Sealed battery

Abstract

According to the present invention, a cylindrical battery (10) is provided with an insulating film (30) that is disposed between an outer package can (16) and a sealing plate (17). The insulating film (30) is a coating film that contains a filler which has a D50 of 10 µm or more and a resin which forms a film structure, and the adhesion strength of the insulating film (30) to the sealing plate (17) is 100 gf or more. The average thickness of the resin portion of the insulating film (30) is 100 µm or more, and the D50 of the filler is less than or equal to the average thickness of the resin portion of the insulating film (30). The content of the filler in the insulating film (30) is 10 vol% to 90 vol% inclusive.

Description

sealed battery

[0001] The present disclosure relates to sealed batteries.

[0002] Conventionally, sealed batteries including a cylindrical outer can with a bottom and a sealing plate that closes the opening of the outer can have been widely known. Examples of sealed batteries include cylindrical batteries and prismatic batteries. Patent Document 1 discloses a cylindrical battery including a gasket interposed between the outer can and the sealing plate. As described in Patent Document 1, the gasket is generally made of a resin such as polypropylene or polyethylene. In this case, however, there is a concern that the sealing performance may be reduced due to deterioration of the resin. Furthermore, if the gasket functions as an insulating member, there is a concern that the insulating performance may be reduced. It is also anticipated that the gasket may melt and cause a short circuit when the battery generates abnormal heat.

[0003] In light of this situation, Patent Document 2 discloses a cylindrical battery equipped with an insulator that is applied to the inner surface of the outer can and interposed between the outer can and the sealing plate, instead of a conventional gasket. The insulator contains a filler that is harder than the sealing plate, and has excellent durability and heat resistance.

[0004] JP 2007-184270 A International Publication No. 2015 / 125413

[0005] As described above, maintaining the excellent sealing and insulating performance of a sealed battery over a long period of time is an important issue, but conventional technologies including the battery disclosed in Patent Document 2 still have room for improvement.

[0006] The sealed battery according to the present disclosure is a sealed battery having a battery case, and further comprising an insulating film disposed between a main body and a terminal that constitute the battery case, wherein the insulating film is a coating film containing a filler having a volumetric median diameter of 10 μm or more and a resin that forms a film structure, and wherein the insulating film has an adhesive strength of 100 gf or more to the main body or the terminal, the resin portion of the insulating film having an average thickness of 100 μm or more, the volumetric median diameter of the filler being equal to or less than the average thickness of the resin portion of the insulating film, and the filler content in the insulating film is 10% by volume or more and 90% by volume or less.

[0007] The sealed battery according to the present disclosure can maintain excellent sealing and insulating performance for a long period of time.

[0008] With conventional gaskets made of resins such as polypropylene and polyethylene, the antioxidants added to the resin are consumed by contact with the electrolyte, battery voltage, use in high-temperature environments, etc., making it difficult to guarantee a long lifespan. By using a coating-type insulating film containing filler, it is possible to reduce the amount of resin used, making it possible to use expensive resins with long lifespans, and ensuring long-term storage.

[0009] Fig. 2 is a cross-sectional view of a sealed battery that is one example of an embodiment. Fig. 3 is an enlarged view of part A in Fig. 1. Fig. 4 is an enlarged view of part B in Fig. 2. Fig. 5 is a view for explaining the definition and measurement method of the average thickness of the resin part of the insulating film and the surface roughness of the insulating film. Fig. 6 is a cross-sectional view of a sealed battery that is another example of an embodiment.

[0010] Hereinafter, an example of an embodiment of a sealed battery according to the present disclosure will be described in detail with reference to the drawings. Note that configurations obtained by selectively combining the components of the multiple embodiments and variations described below are included within the scope of the present disclosure.

[0011] In the following, as an example of an embodiment, a cylindrical battery in which a wound-type electrode body is housed in a cylindrical outer can with a bottom is illustrated, but the outer can is not limited to a cylindrical outer can. Another example of a sealed battery of the embodiment may be, for example, a prismatic battery equipped with a prismatic outer can. Furthermore, the electrode body is not limited to a wound type, but may be a stacked type electrode body in which multiple positive electrodes and multiple negative electrodes are alternately stacked with separators interposed therebetween.

[0012] FIG. 1 is a cross-sectional view of a cylindrical battery 10 according to an embodiment. As shown in FIG. 1, the cylindrical battery 10 includes a wound electrode assembly 14, an electrolyte, and an outer can 16 that houses the electrode assembly 14 and the electrolyte. The outer can 16 is a cylindrical metal container with a bottom and an open axial end, and the opening of the outer can 16 is closed by a sealing plate 17. For ease of explanation, the sealing plate 17 side of the battery is referred to as the top, and the bottom side of the outer can 16 is referred to as the bottom. While the electrolyte may be an aqueous electrolyte, a nonaqueous electrolyte is used in this embodiment.

[0013] As described above, the cylindrical battery 10 includes a battery case including a cylindrical outer can 16 with a bottom and a sealing plate 17 disposed at the opening of the outer can 16. The cylindrical battery 10 also includes an insulating film 30 disposed between the outer can 16 and the sealing plate 17. The insulating film 30 functions as a sealant that ensures airtightness inside the battery case, and as an insulating material that prevents electrical contact between the outer can 16, which is the main body of the battery case, and the sealing plate 17, which functions as a terminal. As will be described in detail later, the insulating film 30 is a coating film formed on the outer can 16 or the sealing plate 17, and in this embodiment, it is formed on the sealing plate 17. The insulating film 30 has an adhesion strength to the sealing plate 17 of 100 gf or more.

