WO2025204998A1 - Thermal insulation material for battery pack, and battery pack - Google Patents

Abstract

The present invention provides a thermal insulation material (40) for a battery pack, said thermal insulation material being thin but yet exhibiting excellent thermal insulation properties. This thermal insulation material (40) for a battery pack includes a layered inorganic material sheet (42) obtained by laminating layered inorganic material papers (43), said thermal insulation material characterized by comprising voids, the size of which in the thickness direction is 10-100 μm inclusive, at least between the layered inorganic material papers.

Description

Battery pack heat insulating material and battery pack

The present invention relates to an insulating material for a battery pack and a battery pack using the insulating material for a battery pack.

Battery packs used in electric vehicles, hybrid vehicles, etc. are made up of multiple battery cells.

Battery cells may go into a thermal runaway state due to an internal short circuit or overcharging caused by external factors, which can cause the battery cell to overheat or catch fire. The heat and flames that are generated in this way can spread to the surrounding area, potentially inducing thermal runaway in adjacent battery cells and causing serious damage.

For this reason, battery packs are equipped with various safety components to prevent personal injury from thermal runaway in battery cells, such as partition members that suppress heat transmission between battery cells, and protective members that are placed between the battery cells and the battery case to suppress heat transmission and the release of flames outside the battery pack.

Layered inorganic materials such as mica have a high melting point and excellent fire resistance, making them suitable for use as safety components for battery packs. For example, Patent Document 1 discloses a safety component that combines two mica layers with an aerogel layer filled in a sealed bag, with the two mica layers facing each other on the outside of the sealed bag. Patent Document 2 also discloses a fire-resistant material for batteries that includes a mica layer and a foam coating.

Chinese Utility Model No. 219523264 Chinese Patent No. 109987884

However, while layered inorganic materials have excellent fire resistance, they are characterized by insufficient heat insulating performance, and in Patent Document 1, the heat insulating performance is compensated for by combining a mica layer with an aerogel layer that has heat insulating properties. However, with the trend toward higher energy battery packs, there is a demand for further improvements in the heat insulating performance of safety components used in battery packs, and measures such as increasing the thickness of safety components and stacking multiple heat insulating layers are being considered. However, at the same time, as shown in Patent Document 2, there is a demand for thinner safety components due to the limited space available for installing safety components in battery packs.

An object of the present invention is to provide a thin insulating material for a battery pack that has excellent insulating properties.
Another object of the present invention is to provide a battery pack including a heat insulating material for a battery pack having excellent thinness and heat insulating properties.

The inventors conducted extensive research to provide a thin-walled insulating material that offers excellent thermal insulation. As a result, they discovered a thin-walled insulating material for battery packs that also offers excellent thermal insulation.

The insulating material for a battery pack of the present invention is an insulating material for a battery pack including a layered inorganic sheet formed by laminating layered inorganic paper, and is characterized in that there are gaps between at least the layered inorganic paper sheets, the gaps having a size in the thickness direction of 10 μm or more and 100 μm or less.
Although the insulating material for a battery pack of the present invention is thin, it exhibits excellent insulating properties because the layered inorganic material sheet has fine voids between the layers of layered inorganic material paper, which inhibits heat propagation.

The insulating material for a battery pack of the present invention is further characterized in that the layered inorganic paper has voids with a size of 1 μm or more and 50 μm or less in the thickness direction.
The insulating material for a battery pack of the present invention further has fine voids within the layered inorganic paper, which further suppresses the propagation of heat in the layered inorganic sheet, thereby providing even more excellent insulating effects.

In the heat insulating material for a battery pack of the present invention, it is preferable that the aspect ratio of the voids in the cross section of the layered inorganic material sheet is 2 or more in the width direction/thickness direction.
The voids exist inside the layered inorganic paper or between the layers of the layered inorganic paper, and therefore many of them have a shape that is wide in the width direction.

In the battery pack insulating material of the present invention, the average void occupancy is preferably 5% or more and 70% or less in a 1 mm x 1 mm section of the cross section of the layered inorganic material sheet.
When the void occupancy is within the above range, the strength of the layered inorganic material sheet can be maintained while improving the heat insulating properties.

In the thickness direction of the voids, it is preferable that the average size of the voids between the layered inorganic paper sheets is larger than the average size of the voids within the layered inorganic paper sheets.
The difference in the average size of the voids in the thickness direction between the layered inorganic paper and within the layered inorganic paper creates a graded heat insulating effect.

The layered inorganic paper preferably contains at least one silicate mineral selected from the group consisting of vermiculite, montmorillonite, beidellite, nontronite, saponite, hectorite, stevensite, and mica.
When the layered inorganic material is the silicate mineral, the insulating material for a battery pack of the present invention exhibits excellent heat insulating properties, and the layered inorganic material sheet is likely to expand when heated.
The layered inorganic paper more preferably contains mica, since mica has excellent insulating properties and fire resistance.

The layered inorganic paper preferably has a thickness of 0.05 mm or more and 0.2 mm or less.
When the thickness of the layered inorganic paper is within the above range, it is easy to achieve both thinness and heat insulation properties for the heat insulating material for a battery pack of the present invention.

The layered inorganic material sheet preferably has a thickness of 0.2 mm or more and 2.0 mm or less.
When the thickness of the layered inorganic material sheet is within the above range, it is easy to achieve both thinness and heat insulation properties for the heat insulating material for a battery pack of the present invention.

