Heat transfer suppression sheet and battery pack

Abstract

To further improve a shape-retaining property, strength, compression characteristics and the like which are required for a heat transfer suppressing sheet by improving dispersibility of fibers and particles and further enhancing particle holding performance by the fibers, and to prevent the deterioration of the shape-retaining property, strength, compression characteristics and the like of the sheet as a whole even if a battery pack exhibits a thermal runaway.SOLUTION: A heat transfer suppressing sheet includes fiber components and particle components. Main components of first inorganic fibers 1 included in the fiber components, and main components of first inorganic particles 2 included in the particle components are the same kind, and the content of the main components in the first inorganic particles 2 is greater than the content of the main components in the first inorganic fibers 1.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In recent years, from the viewpoint of environmental protection, development of electric vehicles and hybrid vehicles driven by electric motors has been actively promoted. These electric vehicles, hybrid vehicles, and the like are equipped with an assembled battery in which a plurality of battery cells are connected in series or parallel to serve as a power source for a driving electric motor.

[0003] For these battery cells, lithium-ion secondary batteries, which can provide high capacity and high output compared to lead-acid batteries, nickel-metal hydride batteries, and the like, are mainly used. However, if thermal runaway occurs in one battery cell due to causes such as internal short circuit or overcharging of the battery (that is, in the case of "abnormal battery cell"), heat propagation to other adjacent battery cells may occur, which may trigger thermal runaway in the other battery cells.

[0004] As a technique for suppressing heat propagation from a battery cell that has undergone thermal runaway as described above, a heat transfer suppressing sheet is interposed between battery cells. For example, Patent Document 1 describes a heat transfer suppressing sheet containing fibers and silica aerogel. Further, Patent Document 2 describes a heat transfer suppressing sheet containing at least one of mineral powder and a flame retardant, and a matrix resin as an organic binder selected from thermosetting resins, thermoplastic elastomers, and rubbers. [Prior Art Documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Unexamined Patent Publication No. 2017-215014 [Patent Document 2] Japanese Unexamined Patent Publication No. 2018-206605 [Summary of the Invention] [Problems that the invention aims to solve]

[0006] In heat transfer suppression sheets, it is required that particles having a heat transfer suppression effect be well retained (i.e., powder shedding be suppressed), and in Patent Document 1, silica aerogel is retained with fibers. In this case, it is common practice to use an organic binder to improve the retention performance.

[0007] In the manufacture of heat transfer suppression sheets, a common method involves dewatering an aqueous slurry containing fibers and particles through a filtration mesh to obtain a wet sheet, which is then heated and pressurized. In this process, the polarity of the fibers and particles in the aqueous slurry significantly affects their dispersibility. Furthermore, if an organic binder is included, the affinity between the organic binder and the fibers, and between the organic binder and the particles, significantly affects the binding properties. As a result, the resulting heat transfer suppression sheet may exhibit uneven distribution of fibers and particles, leading to reduced particle retention and decreased overall sheet strength.

[0008] Furthermore, if a battery cell experiences thermal runaway, the cell temperature can rise rapidly, sometimes reaching nearly 1000°C. However, if an organic binder is used, the high temperatures during thermal runaway can cause the organic binder to melt and disappear, significantly reducing the overall shape retention, strength, and compression properties of the sheet.

[0009] This invention has been made in view of the above problems, and aims to further improve the shape retention, strength, and compression characteristics required of heat transfer suppression sheets by improving the dispersibility of fibers and particles and further enhancing the particle retention performance of the fibers, and to prevent a decrease in the shape retention, strength, and compression characteristics of the sheet as a whole even if the battery cell experiences thermal runaway. [Means for solving the problem]

[0010] The above objective of the present invention is achieved by the configuration of the heat transfer suppression sheet described below [1].

[0011] [1] Contains fibrous components and particulate components, The main component of the first inorganic fiber contained in the fiber component and the main component of the first inorganic particle contained in the particle component are of the same type, and A heat transfer suppression sheet in which the content of the main component in the first inorganic particles is greater than the content of the main component in the first inorganic fibers.

[0012] Furthermore, preferred embodiments of the present invention relating to the heat transfer suppression sheet are described in the following [2] to

[15] .

[0013] [2] The heat transfer suppression sheet according to [1], wherein the main component is silica.

[0014] [3] The heat transfer suppression sheet according to [1] or [2], wherein the first inorganic fiber is a glass fiber and the first inorganic particle is a silica particle.

[0015] [4] The heat transfer suppression sheet according to any one of [1] to [3], wherein the fiber component comprises a second inorganic fiber having a higher glass transition temperature than the first inorganic fiber and the first inorganic particle.

[0016] [5] The heat transfer suppression sheet according to [4], wherein the average fiber diameter of the first inorganic fiber is greater than the average fiber diameter of the second inorganic fiber.

[0017] [6] The heat transfer suppression sheet according to [4] or [5], wherein the average fiber length of the first inorganic fiber is greater than the average fiber length of the second inorganic fiber.

[0018] [7] A heat transfer suppression sheet according to any one of [4] to [6], wherein the degree of crimp of the first inorganic fiber is smaller than the degree of crimp of the second inorganic fiber.

[0019] [8] The heat transfer suppression sheet according to any one of [4] to [7], wherein the first inorganic fiber is linear or needle-shaped, and the second inorganic fiber is dendritic or curly.

[0020] [9] The first inorganic fiber is an amorphous fiber, the heat transfer suppression sheet according to any one of [4] to [8], wherein the second inorganic fiber is composed of at least one selected from the group consisting of amorphous fibers and crystalline fibers.

[0021]

[10] The heat transfer suppression sheet according to any one of [4] to [9], wherein the second inorganic fiber is a fiber composed of at least one selected from the group consisting of alumina fibers, mullite fibers, alumina silicate fibers, carbon fibers, silicon carbide fibers, mineral fibers and zirconia fibers.

[0022]

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

[10] , wherein the particle component includes second inorganic particles having a glass transition point higher than that of the first inorganic fiber and the first inorganic particles.

[0023]

[12] The heat transfer suppression sheet according to

[11] , wherein the second inorganic particles are particles composed of at least one selected from the group consisting of titania particles, zirconia particles, zircon particles and barium titanate particles.

[0024]

[13] The inorganic particles constituting the particle component are uniformly dispersed, the first inorganic fibers are uniformly dispersed and oriented in one direction parallel to the main surface of the sheet, the heat transfer suppression sheet according to any one of [4] to

[12] , wherein the second inorganic fibers are entangled with the first inorganic fibers to form a three-dimensional web structure.

[0025]

[14] The heat transfer suppression sheet according to

[13] , wherein the thermal conductivity of the second inorganic fiber is 41 [W / m·K] or less.

