Thermal runaway suppression sheet and battery pack using the same

Abstract

To provide a thermal runaway suppression sheet having a maximum thickness of 3 mm or less and capable of providing heat insulation to a temperature that can suppress a chain of thermal runaway in a lithium-ion battery.SOLUTION: Provided is a thermal runaway suppression sheet which has a thickness of 3 mm or less, and which includes a thermal energy consumption layer configured by a sheet of silica inorganic fibers having a hydroxyl group, and a heat dissipation layer having an in-plane thermal conductivity of 10-200 times greater than the thermal conductivity in a thickness direction. It is preferable that the sheet of silica inorganic fibers is a woven or non-woven fabric with a thickness of 0.5-2.0 mm, and the heat dissipation layer is an expanded graphite sheet with a thickness of 0.1-0.8 mm.EFFECT: The thermal runaway suppression sheet is thin and can provide an excellent heat insulation effect because the heat dissipation layer allows the silica inorganic fibers configuring the thermal energy consumption layer to efficiently consume thermal energy for localized heat production.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a thermal runaway suppression sheet that can be interposed between battery cells in a battery pack that serves as a power source for an electric motor that drives electric vehicles and hybrid vehicles, a thermal runaway suppression sheet that can be used for heat insulation of a housing that packages an assembly of battery cells (battery module), and a battery pack using these. [Background technology]

[0002] Electric vehicles and hybrid vehicles, which are driven by electric motors, are equipped with battery packs consisting of multiple battery cells connected in series or parallel, arranged in a modular design, as the power source for the drive motor. These battery cells primarily utilize lithium-ion rechargeable batteries, which offer high capacity and high output.

[0003] If a battery cell rapidly overheats and experiences thermal runaway due to an internal short circuit or overcharging, the heat from the overheated cell can spread to other adjacent cells, causing a chain reaction of thermal runaway in those cells and potentially leading to a major accident such as a fire. Therefore, in battery packs, a thermal runaway suppression sheet is interposed between battery cells as a technique to suppress the transfer of heat to adjacent cells when one battery cell experiences thermal runaway.

[0004] For example, Patent Document 1 (Patent No. 6885791) proposes a laminated thermal runaway suppression sheet comprising a heat-absorbing material layer in which at least one of mineral powder and a flame retardant is dispersed in a matrix resin selected from thermosetting resins, thermoplastic elastomers, and rubbers, and a fire-resistant heat-insulating layer composed of metal foil or metal foil laminated inorganic fiber cloth (e.g., aluminum foil laminated glass cloth, copper foil laminated glass cloth). Furthermore, Patent No. 7000625 (Patent Document 2) proposes a thermal runaway suppression sheet that includes two types of inorganic fibers with different glass transition temperatures and inorganic particles having voids. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 6885791 [Patent Document 2] Patent No. 7000625 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Patent Document 1 evaluates the thermal runaway sheet in a thermal runaway test where one side of the thermal runaway sheet is heated to 400°C for 10 minutes. However, thermal runaway suppression sheets used in battery packs for power supply of electric motors for electric vehicles or hybrid vehicles are required to withstand heating to high temperatures of nearly 1000°C for about 10 minutes. Under such high-temperature conditions, the matrix resin of the heat-absorbing material layer that absorbs heat from the thermally runaway cell melts and carbonizes, making it difficult to retain the mineral powder and flame retardant that provide the heat-absorbing effect. Furthermore, the matrix resin also suffers from poor fire resistance in the event of ignition.

[0007] The thermal runaway suppression sheet proposed in Patent Document 2 is formed into a sheet using an organic binder such as PVA, and consists of inorganic particles that exhibit a thermal runaway suppression effect and two types of inorganic fibers. In this thermal runaway suppression sheet, by using inorganic fibers with a melting point of less than 700°C (e.g., glass fibers) and fibers with a melting point of 1000°C or higher (ceramic fibers such as silica fibers and alumina fibers) as the two types of inorganic fibers, it is said that even if the organic binder burns out when exposed to a high temperature of 1000°C, the low-melting-point fibers melt, retaining the inorganic particles and exhibiting a heat transfer suppression effect.

[0008] In the thermal runaway suppression sheet proposed in Patent Document 2, the element that prevents and suppresses the heat from a thermally runaway cell from being transferred to adjacent cells, that is, the element that exhibits a heat insulation effect, is inorganic particles. Therefore, increasing the content rate and content of inorganic particles will enhance the heat insulation effect. However, increasing the content rate of inorganic particles will relatively decrease the content rate of inorganic fibers for exhibiting the retention effect. On the other hand, increasing both the content of inorganic particles and the content of inorganic fibers will result in an increase in the thickness of the thermal runaway suppression sheet.

