Exterior material for power storage device, exterior case for power storage device, and power storage device

Abstract

This exterior material for a power storage device comprises a base material layer, a barrier layer, and a heat-fusible resin layer in the stated order, wherein the developed interfacial area ratio Sdr of the outer surface of the heat-fusible resin layer is 3% or more.

Description

Exterior material for power storage device, exterior case for power storage device, and power storage device 【0001】 The present disclosure relates to an exterior material for a power storage device, an exterior case for a power storage device, and a power storage device. 【0002】 Power storage devices are used as energy suppliers for mobile devices such as electric vehicles and hybrid vehicles, and for portable devices such as power tools and mobile terminals. Conventionally, metal cans have been mainly used as the casings of power storage devices. However, in order to facilitate movement and carrying, weight reduction and miniaturization of power storage devices are required. Therefore, an exterior material (also referred to as a laminate material) having a base material layer, a barrier layer, and a heat-sealable resin layer (also referred to as a sealant layer) in this order is often used as the casing of the power storage device. The above-mentioned exterior material is arranged such that the heat-sealable resin layers face each other, sandwiches the main body of the power storage device, and heat-seals the heat-sealable resin layers at the outer edge of the exterior material, thereby housing and enclosing the main body of the power storage device in the exterior member (see, for example, Patent Document 1). 【0003】 In recent years, with the high-speed and high-capacity data communication of smartphones, increasing the capacity of power storage devices has been studied. With the increase in the capacity of power storage devices, an increase in the container size and an increase in reactive substances are accompanied. When the power storage device is exposed to high temperatures, the amount of gas generated by the decomposition of the electrolytic solution also increases. 【0004】 Therefore, in Patent Document 1, an adhesive film is interposed between the heat-sealable resin layers. In this form, the power storage device is sealed until the power storage device reaches a high temperature. When the power storage device reaches a high temperature (for example, about 100°C to 125°C), the power storage device is opened at the position of the adhesive film between the heat-sealable resin layers, and the gas generated inside the power storage device can be released to the outside. 【0005】 Japanese Patent Application Laid-Open No. 2023-89020 【0006】Incidentally, when housing and sealing the main body of the energy storage device within the exterior component made of exterior material, first, the energy storage device elements such as electrodes and electrolyte are placed inside the exterior component and temporarily sealed to allow the electrodes to become accustomed to the electrolyte. At this time, some of the electrolyte decomposes and gas is generated, so after releasing the generated gas to the outside, the seal is performed again. This seal is performed with the electrolyte (impurities) adhering between the heat-fusible resin layers (see Figure 7). Hereafter, this seal will be referred to as an impurity seal. Due to the above method of sealing the main body of the energy storage device with the exterior component, it has been found that even if the exterior material itself has high electrical resistance and excellent insulating properties, the electrical resistance may decrease after the impurity seal. 【0007】 This disclosure aims to provide an exterior material for energy storage devices that exhibits excellent insulating properties even after sealing with impurities. Furthermore, this disclosure aims to provide an exterior case for energy storage devices and an energy storage device that utilizes this exterior material. 【0008】 This disclosure includes the following embodiments: <1> An exterior material for an energy storage device comprising a base layer, a barrier layer, and a heat-fusible resin layer in this order, wherein the interfacial development area ratio Sdr of the outer surface of the heat-fusible resin layer is 3% or more. <2> The exterior material for an energy storage device according to <1>, wherein the heat-fusible resin layer contains particles with an average particle diameter of 5 μm or more. <3> The exterior material for an energy storage device according to <2>, wherein the heat-fusible resin layer comprises a laminate layer portion, an intermediate layer portion, and a seal layer portion in order from the barrier layer side, wherein the seal layer portion contains the particles. <4> The exterior material for an energy storage device according to <3>, wherein the content of the particles in the seal layer portion is 2000 ppm by mass or more. <5> The exterior material for an energy storage device according to any one of <1> to <4>, which is applied to an energy storage device using at least one selected from the group consisting of ethylene carbonate and diethyl carbonate as the electrolyte. <6> An exterior case for an energy storage device, which is a molded body of the exterior material for an energy storage device described in any one of <1> to <5>. <7> An energy storage device comprising an energy storage device body and an exterior member including the exterior material for an energy storage device described in any one of <1> to <5>, wherein the energy storage device body is exteriorized by the exterior member. 【0009】 This disclosure provides an exterior material for energy storage devices that exhibits excellent insulating properties even after sealing with impurities. This disclosure also provides an exterior case for energy storage devices and an energy storage device that uses this exterior material. 【0010】 This is a schematic cross-sectional view showing an example of an exterior material for an energy storage device. This is a schematic cross-sectional view showing an example of an energy storage device. This is a schematic perspective view showing the components constituting the energy storage device in Figure 2 in a separated state. These are photographs (bottom) of the surface of the seal layer side of Comparative Examples 1 to 3 and Example 1 observed with a scanning electron microscope, and the results of a white light interferometer (top). These are photographs (bottom) of the surface of the seal layer side of Examples 2 to 4 observed with a scanning electron microscope, and the results of a white light interferometer (top). This is a diagram illustrating the method for preparing measurement samples for the insulation test after heat sealing, and the state of the insulation test after heat sealing. This is a diagram illustrating the method for preparing measurement samples for the insulation test after interlocking seal, and the state of the insulation test after heat sealing. 