[0026]

[15] The heat transfer suppression sheet according to

[13] or

[14] , wherein the total content of the first inorganic fibers and the second inorganic fibers is 5 mass% or more and 30 mass% or less based on the total mass of the heat transfer suppression sheet.

[0027] Furthermore, the above-mentioned objective of the present invention is achieved by the following configuration of the battery pack

[16] .

[0028]

[16] In a battery pack in which multiple battery cells are connected in series or in parallel, A battery pack using a heat transfer suppression sheet described in any one of [1] to

[15] . [Effects of the Invention]

[0029] In the heat transfer suppression sheet of the present invention, the main component of the first inorganic fiber and the main component of the first inorganic particles are of the same type, resulting in high affinity between the two, good dispersibility during manufacturing, elimination of uneven distribution within the sheet, and improved retention performance of the first inorganic particles by the first inorganic fiber. Furthermore, the fiber components intertwine to form a three-dimensional network (also called a web structure). As a result, the overall shape retention, strength, and compression characteristics of the sheet are further improved.

[0030] Preferably, the sheet also contains second inorganic fibers and second inorganic particles having a higher glass transition temperature than the first inorganic fibers and first inorganic particles. This allows the first inorganic fibers and first inorganic particles, which have a relatively low glass transition temperature, to vitrify (soften) and function as a binder even if the battery cell experiences thermal runaway. At the same time, the second inorganic fibers and second inorganic particles, which have a relatively high glass transition temperature, remain within the heat transfer suppression sheet. Therefore, even if the battery cell experiences thermal runaway, the overall shape retention, strength, and compression properties of the sheet are maintained.

[0031] The battery pack of the present invention utilizes the heat transfer suppression sheet described above. Therefore, the battery pack of the present invention maintains stable operation, and even if thermal runaway occurs in the battery cells, damage can be minimized. [Brief explanation of the drawing]

[0032] [Figure 1] Figure 1 is an SEM image of a cross-section of a heat transfer suppression sheet according to the first embodiment of the present invention, taken immediately after manufacturing (under normal use). [Figure 2] Figure 2 is an SEM image of a cross-section of the heat transfer suppression sheet according to the first embodiment of the present invention when heated to 800°C. [Figure 3] Figure 3 is an SEM image of a cross-section of the heat transfer suppression sheet according to the first embodiment of the present invention when heated to 1000°C. [Figure 4] Figure 4 is a schematic cross-sectional view showing a battery pack using a heat transfer suppression sheet according to the first embodiment. [Figure 5] Figure 5 is a schematic diagram showing the configuration of a heat transfer suppression sheet according to a second embodiment of the present invention. [Modes for carrying out the invention]

[0033] Hereinafter, a heat transfer suppression sheet and a battery pack according to embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the present invention is not limited to the embodiments described below, and can be modified and implemented as such without departing from the spirit of the invention.

[0034] [1. Heat transfer suppression sheet] [First Embodiment] The heat transfer suppression sheet according to the first embodiment of the present invention is It contains fibrous components and particulate components, The main component of the first inorganic fiber contained in the above fiber component and the main component of the first inorganic particle contained in the above particle component are of the same type, and The present invention is characterized in that the content of the main component in the first inorganic particles is greater than the content of the main component in the first inorganic fiber.

[0035] In this invention, "main component" refers to a component that accounts for 50% or more by mass of all components constituting a single material. Preferably, the main component accounts for 60% or more by mass, more preferably 70% or more by mass, even more preferably 80% or more by mass, and even more preferably 90% or more by mass.

[0036] Since the main components of the first inorganic fibers and the first inorganic particles are of the same type, they have high affinity for each other, resulting in good dispersibility during manufacturing and preventing uneven distribution of each component in the resulting heat transfer suppression sheet. Therefore, the retention performance of the first inorganic particles by the first inorganic fibers is enhanced.

[0037] The heat transfer suppression sheet according to the first embodiment of the present invention will be described in detail below. Figure 1 is an SEM image of a cross-section of the heat transfer suppression sheet according to the first embodiment of the present invention immediately after manufacturing (under normal use).

[0038] As shown in Figure 1, the fibrous component includes a first inorganic fiber 1, and the particle component includes a first inorganic particle 2. In this embodiment, the fibrous component also contains a second inorganic fiber 3 having a higher glass transition temperature than the first inorganic fiber 1 and the first inorganic particle 2. Furthermore, the particle component also contains a second inorganic particle 4 having a higher glass transition temperature than the first inorganic fiber 1 and the first inorganic particle 2. Moreover, an organic binder 5 is inserted between the first inorganic fiber 1, the first inorganic particle 2, the second inorganic fiber 3, and the second inorganic particle 4, binding them together.

[0039] (First inorganic fiber) The first inorganic fiber 1 contained in the fiber component is preferably an amorphous fiber, and suitable options include glass fiber, glass wool, slag wool, rock wool, alkali earth silicate fiber, refractory ceramic fiber, basalt fiber, and sorbable fiber. These may be used individually or in combination of multiple types. Among these, inorganic fibers with a melting point of less than 700°C are preferred, and many amorphous inorganic fibers can be used. In particular, it is preferable that the main component is a fiber containing silica, which has excellent heat insulation properties, and glass fiber is more preferable because it is inexpensive, readily available, and easy to handle.

[0040] (First inorganic particle) The first inorganic particles 2 contained in the particulate component have a main component of the same type as the main component of the first inorganic fiber 1. As described above, since the first inorganic fiber 1 is preferably a fiber containing silica as its main component, the first inorganic particles 2 are also preferably silica particles whose main component is the same type of silica.

[0041] Furthermore, it is preferable to use a mixture of large-diameter and small-diameter particles. When small-diameter inorganic particles fill the gaps between large-diameter inorganic particles, a denser structure is created, which can further improve the strength of the heat transfer suppression sheet.

[0042] (Second inorganic fiber) The fiber component may include a second inorganic fiber 3. The second inorganic fiber 3 consists of at least one selected from amorphous fibers and crystalline fibers, each having a higher glass transition temperature than the first inorganic fiber 1 and the first inorganic particle 2. Preferably, the second inorganic fiber 3 has a glass transition temperature of 1000°C or higher, and many crystalline inorganic fibers can be used. Note that the melting point of crystalline inorganic fibers is usually higher than that of amorphous inorganic fibers. Therefore, when exposed to high temperatures, the surfaces of the first inorganic fiber 1 and the first inorganic particle 2 soften before those of the second inorganic fiber 3.

