Heat transfer suppression sheet and assembled battery

Abstract

To realize uniform heat insulation and heat dissipation; and, if thermal runaway occurs in battery cells, block the heat between adjacent battery cells and quickly dissipate the heat generated by the battery cells.SOLUTION: A heat transfer suppression sheet 10 includes: uniformly dispersed inorganic particles 21; first inorganic fibers 23 that are uniformly dispersed and oriented in one direction parallel to main surfaces 10a, 10b of the sheet; and second inorganic fibers 24 that intertwine with the first inorganic fibers 23 to form a 3-dimensional web structure.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a battery pack that serves as a power source for an electric motor that drives, for example, an electric vehicle or a hybrid vehicle, and a heat transfer suppression sheet used in the battery pack. [Background technology]

[0002] BACKGROUND ART Conventionally, in order to suppress heat transfer from a heat-generating body to another object, a heat-transfer-suppressing sheet has been used which is placed close to the heat-generating body or at least a portion of which is in contact with the heat-generating body.

[0003] In recent years, there has been an increasing demand for lithium-ion secondary batteries, which offer higher capacity and higher output than lead-acid batteries, nickel-metal hydride batteries, etc., and they are used not only as small-capacity secondary batteries for mobile phones, personal computers, and small electronic devices, but also as large-capacity secondary batteries for automobiles, backup power supplies, etc. In particular, in the automotive field, active development of electric vehicles and hybrid vehicles driven by electric motors has been underway from the perspective of environmental protection. These electric vehicles and hybrid vehicles are equipped with assembled batteries in which multiple battery cells are connected in series or parallel to provide the power source for the drive electric motor.

[0004] However, lithium-ion secondary batteries can generate heat due to chemical reactions during charging and discharging, which can cause battery malfunctions. For example, if a battery cell suddenly heats up and causes thermal runaway, the heat can spread to other adjacent battery cells, potentially causing thermal runaway in those cells.

[0005] In the field of battery packs such as those described above, various heat transfer suppression sheets have been proposed to be placed between battery cells in order to suppress the propagation of heat from a battery cell that has experienced thermal runaway to adjacent battery cells and to prevent problems such as the spread of battery fire and explosion due to a chain reaction of thermal runaway.

[0006] For example, Patent Document 1 describes a heat-transfer-suppressing sheet that includes a composite layer containing fibers and silica aerogel and resin struts arranged in the thickness direction of the composite layer. With such a heat-transfer-suppressing sheet, the resin struts can distribute compressive stress applied to the sheet, thereby maintaining its insulating properties. By using the heat-transfer-suppressing sheet between battery cells, the resin struts can distribute compressive stress applied to the silica aerogel in the sheet, thereby maintaining thermal insulation between the battery cells for a long period of time. As a result, it is possible to suppress the spread of fire due to thermal runaway between battery cells, thereby providing a safe vehicle battery. Furthermore, it is described that using a porous resin for the insulating resin struts can suppress heat conduction from the battery cells. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2017-215014 Summary of the Invention [Problem to be solved by the invention]

[0008] However, because the heat-transfer-suppressing sheet has high thermal insulation properties, if it comes into close contact with a battery cell, heat may be trapped, accelerating thermal runaway of the battery cell. Furthermore, the heat-transfer-suppressing sheet has different insulating properties between the resin struts where aerogel is not present and the composite layer where aerogel is present, making it difficult to achieve uniform heat-insulating properties and heat dissipation within the sheet. As a result, the transfer of heat generated by the battery cells is also different, and if thermal runaway occurs, the heat-transfer-suppressing sheet may not be able to suppress the heat transfer.

[0009] The present invention has been made in view of the above-mentioned circumstances, and aims to provide a heat-transfer-suppressing sheet that can obtain uniform thermal insulation and heat dissipation properties, and that can block heat between adjacent battery cells and quickly dissipate heat generated by the battery cells in the event of thermal runaway, as well as a battery pack in which the heat-transfer-suppressing sheet is interposed between battery cells. [Means for solving the problem]

[0010] The above object of the present invention is achieved by the heat transfer-suppressing sheet having the following configuration [1].

[0011] [1] Uniformly dispersed inorganic particles; First inorganic fibers that are uniformly dispersed and oriented in one direction parallel to the main surface of the sheet; second inorganic fibers that are entangled with the first inorganic fibers to form a three-dimensional web structure; A heat transfer suppression sheet comprising:

[0012] Furthermore, preferred embodiments of the present invention relating to the heat transfer-suppressing sheet relate to the following [2] to

[13] .

[0013] [2] The heat-transfer-suppressing sheet according to [1], wherein the first inorganic fibers have an average fiber diameter larger than the average fiber diameter of the second inorganic fibers.

