HEAT INSULATION SHEET FOR BATTERY PACK, AND BATTERY PACK
20220367937 · 2022-11-17
Assignee
Inventors
Cpc classification
F16L59/028
MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
Y02E60/10
GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
H01M10/623
ELECTRICITY
H01M50/204
ELECTRICITY
International classification
F16L59/02
MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
H01M50/204
ELECTRICITY
Abstract
To provide a heat insulation sheet for a battery pack that has a good shape retention property and can maintain an excellent heat insulation property even when vibration or pressure is applied, and a battery pack in which a heat insulation sheet for a battery pack is interposed between battery cells. A heat insulation sheet (10) of the present invention is a heat insulation sheet for a battery pack, the heat insulation sheet being interposed between battery cells in a battery pack in which a plurality of battery cells is connected in series or in parallel. The heat insulation sheet (10) includes: a first heat insulation material (21) containing a silica nanoparticle; and a second heat insulation material (22) containing a plate-shaped particle containing a silica component and having a curved surface.
Claims
1. A heat insulation sheet for a battery pack, the heat insulation sheet being interposed between battery cells in the battery pack in which the battery cells are connected in series or in parallel, the heat insulation sheet comprising: a first heat insulation material containing a silica nanoparticle; and a second heat insulation material containing a plate-shaped particle containing a silica component and having a curved surface.
2. The heat insulation sheet for the battery pack according to claim 1, wherein the second heat insulation material is oriented in a plane direction.
3. The heat insulation sheet for the battery pack according to claim 1, wherein a content of the first heat insulation material is 10 mass % or more and 60 mass % or less with respect to a total mass of the heat insulation sheet for the battery pack.
4-14. (canceled)
15. The heat insulation sheet for the battery pack according to claim 2, wherein a content of the first heat insulation material is 10 mass % or more and 60 mass % or less with respect to a total mass of the heat insulation sheet for the battery pack.
16. The heat insulation sheet for the battery pack according to claim 1, wherein the first heat insulation material has an average particle diameter of 1 nm or more and 100 nm or less.
17. The heat insulation sheet for the battery pack according to claim 2, wherein the first heat insulation material has an average particle diameter of 1 nm or more and 100 nm or less.
18. The heat insulation sheet for the battery pack according to claim 3, wherein the first heat insulation material has an average particle diameter of 1 nm or more and 100 nm or less.
19. The heat insulation sheet for the battery pack according to claim 4, wherein the first heat insulation material has an average particle diameter of 1 nm or more and 100 nm or less.
20. The heat insulation sheet for the battery pack according to claim 1, wherein the plate-shaped particle is a fragment of an inorganic balloon.
21. The heat insulation sheet for the battery pack according to claim 20, wherein the inorganic balloon is at least one kind of an inorganic balloon selected from a shirasu balloon, a silica balloon, a fly ash balloon, a perlite balloon, and a glass balloon.
22. The heat insulation sheet for the battery pack according to claim 1, wherein the second heat insulation material is the plate-shaped particle having an average particle length of 0.1 μm or more and 100 μm or less.
23. The heat insulation sheet for the battery pack according to claim 1, wherein a content of the second heat insulation material is 10 mass % or more and 60 mass % or less with respect to the total mass of the heat insulation sheet for the battery pack.
24. The heat insulation sheet for the battery pack according to claim 1, further comprising: a third heat insulation material containing a metal oxide.
25. The heat insulation sheet for the battery pack according to claim 24, wherein the metal oxide is at least one kind of a particle selected from titania, zirconia, zircon, barium titanate, zinc oxide, and alumina.
26. The heat insulation sheet for the battery pack according to claim 24, wherein the metal oxide has an average particle diameter of 0.1 μm or more and 50 μm or less.
27. The heat insulation sheet for the battery pack according to claim 24, wherein a content of the third heat insulation material is 5 mass % or more and 40 mass % or less with respect to a total mass of the heat insulation sheet for the battery pack.
28. The heat insulation sheet for the battery pack according to claim 1, further comprising: a binding material which contains at least one kind selected from an inorganic fiber, a binder, and a heat resistant resin, wherein a content of the binding material is 10 mass % or more and 60 mass % or less with respect to the total mass of the heat insulation sheet.