The heat insulating material for a battery pack of the present invention preferably further comprises a heat insulating sheet laminated on the layered inorganic material sheet.
If the battery pack insulating material of the present invention further contains an insulating sheet, it can compensate for the lack of insulating properties and thermal shock resistance to ejected material from battery cells in a thermal runaway state that are insufficient with the layered inorganic material sheet alone.

The heat insulating sheet preferably has a thickness of 0.5 mm or more and 5.0 mm or less.
When the thickness of the heat insulating sheet is within the above range, it is easy to achieve both thinness and heat insulating properties for the heat insulating material for a battery pack of the present invention.

The heat insulating sheet preferably contains at least one material selected from the group consisting of inorganic fibers, organic fibers, inorganic particles, and organic particles.
When the heat insulating sheet contains inorganic fibers, organic fibers, inorganic particles and/or organic particles, the fire resistance and heat insulating properties of the heat insulating material for a battery pack of the present invention are improved.

The heat insulating sheet preferably contains at least one material selected from the group consisting of silica nanoparticles, titania, alumina fiber, carbon fiber, mica, basalt fiber, soluble fiber, refractory ceramic fiber, glass fiber, aerogel composite material, microporous particles, hollow silica particles, thermally expandable inorganic materials, aerogel, silica, zirconia, zircon, barium titanate, zinc oxide, alumina, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, zinc hydroxide, iron hydroxide, manganese hydroxide, zirconium hydroxide, gallium hydroxide, cellulose fiber, fiber containing _SiO2 , silica fiber, mullite fiber, alumina fiber, alumina silicate fiber, ceramic fiber, rock wool, alkaline earth silicate fiber, zirconia fiber, and mineral fiber.

The heat insulating material for a battery pack of the present invention preferably has an air layer between the layered inorganic material sheet and the heat insulating sheet.
This is because the presence of an air layer between the layered inorganic material sheet and the heat insulating sheet improves the heat insulating performance of the heat insulating material for a battery pack of the present invention.

The battery pack of the present invention includes the insulating material for a battery pack of the present invention.
By including the insulating material for a battery pack of the present invention, the battery pack of the present invention has excellent fire resistance and insulating properties.

According to the present invention, it is possible to provide a thin insulating material for a battery pack that has excellent insulating properties.
Furthermore, according to the present invention, it is possible to provide a battery pack including a battery pack insulating material having excellent thinness and heat insulating properties.

FIG. 1 is a schematic cross-sectional view showing an example of the insulating material for a battery pack of the present invention. FIG. 2 is an enlarged photograph showing an example of the insulating material for a battery pack of the present invention. FIG. 3A is a perspective view schematically showing an example of a battery pack of the present invention. FIG. 3B is a cross-sectional view taken along line AA in FIG. 3A. FIG. 3C is an exploded view of the battery pack shown in FIG. 3A. FIG. 4 is a schematic cross-sectional view showing a heated surface and a non-heated surface in a simulation of heat insulation. FIG. 5 is a graph showing the temperature difference between the heated surface and the unheated surface of the heat insulating material for Comparative Example 1 and Examples 1 to 4 at different thicknesses before heating.

(Insulating material for battery packs)
The battery pack insulating material and the battery pack according to the present invention will be described in detail below 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.

FIG. 1 is a schematic cross-sectional view showing an example of the insulating material for a battery pack of the present invention.
The battery pack insulating material 40 shown in Figure 1 has an insulating sheet 41 laminated on a layered inorganic material sheet 42. The layered inorganic material sheet 42 has a plurality of layered inorganic material papers 43 laminated thereon. In the battery pack insulating material 40 shown in Figure 1, three sheets of layered inorganic material papers 43 are laminated. The layered inorganic material papers 43 include voids 45a, 45b inside the layered inorganic material papers and between the layered inorganic material papers.
The number of sheets of layered inorganic paper 43 to be stacked is not particularly limited, but is preferably in the range of 2 to 20 sheets, more preferably 3 to 10 sheets.
As described below, the voids 45a and 45b can be formed by gasifying the hydroxyl groups and alkyl groups contained in the resin contained in the layered inorganic paper 43 through heating, but the layered inorganic paper 43 may also contain compounds (not shown) derived from the above resin.
The battery pack heat insulating material 40 may have a layered inorganic material sheet 42 laminated on the heat insulating sheet 41. That is, the heat insulating sheet 41 may be sandwiched between two layered inorganic material sheets 42 in the thickness direction.
The heat insulating material for a battery pack of the present invention does not necessarily need to include a heat insulating sheet.

(Layered inorganic material sheet)
The layered inorganic sheet is formed by stacking multiple sheets of layered inorganic paper, and preferably has gaps between the layers of layered inorganic paper that are 10 μm or more and 100 μm or less in the thickness direction, and more preferably has gaps of 20 μm or more and 80 μm or less.

The insulating material for a battery pack of the present invention preferably has voids in the layered inorganic paper with a size in the thickness direction of 1 μm or more and 50 μm or less, more preferably 2 μm or more and 20 μm or less.
In this specification, the gaps formed between and within the layered inorganic paper are referred to as "voids." The shape of the voids is not particularly limited, but it is preferable that they are not of uniform size or shape but are sparse. Varying the size and shape of the voids is preferable because it complicates heat transfer and improves the heat insulating performance of the layered inorganic sheet.