[0014] The electrode assembly 14 has a positive electrode 11, a negative electrode 12, and a separator 13, and has a wound structure in which the positive electrode 11 and the negative electrode 12 are spirally wound with the separator 13 interposed therebetween. The positive electrode 11, the negative electrode 12, and the separator 13 are all long, strip-shaped bodies, and are spirally wound so that they are alternately stacked in the radial direction of the electrode assembly 14. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer in the longitudinal direction and width direction (short direction) than the positive electrode 11. The separator 13 is formed to be at least slightly larger than the positive electrode 11, and two separators 13 are arranged to sandwich the positive electrode 11.

[0015] The non-aqueous electrolyte has lithium ion conductivity. The non-aqueous electrolyte may be a liquid electrolyte (electrolytic solution) or a solid electrolyte. The cylindrical battery 10 is a non-aqueous electrolyte secondary battery, and is preferably a lithium ion battery.

[0016] The liquid electrolyte (electrolytic solution) contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, and mixed solvents of two or more of these. Examples of the non-aqueous solvent include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixed solvents of these. The non-aqueous solvent may contain a halogen-substituted compound (e.g., fluoroethylene carbonate) in which at least a portion of the hydrogen atoms of these solvents are substituted with halogen atoms such as fluorine. Examples of the electrolyte salt include LiPF ６ Lithium salts such as

[0017] As the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc. can be used. As the inorganic solid electrolyte, a material known in all-solid-state lithium ion secondary batteries, etc. (for example, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, a halogen-based solid electrolyte, etc.) can be used. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt, and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs the non-aqueous solvent and gels is used. As the polymer material, for example, a fluororesin, an acrylic resin, a polyether resin, etc. can be used.

[0018] The positive electrode 11 includes a long positive electrode core and a positive electrode mixture layer disposed on the positive electrode core. The positive electrode core can be a foil of a metal, such as aluminum, an aluminum alloy, stainless steel, or titanium, that is stable within the potential range of the positive electrode 11, or a film with such a metal disposed on the surface. The positive electrode mixture layer preferably contains a positive electrode active material, a conductive agent such as acetylene black, and a binder such as polyvinylidene fluoride (PVdF), and is formed on both sides of the positive electrode core. For example, a lithium transition metal composite oxide containing Ni, Co, Mn, Al, or the like is used as the positive electrode active material. The positive electrode 11 can be fabricated by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, and a binder to the positive electrode core, drying the coating, and then compressing it to form a positive electrode mixture layer on both sides of the positive electrode core.

[0019] The negative electrode 12 has a long negative electrode core and a negative electrode mixture layer provided on the negative electrode core. The negative electrode core can be made of a foil of a metal that is stable within the potential range of the negative electrode 12, such as copper, a copper alloy, stainless steel, nickel, or a nickel alloy, or a film with such a metal disposed on its surface. The negative electrode mixture layer contains a negative electrode active material and a binder such as styrene-butadiene rubber (SBR), and is preferably formed on both sides of the negative electrode core. Examples of the negative electrode active material include graphite and Si-containing materials. The negative electrode 12 can be fabricated, similar to the positive electrode 11, by applying a negative electrode mixture slurry containing a negative electrode active material and a binder onto the negative electrode core, drying the coating, and then compressing it to form a negative electrode mixture layer on both sides of the negative electrode core.

[0020] The electrode body 14 further has a positive electrode lead 20 connected to the positive electrode 11 by welding or the like, and a negative electrode lead 21 connected to the negative electrode 12 by welding or the like. Insulating plates 18, 19 are disposed above and below the electrode body 14. In the example shown in FIG. 1 , the positive electrode lead 20 passes through a through hole in the insulating plate 18 and extends toward the sealing plate 17, and the negative electrode lead 21 passes outside the insulating plate 19 and extends toward the bottom of the outer can 16. The positive electrode lead 20 is connected to the underside of an internal terminal plate 23 of the sealing plate 17 by welding or the like, and a cap 27, which is the top plate of the sealing plate 17 and is electrically connected to the internal terminal plate 23, serves as a positive electrode terminal. The negative electrode lead 21 is connected to the inner bottom surface of the outer can 16 by welding or the like, and the outer can 16 serves as a negative electrode terminal.

[0021] As described above, the cylindrical battery 10 includes an insulating film 30 interposed between the outer can 16 and the sealing plate 17. That is, the insulating film 30 is disposed between the main body and terminal portions that constitute the battery case. In this embodiment, the outer can 16 functions as the negative electrode terminal, and the sealing plate 17 functions as the positive electrode terminal. Therefore, the insulating film 30 can be said to be disposed between the positive and negative electrode terminals. The outer can 16 has a grooved portion 22 formed on its side surface that protrudes inward and supports the sealing plate 17. The grooved portion 22 is preferably formed in an annular shape along the circumferential direction of the outer can 16, and its upper surface supports the sealing plate 17. The radial length of the grooved portion 22 protruding from the inner circumferential surface of the outer can 16 is, for example, 2 mm or more and 4 mm or less.

[0022] The sealing plate 17 is fixed to the upper end (opening edge) of the outer can 16 by the grooved portion 22 and a crimped portion 28, which is the opening edge of the outer can 16 that is crimped to the sealing plate 17. The crimped portion 28 is formed by bending the opening edge of the outer can 16 radially inward, and together with the grooved portion 22, it sandwiches the sealing plate 17 from both sides in the thickness direction. The radial length of the crimped portion 28 is, for example, 2 mm or more and 4 mm or less. An insulating film 30 is always present between the sealing plate 17 and the grooved portion 22 and the crimped portion 28.