[0014] [3] The heat-transfer-suppressing sheet according to [1] or [2], wherein the average fiber length of the first inorganic fibers is greater than the average fiber length of the second inorganic fibers.

[0015] [4] The heat transfer-suppressing sheet according to any one of [1] to [3], wherein the first inorganic fibers have a lower degree of crimp than the second inorganic fibers.

[0016] [5] The heat-transfer-suppressing sheet according to any one of [1] to [4], wherein the first inorganic fibers are linear or needle-like, and the second inorganic fibers are dendritic or crimped.

[0017] [6] The first inorganic fiber is an amorphous fiber; The heat transfer-suppressing sheet according to any one of [1] to [5], wherein the second inorganic fibers are at least one type selected from amorphous fibers and crystalline fibers having a glass transition point higher than that of the first inorganic fibers.

[0018] [7] The heat-transfer-suppressing sheet according to any one of [1] to [6], wherein the second inorganic fibers have a thermal conductivity of 41 [W / m·K] or less.

[0019] [8] The heat-transfer-suppressing sheet according to any one of [1] to [7], wherein the first inorganic fibers are at least one type of fibers selected from the group consisting of glass fibers, glass wool, slag wool, rock wool, alkaline earth silicate fibers, and refractory ceramic fibers.

[0020] [9] The heat-transfer-suppressing sheet according to any one of [1] to [8], wherein the second inorganic fibers are at least one type of fibers selected from alumina fibers, mullite fibers, alumina silicate fibers, mineral fibers, and zirconia fibers.

[0021]

[10] The heat transfer-suppressing sheet according to any one of [1] to [9], wherein the inorganic particles are particles of at least one type selected from silica particles, titania particles, zirconia particles, zircon particles, barium titanate particles, zinc oxide particles, and alumina particles.

[0022]

[11] The heat-transfer-suppressing sheet according to any one of [1] to

[10] , wherein the content of the inorganic particles is from 30% by mass to 80% by mass, based on the total mass of the heat-transfer-suppressing sheet.

[0023]

[12] The heat-transfer-suppressing sheet according to any one of [1] to

[11] , wherein the inorganic particles have an average secondary particle diameter of 1 nm or more and 100 nm or less.

[0024]

[13] The heat-transfer-suppressing sheet according to any one of [1] to

[12] , wherein the combined content of the first inorganic fibers and the second inorganic fibers is from 5% by mass to 30% by mass, based on the total mass of the heat-transfer-suppressing sheet.

[0025] The above object of the present invention is also achieved by the following configuration

[14] relating to a battery pack.

[0026]

[14] In a battery pack in which multiple battery cells are connected in series or parallel, A battery pack using the heat transfer-suppressing sheet according to any one of [1] to

[13] . [Effects of the Invention]

[0027] According to the present invention, the first inorganic fibers are dispersed within the heat-transfer-suppressing sheet while oriented in one direction parallel to the main surface, resulting in excellent and uniform insulation and heat dissipation within the sheet, allowing for effective heat dissipation from the battery cells. Therefore, even if a battery cell experiences thermal runaway, heat can be blocked from adjacent battery cells, preventing a chain reaction. Furthermore, the first inorganic fibers and the second inorganic fibers are entangled to form a three-dimensional web structure, and the second inorganic fibers function as a heat transfer path connecting the first inorganic fibers, further improving heat transfer. The three-dimensional web structure also provides excellent strength.

[0028] The battery pack of the present invention uses the heat transfer-suppressing sheet described above, and therefore the battery pack of the present invention can maintain stable operation and minimize damage even if thermal runaway occurs in a battery cell. [Brief explanation of the drawings]

[0029] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a heat-transfer-suppressing sheet according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view schematically showing the battery pack according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0030] The present inventors conducted extensive research to provide a heat-transfer-suppressing sheet with excellent heat insulation and heat dissipation properties that can insulate heat between adjacent battery cells and rapidly dissipate heat generated by the battery cells in the event of thermal runaway. As a result, they discovered that the orientation of the inorganic fibers contained in the sheet is important. The inventors also discovered that oriented first inorganic fibers facilitate heat conduction, resulting in excellent and uniform heat insulation and heat dissipation within the sheet, allowing for effective dissipation of heat generated by the battery cells. They also discovered that entanglement of the first inorganic fibers with the second inorganic fibers to form a three-dimensional web structure allows the second inorganic fibers to act as heat transfer paths connecting the oriented first inorganic fibers, further enhancing heat transfer, and that the three-dimensional web structure also provides excellent strength. The present invention is based on these findings.

[0031] Hereinafter, a heat transfer-suppressing sheet and a battery pack according to an embodiment of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiment described below, and can be implemented with any modifications within the scope of the gist of the present invention.