【0011】Embodiments of the present disclosure will be described in detail below. However, embodiments of the present disclosure are not limited to the embodiments described below. In the embodiments described below, the components (including elemental steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and do not limit embodiments of the present disclosure. Numerical ranges indicated using "~" in the present disclosure include the numerical values ​​before and after "~" as the minimum and maximum values, respectively. In numerical ranges described in stages in the present disclosure, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Also, in numerical ranges described in the present disclosure, the upper or lower limit of that numerical range may be replaced with the value shown in the example. In the present disclosure, each component may contain multiple types of the corresponding substance. If multiple types of the substance corresponding to each component are present in the composition, the content or amount of each component means the total content or amount of the multiple types of substances present in the composition unless otherwise specified. In the present disclosure, each component may contain multiple types of particles. If multiple types of particles corresponding to each component exist in a composition, the particle size of each component refers to the value for a mixture of such multiple types of particles present in the composition, unless otherwise specified. In this disclosure, the terms “layer” and “layer portion” include cases where the layer or “layer portion” is formed not only over the entire region when the region in which it exists is observed, but also where it is formed only in a part of the region. 【0012】 When embodiments in this disclosure are described with reference to the drawings, the configuration of such embodiments is not limited to the configuration shown in the drawings. Furthermore, the sizes of the components in each figure are conceptual, and the relative relationships between the components are not limited thereto. In this disclosure, the thickness of each layer and layer section can be measured by a scanning electron microscope (SEM). The thickness in this disclosure is the average value obtained when measured at five locations. 【0013】<Exterior Material for Energy Storage Devices> The exterior material for energy storage devices of this disclosure (hereinafter sometimes abbreviated as "exterior material") comprises a base layer, a barrier layer, and a heat-fusible resin layer in this order, wherein the interface area ratio Sdr of the outer surface of the heat-fusible resin layer is 3% or more. In this disclosure, the outer surface of the heat-fusible resin layer refers to the surface of the heat-fusible resin layer on the side opposite to the barrier layer. 【0014】 The exterior material having the above configuration exhibits excellent insulation properties even after interlocking seal. The reason for this is not clear, but it is presumed to be as follows: In interlocking seal, the electrolyte is trapped between the heat-fusible resin layers. Therefore, it is presumed that gas is generated from the electrolyte present between the heat-fusible resin layers after interlocking seal, damaging part of the exterior material and resulting in a decrease in insulation properties. In contrast, the exterior material of this disclosure has an interface area ratio Sdr of 3% or more on the outer surface of the heat-fusible resin layer and has an appropriate roughness. This makes it easier for the electrolyte present between the heat-fusible resin layers to escape and be removed. Therefore, it is presumed that damage to the exterior material caused by the presence of electrolyte between the heat-fusible resin layers after interlocking seal is suppressed, and as a result, excellent insulation properties are maintained even after interlocking seal. Note that the effective numerical range of the interface area ratio Sdr (i.e., 3% or more) was found experimentally. 【0015】 In this disclosure, the interface area ratio Sdr is defined in ISO 25178 and is an index that represents how much the developed area (surface area) of the target region increases relative to the area of ​​the target region. The Sdr of a perfectly flat surface is 0. The interface area ratio Sdr is measured using a scanning white-light interference microscope (for example, Hitachi High-Tech Corporation, model: VS1330). 【0016】 The Sdr of the outer surface of the heat-fusible resin layer is 3% or more, may be 4% or more, may be 5% or more, may be 6% or more, or may be 7% or more. The Sdr of the outer surface of the heat-fusible resin layer is not particularly limited, and from the viewpoint of heat fusibility, it may be 10% or less. 【0017】Figure 1 is a schematic cross-sectional view showing an example of an exterior material for an energy storage device. Referring to Figure 1, an example of the layer structure of the exterior material for an energy storage device will be explained. The exterior material 1 includes a base layer 2, a barrier layer 4, and a heat-sealable resin layer 3 in this order. 【0018】 In Figure 1, a base layer 2 is provided on one side of the barrier layer 4 via a first adhesive layer 5. A heat-fusible resin layer 3 is provided on the other side of the barrier layer 4. The heat-fusible resin layer 3 may be provided via a second adhesive layer (not shown), or it may be provided without the second adhesive layer. 【0019】 (Base layer) The base layer 2 is preferably made of a heat-resistant resin. A heat-resistant resin is a resin that does not melt at the heat-sealing temperature when heat-sealing the exterior material 1. The heat-resistant resin is preferably one that has a melting point 10°C or more higher than the melting point of the heat-fusible resin layer 3 (the melting point of the layer with the highest melting point among the multiple heat-fusible resin layers), and more preferably one that has a melting point 20°C or more higher than the melting point of the heat-fusible resin layer 3 (the melting point of the layer with the highest melting point among the multiple heat-fusible resin layers). 【0020】 Examples of heat-resistant resin layers include polyamide films such as nylon films and polyester films, and stretched films of these are preferably used. Among these, biaxially oriented polyamide films such as biaxially oriented nylon films, biaxially oriented polybutylene terephthalate (PBT) films, biaxially oriented polyethylene terephthalate (PET) films, or biaxially oriented polyethylene naphthalate (PEN) films are more preferred as heat-resistant resin layers. Examples of nylon films include nylon 6 films, nylon 6,6 films, and MXD nylon films. 【0021】 The base layer may be formed as a single layer or composed of two or more layers. An example of a base layer composed of two or more layers is a polyester film / polyamide film, specifically a PET film / nylon film. 