[0023] The sealing plate 17 has a structure in which, in order from the electrode body 14 side, an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked. Each member constituting the sealing plate 17 has, for example, a disk or ring shape, and each member except for the insulating member 25 is electrically connected to one another. The lower valve body 24 and the upper valve body 26 are connected at their respective centers, and the insulating member 25 is interposed between their respective peripheral edges. When the internal pressure increases due to abnormal heat generation in the battery, the lower valve body 24 deforms and breaks, pushing the upper valve body 26 toward the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure further increases, the upper valve body 26 breaks, and gas is discharged from the opening of the cap 27.

[0024] The insulating film 30 will be described in detail below with reference to Figures 2 and 3. Figure 2 is an enlarged view of part A in Figure 1, and Figure 3 is an enlarged view of part B in Figure 2. The sealing plate 17 has a structure in which multiple members are stacked, but Figure 2 simplifies the cross-sectional structure of the sealing plate 17. As shown in Figure 2, the sealing plate 17 may be made of a single metal plate.

[0025] As shown in Figures 2 and 3, the insulating film 30 is a coating formed on the sealing plate 17. It seals the gap between the outer can 16 and the sealing plate 17, ensuring airtightness within the battery case and preventing electrical contact between the outer can 16 and the sealing plate 17. The insulating film 30 functions as a sealant and an insulator and is used in place of conventional gaskets made of resins such as polypropylene. That is, the cylindrical battery 10 does not have a conventional gasket; instead, the insulating film 30 is disposed adjacent to the inner surface of the outer can 16. As will be described in more detail below, the use of the insulating film 30 makes it possible to maintain excellent sealing and insulating performance over a long period of time. Furthermore, because the insulating film 30 is a thin film, it can improve the volumetric energy density compared to batteries using conventional gaskets.

[0026] The insulating film 30 is a coating film containing filler 31 having a volume-based median diameter D50 of 10 μm or more and resin 32 that forms a film structure, and has an adhesion strength of 100 gf or more to the sealing plate 17. The filler 31 is an insulating particle that imparts sealing and insulating functions to the insulating film 30 and improves the durability and heat resistance of the insulating film 30. The resin 32 is an insulating resin that bonds the particles of the filler 31 together to ensure the shape of the film and imparts adhesive strength to the sealing plate 17. The resin 32 also fills gaps between the particles of the filler 31, improving the sealing performance of the insulating film 30.

[0027] If the D50 of the filler 31 is 10 μm or greater, the insulating performance of the insulating film 30 can be maintained over a long period of time, provided that other conditions are met. On the other hand, if the D50 of the filler 31 is less than 10 μm, for example, the crimping portion 28 may break through the insulating film 30 and contact the sealing plate 17, preventing the cylindrical battery 10 from achieving the required insulating performance. In this specification, D50 refers to the particle size at which the cumulative frequency of the smallest particle size in the volume-based particle size distribution is 50%. The particle size distribution of the filler 31 can be measured using a laser diffraction particle size distribution analyzer (e.g., the MT3000II manufactured by Microtrac-Bell) with water as the dispersion medium.

[0028] If the adhesion strength of the insulating film 30 to the sealing plate 17 is 100 gf or more, the sealing and insulating properties of the insulating film 30 can be maintained for a long period of time. On the other hand, if the adhesion strength is less than 100 gf, problems such as peeling of the insulating film 30 and collapse of the film structure are expected. In this specification, the adhesion strength of the insulating film 30 to the sealing plate 17 is measured using a tacking tester (e.g., TAC-II manufactured by Rhesca Corporation). Specific measurement conditions are as follows. Measurement conditions: Double-sided tape (e.g., double-sided tape #515 manufactured by Nitto Denko Corporation) with an adhesive strength to a stainless steel plate of 16.5 N / 20 mm or more is attached to the tip of a 2 mm diameter metal rod, and the tape is pressed against the insulating film 30 formed on the sealing plate 17 with a preload of 400 gf for 10 seconds, and then the metal rod is pulled at a speed of 600 mm / min. The stress required to peel the insulating film 30 at this time is defined as the adhesion strength of the insulating film 30 to the sealing plate 17.

[0029] The average thickness T of the resin portion of the insulating film 30 is at least 100 μm. The D50 of the filler 31 needs to be equal to or less than the average thickness T of the resin portion of the insulating film 30. The content of the filler 31 in the insulating film 30 is 10% by volume or more and 90% by volume or less. The insulating film 30 is preferably composed essentially of only the filler 31 and the resin 32, and contains at least 10% by volume of the resin 32. Here, the average thickness T of the resin portion means the average value of the thickness of the portion excluding the filler 31 protruding from the surface of the resin 32, as shown in FIG. 4. Hereinafter, the thickness of the resin portion may be referred to as the "coating film thickness."

[0030] If the average thickness T of the resin portion of the insulating film 30 is 100 μm or more, the sealing performance of the insulating film 30 can be maintained over a long period of time, provided that other conditions are met. On the other hand, if the average thickness T of the resin portion is less than 100 μm, the sealing performance required for the cylindrical battery 10 cannot be achieved. In this specification, the average thickness T of the resin portion is calculated by observing the cross section of the insulating film 30 with a scanning electron microscope (SEM) and averaging the thickness of the portion excluding the filler 31 protruding from the surface of the resin 32 (coating surface).

[0031] The insulating film 30 is bonded to the peripheral edges of the first and second main surfaces 17a, 17b of the sealing plate 17. The first main surface 17a is the outer surface of the sealing plate 17 facing outward from the cylindrical battery 10, and the second main surface 17b is the inner surface of the sealing plate 17 facing inward from the cylindrical battery 10. The main surfaces 17a, 17b are perpendicular to the thickness direction of the sealing plate 17. The insulating film 30 need only be present in the area that contacts the outer can 16. In this embodiment, the peripheral edge of the first main surface 17a of the sealing plate 17 contacts the crimping portion 28, and the peripheral edge of the second main surface 17b contacts the grooved portion 22. Therefore, the insulating film 30 is bonded only to the peripheral edges of the main surfaces 17a, 17b. However, to more reliably prevent contact between the outer can 16 and the sealing plate 17, it is preferable to form the insulating film 30 over an area slightly wider than the area that contacts the outer can 16.