[0043] On the other hand, the second inorganic fiber 3, which has a relatively high glass transition temperature, can remain within the sheet and maintain its sheet shape, even when the first inorganic fiber 1 and first inorganic particles 2 soften and melt during thermal runaway of the battery cells, and can continue to exist between the battery cells. Therefore, the softened first inorganic fiber 1 can bind the second inorganic particles 4 and the second inorganic fiber 3, etc., as described later, and improve the mechanical strength of the heat transfer suppression sheet 10. Furthermore, since the second inorganic fiber 3 does not melt or soften even when exposed to high temperatures, minute spaces between it and the second inorganic particles 4, and even minute spaces between any remaining fibers in the first inorganic fiber 1 or first inorganic particles 2, are maintained, allowing for an insulating effect by air and demonstrating excellent heat transfer suppression performance.

[0044] Specifically, alumina fibers, mullite fibers, aluminasilicate fibers, carbon fibers, silicon carbide fibers, mineral fibers, and zirconia fibers can be suitably used as the second inorganic fiber 3. These fibers may be used individually or in combination of multiple types. Among these, those with a melting point exceeding 1000°C are particularly suitable because, even if thermal runaway occurs in the battery cell, the second inorganic fiber 3 will not melt or soften and will maintain its shape.

[0045] Even if the second inorganic fiber 3 is amorphous, it can be used as long as it has a higher glass transition temperature than the first inorganic fiber 1. For example, a glass fiber with a higher glass transition temperature than the first inorganic fiber 1 may be used as the second inorganic fiber 3.

[0046] As described above, the first inorganic fiber 1 has a lower glass transition temperature than the second inorganic fiber 3, and when exposed to high temperatures, the first inorganic fiber 1 softens first, allowing the first inorganic fiber 1 to bind the second inorganic particles 4 and the second inorganic fiber 3. However, if, for example, the second inorganic fiber 3 is amorphous and its fiber diameter is smaller than that of the first inorganic fiber 1, and the glass transition temperatures of the first inorganic fiber 1 and the second inorganic fiber 3 are close together, the second inorganic fiber 3 may soften first. Therefore, when the second inorganic fiber 3 is amorphous, it is preferable that the glass transition temperature of the second inorganic fiber 3 be 100°C or more higher than the glass transition temperature of the first inorganic fiber 1, and more preferably 300°C or more higher.

[0047] (Second inorganic particle) The particle components may include second inorganic particles 4 having a higher glass transition temperature than the first inorganic fiber 1 and first inorganic particles 2. The material of the second inorganic particles 4 is not particularly limited, but oxide particles, carbide particles, nitride particles, etc., can be used. Among these, oxide particles are preferred, and it is preferable that they have a glass transition temperature of 1000°C or higher. Oxide particles have a high refractive index and a strong effect of diffusely reflecting light, so when oxide particles are used as the second inorganic particles 4, radiative heat transfer can be suppressed, especially in high-temperature regions such as abnormal heat generation. Specifically, titania particles, zirconia particles, zircon particles, barium titanate particles, zinc oxide particles, alumina particles, etc., can be suitably used, and among these, titania particles are preferred. Compared to other metal oxides, titania particles have a high refractive index and a high effect of diffusely reflecting light and blocking radiant heat in high-temperature regions of 500°C or higher, making them preferable for improving the heat resistance of the heat transfer suppression sheet. In other words, it is particularly preferable to use silica particles as the first inorganic particle 2 and titania particles as the second inorganic particle 4.

[0048] Furthermore, these particles may be used individually or in combination of multiple types. By using two or more inorganic particles with different heat transfer suppression effects, the heat-generating element can be cooled in multiple stages, and the endothermic effect can be expressed over a wider temperature range. When combining multiple types, it is also preferable to use a mixture of large-diameter and small-diameter particles, similar to the first inorganic particle. The small-diameter inorganic particles can fill the gaps between the large-diameter inorganic particles, resulting in a denser structure, which can improve the heat transfer suppression effect and increase strength.

[0049] When either or both of the first inorganic particles 2 and the second inorganic particles 4 are oxide particles, the particle size of the oxide particles can affect the effect of reflecting radiant heat. Therefore, limiting the mean primary particle size to a predetermined range can result in even higher thermal insulation.

[0050] In other words, if the average primary particle diameter of the oxide particles is 0.001 μm or larger, it is sufficiently larger than the wavelength of light that contributes to heating, and efficiently diffusely reflects light. As a result, radiative heat transfer within the sheet is suppressed in the high-temperature region of 500°C or higher, and the thermal insulation can be further improved. On the other hand, if the average primary particle diameter of the oxide particles is 50 μm or less, the number of contact points between particles does not increase even when compressed, making it difficult to form conduction heat transfer paths. Therefore, the impact on thermal insulation, especially in the normal temperature range where conduction heat transfer is dominant, can be reduced.

[0051] When using two or more types of oxide particles, it is also preferable to use a mixture of large-diameter particles and small-diameter particles (nanoparticles). In this case, the average primary particle diameter of the large-diameter particles is more preferably 1 μm to 50 μm, even more preferably 5 μm to 30 μm, and most preferably 10 μm or less. In this invention, the average primary particle diameter can be determined by observing the particles under a microscope, comparing them to a standard scale, and taking the average of 10 arbitrary particles. Nanoparticles will be described later.

[0052] Furthermore, for better compatibility at higher temperatures, the second inorganic fiber and second inorganic particles are preferable if they have a higher glass transition temperature.

[0053] The effects obtained by including the second inorganic fiber 3 and the second inorganic particles 4 will be explained below with reference to Figures 1 to 4. Figure 2 is an SEM image of a cross-section of the heat transfer suppression sheet according to the first embodiment of the present invention when heated to 800°C. Figure 3 is an SEM image of a cross-section of the heat transfer suppression sheet according to the first embodiment of the present invention when heated to 1000°C. Figure 4 is a schematic cross-sectional view showing a battery pack using the heat transfer suppression sheet according to the first embodiment.

[0054] As shown in Figure 4, the heat transfer suppression sheet 10 according to this embodiment is used, for example, in a battery pack 100. Specifically, the battery pack 100 has a plurality of battery cells 20a, 20b, and 20c arranged side by side, connected in series or parallel and housed in a battery case 30. The heat transfer suppression sheet 10 can be interposed, for example, between the battery cells 20a, 20b, and 20c.

[0055] When a battery cell experiences thermal runaway (a malfunction in the battery cell), the heat transfer suppression sheet is heated to a high temperature. First, the organic binder 5, which has a low melting point, disappears (see Figure 2, which shows the heat transfer suppression sheet after heating to 800°C), potentially leading to a significant decrease in the overall shape retention, strength, and compressive properties of the sheet. As the temperature rises further, exceeding the glass transition temperatures of the first inorganic fibers 1 and first inorganic particles 2, which have relatively low glass transition temperatures, the first inorganic fibers 1 and first inorganic particles 2 vitrify (soften) and form a film. This film then replaces the disappeared organic binder 5 and functions as a binder, contributing to the overall shape retention, strength, and compressive properties of the sheet.