[0009] However, for the assembled battery used as the power source of a drive electric motor for an electric vehicle or a hybrid vehicle, etc., there is a high demand for compactness, and the thickness is required to be at most 3 mm or less, preferably 2 mm or less, more preferably 1.8 mm or less, and preferably 1.6 mm or less.

[0010] The present invention has been made in view of the above circumstances, and the object thereof is, as a component that exhibits a heat insulation effect, even without using inorganic particles (flame retardants, porous inorganic particles) that cause powdering, at a maximum thickness of 3 mm or less, even when exposed to a high temperature of about 1000 °C or a flame, to provide a thermal runaway suppression sheet that can insulate heat to less than 400 °C, preferably less than 300 °C, where there is a risk of thermal runaway.

Means for Solving the Problem

[0011] The thermal runaway suppression sheet of the present invention is A thermal runaway suppression sheet interposed between the battery cells of a battery pack in which multiple battery cells are connected in series or parallel, or between the inner wall of a housing that houses the battery pack and the battery cells of the battery pack, wherein the thermal energy from a cell that has experienced thermal runaway is dispersed in the planar direction of the thermal runaway suppression sheet; and a heat energy consumption layer composed of a sheet of silica-based inorganic fiber having a hydroxyl group Includes, The heat dispersing layer is an expanded graphite sheet with a thickness of 0.1 to 0.8 mm. and is a thermal runaway suppression sheet with a thickness of 3 mm or less 。

[0012] The silica-based inorganic fiber sheet is preferably a woven fabric or a non-woven fabric with a thickness of 0.5 to 2.0 mm, and more preferably, it is formed into a sheet with a thickness of 0.5 to 1.5 mm by papermaking of the staple fibers of the silica-based inorganic fiber.

[0013] The content of silica-based inorganic fibers in the silica-based inorganic fiber sheet is 100 kg / m 3 ~400kg / m 3 It is preferable that this be the case. A preferred embodiment of the thermal runaway suppression sheet of the present invention comprises the expanded graphite sheet, the thermal energy consumption layer, and the adhesive layer. Furthermore, in the thermal runaway suppression sheet of the present invention, the thermal energy layer may be impregnated with at least one selected from the group consisting of porous inorganic particles, colloidal silica, alumina hydrate, and minerals, and preferably silica aerogel particles.

[0014] From another viewpoint, the present invention relates to a battery pack in which a plurality of battery cells are connected in series or parallel, wherein the thermal runaway suppression sheet of the present invention is interposed between the battery cells. [Effects of the Invention]

[0015] The thermal runaway suppression sheet of the present invention exhibits an insulating effect by having silica-based inorganic fibers having hydroxyl groups that consume thermal energy caused by thermal runaway. Furthermore, the heat dispersion layer allows the silica-based inorganic fibers constituting the thermal energy consumption layer to effectively dissipate thermal energy in response to localized heat generation, thus enabling it to exhibit excellent insulating effect despite being thin. Therefore, by interposing the thermal runaway suppression sheet of the present invention between the battery cells constituting a battery pack, it is possible to suppress the occurrence of chain-reaction thermal runaway based on the above insulating effect. [Brief explanation of the drawing]

[0016] [Figure 1] This is a schematic cross-sectional view showing the configuration of a thermal runaway suppression sheet according to one embodiment of the present invention. [Figure 2] This is a schematic diagram illustrating the configuration of a thermal runaway suppression sheet for use in a battery pack. [Figure 3] This is a diagram illustrating the thermal insulation performance evaluation test 1 performed in the example. [Figure 4] This is a diagram illustrating the thermal insulation performance evaluation test 2 performed in the example. [Figure 5] This graph shows the change in back surface temperature measured in the example. [Figure 6] This graph shows the change in back surface temperature measured in the example. [Figure 7]This graph shows the change in back surface temperature measured in the example. [Figure 8] This graph shows the change in back surface temperature measured in the example. [Modes for carrying out the invention]

[0017] Figure 1 is a schematic cross-sectional view showing the configuration of a typical embodiment of the thermal runaway suppression sheet according to the present invention. The thermal runaway suppression sheet 10 shown in Figure 1 is a sheet-like laminate in which a thermal energy consumption layer 1 and a thermal dispersion layer 2, which are aggregates of silica-based inorganic fibers having hydroxyl groups, are laminated together via an adhesive layer 3.

[0018] (1) Thermal energy consumption layer (F) A thermal energy consuming layer is a material that reduces the amount of thermal energy transferred by consuming thermal energy itself. Specifically, it is a sheet made of an aggregate of silica-based inorganic fibers having hydroxyl groups (hereinafter sometimes simply referred to as a "silica-based fiber sheet").

