Heat diffusion sheet

Abstract

To provide a heat diffusion sheet that shows reduced tendency to catch fire at high temperatures, while showing a reduced volumetric change.SOLUTION: A heat diffusion sheet comprises a first heat insulation layer, and a first heat transfer layer disposed on each side of the first heat insulation layer. The heat transfer rate of the first heat transfer layer in a plane direction is at least 10 times the heat transfer rate of the first heat insulation layer in the plane direction.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a thermal diffusion sheet. [Background technology]

[0002] Thermal diffusion sheets and heat dissipation sheets for promoting heat dissipation from heat generating bodies are used in various applications. For example, in vehicle-mounted or stationary power supply devices in which multiple secondary battery cells are stacked to achieve high output and high capacity, it is known that the secondary battery cells generate heat when they are charged and discharged. In order to improve the heat dissipation of such secondary battery cells, a thermal diffusion sheet is attached to the exterior can of the battery cell. In order to improve the heat dissipation with a thermal diffusion sheet, it is necessary to increase the thermal conductivity.

[0003] On the other hand, when a large number of high-capacity secondary battery cells such as lithium-ion secondary batteries are used, there is a concern that one secondary battery cell may become too hot for some reason, causing thermal runaway and adversely affecting other adjacent secondary battery cells. For this reason, it is necessary to thermally insulate adjacent secondary battery cells from each other during thermal runaway. However, in order to provide thermal insulation performance, it is necessary to suppress thermal conductivity at high temperatures, which is inconsistent with improving heat dissipation at low temperatures, i.e., improving thermal conductivity.

[0004] To meet these conflicting demands, laminates equipped with a thermal diffusion layer and a heat insulating layer have been proposed (Patent Documents 1 to 4). However, these configurations have concerns about their stability in environments where temperatures can reach several hundred degrees due to thermal runaway, and there are doubts about whether they can effectively prevent a chain reaction of thermal runaway between secondary battery cells.

[0005] Also, as a means of preventing a chain reaction of thermal runaway, a thermal runaway prevention sheet has been proposed in which at least one of the following structural changes occurs when the temperature rises: phase change, expansion, foaming, and hardening (for example, Patent Document 5). According to this sheet, a laminated structure is formed with an intermediate layer that undergoes a structural change at a certain temperature, and at high temperatures the intermediate layer expands or foams, inhibiting heat transfer through the air layer and providing thermal insulation.

[0006] However, this configuration has a problem that the volume of the intermediate layer increases due to foaming, and the thermal diffusion sheet becomes thick. A secondary battery cell such as a lithium-ion secondary battery is configured by inserting a current collector into a hard aluminum exterior can, and it is known that the exterior can expands due to rapid charging and discharging. For this reason, the thermal diffusion sheet interposed between the exterior cans that expand during thermal runaway is pressed with high pressure, making it difficult to secure a space that allows the expansion. In particular, power supply devices including a thermal diffusion sheet are strongly required to be miniaturized in order to secure cabin space in a vehicle, and enlarging the power supply device is often not allowed. For these reasons, it is practically difficult to adopt a thermal diffusion sheet whose volume expands at high temperatures, and a thermal diffusion sheet with little volume change has been required. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent Publication No. 2017-159527 [Patent Document 2] JP 2019-147357 A [Patent Document 3] JP 2015-196332 A [Patent Document 4] JP 2011-108617 A [Patent Document 5] JP 2018-206605 A Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made in view of the above-mentioned background, and an object of the present invention is to provide a thermal diffusion sheet that prevents the spread of fire at high temperatures and suppresses volumetric changes.

[0009] According to a first embodiment of the thermal diffusion sheet of the present invention, there is provided a sheet-shaped thermal diffusion sheet comprising a first insulating layer and a first heat transfer layer arranged on both sides of the first insulating layer, wherein the thermal conductivity of the first heat transfer layer in the surface direction is 10 times or more greater than the thermal conductivity of the first insulating layer in the surface direction.

[0010] A thermal diffusion sheet according to a second embodiment of the present invention is a sheet-shaped thermal diffusion sheet comprising a first insulation layer and first heat transfer layers disposed on both sides of the first insulation layer, wherein the thermal conductivity of the first insulation layer is 1.7 W / m·K or less in the plane direction and 0.14 W / m·K or less in the thickness direction, and the thermal conductivity of the first heat transfer layer is 19 W / m·K or more in the plane direction and 1.7 W / m·K or less in the thickness direction, and the sheet is electrically insulating. The above configuration provides the advantage of diffusing heat from a heat source without transmitting it.