29. A battery pack, wherein battery cells are arranged so as to interpose the heat insulation sheet for the battery pack according to claim 1, and the battery cells are connected in series or in parallel.
Description
BRIEF DESCRIPTION OF DRAWINGS
[0042]
[0043]
[0044]
[0045]
[0046]
[0047]
DESCRIPTION OF EMBODIMENTS
[0048] In order to provide a heat insulation sheet for a battery pack (hereinafter also referred to as “heat insulation sheet”) that has a good shape retention property and can maintain an excellent heat insulation property even when pressure is applied, inventors of the present application conducted diligent studies. As a result, it is found that the excellent shape retention property and heat insulation property of the heat insulation sheet can be obtained by containing a first heat insulation material containing a silica nanoparticle, and a second heat insulation material containing a plate-shaped particle containing a silica component and having a curved surface, in the heat insulation sheet.
[0049] Since the silica nanoparticle contained as the first heat insulation material in the heat insulation sheet is a fine particle and has a large number of contacts, so that the first heat insulation material is a component having an excellent heat insulation property that reduces conductive heat transfer in a wide temperature range.
[0050] The inventors of the present application find that when silica nanoparticles having a small average particle diameter are used for the heat insulation sheet, even if the heat insulation sheet is compressed due to swelling of batteries and a density thereof increases, increase in conductive heat transfer of the heat insulation sheet can also be prevented.
[0051] It is considered that this is because the silica nanoparticles are insulators, fine voids are likely to be formed between the particles by repulsive force due to static electricity, and the particles are filled so as to have a low bulk density and a cushioning property. That is, when the heat insulation sheet contains silica nanoparticles having an average particle diameter of 1 nm or more and 100 nm or less, even when compressive stress is applied, the voids between the silica nanoparticles and the large number of contacts between the particles reduce conductive heat transfer, and the heat insulation property of the heat insulation sheet can be maintained.
[0052] Furthermore, the inventors of the present application find that a size of the voids contained in the heat insulation sheet affects the heat insulation property of the heat insulation sheet. That is, if the voids formed between the particles are, for example, several hundred nm or more, convection and air flow are likely to occur in the voids, and the heat insulation property of the heat insulation sheet may be decreased.
[0053] However, in the heat insulation sheet using the silica nanoparticles having a small particle diameter as the first heat insulation material, it is considered that the voids between the particles become as small as several tens of nm, the air flow in the voids is unlikely to occur, generation of convective heat transfer can be prevented, and the heat insulation property can be further improved.
[0054] In the present invention, since it is important to form a large number of fine voids and increase the number of contacts between the particles by the silica nanoparticles, the silica nanoparticles may be contained as primary particles or aggregated secondary particles.
[0055] A heat insulation sheet using a heat insulation material containing only the first heat insulation material (the silica nanoparticle) may not have a sufficient shape retention property as a sheet since the contacts between the particles are weak. However, in the present invention, since the heat insulation sheet contains the second heat insulation material containing the plate-shaped particle having a curved surface, the excellent shape retention property of the heat insulation sheet can be obtained.
[0056] In the present invention, since the plate-shaped particle having a curved surface is used as the second heat insulation material, even when the plurality of the plate-shaped particles are overlapped with each other, the plate-shaped particles are dispersed in the heat insulation sheet in point contact or close to each other while forming appropriate dome-shaped voids. Therefore, the plate-shaped particles have an effect of retaining the silica nanoparticles in the dome-shaped voids and retaining the shape of the entire heat insulation sheet so as not to fall due to vibration or the like.
[0057] Furthermore, since the voids are filled with the silica nanoparticles, the air flow can be blocked, the convective heat transfer can be reduced, and the excellent heat insulation property can be obtained.
[0058] If the second heat insulation material is simply a flat plate-shaped particle, since the particles adhere to each other in the heat insulation sheet, the heat transmission facilitate. Since it is difficult to form the voids to retain the silica nanoparticles, the shape retention property is reduced, and the silica nanoparticles are likely to fall due to vibration or the like. In the heat insulation sheet of the present invention, since the second heat insulation material has a curved surface, the shape is maintained and the heat insulation property can be obtained.
