JP7477591B1 - Heat transfer suppression sheet and battery pack - Google Patents

Abstract

[Problem] To provide a heat-transfer-suppressing sheet that can suppress powder falling and maintain excellent heat insulation. [Solution] A heat-transfer-suppressing sheet (10) comprises a heat-insulating material (11) containing inorganic particles, a resin film (12) that contains the heat-insulating material (11) and has a plurality of first holes (14), and a covering material (13) that is laminated to the resin film (12) and covers at least some of the plurality of first holes (14). [Selected Figure] Figure 1

Description

The present invention relates to a heat transfer suppression sheet and a battery pack having the heat transfer suppression sheet.

In recent years, from the perspective of environmental protection, there has been active development of electric vehicles and hybrid vehicles that are driven by electric motors. These electric vehicles and hybrid vehicles are equipped with a battery pack in which multiple battery cells are connected in series or parallel to serve as the power source for the driving electric motor.

These battery cells mainly use lithium-ion secondary batteries, which have higher capacity and higher output than lead-acid batteries or nickel-metal hydride batteries. If a battery cell experiences thermal runaway, where the temperature rises suddenly and the heat continues to be generated due to an internal short circuit or overcharging, the heat from the battery cell experiencing thermal runaway may propagate to other adjacent battery cells, causing thermal runaway in those other battery cells.

A common method for preventing the spread of heat from a battery cell that has experienced thermal runaway as described above is to place an insulating sheet between the battery cells.

However, when producing an insulating sheet using inorganic particles such as dry silica or silica aerogel as the insulating material and a dry molding method, the inorganic particles may fall off (hereinafter referred to as powder fall) due to pressure, impact, etc.

For example, Patent Document 1 discloses a battery cell thermal runaway barrier having a nonwoven fibrous insulation material containing a fiber matrix of inorganic fibers, thermally insulating inorganic particles, and a binder, and an organic sealing layer that seals the insulation material. In addition, the organic sealing layer has one or more vent holes formed therein so that gas trapped inside can be discharged to the outside when heated to a high temperature.

International Publication No. 2022/024076

However, the battery cell thermal runaway barrier described in Patent Document 1 has vents formed to allow gas trapped inside to escape, and moisture can easily penetrate the interior through the vents when the battery is in use. Specifically, since the temperature inside the battery case that contains the battery cells and other components is prone to change, if the insulating sheet is placed in a hot and humid environment, moisture may penetrate the interior through the vents, reducing the insulating properties.

The present invention was made in consideration of the above problems, and aims to provide a heat transfer suppression sheet and a battery pack having this heat transfer suppression sheet that can suppress powder falling and maintain excellent thermal insulation properties.

The above object of the present invention is achieved by the following configuration [1] relating to the heat transfer suppression sheet.

[1] A heat insulating material containing inorganic particles;
A resin film containing the heat insulating material and having a plurality of first holes;
a covering material laminated on the resin film and covering at least a portion of the plurality of first holes.

Furthermore, preferred embodiments of the present invention relating to the heat transfer suppression sheet relate to the following [2] to [10].

[2] The heat-transfer-suppressing sheet according to [1], characterized in that the internal region enclosed by the resin film and the external region of the heat-transfer-suppressing sheet are at least partially connected.

[3] The heat transfer suppression sheet according to [1] or [2], characterized in that the resin film contains at least one resin selected from polyethylene, polypropylene, polystyrene, polyethylene terephthalate, and vinyl chloride.

[4] The heat transfer suppression sheet according to any one of [1] to [3], characterized in that the coating material contains at least one resin selected from polyethylene, polypropylene, polystyrene, polyethylene terephthalate, and vinyl chloride.

[5] The resin film has a main surface side portion located on a main surface side perpendicular to a thickness direction of the thermal insulation material, and an end surface side portion covering an end surface side approximately parallel to the thickness direction of the thermal insulation material,
The first hole is formed at least in a side portion of the main surface,
The heat transfer-suppressing sheet according to any one of [1] to [4], wherein the covering material is laminated on at least a part of the main surface side portion.

[6] The heat transfer suppression sheet described in any one of [1] to [5], characterized in that the coating material is adhered to the resin film.

[7] The covering material has a plurality of second holes and contains the insulating material and the resin film,
The heat transfer suppressing sheet according to any one of [1] to [6], characterized in that, when viewed in the lamination direction of the resin film and the covering material, at least a portion of the plurality of second holes are arranged in a position offset from the plurality of first holes.

[8] Further, the insulating material has an elastic sheet laminated thereon,
The heat transfer-suppressing sheet according to any one of [1] to [7], wherein a laminate in which the heat insulating material and the elastic sheet are laminated is encapsulated in the resin film.

[9] The heat transfer suppression sheet according to any one of [1] to [8], characterized in that the thermal conductivity of the insulating material is less than 1 (W/m·K).

[10] The heat transfer suppression sheet according to any one of [1] to [9], characterized in that the heat insulating material further contains at least one selected from inorganic fibers, organic fibers, and organic particles.

The above object of the present invention is also achieved by the following configuration [11] relating to the battery pack.

[11] An assembled battery having a plurality of battery cells and a heat transfer suppression sheet according to any one of [1] to [10], the plurality of battery cells being connected in series or parallel.

The heat transfer suppression sheet of the present invention has an insulating material containing inorganic particles and a resin film containing this insulating material, so that it can obtain an excellent insulating effect and suppress powder falling. In addition, because at least a portion of the holes formed in the resin film is covered with a coating material, it is possible to suppress the moisture present outside the heat transfer suppression sheet from penetrating into the area of the insulating material, and thus suppress a decrease in the insulating properties.

The battery pack of the present invention has excellent insulation properties and powder fall prevention effects as described above, and has a heat transfer suppression sheet that suppresses moisture penetration, so it is possible to maintain excellent insulation properties and suppress thermal runaway of the battery cells in the battery pack and the spread of flames to the outside of the battery case.

FIG. 1 shows a heat-transfer-suppressing sheet according to a first embodiment of the present invention, where (a) is a perspective view and (b) is a cross-sectional view taken along line II. FIG. 2 is a cross-sectional view that illustrates a schematic diagram of a battery pack to which the heat transfer-suppressing sheet according to the first embodiment is applied. FIG. 3 shows a heat-transfer-suppressing sheet according to a second embodiment of the present invention, where (a) is a top view and (b) is a cross-sectional view taken along line II-II.

