 30 μm using a T-die extruder. The adhesion promoter and PPa were then applied to the other side of the PEN film in the same manner. The film was then aged at 45°C for 72 hours to obtain an adhesive film for metal terminals (total thickness 72 μm) consisting of PPa layer/adhesion promoter layer/PEN film/adhesion promoter layer/PPA layer.

<Preparation of packaging materials>
A barrier layer made of aluminum foil (40 μm thick) previously treated on both sides with a chemical conversion treatment solution containing three components: phenolic resin, a trivalent chromium fluoride compound, and phosphoric acid (phosphoric acid chromate treatment) was laminated on one side of a biaxially oriented nylon film (25 μm thick) by dry lamination. Specifically, a polyester adhesive was applied to one side of the barrier layer by gravure printing and dried (dry mass 4.0 g/m ² ). The substrate layer was then bonded and aged. Next, an adhesive layer (22.5 μm thick) made of maleic anhydride-modified polypropylene and a heat-sealable resin layer (22.5 μm thick) made of random polypropylene were co-extruded on the other side of the barrier layer and heated to obtain a battery packaging material consisting of the substrate layer/adhesive layer/metal foil/adhesive layer/heat-sealable resin layer in this order.

<Preparation of test battery>
The resulting packaging material was cut into a size of 160 mm (MD: Machine Direction, longitudinal direction) x 90 mm (TD: Transverse Direction, transverse direction). This was cold-formed (single-stage, pull-in molding) to a molding depth of 3.0 mm at a pressure of 0.4 MPa using a rectangular molding die (female die, surface having a maximum height roughness (nominal Rz value) of 3.2 μm as specified in Table 2 of the comparative surface roughness standard specimens in Appendix 1 (Reference) of JIS B 0659-1:2002) and a corresponding molding die (male die, surface having a maximum height roughness (nominal Rz value) of 1.6 μm as specified in Table 2 of the comparative surface roughness standard specimens in Appendix 1 (Reference) of JIS B 0659-1:2002). The heat-sealable resin layer was placed on the male die, with a clearance of 0.5 mm between the male and female dies. The resulting molded cup position M is shown in FIG. 6. Next, the molded packaging material was folded in half in the MD at the fold (mid-direction P) so that the heat-sealable resin layer surfaces faced each other. A dummy cell (PET plate, 45 mm x 28 mm x 3 mm thick) was placed in the molding cup. Two adhesive films for metal terminals and two dummy metal terminals (0.1 mm thick, 5 mm wide, 30 mm long aluminum foil) were positioned as shown in Figure 7, and the two sides were heat-sealed along the molding cup, starting from the short side and then the long side. The two dummy metal terminals were positioned so that they would be removed from the short side. The heat-sealing conditions were 190°C, 3 seconds, and a pressure of 1.4 MPa using a 7 mm wide head. One side of the adhesive film for metal terminals was heat-sealed to the dummy metal terminals, and the other side was heat-sealed to the heat-sealable resin layer. After heat sealing the two sides, the battery was dried in a dry room for 24 hours, and then 0.5 g of water as a virtual electrolyte was sealed in the other side that was not heat-sealed in the dry room to form a case having an internal space (pressure 1 atm). Next, the peripheral portion was cut so that the width of the portion where the heat-sealable resin layers were heat-sealed was 3 mm, and test battery 13 was obtained.

<Packaging material opening test>
As shown in Figure 8(a), the test battery 13 obtained above was placed in the space between two stainless steel plates, and the fixing spacer 20 was adjusted so that the distance W between the two stainless steel plates was 7.0 mm. Next, in this state, the battery was placed in an oven capable of reducing pressure (AVO-310NS-D vacuum drying oven manufactured by AS ONE Corporation), the pressure inside the oven was set to 5000 Pa, and the temperature was raised to 120°C at a heating rate of 35°C/min (as shown in Figure 8(b) , the test battery 13 expanded), and the presence or absence of opening at the portion where the adhesive film for metal terminal was located was confirmed. The results are shown in Table 1.

In the batteries of Comparative Examples 1 and 2, visual inspection of the area where the packaging material had been opened confirmed that cohesive failure had occurred at the base film of the adhesive film for the metal terminal.

