Thermal insulation material for battery pack, and battery pack

Abstract

The present invention provides a thermal insulation material for a battery pack, said thermal insulation material being thin but yet exhibiting excellent thermal insulation properties.　This thermal insulation material for a battery pack includes a layered inorganic material sheet formed by laminating a plurality of layered inorganic material papers, said thermal insulation material characterized in that the layered inorganic material papers are impregnated with a resin, and the layered inorganic material sheet is expanded by heating at 500°C so as to create voids in the layered inorganic material sheet.

Description

Battery pack heat insulating material and battery pack

[0001] The present invention relates to a heat insulating material for a battery pack and a battery pack using the heat insulating material for a battery pack.

[0002] 2. Description of the Related Art Battery packs used in electric vehicles, hybrid vehicles, and the like are composed of a plurality of battery cells.

[0003] Battery cells may go into a thermal runaway state due to an internal short circuit or overcharging caused by external factors, which can cause high temperatures, fire, etc. The heat and fire generated in this way can spread to the surrounding area, inducing thermal runaway in adjacent battery cells and causing serious damage.

[0004] Therefore, in order to prevent personal injury caused by thermal runaway of battery cells, various safety components are applied to battery packs, such as partition members that suppress heat propagation between battery cells, and protective members that are placed between the battery cells and the battery case and suppress the propagation of heat and the release of flames outside the battery pack.

[0005] Layered inorganic materials such as mica have a high melting point and excellent fire resistance, and are therefore used as safety components for battery packs. For example, Patent Document 1 discloses a safety component that combines two mica layers with an aerogel layer filled in a sealed bag, with the two mica layers facing each other on the outside of the sealed bag. Patent Document 2 also discloses a fire-resistant material for batteries that includes a mica layer and a foam coating.

[0006] Chinese Utility Model No. 219523264 Chinese Patent No. 109987884

[0007] However, while layered inorganic materials have excellent fire resistance, they are characterized by insufficient heat insulating performance, and Patent Document 1 also compensates for the heat insulating performance by combining a mica layer with an aerogel layer having heat insulating properties. However, against the backdrop of the trend toward higher energy battery packs, safety members used in battery packs are required to have further improved heat insulating performance, and measures such as increasing the thickness of the safety member or stacking multiple heat insulating layers are being considered. However, as shown in Patent Document 2, due to the limited installation space for safety members in battery packs, thin-walled safety members are also required.

[0008] An object of the present invention is to provide a battery pack insulating material that is thin yet has excellent heat insulating properties. Another object of the present invention is to provide a battery pack including a battery pack insulating material that has excellent thinness and heat insulating properties.

[0009] The present inventors have conducted extensive research to provide a heat insulating material that is thin yet has excellent heat insulating properties during thermal runaway of a battery pack.

[0010] Conventional insulating materials have had difficulty achieving both insulating function and thinness, but the inventors have discovered an insulating material for battery packs that is thin during normal battery pack use, but expands in response to temperature increases caused by thermal runaway in the battery pack.

[0011] The battery pack insulating material of the present invention is a battery pack insulating material including a layered inorganic sheet formed by stacking multiple layers of layered inorganic paper, wherein the layered inorganic paper is impregnated with a resin, and the layered inorganic sheet expands when heated to 500°C, creating voids within the layered inorganic sheet. Due to the above configuration, the battery pack insulating material of the present invention is thin within the normal operating temperature range of the battery pack, but when heated due to thermal runaway or the like in the battery pack, the resin within and between the layers of layered inorganic paper generates gas, creating voids within and between the layers of layered inorganic paper, causing the layered inorganic sheet to expand and suppress heat propagation, thereby exhibiting excellent insulating properties. The size and shape of the voids are not particularly limited, and they may be formed in layers between and within the layers of layered inorganic paper, but it is preferable that multiple small, independent voids are formed. The size of the voids in the thickness direction of the battery pack insulating material is preferably 10 μm to 100 μm.

[0012] The layered inorganic paper preferably contains at least one silicate mineral selected from the group consisting of vermiculite, montmorillonite, beidellite, nontronite, saponite, hectorite, stevensite, and mica. When the layered inorganic paper contains the silicate mineral, the battery pack insulating material of the present invention exhibits excellent thermal insulation properties while the layered inorganic sheet is prone to expansion when heated. The layered inorganic paper more preferably contains mica, as mica has excellent insulating properties and fire resistance.

[0013] The resin is preferably at least one selected from the group consisting of epoxy resin, silicone resin, acrylic resin, and fluororesin, and when the resin is one of the above, the amount of gas generated is appropriate even during thermal runaway of the battery pack, and voids are generated both within the layered inorganic paper and between the layers of the layered inorganic paper.

[0014] The resin preferably has a group that generates gas upon heating, and the amount of mass loss of the resin after heating for 1 hour at 500° C. is preferably 1.0% by mass or more and 20.0% by mass or less. If the amount of mass loss of the resin after heating is within the above range, voids will be generated both within the layered inorganic paper and between the layered inorganic papers during thermal runaway of the battery pack.