The inventors of the present invention have come to the conclusion that in a heat-transfer-suppressing sheet having a thermal insulating material and a resin film containing the thermal insulating material, forming a plurality of holes in the resin film on the main surface side of the thermal insulating material and covering at least some of the holes with a covering material would be effective in solving the problem.

The following describes in detail an embodiment of the present invention with reference to the drawings. Note that the present invention is not limited to the embodiment described below, and can be modified as desired without departing from the spirit of the present invention.

[1. Heat transfer suppression sheet]
First Embodiment
Fig. 1 shows a heat-transfer-suppressing sheet according to a first embodiment of the present invention, (a) being a perspective view and (b) being a cross-sectional view taken along line II in Fig. 1. Fig. 2 is a cross-sectional view showing a schematic view of a battery pack to which the heat-transfer-suppressing sheet according to the first embodiment is applied.
A heat transfer-suppressing sheet 10 according to the first embodiment has a thermal insulating material 11 containing inorganic particles, a resin film 12 encapsulating the thermal insulating material 11, and a coating material 13 laminated on the resin film 12. The thermal insulating material 11 has a pair of main surfaces 11a perpendicular to its thickness direction, and two pairs of opposing end surfaces 11b, 11c substantially parallel to the thickness direction.

The resin film 12 has a main surface side portion 12a located on the main surface 11a side of the insulating material 11, and end surface side portions 12b, 12c covering the end surfaces 11b, 11c sides, and covers the entire surface of the insulating material 11. In this embodiment, a heat-shrinkable resin film 12 is used, and the resin film 12 is heat-shrinked (shrink-wrapped) to adhere to the surface of the insulating material 11. In addition, at this time, a plurality of first holes 14 are formed in the main surface side portion 12a of the resin film 12 to exhaust air in the internal area contained in the resin film 12 to the outside. In addition, the resin films 12 are fused to each other at the end surface side portions 12b, 12c, thereby forming fused portions 16.

A covering material 13 is laminated on the outer surface of the main side portion 12a of the resin film 12, and the covering material 13 and the resin film 12 are adhered to each other with an adhesive. As a result, at least a portion of the first hole 14 is covered by the covering material 13.

The configuration of the heat transfer suppression sheet 10 configured as described above when applied to a battery pack will be specifically described below with reference to FIG. 2. As shown in FIG. 2, the heat transfer suppression sheet 10 according to this embodiment is used, for example, in a battery pack. The battery pack 100 has a battery case 30 and a plurality of battery cells 20a, 20b, and 20c stored inside the battery case 30. The heat transfer suppression sheet 10 is interposed between the battery cells 20a and 20b, and between the battery cells 20b and 20c. The plurality of battery cells 20a, 20b, and 20c are connected in series or in parallel by bus bars (not shown) or the like.

The battery cells 20a, 20b, and 20c are preferably, for example, lithium ion secondary batteries, but are not limited thereto and may also be other secondary batteries.

In the first embodiment configured in this manner, the insulating material 11 is encapsulated in the resin film 12, which can prevent particles and the like from falling off when the heat transfer suppression sheet 10 is incorporated into the battery pack 100 or when the battery pack 100 is in use. In addition, the insulating material 11 contains inorganic particles and has high insulating properties, so it can suppress the transfer of heat from a battery cell that has experienced thermal runaway to adjacent battery cells.

Furthermore, according to the first embodiment, the first hole 14 of the resin film 12 is covered with the covering material 13, so that even if the temperature inside the battery case changes and the atmosphere becomes high humidity, the heat insulating material 11 can be prevented from absorbing moisture. Therefore, the heat insulating property of the heat insulating material 11 can be prevented from decreasing.

In the first embodiment, the covering material 13 and the resin film 12 are bonded with an adhesive, but if the surface of the resin film 12 is not completely smooth, a gap 17 may be formed between the covering material 13 and the resin film 12. In addition, when the insulating material 11 is covered with the resin film 12 by shrink packaging, a first hole (not shown) may also be formed in the end surface side portion 12c of the resin film 12 depending on the manufacturing method. In such a case, the internal region enclosed in the resin film 12 and the external region of the heat transfer suppressing sheet 10 are at least partially connected through the first hole 14 and the gap 17, or through the first hole 14, etc. As a result, when the heat transfer suppressing sheet 10 is heated to a high temperature due to an increase in the temperature of the battery cells 20a, 20b, and 20c, the internal gas can be discharged to the outside.

On the other hand, in the first embodiment, when the coating material 13 and the resin film 12 are completely adhered to each other without any gaps and no holes are formed in the end surface side portion 12c of the resin film 12, it is possible to completely prevent moisture in the battery case 30 from penetrating into the heat transfer suppressing sheet 10.

In this embodiment, the covering material 13 is arranged on the main surface side portion 12a of the resin film 12 by adhering the covering material 13 of the same size as the main surface side portion 12a, but the position and size of the covering material 13 are not limited to this. For example, a covering material 13 of a size smaller than the main surface side portion 12a may be adhered to at least a part of the main surface side portion 12a of the resin film 12. However, if there is a step between the resin film 12 and the covering material 13, the contact surface with the battery cells 20a, 20b, 20c may have an uneven shape, which may affect the battery performance. Therefore, it is preferable to arrange the covering material 13 to have approximately the same size as the main surface side portion 12a or a size larger than the main surface side portion 12a so that at least the entire main surface side portion 12a of the resin film 12 can be covered with the covering material 13.

Alternatively, the covering material 13 may be disposed between the insulating material 11 and the resin film 12. Furthermore, the covering material 13 may be disposed so as to surround the pair of main surface side portions 12a and the pair of end surface side portions 12c of the resin film 12, which makes it possible to cover all of the first holes 14 in the resin film 12 with the covering material 13. Furthermore, the covering material 13 may be disposed between the insulating material 11 and the resin film 12. However, in order to obtain a sufficient effect of suppressing the intrusion of moisture into the internal region enclosed in the resin film 12, it is preferable that the covering material 13 is disposed so as to cover the outer surface of the resin film 12.