[0032] [1. Heat transfer suppression sheet] The heat transfer-suppressing sheet of the present invention comprises: (1) Uniformly dispersed inorganic particles; (2) first inorganic fibers that are uniformly dispersed and oriented in one direction parallel to the main surface of the sheet; (3) second inorganic fibers that are entangled with the first inorganic fibers to form a three-dimensional web structure; Includes.

[0033] FIG. 1 is a schematic diagram showing the configuration of a heat-transfer-suppressing sheet 10 according to an embodiment of the present invention. As shown in the figure, first inorganic fibers 23 are oriented in layers in one direction parallel to the main surfaces 10a and 10b of the heat-transfer-suppressing sheet 10. The first inorganic fibers 23 are entangled with second inorganic fibers 24 to form a three-dimensional web structure. At the same time, inorganic particles 21 are uniformly spread and held in the spaces between the first inorganic fibers 23 and the second inorganic fibers 24. The inorganic particles 21, the first inorganic fibers 23, and the second inorganic fibers 24 are all made of heat-resistant materials. Furthermore, countless tiny spaces are formed between the particles, between the particles and the fibers, and between the fibers, providing an insulating effect due to the air, resulting in excellent heat-transfer suppression performance.

[0034] In the present invention, "oriented in one direction" does not necessarily mean that all of the first inorganic fibers 23 are oriented in that direction, but rather that there is a strong tendency for the first inorganic fibers 23 to be aligned in one specific direction. Whether the first inorganic fibers 23 are oriented in a specific direction can be determined by visual inspection, but if it is difficult to distinguish the fibers, it can be confirmed by measuring the bending strength in that direction and finding that it is 20% or more greater than in other directions.

[0035] (First inorganic fiber) First inorganic fibers 23 are amorphous fibers, and second inorganic fibers 24 are at least one type of fibers selected from amorphous fibers and crystalline fibers having a glass transition point higher than that of first inorganic fibers 23. The melting point of crystalline inorganic fibers is usually higher than the glass transition point of amorphous inorganic fibers. Therefore, when exposed to high temperatures, the surfaces of first inorganic fibers 23 soften before the surfaces of second inorganic fibers 24 do, and bind together inorganic particles 21 and second inorganic fibers 24, thereby improving the mechanical strength of heat transfer-suppressing sheet 10.

[0036] Suitable examples of the first inorganic fibers 23 include glass fibers, glass wool, slag wool, rock wool, alkaline earth silicate fibers, and refractory ceramic fibers, which may be used alone or in combination. Among these, inorganic fibers with a melting point of less than 700°C are preferred, and many amorphous inorganic fibers can be used. Fibers containing SiO2 are particularly preferred, and glass fibers are even more preferred because they are inexpensive, readily available, and easy to handle.

[0037] (Second inorganic fiber) As described above, the second inorganic fibers 24 are at least one type of fibers selected from amorphous fibers and crystalline fibers having a glass transition point higher than that of the first inorganic fibers 23. Many crystalline inorganic fibers can be used as the second inorganic fibers 24.

[0038] If the second inorganic fibers 24 are made of crystalline fibers or have a higher glass transition point than the first inorganic fibers 23, the second inorganic fibers 24 will not melt or soften when exposed to high temperatures, even if the first inorganic fibers 23 soften. Therefore, the second inorganic fibers 24 can maintain their shape and remain present between the battery cells even during thermal runaway of the battery cells. Furthermore, if the second inorganic fibers 24 do not melt or soften, minute spaces are maintained between the inorganic particles 21, between the inorganic particles 21 and the first inorganic fibers 23 and the second inorganic fibers 24, and between the first inorganic fibers 23 and the second inorganic fibers 24, thereby providing an insulating effect due to the air, and maintaining excellent heat transfer suppression performance.

[0039] When the second inorganic fibers 24 are crystalline, alumina fibers, mullite fibers, alumina silicate fibers, mineral fibers, and zirconia fibers can be suitably used, either alone or in combination, as the second inorganic fibers 24. Among these, fibers with a melting point of over 1000°C are suitable for use because they do not melt or soften and can maintain their shape even if thermal runaway occurs in the battery cell.

[0040] Furthermore, even if the second inorganic fibers 24 are amorphous, they can be used as long as they have a higher glass transition point than the first inorganic fibers 23. For example, glass fibers having a higher glass transition point than the first inorganic fibers 23 may be used as the second inorganic fibers 24.

[0041] As described above, the first inorganic fibers 23 have a lower glass transition point than the second inorganic fibers 24, and when exposed to high temperatures, the first inorganic fibers 23 soften first, allowing the first inorganic fibers 23 to bond the inorganic particles 21 and the second inorganic fibers 24. However, for example, when the second inorganic fibers 24 are amorphous and have a smaller fiber diameter than the first inorganic fibers 23, if the glass transition points of the first inorganic fibers 23 and the second inorganic fibers 24 are close to each other, the second inorganic fibers 24 may soften first. Therefore, when the second inorganic fibers 24 are amorphous, the glass transition point of the second inorganic fibers 24 is preferably at least 100°C higher than the glass transition point of the first inorganic fibers 23, and more preferably at least 300°C higher.

