Method for manufacturing a flame-retardant structure

Abstract

To provide a fire-proof structure which enhances joint strength between a battery case and a heat insulation material in addition to more excellent heat insulation effect and fire-proof effect, suffers less aging deterioration of the joint strength and is also excellent in reliability, and is also excellent in followability to the internal shape of the battery case.SOLUTION: A fire-proof structure 1 is composed of a metal substrate 20 and a heat insulation material 10 containing inorganic fibers or infusibilized fibers, and in a joint layer 30 obtained by joining the metal substrate 20 and the heat insulation material 10, the formation material of the metal substrate 20 enters into a gap of the formation material of the heat insulation material 10 and the formation materials are integrated. The fire-proof structure 1 is obtained by using the heat insulation material 10 as an insert member, and casting the formation material of the metal substrate 20. A battery module 100 stores a storage battery 110, and a battery case which stores the storage battery 110 and where at least one of a top lid, a side wall and a bottom wall is the fire-proof structure 1.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fire-resistant structure, a method for manufacturing the same, and a battery package equipped with the fire-resistant structure. [Background technology]

[0002] In recent years, in order to protect the environment, lithium-ion secondary batteries have been used in electric vehicles, etc. However, because lithium-ion secondary batteries use an organic electrolyte, there is a risk of fire if they ignite during thermal runaway, causing damage to the battery pack.

[0003] As a countermeasure, for example, Patent Document 1 proposes joining a multi-layer heat insulating element for thermal insulation to the canopy of the housing that accommodates the battery. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2021-507483 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in Patent Document 1, an adhesive is used to bond the multilayer insulating element to the housing canopy, etc. The adhesive deteriorates over time due to vibrations while the vehicle is running and repeated temperature changes inside the housing caused by charging and discharging the battery. When the adhesive strength decreases, partial peeling occurs, and there is a risk that gas or flames may enter the peeled area in the event of thermal runaway.

[0006] Furthermore, the use of adhesive requires adhesive application and curing processes, and the multi-layer insulation element must be attached to the housing in accordance with its internal shape, which reduces work efficiency. In particular, it is extremely difficult to attach the multi-layer insulation element to every corner of the bent portion of the housing.

[0007] On the other hand, as battery capacity increases, the number of stacks also increases, and the amount of organic electrolyte also increases, so there is a strong demand for safety measures in case the battery experiences thermal runaway.

[0008] Therefore, the present invention aims to provide a flame-resistant structure and a manufacturing method thereof, as well as a battery module, which not only have excellent insulating and flame-resistant effects, but also have increased bonding strength between the battery case and the insulating material, have little deterioration in bonding strength over time, are highly reliable, and are excellent in terms of conformability to the internal shape of the battery case. [Means for solving the problem]

[0009] The above object of the present invention is achieved by the following flameproof structure [1].

[0010] [1] A metal substrate and an insulating material containing inorganic fibers or infusible fibers, A flame-retardant structure in which, in a bonding layer formed by bonding the metal substrate and the insulating material, the material forming the metal substrate penetrates into gaps in the material forming the insulating material and integrates them.

[0011] Further, preferred embodiments of the present invention relating to the flame-proof structure relate to the following [2] to

[20] .

[0012] [2] The flame-retardant structure according to [1], wherein the metal substrate is at least one of the top, side wall, and bottom wall of the battery case. [3] The flame-retardant structure according to [1] or [2], characterized in that the base material of the metal substrate is at least one of iron, copper, aluminum, magnesium, zinc, nickel, titanium, and alloys thereof. [4] The flame-retardant structure according to [3], characterized in that the base material of the metal substrate is aluminum, magnesium, or an alloy thereof. [5] The flame-retardant structure according to any one of [1] to [4], characterized in that the inorganic fibers have first inorganic fibers and second inorganic fibers that differ from each other in at least one property selected from the group consisting of average fiber diameter, shape, and glass transition point. [6] The average fiber diameter of the first inorganic fibers is larger than the average fiber diameter of the second inorganic fibers; The flame-retardant structure according to [5], characterized in that the first inorganic fibers are linear or needle-like, and the second inorganic fibers are dendritic or crimped. [7] The first inorganic fiber is an amorphous fiber; the second inorganic fibers are at least one type of fibers selected from amorphous fibers and crystalline fibers having a glass transition temperature higher than that of the first inorganic fibers, The flame-retardant structure according to [5] or [6], wherein the average fiber diameter of the first inorganic fibers is larger than the average fiber diameter of the second inorganic fibers. [8] The flame-proof structure according to any one of [1] to [7], wherein the infusible fiber has a carbon content of 55 to 95 mass %. [9] The flame-proof structure according to any one of [1] to [8], wherein the infusible fibers are short fibers.

[10] The flame-proof structure according to any one of [1] to [9], wherein the infusible fibers have a fiber diameter of 1 to 30 μm.

[11] The flame-resistant structure according to any one of [1] to

[10] , wherein the heat insulating material contains organic fibers.

[12] The flame-retardant structure according to

[11] , wherein the organic fiber has a lower glass transition point than the base material of the metal substrate.

[13] The flame-resistant structure according to any one of [1] to

[12] , wherein the heat insulating material contains inorganic particles.

[14] The flame-retardant structure according to

[13] , wherein the inorganic particles include first inorganic particles and second inorganic particles having different average particle diameters.

[15] The flame-retardant structure according to

[14] , wherein the first inorganic particles are at least one selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles.

[16] The flame-retardant structure according to

[14] or

[15] , characterized in that the first inorganic particles are at least one type selected from nanoparticles, hollow particles, and porous particles.

[17] The flame-proof structure according to any one of

[14] to

[16] , characterized in that the first inorganic particles are at least one selected from oxide particles, carbide particles, nitride particles and inorganic hydrate particles.

[18] The flame-proof structure according to any one of

[14] to

[17] , wherein the second inorganic particles are metal oxide particles.