[0015] The resin content of the layered inorganic material sheet is preferably 5% by mass or more and 20% by mass or less in terms of solid content relative to the layered inorganic material sheet. When the resin content of the layered inorganic material sheet is within the above range, voids are generated both within the layered inorganic material paper and between the layered inorganic material papers during thermal runaway of the battery pack.

[0016] The layered inorganic paper preferably has a thickness of 0.05 mm or more and 0.2 mm or less, because when the thickness of the layered inorganic paper is in this range, it is easy to achieve both thinness and heat insulation properties for the battery pack insulating material of the present invention.

[0017] The layered inorganic material sheet preferably has a thickness of 0.2 mm or more and 2.0 mm or less, because when the thickness of the layered inorganic material sheet is in this range, it is easy to achieve both thinness and heat insulation properties for the insulating material for a battery pack of the present invention.

[0018] The battery pack insulating material of the present invention preferably further comprises a heat insulating sheet laminated on the layered inorganic material sheet. When the battery pack insulating material of the present invention further comprises a heat insulating sheet, the insufficient heat insulating effect of the layered inorganic material sheet in the early stage of thermal runaway of the battery cells can be compensated for, and heat propagation within the battery pack, such as heat propagation between battery cells and heat release to the outside of the battery pack, can be prevented over a wide temperature range from the temperature range in the early stage of thermal runaway to the high temperature range.

[0019] The heat insulating sheet preferably has a thickness of 0.5 mm to 5.0 mm. When the thickness of the heat insulating sheet is within this range, it is easy to achieve both thinness and heat insulating properties for the battery pack heat insulating material of the present invention.

[0020] The heat insulating sheet preferably contains at least one selected from the group consisting of inorganic fibers, organic fibers, inorganic particles, and organic particles, because the heat insulating sheet contains inorganic fibers, organic fibers, inorganic particles, and / or organic particles, thereby providing the battery pack insulating material of the present invention with better fire resistance and heat insulating properties.

[0021] The heat insulating sheet may be made of any of silica nanoparticles, titania, alumina fiber, carbon fiber, mica, basalt fiber, soluble fiber, refractory ceramic fiber, glass fiber, aerogel composite material, microporous particles, hollow silica particles, thermally expandable inorganic material, aerogel, silica, zirconia, zircon, barium titanate, zinc oxide, alumina, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, zinc hydroxide, iron hydroxide, manganese hydroxide, zirconium hydroxide, gallium hydroxide, cellulose fiber, SiO ２ It is preferable that the fiber contains at least one selected from the group consisting of fibers containing the above-mentioned compound, silica fibers, mullite fibers, alumina fibers, alumina silicate fibers, ceramic fibers, rock wool, alkaline earth silicate fibers, zirconia fibers, and mineral fibers.

[0022] In the battery pack insulating material of the present invention, the layered inorganic material sheet and the heat insulating sheet are preferably bonded together with an organic adhesive. By bonding the layered inorganic material sheet and the heat insulating sheet together with an organic adhesive, when the battery pack experiences thermal runaway, gas is generated between the layered inorganic material sheet and the heat insulating sheet, creating voids between the layered inorganic material sheet and the heat insulating sheet, thereby improving the heat insulating performance.

[0023] The battery pack of the present invention includes the insulating material for a battery pack of the present invention. By including the insulating material for a battery pack of the present invention, the battery pack of the present invention has excellent fire resistance and insulating properties.

[0024] According to the present invention, it is possible to provide a battery pack including a battery pack insulating material that is thin and has excellent insulating properties.

[0025] FIG. 1 is a schematic cross-sectional view showing an example of a battery pack insulating material of the present invention. FIG. 2 is an enlarged photograph showing an example of an initial state of a battery pack insulating material of the present invention and a state after heating. FIG. 3A is a perspective view showing a schematic view of an example of a battery pack of the present invention. FIG. 3B is a cross-sectional view taken along line A-A in FIG. 3A. FIG. 3C is an exploded view of the battery pack shown in FIG. 3A. FIG. 4 is a schematic cross-sectional view showing a heated surface and an unheated surface in a simulation of thermal insulation properties. FIG. 5 is a graph showing the temperature difference between the heated surface and the unheated surface at different thicknesses of the insulating material before heating for Comparative Example 1 and Examples 1 to 4.

[0026] (Insulating material for battery pack) Hereinafter, the insulating material for battery pack and the battery pack according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments described below, and can be implemented with any modifications within the scope of the gist of the present invention.

[0027] FIG. 1 is a schematic cross-sectional view showing an example of a battery pack insulating material of the present invention. The battery pack insulating material 40 shown in FIG. 1 has a layered inorganic material sheet 42 and a heat insulating sheet 41 laminated thereon. The layered inorganic material sheet 42 is laminated with multiple layered inorganic material papers 43. In the battery pack insulating material 40 shown in FIG. 1, three layers of layered inorganic material papers 43 are laminated. The layered inorganic material papers 43 are impregnated with resin 44. The number of layers of layered inorganic material papers 43 is not particularly limited, but is preferably in the range of 2 to 20 sheets. More preferably, it is 3 to 10 sheets. The battery pack insulating material 40 may have a layered inorganic material sheet 42 laminated on the heat insulating sheet 41. That is, the heat insulating sheet 41 may be sandwiched between two layered inorganic material sheets 42 in the thickness direction. The battery pack insulating material of the present invention does not necessarily have to include a heat insulating sheet.