[0032] The insulating film 30 is formed in a ring shape with a substantially constant width along the periphery of each of the main surfaces 17a, 17b of the sealing plate 17. The insulating film 30 preferably extends 1 mm or more radially inward from the radially inner edge of the portion where the outer can 16 contacts the sealing plate 17. In other words, the insulating film 30 is formed 1 mm wider than the portion where the outer can 16 overlaps, and more preferably 1 mm or more and 5 mm or less.

[0033] The insulating film 30 is preferably formed over the entire area of ​​the first main surface 17a of the sealing plate 17 that overlaps with the crimping portion 28 in the vertical direction (the axial direction of the outer can 16), and is preferably formed over the entire area of ​​the second main surface 17b that overlaps with the grooved portion 22 in the vertical direction. The insulating film 30 is also preferably bonded to the side surface 17c of the sealing plate 17. The side surface 17c of the sealing plate 17 is a surface that faces radially outward of the sealing plate 17 and is perpendicular to the main surfaces 17a, 17b in the example shown in FIG. 2 . The insulating film 30 is preferably bonded over the entire area of ​​the side surface 17c of the sealing plate 17.

[0034] The insulating film 30 is preferably formed along the periphery of each of the main surfaces 17a, 17b of the sealing plate 17, and is formed continuously from the first main surface 17a, around the side surface 17c, and over to the second main surface 17b of the sealing plate 17. Because the diameter of the sealing plate 17 is slightly smaller than the inner diameter of the outer can 16, the sealing plate 17 can be positioned without the side surface 17c of the sealing plate 17 coming into contact with the inner peripheral surface of the outer can 16. However, if the sealing plate 17 is misaligned, the side surface 17c of the sealing plate 17 may come into contact with the inner peripheral surface of the outer can 16. Covering the side surface 17c of the sealing plate 17 with the insulating film 30 further improves the insulating performance.

[0035] As described above, the insulating film 30 contains the filler 31 in an amount of 10% by volume or more and 90% by volume or less. The content of the filler 31 is preferably 15% by volume or more and 80% by volume or less, more preferably 20% by volume or more and 60% by volume or less, and particularly preferably 20% by volume or more and 50% by volume or less, relative to the total volume of the insulating film 30. If the content of the filler 31 is within this range, the excellent sealing and insulating performance of the insulating film 30 can be easily maintained over a long period of time, and excellent insulating performance can be ensured even when the battery abnormally heats up. Note that if the content of the filler 31 is less than 10% by volume, the insulating performance will be significantly reduced. On the other hand, if the content of the filler 31 exceeds 90% by volume, the sealing performance will be significantly reduced.

[0036] The D50 of the filler 31 is required to be 10 μm or more, more preferably 15 μm or more, and particularly preferably 20 μm or more, in order to ensure the insulating function of the insulating film 30. The upper limit of the D50 of the filler 31 is not particularly limited from the viewpoint of the insulating performance and sealing performance of the insulating film 30, but since a larger D50 requires a larger coating film thickness, the upper limit is preferably 300 μm. An example of a suitable range for the D50 of the filler 31 is 10 μm or more and 300 μm or less, or 15 μm or more and 200 μm or less, or 20 μm or more and 100 μm or less, from the viewpoints of insulating properties, sealing properties, high capacity, etc.

[0037] The filler 31 may be any particle that satisfies the insulating properties and the above-mentioned D50 requirements. Either resin particles or inorganic particles can be used for the filler 31, but inorganic particles are preferred from the viewpoint of improving the heat resistance of the insulating film 30. Specifically, the melting point of the filler 31 is preferably 300°C or higher. When the filler 31 is inorganic particles, it preferably has a melting point of 600°C or higher. In this case, it is particularly easy to ensure the insulating function of the insulating film 30 even when the battery generates abnormal heat. Note that when the filler 31 is made of a material that does not have a melting point, for example, the decomposition initiation temperature is preferably 300°C or higher, and more preferably 600°C or higher.

[0038] Examples of inorganic substances constituting the filler 31 include metal oxides, metal nitrides, metal fluorides, and sulfates such as barium sulfate. Examples of metal oxides include aluminum oxide, titanium oxide, zirconium oxide, silicon oxide, manganese oxide, magnesium oxide, and nickel oxide. Examples of metal nitrides include boron nitride, aluminum nitride, magnesium nitride, and silicon nitride. Examples of metal fluorides include aluminum fluoride, lithium fluoride, sodium fluoride, magnesium fluoride, calcium fluoride, and barium fluoride. Among these, aluminum oxide and titanium oxide are preferred from the viewpoint of heat resistance, and barium sulfate is preferred from the viewpoint of cost.

[0039] The resin 32 forming the film structure of the insulating film 30 preferably has excellent insulating properties, electrolyte resistance, and adhesion to the sealing plate 17 and the filler 31. Furthermore, the resin 32 is preferably a resin with better heat resistance than polypropylene, which constitutes conventional gaskets. Since the insulating film 30 is thinner and uses less resin than conventional gaskets, an expensive resin can be used for the resin 32 without increasing material costs. Furthermore, a resin with a cross-linked structure that has excellent durability and heat resistance can be used for the resin 32.