[0059] Moreover, in the present invention, even if battery cells thermally expand and a pressure is applied to the heat insulation sheet, since the second heat insulation material having the dome-shaped voids filled with the first heat insulation material (the silica nanoparticle) resists the pressure while bending, it is possible to prevent the first heat insulation material (the silica nanoparticle) that maintains a heat insulation effect from falling.
[0060] The second heat insulation material contain a silica component. Silicon constituting silica is tetravalent, and it is considered that it can be combined with divalent oxygen to form an irregular network structure. Therefore, when silica is melted, it becomes a viscous fluid, and inorganic hollow particles (inorganic balloons) can be easily obtained by a method such as a medium fluidized bed. Using the inorganic hollow particles as a raw material, curved plate-shaped particles containing a silica component can be easily obtained.
[0061] <Basic Configuration of Heat Insulation Sheet for Battery Pack>
[0062]
[0063] As shown in
[0064] As a specific usage of the heat insulation sheet 10 for battery pack, as shown in
[0065] In the following description, it is assumed that a heat-generating battery cell 20 exists on one surface 10a side of the heat insulation sheet 10. In the heat insulation sheet configured in this way, when the battery cell 20 generates heat, a part of the incident heat from a side of the surface 10a of the heat insulation sheet 10 is conducted (solid conduction) toward the other surface 10b of the heat insulation sheet 10 as shown by an arrow 15a by mediating the first heat insulation material 21 which is in contact with each other or is adjacent to each other via a binder or the like. In this case, since the silica nanoparticle having a heat insulation property is used as the first heat insulation material 21 and contact points between the particles are small, an amount of heat conducted by the silica nanoparticles is smaller than that when a silica particle having a large particle diameter is used. Therefore, the amount of heat transmitted is reduced as approaching the other surface 10b of the heat insulation sheet 10.
[0066] As shown by an arrow 15c, a part of the heat generated by the heat generation of the battery cell 20 may be conducted through the first heat insulation material 21 and the second heat insulation material 22. In the present embodiment, the fragment of the inorganic balloon containing a silica component is used as the second heat insulation material 22, a strength in a plane direction is strengthened, a shape retention property is enhanced, and the same heat insulation property as that of the first heat insulation material 21 is obtained, so that it is difficult to transmit heat in a thickness direction. Therefore, the amount of heat transmitted is reduced as approaching the other surface 10b of the heat insulation sheet 10. Since the second heat insulation material 22 contains the plate-shaped particle having a curved surface, even if the second heat insulation material 22 overlaps each other, an appropriate void portion is formed, and the first heat insulation material having the excellent heat insulation property can be retained in the void portion, and the conduction of heat can be prevented.
[0067] Moreover, in the present embodiment, when the battery cells 20 arranged at both sides of the heat insulation sheet 10 thermally expand and a large compressive stress is applied to the heat insulation sheet 10, the second heat insulation material having the dome-shaped voids filled with the first heat insulation material (the silica nanoparticle) resists the stress while bending, and at the same time, it is difficult to apply a large force to the first heat insulation material having an excellent heat insulation effect. Therefore, it is possible to prevent the silica nanoparticles from falling.
[0068] Accordingly, according to the present invention, even if a thermal runaway occurs in a certain battery cell 20, since heat transmission to other adjacent battery cells 20 can be effectively prevented, it is possible to prevent the thermal runaway of the other battery cells 20 from being caused.
[0069]
[0070] In the second embodiment configured in this way, titania is used as the third heat insulation material 23 containing a metal oxide. The metal oxide is a component having a high refractive index and diffusely reflecting light. When the battery cell 20 generates heat and a part of the heat reaches the third heat insulation material 23 by radiation from one surface 40a side of the heat insulation sheet 40, the heat is reflected by the third heat insulation material 23 (titania) as shown by an arrow 15d. Therefore, due to presence of titania, even in a high temperature range of 500° C. or higher, where influence of radiation is particularly large, it is possible to prevent heat from being transmitted to the other surface 40b of the heat insulation sheet 10.
[0071] <Details of Heat Insulation Sheet for Battery Pack>
[0072] Next, the first heat insulation material 21 and the second heat insulation material 22 constituting the heat insulation sheet 10 for battery pack will be described in detail.