Second Embodiment
Fig. 3 shows a heat-transfer-suppressing sheet according to a second embodiment of the present invention, where (a) is a top view and (b) is a cross-sectional view taken along line II-II. In the second embodiment shown in Fig. 3, the same components as those in the first embodiment shown in Fig. 1 are given the same reference numerals, and detailed descriptions thereof will be omitted or simplified. Also, the fused portion 16 shown in Fig. 1 is omitted in Fig. 3. Below, the heat-transfer-suppressing sheet according to the second embodiment will be described as being applied to the battery pack 100 shown in Fig. 2.

As shown in FIG. 3, in the heat transfer suppression sheet 40 according to the second embodiment, the main surface 11a and end surfaces 11b, 11c of the heat insulating material 11 are covered with the resin film 12 by shrink packaging. Furthermore, the main surface side portion 12a and end surface side portions 12b, 12c of the resin film 12 are covered with the covering material 23 by shrink packaging. The main surface side portion 23a of the covering material 23 has a plurality of second holes 15 formed therein to allow the air inside the covering material 23 to be discharged to the outside when the covering material 23 is shrink packaged. Furthermore, when viewed in the lamination direction of the resin film 12 and the covering material 13, i.e., when viewed from the top as shown in FIG. 3(a), at least some of the plurality of second holes 15 are positioned at positions offset from the plurality of first holes 14.

Even in the second embodiment configured in this manner, the insulating material 11 is covered with the resin film 12, so that powder falling can be suppressed. Furthermore, the first hole 14 and the second hole 15 are formed at positions offset from each other, and the first hole 14 of the resin film 12 is covered with the covering material 23, so that the surface of the insulating material 11 is not exposed. Therefore, it is possible to suppress the penetration of moisture into the area of the insulating material 11, and to suppress the deterioration of the insulating properties.

Furthermore, in the second embodiment, the covering material 13 and the resin film 12 are not completely bonded, and the covering material 13 is made of a film that shrinks when heated, and is then heated and shrunk to adhere to the resin film 12. As a result, a small gap 17 exists between the resin film 12 and the covering material 13, and the region where the insulating material 11 is contained in the resin film 12 communicates with the external region of the heat transfer suppressing sheet 40 via the first hole 14, the gap 17, and the second hole 15. Therefore, when the heat transfer suppressing sheet 40 is heated to a high temperature due to an increase in the temperature of the battery cells 20a, 20b, and 20c, the gas in the internal region contained in the resin film 12 can be discharged to the outside.

Third Embodiment
In the first and second embodiments, only the heat insulating material 11 is enclosed in the resin film 12, but in the third embodiment, a laminate in which the heat insulating material 11 and an elastic sheet are laminated is enclosed in the resin film 12. The third embodiment having an elastic sheet configured in this manner can be explained in the same manner as the first and second embodiments by replacing the heat insulating material 11 with the laminate in Figures 1 to 3, so detailed drawings are omitted. When an elastic sheet is laminated on the heat insulating material 11, the heat insulating material may be disposed between a pair of elastic sheets, or the elastic sheet may be disposed between a pair of heat insulating materials.

In this way, by encasing the laminate having the elastic sheet in the resin film 12, the resin film 12 can prevent misalignment between the insulating material and the elastic sheet. In addition, the elastic sheet has a predetermined elasticity, and when the heat transfer suppression sheet is pressed due to the expansion of the battery cell, the elastic sheet deforms by an appropriate amount, thereby suppressing the repulsive force on the battery cell. Therefore, it is possible to prevent a decrease in battery performance caused by repeated pressing and releasing of the battery cell.

In the first to third embodiments, the resin film 12 is shaped to cover the surface of the insulating material 11 or the laminate by shrink wrapping using heat shrinkage, but the present invention is not limited to shrink wrapping. For example, after wrapping the surface of the insulating material 11 (laminate) with the resin film 12, the overlapping resin films 12 can be bonded together using heat or an adhesive. Even with this configuration, if the first hole is not formed in the resin film 12, air may remain in the internal area after bonding. Therefore, it is preferable to form the first hole 14 in the resin film 12, and the configuration of the present invention can be used preferably.

Next, examples of materials that make up the heat transfer suppression sheets according to the first to third embodiments will be described in detail.

[Resin film]
The material constituting the resin film 12 can be at least one resin selected from polyethylene, polypropylene, polystyrene, vinyl chloride, nylon, acrylic, epoxy resin, polyurethane, polyether ether ketone, polyetherimide, polyethylene terephthalate, polyphenyl sulfide, polycarbonate, and aramid.

As shown in the first to third embodiments, it is preferable to use shrink packaging when covering the entire surface of the insulating material 11 or the laminate having the insulating material 11 and the elastic sheet with a resin film 12. Therefore, it is more preferable to use a resin film 12 made of a material suitable for shrink packaging. Such materials include polyethylene, polypropylene, polystyrene, polyethylene terephthalate, and polyvinyl chloride.

(Thickness of resin film)
If the thickness of the resin film 12 exceeds 1 mm, it becomes difficult to conform to the shape of the thermal insulation material 11, and there is a risk of cracks or breaks occurring in the resin film 12. Therefore, the thickness of the resin film 12 is preferably 1 mm or less, more preferably 0.1 mm or less, and even more preferably 0.05 mm or less.
On the other hand, the lower limit of the thickness of the resin film 12 is not particularly limited, but in order to obtain a desired strength, it is preferably 0.005 mm or more, and more preferably 0.01 mm or more.

<Other materials contained in the resin film>
In addition, since the resin film 12 is required to be resistant to the high temperatures of the battery cells 20a, 20b, and 20c, it is preferable that the resin film 12 has flame retardancy, and specifically, it is preferable that the resin film 12 contains an inorganic substance or a flame retardant. Other materials contained in the resin film 12 include inorganic substances such as talc, calcium carbonate, aluminum hydroxide, titanium oxide, vermiculite, zeolite, synthetic silica, zirconia, zircon, barium titanate, zinc oxide, and alumina, and flame retardants such as bromine-based flame retardants, chlorine-based flame retardants, phosphorus-based flame retardants, boron-based flame retardants, silicone-based flame retardants, and nitrogen-containing compounds.