<Measurement of Lamination Strength Between PEN Film and PPa Layer of Adhesive Film for Metal Terminal>
The adhesive film for metal terminals obtained above was cut to a size of 100 mm (longitudinal) x 15 mm (transverse) to obtain samples. For the samples of Examples 1 to 3 and Comparative Examples 1 and 2, the adhesive film for metal terminals was cut so that the angle between the longitudinal direction of the sample and the Y _max direction of the adhesive film for metal terminals corresponded to the angle θ in Table 1. Next, in a room temperature environment (25°C), the PEN film and PPa layer of the adhesive film for metal terminals were each chucked (chuck distance 50 mm) and pulled in the 180° direction (longitudinal direction) at a rate of 50 mm/min using a tensile tester (Shimadzu Corporation AGS-1kNX), and the laminate strength (N/15m) between the PEN film and PPa layer of the adhesive film for metal terminals was measured. The results are shown in Table 1. Each laminate strength (N/15m) is the average value of 20 samples.

REFERENCE SIGNS LIST 1 Adhesive film for metal terminal 2 Metal terminal 3 Packaging material 3a Peripheral edge of packaging material 4 Battery element 5 Metal terminal with adhesive film for metal terminal 10 Battery 11 Base film 12a First polyolefin layer 12b Second polyolefin layer 13 Test battery 13a Edge 20 Fixing spacer 21 Stainless steel plate 31 Base layer 32 Adhesive layer 33 Barrier layer 34 Adhesive layer 35 Heat-sealable resin layer

Claims (12)