[0056] Subsequently, even as the temperature rises, the second inorganic fibers 3 and second inorganic particles 4, which have relatively high glass transition temperatures, remain in the heat transfer suppression sheet (see Figure 3, which shows the heat transfer suppression sheet after heating to 1000°C). Furthermore, as shown in parts A and B of Figure 3, the first inorganic fibers 1 and first inorganic particles 2 soften and deform, spreading out to fill the gaps between the second inorganic fibers 3 and second inorganic particles 4. Therefore, the overall shape retention, strength, and compression properties of the sheet can be maintained. At the same time, minute spaces are maintained between the second inorganic fibers 3, between the second inorganic particles 4, and between the second inorganic fibers 3 and second inorganic particles 4, and in these spaces, the insulating effect of air is exerted, resulting in excellent heat transfer suppression performance.

[0057] (Shapes of the first and second inorganic fibers) The first inorganic fiber and the second inorganic fiber preferably have the shapes shown below.

[0058] 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 suppression sheet. The above effect can be obtained by making either the first inorganic fiber 1 or the second inorganic fiber 3 large diameter. Since the heat transfer suppression sheet may be subjected to external impacts, the inclusion of large diameter inorganic fibers increases its impact resistance. Examples of external impacts include the pressing force due to the expansion of battery cells and the wind pressure due to the ignition of battery cells.

[0059] Furthermore, in order to further improve mechanical strength and shape retention, it is particularly preferable that the large-diameter inorganic fibers be linear or needle-shaped. Linear or needle-shaped fibers refer to fibers whose crimp degree, as described later, is, for example, less than 10%, preferably 5% or less.

[0060] More specifically, in order to improve the mechanical strength and shape retention of the heat transfer suppression 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, the moldability and processability of the heat transfer suppression sheet may decrease, so the average fiber diameter is preferably 20 μm or less, and more preferably 15 μm or less.

[0061] Furthermore, if the large-diameter inorganic fibers are too long, their moldability and processability may decrease, so it is preferable to keep the fiber length to 100 mm or less. In addition, if the large-diameter inorganic fibers are too short, their shape retention and mechanical strength may decrease, so it is preferable to keep the fiber length to 0.1 mm or more.

[0062] On the other hand, inorganic fibers with a small average fiber diameter (fine diameter) have the effect of improving the retention of inorganic particles and increasing the flexibility of the heat transfer suppression sheet 10. Therefore, the above effect can be obtained by making the other of the first and second inorganic fibers smaller in diameter.

[0063] More specifically, in order to improve the retention of inorganic particles, it is preferable that the small-diameter inorganic fibers are easily deformable and flexible. Therefore, it is preferable that the average fiber diameter of the small-diameter inorganic fibers be 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 decreases. In addition, a large proportion of the fibers remain entangled in the heat transfer suppression sheet 10 without retaining the inorganic particles, resulting in a decrease in the ability to retain inorganic particles, as well as poor moldability and shape retention. Therefore, it is preferable that the average fiber diameter of the small-diameter inorganic fibers be 1 nm or more, and more preferably 10 nm or more.

[0064] Furthermore, since the moldability and shape retention of small-diameter inorganic fibers decrease if they become too long, it is preferable that the fiber length be 0.1 mm or less.

[0065] Furthermore, it is preferable that the small-diameter inorganic fibers are dendritic or crimped. When the small-diameter inorganic fibers have such a shape, they intertwine with the large-diameter inorganic fibers and inorganic particles in the heat transfer suppression sheet. As a result, the ability to hold inorganic particles is improved. In addition, when the heat transfer suppression sheet is subjected to pressing force or wind pressure, the sliding movement of the small-diameter inorganic fibers is suppressed, thereby improving the mechanical strength, especially against external pressing force and impact.

[0066] A dendritic structure is a two-dimensional or three-dimensional branching structure, such as a feathery, tetrapod-shaped, radial, or three-dimensional network-like structure. When small inorganic fibers are dendritic, their average fiber diameter can be obtained by measuring the diameters of the trunk and branches at several points using a scanning electron microscope (SEM) and calculating the average value of these measurements.

[0067] Furthermore, a crimped structure is one in which fibers are bent in various directions. One method for quantifying the crimp morphology is to calculate the degree of crimp from electron microscope images, which can be calculated, for example, using the following formula. Crimping (%) = (Fiber length - Distance between fiber ends) / (Fiber length) × 100

[0068] Here, both fiber length and fiber end-to-end distance are measured values ​​from electron microscope images. That is, these are fiber length and fiber end-to-end distance projected onto a two-dimensional plane, and are shorter than the actual values. Based on this formula, the crimp of small-diameter inorganic fibers is preferably 10% or more, and more preferably 30% or more. If the crimp is small, the ability to hold the first and second inorganic particles, and the entanglement (network) of large-diameter inorganic fibers with each other and with other large-diameter inorganic fibers becomes difficult to form.

[0069] As described above, it is preferable that the average fiber diameter of either the first inorganic fiber 1 or the second inorganic fiber 3 is larger than the average fiber diameter of the other, but in the present invention, it is more preferable that the average fiber diameter of the first inorganic fiber 1 is larger than the average fiber diameter of the second inorganic fiber 3. If the average fiber diameter of the first inorganic fiber 1 is large, the first inorganic fiber 1, which has a lower glass transition temperature, softens faster and hardens into a film as the temperature rises. On the other hand, if the average fiber diameter of the second inorganic fiber 3 is small, the small second inorganic fiber 3 remains in the shape of fibers even when the temperature rises, thus maintaining the structure of the heat transfer suppression sheet and preventing powder shedding.

[0070] Furthermore, in the present invention, when the average fiber diameter of the first inorganic fiber 1 is large and the average fiber length of the second inorganic fiber 3 is small, it is more preferable that the average fiber length of the first inorganic fiber 1 is greater than the average fiber length of the second inorganic fiber 3, and it is more preferable that the crimp degree of the first inorganic fiber 1 is smaller than the crimp degree of the second inorganic fiber 3.

[0071] Furthermore, it is most preferable that the first inorganic fiber 1 uses both a large-diameter, linear or needle-shaped inorganic fiber and a small-diameter, dendritic or crimped inorganic fiber, and the second inorganic fiber 3 uses both a large-diameter, linear or needle-shaped inorganic fiber and a small-diameter, dendritic or crimped inorganic fiber, as this further enhances the retention effect, mechanical strength, and shape retention of the first inorganic particles 2 and the second inorganic particles 4.