[0042] (Average fiber diameter and average fiber length of first inorganic fiber and second inorganic fiber) In the present invention, inorganic fibers with a large average fiber diameter (large diameter) have the effect of improving the mechanical strength and shape retention of the heat-transfer-suppressing sheet 10. This effect can be achieved by making either the first inorganic fibers 23 or the second inorganic fibers 24 have a large diameter. Because the heat-transfer-suppressing sheet 10 may be subjected to external impacts, the inclusion of large diameter inorganic fibers increases the impact resistance. Examples of external impacts include pressure caused by the expansion of battery cells and wind pressure caused by the ignition of battery cells.

[0043] In order to improve mechanical strength and shape retention, it is particularly preferable that the large-diameter inorganic fibers are linear or needle-shaped. Note that linear or needle-shaped fibers refer to fibers having a crimp degree (described later), for example, of less than 10%, preferably 5% or less.

[0044] More specifically, to improve the mechanical strength and shape retention of the heat-transfer-suppressing sheet 10, the average fiber diameter of the large-diameter inorganic fibers is preferably 1 μm or more, and more preferably 3 μm or more. However, if the large-diameter inorganic fibers are too thick, there is a risk that the moldability and processability of the heat-transfer-suppressing sheet 10 may decrease, so the average fiber diameter is preferably 20 μm or less, and more preferably 15 μm or less. Furthermore, if the large-diameter inorganic fibers are too long, there is a risk that the moldability and processability may decrease, so the fiber length is preferably 100 mm or less. Furthermore, if the large-diameter inorganic fibers are too short, there is a risk that the shape retention and mechanical strength may decrease, so the fiber length is preferably 0.1 mm or more.

[0045] On the other hand, inorganic fibers with a small average fiber diameter (thin diameter) have the effect of improving the retention of inorganic particles 21 and increasing the flexibility of heat transfer-suppressing sheet 10. Therefore, by making the other of first inorganic fibers 23 and second inorganic fibers 24 have a small diameter, the above effect can be obtained.

[0046] More specifically, to improve the retention of inorganic particles 21, it is preferable that the small-diameter inorganic fibers be easily deformed and flexible. Therefore, it is preferable that the small-diameter inorganic fibers have an average fiber diameter of less than 1 μm, and more preferably 0.1 μm or less. However, if the small-diameter inorganic fibers are too thin, they are prone to breakage, and the ability to retain inorganic particles 21 decreases. Furthermore, a large proportion of the fibers remain entangled in the sheet without retaining inorganic particles 21, which not only reduces the ability to retain inorganic particles 21 but also leads to poor moldability and shape retention. Therefore, the average fiber diameter of the small-diameter inorganic fibers is preferably 1 nm or more, and more preferably 10 nm or more. In addition, if the fine inorganic fibers are too long, moldability and shape retention will decrease, so the fiber length is preferably 0.1 mm or less.

[0047] The fine inorganic fibers are preferably dendritic or crimped. When the fine inorganic fibers have such a shape, they become entangled with the thick inorganic fibers and inorganic particles 21. This improves the ability to retain the inorganic particles 21. Furthermore, when the heat transfer-suppressing sheet 10 is subjected to pressure or wind pressure, the fine inorganic fibers are prevented from sliding and moving, thereby improving the mechanical strength, particularly against external pressure and impact.

[0048] The term "dendritic" refers to a two-dimensionally or three-dimensionally branched structure, such as feather-like, tetrapod-like, radial, or three-dimensional mesh-like. When the fine inorganic fibers are dendritic, the average fiber diameter can be obtained by measuring the diameters of the trunk and branches at several points using an SEM and calculating the average value.

[0049] The crimped structure refers to a structure in which fibers are bent in various directions. One method for quantifying the crimped structure is to calculate the crimp degree from an electron microscope photograph, which can be calculated, for example, using the following formula: Crimp degree (%) = (fiber length - distance between fiber ends) / (fiber length) × 100 Here, both the fiber length and the distance between fiber ends are measured values ​​on an electron microscope photograph. In other words, they are the fiber length and the distance between fiber ends projected onto a two-dimensional plane, and are shorter than the actual values. Based on this formula, the crimp degree of the small diameter inorganic fibers is preferably 10% or more, and more preferably 30% or more. If the crimp degree is low, it becomes difficult to retain the inorganic particles 21 and to form entanglements (networks) between the large diameter inorganic fibers and between the large diameter inorganic fibers.