[0040] Examples of resin 32 include polyester, epoxy resin, acrylic resin, fluororesin, silicone resin, polyamide, polyimide, polyamideimide, polyetherimide, and polyphenylene sulfide, and at least one selected from these can be used for resin 32. Among these, curable resins containing a crosslinked structure are preferred, and ultraviolet (UV) curable resins are particularly preferred from the viewpoint of improving productivity. Examples of UV curable resins constituting resin 32 include urethane acrylate, epoxy acrylate, acrylic acrylate, polyester acrylate, and vinyl ester resin, and at least one selected from these can be used. Resin 32 can be a solventless type or a dispersion or emulsion type UV curable resin.

[0041] The insulating film 30 is formed, for example, by applying an uncured UV-curable resin (paint) with filler 31 dispersed therein to the surface of the sealing plate 17, and then irradiating the coating with UV light to cure the resin. The initiator added to the UV-curable resin may be any of conventionally known initiators, such as alkylphenone-based, acylphosphine oxide-based, oxime ester-based, or cationic initiators, or intramolecular hydrogen abstraction photopolymerization initiators. Furthermore, the light source that outputs the UV light may be a high-pressure mercury lamp, a metal halide lamp, a UV electrodeless lamp, or a UV-LED. The irradiation energy of the UV light is appropriately selected depending on the composition of the resin 32, the type of initiator, the composition of the filler 31, and the like. For example, the UV-curable resin may be applied to a UV-A wavelength region with an illuminance of 100 mJ / cm. ２ More than 5000mJ / cm ２ or less, or 200 mJ / cm ２ More than 1000mJ / cm ２ The following is the result.

[0042] The average thickness T of the resin portion of the insulating film 30 (average coating thickness T) is required to be 100 μm or more, and more preferably 150 μm or more, in order to ensure the sealing function of the insulating film 30. The upper limit of the average coating thickness T is not particularly limited from the viewpoint of the insulating and sealing performance of the insulating film 30. However, as the coating thickness increases, the volumetric energy density of the battery decreases, while the improvement effect of the sealing performance reaches a plateau. Therefore, the upper limit is preferably 500 μm, and more preferably 300 μm. An example of a suitable range for the average coating thickness T is 100 μm or more and 500 μm or less, or 150 μm or more and 300 μm or less, or 150 μm or more and 200 μm or less, from the viewpoint of insulation properties, sealing properties, high capacity, etc.

[0043] The ratio of the D50 of the filler 31 to the average coating thickness T of the insulating film 30 (hereinafter referred to as "ratio X" for convenience of explanation) is 0.3 or more and 1.0 or less. If the D50 of the filler 31 exceeds the average coating thickness T, i.e., if the ratio X exceeds 1.0, the sealing performance of the insulating film 30 is significantly reduced. Furthermore, if the D50 of the filler 31 becomes too small relative to the average coating thickness T and the ratio X falls below 0.3, the sealing performance, insulating performance, durability, etc. of the insulating film 30 tend to decrease, so it is preferable to set the ratio X to 0.3 or more. Examples of suitable ranges for the ratio X are 0.3 or more and 1.0 or less, or 0.4 μm or more and 0.8 μm or less, or 0.4 μm or more and 0.6 μm or less.

[0044] The thickness of the insulating film 30 is preferably substantially constant throughout the entire film or gradually decreases toward the film edges in the direction along the first and second main surfaces 17a and 17b (the surfaces of the terminal portions) of the sealing plate 17. In the example shown in FIG. 2 , the insulating film 30 on the first and second main surfaces 17a and 17b of the sealing plate 17 has regions of substantially constant thickness and regions where the thickness gradually decreases toward the film edges. In particular, when the D50 of the filler 31 and the average coating thickness T are similar, for example, when the ratio X is close to 1.0, unevenness is likely to form on the surface of the insulating film 30. Furthermore, if locally thick raised portions exist near the film edges of the insulating film 30, sealing performance is likely to deteriorate. Therefore, it is preferable to gradually decrease the thickness of the insulating film 30 toward the film edges. Gradually decreasing the thickness of the insulating film 30 reduces the likelihood of raised portions forming near the film edges, improving the sealing performance of the insulating film 30.

[0045] The region where the thickness of the insulating film 30 gradually decreases toward the film end (hereinafter referred to as "region Y" for convenience of explanation) is preferably formed in a circular ring shape along the periphery of the sealing plate 17. Furthermore, region Y is preferably formed in a portion on the first main surface 17a of the sealing plate 17 that does not overlap with the radially inner end of the portion with which the crimping portion 28 contacts. In this case, the effect of improving sealing performance becomes more pronounced. Similarly, on the second main surface 17b of the sealing plate 17, region Y is preferably formed in a portion that overlaps with the radially inner end of the portion with which the grooved portion 22 contacts. Region Y is formed, for example, by reducing the viscosity of the paint.

[0046] The surface roughness of the insulating film 30 is preferably 70 μm or less, and more preferably 50 μm or less. The surface roughness of the insulating film 30 is an index indicating the degree of unevenness on the film surface and has a significant effect on sealing performance. If the surface roughness of the insulating film 30 is 50 μm or less, excellent sealing performance can be obtained. The surface roughness of the insulating film 30 can be made 70 μm or less, for example, by setting the ratio X to 1.0 or less. Furthermore, the smaller the ratio X and the smaller the D50 of the filler 31, the smaller the surface roughness of the insulating film 30 tends to be. The surface roughness is measured as follows. Measurement method: The cross section of the insulating film 30 is observed with a scanning electron microscope (SEM), and the maximum height H of the apex of the filler 31 protruding from a position corresponding to the average coating thickness T is measured, and the surface roughness is calculated by averaging the measured values ​​at five locations (see FIG. 4 ).