[0073] (Kind of First Heat Insulation Material)
[0074] In the present invention, the silica nanoparticle is used as the first heat insulation material 21. As the silica nanoparticle, wet silica, fumed silica, aerogel, and the like can be used.
[0075] In the present invention, the silica nanoparticle is a nanometer-order silica particle having an average particle diameter of less than 1 μm, which is spherical or close to spherical.
[0076] (Average Particle Diameter of First Heat Insulation Material: 1 nm or More and 100 nm or Less)
[0077] As described above, the particle diameter of the first heat insulation material 21 may affect the heat insulation property of the heat insulation sheet 10. Therefore, when the average particle diameter of the first heat insulation material 21 is limited to a predetermined range, a higher heat insulation property can be obtained. That is, when the average particle diameter of the first heat insulation material 21 is 1 nm or more and 100 nm or less, especially in a temperature range below 500° C., convective heat transfer and conductive heat transmission of the heat in the heat insulation sheet 10 can be reduced, and the heat insulation property can be further improved.
[0078] The average particle diameter of the first heat insulation material 21 is more preferably 2 nm or more, and still more preferably 3 nm or more. The average particle diameter of the first heat insulation material 21 is more preferably 50 nm or less, and still more preferably 10 nm or less.
[0079] In the present invention, the average particle diameter is obtained by photographing the heat insulation sheet 10 with a microscope, comparing a major axis of any 10 particles with a standard scale, and taking an average value thereof. Any microscope may be used, and an SEM, a polarizing microscope, or the like can be used.
[0080] (Kind of Second Heat Insulation Material)
[0081] In the present invention, as the second heat insulation material 22, the plate-shaped particle containing a silica component and having a curved surface is used. As described above, since the second heat insulation material 22 has such a shape, the strength in the plane direction is strengthened, the shape retention property is enhanced, and it is difficult to transmit heat in the thickness direction. When a large compressive stress is applied to the heat insulation sheet 10, since the second heat insulation material 22 having the dome-shaped voids filled with the first heat insulation material 21 (the silica nanoparticle) resists the compressive stress while bending, it is possible to prevent the first heat insulation material 21 (the silica nanoparticle) having an excellent heat insulation effect from falling. As the second heat insulation material 22, at least one kind of fragment of a balloon selected from a shirasu balloon, a silica balloon, a fly ash balloon, a perlite balloon, and a glass balloon can be used.
[0082] (Orientation of Second Heat Insulation Material)
[0083] As shown in the heat insulation sheet 10 in
[0084] A content of the silica component of the second heat insulation material 22 is not particularly limited, but is preferably, for example, 40 mass % or more with respect to a total mass of the second heat insulation material. Since silica has an irregular network structure, when silica is melted, it becomes a viscous fluid. When a content of the silica component of the second heat insulation material 22 is 40 mass % or more, a curved surface having a good shape can be obtained. The content of the silica component of the second heat insulation material 22 is preferably 90 mass % or less. When the content of the silica component of the second heat insulation material 22 is 90 mass % or less, it can be easily obtained by using a natural mineral as a raw material.
[0085] When the fragment of an inorganic balloon is used as the second heat insulation material 22, the fragment of an inorganic balloon previously crushed to a desired size may be used, or the inorganic balloon may be crushed to a desired size during manufacture of the heat insulation sheet 10. Accordingly, in the present invention, an inexpensive inorganic balloon can be used, and conventional manufacturing equipment can be used without modification. Therefore, the heat insulation sheet 10 having an excellent heat insulation property can be easily manufactured at a low cost.
[0086] (Average Particle Length of Second Heat Insulation Material: 0.1 μm or More and 100 μm or Less)
[0087] When the second heat insulation material 22 has an appropriate size, the above effect of the second heat insulation material 22 can be sufficiently obtained, and voids having an appropriate size are formed. That is, when an average particle length of the second heat insulation material 22 is 0.1 μm or more, the voids are filled with a large amount of the first heat insulation material 21, and when a compressive stress is applied from outside, the curved surface is deformed to counter the stress, the first heat insulation material 21 can be prevented from falling, and so it is preferable.
[0088] When the average particle length of the second heat insulation material 22 is 100 μm or less, a distance that one particle of the second heat insulation material 22 transmits heat can be shortened. Therefore, even if there are particles oriented in the thickness direction, no path for the conduction heat transmission is formed, and it is possible to prevent the heat insulation property from being lowered, and so it is preferable.