[0019] The silica-based inorganic fiber having the above-mentioned hydroxyl group is a thermoformable glass fiber containing 81% by weight or more of SiO2, with Si(OH) present in part of the SiO- network. Such hydroxyl groups are formed during the process of manufacturing filaments or staple fibers from a starting glass material, when metal or metal oxide ions (e.g., Al) contained in the starting glass material are introduced. 3+ , TiO 2+ or action 4+ , and ZrO 2+ or Zr 4+ It is thought that these remain after proton substitution. The hydroxyl groups contained in silica fibers can undergo a condensation reaction at around 600-800°C as shown in equation (1) below, forming new siloxane bonds (Si-O-Si bonds) and releasing H2O.

[0020] [ka]

[0021] The composition of the above silica-based inorganic fiber is not particularly limited, but preferably has the following composition. SiO2: 81 - 97% by weight; Al2O3: 3 - 19% by weight; and Components selected from ZrO2, TiO2, Na2O, Li2O, K2O, CaO, MgO, SrO, BaO, Y2O3, La2O3, Fe2O3, and mixtures thereof (referred to as "other components") are 2% by weight or less.

[0022] Specifically, a starting glass material having the following composition is melted, 55 - 80% by weight of SiO2, 5 - 19% by weight of Al2O3, 15 - 26% by weight of Na2O, 0 - 12% by weight of ZrO2, 0 - 12% by weight of TiO2, and Li2O, K2O, CaO, MgO, SrO, BaO, Y2O3, La2O3, Fe2O3, and mixtures thereof: 1.5% by weight or less; Filaments or staple fibers are formed from the melt; The obtained filaments or staple fibers are acid-extracted; It can be produced by removing the remaining acid and / or salt residues from the extracted filaments or staple fibers and then drying.

[0023] In the acid treatment, alkali metal ions are replaced by protons by the acid treatment, but ions (Al 3+ , TiO 2+ or Ti 4+ , and ZrO 2+ or Zr 4+) will remain. The metal ions substituted by protons in the silicon dioxide skeleton are thought to retain a certain number of hydroxyl groups, depending on their valence. These hydroxyl groups undergo a condensation reaction at around 600-800°C as shown in equation (1) above, forming a new Si-O-Si bond and releasing H2O.

[0024] The water produced by dehydration condensation vaporizes under high-temperature conditions. At this time, the heat energy supplied to the silica fiber sheet is consumed as latent heat of vaporization, thus suppressing the temperature rise of the sheet. In this way, the heat energy from the thermally runaway cell is consumed, and a temperature reduction can be achieved on the side opposite to the side in contact with the thermally runaway cell (the back side).

[0025] Furthermore, the silica-based inorganic fibers that make up the sheet are not particularly limited as long as they contain Si(OH) in their composition, but for example, AlO 1.5 ·18 [(SiO2)] 0.6 (SiO 1.5 OH) 0.4 Compositions represented by ] are examples. Inorganic fibers having such a composition can be manufactured by melt spinning as staple fibers with a diameter of 6 to 13 μm, preferably about 7 to 10 μm, and a length of 3 to 30 mm, or as staple fibers with a diameter of 6 to 13 μm, preferably about 7 to 10 μm, and generally a length of 1 to 50 mm, preferably about 3 to 30 mm, or as filaments with a length of 30 to 150 mm. Alternatively, staple fibers may be spun or filaments may be twisted to form yarn. In either the case of staple fibers or filaments, they are manufactured by cutting continuously spun fibers after melting, and therefore substantially contain no shots. Accordingly, the silica-based inorganic fibers used in this invention, in any form—staple fibers, filaments, yarn, or sheets as aggregates thereof—meet the safety standards of the Industrial Safety and Health Enforcement Order and are not subject to the regulations of the Specified Chemical Substances Hazard Prevention Regulations.

[0026] Such silica-based inorganic fibers can be commercially available, for example, BELCOTEX® from BELCHEM GmbH. BELCOTEX® fibers are generally made from alumina-modified silicic acid and contain approximately 94.5% by mass silica, approximately 4.5% by mass alumina, less than 0.5% by mass oxide, and less than 0.5% by mass other components. They have a melting point of 1500°C to 1550°C and heat resistance down to 1100°C.

[0027] The silica fiber sheet that serves as the thermal energy consumption layer can be a nonwoven fabric (paper) made by wet-processing staple fibers as described above, or a woven fabric made by weaving the yarn or filaments as described above. Of these, the paper-making type sheet (paper) is preferred because it allows for adjustment of the fiber content in the sheet while maintaining the uniform dispersion of silica inorganic fibers in the sheet.