[0047] FIG. 5 is a cross-sectional view of a battery case constituting a prismatic battery 50, which is another example of an embodiment. As shown in FIG. 5, the prismatic battery 50 includes an insulating film 55 disposed between a main body 51 and a terminal 52 that constitute the battery case. The main body 51 is composed of a bottomed, rectangular cylindrical outer can 53 and a sealing plate 54 that closes the opening of the outer can 53. The outer can 53 and the sealing plate 54 are welded together. The prismatic battery 50 has a positive terminal and a negative terminal as terminals 52, which are respectively disposed on the sealing plate 54. The terminals 52 are cylindrical members that are inserted into through holes 56 formed in the sealing plate 54. Note that FIG. 5 is a schematic diagram, and the structure of the battery case of the prismatic battery 50 is the same as that of a conventional battery, except that the insulating film 55 is provided instead of a gasket.

[0048] The insulating film 53 can be a film of the same composition as the insulating film 30. The insulating film 53 may be a coating adhered to the first and second main surfaces 54a and 54b of the sealing plate 54. In the example shown in FIG. 5, the insulating film 53 is adhered to the surface of the terminal portion 52 that faces the first and second main surfaces 54a and 54b. The insulating film 53 is also adhered to the surface of the sealing plate 54 that faces the side surface 56c of the through hole 56. The insulating film 53 prevents electrical contact between the main body portion 51 and the terminal portion 52 and ensures airtightness inside the battery case. The first main surface 54a is the outer surface of the sealing plate 54 facing the outside of the prismatic battery 50, and the second main surface 54b is the inner surface of the sealing plate 54 facing the inside of the prismatic battery 50. Similar to the insulating film 30, the thickness of the insulating film 53 may gradually decrease toward the film edge in the direction along the surface of the main body portion 51 (sealing plate 54).

[0049] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0050] Example 1 A cylindrical simulated cell was fabricated using a bottomed cylindrical outer can (inner diameter 20.5 mm, wall thickness 0.25 mm) made of Fe—Ni-plated steel sheet and a disk-shaped simulated sealing plate (diameter 20.0 mm, thickness 1.0 mm) made of an aluminum alloy (5000 series). A grooved portion measuring 3.1 mm in the radial direction from the inner peripheral surface was formed in the outer can. Furthermore, an insulating film was formed on each main surface and side of the sealing plate using the following paint. The sealing plate with the insulating film formed thereon was inserted into the outer can and positioned on the grooved portion. The opening edge of the outer can was then bent radially inward and crimped against the sealing plate, thereby obtaining a simulated cell in which the opening of the outer can was sealed by the sealing plate. The thickness of the insulating film gradually decreased toward the film edge (coated edge) along the main surface of the sealing plate. The region where the thickness of the insulating film gradually decreases is in a range where the crimped portion of the outer can does not overlap.

[0051] [Insulating film forming paint] Filler: aluminum oxide with a D50 of 10 μm Filler content: 50% by volume Resin: UV-curable resin (urethane acrylate, R-1302XT manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) Initiator: Irgacure 184 Viscosity: 3000 cp (measured at 25°C and 20 rpm using a Brookfield viscometer) Coating conditions: applied to an average coating thickness of 100 μm, and a coating film of the desired thickness was created by scraping the coating surface with a slit of a certain height from the sealing plate surface Curing conditions: 365 nm UV-LED, 600 mJ / cm ２

[0052] The insulating performance and sealing performance of the above-mentioned simulated cell were evaluated by the following methods. The surface roughness of the insulating film was also measured. The evaluation results are shown in Table 1 below, along with the D50 of the filler constituting the insulating film and the average thickness of the coating film. The D50 of the filler, the average thickness of the coating film, and the surface roughness of the insulating film were measured by the above-mentioned methods.

[0053] [Evaluation of Insulation Performance] The following measuring device was used to check for continuity between the outer can and the sealing plate of the simulated cell, and simulated cells for which continuity was confirmed were rated as NG. Measuring device: Resistance meter RM3544 manufactured by Hioki E.E. Measuring current: [30 mΩ range] DC 300 mA to [3 MΩ range] DC 500 nA Open terminal voltage: DC 5.5 V max

[0054] [Evaluation of sealing performance] A through-hole formed in the bottom of the exterior can of a simulated cell was placed over the hole in the partition plate that separated the two sealed spaces (upper space and lower space), and the gap between the outer surface of the exterior can and the hole in the partition plate was sealed with a filler. In this state, helium was filled into the lower space, and the helium concentration leaking into the upper space was measured with a detector. Measuring device: Helium leak detector HELIOT900 manufactured by ULVAC. Minimum required level: 1.0 x E －６ [Pa·m ３ / sec] Excellent level: 1.0 x E －９ [Pa·m ３ / sec] Excellent level sealing performance is referred to as "sealability B" in Tables 2 and 5 described below. In Table 2, the minimum required level of sealing performance is referred to as "sealability A" to distinguish it from sealability B. Unless otherwise specified, sealing performance is evaluated based on whether or not it satisfies the minimum required level (sealability A).

[0055] Examples 2 and 3, Comparative Examples 13 to 15 Insulating films were formed on each main surface of a sealing plate in the same manner as in Example 1, except that aluminum oxide having a D50 of 50 μm or 100 μm as shown in Table 1 was used as the filler constituting the insulating film instead of aluminum oxide having a D50 of 10 μm, and simulated cells were fabricated using the resulting sealing plates.

[0056] Comparative Examples 1 to 6 Insulating films were formed on each main surface of a sealing plate in the same manner as in Examples 1 to 3 and Comparative Examples 13 to 15, except that the amount of paint applied was adjusted so that the average coating thickness was 5 μm, and simulated cells were produced using the sealing plates.

[0057] Comparative Examples 7 to 12 Insulating films were formed on each main surface of a sealing plate in the same manner as in Examples 1 to 3 and Comparative Examples 13 to 15, except that the amount of paint applied was adjusted so that the average coating thickness was 50 μm, and simulated cells were produced using the sealing plates.