[0072] Furthermore, because the average fiber length of the first inorganic fiber 1 is greater than that of the second inorganic fiber 3, the orientation length is extended, resulting in improved heat dissipation. Moreover, because the second inorganic fiber 3 is dendritic or crimped, it easily entangles with the first inorganic fiber 1, which is effective for heat transfer paths and shape retention.

[0073] (Shapes of the first and second inorganic particles) Furthermore, the first inorganic particle 2 and the second inorganic particle 4 are preferably shaped as follows.

[0074] The shape and size of both the first inorganic particles 2 and the second inorganic particles 4 are not particularly limited, but it is preferable that they contain at least one selected from nanoparticles, hollow particles, and porous particles. Furthermore, if the average secondary particle diameter is 0.01 μm or more, it is easier 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 first inorganic particles 2 and the second inorganic particles 4 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.

[0075] It is more preferable that at least one of the particle components in the heat transfer suppression sheet 10 includes nanoparticles. Nanoparticles refer to particles on the order of nanometers with an average primary particle diameter of less than 1 μm that are spherical or nearly spherical. Because nanoparticles have a low density, they have the effect of suppressing conductive heat transfer. Therefore, by using nanoparticles, the voids are further dispersed, and excellent heat insulation properties that suppress convective heat transfer can be obtained. For this reason, when using a battery in the normal room temperature range, heat conduction between adjacent nanoparticles can be suppressed. In addition, when nanoparticles are used as the first inorganic particles 2, for example, there are no particular limitations on components other than the main component, as long as they conform to the above definition of nanoparticles and have the same main component as the first inorganic fiber 1.

[0076] Furthermore, by limiting the average primary particle diameter of the nanoparticles to a predetermined range, even higher thermal insulation can be obtained. Specifically, by setting the average primary particle diameter of the nanoparticles to 1 nm or more and 100 nm or less, convective and conductive heat transfer within the heat transfer suppression sheet can be suppressed, particularly in the temperature range below 500°C, thereby further improving thermal insulation. In addition, even when compressive stress is applied, the voids remaining between the nanoparticles and the numerous contact points between particles suppress conductive heat transfer, maintaining the thermal insulation of the heat transfer suppression sheet. 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.

[0077] When either or both of the first inorganic particles 2 and the second inorganic particles 4 are oxide particles, if nanoparticles with a small average primary particle diameter are used as the oxide particles, the increase in conductive heat transfer of the heat transfer suppression sheet 10 can be suppressed even when the heat transfer suppression sheet 10 is compressed and its internal density increases due to expansion caused by thermal runaway of the battery cell. This is thought to be because nanoparticles easily create fine voids between particles due to electrostatic repulsion, and because their bulk density is low, the particles are packed in a way that provides cushioning.

[0078] As nanoparticles, for example, nanosilica particles are highly insulating materials, and because the contact points between particles are small, the amount of heat conducted by nanosilica particles is smaller compared to when using silica particles with a larger particle size. In addition, commonly available nanosilica particles have a bulk density of 0.1 g / cm³. 3Therefore, even if, for example, battery cells arranged on both sides of the heat transfer suppression sheet undergo thermal expansion and a large compressive stress is applied to the heat transfer suppression sheet, the size (area) and number of contact points between nanosilica particles will not increase significantly, and the heat insulation properties can be maintained. For this reason, it is preferable to use nanosilica particles as the first inorganic particles, which are silica particles. As nanosilica particles, wet silica, dry silica, aerogel, etc., can be used.

[0079] As described above, titania has a high effect in blocking radiant heat, and nanosilica particles have extremely low conductive heat transfer. Furthermore, they can maintain excellent heat insulation even when compressive stress is applied to the heat transfer suppression sheet 10. Therefore, it is most preferable to use both titania particles and silica nanoparticles as the first inorganic particles 2 and the second inorganic particles 4.

[0080] (Content of the first inorganic fiber, first inorganic particle, second inorganic fiber, and second inorganic particle in the heat transfer suppression sheet) In the first embodiment, the content of the first inorganic particles 2 is preferably 25% to 80% by mass and the content of the second inorganic particles 4 is preferably 1% to 30% by mass relative to the total mass of the heat transfer suppression sheet 10. However, as described above, the first inorganic fibers 1 and the first inorganic particles 2 are replaced when the organic binder disappears, so it is preferable that their content be equal to or greater than the content of the organic binder 5. Furthermore, considering the binding performance, the content of the organic binder 5 is preferably 5% to less than 25% by mass.

[0081] Furthermore, the content of the first inorganic fiber 1 is preferably 3% by mass or more and 30% by mass or less, and more preferably 5% by mass or more and 15% by mass or less. The content of the second inorganic fiber 3 is preferably 3% by mass or more and 30% by mass or less, and more preferably 5% by mass or more and 15% by mass or less. The first inorganic fiber 1 and the second inorganic fiber 3 intertwine to form a three-dimensional network that holds the first inorganic particles 2 and the second inorganic particles 4, and the other compounding materials described later. Therefore, if the content is less than the above amounts, these effects cannot be fully obtained.

[0082] (Other ingredients) The heat transfer suppression sheet of the present invention may contain, as needed, other inorganic particles different from the first inorganic particles 2 and the second inorganic particles 4, other inorganic fibers different from the first inorganic fiber 1 and the second inorganic fiber 3, organic fibers, organic binders, and other materials that have been conventionally incorporated into heat transfer suppression sheets. All of these are useful for reinforcing the heat transfer suppression sheet 10 and improving its moldability, and it is preferable that the total amount of these materials relative to the total mass of the heat transfer suppression sheet 10 be 10% by mass or less.

[0083] As inorganic fibers different from the first and second inorganic fibers, aerogel composite materials and the like can be used.

[0084] As organic fibers, cellulose fibers and the like can be used.

[0085] These fibers may be used individually or in combination of two or more types.

[0086] As an organic binder, polymer flocculants and acrylic emulsions that have been conventionally used in heat transfer suppression sheets can be used as appropriate.

[0087] Other inorganic particles that can be used include mica, microporous particles, thermally expandable inorganic materials, aerogels, and inorganic hydrate particles. Examples of thermally expandable inorganic materials include vermiculite, bentonite, mica, and perlite. Organic particles that can be used include hollow polystyrene particles.

[0088] In particular, inorganic hydrate particles are preferred. When inorganic hydrate particles receive heat from a heating element and reach a temperature above the thermal decomposition start temperature, they undergo thermal decomposition, releasing their own crystalline water and lowering the temperature of the heating element and its surroundings, exhibiting a so-called "endothermic effect." Furthermore, after releasing the crystalline water, they become porous and exhibit an insulating effect due to the countless air pores.