[0028] Wet papermaking is a method in which the above-mentioned stable fibers are dispersed in water to form a uniform slurry, this slurry is paper-made using a paper machine, the water is removed by pressing, and then it is dried to obtain a sheet-like material. As paper machines, cylinder paper machines, long-wire paper machines, inclined paper machines, inclined short-wire paper machines, and combinations thereof can be used. In addition to stable fibers, binders (such as polyvinyl alcohol and hydrophilic resins containing hydroxyl groups such as cellulose), dispersants, paper strength enhancers, thickeners, inorganic fillers, organic fillers, and defoamers may be added to the slurry as needed.

[0029] In the case of woven fabrics, the weaving method is not particularly limited, and examples include plain weave, twill weave, and satin weave. Plain weave is preferred because it allows for a larger contact area with the heat dissipation layer.

[0030] The thickness of the silica fiber sheet is 0.4 to 2.0 mm, preferably 0.5 to 1.8 mm, and more preferably 0.8 to 1.6 mm. If it is too thin, sufficient thermal energy attenuation cannot be obtained in relation to the amount of fiber, and consequently, sufficient thermal insulation performance cannot be obtained. On the other hand, in relation to the intercellular gap to which it is applied, the overall thickness of the thermal runaway suppression sheet must be 3.0 mm or less, preferably 2.5 mm or less, and more preferably 2.0 mm or less. In relation to this requirement, a sheet with a thickness of 1.6 mm or less is preferred.

[0031] The fiber content (density) in a sheet is typically 100 kg / m³. 3 ~1500kg / m 3 In the case of woven fabrics, the weight varies depending on the yarn used and the weight of the fabric, but it is approximately 400 kg / m 3 ~1500kg / m 3 Preferably 400-1000 kg / m 3 On the other hand, in the case of sheets obtained by papermaking, the weight is 100 kg / m². 3 ~400kg / m 3 The range is preferably 120 kg / m 3 ~400kg / m 3 More preferably 140 kg / m 3 ~250kg / m 3 Therefore, this level of density is necessary to obtain the insulating effect through thermal energy consumption. On the other hand, if the density becomes too high, the void space in the sheet decreases too much, making it difficult to obtain the insulating effect from the pores (air).

[0032] Furthermore, the thermal energy consumption layer is not limited to the silica fiber sheet described above, and may optionally contain porous inorganic particles such as silica aerogel; inorganic particles that exhibit adhesiveness in aqueous solutions such as colloidal silica and alumina hydrate (e.g., boehmite); or inorganic particles such as minerals such as kaolin and mica.

[0033] Silica aerogel refers to gel particles having nano-sized pores with a porosity of 70% or more by volume, preferably 80% or more by volume, and more preferably 90% or more by volume, with a particle size of 50 nm to 2 mm, and a porosity of 90% or more in the particle size range of 1 μm to 2 mm, more preferably 1 μm to 500 μm, and even more preferably 5 μm to 400 μm. Such aerogels have a large pore volume per particle, thus providing an increased thermal insulation effect.

[0034] By immersing a silica fiber sheet in an aqueous solution in which such inorganic particles are dispersed together with an inorganic binder, it is possible to impregnate the sheet with inorganic particles.

[0035] (2) Heat dispersing layer (expanded graphite sheet (G)) A heat-dispersing layer is a layer in which the thermal conductivity in the planar direction is 10 to 200 times greater than the thermal conductivity in the thickness direction, and is usually 20 to 100 times greater, allowing heat to be dispersed in the planar direction. As a result, when a part of the thermal runaway suppression sheet is exposed to high heat locally, the heat is propagated and diffused mainly in the planar direction rather than in the thickness direction, thereby dispersing the thermal energy from the runaway cell throughout the entire sheet.

[0036] Specifically, as the heat dispersing layer, an expanded graphite sheet with a graphite content of 80-100% by weight, preferably 90-100% by weight, is used. As the expanded graphite sheet, an expanded graphite sheet that can be formed into a sheet by rolling expanded graphite, or a polymer-type expanded graphite sheet that can be obtained by heat-treating a polymer film such as an aromatic polyimide sheet to over 2500°C under a reducing atmosphere and pressure to graphitize it can be used. From the viewpoint of heat resistance and flexibility, an expanded graphite sheet is preferably used.

[0037] Expanded graphite can be produced by treating graphite powder, such as natural scaly graphite, pyrolytic graphite, or quiche graphite, with an inorganic acid such as sulfuric acid or nitric acid and a strong oxidizing agent such as concentrated nitric acid, perchloric acid, dichromate, or hydrogen peroxide to generate graphite intercalation compounds. These compounds are then washed with water, dried, and rapidly heated to over 1000°C, causing the intercalation compounds to gasify and the graphite layers to be pushed up, expanding their volume by several hundred times.

[0038] Expanded graphite sheets typically have a thickness of about 10 μm to 2 mm, depending on the manufacturing method. In the thermal runaway suppression sheet of the present invention, due to the overall thickness limitations of the thermal runaway suppression sheet, it is preferable to use an expanded graphite sheet with a thickness of 1 mm or less, more preferably 0.5 mm or less, and even more preferably 10 μm to 200 μm (0.2 mm).