In the battery pack insulating material of the present invention, the aspect ratio of the voids in the cross section of the layered inorganic material sheet is preferably 2 or more in the width/thickness direction. More preferably, it is 3 or more. The cross section of the layered inorganic material sheet is a cross section cut along the thickness direction. In this specification, the aspect ratio of the voids is the average value calculated from the maximum dimensions in the width and thickness directions for any 10 voids when the cross section of the layered inorganic material sheet is exposed. Since the voids are present inside the layered inorganic material paper or between the layers of layered inorganic material paper, many of them have a wide shape in the width direction.

The insulating material for battery packs of the present invention preferably has an average void ratio of 5% to 70% in 1 mm x 1 mm sections of the cross section of the layered inorganic material sheet. When the average void ratio is within the above range, the strength of the layered inorganic material sheet can be maintained while improving its thermal insulation properties. The average void ratio is calculated by exposing the cross section of the layered inorganic material sheet and dividing the total area of voids in each section by the total area of the section in any 10 of the above sections, and averaging the results. The average void ratio is more preferably 10% to 50%.

In the battery pack insulating material of the present invention, it is preferable that the average size of the voids between the layers of inorganic paper be larger in the thickness direction than the average size of the voids within the layered inorganic paper. As described below, when voids are formed by gasifying the resin through heating, the layered inorganic paper is less likely to break between the layers of inorganic paper than within the layered inorganic paper. Note that the average size of the voids in the thickness direction in this specification is the average of the maximum dimensions in the thickness direction of any 10 voids when the cross section of the layered inorganic sheet is exposed.

(Layered inorganic paper)
The layered inorganic paper is formed from pulverized and exfoliated layered inorganic materials.

The layered inorganic paper is not particularly limited as long as it contains a layered inorganic material that has excellent fire resistance and insulation properties, but it preferably contains at least one silicate mineral selected from the group consisting of vermiculite, montmorillonite, beidellite, nontronite, saponite, hectorite, stevensite, and mica. It is even more preferable for the layered inorganic paper to contain mica. Mica has excellent insulation and fire resistance, making it ideal for use as an insulating material for battery packs. Muscovite and phlogopite are particularly preferred mica.

(Thickness of layered inorganic paper)
The thickness of the layered inorganic paper is preferably in the range of 0.05 mm to 0.2 mm, and more preferably in the range of 0.08 mm to 0.1 mm. If the thickness of the layered inorganic paper is less than 0.05 mm, the layered inorganic paper may be easily torn and difficult to handle. On the other hand, if the thickness of the layered inorganic paper is more than 0.2 mm, it may be difficult to form voids, as described below.

(Method for manufacturing layered inorganic paper)
The layered inorganic paper according to the present invention is produced, for example, by the following method.
First, 1 to 50 parts by weight of a layered inorganic material pulverized and peeled into flakes having a diameter of 50 μm to 1000 μm is placed in a tank filled with water, and stirred for 30 seconds or more to produce a slurry in which the layered inorganic material is uniformly dispersed in the water. The slurry is then poured into a desired mold and subjected to dehydration molding and drying with hot air or a hot plate to produce layered inorganic paper.

(Thickness of layered inorganic material sheet)
The thickness of the layered inorganic material sheet is preferably 0.2 mm or more and 2.0 mm or less, more preferably 0.2 mm or more and 1.0 mm or less, and even more preferably 0.3 mm or more and 1.0 mm or less.
If the thickness of the layered inorganic material sheet is less than 0.2 mm, the strength of the layered inorganic material sheet will be low and the layered inorganic material sheet will be easily broken, whereas if the thickness of the layered inorganic material sheet is more than 2.0 mm, the layered inorganic material sheet will be too thick, making it difficult to miniaturize the entire battery pack.

(Method for producing layered inorganic material sheet)
The method for producing the layered inorganic material sheet is not particularly limited, but it can be produced, for example, by the following method.
First, the layered inorganic paper is impregnated with a resin, and the resin-impregnated layered inorganic papers are stacked and placed in a mold of the desired shape and hot-pressed. The layered inorganic paper stack is heated, for example, at 500°C or higher for 5 minutes or longer, whereby gas is released from the resin, and voids are formed within and between the layers of the layered inorganic paper, thereby obtaining a layered inorganic sheet. The obtained layered inorganic sheet can be used as the insulating material for a battery pack of the present invention as is.

(resin)
The resin used to prepare the layered inorganic material sheet of the present invention contains a group that generates gas when heated to 150°C or higher, and since it releases gas when heated, it preferably has the property of reducing its mass after heating.

The mass loss of the resin after heating at 500°C for 1 hour is preferably 1.0% by mass or more and 20.0% by mass or less. If the mass loss of the resin is less than 1.0% by mass, the layered inorganic sheet may not expand sufficiently. If the mass loss of the resin is large, the amount of gas generated by heating increases, and as a result, the size and number of voids generated between and within the layered inorganic paper increase, providing the layered inorganic sheet with a better heat insulating effect. However, if the mass loss of the resin exceeds 20.0% by mass, the increased amount of gas generated by heating may cause the layered inorganic paper to expand excessively, potentially resulting in tearing. The mass loss of the resin is more preferably 1.5% by mass or more and 12.0% by mass or less, and even more preferably 1.5% by mass or more and 7.0% by mass or less.
The amount of reduction in the mass of the resin can be determined by heating the layered inorganic material sheet at 500°C for 1 hour, subtracting the mass of the layered inorganic material sheet after heating from the mass of the layered inorganic material sheet before heating, and dividing the calculated value by the value calculated by subtracting the mass of the layered inorganic material sheet before resin impregnation from the mass of the layered inorganic material sheet before heating.