[0028] (Layered Inorganic Sheet) The layered inorganic sheet is formed by laminating a plurality of layered inorganic papers, each of which is impregnated with a resin.

[0029] (Layered Inorganic Paper) The layered inorganic paper contains pulverized and peeled layered inorganic materials.

[0030] The layered inorganic paper preferably has excellent fire resistance and insulating properties, and preferably contains at least one silicate mineral selected from the group consisting of vermiculite, montmorillonite, beidellite, nontronite, saponite, hectorite, stevensite, and mica. The layered inorganic paper more preferably contains mica. Mica has excellent insulating properties and fire resistance, so it is suitable for use as an insulating material for battery packs. As the mica, muscovite and phlogopite are particularly preferred.

[0031] (Thickness of Layered Inorganic Paper) The thickness of the layered inorganic paper is preferably in the range of 0.05 mm to 0.2 mm, and more preferably in the range of 0.08 mm to 0.1 mm. If the thickness of the layered inorganic paper is less than 0.05 mm, the layered inorganic paper may be easily torn and difficult to handle. On the other hand, if the thickness of the layered inorganic paper is more than 0.2 mm, voids may not easily form when heated.

[0032] (Method for manufacturing layered inorganic paper) The layered inorganic paper according to the present invention is manufactured, for example, by the following method. First, 1 to 50 parts by weight of layered inorganic material pulverized and peeled into flakes having a diameter of 50 μm to 1000 μm is added to 1000 parts by weight of water in a tank filled with water, and the mixture is stirred for 30 seconds or more to produce a slurry in which the layered inorganic material is uniformly dispersed in the water. The slurry is then poured into a desired mold and subjected to dehydration molding and drying with hot air or a hot plate to produce the layered inorganic paper.

[0033] (Resin) The resin used in the present invention contains a group that generates gas when heated to 150° C. or higher, and since the resin releases gas when heated, it has the property of reducing its mass after heating. Heating due to thermal runaway or the like in the battery pack generates gas from the resin present between the layers of inorganic paper and within the layered inorganic paper, creating voids between the layers of inorganic paper and within the layered inorganic paper, which provides excellent heat insulation to the layered inorganic sheet and the insulating material for battery packs.

[0034] The mass loss of the resin after heating at 500°C for 1 hour is preferably 1.0% by mass or more and 20.0% by mass or less. If the mass loss of the resin is less than 1.0% by mass, the layered inorganic sheet may not expand sufficiently. If the mass loss of the resin is large, the amount of gas generated by heating increases, and as a result, the size and number of voids generated between and within the layered inorganic paper increase, providing the layered inorganic sheet with a better heat insulating effect. However, if the mass loss of the resin exceeds 20.0% by mass, the increased amount of gas generated by heating may cause the layered inorganic paper to expand excessively, potentially resulting in tearing. The mass loss of the resin is more preferably 1.5% by mass or more and 12.0% by mass or less, and even more preferably 1.5% by mass or more and 7.0% by mass or less. The amount of reduction in the mass of the resin can be determined by heating the layered inorganic material sheet at 500°C for 1 hour, subtracting the mass of the layered inorganic material sheet after heating from the mass of the layered inorganic material sheet before heating, and dividing the calculated value by the value calculated by subtracting the mass of the layered inorganic material sheet before resin impregnation from the mass of the layered inorganic material sheet before heating.

[0035] Examples of resins that can be used include epoxy resins, silicone resins, acrylic resins, fluororesins, polypropylene resins (PP), polyurethane resins (PU), polyethylene resins (PE), polyethylene terephthalate resins (PET), polyamide resins (PA), and polybutylene terephthalate resins (PBT). The resin is preferably at least one selected from the group consisting of epoxy resins, silicone resins, acrylic resins, and fluororesins. Silicone resins and / or fluororesins are more preferred.

[0036] Examples of the group that generates a gas when heated include an alkyl group having 1 to 10 carbon atoms, such as a methyl group or an ethyl group, a hydroxyl group, an aldehyde group, etc. The resin used in the present invention may be any resin having the above-mentioned group that generates a gas when heated.

[0037] The greater the amount of gas generated from the resin upon heating, the greater the size and number of voids, providing the layered inorganic sheet with excellent heat insulating properties. Therefore, the resin content of the layered inorganic sheet is preferably 5% by mass or more and 20% by mass or less in solids content relative to the layered inorganic sheet. If the resin content of the layered inorganic sheet is less than 5% by mass, voids are less likely to form between the layers of the layered inorganic paper upon heating. If the resin content of the layered inorganic sheet is more than 20% by mass, the increased amount of gas generated upon heating may cause the layered inorganic paper to expand excessively, potentially resulting in tearing. The resin content of the layered inorganic sheet is preferably 7% by mass or more and 12% by mass or less in solids content relative to the layered inorganic sheet.