[0039] The bulk density of the expanded graphite sheet is 0.5 to 1.6 g / cm³. 3 Preferably 0.5 to 1.1 g / cm³ 3 Materials within this range should be used. Thermal conductivity, an important property for a heat-conducting sheet, changes in proportion to the bulk density of the sheet material. If the bulk density of the expanded graphite sheet becomes too low, it becomes difficult to obtain its effect as a heat-dispersing layer, and its oxidation resistance also tends to decrease. On the other hand, if it becomes too high, the porosity decreases, and it becomes difficult to obtain the insulating effect from the pores (air).

[0040] The expanded graphite sheets described above have a thermal conductivity of 50 to 500 W / mK in the planar direction, preferably 100 to 300 W / mK, and a thermal conductivity of 2 to 10 W / mK in the thickness direction, preferably 3 to 8 W / mK, although this depends on the type of graphite, the acid impregnated, the graphite content, etc. Expanded graphite sheets oxidize and wear down when exposed to high temperatures for extended periods, but they have heat resistance and oxidation resistance to exposure to high temperatures of around 1000°C for about one hour.

[0041] In a laminated unit combining a heat-dispersing layer and a thermal energy-consuming layer (silica fiber sheet) as described above, i.e., a "heat-dispersing layer / thermal energy-consuming layer," if either layer is locally heated due to thermal runaway in a cell it is in contact with, the thermal energy can be attenuated and consumed by the generation of water through the condensation reaction of silica inorganic fibers constituting the thermal energy-consuming layer, and further by the heat of vaporization of the generated water. In addition, the heat-dispersing layer propagates the localized high heat across the entire surface, thereby propagating thermal energy throughout the thermal energy-consuming layer and promoting the condensation reaction of silica fibers throughout the entire sheet. As a result, thermal energy can be consumed throughout the thermal energy-consuming layer, thus achieving an excellent temperature reduction effect. This temperature reduction effect can be obtained similarly whether the heat energy consumption layer is in contact with the heat source or whether the expanded graphite sheet, which is the heat dispersion layer, is in contact with the heat source.

[0042] Expanded graphite sheets tend to have lower dielectric strength compared to silica fiber sheets. If dielectric strength is required, an insulating coating can be applied to the surface of the expanded graphite sheet (the side not in contact with the silica fiber sheet).

[0043] (3)Adhesive layer The thermal runaway suppression sheet of the present invention is a laminate in which the thermal energy consumption layer 1 and the thermal dispersion layer 2 described above are laminated together with an adhesive layer 3 in between as appropriate.

[0044] As the adhesive used in the adhesive layer 3, an elastomer-based adhesive is preferably used, from the viewpoint of not impairing the flexibility and suppleness of the thermal runaway suppression sheet. The elastomer component, which is the main constituent material of the adhesive, is not particularly limited and may be rubber-based, acrylic-based, or silicone-based. Furthermore, the form of the adhesive may be solvent-based, emulsion-based, hot-melt-based, aqueous solution-based, etc., but preferably, from the viewpoint of the bonding process between the heat energy consumption layer 1 and the heat dispersion layer 2 and the ease of application, emulsion-type adhesives and solvent-type adhesives are used.

[0045] The thermal runaway suppression sheet 10 having the above configuration is used by being interposed between the battery cells 11, 11 in a battery pack in which a plurality of battery cells 11 are arranged in a housing 12, as shown in Figure 2. It may also be used by being interposed between the housing 12 and the battery cells 11. The electrical connections of the battery cells 11 in the battery pack may be in series or parallel.

[0046] If one of the battery cells constituting the battery pack experiences thermal runaway, the thermal runaway suppression sheet 10 in contact with that battery cell consumes thermal energy, and the temperature of the battery cells adjacent to the thermal runaway cell decreases based on the thermal insulation effect of the thermal runaway suppression sheet, thus preventing a chain reaction of thermal runaway. Furthermore, if there are multiple battery modules of the same type as shown in Figure 2, the thermal insulation effect of the thermal runaway suppression sheet 10 interposed between the housing 12 and the battery cells 11 can suppress the temperature rise of the other battery modules.

[0047] [Other forms of thermal runaway suppression sheets] The thermal runaway suppression sheet shown in Figure 1 was a laminate in which a thermal energy consumption layer and a thermal dispersion layer were laminated with an adhesive layer in between. However, the thermal runaway prevention sheet of the present invention may optionally include layers other than the thermal energy consumption layer, thermal dispersion layer, and adhesive layer (other layers). Examples of other layers include a reflective material layer and an aerogel-containing layer.