The resin may be epoxy resin, silicone resin, acrylic resin, fluororesin, polypropylene resin (PP), polyurethane resin (PU), polyethylene resin (PE), polyethylene terephthalate resin (PET), polyamide resin (PA), polybutylene terephthalate resin (PBT), etc. The resin is preferably at least one selected from the group consisting of epoxy resin, silicone resin, acrylic resin, and fluororesin. Silicone resin and/or fluororesin is more preferred.

Examples of groups that generate gas when heated include alkyl groups having 1 to 10 carbon atoms, such as methyl groups and ethyl groups, hydroxyl groups, and aldehyde groups. Resins used in the present invention can be those containing the above groups that generate gas when heated.

The greater the amount of gas generated from the resin upon heating, the greater the size and number of voids, providing the layered inorganic material sheet with excellent heat insulation properties. Therefore, the resin content of the layered inorganic material sheet is preferably 5% by mass or more and 20% by mass or less in solids content relative to the layered inorganic material sheet. If the resin content of the layered inorganic material sheet is less than 5% by mass, voids are less likely to form between the layered inorganic material paper upon heating. If the resin content of the layered inorganic material sheet is more than 20% by mass, the increased amount of gas generated upon heating may cause the layered inorganic material paper to expand excessively, resulting in tearing. The resin content of the layered inorganic material sheet is preferably 7% by mass or more and 12% by mass or less in solids content relative to the layered inorganic material sheet.

The resin content of the layered inorganic material sheet can be calculated by subtracting the mass of the layered inorganic material sheet before being impregnated with resin from the mass of the layered inorganic material sheet of the present invention.

The conditions for the heat pressing are not particularly limited, but examples include pressing for 5 minutes or more and 60 minutes or less, at a pressure of 1 MPa or more and 15 MPa or less, and at a temperature of 100 to 300°C.

Figure 2 is an enlarged photograph showing an example of the insulating material for a battery pack of the present invention. The initial state is a laminate of layered inorganic paper, and is the state before heating. In the photograph of the initial state, thick resin can be observed within and between the layered inorganic paper. In the photograph after heating at 800°C for 50 hours, voids can be observed within and between the layered inorganic paper.

(heat insulating sheet)
The insulating material for a battery pack of the present invention preferably further comprises an insulating sheet laminated on the layered inorganic material sheet. The insulating sheet is not limited in terms of the combination and composition ratio of materials constituting the insulating sheet, as long as the insulating sheet has a thermal conductivity of less than 1 (W/m·K). The thermal conductivity can be measured in accordance with JIS R 2251, "Testing method for thermal conductivity of refractories."
The heat insulating sheet preferably contains at least one material selected from the group consisting of inorganic fibers, organic fibers, inorganic particles, and organic particles.

(Types of inorganic fibers)
The inorganic fiber has excellent heat resistance, and at least one selected from alumina fiber, carbon fiber, basalt fiber, soluble fiber, refractory ceramic fiber, glass fiber, glass wool, slag wool, fibers containing _SiO2 , silica fiber, mullite fiber, alumina silicate fiber, ceramic fibers, rock wool, alkaline earth silicate fiber, zirconia fiber, silicon carbide fiber, magnesium silicate fiber, potassium titanate fiber, aerogel composite material, and mineral fibers can be used.

(Average fiber diameter of inorganic fibers)
The inorganic fibers preferably have an average fiber diameter of 1 μm or more and 20 μm or less, and more preferably 3 μm or more and 15 μm or less. Within this range, the heat insulating sheet can be produced without impairing the formability and processability of the heat insulating sheet.

(Average fiber length of inorganic fibers)
The inorganic fibers preferably have an average fiber length of 0.1 mm or more and 100 mm or less. This range prevents problems with moldability and processability that are caused by an average fiber length that is too long, and reduces the reduction in mechanical strength that is caused by an average fiber length that is too short.

Furthermore, in addition to the aforementioned inorganic fibers (hereinafter also referred to as first inorganic fibers), inorganic fibers (hereinafter referred to as second inorganic fibers) with an average fiber diameter smaller than that of the first inorganic fibers may be used. By using two inorganic fibers with different fiber diameters, the flexibility of the heat insulating sheet and its ability to retain the inorganic and organic particles combined with it can be improved.

The average fiber diameter of the second inorganic fibers is preferably 1 nm or more and less than 1 μm, and more preferably 10 nm or more and 0.1 μm or less. Within this range, the second inorganic fibers can maintain their mechanical strength while also being flexible.

Furthermore, the average fiber length of the second inorganic fibers is preferably less than 1 μm so as not to impair moldability.

(Types of organic fibers)
The organic fiber may be at least one selected from polyethylene terephthalate fiber, polybutylene terephthalate fiber, polytrimethylene terephthalate fiber, polyacetal fiber, polytetrafluoroethylene fiber, polyether ether ketone fiber, polyphenylene sulfide fiber, polyamide fiber, polyparaphenylphthalamide fiber, polyvinyl alcohol fiber, polyethylene fiber, nylon fiber, polyurethane fiber, polypropylene fiber, and ethylene-vinyl alcohol copolymer fiber.