[19] The flame-retardant structure according to any one of [1] to

[18] , wherein the thickness of the bonding layer is 10 to 90% of the thickness of the flame-retardant structure.

[20] A flame-retardant structure described in any one of [1] to

[19] , characterized in that the bonding layer has a gradient structure in which the ratio (material forming the metal substrate / material forming the insulation) gradually decreases as the thickness of the insulation increases.

[0013] The above object of the present invention is also achieved by the following configuration

[21] relating to a method for manufacturing a flame-resistant structure.

[0014]

[21] A method for producing a flame-proof structure according to any one of [1] to

[20] , A method for manufacturing a flameproof structure, in which the heat insulating material is used as an insert member and a material for forming the metal substrate is cast.

[0015] Furthermore, the above object of the present invention is achieved by the following configuration

[22] relating to a battery module.

[0016]

[22] A battery module comprising: a storage battery; and a battery case that houses the storage battery and has at least one of a top cover, a side wall, and a bottom wall that is the flame-retardant structure described in any one of [1] to

[20] . [Effects of the Invention]

[0017] The flame-retardant structure of the present invention is formed by bonding a metal substrate and a thermal insulating material. Because the thermal insulating material contains inorganic fibers or infusible fibers, it has excellent thermal insulating and flame-retardant properties. Furthermore, because the material forming the metal substrate penetrates between the fibers of the thermal insulating material in the bonding layer between the metal substrate and the thermal insulating material, the bonding strength is stronger than when an adhesive is used, and it is less susceptible to deterioration over time, resulting in high reliability. Furthermore, because the structure can be manufactured by using the thermal insulating material as an insert member and casting the material forming the metal substrate, the manufacturing process is simple and the structure can easily conform to the internal shape of the battery case.

[0018] In the battery module of the present invention, the battery case that houses the storage battery is the flameproof structure of the present invention, so that even if a flame breaks out during thermal runaway, the fire can be more reliably prevented from spreading to the outside. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic diagram showing a cross section of a flame-proof structure according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing an embodiment of a battery module of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments described below, and can be implemented with any modifications within the scope of the gist of the present invention.

[0021] [Flame-retardant structure] <<1. First embodiment of flame-retardant structure>> The flame-proof structure of the present invention is formed by bonding a metal substrate and a heat insulating material, and in the first embodiment, the heat insulating material contains inorganic fibers.

[0022] <Metal base material> The metal substrate is, for example, a member that conventionally forms the housing of the battery case of a battery module.

[0023] Suitable metals for the base material include iron, copper, aluminum, magnesium, zinc, nickel, titanium, and alloys thereof. Among these, aluminum, magnesium, and alloys thereof are more preferred because they are inexpensive, lightweight, and have low melting points in consideration of the thermal influence on the materials forming the thermal insulation. These metals may also contain reinforcing fibers such as ceramic.

[0024] <Insulation material> (inorganic fiber) The inorganic fibers that form the thermal insulating material can be inorganic fibers that are commonly used in thermal insulating materials, but it is preferable to have first and second inorganic fibers that differ from each other in at least one property selected from the average fiber diameter, shape, and glass transition point. By containing two types of inorganic fibers that differ from each other in properties, the mechanical strength of the thermal insulating material and, when inorganic particles are contained, the retention of inorganic particles can be improved, as described below.

[0025] (Two types of inorganic fibers with different average fiber diameters and fiber shapes) When two types of inorganic fibers are contained, it is preferable that the average fiber diameter of the first inorganic fibers is larger than that of the second inorganic fibers, that the first inorganic fibers are linear or needle-like, and that the second inorganic fibers are dendritic or crimped. The first inorganic fibers with a larger average fiber diameter (large diameter) have the effect of improving the mechanical strength and shape retention of the thermal insulation material. The above effect can be achieved by making one of the two types of inorganic fibers, for example, the first inorganic fibers, larger in diameter than the second inorganic fibers. Because flame-retardant structures may be subjected to external impacts, the inclusion of the first inorganic fibers in the thermal insulation material improves impact resistance. Examples of external impacts include compressive force due to expansion of battery cells and wind pressure due to battery cell ignition.

[0026] In order to improve the mechanical strength and shape retention of the heat insulating material, it is particularly preferable that the first inorganic fibers are linear or needle-shaped. Note that linear or needle-shaped fibers refer to fibers having a crimp degree (described later), for example, of less than 10%, preferably 5% or less.

[0027] More specifically, in order to improve the mechanical strength and shape retention of the heat insulating material, the average fiber diameter of the first inorganic fibers is preferably 1 μm or more, more preferably 3 μm or more. If the first inorganic fibers are too thick, moldability and processability may be reduced, so the average fiber diameter of the first inorganic fibers is preferably 20 μm or less, more preferably 15 μm or less.

[0028] If the first inorganic fibers are too long, moldability and processability may decrease, so the fiber length is preferably 100 mm or less.Furthermore, if the first inorganic fibers are too short, shape retention and mechanical strength may decrease, so the fiber length is preferably 0.1 mm or more.

[0029] On the other hand, when organic fibers or inorganic particles are blended, the second inorganic fibers having a small average fiber diameter (thin diameter) have the effect of improving the retention of these and increasing the flexibility of the heat insulating material. Therefore, it is preferable that the second inorganic fibers have a smaller diameter than the first inorganic fibers.

[0030] More specifically, to improve the retention of organic fibers and inorganic particles, the second inorganic fibers are preferably flexible and easily deformable. Therefore, the second inorganic fibers, which are thin, preferably have an average fiber diameter of less than 1 μm, more preferably 0.1 μm or less. However, if they are too thin, they are prone to breakage, reducing their ability to retain organic fibers and inorganic particles. Furthermore, a large proportion of the fibers remain entangled in the insulating material without retaining the organic fibers and inorganic particles. This not only reduces the ability to retain the organic fibers and inorganic particles, but also leads to poor moldability and shape retention. Therefore, the average fiber diameter of the second inorganic fibers is preferably 1 nm or more, more preferably 10 nm or more.