[0058] Examples 4 to 6 and Comparative Examples 16 to 18 Insulating films were formed on each main surface of a sealing plate in the same manner as in Examples 1 to 3 and Comparative Examples 13 to 15, respectively, except that the amount of paint applied was adjusted so that the average coating thickness was 150 μm, and simulated cells were produced using the sealing plates.

[0059] Examples 7 to 10, Comparative Examples 19 and 20 Insulating films were formed on each main surface of a sealing plate in the same manner as in Examples 1 to 3 and Comparative Examples 13 to 15, respectively, except that the amount of paint applied was adjusted so that the average coating thickness was 300 μm, and simulated cells were produced using the sealing plates.

[0060]

[0061] As shown in Table 1, all of the simulated cells of the Examples exhibited both excellent insulating and sealing performance, and maintained good insulating performance even when heated to a high temperature of 600°C. In contrast, the simulated cells of the Comparative Examples were unable to maintain the desired insulating or sealing performance, or both. Furthermore, all of the simulated cells of the Examples had an insulating film surface roughness of 50 μm or less, whereas the simulated cells of Comparative Examples 5, 6, 12, 15, and 18 had a surface roughness of 100 μm or more. It is believed that the surface roughness of the insulating film significantly affects sealing performance.

[0062] The insulating film of the example is composed of a filler and resin that are highly durable and heat-resistant, and therefore, by using this insulating film, it is possible to maintain excellent sealing and insulating performance for a long period of time. Furthermore, since the insulating film is thinner than conventional gaskets, using the insulating film can improve the volumetric energy density of cylindrical batteries. Furthermore, in cylindrical batteries using conventional gaskets, when abnormal heat generation occurs, the gasket softens, reducing the fixing strength of the sealing plate, and the sealing plate itself is expected to pop out as the internal pressure of the battery increases. However, the insulating film of the example can address this issue.

[0063] Examples 11 and 12, Comparative Examples 21 and 22 Insulating films were formed on each main surface of a sealing plate in the same manner as in Example 2, except that the compounding ratio of the filler and UV-curable resin constituting the insulating film was adjusted to change the filler content in the insulating film to the value shown in Table 2. Simulation cells were fabricated using the resulting sealing plates. Furthermore, the insulation performance and sealing performance of each simulation cell were evaluated in a room temperature environment in the same manner as in Example 2. The evaluation results, along with the volume ratio of the filler to the resin, are shown in Table 2.

[0064]

[0065] As shown in Table 2, when the filler content in the insulating film is 10% by volume or more and 90% by volume or less, both excellent insulating performance and sealing performance can be achieved. However, when the filler content is 90% by volume (Example 12), although sealing performance A is fully satisfied, a tendency for sealing performance B to decrease was confirmed. As described above, the filler content is preferably 80% by volume or less, and more preferably 60% by volume or less, relative to the total volume of the insulating film.

[0066] Example 13 An insulating film was formed on each main surface of a sealing plate in the same manner as in Example 2, except that a fluororesin (PVdF) was used instead of a UV-curable resin as the resin constituting the insulating film, and a simulated cell was fabricated using the resulting sealing plate. Furthermore, the insulating performance and sealing performance were evaluated in the same manner as in Example 2. The evaluation results are shown in Table 3, along with the type of resin constituting the insulating film.

[0067]

[0068] As shown in Table 3, excellent insulating and sealing performance can be ensured even when a fluororesin is used as the resin constituting the insulating film. However, by using a UV-curable resin, the drying process of the coating film, which is necessary when a fluororesin is used, becomes unnecessary, and this can lead to, for example, a reduction in manufacturing time, a reduction in environmental load, and a reduction in manufacturing costs.

[0069] Example 14 A simulated cell was fabricated in the same manner as in Example 2, except that a simulated sealing plate with a diameter of 20.4 mm was used, and its insulating performance in a room temperature environment was evaluated. Note that, like the sealing plate of Example 2, the side surface of the sealing plate of Example 14 was coated with an insulating film.

[0070] Example 15 A simulated cell was fabricated using a simulated sealing plate having a diameter of 20.4 mm in the same manner as in Example 14, except that an insulating film was formed only on each main surface of the sealing plate and not on the side surfaces, and insulation performance in a room temperature environment was evaluated. The evaluation results, along with the presence or absence of an insulating film on the side surfaces of the sealing plate (side coating), are shown in Table 4.

[0071]

[0072] As shown in Table 4, when the clearance between the inner peripheral surface of the outer can and the side surface of the sealing plate is small, in the simulated cell of Example 15, in which no insulating film is present on the side surface of the sealing plate, electrical conduction between the outer can and the sealing plate is possible. On the other hand, if an insulating film (side surface coating) is provided on the side surface of the sealing plate, as in Example 14, electrical conduction between the outer can and the sealing body is reliably prevented even if the clearance is small. Note that if the clearance is sufficient (for example, about 0.5 mm), the insulating film side surface coating is not necessary.

[0073] Example 16 A simulated cell was fabricated in the same manner as in Example 2, except that the viscosity of the insulating film-forming paint was changed to 7000 cp (25° C.), and the insulating performance was evaluated in a room temperature environment. In this case, a protrusion that was thicker than the other parts was present at the film edge (coating edge) in the direction along the main surface of the sealing plate.

[0074]

[0075] As shown in Table 5, when there was a protrusion at the coating edge of the insulating film (Example 16), sealing performance A was fully satisfied, but a tendency for sealing performance B to decrease was confirmed. On the other hand, when the thickness of the coating edge gradually decreased (Example 2), excellent evaluation results were also obtained for sealing performance B.