(Average fiber length of organic fibers)
The average fiber length of the organic fiber according to the present invention is not particularly limited, but is preferably 0.5 mm or more and 10 mm or less. If the average fiber length is within this range, sufficient compressive strength can be obtained without impairing the formability and shape retention of the heat insulating sheet.

(Types of inorganic particles)
The inorganic particles can be made of a material having an average secondary particle diameter in the range of 0.01 μm to 200 μm, for example, at least one selected from oxide particles, nanoparticles, inorganic hydrate particles, particles made of a thermally expandable inorganic material, and particles made of a hydrous porous body. If the average secondary particle diameter is within the above range, the material can be easily obtained and the desired heat insulating effect can be obtained. Furthermore, the average secondary particle diameter of the inorganic particles is preferably 0.05 μm to 100 μm.

Two or more types of inorganic particles with different average secondary particle sizes may be used in combination. Different inorganic particle sizes have different heat transfer suppression effects, making it possible to cool the heat transfer from the battery cell in multiple stages and achieve a heat absorption effect over a wide temperature range.

(oxide particles)
The oxide particles may be at least one selected from the group consisting of silica, titania, zirconia, zircon, barium titanate, zinc oxide, and alumina. The oxide particles have a high refractive index, which can prevent radiant heat generated by thermal runaway in a battery cell from propagating to adjacent cells or outside the battery pack.

The average primary particle size of the oxide particles used in the present invention is preferably in the range of 1 μm to 50 μm in order to maximize the radiant heat blocking effect.
The average primary particle size in the present invention is determined by measuring the particle sizes of 10 random particles under a microscope by comparing them with a standard scale, and averaging the particle sizes of the 10 measured particles.

(Nanoparticles)
Nanoparticles are inorganic particles with an average primary particle size of less than 1 μm. Nanoparticles have extremely low conductive heat transfer and excellent thermal insulation properties.

For example, if oxide particles are used as the nanoparticles, even if the internal density increases due to the compression of the insulating sheet caused by expansion associated with thermal runaway in the battery cell, the repulsive force of the nanoparticles' static electricity tends to create tiny gaps between the particles, filling the particles with a cushioning effect and suppressing an increase in conductive heat transfer.

Silica nanoparticles have high thermal insulation properties, and because the contact points between particles are small, the amount of heat transfer between particles is small. Therefore, using silica nanoparticles as the nanoparticles can further improve the thermal insulation properties of insulation sheets. Wet silica, dry silica, aerogel, etc. can be used as silica nanoparticles.

The average primary particle diameter of the nanoparticles is preferably 1 nm or more and 100 nm or less. This range makes it possible to suppress convective and conductive heat transfer within the battery pack insulation material in the temperature range during thermal runaway of the battery cell. Furthermore, even when compressive stress is applied to the insulation sheet due to the expansion of the battery pack, the voids between the nanoparticles and the contact points between many particles suppress heat transfer within the insulation sheet, thereby maintaining the insulating properties of the insulation material. The average primary particle diameter of the nanoparticles is more preferably 2 nm or more, and even more preferably 3 nm or more. On the other hand, the average primary particle diameter of the nanoparticles is preferably 50 nm or less, and even more preferably 10 nm or less.

(Inorganic hydrate particles)
Examples of inorganic hydrate particles include particles of aluminum hydroxide, magnesium hydroxide, calcium hydroxide, zinc hydroxide, iron hydroxide, manganese hydroxide, zirconium hydroxide, gallium hydroxide, etc. The inorganic hydrate particles mentioned above begin to thermally decompose in a thermal runaway environment of the battery cell, releasing water of crystallization, thereby releasing heat from the heating element, thereby suppressing a sudden temperature rise inside the battery pack.

(Particles made of thermally expandable inorganic material)
Examples of particles made of a thermally expandable inorganic material include particles of vermiculite, bentonite, mica, and perlite.

(Particles made of a water-containing porous body)
Examples of particles made of a hydrous porous material include particles of zeolite, montmorillonite, acid clay, diatomaceous earth, wet silica, dry silica, aerogel, mica, and vermiculite.

In addition to the aforementioned inorganic fibers, organic fibers, inorganic particles, and organic particles, a resin binder may also be added to the insulating sheet. Adding a resin binder to the insulating sheet improves the sheet's mechanical strength, allowing the sheet to maintain its shape even when pressure is applied due to the expansion of the battery cell during thermal runaway, thereby preventing a decrease in insulating performance. Examples of resin binders that can be used include styrene-butadiene resin, acrylic resin, silicone-acrylic resin, and styrene resin.

(Thickness of the heat insulating sheet)
The thickness of the insulating sheet is not particularly limited, but is preferably in the range of 0.5 mm to 5.0 mm, and more preferably in the range of 0.8 mm to 3.0 mm. If the thickness of the insulating sheet is within the above range, the insulating material for a battery pack of the present invention can obtain sufficient mechanical strength. If the thickness of the insulating sheet is less than 0.5 mm, sufficient insulating performance commensurate with the addition of the insulating sheet cannot be obtained. On the other hand, if the thickness of the insulating sheet exceeds 5.0 mm, the insulating material for a battery pack of the present invention becomes too thick and occupies a large amount of space within the battery pack.