【0022】The thickness of the base layer 2 is preferably 2 μm to 50 μm. When a polyester film is used as the base layer, the thickness is preferably 2 μm to 50 μm, and when a nylon film is used, the thickness is preferably 7 μm to 50 μm. Setting the thickness above the lower limit tends to maintain sufficient strength as an exterior material. Setting the thickness below the upper limit tends to reduce stress during molding such as stretch molding and deep drawing, and improve moldability. If the base layer 2 is multilayered, the total thickness shall be the thickness mentioned above. Also, if the base layer 2 is multilayered, the thickness of the adhesive used to bond the multiple layers is included in the thickness mentioned above. 【0023】 (Barrier Layer) The barrier layer 4 plays a role in providing gas barrier properties to the exterior material 1, preventing the intrusion of oxygen and moisture. The barrier layer 4 is not particularly limited and can be a metal foil, a vapor-deposited film, a resin layer, etc. Examples of vapor-deposited films include metal vapor-deposited films, inorganic oxide vapor-deposited films, and carbon-containing inorganic oxide vapor-deposited films. Examples of resins used in the resin layer include fluorine-containing resins and ethylene vinyl alcohol copolymers. Examples of fluorine-containing resins include polymers mainly composed of polyvinylidene chloride and chlorotrifluoroethylene (CTFE), polymers mainly composed of tetrafluoroethylene (TFE), polymers having fluoroalkyl groups, and polymers mainly composed of fluoroalkyl units. 【0024】 The barrier layer 4 may be a single layer or a multilayer of two or more layers. In the case of a multilayer, it may be a laminate of the same type of layer or a laminate of different types of layers. An example of a laminate of different types of layers is a combination of a vapor-deposited film and a resin layer. 【0025】 Among the above, it is preferable that the barrier layer 4 includes a layer made of a metallic material. Examples of metallic materials constituting the barrier layer 4 include aluminum alloy, stainless steel, copper, nickel, titanium steel, and steel sheet. When used as a metallic foil, it is preferable that it includes at least one of aluminum alloy foil and stainless steel foil. 【0026】The thickness of the barrier layer 4 can be set as appropriate, preferably between 5 μm and 120 μm, and more preferably between 10 μm and 80 μm. When the thickness of the barrier layer 4 is 5 μm or more, pinhole formation during rolling tends to be prevented when the barrier layer 4 is a metal foil. When the thickness of the barrier layer 4 is 120 μm or less, the stress during forming such as stretch forming and deep drawing can be reduced, and formability tends to improve. If the barrier layer 4 is multilayered, the total thickness shall be the thickness described above. Furthermore, if the barrier layer 4 is multilayered and an adhesive is used to bond the multiple layers together, the thickness of the adhesive shall also be included in the thickness described above. 【0027】 When using metal foil, from the viewpoint of preventing surface corrosion, the metal foil may be treated with a chemical conversion treatment, and it is preferable that at least the side facing the heat-fusible resin layer is treated with the chemical conversion treatment. The following methods can be used for the chemical treatment. For example, one method is to apply an aqueous solution of any of the following 1) to 3) to the surface of a degreased metal foil, and then dry it to perform the chemical conversion treatment. 1) An aqueous solution containing phosphoric acid, chromic acid, and at least one compound selected from the group consisting of metal salts of fluoride and nonmetallic salts of fluoride. 2) An aqueous solution containing phosphoric acid, at least one resin selected from the group consisting of acrylic resins, chitosan derivative resins, and phenolic resins, and at least one compound selected from the group consisting of chromic acid and chromium(III) salt. 3) An aqueous solution containing phosphoric acid, at least one resin selected from the group consisting of acrylic resins, chitosan derivative resins, and phenolic resins, at least one compound selected from the group consisting of chromic acid and chromium(III) salt, and at least one compound selected from the group consisting of metal salts of fluoride and nonmetallic salts of fluoride. 【0028】 The chemical conversion coating formed by the chemical conversion treatment has a chromium content of 0.1 mg / m² (per side). ２ ~50 mg / m² ２ Preferably, 2 mg / m² ２ ~20 mg / m² ２ It is preferable. 【0029】(Heat-fusible resin layer) The heat-fusible resin layer 3 plays a role in providing heat-sealability to the exterior material. The heat-fusible resin layer contains a heat-fusible resin. The heat-fusible resin is selected to have a melting point below the heat-fussing temperature so that it melts at the heat-fussing temperature. The heat-fusible resin is not particularly limited as long as it has the above melting point, but it is preferably at least one selected from the group consisting of polyethylene, polypropylene, olefin copolymers, acid-modified products thereof, and ionomers. "Polyethylene, polypropylene, olefin copolymers, acid-modified products thereof, and ionomers" is also called "specific polyolefins". 【0030】 The proportion of specific polyolefins in the resin contained in the heat-fusible resin layer 3 is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, particularly preferably 80% by mass or more, extremely preferably 90% by mass or more, and may also be 95% by mass or more, 98% by mass or more, or 99% by mass or more. 【0031】 The heat-fusible resin layer 3 may consist of one type of heat-fusible resin, or it may consist of two or more types of heat-fusible resins. 【0032】 In Figure 1, the heat-sealable resin layer 3 includes, in order from the barrier layer 4 side, a laminate layer portion 33, an intermediate layer portion 32, and a sealing layer portion 31. In Figure 1, the heat-sealable resin layer 3 is composed of three layers, but it may be composed of one layer, two layers, or four or more layers. The laminate layer portion 33, the intermediate layer portion 32, and the sealing layer portion 31 may each be composed of the same type of heat-sealable resin, or they may be composed of different heat-sealable resins. 【0033】 In Figure 1, since the seal layer 31 is provided on the outer surface side of the heat-fusible resin layer 3, the interface development area ratio Sdr of the outer surface of the seal layer 31 (i.e., the surface opposite to the intermediate layer 32) is 3% or more. 【0034】From the viewpoint of ensuring that the Sdr on the outer surface of the heat-fusible resin layer 3 is 3% or more, it is preferable that the heat-fusible resin layer 3 contains particles A (hereinafter also referred to as specific particles A) with an average particle diameter of 5 μm or more. The average particle diameter of specific particles A may be 7 μm or more, or 10 μm or more. Furthermore, from the viewpoint of heat fusibility, the average particle diameter of specific particles A is preferably 30 μm or less, more preferably 25 μm or less, and even more preferably 20 μm or less. 