[0089] 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).

[0090] For example, aluminum hydroxide contains approximately 35% crystal water, and as shown in the formula below, it undergoes thermal decomposition to release crystal water, exhibiting an endothermic effect. After releasing the crystal water, it becomes a porous alumina (Al2O3) and functions as an insulating material. 2Al(OH)3 → Al2O3 + 3H2O

[0091] As will be described later, the battery pack of the present invention preferably has a heat transfer suppression sheet 10 interposed between battery cells. However, in a battery cell that experiences thermal runaway, the temperature rapidly rises to over 200°C and continues to rise to around 700°C. Therefore, it is preferable that the inorganic particles consist of inorganic hydrates whose thermal decomposition initiation temperature is 200°C or higher.

[0092] The thermal decomposition initiation temperatures for the inorganic hydrates listed above are approximately 200°C for aluminum hydroxide, 330°C for magnesium hydroxide, 580°C for calcium hydroxide, 200°C for zinc hydroxide, 350°C for iron hydroxide, 300°C for manganese hydroxide, 300°C for zirconium hydroxide, and 300°C for gallium hydroxide. These temperatures largely overlap with the temperature range of rapid temperature increases in battery cells experiencing thermal runaway, and since they can efficiently suppress temperature rise, they can be considered desirable inorganic hydrates.

[0093] Furthermore, when using inorganic hydrate particles, if the average particle size is too large, it may take a certain amount of time for the inorganic hydrate particles near the center of the heat transfer suppression sheet to reach their thermal decomposition temperature, and thus the inorganic hydrate particles near the center of the heat transfer suppression sheet 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.

[0094] Furthermore, it is preferable to include a water-containing porous material as inorganic particles. Specific examples of water-containing porous materials include zeolite, kaolinite, montmorillonite, acid clay, diatomaceous earth, wet silica, dry silica, aerogel, mica, and vermiculite. It is also preferable to use a combination of multiple types of the above-mentioned water-containing porous material. Furthermore, it is preferable to provide a layer containing a larger amount of the above-mentioned water-containing porous material on the surface in order to suppress temperature rise.

[0095] Furthermore, it is preferable that the total amount of other compounding materials be 10% by mass or less relative to the total mass of the heat transfer suppression sheet.

[0096] <Method for manufacturing a heat transfer suppression sheet according to the first embodiment> In the first embodiment, the heat transfer suppression sheet 10 is manufactured by molding fibrous components, particle components, and other compounding materials using a dry molding method or a wet molding method. For the dry molding method, for example, a press molding method (dry press molding method) and an extrusion molding method (dry extrusion molding method) can be used.

[0097] (Manufacturing method using dry press molding) In the dry press molding method, fiber components, particle components, and other compounding materials are put into a mixer such as a V-type mixer in predetermined proportions. After the materials put into the mixer are thoroughly mixed, this mixture is put into a predetermined mold and press-molded to obtain a heat transfer suppression sheet. Heating may be performed during press molding as needed.

[0098] Furthermore, the press pressure during press forming is preferably in the range of 0.98 MPa to 9.80 MPa. If the press pressure is less than 0.98 MPa, the resulting heat transfer suppression sheet may not be able to maintain its strength and may collapse. On the other hand, if the press pressure exceeds 9.80 MPa, excessive compression may reduce processability, and the increased bulk density may lead to increased solid heat transfer and a decrease in thermal insulation performance.

[0099] Furthermore, when using the dry press molding method, it is preferable to use ethylene-vinyl acetate copolymer (EVA) as the organic binder, but any organic binder commonly used when using the dry press molding method can be used without particular limitation.

[0100] (Manufacturing method using dry extrusion molding) In the dry extrusion molding method, a paste is prepared by adding fiber components, particle components, and other compounding materials to water in predetermined proportions and kneading them in a kneader. The resulting paste is then extruded through a slit-shaped nozzle using an extruder and further dried to obtain a heat transfer suppression sheet. When using the dry extrusion molding method, it is preferable to use methylcellulose and water-soluble cellulose ether as the organic binder; however, any organic binder commonly used in dry extrusion molding can be used without particular limitation.

[0101] (Manufacturing method using wet molding) In the wet molding method, fiber components, particle components, and other compounding materials are added to water in predetermined proportions, mixed in the water, and stirred with a stirrer to prepare a mixture. Then, the resulting mixture is dewatered through a filtration mesh to produce a wet sheet. Subsequently, the resulting wet sheet is heated and pressurized to obtain a heat transfer suppression sheet.

[0102] Furthermore, before the heating and pressurizing process, a ventilated drying treatment may be performed in which hot air is passed through the wet sheet to dry it. However, this ventilated drying treatment may be omitted, and the sheet may be heated and pressurized while still wet. In addition, when using a wet molding method, cationized starch or acrylic resin can be selected as the organic binder.

[0103] As described above, when the heat transfer suppression sheet 10 includes a second inorganic fiber, it is preferable that the first inorganic fiber and the second inorganic fiber intertwine to form a three-dimensional network. A second embodiment having a three-dimensional network formed by inorganic fibers will be described with reference to the drawings. Hereinafter, a structure having a three-dimensional network will be referred to as a three-dimensional web structure.

[0104] [Second Embodiment] Figure 5 is a schematic diagram showing the configuration of a heat transfer suppression sheet according to a second embodiment of the present invention. In the heat transfer suppression sheet 32 ​​according to the second embodiment, (1) The inorganic particles 21 constituting the above particle component are uniformly dispersed, (2) The first inorganic fiber 23 is uniformly dispersed and oriented in one direction parallel to the main surface of the sheet. (3) The second inorganic fiber 24 is intertwined with the first inorganic fiber 23 to form a three-dimensional web structure.

[0105] Furthermore, if the inorganic particles 21 contain multiple types of inorganic particles, one type selected from the multiple types of inorganic particles can be designated as the first inorganic particle 2 in the first embodiment. In other words, in the second embodiment as well, the main component of the inorganic particles 21 (first inorganic particle 2) constituting the particle component and the main component of the first inorganic fiber 23 are the same type. In addition, the content of the main component in the first inorganic particles is greater than the content of the main component in the first inorganic fiber 23.

[0106] As shown in Figure 5, in this embodiment, the first inorganic fibers 23 are oriented in layers in one direction parallel to the main surfaces 10a and 10b of the heat transfer suppression sheet 32. Furthermore, the first inorganic fibers 23 are intertwined with the 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 space 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 heat-resistant materials. In addition, countless minute spaces are formed between particles, between particles and fibers, and between fibers, and an insulating effect by air is also exerted, resulting in excellent heat transfer suppression performance.