[Coating material]
The materials constituting the covering materials 13, 23 may be the same as those of the resin film 12, but they may be made of the same material as the resin film 12 or may be made of a different material. When the covering material 23 is attached to the surface of the resin film 12 by shrink packaging as shown in Fig. 3, it is preferable that the covering material 23 contains a material suitable for shrink packaging.

[Elastic sheet]
As shown in the third embodiment, a known elastic sheet can be used when the laminate of the elastic sheet and the heat insulating material 11 is enclosed in the resin film 12. Specifically, a sheet formed of rubber or a thermoplastic elastomer having elasticity that flexibly deforms in response to deformation of the battery cells 20a, 20b, and 20c can be used.

The rubber may be either synthetic or natural rubber. Examples of synthetic rubber include styrene butadiene rubber, butadiene rubber, chloroprene rubber, isoprene rubber, butyl rubber, ethylene propylene rubber, nitrile rubber, silicone rubber, fluororubber, acrylic rubber, urethane rubber, polysulfide rubber, epichlorohydrin rubber, and foamed silicone.

Examples of thermoplastic elastomers include polystyrene-based, polyolefin-based, vinyl chloride-based, polyurethane-based, polyester-based, polyamide-based, and polybutadiene-based thermoplastic elastomers. The elastomer may be either porous or non-porous. If the elastomer is porous, the cell structure may be either closed-cell type or open-cell type.

(Elastic sheet size)
The thickness of the elastic sheet is not particularly limited, but in order to effectively obtain the effect of the elastic sheet, it is preferable that the thickness be 1 mm or more and 10 mm or less.

[Thermal insulation]
The heat insulating material 11 used in the heat transfer suppressing sheet according to the present embodiment is not particularly limited as long as it has a heat insulating effect. Thermal conductivity can be mentioned as an index showing the heat insulating effect, and in the present embodiment, the heat conductivity of the heat insulating material is preferably less than 1 (W/m·K), more preferably less than 0.5 (W/m·K), and more preferably less than 0.2 (W/m·K). Furthermore, the heat conductivity of the heat insulating material is more preferably less than 0.1 (W/m·K), more preferably less than 0.05 (W/m·K), and particularly preferably less than 0.02 (W/m·K).
The thermal conductivity of the insulating material can be measured in accordance with the "Test method for thermal conductivity of refractories" described in JIS R 2251.

(Insulation size)
When laminating the insulating material 11 and the elastic sheet, it is preferable that the size of the main surface 11a of the insulating material 11 and the size of the main surface perpendicular to the thickness direction of the elastic sheet are approximately the same, but this is not particularly limited.

The heat insulating material 11 contains inorganic particles and, as other components, may contain at least one selected from inorganic fibers, organic fibers, and organic particles. Specific examples of each are shown below.
<Inorganic particles>
As the inorganic particles, a single inorganic particle may be used, or two or more types of inorganic particles may be used in combination. As the type of inorganic particles, from the viewpoint of the heat transfer suppression effect, it is preferable to use particles made of at least one inorganic material selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles, and it is more preferable to use oxide particles. In addition, the shape is not particularly limited, but it is preferable to include at least one selected from nanoparticles, hollow particles, and porous particles, and specifically, silica nanoparticles, metal oxide particles, inorganic balloons such as microporous particles and hollow silica particles, particles made of thermally expandable inorganic materials, particles made of hydrous porous bodies, etc. can also be used.

If the average secondary particle diameter of the inorganic particles is 0.01 μm or more, they are easy to obtain and the increase in manufacturing costs can be suppressed. Furthermore, if it 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.

When two or more types of inorganic particles with different heat transfer suppression effects are used in combination, the heat generating body can be cooled in multiple stages, and the heat absorbing 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. In the following, 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.

<First Inorganic Particles>
(Oxide particles)
Since oxide particles have a high refractive index and a strong effect of scattering light, when oxide particles are used as the first inorganic particles, radiation heat transfer can be suppressed, particularly in high temperature regions such as 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. That is, among the above oxide particles that can be used as inorganic particles, only one type may be used, or two or more types of oxide particles may be used. In particular, silica is a component with high thermal insulation properties, and titania is a component with a high refractive index compared to other metal oxides, and has a high effect of scattering light and blocking radiant heat in high temperature regions of 500 ° C. or more, so it is most preferable to use silica and titania as oxide particles.

(Average primary particle size of oxide particles: 0.001 μm or more and 50 μm or less)
The particle size of the oxide particles can affect the effect of reflecting radiant heat, so if the average primary particle size is limited to a predetermined range, even higher heat insulation can be obtained.
In other words, when the average primary particle size of the oxide particles is 0.001 μm or more, the average primary particle size is sufficiently larger than the wavelength of light that contributes to heating and efficiently diffuses light, thereby suppressing the radiation and transfer of heat within the heat-transfer-inhibiting sheet in a high-temperature region of 500° C. or more, and further improving the thermal insulation properties.
On the other hand, when the average primary particle diameter of the oxide particles is 50 μm or less, the number and number of contact points between the particles do not increase even when compressed, making it difficult to form a conductive heat transfer path, and therefore, the effect on the insulation properties in the normal temperature range where conductive heat transfer is dominant can be reduced.

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

(Nanoparticles)
In the present invention, nanoparticles refer to particles of the order of nanometers having a spherical or nearly spherical average primary particle diameter of less than 1 μm. Nanoparticles have a low density and therefore suppress conductive heat transfer, and when nanoparticles are used as the first inorganic particles, finer voids are dispersed, so that excellent heat insulation properties that suppress convective heat transfer can be obtained. For this reason, it is preferable to use nanoparticles in order to suppress the conduction of heat between adjacent nanoparticles when the battery is used in the normal room temperature range.
Furthermore, if nanoparticles with a small average primary particle size are used as the oxide particles, an increase in conductive heat transfer in the heat-transfer-suppressing sheet can be suppressed even if the heat-transfer-suppressing sheet is compressed by expansion accompanying thermal runaway of the battery cell, causing the internal density to increase. This is thought to be because nanoparticles are prone to forming small voids between particles due to static electricity repulsion, and because their bulk density is low, the particles are packed in a way that provides cushioning properties.