【0035】 The average particle size of specific particle A can also be measured by observing and measuring the cross-section of the heat-fusible resin layer 3 using a scanning electron microscope. Specifically, the heat-fusible resin layer 3 is embedded in transparent epoxy resin, polished with a polisher, slurry, etc., and the cross-section of the heat-fusible resin layer is observed and the particle size is measured. The average particle size is the arithmetic mean of the particle sizes of 50 specific particles A. 【0036】 When the heat-sealable resin layer 3 has a laminate layer portion 33, an intermediate layer portion 32, and a sealing layer portion 31, it is preferable that at least the sealing layer portion 31 contains specific particles A. 【0037】 The specified particle A is preferably a non-melting particle. In this disclosure, "non-melting particle" means a particle that does not melt at the typical heating temperature of 200°C for heat fusion. The specified particle A can be made of a material known as an antiblocking agent, and may be inorganic particles, organic particles, metal particles, composite particles thereof, etc. Antiblocking agents are added to improve the slipperiness of the surface of the heat-fusible resin layer, and their purpose and function differ from the specified particle A in this disclosure, and they have a smaller particle size than the specified particle A. 【0038】 From the viewpoint of suppressing thermal deformation during thermal melting, the specific particle A is preferably inorganic particles, metal particles, or composite particles thereof. From the viewpoint of further ensuring the insulating function of the heat-fusible resin layer 3 and reducing weight, it is also preferable that it be inorganic particles, organic particles, or composite particles thereof. From these overall viewpoints, it is more preferable that the specific particle A includes inorganic particles. The specific particle A may be used alone or in combination of two or more types. 【0039】 Examples of the inorganic particles include inorganic oxide particles (such as silica particles, alumina particles, titanium oxide particles, etc.), inorganic carbonate particles (such as calcium carbonate particles, barium carbonate particles, etc.), and inorganic silicate particles (such as aluminum silicate particles, talc particles, kaolin particles, etc.). 【0040】 Examples of the organic particles include acrylic resin particles, polyolefin resin particles (such as polyethylene resin particles, polypropylene resin particles, etc.), and polystyrene resin particles. 【0041】 Examples of the metal particles include aluminum particles, etc. 【0042】 The specific particle A may be contained only in the seal layer portion 31, may be contained in the seal layer portion 31 and the laminate layer portion 33, or may be contained in the seal layer portion 31, the intermediate layer portion 32, and the laminate layer portion 33. 【0043】 From the viewpoint of obtaining an exterior material with excellent insulation even after sandwiching and sealing, the content rate of the specific particle A in the seal layer portion 31 is preferably 2000 mass ppm or more, and may be 4000 mass ppm or more, 5000 mass ppm or more, 7000 mass ppm or more, 9000 mass ppm or more, 10000 mass ppm or more, 11000 mass ppm or more, or 12000 mass ppm or more. 【0044】 From the viewpoint of maintaining the laminating property and suppressing peeling between the barrier layer 4 and the heat-sealable resin layer 3, the content rate of the specific particle A in the seal layer portion 31 may be 20000 mass ppm or less. 【0045】 The laminate layer portion 33 may or may not contain the specific particle A. When the laminate layer portion 33 contains the specific particle A, from the viewpoint of adhesion to the barrier layer through the adhesive layer 5 of the laminate layer portion 33, it is preferable that the content rate of the specific particle A in the laminate layer portion 33 is less than that in the seal layer portion 31. The content rate of the specific particle A in the laminate layer portion 33 may be 5000 mass ppm or less. 【0046】The intermediate layer 32 may or may not contain specific particles A. From the viewpoint of improving electrical insulation and impact resistance by the intermediate layer 32, it is preferable that the intermediate layer 32 does not contain specific particles A. The content of specific particles A in the intermediate layer 32 may be 1000 ppm by mass or less. If the intermediate layer 32 contains specific particles A, the content of specific particles A in the intermediate layer 32 may be 1000 ppm by mass or more, 1500 ppm by mass or more, 2000 ppm by mass or more, 3000 ppm by mass or more, or 4000 ppm by mass or more. 【0047】 The content of specific particles A in the entire heat-fusible resin layer 3 is preferably 500 ppm by mass or more, may be 600 ppm by mass or more, may be 1000 ppm by mass or more, may be 1500 ppm by mass or more, or may be 2000 ppm by mass or more. 【0048】 Furthermore, the content of specific particles A in the entire heat-fusible resin layer 3 may be 3000 ppm by mass or less. 【0049】 The content of specific particles A in the sealing layer 31, the intermediate layer 32, and the laminate layer 33 is calculated from the composition used to form the sealing layer 31, the intermediate layer 32, and the laminate layer 33, respectively. 【0050】 The heat-sealable resin layer 3 may contain other particles B that are smaller than specific particle A. The material of the other particles B is the same as the material of specific particle A. Other particles B may be those known as antiblocking agents. Other particles B may be used alone or in combination of two or more types. 【0051】 The average particle diameter of the other particles B is preferably 4 μm or less, more preferably 3 μm or less, and even more preferably 2 μm or less, from the viewpoint of ensuring sealing performance. The lower limit of the average particle diameter of the other particles B is not particularly limited and may be 0.1 μm or more, or 0.2 μm or more. The average particle diameter of the other particles B can be measured in the same way as the average particle diameter of the specific particle A. 【0052】Other particles B may be contained in any of the seal layer 31, the intermediate layer 32, and the laminate layer 33. Other particles B may be contained in one layer of the heat-sealable resin layer 3, or in two or more layers. For example, other particles B may be contained only in the seal layer 31, only in the intermediate layer 32, only in the laminate layer 33, or, as shown in Figure 1, in both the seal layer 31 and the laminate layer 33. 