[0089] In the present invention, the average particle length is obtained by photographing the heat insulation sheet 10 with a microscope, comparing a major axis of any 10 particles with a standard scale, and taking an average value thereof. Any microscope may be used, and an SEM, a polarizing microscope, or the like can be used.
[0090] A radius of curvature of the second heat insulation material 22 is preferably 0.5 μm to 50 μm. When the inorganic balloon is used as the second heat insulation material 22, it is considered that a radius of the inorganic balloon corresponds to it, and the second heat insulation material 22 having a desired size can be obtained.
[0091] The radius of curvature of the second heat insulation material 22 can be measured by embedding the heat insulation sheet 10 in resin so that a cross section of the heat insulation sheet 10 can be confirmed, identifying a center of the curved surface from an enlarged image of the microscope, and comparing it with a standard scale. A kind of the microscope can be appropriately selected depending on an object, and a polarizing microscope, an SEM, or the like can be used.
[0092] (Content of First Heat Insulation Material: 10 Mass % or More and 60 Mass % or Less with Respect to Total Mass of Heat Insulation Sheet)
[0093] In the present invention, it is preferable to appropriately adjust a ratio of the first heat insulation material 21 so as to secure an appropriate heat insulation property. When the content of the first heat insulation material 21 is 10 mass % or more with respect to the total mass of the heat insulation sheet, since the first heat insulation material 21 is originally a material having a high heat insulation property against conductive heat transfer and convective heat transfer, it is possible to obtain the heat insulation sheet 10 having a high heat insulation property, and so it is preferable. Therefore, the content of the first heat insulation material 21 is preferably 10 mass % or more, more preferably 15 mass % or more, and still more preferably 20 mass % or more, with respect to the total mass of the heat insulation sheet.
[0094] When the content of the first heat insulation material 21 is 60 mass % or less with respect to the total mass of the heat insulation sheet, the silica nanoparticles are supported by other materials, and so it is preferable. Therefore, even if vibration, pressure, deformation, or the like is applied, it is possible to further prevent the silica nanoparticles from falling. Therefore, the content of the first heat insulation material 21 is preferably 60 mass % or less, more preferably 55 mass % or less, and still more preferably 50 mass % or less, with respect to the total mass of the heat insulation sheet.
[0095] (Content of Second Heat Insulation Material: 10 Mass % or More and 60 Mass % or Less with Respect to Total Mass of Heat Insulation Sheet)
[0096] In the present invention, it is preferable to appropriately adjust a ratio of the second heat insulation material 22 so as to secure appropriate heat insulation property and shape retention property. When the content of the second heat insulation material 22 is 10 mass % or more with respect to the total mass of the heat insulation sheet, the plate-shaped particles having a curved surface of the second heat insulation material 22 can wrap the first heat insulation material 21 and even if vibration, stress, or deformation is applied, it is possible to prevent from falling, and so it is preferable. Therefore, the content of the second heat insulation material 22 is preferably 10 mass % or more, more preferably 15 mass % or more, and still more preferably 20 mass % or more, with respect to the total mass of the heat insulation sheet.
[0097] When the content of the second heat insulation material 22 is 60 mass % or less with respect to the total mass of the heat insulation sheet, it is possible to sufficiently secure other heat insulation components retained in the voids, block air flow, and block convective heat transfer, and so it is preferable. Therefore, the content of the second heat insulation material 22 is preferably 60 mass % or less, more preferably 55 mass % or less, and still more preferably 50 mass % or less, with respect to the total mass of the heat insulation sheet.
[0098] In addition to the first heat insulation material 21 and the second heat insulation material 22, the heat insulation sheet 10 for battery pack may contain a third heat insulation material 23 containing a metal oxide as a component that further enhances the heat insulation effect in a high temperature range of 500° C. or higher, and may further contain components necessary for molding into a heat insulation material, such as a binding material and a colorant. Hereinafter, other components will be described in detail.
[0099] (Kind of Third Heat Insulation Material)
[0100] The heat insulation sheet 10 according to the present invention preferably contains the third heat insulation material 23 containing a metal oxide. As the metal oxide, titania, zirconia, zircon, barium titanate, zinc oxide, alumina, or the like can be used. Particularly, titania is a component having a higher refractive index than other metal oxides, and has a high effect of diffusely reflecting light in a high temperature range of 500° C. or higher. Therefore, it is most preferable to use titania.