In addition, when nanoparticles are used as the first inorganic particles, the material is not particularly limited as long as it conforms to the definition of nanoparticles. For example, silica nanoparticles are a material with high heat insulation, and the contact points between particles are small, so the amount of heat conducted by silica nanoparticles is smaller than that when silica particles with a large particle diameter are used. In addition, since commonly available silica nanoparticles have a bulk density of about 0.1 (g/cm ³ ), for example, even if the battery cells arranged on both sides of the heat transfer suppression sheet thermally expand and a large compressive stress is applied to the heat transfer suppression sheet, the size (area) and number of contact points between the silica nanoparticles do not significantly increase, and the heat insulation can be maintained. Therefore, it is preferable to use silica nanoparticles as the nanoparticles. Examples of silica nanoparticles include wet silica, dry silica, and aerogel, but silica nanoparticles that are particularly suitable for this embodiment will be described below.

Generally, wet silica has agglomerated particles, whereas dry silica can disperse particles. Since heat conduction is predominant in the temperature range of 90° C. or less, dry silica, which can disperse particles, can provide superior heat insulating performance compared to wet silica.
The heat-transfer-suppressing sheet according to the present embodiment is preferably produced by a manufacturing method in which a mixture containing materials is processed into a sheet shape by a dry method, and therefore, it is preferable to use dry silica, silica aerogel, or the like, which have low thermal conductivity, as the inorganic particles.

(Average primary particle size of nanoparticles: 1 nm or more and 100 nm or less)
By limiting the average primary particle size of the nanoparticles to a predetermined range, even higher heat insulation properties can be obtained.
That is, when the average primary particle size of the nanoparticles is 1 nm or more and 100 nm or less, it is possible to suppress convective heat transfer and conductive heat transfer within the heat-transfer-suppressing sheet, particularly in a temperature range below 500° C., and to further improve the heat insulation. Furthermore, even when compressive stress is applied, the voids remaining between the nanoparticles and the contact points between many of the particles suppress conductive heat transfer, and the heat insulation of the heat-transfer-suppressing sheet can be maintained.
The average primary particle size of the nanoparticles is more preferably 2 nm or more, and even more preferably 3 nm or more, while the average primary particle size of the nanoparticles is more preferably 50 nm or less, and even more preferably 10 nm or less.

(Inorganic hydrate particles)
When inorganic hydrate particles receive heat from a heating element and reach a temperature above the thermal decomposition initiation temperature, they undergo thermal decomposition and release their own water of crystallization to lower the temperature of the heating element and its surroundings, thus exerting the so-called "heat absorption effect". After releasing the water of crystallization, the particles become porous and exert a heat insulating effect due to the countless air holes.
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 ).

For example, aluminum hydroxide has about 35% water of crystallization, and as shown in the following formula, it thermally decomposes and releases water of crystallization, thereby exerting an endothermic effect. After releasing the water of crystallization, it becomes a porous body, _alumina ( _Al2O3 ), and functions as a heat insulating material.
2Al ₍ OH) ₃ → _Al2O3 + _3H2O

As described above, it is preferable that the heat-transfer-suppressing sheet 10 is interposed between battery cells, for example, but in a battery cell that has experienced thermal runaway, the temperature rises rapidly to over 200° C. and continues to rise to around 700° C. Therefore, it is preferable that the inorganic particles contained in the thermal insulation material are made of inorganic hydrates whose thermal decomposition starting temperature is 200° C. or higher.
The thermal decomposition onset 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 of the sudden temperature rise in a battery cell that has experienced thermal runaway, and can efficiently suppress the temperature rise, making these inorganic hydrates preferable.

(Average secondary particle size of inorganic hydrate particles: 0.01 μm or more and 200 μm or less)
In addition, when inorganic hydrate particles are used as the first inorganic particles, if the average particle size is too large, the first inorganic particles (inorganic hydrate) near the center of the heat insulating material may not be completely decomposed because it takes a certain amount of time for the first inorganic particles (inorganic hydrate) near the center of the heat insulating material to reach their thermal decomposition temperature. 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.

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

(Particles made of water-containing porous body)
Specific examples of the hydrous porous body include zeolite, kaolinite, montmorillonite, acid clay, diatomaceous earth, wet silica, dry silica, aerogel, mica, and vermiculite.

(Inorganic balloon)
The heat insulating material used in the present invention may contain inorganic balloons as the first inorganic particles.
When inorganic balloons are contained, convective or conductive heat transfer within the insulating material can be suppressed in a temperature range below 500° C., and the insulating properties of the insulating material can be further improved.
As the inorganic balloon, at least one selected from the group consisting of shirasu balloons, silica balloons, fly ash balloons, barite balloons, and glass balloons can be used.

(Content of inorganic balloons: 60% by mass or less based on the total mass of the insulation material)
The content of the inorganic balloons is preferably 60 mass % or less based on the total mass of the heat insulating material.

(Average particle size of inorganic balloons: 1 μm or more and 100 μm or less)
The average particle size of the inorganic balloons is preferably 1 μm or more and 100 μm or less.

<Second Inorganic Particles>
When two types of inorganic particles are contained in the heat transfer-suppressing sheet 10, 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. As the second inorganic particles, 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, particles made of a water-containing porous body, etc. can be used, the details of which are as described above.

In addition, 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 have a high effect of blocking radiant heat. Furthermore, when large-diameter inorganic particles and small-diameter inorganic particles are used, the small-diameter inorganic particles enter the gaps between the large-diameter inorganic particles, resulting in a denser structure and improving the heat transfer suppression effect. Therefore, when nanoparticles are used as the first inorganic particles, for example, it is preferable to further include particles made of a metal oxide larger in diameter than the first inorganic particles as the second inorganic particles in the heat transfer-suppressing sheet.
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 it is most preferable to use titania.

When at least one type of particle selected from dry silica particles and silica aerogel is used as the first inorganic particles, and at least one type of particle selected from titania, zircon, zirconia, silicon carbide, zinc oxide, and alumina is used as the second inorganic particles, in order to obtain excellent heat insulating performance within a temperature range of 90°C or less, the first inorganic particles are preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more of the total mass of the inorganic particles. Furthermore, the first inorganic particles are preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 80% by mass or less of the total mass of the inorganic particles.