(Method for manufacturing heat insulating sheet)
The manufacturing method of the heat insulating sheet is not particularly limited, and the sheet can be manufactured by a wet molding method, a dry molding method, an extrusion molding method, etc. Furthermore, after manufacturing the heat insulating sheet by the above-mentioned manufacturing method, needling may be carried out to adjust the shape of the heat insulating sheet.

The insulating material for a battery pack of the present invention preferably has an air layer between the layered inorganic material sheet and the insulating sheet. This is because having an air layer between the layered inorganic material sheet and the insulating sheet improves the insulating performance of the insulating material for a battery pack of the present invention. There are no particular restrictions on the thickness of the air layer, but it is preferably 10 μm or more and 100 μm or less. In this specification, the gap formed between the layered inorganic material sheet and the insulating sheet is referred to as the "air layer."

There are no particular limitations on the method for manufacturing a battery pack insulation material having an air layer between the layered inorganic material sheet and the insulating sheet. For example, when laminating the layered inorganic material paper laminate produced by the above method with the insulating sheet, the layered inorganic material paper laminate and the insulating sheet are bonded together with an organic adhesive, and heated at 500°C or higher for 5 minutes or more. The layered inorganic material sheet and the insulating sheet can also be bonded together with an organic adhesive and heated, but using a layered inorganic material paper laminate is more efficient as it allows the resin within and between the layered inorganic material papers, and the organic adhesive between the layered inorganic material paper laminate and the insulating sheet, to be gasified simultaneously.

(organic adhesive)
The organic adhesive used is one that contains a material that generates gas when heated. When the adhesive contains such a material, gas is generated between the laminate of layered inorganic paper or the layered inorganic sheet and the heat insulating sheet when heated, creating an air layer between the laminate of layered inorganic paper or the layered inorganic sheet and the heat insulating sheet, improving the heat insulating performance.

The material that generates gas when heated is, for example, an organic material having a hydroxy group or an aldehyde group, and more specifically, polyamide-based organic materials, nylon-based organic materials, and the like.
When the organic adhesive contains a polyamide-based organic material or a nylon-based organic material, it undergoes thermal decomposition upon heating, and water vapor and carbon dioxide are easily released from the adhesive due to hydroxyl groups and aldehyde groups, making it easier for an air layer to form between the layered inorganic material sheet and the heat insulating sheet, and therefore it is preferably used.

(battery pack)
The battery pack of the present invention includes the insulating material for a battery pack of the present invention.
A specific example of the battery pack of the present invention, in which the heat insulating material for a battery pack includes a layered inorganic material sheet and a heat insulating sheet, will be described with reference to FIGS. 3A, 3B, and 3C.

FIG. 3A is a perspective view schematically illustrating an example of a battery pack according to the first embodiment of the present invention.
FIG. 3B is a cross-sectional view taken along line AA in FIG. 3A.
FIG. 3C is an exploded view of the battery pack shown in FIG. 3A.
The battery pack 10 shown in FIGS. 3A, 3B, and 3C includes a module 20 having a plurality of battery cells 21 and a case 30 that houses the module 20.
As shown in FIG. 3B, in the battery pack 10, each battery cell 21 is provided with a safety valve 22.
As shown in FIG. 3B, the case 30 includes a housing portion 31 made up of a bottom portion 31b and a side wall 31s, and a lid portion 32 that covers the housing portion 31. The housing portion 31 houses the module 20.
In addition, in the battery pack 10 , a battery pack heat insulating material 40 is provided between the module 20 and the case 30 .
As shown in Fig. 3B , the battery pack insulating material 40 has a heat insulating sheet 41 laminated on a layered inorganic material sheet 42. In Fig. 3B , the heat insulating sheet 41 is provided so as to contact the module 20. The battery pack insulating material 40 may also be provided so that the layered inorganic material sheet 42 is in contact with the module 20. The battery pack insulating material 40 may also be provided so as to contact the case 30.

The battery cell 21 stores electric power and is preferably a rechargeable secondary battery, such as a lithium ion battery, a nickel-metal hydride battery, or a sodium ion battery.
3B and 3C has a rectangular parallelepiped shape. In the battery pack of the present invention, the battery cells may have a three-dimensional shape other than a rectangular parallelepiped shape (for example, a cube or an irregular shape).

As shown in FIGS. 3B and 3C, in the module 20, a plurality of battery cells 21 are arranged in a row and fixed by a connecting module member 20a.
As shown in FIG. 3C, the battery cells 21 have terminals 23, and adjacent battery cells 21 are electrically connected by connecting each terminal 23 to a bus bar 20b arranged on the connection module member 20a.

The bus bar 20b is a flat, electrically conductive metal member, and may be made of, for example, copper, a copper alloy, stainless steel (SUS), or aluminum.
The bus bar 20b may be fixed to the terminal 23 by any fixing means (for example, screwing, welding, etc.).

Materials that can be used to make the case 30 include steel and aluminum. Stainless steel (SUS) is preferred as a steel material.

This specification discloses the following:

[1] An insulating material for a battery pack, comprising a layered inorganic sheet formed by laminating layered inorganic paper, characterized in that there are voids between at least the layered inorganic paper, the voids having a thickness direction dimension of 10 μm to 100 μm.