[0107] In this invention, "oriented in one direction" does not mean that all of the first inorganic fibers 23 must be facing that direction; it is sufficient that the first inorganic fibers 23 have a strong tendency to align in a specific direction. Furthermore, while the orientation of the first inorganic fibers 23 in a specific direction can be determined by visual inspection, if it is difficult to distinguish the fibers, it can be confirmed by measuring the bending strength in that direction and checking that it is 5% or more greater than in other directions.

[0108] Furthermore, in this invention, "uniformly dispersed" of the inorganic particles 21 and the first inorganic fibers 23 means that the inorganic particles 21 and the first inorganic fibers 23 are spread out evenly without being extremely concentrated in one area.

[0109] The material, shape, average fiber diameter, and average fiber length of the first inorganic fiber 23 and the second inorganic fiber 24 are the same as those of the first inorganic fiber 1 and the second inorganic fiber 3 in the first embodiment described above. Similarly, the material, shape, and particle diameter of the inorganic particles 21 are the same as those of the first inorganic particles 2 and the second inorganic particles 4 in the first embodiment described above, and it is sufficient that at least one of the inorganic particles 21 corresponds to the first inorganic particle 2 in the first embodiment described above.

[0110] The heat transfer suppression sheet 32 ​​according to the second embodiment can be applied to the battery pack shown in Figure 4. That is, the heat transfer suppression sheet 32 ​​can be interposed, for example, between battery cells 20a, 20b, and 20c.

[0111] In this second embodiment, the main component of at least one of the inorganic particles in the first inorganic fiber 23 and the inorganic particles 21 is the same, and the content of the main component in the inorganic particles is greater than the content of the main component in the first inorganic fiber 23, so the same effects as in the first embodiment can be obtained. Furthermore, in this embodiment, the first inorganic fiber 23 is uniformly dispersed inside the heat transfer suppression sheet 32 ​​while being oriented in one direction parallel to the main surface, so the heat insulation and heat dissipation within the sheet are excellent and uniform, and the heat generated from the battery cell can be effectively dissipated. Therefore, even if a battery cell experiences thermal runaway, the heat to adjacent battery cells can be blocked to prevent a chain reaction. In addition, the first inorganic fiber 23 and the second inorganic fiber 24 are intertwined to form a three-dimensional web structure, and the second inorganic fiber 24 functions as a heat transfer path connecting the first inorganic fiber and the second inorganic fiber 24. In other words, the heat transferred in the thickness direction of the heat transfer suppression sheet 32 ​​by the second inorganic fiber 24 is transferred by the first inorganic fiber 23 in a direction parallel to the main surface of the heat transfer suppression sheet 32, allowing for heat dissipation. Furthermore, the three-dimensional web structure provides superior strength.

[0112] (Thermal conductivity of the first inorganic fiber and the second inorganic fiber) In the second embodiment, the heat transfer suppression sheet 32 ​​is preferably as good as its thermal insulation performance, and it is preferable that both the first inorganic fiber 23 and the second inorganic fiber 24 have low thermal conductivity. However, since the second inorganic fiber 24 forms a heat transfer path connecting the first inorganic fibers which are oriented in layers, it is preferable that it has a higher thermal conductivity than the first inorganic fiber 23. Therefore, considering thermal insulation performance, it is preferable that the thermal conductivity of the second inorganic fiber 24 is 41 [W / m·K] or less.

[0113] (Content of inorganic particles, first inorganic fibers, and second inorganic fibers) The inorganic particle content 21 is preferably 30% to 80% by mass relative to the total mass of the heat transfer suppression sheet 32. More preferably, the inorganic particle content 21 is 40% to 70% by mass, and 50% to 60% by mass. Furthermore, the total content of the first inorganic fiber 23 and the second inorganic fiber 24 is preferably 5% by mass or more and 30% by mass or less, relative to the total mass of the heat transfer suppression sheet 32. More preferably, the total content of the first inorganic fiber 23 and the second inorganic fiber 24 is 10% by mass or more and 25% by mass or less, and 15% by mass or more and 20% by mass or less. By using this composition, the heat absorption and heat insulation effects of the inorganic particles 21, the shape retention, pressure resistance, and wind pressure resistance of the first inorganic fiber 23, and the heat transfer path function and the ability to retain the inorganic particles 21 of the second inorganic fiber 24 are all expressed in a well-balanced manner.

[0114] <Method for manufacturing a heat transfer suppression sheet according to the second embodiment> The method for manufacturing the heat transfer suppression sheet according to the second embodiment involves first adding inorganic particles 21, first inorganic fibers 23, and other compounding materials to water in a predetermined ratio and kneading them in a kneader to prepare a paste. Then, the obtained paste is 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.

[0115] Furthermore, a second member is obtained by dry mixing the inorganic particles 21, the second inorganic fibers 24, and other compounding materials in predetermined proportions and then press-molding. This second member is in the form of a sheet, with the second inorganic fibers 24 randomly distributed and the inorganic particles 21 held between the fibers.

[0116] Then, multiple layers of the first and second members are stacked alternately and the whole is press-molded and dried to obtain a heat transfer suppression sheet 32. During press molding, the second inorganic fibers 24, which are randomly present in the second member, penetrate the first member, which is in a wet state, and become entangled with the first inorganic fibers 23. After drying, this state is maintained, and the heat transfer suppression sheet 32 ​​is formed.

[0117] (Thickness of the heat transfer suppression sheet) In each of the above embodiments, the thickness of the heat transfer suppression sheet is not particularly limited, but it is preferably in the range of 0.05 to 6 mm. If the thickness of the heat transfer suppression sheet is 0.05 mm or more, sufficient mechanical strength can be imparted to the heat transfer suppression sheet. On the other hand, if the thickness of the heat transfer suppression sheet is 6 mm or less, good assembly properties can be obtained.

[0118] (Thermal insulation performance of heat transfer suppression sheets) Thermal conductivity can be cited as an indicator of thermal insulation performance. In each of the above embodiments, the thermal conductivity of the heat transfer suppression sheet 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 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). Note that the thermal conductivity can be measured in accordance with the "Test Method for Thermal Conductivity of Refractories" described in JIS R 2251.