[0031] If the second inorganic fibers are too long, moldability and shape retention will decrease, so the fiber length of the second inorganic fibers is preferably 0.1 mm or less.

[0032] The second inorganic fibers are preferably dendritic or crimped. Such a shape allows the second inorganic fibers to be well entangled with the organic fibers and inorganic particles, improving their ability to retain the organic fibers and inorganic particles. Furthermore, when the flame-retardant structure is subjected to pressure or wind pressure, the second inorganic fibers are prevented from sliding and moving, thereby improving the mechanical strength, particularly against external pressure and impact.

[0033] The term "dendritic" refers to a two-dimensionally or three-dimensionally branched structure, such as feather-like, tetrapod-like, radial, or three-dimensional mesh-like.

[0034] When the second inorganic fibers are dendritic, the average fiber diameter can be obtained by measuring the diameters of the trunk and branches at several points using an SEM and calculating the average value of these.

[0035] The crimped structure refers to a structure in which fibers are bent in various directions. One method for quantifying the crimped structure is to calculate the crimp degree from an electron microscope photograph, which can be calculated, for example, using the following formula: Crimp degree (%) = (fiber length - distance between fiber ends) / (fiber length) × 100 Here, both the fiber length and the distance between fiber ends are measured values ​​on an electron microscope photograph. In other words, they are the fiber length and the distance between fiber ends projected onto a two-dimensional plane, and are shorter than the actual values. Based on this formula, the crimp degree of the second inorganic fiber is preferably 10% or more, and more preferably 30% or more. If the crimp degree is low, the retention ability of the organic fibers and inorganic particles decreases, making it difficult to form entanglements (networks) between the second inorganic fibers and between the first inorganic fibers and the second inorganic fibers.

[0036] (Two types of inorganic fibers with different glass transition temperatures) When two types of inorganic fibers are contained, it is preferable that the first inorganic fiber is an amorphous fiber, and the second inorganic fiber is at least one type of fiber selected from an amorphous fiber having a glass transition point higher than that of the first inorganic fiber and a crystalline fiber.

[0037] The melting point of crystalline inorganic fibers is usually higher than the glass transition point of amorphous inorganic fibers. Therefore, when exposed to high temperatures, the surface of the first inorganic fibers softens before the second inorganic fibers, bonding the organic fibers and inorganic particles. Therefore, by incorporating the first inorganic fibers, the mechanical strength of the thermal insulation material can be improved.

[0038] Specifically, the first inorganic fiber is preferably an inorganic fiber having a melting point of less than 700°C, and many amorphous inorganic fibers can be used. Among them, a fiber containing SiO2 is preferable, and glass fiber is more preferable because it is inexpensive, easily available, and has excellent handleability.

[0039] As described above, the second inorganic fibers are at least one type of fibers selected from amorphous fibers and crystalline fibers having a glass transition temperature higher than that of the first inorganic fibers. Many crystalline inorganic fibers can be used as the second inorganic fibers.

[0040] If the second inorganic fiber is made of crystalline fiber or has a glass transition temperature higher than that of the first inorganic fiber, the second inorganic fiber will not melt or soften even if the first inorganic fiber softens when exposed to high temperatures, and therefore, when applied to, for example, a battery module, the second inorganic fiber will maintain its shape even if thermal runaway occurs.

[0041] Furthermore, if the second inorganic fibers do not melt or soften, minute spaces are maintained between the particles, between the particles and the fibers, and between the fibers, so that the heat insulating effect of the air is exerted.

[0042] When the second inorganic fiber is crystalline, specific examples that can be used include ceramic fibers such as silica fiber, alumina fiber, alumina silicate fiber, zirconia fiber, carbon fiber, soluble fiber, refractory ceramic fiber, aerogel composite, magnesium silicate fiber, alkaline earth silicate fiber, and potassium titanate fiber; glass fibers such as glass fiber and glass wool; and mineral fibers such as rock wool, basalt fiber, and wollastonite.

[0043] Furthermore, if the melting point exceeds 1000°C, the second inorganic fiber will not melt or soften and will be able to maintain its shape even if thermal runaway occurs in the battery cell, and therefore can be used favorably. Of the fibers listed as the second inorganic fiber, it is more preferable to use ceramic fibers such as silica fibers, alumina fibers, and alumina silicate fibers, as well as mineral fibers, and it is even more preferable to use fibers with a melting point exceeding 1000°C.

[0044] Furthermore, even if the second inorganic fibers are amorphous, they can be used as long as they have a higher glass transition temperature than the first inorganic fibers. For example, glass fibers having a higher glass transition temperature than the first inorganic fibers may be used as the second inorganic fibers.

[0045] As the second inorganic fiber, the various inorganic fibers exemplified above may be used alone or in combination of two or more kinds.

[0046] As described above, the first inorganic fibers have a lower glass transition point than the second inorganic fibers, and when exposed to high temperatures, the first inorganic fibers soften first, allowing the first inorganic fibers to bind organic fibers and inorganic particles. However, for example, if the second inorganic fibers are amorphous and have a smaller fiber diameter than the first inorganic fibers, and the glass transition points of the first and second inorganic fibers are close, the second inorganic fibers may soften first. Therefore, when the second inorganic fibers are amorphous, the glass transition point of the second inorganic fibers is preferably at least 100°C higher than the glass transition point of the first inorganic fibers, and more preferably at least 300°C higher.

[0047] The fiber length of the first inorganic fibers is preferably 100 mm or less, and more preferably 0.1 mm or more, and the fiber length of the second inorganic fibers is preferably 0.1 mm or less, for the reasons described above.

[0048] (Two types of inorganic fibers with different glass transition temperatures and average fiber diameters) When two types of inorganic fibers are contained, it is preferable that the first inorganic fibers are amorphous fibers, the second inorganic fibers are at least one type of fiber selected from amorphous fibers having a glass transition point higher than that of the first inorganic fibers and crystalline fibers, and the average fiber diameter of the first inorganic fibers is larger than the average fiber diameter of the second inorganic fibers.