[0038] The resin content of the layered inorganic material sheet can be calculated by subtracting the mass of the layered inorganic material sheet before being impregnated with the resin from the mass of the layered inorganic material sheet of the present invention.

[0039] (Thickness of Layered Inorganic Sheet) The thickness of the layered inorganic sheet is preferably 0.2 mm or more and 2.0 mm or less, more preferably 0.2 mm or more and 1.0 mm or less, even more preferably 0.3 mm or more and 1.0 mm or less, and particularly preferably 0.3 mm or more and 0.5 mm or less. If the thickness of the layered inorganic sheet is less than 0.2 mm, the strength of the layered inorganic sheet is low and it becomes easily broken. If the thickness of the layered inorganic sheet exceeds 2.0 mm, the layered inorganic sheet becomes too thick, making it difficult to miniaturize the entire battery pack.

[0040] (Method for manufacturing layered inorganic sheet) The layered inorganic sheet is manufactured by impregnating layered inorganic paper with resin, stacking the resin-impregnated layered inorganic paper, and placing the stacked sheets in a mold of the desired shape and performing heat pressing.

[0041] The conditions for the hot pressing are not particularly limited, but examples include pressing for 5 minutes or more and 60 minutes or less, at 1 MPa or more and 15 MPa or less, and at 100 to 300°C.

[0042] The insulating material for a battery pack of the present invention is thin in the temperature range in which a battery pack is normally used, but when heated due to thermal runaway or the like in the battery pack, the resin between the layers of the layered inorganic paper and within the layers of the layered inorganic paper generates gas, creating voids between the layers of the layered inorganic paper and within the layers of the layered inorganic paper, causing the layered inorganic sheet to expand. The layered inorganic sheet expands when heated to 500°C, and for example, when exposed to gas at 500°C.

[0043] 2 is an enlarged photograph showing an example of the initial state and the state after heating of the insulating material for a battery pack of the present invention. The initial state of the insulating material for a battery pack of the present invention is the state before heating. In the photograph of the initial state, thick resin is observed inside the layered inorganic paper and between the layers of the layered inorganic paper. In the photograph after heating at 800°C for 50 hours, voids are observed inside the layered inorganic paper and between the layers of the layered inorganic paper.

[0044] (Thermal Insulation Sheet) The battery pack insulating material of the present invention preferably further comprises a thermal insulation sheet laminated on the layered inorganic material sheet. The thermal insulation sheet is not limited in terms of the combination and composition ratio of materials constituting the thermal insulation sheet, as long as the thermal conductivity of the thermal insulation sheet is less than 1 (W / m·K). The thermal conductivity can be measured in accordance with JIS R 2251, "Test Method for Thermal Conductivity of Refractories." The thermal insulation sheet preferably contains at least one material selected from the group consisting of inorganic fibers, organic fibers, inorganic particles, and organic particles.

[0045] (Types of inorganic fibers) Inorganic fibers have excellent heat resistance and include alumina fiber, carbon fiber, basalt fiber, soluble fiber, refractory ceramic fiber, glass fiber, glass wool, slag wool, and SiO ２ At least one selected from fibers containing the above, silica fibers, mullite fibers, alumina silicate fibers, ceramic fibers, rock wool, alkaline earth silicate fibers, zirconia fibers, silicon carbide fibers, magnesium silicate fibers, potassium titanate fibers, aerogel composite materials, and mineral fibers can be used.

[0046] (Average fiber diameter of inorganic fibers) The average fiber diameter of the inorganic fibers is preferably 1 μm or more and 20 μm or less, and more preferably 3 μm or more and 15 μm or less. Within this range, the heat insulating sheet can be produced without impairing the formability and processability of the heat insulating sheet.

[0047] (Average fiber length of inorganic fibers) The average fiber length of the inorganic fibers is preferably 0.1 mm or more and 100 mm or less. Within this range, problems of moldability and processability that are caused by an average fiber length that is too long and problems of mechanical strength that are caused by an average fiber length that is too short are less likely to occur.

[0048] In addition to the inorganic fibers (hereinafter referred to as "first inorganic fibers"), inorganic fibers (hereinafter referred to as "second inorganic fibers") having an average fiber diameter smaller than that of the first inorganic fibers may be used. By using two inorganic fibers with different fiber diameters, the flexibility of the heat insulating sheet and the retention of the inorganic particles and organic particles to be combined can be improved.

[0049] The average fiber diameter of the second inorganic fibers is preferably 1 nm or more and less than 1 μm, and more preferably 10 nm or more and 0.1 μm or less. Within this range, the second inorganic fibers can have flexibility while maintaining mechanical strength.

[0050] The average fiber length of the second inorganic fibers is preferably less than 1 μm so as not to impair moldability.

[0051] (Types of Organic Fibers) The organic fibers may be at least one selected from polyethylene terephthalate fibers, polybutylene terephthalate fibers, polytrimethylene terephthalate fibers, polyacetal fibers, polytetrafluoroethylene fibers, polyether ether ketone fibers, polyphenylene sulfide fibers, polyamide fibers, polyparaphenylphthalamide fibers, polyvinyl alcohol fibers, polyethylene fibers, nylon fibers, polyurethane fibers, polypropylene fibers, and ethylene-vinyl alcohol copolymer fibers.