[0050] As described above, it is preferable that the average fiber diameter of either the first inorganic fibers 23 or the second inorganic fibers 24 is larger than the average fiber diameter of the other. In the present invention, however, it is more preferable that the average fiber diameter of the first inorganic fibers 23 is larger than the average fiber diameter of the second inorganic fibers 24. If the average fiber diameter of the first inorganic fibers 23 is large, the first inorganic fibers 23 have a low glass transition point and soften quickly, so that they become film-like and harden as the temperature rises. On the other hand, if the average fiber diameter of the second inorganic fibers 24 is small, the small-diameter second inorganic fibers 24 remain in their fibrous form even when the temperature rises, so the structure of the heat-transfer-suppressing sheet 10 can be maintained and powder shedding can be prevented.

[0051] It is most preferable to use both thick, linear or needle-like inorganic fibers and thin, dendritic or crimped inorganic fibers as the first inorganic fibers 23, and to use both thick, linear or needle-like inorganic fibers and thin, dendritic or crimped inorganic fibers as the second inorganic fibers 24, as this can further enhance the retention effect, mechanical strength, and shape retention of the inorganic particles 21.

[0052] In addition, since the average fiber length of the first inorganic fibers 23 is longer than that of the second inorganic fibers 24, the orientation length is extended, thereby further improving heat dissipation. Furthermore, since the second inorganic fibers 24 are dendritic or crimped, they can be easily entangled with the first inorganic fibers, which is effective in providing a heat transfer path and maintaining the shape.

[0053] (Thermal Conductivity of First Inorganic Fiber and Second Inorganic Fiber) The better the heat-insulating performance of the heat-transfer-suppressing sheet 10, the lower the thermal conductivity of both the first inorganic fibers 23 and the second inorganic fibers 24. However, since the second inorganic fibers 24 act as heat transfer paths connecting the first inorganic fibers oriented in layers, it is preferable that the second inorganic fibers 24 have a higher thermal conductivity than the first inorganic fibers 23. Therefore, in consideration of the heat-insulating performance, the thermal conductivity of the second inorganic fibers 24 is preferably 41 W / m K or less.

[0054] (Inorganic particles) The material of the inorganic particles 21 is not particularly limited, but oxide particles, carbide particles, nitride particles, and inorganic hydrate particles can be used. Of these, oxide particles are preferred. The shape and size of the inorganic particles 21 are also not particularly limited, but they preferably include at least one type selected from nanoparticles, hollow particles, and porous particles, and more preferably include nanoparticles.

[0055] The inorganic particles 21 may be used alone or in combination of two or more types. When two or more types of inorganic particles 21 with different heat transfer suppression effects are used in combination, the heat generating body can be cooled in multiple stages, and the heat absorption effect can be exerted over a wider temperature range. It is also preferable to use a mixture of large-diameter particles and small-diameter particles as the inorganic particles 21. When small-diameter inorganic particles fill the gaps between large-diameter inorganic particles, a denser structure is formed, thereby improving the heat transfer suppression effect.

[0056] When the average secondary particle diameter of the inorganic particles 21 is 0.01 μm or more, they are easily available and the increase in production costs can be suppressed. Furthermore, when the average secondary particle diameter is 200 μm or less, the desired heat insulating effect can be obtained. Therefore, the average secondary particle diameter of the inorganic particles 21 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.

[0057] The inorganic particles 21 will be described in detail below.

[0058] (oxide particles) Oxide particles preferred as inorganic particles 21 have a high refractive index and a strong effect of diffusely reflecting light, and therefore, when oxide particles are used as inorganic particles 21, radiative heat transfer can be suppressed, particularly in high-temperature regions such as those caused by abnormal heat generation. Specifically, silica particles, titania particles, zirconia particles, zircon particles, barium titanate particles, zinc oxide particles, and alumina particles are preferred. In particular, silica particles are a component with high heat insulating properties, and titania particles are a component with a higher refractive index than other metal oxides, and are highly effective in diffusely reflecting light and blocking radiant heat in high-temperature regions of 500°C or higher, so it is most preferred to use silica particles and titania particles as oxide particles.

[0059] (Average primary particle size of oxide particles: 0.001 μm to 50 μm) 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 insulating properties can be obtained.

[0060] That is, when the average primary particle size of the oxide particles is 0.001 μm or more, it is sufficiently larger than the wavelength of light that contributes to heating, and efficiently diffuses light, thereby suppressing radiative heat transfer within the sheet in high-temperature ranges of 500°C or higher, thereby further improving thermal insulation. On the other hand, when the average primary particle size of the oxide particles is 50 μm or less, the number and number of contact points between particles do not increase even when compressed, making it difficult to form paths for conductive heat transfer, thereby reducing the impact on thermal insulation, especially in normal temperature ranges where conductive heat transfer is dominant.