[0101] (Average Particle Diameter of Third Heat Insulation Material: 0.1 μm or More and 50 μm or Less)
[0102] Since a particle diameter of the third heat insulation material 23 may affect an effect of reflecting heat, when the average particle diameter of the third heat insulation material 23 is limited to a predetermined range, a higher heat insulation property can be obtained.
[0103] That is, when the average particle diameter of the third heat insulation material 23 is 0.1 μm or more, it is sufficiently larger than a wavelength of light that contributes to heating. Therefore, light can be diffusely reflected efficiently. Therefore, when the third heat insulation material 23 is in a preferable existence range (mass ratio) in the present invention, radiation heat transmission of the heat in the heat insulation sheet 10 is reduced in a high temperature range of 500° C. or higher, and the heat insulation property can be further improved. When the average particle diameter of the third heat insulation material 23 is 50 μm or less, even if itis compressed, the number of contact points between the particles does not increase, it is difficult to form a path for conductive heat transfer, and influence on the heat insulation property in a normal temperature range where the conductive heat transfer is particularly dominant can be reduced.
[0104] The average particle diameter of the third heat insulation material 23 is more preferably 1 μm or more, and still more preferably 5 μm or more. The average particle diameter of the third heat insulation material 23 is more preferably 30 μm or less, and still more preferably 10 μm or less.
[0105] (Content of Third Heat Insulation Material: 5 Mass % or More and 40 Mass % or Less with Respect to Total Mass of Heat Insulation Sheet)
[0106] In the present invention, in order to improve the heat insulation property in a high temperature range of 500° C. or higher, although it is preferable that the heat insulation sheet 10 contains the third heat insulation material 23, even if an addition amount of the third heat insulation material 23 is small, the effect of reducing radiation heat transmission can be obtained. In order to obtain the effect of reducing convective heat transfer and conductive heat transfer by the first heat insulation material 21 and the second heat insulation material 22, it is preferable to increase addition amount of the first heat insulation material 21 and the second heat insulation material 22. As described above, the mass ratio of the third heat insulation material 23 affects the heat insulation property in a range from a normal temperature to a high temperature of 500° C. or higher. Therefore, in the present invention, when the heat insulation sheet 10 contains a metal oxide as the third heat insulation material 23, it is preferable to appropriately adjust the mass ratio of the third heat insulation material 23.
[0107] In the heat insulation sheet 10 of the present invention, a desirable mass ratio of the third heat insulation material 23 is 5 mass % or more with respect to the total mass of the heat insulation sheet. When the content of the third heat insulation material 23 is 5 mass % or more with respect to the total mass of the heat insulation sheet, it is considered that radiation heat transmission can be reduced particularly in a temperature range of 500° C. or higher where influence of radiation is large, and a high heat insulation property can be obtained.
[0108] The desirable mass ratio of the third heat insulation material 23 of the heat insulation sheet 10 of the present invention is 40 mass % or less with respect to the total mass of the heat insulation sheet. When the content of the third heat insulation material 23 exceeds 40 mass % with respect to the total mass of the heat insulation sheet, the first heat insulation material 21 and the second heat insulation material 22 may not achieve a sufficient effect, it becomes difficult to reduce the convective heat transfer or solid conduction of heat in the heat insulation sheet 10 in a temperature range of less than 500° C., and the heat insulation property may be reduced.
[0109] In addition to the first heat insulation material 21, the second heat insulation material 22, and preferably the third heat insulation material 23, the heat insulation sheet 10 for battery pack may further contain components necessary for molding into a heat insulation material, such as a binding material and a colorant. Hereinafter, other components will be described in detail.
[0110] (Binding Material: 10 Mass % or More and 60 Mass % or Less with Respect to Total Mass of Heat Insulation Sheet)
[0111] The heat insulation sheet 10 for battery pack according to the present invention can be formed by sintering or the like even if it does not contain a binding material, but in particular, when the heat insulation sheet 10 for battery pack contains the silica nanoparticle as the first heat insulation material 21, it is preferable to add a binding material in an appropriate content in order to maintain the shape of the heat insulation sheet 10. In the present invention, the binding material may be any material as long as it can hold the first heat insulation material 21 and the second heat insulation material 22, no matter what the form thereof is, such as a binder with adhesion, a fiber that physically entangles particles, or a heat-resistant resin that adheres by adhesive force.