【0053】 If the seal layer 31 contains other particles B, from the viewpoint of maintaining airtightness (sealing ability), the content of other particles B in the seal layer 31 is preferably 10,000 ppm by mass or less, more preferably 5,000 ppm by mass or less, even more preferably 3,000 ppm by mass or less, and may not contain particles B at all. If the intermediate layer 32 contains other particles B, the content of other particles B in the intermediate layer 32 is preferably 10,000 ppm by mass or less, more preferably 5,000 ppm by mass or less, even more preferably 3,000 ppm by mass or less, and may not contain particles B at all. If the laminate layer 33 contains other particles B, the content of other particles B in the laminate layer 33 is preferably 10,000 ppm by mass or less, more preferably 5,000 ppm by mass or less, even more preferably 3,000 ppm by mass or less, and may not contain particles B at all. 【0054】 The total thickness of the heat-fusible resin layer 3 is preferably 20 μm or more, and more preferably 25 μm or more, from the viewpoint of ensuring insulation. Furthermore, from the viewpoint of weight reduction and thinning, the thickness of the heat-fusible resin layer 3 is preferably 100 μm or less, and may be 80 μm or less, or 50 μm or less. 【0055】From the viewpoint of sealing performance, the thickness of the sealing layer 31 is preferably 3 μm or more, and may be 4 μm or more. Furthermore, when the sealing layer 31 contains specific particles A, from the viewpoint of easily obtaining sufficient effect from the unevenness caused by the specific particles A, the thickness of the sealing layer 31 is preferably 20 μm or less, more preferably 15 μm or less, and even more preferably 10 μm or less. 【0056】 Furthermore, from the viewpoint of ensuring that the effect of the unevenness on the outer surface of the exterior material caused by the specific particles A is sufficiently obtained, the ratio of the average particle diameter of the specific particles A to the thickness of the seal layer 31 is preferably 0.5 or more, more preferably 0.6 or more, may also be 0.7 or more, may be 0.8 or more, may be 1.0 or more, or may be 1.5 or more. From the viewpoint of the heat-sealability of the exterior material, the ratio of the average particle diameter of the specific particles A to the thickness of the seal layer 31 is preferably 2.0 or less, more preferably 1.8 or less, may also be 1.6 or less, may be 1.5 or less, may be 1.4 or less, or may be 1.3 or less. 【0057】 The thickness of the sealing layer 31 is preferably 5% or more, more preferably 10% or more, and may be 15% or more, relative to the total thickness of the heat-fusible resin layer 3. Furthermore, the thickness of the sealing layer 31 is preferably 40% or less, more preferably 30% or less, even more preferably 25% or less, and may be 20% or less, relative to the total thickness of the heat-fusible resin layer 3. 【0058】 The thickness of the intermediate layer 32 is preferably 10 μm or more, more preferably 15 μm or more, and may be 20 μm or more, from the viewpoint of improving electrical insulation and impact resistance. Furthermore, from the viewpoint of reducing the total thickness of the exterior material, the thickness of the intermediate layer 32 is preferably 50 μm or less, more preferably 40 μm or less, and even more preferably 30 μm or less. 【0059】The thickness of the intermediate layer 32 is preferably 25% or more, more preferably 30% or more, even more preferably 40% or more, and particularly preferably 50% or more, relative to the total thickness of the heat-fusible resin layer 3. Furthermore, the thickness of the intermediate layer 32 is preferably 90% or less, more preferably 80% or less, and even more preferably 75% or less, relative to the total thickness of the heat-fusible resin layer 3. 【0060】 The thickness of the laminate layer 33 is preferably 3 μm or more, more preferably 4 μm or more, and may be 5 μm or more, from the viewpoint of obtaining a sufficient delamination suppression effect by improving adhesion with the adhesive layer 5. Furthermore, from the viewpoint of reducing the total thickness of the exterior material, the thickness of the laminate layer 33 is preferably 20 μm or less, more preferably 15 μm or less, and even more preferably 10 μm or less. 【0061】 The thickness of the laminate layer 33 is preferably 5% or more, more preferably 10% or more, and may be 15% or more, relative to the total thickness of the heat-sealable resin layer 3. Furthermore, the thickness of the laminate layer 33 is preferably 45% or less, more preferably 40% or less, even more preferably 30% or less, and may be 20% or less, relative to the total thickness of the heat-sealable resin layer 3. 【0062】 The heat-fusible resin layer 3 may further contain a lubricant. The lubricant is not particularly limited, and examples include fatty acid amides. Examples of fatty acid amides are not particularly limited, and include saturated fatty acid amides, unsaturated fatty acid amides, substituted amides, methylolamides, saturated fatty acid bisamides, unsaturated fatty acid bisamides, fatty acid ester amides, aromatic bisamides, and the like. 【0063】 The lubricant may be included in any of the layers of the laminate layer 33, the intermediate layer 32, and the seal layer 31, or it may not be included at all. 【0064】If the seal layer 31 contains a lubricant, the lubricant content in the seal layer 31 is preferably set to more than 0 ppm and 5000 ppm or less, more preferably to 50 ppm to 3000 ppm, and even more preferably to 100 ppm to 2000 ppm. 【0065】 If the intermediate layer 32 contains a lubricant, the lubricant content in the intermediate layer 32 is preferably set to be greater than 0 ppm and 5000 ppm or less, more preferably set to 50 ppm to 3000 ppm, and even more preferably set to 100 ppm to 2000 ppm. If the laminate layer 33 contains a lubricant, the lubricant content in the laminate layer 33 is preferably set to be greater than 0 ppm and 5000 ppm or less, more preferably set to 50 ppm to 3000 ppm, and even more preferably set to 100 ppm to 2000 ppm, from the viewpoint of maintaining laminating properties. 【0066】 The laminate layer 33, the intermediate layer 32, and the seal layer 31 may be formed from the same composition or from different compositions. When these layers are formed from different compositions, examples include compositions with different types of heat-fusible resins, compositions with different concentrations of each component, and compositions containing other components. 【0067】 The heat-fusible resin layer 3 may be one that has been pre-formed on a resin film. The resin film used as the heat-fusible resin layer 3 may be a heat-fusible unstretched resin film layer. Alternatively, the heat-fusible resin that forms the heat-fusible resin layer 3 may be applied to the surface of the barrier layer 4 by extrusion molding, coating, or the like to form the heat-fusible resin layer 3. 