[0076] The above-described embodiments can be modified in design without departing from the scope of the present disclosure. For example, in the above-described embodiments, an insulating film is formed on the sealing plate. However, it is also possible to form an insulating film on the inner circumferential surface of the outer can, or to form insulating films on both the sealing plate and the outer can. However, from the viewpoints of process control, product stability, and the like, it is preferable to form an insulating film only on the sealing plate, as in the above-described embodiments.

[0077] The present disclosure is further described by the following embodiments. Configuration 1: A sealed battery including a battery case, the sealed battery including an insulating film disposed between a main body and a terminal portion constituting the battery case, the insulating film being a coating film containing a filler having a volumetric median diameter of 10 μm or more and a resin forming a film structure, the insulating film having an adhesive strength of 100 gf or more to the main body or the terminal portion, the average thickness of the resin portion of the insulating film being 100 μm or more, the volumetric median diameter of the filler being equal to or less than the average thickness of the resin portion of the insulating film, and the content of the filler in the insulating film being 10% by volume or more and 90% by volume or less. Configuration 2: The sealed battery according to Configuration 1, wherein the ratio of the volumetric median diameter of the filler to the average thickness of the resin portion of the insulating film is 0.3 to 1.0. Configuration 3: The sealed battery according to Configuration 1 or 2, wherein the thickness of the insulating film gradually decreases toward the film end. Configuration 4: The sealed battery according to any one of Configurations 1 to 3, wherein the battery case includes a cylindrical outer can with a bottom and a sealing plate disposed at the opening of the outer can, and the insulating film is bonded to the peripheral edges of the first and second main surfaces of the sealing plate. Configuration 5: The sealed battery according to Configuration 4, wherein the insulating film is further bonded to the side surface of the sealing plate. Configuration 6: The sealed battery according to Configuration 4 or 5, wherein the insulating film is disposed adjacent to the inner surface of the outer can. Configuration 7: The sealed battery according to Configuration 6, wherein the thickness of the insulating film gradually decreases toward the film edge in a direction along the first and second main surfaces of the sealing plate. Configuration 8: The sealed battery according to claim 7, wherein the region where the thickness of the insulating film gradually decreases toward the film edge is formed on the first main surface of the sealing plate in a portion that does not overlap with the radially inner edge of the portion that contacts the edge of the opening of the outer can. Configuration 9: The sealed battery according to any one of Configurations 1 to 8, wherein the melting point of the filler is 300°C or higher. Aspect 10: The sealed battery of any one of Aspects 1 to 9, wherein the resin is an ultraviolet curable resin. Aspect 11: The sealed battery of Aspect 10, wherein the ultraviolet curable resin is at least one selected from the group consisting of urethane acrylate, epoxy acrylate, acrylic acrylate, polyester acrylate, and vinyl ester resin.Configuration 12: The sealed battery of any one of Configurations 1 to 9, wherein the resin is at least one selected from polyester, epoxy resin, acrylic resin, fluororesin, silicone resin, polyamide, polyimide, polyamideimide, polyetherimide, and polyphenylene sulfide.

[0078] REFERENCE SIGNS LIST 10 Cylindrical battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 16 Outer can, 17 Sealing plate, 17a First main surface, 17b Second main surface, 17c Side surface, 18, 19 Lower insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 22 Grooved portion, 23 Internal terminal plate, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cap, 28 Crimping portion, 30 Insulating film, 31 Filler, 32 Resin

Claims

1. A sealed battery having a battery case, comprising an insulating film disposed between a main body and a terminal that constitute the battery case, wherein the insulating film is a coating film containing a filler having a volumetric median diameter of 10 μm or more and a resin that forms a film structure, and wherein the adhesive strength to the main body or the terminal is 100 gf or more, wherein the average thickness of the resin portion of the insulating film is 100 μm or more, wherein the volumetric median diameter of the filler is equal to or less than the average thickness of the resin portion of the insulating film, and wherein the content of the filler in the insulating film is 10% by volume or more and 90% by volume or less.

2. The sealed battery according to claim 1, wherein the ratio of the volumetric median diameter of the filler to the average thickness of the resin portion of the insulating film is 0.3 or more and 1.0 or less.

3. The sealed battery according to claim 1 or 2, wherein the thickness of the insulating film gradually decreases toward the film ends.

4. The sealed battery according to claim 1 or 2, wherein the battery case includes a cylindrical outer can with a bottom and a sealing plate placed at the opening of the outer can, and the insulating film is bonded to the peripheral edges of the first and second main surfaces of the sealing plate.

5. The sealed battery according to claim 4, wherein the insulating film is further adhered to a side surface of the sealing plate.

6. The sealed battery according to claim 4, wherein the insulating film is disposed adjacent to the inner surface of the outer can.

7. The sealed battery according to claim 4, wherein the thickness of the insulating film gradually decreases toward the film ends in a direction along the first and second main surfaces of the sealing plate.

8. A sealed battery as described in claim 7, wherein the region in which the thickness of the insulating film gradually decreases toward the film end is formed in a portion on the first main surface of the sealing plate that does not overlap with the radially inner edge of the portion that contacts the opening edge of the outer can.

9. The sealed battery according to claim 1 or 2, wherein the melting point of the filler is 300°C or higher.

10. The sealed battery according to claim 1 or 2, wherein the resin is an ultraviolet curing resin.

11. The sealed battery according to claim 10, wherein the ultraviolet curable resin is at least one selected from the group consisting of urethane acrylate, epoxy acrylate, acrylic acrylate, polyester acrylate, and vinyl ester resin.

12. The sealed battery according to claim 1 or 2, wherein the resin is at least one selected from polyester, epoxy resin, acrylic resin, fluororesin, silicone resin, polyamide, polyimide, polyamideimide, polyetherimide, and polyphenylene sulfide.

Images