[0112] As the binder, an organic binder, an inorganic binder, or the like can be used. The present invention is not particularly limited to these kinds, but as the organic binder, a polymer flocculant, an acrylic emulsion, or the like can be used, and as the inorganic binder, for example, silica sol, alumina sol, sulfate band, or the like can be used. These binders function as an adhesive when a solvent such as water is removed.
[0113] As the fiber, organic fibers, inorganic fibers, or the like can be used. The organic fibers are not particularly limited, but synthetic fibers, natural fibers, pulps, or the like can be used. The inorganic fibers are not particularly limited, but it is preferable to use alumina fiber, silica-alumina fiber, silica fiber, glass fiber, glass wool, rock wool, or the like.
[0114] Since the binding material contains a component having higher heat conductivity than the first heat insulation material 21, the second heat insulation material 22, and the like, when the binder is present in the voids formed in the heat insulation sheet 10 to such an extent that conductive heat transfer does not occur, the reduction of convective heat transfer and conductive heat transfer by the first heat insulation material 21 will be affected. Therefore, in the heat insulation sheet 10 for battery pack of the present invention, a content of the binding material is preferably 60 mass % or less, more preferably 50 mass % or less, with respect to the total mass of the heat insulation sheet. In the heat insulation sheet 10 for battery pack of the present invention, the content of the binding material is preferably 10 mass % or more, more preferably 20 mass % or more, with respect to the total mass of the heat insulation sheet.
[0115] (Average Fiber Diameter of Inorganic Fiber: 0.1 μm or More and 20 μm or Less)
[0116] The inorganic fiber is a linear or needle-shaped fiber, and contributes to improvement of mechanical strength and shape retention property against the compressive stress from the battery cells 20 of the heat insulation sheet 10.
[0117] In order to obtain such an effect, when an inorganic fiber is used as the binding material, an average fiber diameter thereof is preferably 0.1 μm or more, and more preferably 2 μm or more. However, if the inorganic fiber is too thick, since moldability and processability on the heat insulation sheet 10 may decrease, the average fiber diameter is preferably 20 μm or less, and more preferably 15 μm or less.
[0118] (Average Fiber Length of Inorganic Fiber: 0.1 mm or More and 20 mm or Less)
[0119] When an inorganic fiber is used as the binding material, the fibers are suitably entangled with each other when molded as the heat insulation sheet 10, and a sufficient surface pressure can be obtained.
[0120] In order to obtain such an effect, when an inorganic fiber is used, an average fiber length thereof is preferably 0.1 mm or more, and more preferably 0.5 mm or more. However, if the average fiber length of the inorganic fiber is too long, during preparation of a slurry solution in which the inorganic fiber is dispersed in water in a sheet forming process, the entanglement between the inorganic fibers may become too strong, and the inorganic fibers may easily accumulate non-uniformly after being formed into a sheet.
[0121] Therefore, the average fiber length of the inorganic fiber is preferably 20 mm or less, and more preferably 10 mm or less.
[0122] The fiber diameter and fiber length of the inorganic fiber can be measured by extracting the inorganic fiber from a molded sheet without breaking it by tweezers, observing the inorganic fiber with a microscope, and comparing it with a standard scale. The average fiber diameter and the average fiber length of the inorganic fiber are obtained from an average value of any 10 fibers.
[0123] (Thickness of Heat Insulation Sheet: 0.1 mm or More and 30 mm or Less)
[0124] A thickness of the heat insulation sheet 10 for battery pack according to the present invention is not particularly limited, but is preferably in a range of 0.1 mm or more and 30 mm or less. When the thickness of the heat insulation sheet 10 is within the above range, sufficient mechanical strength can be obtained and molding can be easily performed.
[0125] (Method for Manufacturing Heat Insulation Sheet for Battery Pack)
[0126] Next, a method for manufacturing the heat insulation sheet for the battery pack according to the present invention will be described in detail.