[0061] When two or more types of oxide particles are used, it is also preferable to use a mixture of large particles and small particles (nanoparticles), and in this case, the average primary particle size of the large particles is more preferably 1 μm or more and 50 μm or less, even more preferably 5 μm or more and 30 μm or less, and most preferably 10 μm or less. 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.

[0062] (nanoparticles) In the present invention, nanoparticles refer to particles on the order of nanometers that are spherical or nearly spherical and have an average primary particle diameter of less than 1 μm. Nanoparticles have a low density, which suppresses conductive heat transfer. Furthermore, when nanoparticles are used as inorganic particles, the finely dispersed voids provide excellent heat insulation, suppressing convective heat transfer. Therefore, the use of nanoparticles is preferred because they can suppress heat transfer between adjacent nanoparticles during normal use at room temperature.

[0063] In the present invention, at least one of oxide particles, carbide particles, nitride particles, and inorganic hydrate particles selected as inorganic particles 21 is preferably nanoparticles. Furthermore, when nanoparticles with a small average primary particle size are used as the oxide particles, an increase in conductive heat transfer in heat-transfer-suppressing sheet 10 can be suppressed even when heat-transfer-suppressing sheet 10 is compressed due to expansion associated with thermal runaway of the battery cell, increasing the internal density. This is thought to be because nanoparticles are prone to forming fine voids between particles due to electrostatic repulsion, and because their bulk density is low, the particles are packed together to provide cushioning.

[0064] In the present invention, when nanoparticles are used as inorganic particles 21, there are no particular limitations on the material as long as they comply with the definition of nanoparticles. For example, silica nanoparticles are a material with high heat insulating properties, and the contact points between particles are small, so the amount of heat conducted by silica nanoparticles is smaller than when silica particles with a larger particle diameter are used. Furthermore, commonly available silica nanoparticles have a bulk density of 0.1 g / cm. 3 Therefore, even if, for example, battery cells arranged on both sides of the heat-transfer-suppressing sheet 10 thermally expand and a large compressive stress is applied to the heat-transfer-suppressing sheet 10, the size (area) and number of contact points between the silica nanoparticles do not increase significantly, and heat insulation properties can be maintained. Therefore, it is preferable to use silica nanoparticles as the nanoparticles. Wet silica, dry silica, aerogel, etc. can be used as the silica nanoparticles.

[0065] As described above, titania has a high effect of blocking radiant heat, and silica 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 10. Therefore, it is most preferable to use both titania particles and silica nanoparticles as the inorganic particles 21.

[0066] (Average primary particle diameter of nanoparticles: 1 nm to 100 nm) If the average primary particle size of the nanoparticles is limited to a predetermined range, even higher heat insulating properties can be obtained.

[0067] That is, when the average primary particle diameter of the nanoparticles is 1 nm or more and 100 nm or less, convective heat transfer and conductive heat transfer within the heat-transfer-suppressing sheet 10 can be suppressed, particularly in the temperature range below 500°C, and the heat insulation properties can be further improved. Furthermore, even when compressive stress is applied, the voids remaining between the nanoparticles and the contact points between the many particles suppress conductive heat transfer, thereby maintaining the heat insulation properties of the heat-transfer-suppressing sheet 10. 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 more preferably 50 nm or less, and even more preferably 10 nm or less.

[0068] (Inorganic hydrate particles) Inorganic hydrate particles are also preferred as the inorganic particles 21. When heated by heat from a heating element and the temperature exceeds the thermal decomposition starting temperature, these inorganic hydrate particles undergo thermal decomposition and release their own water of crystallization, lowering the temperature of the heating element and its surroundings, thereby exhibiting a so-called "endothermic effect." After releasing the water of crystallization, the particles become porous, exhibiting a heat insulating effect due to the countless air holes.

[0069] 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).

[0070] For example, aluminum hydroxide has about 35% water of crystallization, and as shown in the following formula, it thermally decomposes, releasing the water of crystallization and exhibiting an endothermic effect. After releasing the water of crystallization, it becomes a porous alumina (Al2O3) and functions as a heat insulating material. 2Al(OH)3 → Al2O3 + 3H2O

[0071] As will be described later, the battery pack of the present invention has heat-transfer-suppressing sheet 10 interposed between battery cells, and in a battery cell that experiences thermal runaway, the temperature rises sharply to over 200°C and continues to rise to around 700°C. Therefore, it is preferable that the inorganic particles be made of an inorganic hydrate whose thermal decomposition temperature is 200°C or higher.