[2] The insulating material for a battery pack described in [1], further characterized in that the layered inorganic paper has voids with a thickness direction dimension of 1 μm or more and 50 μm or less.

[3] The insulating material for a battery pack according to [1] or [2], wherein the aspect ratio of the voids in the cross section of the layered inorganic material sheet in the width direction/thickness direction is 2 or more.

[4] The insulating material for a battery pack described in any one of [1] to [3], wherein the average void occupancy is 5% or more and 70% or less in a 1 mm x 1 mm section of the cross section of the layered inorganic material sheet.

[5] The insulating material for a battery pack described in any one of [1] to [4], wherein the average size of the voids between the layered inorganic paper sheets is larger than the average size of the voids within the layered inorganic paper sheets in the thickness direction of the voids.

[6] The insulating material for a battery pack described in any one of [1] to [5], wherein the layered inorganic paper contains at least one silicate mineral selected from the group consisting of vermiculite, montmorillonite, beidellite, nontronite, saponite, hectorite, stevensite, and mica.

[7] The insulating material for a battery pack according to any one of [1] to [6], wherein the layered inorganic paper contains mica.

[8] The insulating material for a battery pack described in any one of [1] to [7], wherein the layered inorganic paper has a thickness of 0.05 mm or more and 0.2 mm or less.

[9] The insulating material for a battery pack described in any one of [1] to [8], wherein the layered inorganic material sheet has a thickness of 0.2 mm or more and 2.0 mm or less.

[10] The insulating material for a battery pack described in any one of [1] to [9], further comprising an insulating sheet laminated on the layered inorganic material sheet.

[11] The insulating material for a battery pack described in [10], wherein the insulating sheet has a thickness of 0.5 mm or more and 5.0 mm or less.

[12] The insulating material for a battery pack according to [10] or [11], wherein the insulating sheet contains at least one material selected from the group consisting of inorganic fibers, organic fibers, inorganic particles, and organic particles.

[13] The insulating sheet for a battery pack according to any one of [10] to [12], which contains at least one selected from the group consisting of silica nanoparticles, titania, alumina fiber, carbon fiber, mica, basalt fiber, soluble fiber, refractory ceramic fiber, glass fiber, aerogel composite material, microporous particles, hollow silica particles, thermally expandable inorganic materials, aerogel, silica, zirconia, zircon, barium titanate, zinc oxide, alumina, aluminum _hydroxide , magnesium hydroxide, calcium hydroxide, zinc hydroxide, iron hydroxide, manganese hydroxide, zirconium hydroxide, gallium hydroxide, cellulose fiber, fiber containing SiO2, silica fiber, mullite fiber, alumina fiber, alumina silicate fiber, ceramic fiber, rock wool, alkaline earth silicate fiber, zirconia fiber, and mineral fiber.

[14] The insulating material for a battery pack described in any one of [10] to [13], which has an air layer between the layered inorganic material sheet and the insulating sheet.

[15] A battery pack equipped with the insulating material for a battery pack described in any one of [1] to [14].

Below, we will explain examples that more specifically disclose the insulating material for battery packs of the present invention, but the present invention is not limited to these examples.

To confirm the insulating properties of the layered inorganic material sheet, the following simulation model was created and a simulation of its insulating properties was performed.

Comparative Example 1, Examples 1 to 4
A layered inorganic sheet consisting of one sheet of 1.0 mm thick layered inorganic paper was used as the battery pack insulating material of Comparative Example 1. For the battery pack insulating materials of Examples 1 to 4, the thickness and number of layers of layered inorganic paper forming the layered inorganic sheet were changed as shown in Table 1, and gaps of the thickness and number of layers shown in Table 1 were provided between the layered inorganic paper. A simulation model was prepared in which the heated battery pack insulating material (thickness 1.0 mm) and a steel material made of SPCC (thickness 149 mm) were layered in the thickness direction.

As shown in Figure 4, in the simulation model, layered voids 45 are arranged between layers of layered inorganic paper 43 to form a layered inorganic sheet 42, and steel SP is arranged on top of the layered inorganic sheet 42.
Then, when the main surface of the layered inorganic material sheet 42 opposite to the main surface on which the steel material SP is laminated (hereinafter also referred to as the heated surface S1) is heated at 1050°C, the temperature of the main surface of the steel material SP opposite to the main surface in contact with the layered inorganic material sheet 42 (hereinafter also referred to as the non-heated surface S2) is calculated by simulation, and the temperature difference (S1-S2) between the heated surface S1 and the non-heated surface S2 is determined. Figure 4 is a schematic cross-sectional view showing the heated surface and the non-heated surface in the simulation of thermal insulation. In Comparative Example 1 and Examples 1 to 4, the battery pack insulating material 40 does not have a thermal insulation sheet 41.

The layered inorganic material sheet used in the simulation models of Comparative Example 1 and Examples 1 to 4 was assumed to be a sheet made of muscovite, which has a thermal conductivity of 0.2 W/m·K at 25°C, a density of 2.0 g/cm ³ , and a specific heat of 880 J/kg·K.

Ansys Mechanical (manufactured by Ansys) was used as the thermal insulation simulation software. The results are shown in Table 1 and Figure 5.