[0049] As described above, it is preferable that the average fiber diameter of the first inorganic fibers be larger than that of the second inorganic fibers. It is also preferable that the thick first inorganic fibers be amorphous fibers, and the thin second inorganic fibers be at least one type of fiber selected from amorphous fibers and crystalline fibers having a higher glass transition point than the first inorganic fibers. This allows the first inorganic fibers to have a low glass transition point and soften quickly, forming a film and hardening as the temperature rises. On the other hand, if the thin second inorganic fibers are at least one type of fiber selected from amorphous fibers and crystalline fibers having a higher glass transition point than the first inorganic fibers, the thin second inorganic fibers remain in their fibrous form even when the temperature rises, thereby maintaining the structure of the thermal insulating material and preventing powder shedding.

[0050] Even in this case, the fiber length of the first inorganic fibers is preferably 100 mm or less, and more preferably 0.1 mm or more. The fiber length of the second inorganic fibers is preferably 0.1 mm or less. The reasons for this are as described above.

[0051] (Contents of first inorganic fibers and second inorganic fibers) When two types of inorganic fibers are contained, the content of the first inorganic fiber is preferably 3% by mass or more and 30% by mass or less relative to the total mass of the insulating material, and the content of the second inorganic fiber is preferably 3% by mass or more and 30% by mass or less relative to the total mass of the insulating material.

[0052] The content of the first inorganic fibers is more preferably 5% by mass to 15% by mass, both inclusive, of the total mass of the thermal insulation material, and the content of the second inorganic fibers is more preferably 5% by mass to 15% by mass, both inclusive, of the total mass of the thermal insulation material. By setting the contents in this range, the shape retention, compression force resistance, and wind pressure resistance provided by the first inorganic fibers, and the inorganic particle retention ability provided by the second inorganic fibers are exhibited in a balanced manner.

[0053] (Other compounding materials) The heat insulating material may contain different inorganic fibers in addition to the first and second inorganic fibers, and may also contain an organic binder, organic fibers, and inorganic particles.

[0054] (resin binder) The inorganic fibers can also be bound by a resin binder. The resin binder is not particularly limited as long as it has a glass transition point lower than that of the organic fibers described below. For example, a resin binder 9 containing at least one resin selected from styrene-butadiene resin, acrylic resin, silicon-acrylic resin, and styrene resin can be used.

[0055] The glass transition point of the resin binder is not particularly specified, but is preferably -10°C or higher. If the glass transition point of the resin binder 9 is room temperature or higher, the strength of the insulating material can be further improved when the insulating material containing the resin binder is used at room temperature. Therefore, the glass transition point of the resin binder is more preferably 20°C or higher, even more preferably 30°C or higher, even more preferably 50°C or higher, and particularly preferably 60°C or higher.

[0056] The content of the resin binder is preferably 0.5% by mass or more, more preferably 1% by mass or more, relative to the total mass of the heat insulating material, and is preferably 20% by mass or less, more preferably 10% by mass or less.

[0057] (organic fiber) In addition to the inorganic fibers, organic fibers may be contained, such as at least one selected from polyvinyl alcohol (PVA) fibers, polyethylene fibers, nylon fibers, polyurethane fibers, and ethylene-vinyl alcohol copolymer fibers.

[0058] The heat insulating material can be manufactured by a papermaking method, but since it is difficult to raise the heating temperature above 250°C, the glass transition point of the organic fiber is preferably 250°C or lower, and more preferably 200°C or lower.

[0059] Although the lower limit of the glass transition point of the organic fiber is not particularly limited, if the difference between the glass transition point of the organic fiber and that of the resin binder is 10°C or more, the resin binder will solidify after the organic fiber, which was in a semi-molten state, has completely solidified during the cooling step during production, and therefore the skeleton reinforcing effect of the resin binder can be sufficiently obtained. Therefore, the difference between the glass transition point of the resin binder and that of the organic fiber is preferably 10°C or more, and more preferably 30°C or more.

[0060] On the other hand, if the difference in glass transition point between the two is 130°C or less, the time from when the organic fibers completely solidify until the resin binder starts to solidify can be appropriately adjusted, and the resin binder solidifies while remaining well dispersed, thereby achieving an even greater skeleton reinforcement effect. Therefore, the difference between the glass transition point of the resin binder and the glass transition point of the organic fibers is preferably 130°C or less, more preferably 120°C or less, even more preferably 100°C or less, even more preferably 80°C or less, and particularly preferably 70°C or less.

[0061] Two or more types of organic fibers may also be included, in which case at least one type of organic fiber should act as the skeleton, i.e., should have a glass transition point higher than that of the resin binder. As mentioned above, the difference between the glass transition point of the resin binder and that of the at least one organic fiber is preferably 10°C or more, more preferably 30°C or more, and preferably 130°C or less, more preferably 120°C or less, even more preferably 100°C or less, even more preferably 80°C or less, and particularly preferably 70°C or less.

[0062] By appropriately controlling the contents of the organic fibers and the resin binder, the organic fibers can fully function as a skeleton, and the resin binder can fully reinforce the skeleton. The organic fiber content is preferably 0.5% by mass or more, more preferably 1% by mass or more, based on the total mass of the insulating material. It is also preferably 12% by mass or less, more preferably 8% by mass or less. When the insulating material contains multiple organic fibers with glass transition points higher than that of the resin binder, it is preferable that the total amount of these multiple organic fibers be within the above-mentioned range of the organic fiber content.

[0063] As described above, when two or more types of organic fibers are contained, it is sufficient that at least one of the organic fibers has a glass transition point higher than the glass transition point of the resin binder. However, it is more preferable that the other organic fibers contain crystalline organic fibers that do not have a glass transition point.

[0064] Although crystalline organic fibers that do not have a glass transition point can be contained, these crystalline organic fibers do not have a softening point, and therefore the strength of the entire insulating material can be maintained even when exposed to high temperatures that soften the organic fibers that form the skeleton. Furthermore, by containing crystalline organic fibers, these organic fibers also function as the skeleton of the insulating material at room temperature. Therefore, the flexibility and handling of the heat insulating material can be improved.