[0052] (Average fiber length of organic fibers) The average fiber length of the organic fibers according to the present invention is not particularly limited, but is preferably 0.5 mm or more and 10 mm or less. Within this range, sufficient compressive strength can be obtained without impairing the formability and shape retention of the heat insulating sheet.

[0053] (Types of inorganic particles) The inorganic particles can be materials having an average secondary particle diameter in the range of 0.01 μm to 200 μm, and can be, for example, at least one selected from oxide particles, nanoparticles, inorganic hydrate particles, particles made of thermally expandable inorganic materials, and particles made of hydrous porous bodies. If the average secondary particle diameter is within the above range, the material can be easily obtained and the desired heat insulating effect can be obtained. Furthermore, the average secondary particle diameter of the inorganic particles is preferably 0.05 μm to 100 μm.

[0054] Two or more types of inorganic particles having different average secondary particle diameters may be used in combination. Different sizes of inorganic particles have different heat transfer suppression effects, making it possible to cool the heat transferred from the battery cell in multiple stages and to exert a heat absorption effect over a wide temperature range.

[0055] (Oxide particles) The oxide particles may be at least one type of particles selected from silica, titania, zirconia, zircon, barium titanate, zinc oxide, and alumina. The oxide particles have a high refractive index, and therefore can prevent radiant heat generated by thermal runaway in a battery cell from propagating to adjacent cells or outside the battery pack.

[0056] The average primary particle size of the oxide particles used in the present invention is preferably in the range of 1 μm to 50 μm in order to maximize the radiant heat blocking effect. The average primary particle size in the present invention is determined by measuring the particle sizes of 10 random particles using a microscope by comparing them with a standard scale and averaging the particle sizes of the measured 10 particles.

[0057] (Nanoparticles) Nanoparticles refer to inorganic particles with an average primary particle size of less than 1 μm. Nanoparticles have extremely low conductive heat transfer and excellent thermal insulation properties.

[0058] For example, if oxide particles are used as nanoparticles, even if the internal density increases due to the compression of the insulating sheet caused by expansion associated with thermal runaway of the battery cell, the electrostatic repulsion force of the nanoparticles tends to create small gaps between the particles, and the particles are packed together to provide cushioning, thereby suppressing an increase in conductive heat transfer.

[0059] Silica nanoparticles have high thermal insulation properties and are characterized by small contact points between particles, which reduces the amount of heat transfer between particles. Therefore, using silica nanoparticles as nanoparticles can further improve the thermal insulation properties of insulation sheets. Wet silica, dry silica, aerogel, etc. can be used as silica nanoparticles.

[0060] The average primary particle diameter of the nanoparticles is preferably 1 nm or more and 100 nm or less. Within the aforementioned range, convective heat transfer and conductive heat transfer in the battery pack insulation material can be suppressed in the temperature range during thermal runaway of the battery cell. Furthermore, even when compressive stress is applied to the insulation sheet due to expansion of the battery pack, the voids between the nanoparticles and the contact points between many particles suppress heat transfer in the insulation sheet, thereby maintaining the insulating properties of the insulation material. The average primary particle diameter of the nanoparticles is more preferably 2 nm or more, and even more preferably 3 nm or more. Meanwhile, the average primary particle diameter of the nanoparticles is preferably 50 nm or less, and even more preferably 10 nm or less.

[0061] (Inorganic hydrate particles) Examples of inorganic hydrate particles include particles of aluminum hydroxide, magnesium hydroxide, calcium hydroxide, zinc hydroxide, iron hydroxide, manganese hydroxide, zirconium hydroxide, gallium hydroxide, etc. The inorganic hydrate particles described above begin to thermally decompose in a thermal runaway environment of the battery cell, releasing water of crystallization, thereby releasing heat from the heating element, thereby suppressing a sudden temperature rise inside the battery pack.

[0062] (Particles Made of Thermally Expandable Inorganic Material) Examples of particles made of thermally expandable inorganic material include particles of vermiculite, bentonite, perlite, and the like.

[0063] (Particles Made of Hydrous Porous Material) Examples of particles made of hydrous porous material include particles of zeolite, montmorillonite, acid clay, diatomaceous earth, wet silica, dry silica, aerogel, mica, and vermiculite.

[0064] In addition to the inorganic fibers, organic fibers, inorganic particles, and organic particles, a resin binder may be added to the heat insulating sheet. Adding a resin binder to the heat insulating sheet improves the mechanical strength of the heat insulating sheet, allowing the heat insulating sheet to maintain its shape even when pressure is applied due to the expansion of the battery cells during thermal runaway, thereby preventing a decrease in heat insulating performance. Examples of resin binders that can be used include styrene-butadiene resin, acrylic resin, silicone-acrylic resin, and styrene resin.