FIG. 5 is a graph showing the temperature difference between the heated surface and the unheated surface of the heat insulating material for Comparative Example 1 and Examples 1 to 4 at different thicknesses before heating.
As shown in Table 1 and FIG. 5 , the thickness of the layered inorganic material sheets of Comparative Example 1 and Examples 1 to 4 before heating was 1.0 mm, but in Examples 1 to 4, heating caused air layers to form between the layered inorganic material papers, which expanded, resulting in a calculated temperature difference that was greater than the temperature difference between the heated and unheated surfaces of the layered inorganic material sheet of Comparative Example 1, which did not have an air layer, demonstrating that the heat insulating effect was increased by the expansion of the layered inorganic material sheet.

Example 5: Preparation of a Battery Pack Insulating Material. A 0.2 mm thick mica paper was placed in a stainless steel container, and silicone resin (containing hydroxyl and methyl groups that generate gas) was poured in little by little from above, allowing a predetermined amount of silicone resin to soak into the mica paper. The silicone resin-soaked mica paper was dried in a hot air dryer at 90°C for 60 minutes. Five dried mica papers were stacked and pressed in a heat press at 200°C for 60 minutes to produce a laminate of layered inorganic material sheets. The silicone resin content in the laminate was 11% by mass. Furthermore, the mass loss of the silicone resin after heating at 500°C for 1 hour was 2% by mass.
The laminate was heated in a muffle furnace at 500°C for 10 minutes to obtain a layered inorganic sheet in which voids were formed within and between the layered inorganic papers, and this was used as a battery pack insulating material. In the obtained battery pack insulating material, the average size of the voids in the thickness direction within the layered inorganic paper was 3 μm, and the average size of the voids between the layered inorganic papers in the thickness direction was 15 μm. Furthermore, in the cross section of the layered inorganic sheet, the aspect ratio of the voids in the width direction/thickness direction was 5, and the average void occupancy was 50%.

REFERENCE SIGNS LIST 10 Battery pack 20 Module 20a Connection module member 20b Bus bar 21 Battery cell 22 Safety valve 23 Terminal 30 Case 31 Storage section 31b Bottom 31s Side wall 32 Lid section 40 Battery pack heat insulating material 41 Heat insulating sheet 42 Layered inorganic material sheet 43 Layered inorganic material paper 45, 45a, 45b Space SP Steel plate S1 Non-heated surface S2 Heating surface

Claims (15)

A heat insulating material for a battery pack, comprising a layered inorganic sheet formed by laminating layered inorganic paper,
A heat insulating material for a battery pack, characterized in that there are voids between at least the layered inorganic paper, the voids having a size of 10 μm or more and 100 μm or less in the thickness direction. The insulating material for a battery pack according to claim 1, further characterized in that the layered inorganic paper has voids with a thickness direction dimension of 1 μm or more and 50 μm or less. The insulating material for a battery pack according to claim 1 or 2, wherein the aspect ratio of the voids in the cross section of the layered inorganic material sheet is 2 or more in the width direction/thickness direction. The insulating material for a battery pack according to any one of claims 1 to 3, wherein the average void occupancy is 5% or more and 70% or less in a 1 mm x 1 mm section of the cross section of the layered inorganic material sheet. The insulating material for a battery pack according to any one of claims 1 to 4, wherein the average size of the voids between the layered inorganic paper sheets is larger than the average size of the voids within the layered inorganic paper sheets in the thickness direction of the voids. The insulating material for a battery pack according to any one of claims 1 to 5, wherein the layered inorganic paper contains at least one silicate mineral selected from the group consisting of vermiculite, montmorillonite, beidellite, nontronite, saponite, hectorite, stevensite, and mica. The insulating material for a battery pack according to any one of claims 1 to 6, wherein the layered inorganic paper contains mica. The insulating material for a battery pack according to any one of claims 1 to 7, wherein the layered inorganic paper has a thickness of 0.05 mm or more and 0.2 mm or less. The insulating material for a battery pack according to any one of claims 1 to 8, wherein the layered inorganic material sheet has a thickness of 0.2 mm or more and 2.0 mm or less. The insulating material for a battery pack according to any one of claims 1 to 9, further comprising an insulating sheet laminated on the layered inorganic material sheet. The insulating material for a battery pack according to claim 10, wherein the insulating sheet has a thickness of 0.5 mm or more and 5.0 mm or less. The insulating material for a battery pack according to claim 10 or 11, wherein the insulating sheet contains at least one material selected from the group consisting of inorganic fibers, organic fibers, inorganic particles, and organic particles. The insulating sheet is silica nanoparticles, titania, alumina fiber, carbon fiber, mica, basalt fiber, soluble fiber, refractory ceramic fiber, glass fiber, aerogel composite, microporous particles, hollow silica particles, thermally expandable inorganic material, aerogel, silica, zirconia, zircon, barium titanate, zinc oxide, alumina, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, zinc hydroxide, iron hydroxide, manganese hydroxide, zirconium hydroxide, gallium hydroxide, cellulose fiber, SiO _2- containing fiber, silica fiber, mullite fiber, alumina fiber, alumina silicate fiber, ceramic fiber, rock wool, alkaline earth silicate fiber, zirconia fiber, and at least one selected from the group consisting of mineral-based fibers. The insulating material for a battery pack according to any one of claims 10 to 12. The insulating material for a battery pack according to any one of claims 10 to 13, having an air layer between the layered inorganic material sheet and the insulating sheet. A battery pack comprising the insulating material for a battery pack according to any one of claims 1 to 14.