[0065] An example of the crystalline organic fiber is polyester (PET) fiber.

[0066] In addition, when a papermaking method is used to manufacture a heat insulating material, it is preferable to use water as a dispersion liquid, and it is preferable that the organic fiber has low solubility in water. The "water dissolution temperature" can be used as an index of solubility in water, and the water dissolution temperature of the organic fiber is preferably 60°C or higher, more preferably 70°C or higher, and even more preferably 80°C or higher.

[0067] The fiber length of the organic fibers is not particularly limited, but from the viewpoint of ensuring moldability and processability, the average fiber length is preferably 10 mm or less, while from the viewpoint of making the organic fibers function as a skeleton and ensuring the compressive strength of the thermal insulation material, the average fiber length is preferably 0.5 mm or more.

[0068] (Inorganic particles) Furthermore, inorganic particles may also be contained. If the average secondary particle diameter of the inorganic particles is 0.01 μm or more, they are easily available and an increase in production costs can be suppressed. Furthermore, if the average secondary particle diameter is 200 μm or less, the desired heat insulating effect can be obtained. Therefore, the average secondary particle diameter of the inorganic particles is preferably 0.01 μm or more and 200 μm or less, and more preferably 0.05 μm or more and 100 μm or less.

[0069] The inorganic particles may be a single inorganic particle or a combination of two or more inorganic particles (first inorganic particles and second inorganic particles). From the viewpoint of the heat transfer suppression effect, the first inorganic particles and the second inorganic particles are preferably particles made of at least one inorganic material selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles, and more preferably oxide particles. The shapes of the first inorganic particles and the second inorganic particles are not particularly limited, but preferably include at least one selected from nanoparticles, hollow particles, and porous particles. Specific examples include silica nanoparticles, metal oxide particles, inorganic balloons such as microporous particles and hollow silica particles, particles made of thermally expandable inorganic materials, and particles made of hydrous porous bodies.

[0070] In addition, when two or more inorganic particles with different heat transfer suppression effects are used in combination, multi-stage cooling is possible, and the endothermic effect can be exerted over a wider temperature range. Specifically, it is preferable to use a mixture of large-diameter particles and small-diameter particles. For example, when nanoparticles are used as one of the inorganic particles, it is preferable to include inorganic particles made of a metal oxide as the other inorganic particle. Hereinafter, the inorganic particles will be described in more detail, with the small-diameter inorganic particles referred to as the first inorganic particles and the large-diameter inorganic particles referred to as the second inorganic particles.

[0071] (First inorganic particles) (oxide particles) The first inorganic particles are preferably oxide particles. Oxide particles have a high refractive index and a strong effect of diffusely reflecting light, and therefore can suppress radiant heat transfer, particularly in high-temperature regions such as those experiencing abnormal heat generation. As the oxide particles, at least one type of particle selected from silica, titania, zirconia, zircon, barium titanate, zinc oxide, and alumina can be used. In particular, silica is a component with high heat insulating properties, and titania is a component with a higher refractive index than other metal oxides, and is highly effective in diffusely reflecting light and blocking radiant heat in high-temperature regions of 500°C or higher. Therefore, it is most preferable to use silica and titania as the oxide particles.

[0072] Because the particle size of the oxide particles can affect their ability to reflect radiant heat, limiting the average primary particle size to a specific range can achieve even higher thermal insulation. That is, if the average primary particle size of the oxide particles is 0.001 μm or more, the particles are sufficiently larger than the wavelength of light that contributes to heating and efficiently diffusely reflect light, thereby suppressing radiant heat transfer within the heat-transfer-suppressing sheet in high-temperature regions of 500°C or higher, thereby further improving thermal insulation. On the other hand, if the average primary particle size of the oxide particles is 50 μm or less, the number and number of contact points between particles do not increase even when compressed, making it difficult to form paths for conductive heat transfer. This reduces the impact on thermal insulation, particularly in normal temperature regions where conductive heat transfer is dominant.

[0073] In the present invention, the average primary particle size can be determined by observing particles under a microscope, comparing with a standard scale, and taking the average of any 10 particles.

[0074] (nanoparticles) Nanoparticles are preferred as the first inorganic particles, because nanoparticles have a low density, which suppresses conductive heat transfer, and because the voids are finely dispersed, they provide excellent heat insulation by suppressing convective heat transfer. Therefore, it is preferable to use nanoparticles because they can suppress heat transfer between adjacent nanoparticles when the battery is used at normal room temperature.

[0075] Nanoparticles refer to particles on the order of nanometers that are spherical or nearly spherical and have an average primary particle diameter of less than 1 μm.

[0076] Furthermore, if nanoparticles with a small average primary particle size are used as oxide particles, the increase in conductive heat transfer of the insulating material can be suppressed even if the internal density of the insulating material increases due to expansion caused by thermal runaway of the battery cell. This is thought to be because nanoparticles are prone to forming fine voids between particles due to electrostatic repulsion, and because their bulk density is low, the particles are packed together to provide cushioning.

[0077] When nanoparticles are used as the first inorganic particles, there are no particular limitations on the material as long as they comply with the definition of nanoparticles. For example, silica nanoparticles are a material with high heat insulating properties, and the contact points between particles are small, so the amount of heat conducted by silica nanoparticles is smaller than when silica particles with a large particle diameter are used. Furthermore, commonly available silica nanoparticles have a bulk density of 0.1 (g / cm 3 ), for example, even if a large compressive stress is applied to the heat insulating material, the size (area) and number of contact points between the silica nanoparticles do not increase significantly, and heat insulating properties can be maintained. Therefore, it is preferable to use silica nanoparticles as the nanoparticles. As the silica nanoparticles, wet silica, dry silica, aerogel, etc. can be used.