[0048] (4) Reflective layer (R) A reflective layer is a layer that acts as a reflector for radiant heat. The reflective layer may be laminated on the thermal energy consumption layer or the thermal dispersion layer, or it may be interposed between the thermal energy consumption layer and the thermal dispersion layer. Preferably, it is interposed between the thermal energy consumption layer and the thermal dispersion layer. This allows radiant heat to be reflected back to the heat source side, regardless of whether the thermally runaway cell side is on the thermal energy consumption layer side or the thermal dispersion layer side, thereby suppressing heat conduction to the back side. In other words, the thermal insulation effect can be enhanced.

[0049] Specifically, such reflective layers consist of metal foil and metal vapor-deposited layers. Examples of metals used in metal foil or metal vapor deposition include highly reflective metals such as aluminum, stainless steel, titanium, chromium, nickel, and gold, with aluminum being preferred. The thickness of the reflective layer is typically 5 to 25 μm, preferably 10 to 18 μm. This thickness is sufficient for the reflective layer to function effectively; if it becomes too thick, the rigidity increases excessively, reducing the flexibility of the thermal runaway suppression sheet and consequently worsening the sheet's handling properties.

[0050] (5) Aerogel-containing layer (A) The silica aerogel may be impregnated into the energy consumption layer or supported on silica-based fibers constituting the energy consumption layer, but a silica aerogel-containing layer, separately supported on other fibers to form a sheet, may also be included as a constituent layer of the laminate.

[0051] As the sheet-like fibrous mass that serves as the support for silica aerogel, glass fibers; ceramic fibers such as silica fibers, alumina fibers, titania fibers, and silicon carbide fibers; metal fibers; artificial mineral fibers such as rock wool and basalt fibers; carbon fibers, whiskers, etc. can be used, either formed into paper-like or board-like forms by papermaking, or molded into sheets by adding a binder as appropriate. The content ratio (by weight) of the sheet-like fiber mass that serves as the carrier and the silica aerogel is preferably 9:1 to 5:5, and more preferably 8:2 to 6:4.

[0052] When the thermal runaway suppression sheet includes the aerogel-supported sheet (A), the arrangement relationship (layer configuration) with the thermal energy consumption layer (F), the heat dispersion layer (G), and the reflective material layer (R) is not particularly limited. If other layers are included as described above, the combination and configuration of the layers to be selected will be appropriately chosen depending on the type of other layers, their relationship to the overall thickness of the thermal runaway suppression sheet, the required thermal insulation properties, and the usage conditions. However, in order to fully utilize the thermal energy consumption effect of silica-based inorganic fibers, it is preferable that the layer interposed between the thermal energy consumption layer (F) and the thermal dispersion layer (G) be thin and few in number. [Examples]

[0053] [Method for measuring and evaluating the heat transfer suppression effect] (1)Measurement method 1: As shown in Figure 3, a sample piece of the sheet to be evaluated (150mm x 150mm) is placed on the top surface of the electric heating furnace (a 100mm x 100mm stainless steel plate), and a steel plate (0.6mm thick) is placed on top of it (on the back of the sample piece). The temperature change of the steel plate surface is monitored with a thermometer.

[0054] (2)Measurement method 2: As shown in Figure 4, a sample piece of the sheet to be evaluated (150 mm x 150 mm) is fixed vertically, and one side is heated with a horizontally fixed burner flame. A steel plate (0.6 mm thick) is then placed against the opposite side (back) of the sample piece, and the temperature change of the steel plate surface is monitored with a thermometer.

[0055] [Thermal runaway suppression sheet using a woven fabric type thermal energy consumption layer] (1) Thermal energy consumption layer As the thermal energy consumption layer (F), BELCOTEX® 110 (composition is AlO) from BELCHEM GmbH is used. 1.5 ·18 [(SiO2)] 0.6 (SiO 1.5 OH) 0.4 A woven fabric (1.8 mm thick, 444 kg / m²) made in a plain weave using pre-yarn (550 Tex; spun yarn of staple fibers with a diameter of 9 μm and a length of 3-5 mm) of ] 3 ) was used.

[0056] (2) Effects of the thermal energy consumption layer The thermal runaway suppression sheet prepared as described above was cut out to obtain a 150mm x 150mm sample piece. The heat transfer suppression effect of this sample piece was evaluated based on the measurement method 1 described above. The temperature of the top surface of the electric furnace was 700°C, and the silica fiber sheet was placed so that its center was in contact with the top surface of the electric furnace. Under these conditions, the temperature change of the side not in contact with the electric furnace (back side: expanded graphite sheet side) was monitored from immediately after placement (1 second) for 11 minutes (700 seconds).

[0057] A newly cut sample piece (150 mm x 150 mm) was fired at 700°C for 8 hours. Then, using the thermal runaway suppression sheet sample piece after firing, it was placed on the top surface of the electric furnace in the same manner as described above, and the temperature change from immediately after placement (1 second) to 11 minutes (700 seconds) was measured.