[0072] The thermal decomposition starting temperatures of the inorganic hydrates listed above are approximately 200°C for aluminum hydroxide, approximately 330°C for magnesium hydroxide, approximately 580°C for calcium hydroxide, approximately 200°C for zinc hydroxide, approximately 350°C for iron hydroxide, approximately 300°C for manganese hydroxide, approximately 300°C for zirconium hydroxide, and approximately 300°C for gallium hydroxide.All of these temperatures roughly overlap with the temperature range in which a battery cell experiencing thermal runaway experiences a sudden rise in temperature, and can efficiently suppress temperature rise, making these inorganic hydrates preferable.

[0073] Furthermore, when inorganic hydrate particles are used as the inorganic particles 21, if the average particle size is too large, it will take some time for the inorganic hydrate particles near the center of the sheet to reach their thermal decomposition temperature, and the inorganic hydrate particles near the center of the heat-transfer-suppressing sheet 10 may not be completely thermally decomposed. For this reason, 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.

[0074] (Contents of inorganic particles, first inorganic fibers, and second inorganic fibers) The content of inorganic particles 21 is preferably 30% by mass or more and 80% by mass or less relative to the total mass of heat transfer-suppressing sheet 10. The content of inorganic particles 21 is more preferably 40% by mass or more and 70% by mass or less, and more preferably 50% by mass or more and 60% by mass or less. The total content of the first inorganic fibers 23 and the second inorganic fibers 24 is preferably 5% by mass or more and 30% by mass or less, relative to the total mass of the heat transfer-suppressing sheet 10. The total content of the first inorganic fibers 23 and the second inorganic fibers 24 is more preferably 10% by mass or more and 25% by mass or less, and more preferably 15% by mass or more and 20% by mass or less. By setting the content at this level, the heat absorption and insulation effects of the inorganic particles 21, the shape retention, pressure resistance, and wind pressure resistance of the first inorganic fibers 23, and the heat transfer path function and inorganic particle 21 retention ability of the second inorganic fibers 24 are all balanced.

[0075] (Other compounding ingredients) If necessary, heat-transfer-suppressing sheet 10 may be blended with other materials that have traditionally been blended with heat-transfer-suppressing sheets 10. For example, organic fibers, organic binders, etc. may be blended. These are all useful for reinforcing heat-transfer-suppressing sheet 10 and improving its formability, and their total amount based on the total mass of heat-transfer-suppressing sheet 10 is preferably 10 mass % or less.

[0076] (Thickness of heat transfer suppression sheet) In this embodiment, the thickness of heat-transfer-suppressing sheet 10 is not particularly limited, but is preferably in the range of 0.05 to 6 mm. When heat-transfer-suppressing sheet 10 has a thickness of 0.05 mm or more, sufficient mechanical strength can be imparted to heat-transfer-suppressing sheet 10. On the other hand, when the thickness of heat-transfer-suppressing sheet 10 is 6 mm or less, good assembly properties can be obtained.

[0077] (Thermal insulation performance of heat transfer suppression sheet) Thermal conductivity can be used as an index of thermal insulation performance, and in this embodiment, the thermal conductivity is preferably less than 1 (W / m·K), more preferably less than 0.5 (W / m·K), and even more preferably less than 0.2 (W / m·K). Furthermore, the thermal conductivity 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 can be measured in accordance with JIS R 2251, "Testing Method for Thermal Conductivity of Refractories."

[0078] [2. Method for manufacturing heat transfer suppression sheet] First, inorganic particles 21, first inorganic fibers 23, and other ingredients are added to water in a predetermined ratio and kneaded in a kneader to prepare a paste. The resulting paste is then extruded from a slit-shaped nozzle using an extrusion molding machine to obtain a first member. This first member is a sheet-like wet material in which the first inorganic fibers 23 are oriented in one direction and the inorganic particles 21 are held between the fibers.

[0079] The second member is obtained by dry-mixing the inorganic particles 21, the second inorganic fibers 24, and other compounding materials in a predetermined ratio and press-molding the mixture. The second member is in the form of a sheet, with the second inorganic fibers 24 randomly present and the inorganic particles 21 held between the fibers.

[0080] Then, multiple layers of the first and second members are alternately stacked, and the whole is press-molded and dried to obtain heat-transfer-suppressing sheet 10. During press-molding, second inorganic fibers 24 present randomly in the second member penetrate into the wet first member and become entangled with first inorganic fibers 23. This state is then maintained by drying, resulting in heat-transfer-suppressing sheet 10.

[0081] [3. Battery pack] As shown in FIG. 2, the battery pack 100 according to this embodiment has a plurality of battery cells 20a, 20b, and 20c arranged side by side, connected in series or parallel, and stored in a battery case 30, with the heat transfer suppression sheet 10 interposed between the battery cells 20a, 20b, and 20c.

[0082] In such a battery pack 100, the heat transfer suppressing sheets 10 are interposed between the battery cells 20a, 20b, and 20c, so that heat transfer between the battery cells 20a, 20b, and 20c can be suppressed during normal use.