[0078] Limiting the average primary particle size of the nanoparticles to a predetermined range can achieve even higher thermal insulation. That is, when the average primary particle size of the nanoparticles is 1 nm or more and 100 nm or less, convective and conductive heat transfer within the thermal insulation material can be suppressed, particularly in the temperature range below 500°C, thereby further improving thermal insulation. Furthermore, even when compressive stress is applied, the voids remaining between the nanoparticles and the contact points between many particles suppress conductive heat transfer, thereby maintaining the thermal insulation properties of the heat-transfer-suppressing sheet. Furthermore, the average primary particle size of the nanoparticles is more preferably 2 nm or more, and even more preferably 3 nm or more. Meanwhile, the average primary particle size of the nanoparticles is more preferably 50 nm or less, and even more preferably 10 nm or less.

[0079] (Inorganic hydrate particles) When inorganic hydrate particles receive heat from a heating element and reach a temperature above their thermal decomposition initiation temperature, they undergo thermal decomposition and release their own water of crystallization, lowering the temperature of the heating element and its surroundings, thereby exhibiting a so-called "endothermic effect." After releasing the water of crystallization, the particles become porous, and the numerous air holes provide thermal insulation.

[0080] Specific examples of inorganic hydrates include aluminum hydroxide (Al(OH)3), magnesium hydroxide (Mg(OH)2), calcium hydroxide (Ca(OH)2), zinc hydroxide (Zn(OH)2), iron hydroxide (Fe(OH)2), manganese hydroxide (Mn(OH)2), zirconium hydroxide (Zr(OH)2), and gallium hydroxide (Ga(OH)3).

[0081] For example, aluminum hydroxide has about 35% water of crystallization, and as shown in the following formula, it thermally decomposes, releasing the water of crystallization and exhibiting an endothermic effect. After releasing the water of crystallization, it becomes a porous alumina (Al2O3) and functions as a heat insulating material. 2Al(OH)3 → Al2O3 + 3H2O

[0082] In a battery cell that has experienced thermal runaway, the temperature rises sharply to over 200°C and continues to rise to around 700°C. Therefore, it is preferable that the inorganic particles be made of an inorganic hydrate whose thermal decomposition temperature is 200°C or higher.

[0083] The thermal decomposition starting temperatures of the inorganic hydrates listed above are approximately 200°C for aluminum hydroxide, approximately 330°C for magnesium hydroxide, approximately 580°C for calcium hydroxide, approximately 200°C for zinc hydroxide, approximately 350°C for iron hydroxide, approximately 300°C for manganese hydroxide, approximately 300°C for zirconium hydroxide, and approximately 300°C for gallium hydroxide.All of these temperatures roughly overlap with the temperature range in which a battery cell experiencing thermal runaway experiences a sudden rise in temperature, and can efficiently suppress temperature rise, making these inorganic hydrates preferable.

[0084] Furthermore, if the average particle size of the inorganic hydrate particles is too large, it takes a certain amount of time for the inorganic hydrate particles near the center of the thermal insulating material to reach their thermal decomposition temperature, and the inorganic hydrate particles near the center of the thermal insulating material may not be completely thermally decomposed. Therefore, the average secondary particle size of the inorganic hydrate particles is preferably 0.01 μm or more and 200 μm or less, and more preferably 0.05 μm or more and 100 μm or less.

[0085] (Particles made of thermally expandable inorganic material) Examples of thermally expandable inorganic materials include vermiculite, bentonite, mica, and perlite.

[0086] (Particles made of hydrous porous material) Specific examples of the hydrous porous material include zeolite, kaolinite, montmorillonite, acid clay, diatomaceous earth, wet silica, dry silica, aerogel, mica, and vermiculite.

[0087] (inorganic balloons) When inorganic balloons are contained, convective or conductive heat transfer within the heat insulating material can be suppressed in the temperature range below 500°C, and the heat insulating properties of the heat insulating material can be further improved.

[0088] As the inorganic balloons, at least one selected from shirasu balloons, silica balloons, fly ash balloons, barite balloons, and glass balloons can be used.

[0089] The content of the inorganic balloons is preferably 60 mass % or less based on the total mass of the heat insulating material.

[0090] The average particle size of the inorganic balloons is preferably 1 μm or more and 100 μm or less.

[0091] (Second inorganic particles) The second inorganic particles are not particularly limited as long as they are different from the first inorganic particles in terms of material, particle size, etc. Examples of the second inorganic particles that can be used include oxide particles, carbide particles, nitride particles, inorganic hydrate particles, silica nanoparticles, metal oxide particles, inorganic balloons such as microporous particles and hollow silica particles, particles made of a thermally expandable inorganic material, and particles made of a hydrous porous body, the details of which are as described above.

[0092] Nanoparticles have extremely low conductive heat transfer and can maintain excellent heat insulation even when compressive stress is applied to the heat transfer-suppressing sheet. Metal oxide particles such as titania are also effective at blocking radiant heat. Furthermore, when large-diameter inorganic particles and small-diameter inorganic particles are used, the small-diameter inorganic particles penetrate into the gaps between the large-diameter inorganic particles, resulting in a denser structure and improved heat transfer suppression. Therefore, when nanoparticles are used as the first inorganic particles, it is preferable to further include second inorganic particles made of a metal oxide that are larger in diameter than the first inorganic particles in the heat insulating material.

[0093] Examples of metal oxides include silicon oxide, titanium oxide, aluminum oxide, barium titanate, zinc oxide, zircon, zirconium oxide, etc. In particular, titanium oxide (titania) is a component with a higher refractive index than other metal oxides, and is highly effective in scattering light and blocking radiant heat in a high temperature range of 500°C or higher, so titania is most preferably used.

[0094] When the average primary particle size of the second inorganic particles is 1 μm or more and 50 μm or less, radiant heat transfer can be efficiently suppressed in a high temperature range of 500° C. or more. The average primary particle size of the second inorganic particles is more preferably 5 μm or more and 30 μm or less, and most preferably 10 μm or less.