[0058] Figure 5 shows the temperature changes of the thermal runaway suppression sheet before and after firing. In Figure 5, the horizontal axis represents elapsed time, and the vertical axis represents temperature. The thermal runaway suppression sheet before firing is shown with a dashed line, and the thermal runaway suppression sheet after firing is shown with a solid line.

[0059] As can be seen in Figure 5, the thermal runaway suppression sheet before firing had a lower temperature on its back side (the side opposite the electric furnace) and a higher heat insulation effect than the thermal runaway suppression sheet after firing. This is because, in the case of silica fiber sheets, heating in an electric furnace causes a condensation reaction of terminal hydroxyl groups, and some of the heating energy is consumed by the heat of vaporization of the resulting water. On the other hand, in the case of thermal runaway suppression sheets after firing, it is thought that the hydroxyl groups of the silica fibers were substantially eliminated by firing, so the effect of heat energy consumption from the condensation reaction and the heat of vaporization of the resulting water could not be obtained.

[0060] (3) Thermal insulation effect of the heat dissipation layer The heat dispersing layer (G) has a thickness of 0.2 mm and a bulk density of 0.8 g / cm³. 3 An expanded graphite sheet (manufactured by Toyo Tanso) was used. Its thermal conductivity (at 25°C) was 200 W / mK in the planar direction and 5 W / mK in the thickness direction.

[0061] For sample pieces (150 mm x 150 mm) of the expanded graphite sheet and the silica fiber cloth (1.8 mm thick) constituting the thermal energy consumption layer, the temperature changes were measured according to Measurement Method 1 (temperature on the top surface of the electric furnace: 700°C, monitoring time: 5 minutes). The measurement results are shown in Figure 6.

[0062] A thermal runaway suppression sheet (2.0 mm thick) having the configuration shown in Figure 1 was created by spraying an aerosol spray-type synthetic rubber adhesive ("AP-2" from No Tape Industry Co., Ltd., whose main component is styrene-butadiene rubber (solid content approximately 20% by weight), and whose solvents are N-hexane and dimethyl ether) onto one side of an expanded graphite sheet, then overlapping it with the silica fiber sheet and pressing it. A sample piece (150 mm x 150 mm) of the created thermal runaway suppression sheet (unfired) was measured for temperature changes using evaluation method 1 in the same manner as described above. The thermal runaway suppression sheet was placed so that the silica fiber sheet was in contact with the top surface of the electric furnace. The measurement results are shown in Figure 6.

[0063] In Figure 6, the horizontal axis represents elapsed time, and the vertical axis represents back surface temperature. The temperature change of the silica fiber cloth (thermal energy consumption layer) alone is shown by a dashed line, the temperature change of the expanded graphite sheet (thermal dispersion layer) alone is shown by a dashed line, and the temperature change of the thermal runaway suppression sheet (laminated structure) is shown by a solid line.

[0064] As can be seen in Figure 6, the silica fiber cloth alone resulted in a slower temperature rise on the back surface than the expanded graphite sheet alone. This is thought to be due to the thermal energy dissipation effect of the silica fiber cloth. However, the back surface temperature, which plateaued, was approximately 260°C for the silica fiber cloth alone and approximately 265°C for the expanded graphite sheet alone, showing no significant temperature difference.

[0065] On the other hand, in the thermal runaway suppression sheet of the present invention, which is made by laminating a silica fiber cloth and an expanded graphite sheet, the temperature rise on the back surface was even slower, and the back surface temperature, which plateaued, was around 245°C. This degree of temperature reduction was greater than in the case of the silica fiber cloth and the expanded graphite sheet alone, and is thought to be due to the synergistic effect of the thermal energy consumption layer and the thermal dispersion layer.

[0066] (4) Usage and thermal insulation effect For sample pieces (150 mm x 150 mm) cut from the thermal runaway suppression sheets prepared as described above, the temperature change on the back side was measured using Measurement Method 1 for both cases: when the heated side was a silica fiber sheet and when it was an expanded graphite sheet. The temperature of the top surface of the electric furnace was set to 1000°C, and monitoring was performed from immediately after placement (1 second) for 5 minutes (300 seconds). The measurement results are shown in Figure 7.

[0067] In Figure 7, the solid line represents the case where the expanded graphite sheet is placed in contact with the top surface of the electric furnace, and the dashed line represents the case where the silica fiber sheet is placed in contact with the top surface of the electric furnace. As can be seen from Figure 7, the temperature changes of both were almost the same. Therefore, although the layer structure of the thermal runaway suppression sheet in this embodiment is asymmetrical, it can exhibit the same level of heat insulation effect regardless of which side is heated. Therefore, in the specifications shown in Figure 2, there are no restrictions on which side should face which cell when interposing between cells, thus simplifying the assembly process.