[0119] [3. Battery Packs] The configuration of the battery pack is as illustrated in the first embodiment shown in Figure 4 above. Here, the configuration and effects of the battery pack using the heat transfer suppression sheet 10 according to the first embodiment of the present invention will be specifically explained with reference to Figure 4. As shown in Figure 4, the battery pack 100 according to the first embodiment has a plurality of battery cells 20a, 20b, and 20c arranged side by side, connected in series or parallel and housed in a battery case 30, with the heat transfer suppression sheet 10 interposed between the battery cells 20a, 20b, and 20c. In Figure 4, the heat transfer suppression sheet 10 is interposed between the battery cells 20a, 20b, and 20c, but the heat transfer suppression sheet 10 does not necessarily have to be interposed between the battery cells 20a, 20b, and 20c. For example, it may be placed between the battery cells 20a, 20b, and 20c and the battery case 30, or it may be attached to the inner surface of the battery case 30.

[0120] In such a battery pack 100, a heat transfer suppression sheet 10 is interposed between each battery cell 20a, 20b, and 20c, so that heat transfer between each battery cell 20a, 20b, and 20c can be suppressed during normal use.

[0121] On the other hand, even if any of the battery cells 20a, 20b, or 20c experience thermal runaway, the heat transfer suppression sheet 10 according to this embodiment can suppress the propagation of heat between the battery cells 20a, 20b, and 20c. Therefore, a chain reaction of thermal runaway can be prevented, and adverse effects on other battery cells can be minimized.

[0122] Although not shown in the diagram, the heat transfer suppression sheet 10 can be interposed between the battery cells 20a, 20b, and 20c, directly attached to the inner bottom surface of the battery case 30, or placed in the space between the top surface or side walls of the battery case 30 and the battery cells 20a, 20b, and 20c. Therefore, it offers high versatility and not only prevents a chain reaction of thermal runaway caused by heat transfer between adjacent battery cells, but also suppresses the spread of flames to the outside of the battery case in the event that one battery cell ignites.

[0123] For example, the battery pack according to this embodiment may be used in electric vehicles (EVs) and placed under the passenger compartment. In this case, even if a battery cell were to catch fire, the safety of the passenger can be ensured. In this case, since the heat transfer suppression sheet interposed between each battery cell can also be placed between the battery cell and the battery case, there is no need to manufacture new fire-retardant materials, and a safe battery pack can be easily constructed at low cost.

[0124] Furthermore, the heat transfer suppression sheets according to each of the above embodiments can be easily bent depending on the selection of constituent components and thickness. Therefore, they can be adapted to any shape, regardless of the shape of the battery cell. Specifically, they can be applied not only to prismatic batteries but also to cylindrical batteries, flat-plate batteries, and the like. [Examples]

[0125] Glass fiber was used as the first inorganic fiber, nanosilica particles as the first inorganic particles, alumina fiber as the second inorganic fiber, titania particles as the second inorganic particles, and acrylic resin as the organic binder. The glass fiber, which is the first inorganic fiber, contains 60% by mass of silica, and the nanosilica particles, which are the first inorganic particles, contain 99% by mass of silica; both have silica as their main component. The mixing ratio (by mass) was glass fiber: nanosilica particles: alumina fiber: titania particles: acrylic resin = 10:55:10:15:10.

[0126] These were then added to water, mixed in the water, and stirred with a stirrer to prepare a mixture. Subsequently, the resulting mixture was dewatered through a filtration mesh to produce a wet sheet. Then, the resulting wet sheet was heated and pressurized to obtain a heat transfer suppression sheet.

[0127] A cross-section of the heat transfer suppression sheet immediately after manufacturing (under normal use) was photographed using a scanning electron microscope (SEM). As shown in Figure 1, it can be seen that the first inorganic fiber (glass fiber) 1 and the second inorganic fiber (alumina fiber) 3 are intertwined to form a three-dimensional network, and that the first inorganic particles (nanosilica particles) 2 and the second inorganic particles (titania particles) 4 are held in place. Furthermore, it can be seen that an organic binder (acrylic resin) 5, which appears black in the figure, has entered and bonded to the gaps between these particles.

[0128] Next, simulating a thermal runaway of the battery cell, the heat transfer suppression sheet was exposed to a high temperature of 800°C, and its cross-section was photographed using a scanning electron microscope (SEM). As shown in Figure 2, the organic binder (acrylic resin) 5 disappeared, leaving behind the first inorganic fiber (glass fiber) 1, the second inorganic fiber (alumina fiber) 3, the first inorganic particle (nanosilica particle) 2, and the second inorganic particle (titania particle) 4.

[0129] Further heating was performed, and Figure 3 shows an SEM image of the cross-section of the heat transfer suppression sheet at 1000°C. It can be seen that the second inorganic fibers (alumina fibers) 3 and the second inorganic particles (titania particles) 4 remain even at this temperature. However, since the heat transfer suppression sheet is exposed to a high temperature of 1000°C, which is much higher than the glass transition temperature (Tg: 500-550°C) of the first inorganic fiber (glass fiber) 1 and the first inorganic particle (nanosilica particle) 2, it can be seen that the first inorganic fiber (glass fiber) 1 and the first inorganic particle (nanosilica particle) 2 are softened and deformed, as shown in parts A and B of Figure 3. It is thought that these particles then spread out to fill the gaps between the second inorganic fiber (alumina fiber) 3 and the second inorganic particle (titania particle) 4, thereby functioning as a binder. [Explanation of Symbols]

[0130] 1,23 First inorganic fiber 2. First inorganic particle 3.24 Second inorganic fiber 4. The second inorganic particle 5 Organic Binder 10,32 Heat transfer suppression sheet 20a, 20b, 20c battery cells 21 Inorganic particles 30 Battery Cases 100 battery packs

Claims

1. It comprises a fibrous component, a particulate component, and at least one of organic fibers and an organic binder, The main component of the first inorganic fiber contained in the fiber component and the main component of the first inorganic particle contained in the particle component are of the same type, and The content of the main component in the first inorganic particles is greater than the content of the main component in the first inorganic fiber. The average fiber diameter of the first inorganic fiber is greater than the average fiber diameter of the second inorganic fiber contained in the fiber component. The average fiber length of the first inorganic fiber is greater than the average fiber length of the second inorganic fiber. The inorganic particles constituting the aforementioned particle component are uniformly dispersed, The first inorganic fibers are uniformly dispersed and oriented in one direction parallel to the main surface of the sheet. A heat transfer suppressing sheet in which the second inorganic fiber is entangled with the first inorganic fiber to form a three-dimensional web structure.

2. The heat transfer suppression sheet according to claim 1, wherein the main component is silica.

3. The heat transfer suppression sheet according to claim 1, wherein the first inorganic fiber is a glass fiber and the first inorganic particle is a silica particle.

4. The heat transfer suppression sheet according to claim 1, wherein the thermal conductivity of the second inorganic fiber is 41 [W / m·K] or less.

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

6. In a battery pack in which multiple battery cells are connected in series or parallel, A battery pack using the heat transfer suppression sheet described in any one of claims 1 to 5.

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