A battery comprising: a battery element including at least a positive electrode, a negative electrode, and an electrolyte; a packaging material for sealing the battery element; and metal terminals electrically connected to the positive electrode and the negative electrode, respectively, and extending outside the packaging material,
an adhesive film for a metal terminal is disposed between the metal terminal and the packaging material;
The adhesive film for a metal terminal includes a first polyolefin layer, a base film containing polyethylene naphthalate, and a second polyolefin layer in this order;
At least one of the first polyolefin layer and the second polyolefin layer contains an acid-modified polyolefin,
The acid-modified polyolefin is a polyolefin in which at least one of an ethylene-butene-propylene terpolymer and a polypropylene block copolymer is acid-modified,
A battery, wherein an angle θ formed between the Y _max direction and a direction in which the metal terminal extends outside the packaging material, as measured by the following method, is 45° or more and 135° or less.
The _Ymax direction is measured by obtaining infrared absorption spectra for the surface of the base film in 18 directions perpendicular to the thickness direction from 0° to 170° at 10° intervals by polarization measurement using a single-reflection ATR method of Fourier transform infrared spectroscopy, and then calculating a value Y in each of the 18 directions by dividing the absorption peak intensity _Y765 at 765 cm ^-1 of the infrared absorption spectrum by the absorption peak intensity _Y1181 at 1181 cm ^-1 . The direction in which the maximum value _Ymax of all the Y values is obtained is defined as the _Ymax direction. The battery described in claim 1, wherein the thickness of the substrate film of the adhesive film for metal terminals is 10 μm or more and 50 μm or less. The battery described in claim 1 or 2, wherein the first polyolefin layer and the second polyolefin layer of the adhesive film for metal terminals contain acid-modified polyolefin. The battery described in any one of claims 1 to 3, wherein the thickness of the first polyolefin layer and the second polyolefin layer of the adhesive film for metal terminals is 5 μm or more and 80 μm or less. The battery described in any one of claims 1 to 4, wherein the thickness of the adhesive film for metal terminals is 20 μm or more and 200 μm or less. The battery described in any one of claims 1 to 5, wherein the packaging material is composed of a laminate having at least a base layer, a barrier layer, and a heat-sealable resin layer in this order. 7. The battery according to claim 1, wherein the first polyolefin layer and the second polyolefin layer each have a thickness of 20 μm or more and 80 μm or less. 7. The battery according to claim 1, wherein the first polyolefin layer and the second polyolefin layer each have a thickness of 20 μm or more and 50 μm or less. The battery according to any one of claims 1 to 8 , wherein the thickness of the substrate film is 30 µm or more and 50 µm or less. A method for manufacturing a battery including: a battery element including at least a positive electrode, a negative electrode, and an electrolyte; a packaging material for sealing the battery element; and metal terminals electrically connected to the positive electrode and the negative electrode, respectively, and protruding outside the packaging material,
and disposing an adhesive film for metal terminals between the metal terminals and the packaging material,
The adhesive film for a metal terminal includes a first polyolefin layer, a base film containing polyethylene naphthalate, and a second polyolefin layer in this order,
At least one of the first polyolefin layer and the second polyolefin layer contains an acid-modified polyolefin,
The acid-modified polyolefin is a polyolefin in which at least one of an ethylene-butene-propylene terpolymer and a polypropylene block copolymer is acid-modified,
A method for manufacturing a battery using a packaging material in which an angle θ formed between a Y _max direction and a direction in which the metal terminal extends outward from the packaging material, as measured by the following method, is 45° or more and 135° or less.
The _Ymax direction is measured by obtaining infrared absorption spectra for the surface of the base film in 18 directions perpendicular to the thickness direction from 0° to 170° at 10° intervals by polarization measurement using a single-reflection ATR method of Fourier transform infrared spectroscopy, and then calculating a value Y in each of the 18 directions by dividing the absorption peak intensity _Y765 at 765 cm ^-1 of the infrared absorption spectrum by the absorption peak intensity _Y1181 at 1181 cm ^-1 . The direction in which the maximum value _Ymax of all the Y values is obtained is defined as the _Ymax direction. A metal terminal with an adhesive film for a metal terminal, in which an adhesive film for a metal terminal is attached to a metal terminal of a battery,
The adhesive film for a metal terminal includes a first polyolefin layer, a base film containing polyethylene naphthalate, and a second polyolefin layer in this order;
At least one of the first polyolefin layer and the second polyolefin layer contains an acid-modified polyolefin,
The acid-modified polyolefin is a polyolefin in which at least one of an ethylene-butene-propylene terpolymer and a polypropylene block copolymer is acid-modified,
A metal terminal with an adhesive film for a metal terminal, wherein the adhesive film for a metal terminal is attached to the metal terminal such that the angle θ formed between the direction in which the metal terminal extends outward from the battery when attached to the battery and the Y _max direction of the adhesive film for a metal terminal, as measured by the method described below, is 45° or more and 135° or less.
The _Ymax direction is measured by obtaining infrared absorption spectra for the surface of the base film in 18 directions perpendicular to the thickness direction from 0° to 170° at 10° intervals by polarization measurement using a single-reflection ATR method of Fourier transform infrared spectroscopy, and then calculating a value Y in each of the 18 directions by dividing the absorption peak intensity _Y765 at 765 cm ^-1 of the infrared absorption spectrum by the absorption peak intensity _Y1181 at 1181 cm ^-1 . The direction in which the maximum value _Ymax of all the Y values is obtained is defined as the _Ymax direction. A roll of an adhesive film for metal terminals is interposed between metal terminals electrically connected to a positive electrode and a negative electrode of a battery element including at least a positive electrode, a negative electrode, and an electrolyte, and a packaging material that seals the battery element ,
The adhesive film for a metal terminal includes a first polyolefin layer, a base film containing polyethylene naphthalate, and a second polyolefin layer in this order;
At least one of the first polyolefin layer and the second polyolefin layer contains an acid-modified polyolefin,
The acid-modified polyolefin is a polyolefin in which at least one of an ethylene-butene-propylene terpolymer and a polypropylene block copolymer is acid-modified,
A roll of adhesive film for metal terminal, wherein the angle θ formed by the Y _max direction and the direction perpendicular to the winding direction of the roll of adhesive film for metal terminal, as measured by the following method, is 45° or more and 135° or less.
The _Ymax direction is measured by obtaining infrared absorption spectra for the surface of the base film in 18 directions perpendicular to the thickness direction from 0° to 170° at 10° intervals by polarization measurement using a single-reflection ATR method of Fourier transform infrared spectroscopy, and then calculating a value Y in each of the 18 directions by dividing the absorption peak intensity _Y765 at 765 cm ^-1 of the infrared absorption spectrum by the absorption peak intensity _Y1181 at 1181 cm ^-1 . The direction in which the maximum value _Ymax of all the Y values is obtained is defined as the _Ymax direction.