[0065] (Thickness of the Heat Insulating Sheet) The thickness of the heat insulating sheet is not particularly limited, but is preferably in the range of 0.5 mm to 5.0 mm, and more preferably in the range of 0.8 mm to 3.0 mm. If the thickness of the heat insulating sheet is within the above range, the heat insulating material for a battery pack of the present invention can obtain sufficient mechanical strength. If the thickness of the heat insulating sheet is less than 0.5 mm, sufficient heat insulating performance cannot be obtained. On the other hand, if the thickness of the heat insulating sheet is more than 5.0 mm, the heat insulating material for a battery pack of the present invention becomes too thick and occupies a large amount of space within the battery pack.

[0066] (Method for manufacturing the heat insulating sheet) The manufacturing method for the heat insulating sheet is not particularly limited, and the heat insulating sheet can be manufactured by a wet molding method, a dry molding method, an extrusion molding method, etc. Furthermore, after manufacturing the heat insulating sheet by the above-mentioned manufacturing method, needling may be performed to adjust the shape of the heat insulating sheet.

[0067] (Organic adhesive) In the battery pack insulating material of the present invention, the layered inorganic material sheet and the insulating sheet are preferably bonded together with an organic adhesive. The organic adhesive used is an adhesive containing a material that generates gas when heated by thermal runaway of the battery pack. If the adhesive contains such a material, gas will be generated between the layered inorganic material sheet and the insulating sheet when the battery pack goes into a thermal runaway state, creating a gap between the layered inorganic material sheet and the insulating sheet, improving the insulating performance.

[0068] The material that generates gas when heated due to thermal runaway of the battery pack is, for example, an organic material having a hydroxy group or an aldehyde group, and more specifically, a polyamide-based organic material, a nylon-based organic material, etc. If the organic adhesive contains a polyamide-based organic material or a nylon-based organic material, thermal decomposition occurs due to heating caused by thermal runaway of the battery pack, and water vapor and carbon dioxide are easily released from the adhesive due to the hydroxy group or aldehyde group, which makes it easy for voids to form between the layered inorganic material sheet and the heat insulating sheet, and therefore the organic adhesive is preferably used.

[0069] (Battery Pack) The battery pack of the present invention includes the insulating material for a battery pack of the present invention. A specific example of the battery pack of the present invention, in which the insulating material for a battery pack includes a layered inorganic material sheet and a heat insulating sheet, will be described with reference to Figures 3A, 3B, and 3C.

[0070] FIG. 3A is a perspective view schematically illustrating an example of a battery pack according to the first embodiment of the present invention. FIG. 3B is a cross-sectional view taken along line A-A in FIG. 3A. FIG. 3C is an exploded view of the battery pack shown in FIG. 3A. The battery pack 10 shown in FIGS. 3A, 3B, and 3C includes a module 20 having a plurality of battery cells 21 and a case 30 that houses the module 20. As shown in FIG. 3B, in the battery pack 10, each battery cell 21 is provided with a safety valve 22. As shown in FIG. 3B, the case 30 includes a housing portion 31 formed of a bottom portion 31b and a side wall 31s, and a lid portion 32 that covers the housing portion 31. The module 20 is housed in the housing portion 31. In the battery pack 10, a battery pack insulating material 40 is provided between the module 20 and the case 30. As shown in FIG. 3B, the battery pack insulating material 40 includes a layered inorganic material sheet 42 and an insulating sheet 41 laminated thereon. In FIG. 3B, the insulating sheet 41 is provided so as to contact the module 20. The battery pack heat insulating material 40 may be provided so that the layered inorganic material sheet 42 is in contact with the module 20. The battery pack heat insulating material 40 may be provided so that it is in contact with the case 30.

[0071] The battery cells 21 store power and are preferably, for example, rechargeable so-called secondary batteries. Examples of secondary batteries include lithium ion batteries, nickel-metal hydride batteries, and sodium ion batteries. The battery cells 21 shown in Figures 3B and 3C are rectangular parallelepiped. Note that in the battery pack of the present invention, the battery cells may have a three-dimensional shape other than a rectangular parallelepiped shape (for example, a cube or a modified shape).

[0072] 3B and 3C, in the module 20, a plurality of battery cells 21 are arranged in a row and fixed by a connecting module member 20a. Also, as shown in Fig. 3C, the battery cells 21 have terminals 23, and adjacent battery cells 21 are electrically connected by connecting each terminal 23 to a bus bar 20b arranged on the connecting module member 20a.

[0073] The bus bar 20b is a flat, electrically conductive metal member. Examples of materials for the bus bar 20b include copper, copper alloy, stainless steel (SUS), and aluminum. The bus bar 20b may be fixed to the terminal 23 by any fixing means (e.g., screwing, welding, etc.).

[0074] Examples of materials that can be used to form the case 30 include steel and aluminum. As the steel, stainless steel (SUS) is preferred.

[0075] The present specification discloses the following:

[0076] [1] An insulating material for a battery pack, comprising a layered inorganic sheet formed by laminating a plurality of layered inorganic papers, wherein the layered inorganic paper is impregnated with a resin, and the layered inorganic sheet expands upon heating at 500°C so as to create voids within the layered inorganic sheet.

[0077] [2] The insulating material for a battery pack according to [1], wherein the layered inorganic paper contains at least one silicate mineral selected from the group consisting of vermiculite, montmorillonite, beidellite, nontronite, saponite, hectorite, stevensite, and mica.