[0083] On the other hand, even if thermal runaway occurs in any of the battery cells 20a, 20b, and 20c, the presence of the heat-transfer-suppressing sheet 10 according to this embodiment can suppress the transfer of heat between the battery cells 20a, 20b, and 20c. This prevents a chain reaction of thermal runaway and minimizes adverse effects on other battery cells.

[0084] Furthermore, although not shown, the heat-transfer-suppressing sheet 10 may be interposed between the battery cells 20a, 20b, and 20c, or may be attached directly to the inner bottom surface of the battery case 30, or may be disposed in the space between the battery cells 20a, 20b, and 20c and the ceiling or sidewall of the battery case 30. This provides high versatility and is effective in preventing a chain reaction of thermal runaway caused by heat transmission between adjacent battery cells, and also prevents the flames from spreading outside the battery case if one battery cell catches fire.

[0085] Furthermore, depending on the selection of the constituent components and thickness of the heat transfer-suppressing sheet, it can be easily bent. Therefore, it is not affected by the shape of the battery cell and can be adapted to any shape. Specifically, it can be applied to cylindrical batteries, flat batteries, etc. in addition to prismatic batteries.

[0086] For example, the battery pack according to this embodiment may be used in an electric vehicle (EV) or the like and placed under the floor of the passenger compartment. In this case, even if a battery cell were to catch fire, the safety of the passengers can be ensured. In this case, the heat transfer suppression sheet that is interposed between each battery cell can also be placed between the battery cell and the battery case, eliminating the need to fabricate additional flame retardant materials, and allowing a safe battery pack to be easily constructed at low cost. [Explanation of symbols]

[0087] 10 Heat transfer suppression sheet 10a, 10b main surface 20, 20b, 20c battery cells 21 Inorganic particles 23 First Inorganic Fiber 24 Second inorganic fiber 30 Battery case 100 battery packs

Claims

1. A composition comprising: uniformly dispersed inorganic particles made of at least one selected from wet silica, dry silica, and aerogel; First inorganic fibers that are uniformly dispersed and oriented in one direction parallel to the main surface of the sheet; second inorganic fibers that are entangled with the first inorganic fibers to form a three-dimensional web structure; A heat transfer suppression sheet comprising:

2. The heat transfer-suppressing sheet according to claim 1 , wherein an average fiber diameter of the first inorganic fibers is larger than an average fiber diameter of the second inorganic fibers.

3. The heat transfer-suppressing sheet according to claim 1 , wherein an average fiber length of the first inorganic fibers is greater than an average fiber length of the second inorganic fibers.

4. 4. The heat transfer-suppressing sheet according to claim 1, wherein the first inorganic fibers have a degree of crimp smaller than the degree of crimp of the second inorganic fibers.

5. 5. The heat transfer-suppressing sheet according to claim 1, wherein the first inorganic fibers are linear or needle-like, and the second inorganic fibers are dendritic or crimped.

6. the first inorganic fibers are amorphous fibers, The heat transfer-suppressing sheet according to any one of claims 1 to 5, wherein the second inorganic fibers are at least one type selected from the group consisting of amorphous fibers and crystalline fibers having a glass transition point higher than that of the first inorganic fibers.

7. The heat transfer-suppressing sheet according to any one of claims 1 to 6, wherein the second inorganic fibers have a thermal conductivity of 41 [W / m·K] or less.

8. The heat transfer-suppressing sheet according to any one of claims 1 to 7, wherein the first inorganic fibers are at least one type of fibers selected from the group consisting of glass fibers, glass wool, slag wool, rock wool, alkaline earth silicate fibers, and refractory ceramic fibers.

9. The heat transfer-suppressing sheet according to any one of claims 1 to 8, wherein the second inorganic fibers are at least one type of fibers selected from the group consisting of alumina fibers, mullite fibers, alumina silicate fibers, mineral fibers, and zirconia fibers.

10. 10. The heat-transfer-suppressing sheet according to claim 1, wherein the content of the inorganic particles is from 30% by mass to 80% by mass, both inclusive, based on the total mass of the heat-transfer-suppressing sheet.

11. 11. The heat transfer-suppressing sheet according to claim 1, wherein the inorganic particles have an average secondary particle diameter of 1 nm or more and 100 nm or less.

12. 12. The heat-transfer-suppressing sheet according to claim 1, wherein a total content of the first inorganic fibers and the second inorganic fibers is 5% by mass or more and 30% by mass or less with respect to a total mass of the heat-transfer-suppressing sheet.

13. In a battery pack in which multiple battery cells are connected in series or in parallel, A battery pack using the heat transfer-suppressing sheet according to any one of claims 1 to 12.

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