On the other hand, in order to obtain excellent heat insulating performance within a temperature range exceeding 90°C, the second inorganic particles are preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more, based on the total mass of the inorganic particles. Also, the second inorganic particles are preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, based on the total mass of the inorganic particles.

(Average primary particle size of second inorganic particles)
When second inorganic particles made of a metal oxide are contained in the heat transfer-suppressing sheet, if the average primary particle diameter of the second inorganic particles is 1 μm or more and 50 μm or less, radiation heat transfer can be efficiently suppressed in a high temperature range of 500° C. or more. The average primary particle diameter of the second inorganic particles is more preferably 5 μm or more and 30 μm or less, and most preferably 10 μm or less.

(Content of inorganic particles)
In this embodiment, when the total content of the inorganic particles in the thermal insulation material is appropriately controlled, the thermal insulation properties of the thermal insulation material can be sufficiently ensured.
The total content of inorganic particles is preferably 60% by mass or more, more preferably 70% by mass or more, based on the total mass of the heat insulating material. If the total content of inorganic particles is too high, the content of organic fibers is relatively reduced, so that in order to sufficiently obtain the reinforcing effect of the skeleton and the retention effect of the inorganic particles, the total content of inorganic particles is preferably 95% by mass or less, more preferably 90% by mass or less, based on the total mass of the heat insulating material.

The content of inorganic particles in the insulating material can be calculated, for example, by heating the insulating material at 800°C, decomposing the organic matter, and then measuring the mass of the remaining part.

<Inorganic fibers>
As the inorganic fiber, a single inorganic fiber may be used, or two or more inorganic fibers may be used in combination. Examples of the inorganic fiber include ceramic fibers such as silica fiber, alumina fiber, alumina silicate fiber, zirconia fiber, carbon fiber, soluble fiber, refractory ceramic fiber, aerogel composite material, magnesium silicate fiber, alkaline earth silicate fiber, potassium titanate fiber, silicon carbide fiber, and potassium titanate whisker fiber, glass fibers such as glass fibers, glass wool, and slag wool, and mineral fibers such as rock wool, basalt fiber, wollastonite, and mullite fiber.
These inorganic fibers are preferred in terms of heat resistance, strength, availability, etc. Among the inorganic fibers, silica-alumina fibers, alumina fibers, silica fibers, rock wool, alkaline earth silicate fibers, and glass fibers are particularly preferred in terms of handling properties.

The cross-sectional shape of the inorganic fibers is not particularly limited, and examples include circular cross-sections, flat cross-sections, hollow cross-sections, polygonal cross-sections, and core cross-sections. Among these, modified cross-section fibers having hollow, flat, or polygonal cross-sections are preferably used because they have slightly improved thermal insulation.

(Average fiber length of inorganic fibers)
The preferred lower limit of the average fiber length of the inorganic fibers is 0.1 mm, and the more preferred lower limit is 0.5 mm. On the other hand, the preferred upper limit of the average fiber length of the inorganic fibers is 50 mm, and the more preferred upper limit is 10 mm. If the average fiber length of the inorganic fibers is less than 0.1 mm, the inorganic fibers are less likely to be entangled with each other, and the mechanical strength of the insulating material may be reduced. On the other hand, if it exceeds 50 mm, although a reinforcing effect is obtained, the inorganic fibers may not be able to be tightly entangled with each other, or may be curled up by a single inorganic fiber, which may lead to a decrease in thermal insulation.

The preferred lower limit of the average fiber diameter of the inorganic fibers is 1 μm, more preferably 2 μm, and even more preferably 3 μm. On the other hand, the preferred upper limit of the average fiber diameter of the inorganic fibers is 15 μm, and more preferably 10 μm. If the average fiber diameter of the inorganic fibers is less than 1 μm, the mechanical strength of the inorganic fibers themselves may decrease. From the viewpoint of the effect on human health, the average fiber diameter of the inorganic fibers is preferably 3 μm or more. On the other hand, if the average fiber diameter of the inorganic fibers is greater than 15 μm, the solid heat transfer through the inorganic fibers may increase, leading to a decrease in insulation, and the moldability and strength of the heat transfer suppression sheet may deteriorate.

(Inorganic fiber content)
In this embodiment, when the thermal insulation material contains inorganic fibers, the content of the inorganic fibers is preferably 3 mass % or more and 15 mass % or less with respect to the total mass of the thermal insulation material.

Moreover, the content of inorganic fibers is more preferably 5% by mass or more and 10% by mass or less based on the total mass of the insulation material. By setting the content at such a level, the shape retention, pressing force resistance, wind pressure resistance, and inorganic particle retention capacity of the inorganic fibers are expressed in a well-balanced manner. Furthermore, by appropriately controlling the content of inorganic fibers, the organic fibers and inorganic fibers become entangled with each other to form a three-dimensional network, which further improves the effect of retaining the inorganic particles and other compounding materials described below.

<Organic Fiber>
The organic fibers have the effect of imparting flexibility to the insulating material, and also have the effect of increasing the strength of the insulating material by forming a skeleton of the organic fibers. In addition, when inorganic particles and other organic fibers are fused to the surface of the organic fibers, the effect of increasing the strength of the sheet and the effect of maintaining the shape can be further improved. In addition, when the insulating material contains an appropriate amount of organic fibers, multiple voids are formed inside the insulating material, and when the insulating material is heated, air and moisture can be released to the outside through the voids.

Although single-component organic fibers such as cellulose fibers can be used as the organic fiber material in the insulation material, it is preferable to use binder fibers with a core-sheath structure. Binder fibers with a core-sheath structure have a core that extends in the longitudinal direction of the fiber and a sheath that is formed to cover the outer periphery of the core. In this case, the core is made of a first organic material, the sheath is made of a second organic material, and the melting point of the first organic material is higher than the melting point of the second organic material.

(First Organic Material)
In the present embodiment, when a binder fiber having a core-sheath structure is used, the first organic material constituting the core is not particularly limited as long as it has a melting point higher than that of the sheath present on the outer peripheral surface of the core, i.e., the second organic material. The first organic material may be at least one selected from the group consisting of polyethylene terephthalate, polypropylene, and nylon.