[0078] [3] The insulating material for a battery pack according to [1] or [2], wherein the layered inorganic paper contains mica.

[0079] [4] The insulating material for a battery pack according to any one of [1] to [3], wherein the resin is at least one selected from the group consisting of epoxy resin, silicone resin, acrylic resin, and fluororesin.

[0080] [5] The insulating material for a battery pack according to any one of [1] to [4], wherein the resin has a group that generates gas when heated, and the amount of mass reduction of the resin after heating at 500°C for 1 hour is 1.0 mass% or more and 20.0 mass% or less.

[0081] [6] The insulating material for a battery pack according to any one of [1] to [5], wherein the content of the resin in the layered inorganic material sheet is 5% by mass or more and 20% by mass or less in terms of solid content relative to the layered inorganic material sheet.

[0082] [7] The insulating material for a battery pack according to any one of [1] to [6], wherein the layered inorganic paper has a thickness of 0.05 mm or more and 0.2 mm or less.

[0083] [8] The insulating material for a battery pack according to any one of [1] to [7], wherein the layered inorganic material sheet has a thickness of 0.2 mm or more and 2.0 mm or less.

[0084] [9] The insulating material for a battery pack according to any one of [1] to [8], further comprising an insulating sheet laminated on the layered inorganic material sheet.

[0085]

[10] The insulating material for a battery pack according to [9], wherein the insulating sheet has a thickness of 0.5 mm or more and 5.0 mm or less.

[0086]

[11] The insulating material for a battery pack according to [9] or

[10] , wherein the insulating sheet contains at least one selected from the group consisting of inorganic fibers, organic fibers, inorganic particles, and organic particles.

[0087]

[12] The heat insulating sheet may be formed of silica nanoparticles, titania, alumina fiber, carbon fiber, mica, basalt fiber, soluble fiber, refractory ceramic fiber, glass fiber, aerogel composite material, microporous particles, hollow silica particles, thermally expandable inorganic material, aerogel, silica, zirconia, zircon, barium titanate, zinc oxide, alumina, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, zinc hydroxide, iron hydroxide, manganese hydroxide, zirconium hydroxide, gallium hydroxide, cellulose fiber, SiO ２

[12] The insulating material for a battery pack according to any one of [9] to

[11] , which contains at least one selected from the group consisting of fibers containing the above-mentioned compound, silica fibers, mullite fibers, alumina fibers, alumina silicate fibers, ceramic fibers, rock wool, alkaline earth silicate fibers, zirconia fibers, and mineral fibers.

[0088]

[13] The insulating material for a battery pack according to any one of [9] to

[12] , wherein the layered inorganic material sheet and the insulating sheet are bonded together with an organic adhesive.

[0089]

[14] A battery pack comprising the insulating material for a battery pack according to any one of [1] to

[13] .

[0090] Examples that more specifically disclose the insulating material for a battery pack of the present invention will be described below, but the present invention is not limited to these examples.

[0091] In order to confirm the heat insulating properties of the layered inorganic material sheet expanded by heating, the following simulation model was created and a simulation of the heat insulating properties was carried out.

[0092] Comparative Example 1 and Examples 1 to 4 A layered inorganic sheet consisting of one sheet of 1.0 mm thick layered inorganic paper was used as the battery pack insulating material of Comparative Example 1. For the battery pack insulating materials of Examples 1 to 4, the thickness and number of layers of layered inorganic paper forming the layered inorganic sheet were changed as shown in Table 1, and in the heated model, air layers of the thickness and number of layers shown in Table 1 were provided between the layered inorganic paper as voids. A simulation model was prepared in which the heated battery pack insulating material (thickness 1.0 mm) and steel material made of SPCC (thickness 149 mm) were layered in the thickness direction.

[0093] As shown in FIG. 4 , in the simulation model, layered air layers (voids) 45 were arranged between layered inorganic paper sheets 43 to form a layered inorganic material sheet 42, and a steel material SP was placed on the layered inorganic material sheet 42. The temperature of the main surface of the layered inorganic material sheet 42 opposite the main surface on which the steel material SP was laminated (hereinafter also referred to as the heated surface S1) was calculated by simulation when the main surface (hereinafter also referred to as the non-heated surface S2) of the steel material SP opposite the main surface in contact with the layered inorganic material sheet 42 when heated at 1050°C, and the temperature difference (S1-S2) between the heated surface S1 and the non-heated surface S2 was determined. FIG. 4 is a schematic cross-sectional view showing the heated surface and the non-heated surface in the thermal insulation simulation. In Comparative Example 1 and Examples 1 to 4, the battery pack insulation material 40 did not have a thermal insulation sheet 41.

[0094] The layered inorganic material sheets used in the simulation models of Comparative Example 1 and Examples 1 to 4 had a thermal conductivity of 0.2 W / m K at 25°C and a density of 2.0 g / cm ３ A sheet of muscovite with a specific heat of 880 J / kg·K was assumed.

[0095] Ansys Mechanical (manufactured by Ansys) was used as simulation software for heat insulation. The results are shown in Table 1 and FIG.