【0068】When a resin film is formed in advance, the heat-sealable resin constituting the laminate layer 33 may be a random copolymer containing "propylene" and "other copolymer components other than propylene" as copolymer components, the heat-sealable resin constituting the intermediate layer 32 may be a block copolymer containing "propylene" and "other copolymer components other than propylene" as copolymer components, and the heat-sealable resin constituting the seal layer 31 may be a random copolymer containing "propylene" and "other copolymer components other than propylene" as copolymer components. The "other copolymer components other than propylene" are not particularly limited and include olefin components such as ethylene, 1-butene, 1-hexene, 1-pentene, and 4-methyl-1-pentene, as well as butadiene. 【0069】 When a heat-fusible resin layer 3 is formed by applying a heat-fusible resin to the surface of the barrier layer 4, the heat-fusible resin constituting the laminate layer 33 may be acid-modified polypropylene, and may further contain polyethylene and an elastomer. The heat-fusible resin constituting the intermediate layer 32 may be a random copolymer containing "propylene" and "other copolymer components other than propylene" as copolymer components, and may further contain polyethylene and an elastomer. The polyethylene that can be contained in the laminate layer 33 and the intermediate layer 32 may be low-density polyethylene (LDPE). 【0070】 (First adhesive layer) The adhesive used in the first adhesive layer 5 may be a chemical reaction type, solvent evaporation type, heat melt type, hot pressure type, etc. It may also be a two-component curing adhesive (two-part adhesive), a one-component curing adhesive (one-part adhesive), or a resin that does not undergo a curing reaction. Furthermore, the first adhesive layer 5 may be a single layer or a multilayer layer of two or more layers. 【0071】Adhesive components include polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polyethylene isophthalate, and copolymerized polyester; polyethers; polyurethanes; epoxy resins; phenolic resins; polyamides such as nylon 6, nylon 66, nylon 12, and copolymerized polyamides; polyolefin resins such as polyolefins, cyclic polyolefins, acid-modified polyolefins, and acid-modified cyclic polyolefins; polyvinyl acetate; cellulose; (meth)acrylic resins; polyimides; polycarbonates; amino resins such as urea resins and melamine resins; rubbers such as chloroprene rubber, nitrile rubber, and styrene-butadiene rubber; and silicone resins. Adhesive components in thermosetting adhesives include polyolefin resins, epoxy resins, and (meth)acrylic resins. The adhesive components may be present individually or in combination of two or more types. 【0072】 The first adhesive layer 5 may contain other components, such as colorants, thermoplastic elastomers, tackifiers, and fillers. Including a colorant in the first adhesive layer 5 yields a colored exterior material for energy storage devices. Known colorants such as pigments and dyes can be used. Furthermore, the colorant may be present alone or in combination of two or more types. 【0073】 The thickness of the first adhesive layer 5 is preferably set to 1 μm to 5 μm, and more preferably to 1 μm to 3 μm from the viewpoint of thinning and lightening the exterior material 1. 【0074】 (Second adhesive layer) The adhesive used for the second adhesive layer is not particularly limited, and the adhesive described in the first adhesive layer 5 is an example. The thickness of the second adhesive layer is preferably set to 1 μm to 5 μm, and more preferably to 1 μm to 3 μm from the viewpoint of thinning and lightening the exterior material 1. As explained in the manufacturing method of the exterior material for energy storage devices described later, the second adhesive layer may be omitted depending on the method of forming the heat-fusible resin layer. 【0075】The base layer 2 and the heat-sealable resin layer 3 constituting the exterior material 1 for energy storage devices may further contain antioxidants, plasticizers, ultraviolet absorbers, antifungal agents, colorants (pigments, dyes, etc.), antistatic agents, rust inhibitors, hygroscopic agents, oxygen absorbers, etc. The plasticizer is not particularly limited and includes glycerin fatty acid ester monoglycerides, glycerin fatty acid ester acetylated monoglycerides, glycerin fatty acid ester organic acid monoglycerides, glycerin fatty acid ester medium-chain fatty acid triglycerides, polyglycerin fatty acid esters, sorbitan fatty acid esters, propylene glycol fatty acid esters, special fatty acid esters, higher alcohol fatty acid esters, etc. 【0076】 (Other layers) The surface of the base layer 2 opposite to the barrier layer 4 becomes the outermost surface of the exterior member when an exterior member is formed to surround the main body of the energy storage device. Therefore, a surface coating layer (not shown) may be provided as needed. The surface coating layer may be formed using a known coating agent or the like. 【0077】 (Applications) The exterior material for energy storage devices disclosed herein is also suitably used as an exterior material for lithium-ion secondary batteries. The exterior material for energy storage devices disclosed herein may be molded into an exterior case, and the main body of the energy storage device may be housed inside this exterior case. Alternatively, the exterior material for energy storage devices disclosed herein may be used without molding, with the main body of the energy storage device being fitted onto the exterior and its periphery being heat-sealed. 【0078】 <Method for Manufacturing Outer Materials for Energy Storage Devices> The method for manufacturing outer materials for energy storage devices is not particularly limited as long as the above-described outer materials for energy storage devices can be obtained. An example of a method for manufacturing outer materials for energy storage devices is as follows. 【0079】A laminate A is prepared in which a base layer 2, a first adhesive layer 5, and a barrier layer 4 are laminated in this order. Laminate A can be manufactured by a dry lamination method in which an adhesive component for forming the first adhesive layer 5 is applied to the base layer 2 or barrier layer 4 by gravure coating, roll coating, etc., and after drying, the barrier layer 4 or base layer 2 is laminated on top of it. If the adhesive component is a curable resin, the first adhesive layer 5 is cured by heating or the like after the barrier layer 4 or base layer 2 is laminated on the first adhesive layer 5. 【0080】 Next, a heat-fusible resin layer 3 is provided on the barrier layer 4 of the laminate A. The heat-fusible resin layer 3 may be formed by placing a pre-formed resin film on top of the barrier layer 4 (first method), or the heat-fusible resin that forms the heat-fusible resin layer 3 may be applied to the barrier layer 4 by extrusion molding, coating, etc. to form the heat-fusible resin layer 3 (second method). In the first method, the resin film, which is a multilayer laminate consisting of a laminate layer 33, an intermediate layer 32, etc., can be manufactured by co-extrusion or the like. 