(Second Organic Material)
The second organic material is not particularly limited as long as it has a melting point lower than that of the first organic material constituting the organic fiber. The second organic material may be at least one selected from the group consisting of polyethylene terephthalate, polyethylene, polypropylene, and nylon.
The melting point of the second organic material is preferably 90° C. or higher, and more preferably 100° C. or higher. The melting point of the second organic material is preferably 150° C. or lower, and more preferably 130° C. or lower.

(Organic fiber content)
When the content of organic fibers in the heat insulating material is appropriately controlled, the effect of reinforcing the skeleton can be sufficiently obtained.
The content of the organic fibers is preferably 5% by mass or more, more preferably 10% by mass or more, based on the total mass of the heat insulating material. If the content of the organic fibers is too high, the content of the inorganic particles is relatively reduced, so that in order to obtain the desired heat insulating performance, the content of the organic fibers is preferably 25% by mass or less, more preferably 20% by mass or less, based on the total mass of the heat insulating material.

(Organic fiber length)
The fiber length of the organic fibers is not particularly limited, but from the viewpoint of ensuring moldability and processability, it is preferable that the average fiber length of the organic fibers is 10 mm or less.
On the other hand, from the standpoint of allowing the organic fibers to function as a skeleton and ensuring the compressive strength of the heat-transfer-suppressing sheet, the average fiber length of the organic fibers is preferably 0.5 mm or greater.

<Organic particles>
As the organic particles, hollow polystyrene particles or the like can be used.

<Other ingredients>
(Hot melt powder)
In addition to the binder fibers and inorganic particles, the heat transfer suppressing sheet may contain hot melt powder in the mixture. The hot melt powder is, for example, a powder containing a third organic material different from the first organic material and the second organic material, and has the property of melting when heated. By containing the hot melt powder in the mixture and heating it, the hot melt powder melts, and when cooled, it hardens in a state containing the surrounding inorganic particles. Therefore, it is possible to further suppress the falling off of the inorganic particles of the heat insulating material.

Hot melt powders include those with various melting points, but a hot melt powder with an appropriate melting point can be selected taking into consideration the melting points of the core and sheath of the binder fiber used. When using binder fibers with a core-sheath structure as the organic fiber, if the third organic material, which is a component of the hot melt powder, has a melting point lower than that of the first organic material that constitutes the organic fiber, the heating temperature can be set to melt the sheath and hot melt powder while leaving the core. For example, if the melting point of the hot melt powder is lower than the melting point of the sheath, the heating temperature during production can be set between the melting points of the core and the sheath, making it even easier to set the heating temperature.

On the other hand, the type of hot melt powder used can be selected so that its melting point is between the melting points of the core and the sheath. When a hot melt powder with such a melting point is used, when the sheath and hot melt powder melt together and then cool and harden, the organic fiber (core) and the molten sheath around it, as well as the hot melt powder present in the gaps between the inorganic particles, harden first. As a result, the position of the organic fiber can be fixed, and then the molten sheath is welded to the organic fiber, making it easier to form a three-dimensional skeleton. This can further improve the strength of the entire sheet.

If the melting point of the third organic material constituting the hot melt powder is sufficiently lower than the melting point of the first organic material constituting the core, the heating temperature setting margin in the heating process can be expanded, making it easier to set the temperature to obtain the desired structure. For example, the melting point of the first organic material is preferably 60°C or more higher than the melting point of the third organic material, more preferably 70°C or more higher, and even more preferably 80°C or more higher.

The melting point of the hot melt powder (third organic material) is preferably 80°C or higher, and more preferably 90°C or higher. The melting point of the hot melt powder (third organic material) is preferably 180°C or lower, and more preferably 150°C or lower. Components constituting the hot melt powder include polyethylene, polyester, polyamide, ethylene vinyl acetate, etc.

(Hot melt powder content)
When hot melt powder is contained in the insulating material in order to suppress the falling off of inorganic particles, the effect of suppressing powder falling can be obtained even with a small amount of the hot melt powder contained. Therefore, the content of the hot melt powder is preferably 0.5 mass% or more, more preferably 1 mass% or more, based on the total mass of the insulating material.
On the other hand, when the content of the hot melt powder is increased, the content of inorganic particles and the like is relatively decreased. Therefore, in order to obtain the desired insulation performance, the content of the hot melt powder is preferably 5 mass % or less, and more preferably 4 mass % or less, based on the total mass of the material of the insulation material.

When the insulating material contains hot melt powder, the heating temperature in the heating step is preferably set to 10°C or more higher than the higher of the melting point of the second organic material constituting the sheath and the melting point of the third organic material constituting the hot melt powder, and more preferably set to 20°C or more higher. On the other hand, the heating temperature is preferably set to 10°C or more lower than the melting point of the first organic material constituting the core, and more preferably set to 20°C or more lower. By setting the heating temperature in this manner, a strong skeleton can be formed, the strength of the sheet can be further improved, and the inorganic particles can be prevented from falling off.

The insulating material may further contain other binders, colorants, etc., as necessary. All of these are useful for reinforcing the insulating material and improving its formability, and it is preferable that the total amount of these be 10% by mass or less of the total mass of the insulating material.

Next, we will explain the manufacturing method of the heat transfer suppression sheet according to this embodiment.

2. Method for producing heat transfer-suppressing sheet
The heat transfer-suppressing sheet 10 according to the first embodiment can be produced, for example, by the following method.
First, the insulating material 11 containing inorganic particles is placed on a planar film having a first hole 14, and then the film is folded to cover the upper surface of the insulating material 11 with the film. Next, the film on the lower surface of the insulating material 11 and the film on the upper surface are bonded by heating while applying pressure around the insulating material 11. The bonded portion in this process becomes the fusion portion 16 shown in FIG. 1. Then, the film around the insulating material 11 is shrunk by heating, thereby forming a resin film 12 in close contact with the main surface 11a and end surfaces 11b and 11c of the insulating material 11. The formation of the first hole 14 may be performed at any timing before the film is shrunk, and a plurality of holes that allow the enclosed air to be discharged to the outside may be formed in any region of the film.