[0095] (Insulating material manufacturing method) The materials for forming the insulating material are as described above, but it is preferable to manufacture the insulating material by a papermaking method, in which inorganic fibers and other compounding materials, which are the materials for forming the insulating material, are dispersed in water, and the dispersion is dehydrated, molded, and dried to produce the insulating material.

[0096] <Method of manufacturing flame-retardant structure and bonding layer> The flame-retardant structure is manufactured by casting a metal substrate material using an insulating material as an insert member. Specifically, a mold is opened, the insulating material is attached to a predetermined location, and the mold is closed. The metal substrate material is then poured into the mold, filled, and solidified. FIG. 1 shows a schematic cross-section of the resulting flame-retardant structure 1. As shown in the figure, in the surface layer of the insulating material 10, the molten material of the metal substrate 20 penetrates and hardens (integrates) into gaps among the inorganic fibers (here, first inorganic fibers 11a and second inorganic fibers 11b), organic fibers 12, and inorganic particles (here, first inorganic particles 13a and second inorganic particles 13b). This hardened (integrated) portion of the metal substrate 20 material is the bonding layer 30.

[0097] In addition, if the organic fibers 12 or the insulating material 10 contain an organic binder, the organic binder will be burned away by high temperatures when it comes into contact with the molten material forming the metal substrate 20, but the material forming the metal substrate 20 will penetrate between the fibers and function as a substitute for the organic fibers 12 and the organic binder, thereby maintaining the shape of the insulating material 10 as a whole.

[0098] (Joining layer) The bonding layer 30 has a gradient structure in which the ratio (material forming the metal base material / material forming the thermal insulating material) gradually decreases as the thickness of the thermal insulating material 10 increases. Furthermore, if the thickness of the bonding layer 30 is 10 to 90% of the thickness of the flame-retardant structure 1, sufficient bonding strength can be obtained.

[0099] <<2. Embodiment 2 of the Flameproof Structure>> In the present embodiment 2, the heat insulating material contains infusible fibers. The metal substrate is the same as that in the embodiment 1, and therefore a description thereof will be omitted.

[0100] <Insulation material> (infusible fiber) Examples of infusible fibers include fibers obtained by infusibility treatment of thermoplastic resins such as polyacrylonitrile, cellulose, pitch, etc. Infusible fibers are, for example, fibers that have been infusible treated, and examples of infusible treatment include a method of crosslinking by irradiation with radiation or electron beams, and a method of exposing the fibers to high temperatures in oxygen or water vapor to make them infusible by the action of oxygen.

[0101] (carbon content) The infusible fiber preferably has a carbon content of 55 to 95% by mass. When the carbon content is 55% by mass or more, weight loss due to thermal decomposition has already progressed, so shrinkage due to thermal decomposition is minimal, and even if directly exposed to flames during thermal runaway, the fiber retains its original shape and maintains its thermal insulation properties. When the carbon content is 95% by mass or less, components other than carbon are eliminated and the fiber changes to a structure consisting only of carbon, causing an endothermic reaction, which can delay the time it takes for heat to reach the back surface of the flame-retardant structure.

[0102] The lower limit of the carbon content is preferably 60% by mass or more, and the upper limit of the carbon content is preferably 90% by mass or less, and more preferably 85% by mass or less.

[0103] The carbon content can be adjusted by heat treatment. For example, heat treatment in air or oxygen at a temperature in the range of 150 to 300°C can further promote infusibility and remove components other than carbon, thereby increasing the carbon content. For example, heat treatment at a temperature in the range of 300 to 1000°C can promote the formation of condensed polycyclic aromatic structures and generate decomposition gases, thereby increasing the carbon content.

[0104] The infusible fibers are not limited to fibers that have been infusible from thermoplastic fibers, and may be inorganic fibers as long as they have a carbon content within the above range.

[0105] (Fiber shape) The infusible fibers are preferably short fibers that are aggregated to form a mat, a paper product, or a blanket as a whole.

[0106] Short fibers mean that they are not continuous fibers. Continuous fibers form fiber bundles with the fibers oriented in the same direction, as in cloth or filament winding, whereas short fibers form aggregates (mats, blankets, and paper products) with the fibers oriented in random directions. Furthermore, insulation materials using short fibers have short conductive paths, so they can reduce conductivity even in highly carbonized fibers or when carbonization progresses due to thermal runaway. Furthermore, randomly oriented fibers tend to form point contacts with each other, reducing thermal conductivity.

[0107] Paper products can be obtained by dispersing infusible milled or chopped fibers (fiber lengths of approximately 0.01 to 10 mm) in water and then papermaking the resulting product. Mats and blankets can be obtained by stacking and compressing infusible fibers with lengths of approximately 10 to 1,000 mm. In this process, a binder may be added to maintain the overall strength and shape. Examples of binders that can be used include organic binders such as resins and inorganic binders such as ceramic precursors.

[0108] The infusible fibers preferably have a fiber diameter of 1 to 30 μm. When the infusible fibers have a fiber diameter of 1 μm or more, the rate of air oxidation and sublimation can be suppressed even when exposed to high temperatures, and the flame-retardant effect can be maintained for a long period of time. On the other hand, when the infusible fibers have a fiber diameter of 30 μm or less, a certain degree of flexibility can be maintained even when exposed to high temperatures and carbonized, and breakage can be reduced even when deformation or impact occurs.

[0109] In this embodiment as well, the heat insulating material may contain organic fibers and inorganic particles similar to those in the first embodiment, in addition to the infusible fibers.

[0110] The heat insulating material is configured as described above, but since the heat insulating material is an aggregate of fibers, preferably short fibers, it easily absorbs moisture, leaked electrolyte, etc. Therefore, it is preferable to cover the surface of the heat insulating material 10 opposite the metal substrate 20, for example, the surface facing the storage battery in a battery module, with a coating layer.

[0111] The coating layer preferably has one or more layers selected from resin, metal foil, and mica, which provides excellent strength, permeation prevention performance, etc. As a method for bonding to the coating layer, an adhesive can be used, or in the case of resin, heat fusion can be used, and in the case of metal foil, vapor deposition can be used.