[0096]

[0097] Fig. 5 is a graph showing the temperature difference between the heated and unheated surfaces of the insulating material before heating for Comparative Example 1 and Examples 1 to 4. As shown in Table 1 and Fig. 5, the thickness of the layered inorganic material sheets before heating was 1.0 mm for each of Comparative Example 1 and Examples 1 to 4, but in Examples 1 to 4, air layers were generated between the layered inorganic material papers upon heating, causing them to expand, resulting in a calculated temperature difference that was greater than the temperature difference between the heated and unheated surfaces of the layered inorganic material sheet of Comparative Example 1, which had no air layer, demonstrating that the insulating effect was increased by the expansion of the layered inorganic material sheet.

[0098] Example 5: Preparation of a Battery Pack Insulating Material. A 0.2 mm thick mica paper was placed in a stainless steel container, and silicone resin (containing hydroxyl and methyl groups that generate gas) was poured in little by little from above, allowing a predetermined amount of silicone resin to penetrate the mica paper. The silicone resin-impregnated mica paper was dried in a hot air dryer at 90°C for 60 minutes. Five dried mica papers were stacked and pressed in a heat press at 200°C for 60 minutes to produce a layered inorganic material sheet, which was used as a battery pack insulating material. The silicone resin content in the layered inorganic material sheet was 11% by mass. Furthermore, the mass loss of the silicone resin after heating at 500°C for 1 hour was 2% by mass.

[0099] REFERENCE SIGNS LIST 10 Battery pack 20 Module 20a Connection module member 20b Bus bar 21 Battery cell 22 Safety valve 23 Terminal 30 Case 31 Storage section 31b Bottom 31s Side wall 32 Lid 40 Battery pack heat insulating material 41 Heat insulating sheet 42 Layered inorganic material sheet 43 Layered inorganic material paper 44 Resin 45 Air layer (gap) SP Steel plate S1 Non-heated surface S2 Heating surface

Claims

1. A thermal insulating material for a battery pack, comprising a layered inorganic sheet formed by laminating multiple layers of layered inorganic paper, wherein the layered inorganic paper is impregnated with a resin, and the layered inorganic sheet expands upon heating to 500°C, creating voids within the layered inorganic sheet.

2. The insulating material for a battery pack according to claim 1, wherein the layered inorganic paper contains at least one silicate mineral selected from the group consisting of vermiculite, montmorillonite, beidellite, nontronite, saponite, hectorite, stevensite, and mica.

3. The insulating material for a battery pack according to claim 1 or 2, wherein the layered inorganic paper contains mica.

4. The insulating material for a battery pack according to any one of claims 1 to 3, wherein the resin is at least one selected from the group consisting of epoxy resin, silicone resin, acrylic resin, and fluororesin.

5. An insulating material for a battery pack according to any one of claims 1 to 4, wherein the resin has a group that generates gas when heated, and the amount of mass loss of the resin after heating at 500°C for 1 hour is 1.0% by mass or more and 20.0% by mass or less.

6. The insulating material for a battery pack according to any one of claims 1 to 5, wherein the resin content of the layered inorganic material sheet is 5% by mass or more and 20% by mass or less in terms of solid content relative to the layered inorganic material sheet.

7. The insulating material for a battery pack according to any one of claims 1 to 6, wherein the layered inorganic paper has a thickness of 0.05 mm or more and 0.2 mm or less.

8. The insulating material for a battery pack according to any one of claims 1 to 7, wherein the layered inorganic material sheet has a thickness of 0.2 mm or more and 2.0 mm or less.

9. The insulating material for a battery pack according to any one of claims 1 to 8, wherein a heat insulating sheet is further laminated on the layered inorganic material sheet.

10. The insulating material for a battery pack according to claim 9, wherein the insulating sheet has a thickness of 0.5 mm or more and 5.0 mm or less.

11. The insulating material for a battery pack according to claim 9 or 10, wherein the insulating sheet contains at least one material selected from the group consisting of inorganic fibers, organic fibers, inorganic particles, and organic particles.

12. The heat insulating sheet is made of any of silica nanoparticles, titania, alumina fiber, carbon fiber, mica, basalt fiber, soluble fiber, refractory ceramic fiber, glass fiber, aerogel composite, microporous particles, hollow silica particles, thermally expandable inorganic material, aerogel, silica, zirconia, zircon, barium titanate, zinc oxide, alumina, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, zinc hydroxide, iron hydroxide, manganese hydroxide, zirconium hydroxide, gallium hydroxide, cellulose fiber, SiO ２ 12. The insulating material for a battery pack according to claim 9, comprising at least one fiber selected from the group consisting of fibers containing the above-mentioned compound, silica fibers, mullite fibers, alumina fibers, alumina silicate fibers, ceramic fibers, rock wool, alkaline earth silicate fibers, zirconia fibers, and mineral fibers.

13. The insulating material for a battery pack according to any one of claims 9 to 12, wherein the layered inorganic material sheet and the insulating sheet are bonded together with an organic adhesive.

14. A battery pack equipped with the insulating material for a battery pack according to any one of claims 1 to 13.

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