[0127] The heat insulation sheet 10 according to the present embodiment may be manufactured by molding materials for the heat insulation sheet including the first heat insulation material 21 and second heat insulation material 22 by a wet sheet forming method, a dry molding method, or a wet molding method, and may also be manufactured by an extrusion molding method. Hereinafter, a manufacturing method under a case where the heat insulation sheet 10 is obtained by each molding method will be described.
[0128] [Manufacturing Method of Heat Insulation Sheet by Wet Sheet Forming Method]
[0129] In the wet sheet forming method, first, a mixed liquid is prepared by mixing the first heat insulation material 21 and the second heat insulation material 22, and if necessary, an inorganic fiber, an organic fiber, or an organic binder, which is the binding material, in water, and stirring with a stirrer. Then, the obtained mixed liquid is poured into a molding device provided with a mesh for filtration on a bottom surface thereof, and the mixed liquid is dehydrated through the mesh to prepare a wet sheet. Then, the heat insulation sheet 10 can be obtained by heating and pressurizing the obtained wet sheet. The second heat insulation material 22 is oriented in the plane direction during the filtration and pressurizing. Before the heating and pressurizing, hot air may be aerated through the wet sheet to dry the sheet, but this aeration-drying treatment may also not be carried out, and the wet sheet may be heated and pressurized in a wet state.
[0130] [Manufacturing Method of Heat Insulation Sheet by Dry Molding Method]
[0131] In the dry molding method, first, the first heat insulation material 21 and the second heat insulation material 22, and if necessary, an inorganic fiber, an organic fiber, or an organic binder as the binding material are put into a V-type mixer or the like in a predetermined ratio. After thoroughly mixing the materials put into the mixer, the heat insulation sheet 10 can be obtained by putting the mixture into a predetermined mold and pressing the mold. During the pressing, the mold may be heated if necessary. The second heat insulation material 22 is oriented in the plane direction during the pressing.
[0132] The pressing pressure is preferably in a range of 0.98 MPa to 9.80 MPa. If the pressing pressure is less than 0.98 MPa, the obtained heat insulation sheet may not be able to maintain a strength thereof and may collapse. If the pressing pressure exceeds 9.80 MPa, workability may be lowered due to excessive compression, and a bulk density may be increased, so that the solid heat transmission may be increased and the heat insulation property may be lowered.
[0133] [Manufacturing Method of Heat Insulation Sheet by Extrusion Molding Method]
[0134] In the extrusion molding method, first, the first heat insulation material 21 and the second heat insulation material 22, and if necessary, an inorganic fiber, an organic fiber, or an organic binder, which is the binding material, are added with water and kneaded with a kneader to prepare a paste. Then, the obtained paste is extruded from a slit-shaped nozzle using an extrusion molding device and further dried to obtain the heat insulation sheet 10. As the organic binder, methyl cellulose, water-soluble cellulose ether, and the like are preferably used, but any organic binder generally used when an extrusion molding method is used can be used without particular limitation. In the extrusion molding method, the second heat insulation material 22 is oriented in an extrusion direction.
[0135] As mentioned above, in any of the manufacturing methods, when an inorganic balloon is used as the second heat insulation material 22, the fragment of the balloon previously crushed to a desired size may be used, or the balloon may be mixed and stirred together with the above materials and crushed to a desired size by adjusting intensity and time of stirring.
[0136] <Battery Pack>
[0137] As illustrated in
[0138] Although various embodiments have been described above with reference to the drawings, it is needless to say that the present invention is not limited to such examples. It is apparent to those skilled in the art that various changes and modifications can be conceived within the scope of the claims, and it is also understood that such variations and modifications belong to the technical scope of the present invention. In addition, constituent elements in the embodiments described above may be combined freely within a range not departing from the spirit of the present invention.
[0139] The present application is based on Japanese Patent Application No. 2019-170437 filed on Sep. 19, 2019, the contents of which are incorporated herein by reference.
REFERENCE SIGNS LIST
[0140] 10, 40: heat insulation sheet (for battery pack) [0141] 10a, 10b, 40a, 40b: surface [0142] 20: battery cell [0143] 21: first heat insulation material [0144] 22: second heat insulation material [0145] 23: third heat insulation material [0146] 30: battery case [0147] 100: battery pack