Then, the covering material 13 is laminated on the main surface side portion 12a of the resin film 12, and the resin film 12 and the covering material 13 are bonded together with an adhesive or the like. When an adhesive tape is used as the covering material 13, it is sufficient to simply attach the covering material 13 to the main surface side portion 12a of the resin film 12. In this way, the heat transfer suppression sheet 10 can be obtained.

The heat transfer-suppressing sheet 40 according to the second embodiment can be manufactured, for example, by the following method.
First, similarly to the first embodiment, a resin film 12 is formed by shrink wrapping in contact with the main surface 11a and end surfaces 11b, 11c of the heat insulating material 11. Next, a film for a covering material having a second hole 15 is used to shrink wrap the heat insulating material 11 and the resin film 12 in the same manner as in the method for forming the resin film 12, and a covering material 23 is formed in close contact with the surface of the resin film 12. At this time, at least a part of the second hole 15 is arranged in a position offset from the first hole 14 when viewed in the lamination direction of the resin film 12 and the covering material 23. This allows the heat transfer suppressing sheet 40 to be obtained.

Furthermore, the heat transfer suppression sheet according to the third embodiment can be obtained in the same manner as the first or second embodiment after laminating the insulating material 11 and an elastic sheet (not shown) to form a laminate.

[3. Battery pack]
The battery pack according to the embodiment of the present invention includes the heat-transfer-inhibiting sheet described above in [1. Heat-transfer-inhibiting sheet]. That is, as shown in Fig. 2, the battery pack 100 includes a plurality of battery cells 20a, 20b, and 20c, and, for example, the heat-transfer-inhibiting sheet 10 described above, with the battery cells 20a, 20b, and 20c connected in series or in parallel. The heat-transfer-inhibiting sheet 10 is interposed between the battery cells 20a and 20b, and between the battery cells 20b and 20c. The battery cells 20a, 20b, and 20c and the heat-transfer-inhibiting sheet 10 are housed in a battery case 30.

In the battery pack 100 configured in this manner, the heat transfer suppression sheet 10 containing the insulating material 11 is disposed between the battery cells, so that the transfer of heat from a battery cell that has experienced thermal runaway to an adjacent battery cell can be suppressed. Furthermore, even if the temperature inside the battery case 30 changes and the atmosphere becomes highly humid, it is possible to suppress the moisture outside the heat transfer suppression sheet 10 from penetrating into the insulating material 11 contained in the resin film 12. Therefore, it is possible to suppress the deterioration of the insulating properties of the insulating material 11.

Furthermore, if the internal region enclosed in the resin film 12 and the external region of the heat transfer suppression sheet 10 are at least partially connected, when the heat transfer suppression sheet 10 is heated to a high temperature due to an increase in the temperature of the battery cells 20a, 20b, and 20c, the gas in the internal region can be discharged to the outside.

Although not shown in the figures, the heat transfer suppression sheet described in [1. Heat transfer suppression sheet] above can be disposed not only between multiple battery cells, but also, for example, between a battery cell and a battery case. In this way, even when the heat transfer suppression sheet is disposed between a battery cell and a battery case, the effect of suppressing the conduction of heat to the outside of the battery case can be maintained for a long period of time.

For example, therefore, when a battery pack 100 incorporating the heat transfer suppression sheets 10, 40 is used in an electric vehicle (EV) or the like and placed under the floor of the vehicle occupants, the safety of the occupants can be ensured even if a battery cell were to catch fire.
Furthermore, in this case, by arranging the heat transfer suppression sheets 10, 40, etc. between the battery cells and the battery case, there is no need to fabricate new fire retardant materials, etc., and a safe assembled battery can be constructed at low cost.

REFERENCE SIGNS LIST 10, 40 heat transfer suppressing sheet 11a principal surface 11b, 11c end surface 11 heat insulating material 12a, 23a principal surface side portion 12b, 12c end surface side portion 12 resin film 13, 23 covering material 14 first hole 15 second hole 16 fusion portion 17 gap portion 20a, 20b, 20c battery cell 30 battery case 100 assembled battery

Claims (10)

A thermal insulation material including inorganic particles;
A resin film containing the heat insulating material and having a plurality of first holes;
a covering material laminated on the resin film and covering at least a portion of the first holes ,
A heat-transfer-suppressing sheet , wherein an internal region enclosed by the resin film and an external region of the heat-transfer-suppressing sheet are at least partially in communication with each other . The heat transfer suppression sheet according to claim 1, characterized in that the resin film contains at least one resin selected from polyethylene, polypropylene, polystyrene, polyethylene terephthalate, and vinyl chloride. The heat transfer suppression sheet according to claim 1, characterized in that the coating material contains at least one resin selected from polyethylene, polypropylene, polystyrene, polyethylene terephthalate, and vinyl chloride. The resin film has a main surface side portion located on a main surface side perpendicular to a thickness direction of the thermal insulation material, and an end surface side portion covering an end surface side substantially parallel to the thickness direction of the thermal insulation material,
The first hole is formed at least in a side portion of the main surface,
The heat transfer suppressing sheet according to claim 1 , wherein the covering material is laminated on at least a part of the side portion of the main surface. The heat transfer suppressing sheet according to claim 4 , wherein the covering material is adhered to the resin film. the covering material has a plurality of second holes and contains the heat insulating material and the resin film;
The heat transfer suppressing sheet according to claim 1 , characterized in that, when viewed in the stacking direction of the resin film and the covering material, at least a portion of the plurality of second holes are positioned at a position offset from the plurality of first holes. Further, the insulating material has an elastic sheet laminated thereon,
The heat transfer-suppressing sheet according to claim 1 , wherein a laminate in which the heat insulating material and the elastic sheet are laminated is enclosed in the resin film. The heat transfer suppression sheet according to claim 1, characterized in that the thermal conductivity of the insulating material is less than 1 (W/m·K). The heat transfer suppression sheet according to claim 1, characterized in that the heat insulating material further contains at least one selected from inorganic fibers, organic fibers, and organic particles. 10. A battery pack comprising: a plurality of battery cells; and the heat transfer-suppressing sheet according to claim 1 , the plurality of battery cells being connected in series or in parallel.

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