【0081】 In the first method, the barrier layer 4 and the heat-fusible resin layer 3 are bonded together by the second adhesive layer. In the second method, the second adhesive layer may be omitted or may be provided. 【0082】When a second adhesive layer is provided between the barrier layer 4 and the heat-fusible resin layer 3, the second adhesive layer and the heat-fusible resin layer 3 can be laminated by methods such as extrusion lamination, thermal lamination, sandwich lamination, and dry lamination. Examples of extrusion lamination methods include lamination by extruding the second adhesive layer and the heat-fusible resin layer 3 (laminate layer portion 33 and intermediate layer portion 32, and optionally a seal layer portion 31) onto the barrier layer 4 of the laminate A (co-extrusion lamination method, tandem lamination method, etc.). Examples of thermal lamination methods include forming a separate laminate B of the second adhesive layer and the heat-fusible resin layer 3, and laminating them so that the second adhesive layer of laminate B and the barrier layer 4 of laminate A face each other, and forming a laminate C with the second adhesive layer on the barrier layer 4 of laminate A, and laminating the second adhesive layer of laminate C with the heat-fusible resin layer 3. Sandwich lamination methods include pouring a molten second adhesive layer between the barrier layer 4 of laminate A and a pre-formed heat-fusible resin layer 3 in film form. Dry lamination methods include solution coating of an adhesive component for forming the second adhesive layer onto the barrier layer 4 of laminate A, drying or baking, and then laminating the pre-formed heat-fusible resin layer 3 in film form onto this second adhesive layer. 【0083】 <Outer Case for Energy Storage Device> The outer case for energy storage device of this disclosure is a molded body of the outer material for energy storage device of this disclosure. The outer material for energy storage device may be formed by deep drawing, stretch molding, etc. An example of the shape of the outer case for energy storage device is the outer case 10 shown in Figures 2 and 3, which will be described later. 【0084】 <Energy Storage Device> The energy storage device of this disclosure comprises an energy storage device body and an exterior member including an exterior material for the energy storage device of this disclosure, wherein the energy storage device body is enclosed by the exterior member. The exterior member may include an exterior case for the energy storage device of this disclosure. 【0085】An example of a power storage device 100 constructed using the exterior material 1 for power storage devices of this disclosure is shown in Figures 2 and 3. Figure 2 is a schematic cross-sectional view showing an example of a power storage device. Figure 3 is a schematic perspective view showing the components constituting the power storage device of Figure 2 separated. The power storage device 100 is a lithium-ion secondary battery. 【0086】 In Figures 2 and 3, the exterior member 15 is composed of an exterior case 10, which is a molded exterior material 1, and a flat exterior material 1. The main body of the energy storage device (electrochemical element, etc.) 110 is housed in a recess in the exterior case 10. The flat exterior material 1 is positioned with the heat-sealable resin layer 3 facing inward (downward in Figures 2 and 3), and the peripheral edge of the heat-sealable resin layer 3 of the flat exterior material 1 and the heat-sealable resin layer 3 of the flange portion (sealing peripheral edge portion) 37 of the exterior case 10 are sealed by heat fusion (heat sealing). 【0087】 In Figure 2, reference numeral 39 denotes a heat-sealed portion where the peripheral edge of the exterior material 1 and the flange portion (sealing peripheral edge) 37 of the exterior case 10 are joined (welded). In the energy storage device 100, the tip of the tab lead connected to the main body portion 110 of the energy storage device is led out to the outside of the exterior member 15, but this is not shown in the figure. 【0088】 The main body 110 of the energy storage device is not particularly limited and may include a battery body, a capacitor body, a capacitor body, etc. 【0089】 From the viewpoint of ensuring a secure seal, the width of the heat-seal portion 39 is preferably set to 0.5 mm or more, and more preferably to 3 mm to 15 mm. 【0090】 The form of the exterior member 15 is not limited to Figures 2 and 3, and may be a pair of planar exterior members 1 with their periphery heat-sealed, or a pair of exterior cases 10 with their periphery heat-sealed. 【0091】The electrolyte contained in the main body 110 of the energy storage device can be one that is commonly used in energy storage devices. A suitable example of the exterior material for energy storage devices of this disclosure is its application to an energy storage device that uses at least one selected from the group consisting of ethylene carbonate and diethyl carbonate as the electrolyte. 【0092】 The following describes examples of the present disclosure, but the present disclosure is not particularly limited to these examples. 【0093】 1. Preparation of film for heat-sealable resin layer A film for the heat-sealable resin layer 3 of the exterior material 1 for energy storage device was prepared, with the content of specific particle A as shown in Table 1. Specifically, a three-layer co-extruded CPP film was prepared as the film for the heat-sealable resin layer 3, using an rPP film for the seal layer (first layer) 31, a bPP film for the intermediate layer 32, and an rPP film for the laminate layer (third layer) 33. 【0094】 【0095】 As specific particle A, we used A1 to A3 as shown in Table 2 below. 【0096】 In Table 2, the loss on ignition is the amount of weight lost (mass%) when heated at 860°C for 20 minutes, in accordance with JIS K 0667:1992. The apparent specific gravity is the value measured in accordance with JIS K 6220-1:2015. The oil absorption is the value measured in accordance with JIS K 5101-13-2:2004. The whiteness is the Hunter whiteness. The pH (25°C) is the value measured in accordance with JIS K 5101-17-1:2004. The average particle size is the value measured by the Coulter counter method. The refractive index is the value measured by the immersion method. 【0097】For the film used for the heat-sealable resin layer 3, silica particles with an average particle size of 0.2 μm (maximum particle size of 2 μm) were used as other particles B. In all of Comparative Examples 1 to 3 and Examples 1 to 4, other particles B were added to the seal layer 31 and the laminate layer 33, and the content of each layer was set to 2000 ppm by mass. In addition, erucic acid amide was used as a lubricant in the film used for the heat-sealable resin layer 3. In all of Comparative Examples 1 to 3 and Examples 1 to 4, erucic acid amide was added to the seal layer 31, the intermediate layer 32, and the laminate layer 33, and the content of each layer was set to 1000 ppm by mass. 