[0112] The covering layer can also be used to cover the heat insulating material in the first embodiment.

[0113] <Joining layer> The flame-retardant structure can be manufactured in the same manner as in embodiment 1, with the material forming the metal substrate penetrating into the gaps in the material forming the heat insulating material to form a bonding layer. The gradient structure and thickness are also the same as in embodiment 1.

[0114] [Battery module] 2, the battery module 100 includes a plurality of storage batteries 110 housed in a battery package 120. The electrode terminals 111 of the storage batteries 110 are connected in series by a bus bar .

[0115] In the present invention, the battery package 120 is formed from the flame-retardant structure 1. The metal substrate 20 forms the housing body of the battery package 120, and the heat insulating material 10 forms the surface facing the storage battery 110, and is formed on the entire surface of the canopy, side walls, and bottom wall. Note that the heat insulating material 10 may be formed on at least one of the canopy, side walls, and bottom wall.

[0116] In a battery package 120 made by bonding a thermal insulator 10 and a metal substrate 20 with an adhesive, it is difficult to bond the thermal insulator 10 to every corner of the metal substrate 20 without leaving any gaps at the bent portion A. In contrast, in a battery package 120 made by insert molding the thermal insulator 10 and the metal substrate 20 as in the present invention, the thermal insulator 10 is bonded to the metal substrate 20 without any gaps, even at the bent portion A. Therefore, even if the internal shape of the battery package 120 becomes more complex, it can be well accommodated. In other words, the flame-retardant structure of the present invention also has excellent shape conformability. [Explanation of symbols]

[0117] 1. Fireproof structure 10. Insulation 11a First inorganic fiber 11b Second inorganic fiber 12 Organic Fibers 13a First inorganic particles 13b Second inorganic particles 20 Metal substrate 30 Bonding layer 100 battery modules 110 Storage battery 111 Electrode terminal 120 battery packages 130 Busbar

Claims

1. A heat insulating material comprising a metal substrate and an insulating material containing inorganic fibers or infusible fibers, A method for manufacturing a flame-retardant structure, wherein in a bonding layer formed by bonding the metal substrate and the thermal insulating material, a material forming the metal substrate penetrates into gaps in a material forming the thermal insulating material and is integrated with the metal substrate, A method for manufacturing a flameproof structure, in which the heat insulating material is used as an insert member and a material for forming the metal substrate is cast.

2. The method for manufacturing a fireproof structure according to claim 1, wherein the metal substrate is at least one of a top wall, a side wall, and a bottom wall of a battery case.

3. 3. The method for manufacturing a flame-retardant structure according to claim 1, wherein the base material of the metal substrate is at least one of iron, copper, aluminum, magnesium, zinc, nickel, titanium, and alloys thereof.

4. 4. The method for manufacturing a flameproof structure according to claim 3, wherein the base material of the metal substrate is aluminum, magnesium, or an alloy thereof.

5. The method for manufacturing a flame-resistant structure according to any one of claims 1 to 4, characterized in that the inorganic fibers include first inorganic fibers and second inorganic fibers that are different from each other in at least one property selected from average fiber diameter, shape, and glass transition point.

6. The average fiber diameter of the first inorganic fibers is larger than the average fiber diameter of the second inorganic fibers, 6. The method for manufacturing a flame-proof structure according to claim 5, wherein the first inorganic fibers are linear or needle-like, and the second inorganic fibers are dendritic or crimped.

7. the first inorganic fibers are amorphous fibers, the second inorganic fibers are at least one type of fibers selected from amorphous fibers and crystalline fibers having a glass transition point higher than that of the first inorganic fibers, 7. The method for manufacturing a flame-resistant structure according to claim 5, wherein the first inorganic fibers have an average fiber diameter larger than the average fiber diameter of the second inorganic fibers.

8. The method for manufacturing a flame-resistant structure according to any one of claims 1 to 7, characterized in that the infusible fiber has a carbon content of 55 to 95 mass%.

9. The method for producing a flame-resistant structure according to any one of claims 1 to 8, wherein the infusible fibers are short fibers.

10. The method for manufacturing a flame-resistant structure according to any one of claims 1 to 9, wherein the infusible fibers have a fiber diameter of 1 to 30 µm.

11. The method for manufacturing a flame-resistant structure according to any one of claims 1 to 10, wherein the heat insulating material contains organic fibers.

12. The method for manufacturing a flame-resistant structure according to claim 11, wherein the organic fiber has a glass transition point lower than that of the base material of the metal substrate.

13. The method for manufacturing a flame-resistant structure according to any one of claims 1 to 12, characterized in that the heat insulating material contains inorganic particles.

14. The method for manufacturing a flame-proof structure according to claim 13, wherein the inorganic particles include first inorganic particles and second inorganic particles having different average particle diameters.

15. 15. The method for manufacturing a flame-proof structure according to claim 14, wherein the first inorganic particles are at least one selected from the group consisting of oxide particles, carbide particles, nitride particles, and inorganic hydrate particles.

16. 16. The method for manufacturing a flame-proof structure according to claim 14, wherein the first inorganic particles are at least one type selected from the group consisting of nanoparticles, hollow particles, and porous particles.

17. The method for manufacturing a flame-resistant structure according to any one of claims 14 to 16, wherein the first inorganic particles are at least one selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles.

18. The method for manufacturing a flame-resistant structure according to any one of claims 14 to 17, wherein the second inorganic particles are metal oxide particles.

19. The method for manufacturing a flame-retardant structure according to any one of claims 1 to 18, wherein the thickness of the bonding layer is 10 to 90% of the thickness of the flame-retardant structure.

20. The method for manufacturing a flame-retardant structure described in any one of claims 1 to 19, characterized in that the bonding layer has a gradient structure in which the ratio (material forming the metal base material / material forming the insulation material) gradually decreases as the thickness of the insulation material increases.

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