[0068] [Thermal runaway suppression sheet using a papermaking-type thermal energy consumption layer] As the thermal energy consumption layer (F), belCotex (registered trademark) 110 from BELCHEM GmbH (composition is AlO 1.5 ·18 [(SiO2)] 0.6 (SiO 1.5 OH) 0.4 A silica fiber sheet (thickness 1.4 mm, density 200 kg / m²) obtained by wet papermaking of chopped strands (fiber diameter 9 μm, fiber length 3-5 mm) of ]) 3) was used.

[0069] The heat dispersion layer (G) and the adhesive layer are the same as those used in the woven fabric type thermal runaway creation sheet, namely, expanded graphite sheet (manufactured by Toyo Tanso, thickness 0.2 mm, bulk density 0.8 g / cm³). 3 A synthetic rubber adhesive (AP-2 from No Tape Industry Co., Ltd.) with a heat transfer coefficient of 200 W / mK in the planar direction and 5 W / mK in the thickness direction was used. After spraying the above adhesive onto one side of the expanded graphite sheet, the above silica fiber sheet was placed on top, pressed, dried, and solidified to create a thermal runaway suppression sheet (thickness 1.6 mm) having the configuration shown in Figure 1.

[0070] The temperature change of a sample piece (150 mm x 150 mm) of the prepared thermal runaway suppression sheet was measured according to measurement method 2. A silica fiber sheet was used as the heating surface, and the temperature change was measured over a period of 10 minutes (600 seconds). The average temperature of the surface in contact with the flame during the measurement was 1005°C. The measurement results are shown in Figure 8.

[0071] As can be seen from Figure 8, the thermal runaway suppression sheet of this embodiment, with a thickness of 1.6 mm, was able to suppress the temperature on the back side to 300°C or less even when exposed to a 1000°C flame for 10 minutes. [Industrial applicability]

[0072] The thermal runaway suppression sheet of the present invention can suppress the temperature rise of adjacent battery cells by efficiently attenuating thermal energy, even when one of the cells constituting a battery pack experiences a localized temperature rise. Furthermore, it can be used for insulation between the ionization cell and the housing, preventing adjacent battery modules from overheating. Therefore, it is useful in preventing chain-reaction thermal runaway in battery packs where battery cells are modularized and packaged. [Explanation of Symbols]

[0073] 1. Thermal energy consumption layer (silica fiber sheet) 2. Heat dispersing layer (expanded graphite sheet) 3 Adhesive layer 10. Thermal runaway suppression sheet 11 battery cells 12 cabinets

Claims

1. A thermal runaway suppression sheet interposed between the battery cells of a battery pack in which multiple battery cells are connected in series or parallel, or between the inner wall of a housing that houses the battery pack and the battery cells of the battery pack, A thermal dispersion layer that disperses the thermal energy from a thermally runaway cell in the planar direction of the thermal runaway suppression sheet; and It includes a thermal energy consumption layer composed of a sheet of silica-based inorganic fibers having hydroxyl groups, A thermal runaway suppression sheet with a thickness of 3 mm or less, wherein the heat dissipation layer is an expanded graphite sheet with a thickness of 0.1 to 0.8 mm.

2. The thermal runaway suppression sheet according to claim 1, wherein the thermal energy consumption layer and the thermal dispersion layer are laminated with an adhesive layer in between.

3. The thermal runaway suppression sheet according to claim 1 or 2, wherein the silica-based inorganic fiber sheet is a woven or nonwoven fabric with a thickness of 0.5 to 2.0 mm.

4. The thermal runaway suppression sheet according to claim 3, wherein the silica-based inorganic fiber sheet is made by papermaking of the silica-based inorganic staple fibers into a sheet with a thickness of 0.5 to 1.5 mm.

5. The silica-based inorganic fiber content in the silica-based inorganic fiber sheet is 100 kg / m ３ ~400 kg / m ３ The thermal runaway suppression sheet according to claim 3 or 4.

6. The thermal runaway suppression sheet according to claim 2 comprises the expanded graphite sheet, the thermal energy consumption layer, and the adhesive layer.

7. The thermal runaway suppression sheet according to any one of claims 1 to 6, wherein the thermal energy consumption layer is impregnated with at least one selected from the group consisting of porous inorganic particles, colloidal silica, alumina hydrate, and minerals.

8. The thermal runaway suppression sheet according to any one of claims 1 to 6, wherein the thermal energy consumption layer is impregnated with silica aerogel particles.

9. A battery pack comprising multiple battery cells connected in series or parallel, wherein a thermal runaway suppression sheet according to any one of claims 1 to 8 is interposed between the battery cells.

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