【0098】 The thickness of each layer in the film for the heat-sealable resin layer 3 is as follows: 【0099】 【0100】 2. Fabrication of exterior material for energy storage device A 40 μm thick aluminum foil (A8021-O) was used as the barrier layer 4. A chemical conversion treatment solution consisting of phosphoric acid, polyacrylic acid (acrylic resin), chromium (III) salt compound, water, and alcohol was applied to both sides, and then dried at 180°C to form a chemical conversion film. The amount of chromium deposited on this chemical conversion film was 10 mg / m² per side. ２ That was the case. 【0101】 Next, a 15 μm thick biaxially oriented nylon 6 (ONy) film was dry-laminated (bonded) to one side (outer surface) of the chemically treated aluminum foil (barrier layer 4) via a two-component curing urethane adhesive (3 μm) to form the base layer 2. Then, a two-component curing adhesive (2 μm) of maleic acid-modified polypropylene resin and isocyanate was applied to the other side (inner surface) of the dry-laminated aluminum foil (barrier layer) 4, and the laminate layer of the heat-fusible resin layer 3 prepared above was placed on top of this so that the laminate layer was on the adhesive layer side. Then, dry lamination was performed by sandwiching the assembly between a rubber nip roll and a laminating roll heated to 100°C and pressing them together. After that, the assembly was aged at 40°C for 10 days to obtain the exterior materials (laminated bodies) of the example and comparative example to be used as samples. 【0102】The surface appearance of the seal layer 31 side of the obtained exterior material (laminated body) was observed. Figure 4 shows photographs (bottom) and white light interferometer results (top) of the surface of the seal layer 31 side of Comparative Examples 1 to 3 and Example 1 observed with a scanning electron microscope. Figure 5 shows photographs (bottom) and white light interferometer results (top) of the surface of the seal layer 31 side of Examples 2 to 4 observed with a scanning electron microscope. 【0103】 The Sdr of the surface on the sealing layer 31 side of the obtained exterior material (laminated body) was measured using a scanning white-light interference microscope (Hitachi High-Tech Corporation, model: VS1330). 【0104】 3. Evaluation Tests for Each Exterior Material 3.1 Insulation Test After Heat Sealing As shown in Figure 6, a measurement sample for the insulation test was prepared. First, an exterior material cut to 80 mm x 100 mm was prepared and folded in half to 80 mm x 50 mm as shown in Figure 6(A). Next, as shown in Figure 6(B), a tab lead 80 equipped with tab sealant was placed between the folded material, and the edge where the tab lead 80 was placed (the bottom edge in Figure 6(B)) and the 80 mm edge (the side edge in Figure 6(B)) were heat-sealed to form a bag. Then, as shown in Figure 6(C), ethylene carbonate:diethyl carbonate = 1:1 (mass ratio), LiPF was placed inside the bag-shaped exterior material. ６ One ml of 1 M electrolyte solution was poured in, and the remaining open 50 mm side (the top side in Figure 6(C)) was sealed. Then, it was left lying flat at 25°C for 24 hours. Next, as shown in Figure 6(D), a portion of the outer layer of the exterior material was scraped to form an exposed aluminum foil (barrier layer). Then, as shown in Figure 6(E), the exposed aluminum foil (barrier layer) and the tab lead 80 were connected to an insulation resistance tester 90 (HIOKI, "3154 DIGITAL MΩ HITESTER"), a voltage of 25 V was applied, and the resistance value was measured. 【0105】 Based on the obtained resistance values, the following criteria were used for evaluation: A: Resistance value greater than 100 MΩ B: Resistance value between 30 MΩ and 100 MΩ C: Resistance value less than 30 MΩ 【0106】3.2 Insulation Test After Interlocking Seal The measurement sample prepared in the insulation test after heat sealing described above was interlocked around the center of the 80 mm side, as shown in Figure 7(A). The interlocking seal was performed by heating at 180°C and 0.15 MPa for 3 seconds. In Figure 7, reference numeral 50 indicates the interlocking seal area. Next, as shown in Figure 7(B), the exposed portion of the aluminum foil (barrier layer) and the tab lead 80 were connected to an insulation resistance tester 90 (HIOKI, "3154 DIGITAL MΩ HITESTER"), a voltage of 25 V was applied, and the resistance value at that time was measured. 【0107】 Based on the obtained resistance values, the following criteria were used for evaluation: A: Resistance value greater than 100 MΩ B: Resistance value between 30 MΩ and 100 MΩ C: Resistance value less than 30 MΩ 【0108】 【0109】 As shown in Table 4, Comparative Examples 1 to 3, which had an Sdr of less than 3%, showed high resistance and excellent insulation after heat sealing, but their resistance decreased significantly after interfering seal, resulting in reduced insulation. In contrast, Examples 1 to 4, which had an Sdr of 3% or more, maintained high insulation even after interfering seal. 【0110】 The disclosure of Japanese Patent Application No. 2024-218225 is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually noted to be incorporated by reference. 【0111】 1...Exterior material for energy storage device 2...Base layer 3...Heat-fusible resin layer 4...Barrier layer 5...Adhesive layer 10...Exterior case 15...Exterior component 31...Seal layer 32...Intermediate layer 33...Laminate layer 50...Interference seal part 80...Tab lead 90...Insulation resistance tester 100...Energy storage device 110...Main body of energy storage device

Claims

1. An exterior material for an energy storage device comprising a base layer, a barrier layer, and a heat-fusible resin layer in this order, wherein the interface area ratio Sdr of the outer surface of the heat-fusible resin layer is 3% or more.

2. The exterior material for an energy storage device according to claim 1, wherein the heat-sealable resin layer contains particles with an average particle diameter of 5 μm or more.

3. The exterior material for an energy storage device according to claim 2, wherein the heat-sealable resin layer comprises, in order from the barrier layer side, a laminate layer, an intermediate layer, and a sealing layer, and the sealing layer contains the particles.

4. The exterior material for an energy storage device according to claim 3, wherein the content of the particles in the sealing layer is 2,000 ppm by mass or more.

5. An exterior material for an energy storage device according to claim 1 or 2, which is applied to an energy storage device that uses at least one selected from the group consisting of ethylene carbonate and diethyl carbonate as an electrolyte.

6. An outer case for an energy storage device, which is a molded body of the outer material for an energy storage device according to claim 1 or claim 2.

7. An energy storage device comprising: an energy storage device main body; and an exterior member including an exterior material for an energy storage device as described in claim 1 or claim 2, wherein the energy storage device main body is covered by the exterior member.

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