[0011] Furthermore, a thermal diffusion sheet according to a third embodiment of the present invention is a sheet-shaped thermal diffusion sheet comprising a first insulation layer and second heat transfer layers disposed on both sides of the first insulation layer, wherein the thermal conductivity of the first insulation layer is 1.7 W / m·K or less in the plane direction and 0.14 W / m·K or less in the thickness direction, and the thermal conductivity of the second heat transfer layer is 120 W / m·K or more in the plane direction and 1.3 W / m·K or less in the thickness direction. The above configuration provides the advantage of diffusing heat from a heat source without transmitting it.

[0012] Furthermore, according to a fourth embodiment of the present invention, there is provided a thermal diffusion sheet in the form of a sheet, comprising a second heat transfer layer and a first heat insulating layer disposed on both sides of the second heat transfer layer, wherein the thermal conductivity of the first heat insulating layer is 1.7 W / m K or less in the plane direction and 0.14 W / m K or less in the thickness direction, and the thermal conductivity of the second heat transfer layer is 120 W / m K or more in the plane direction and 0.14 W / m K or less in the thickness direction. 3 The thermal conductivity is less than W / m K and the material has electrical insulation properties. The above structure has the advantage of diffusing heat from the heat source without transmitting it.

[0013] Furthermore, the present invention 5 According to the thermal diffusion sheet of the embodiment, in addition to any one of the above-mentioned configurations, at least one of inorganic fibers and inorganic fillers is contained in an amount of 80% or more.

[0014] Furthermore, the present invention 6 According to the thermal diffusion sheet of this embodiment, in addition to any one of the configurations described above, when heated from one side at 40° C. for 15 minutes, the temperature difference per unit thickness between the back side and the one side is 3° C. / mm or more.

[0015] Furthermore, the present invention 7 According to the thermal diffusion sheet of this embodiment, in addition to any of the configurations described above, when heated for 10 minutes in accordance with the JIS L 1091 A-1 (1999) test, the temperature difference per unit thickness between the flame contact part and the back surface is 200°C / mm or more.

[0016] Furthermore, the present invention 8 According to the thermal diffusion sheet according to the embodiment of the present invention, in addition to any one of the above configurations, when heated for 10 minutes in accordance with the JIS L 1091 A-1 method (1999) test, the area of ​​the back surface that is incinerated is 500 mm 2 The following is the result.

[0017] Furthermore, the present invention 9 According to the thermal diffusion sheet of this embodiment, in addition to any of the configurations described above, when heated for 10 minutes in accordance with the JIS L 1091 A-1 method (1999) test, the temperature difference between the back side and a distance 50 mm below it is 250°C or less.

[0018] Furthermore, according to a thermal diffusion sheet according to a tenth embodiment of the present invention, in addition to any one of the above configurations, the thermal conductivity in the thickness direction at 150° C. is determined based on the temperature at 15° C. Thickness The change is 18% or less.

[0019] Furthermore, according to the thermal diffusion sheet of the eleventh embodiment of the present invention, in addition to any one of the above configurations, the volume resistance of the entire laminate is 1×10 12 Ω cm The dielectric breakdown voltage for AC is 2.5 kV or more, and the dielectric breakdown voltage for DC is 4.5 kV or more.

[0020] Furthermore, the present invention 12 According to the thermal diffusion sheet of the embodiment, in addition to any one of the configurations described above, when used, it is sandwiched between objects that repeatedly expand and contract.

[0021] Furthermore, according to a thirteenth aspect of the present invention, in addition to any one of the above configurations, there is provided a thermal diffusion sheet for insulating between a plurality of secondary battery cells which are stacked and connected in series and / or parallel to each other, the thermal diffusion sheet comprising an intermediate layer containing inorganic fibers and surface layers stacked on both sides of the intermediate layer so as to sandwich the intermediate layer, the thermal conductivity of the intermediate layer being 1.7 W / m K or less in a planar direction and 0.14 W / m K or less in a thickness direction, and the thermal conductivity of the surface layer being 1.7 W / m K or less in a planar direction. 120 W / m K or more through the thickness 3 W / m K or less. The above structure has the advantage of diffusing heat from the heat source without transmitting it. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 is an exploded perspective view showing a power supply device according to a first embodiment of the present invention. [Diagram 2] 1 is a schematic cross-sectional view of a thermal diffusion sheet according to a first embodiment. [Diagram 3] FIG. 6 is a schematic cross-sectional view of a thermal diffusion sheet according to a second embodiment. [Figure 4] FIG. 11 is a schematic cross-sectional view of a thermal diffusion sheet according to a third embodiment. [Diagram 5] FIG. 5A is a perspective view showing a power supply device according to a fourth embodiment of the present invention, and FIG. 5B is a perspective view showing the power supply device with secondary battery cells in a horizontally placed position. [Figure 6]4 is a schematic cross-sectional view of a thermal diffusion sheet according to Comparative Example 1. FIG. [Figure 7] FIG. 11 is a schematic cross-sectional view of a thermal diffusion sheet according to Comparative Example 2. [Figure 8] FIG. 2 is a schematic diagram showing a combustion test of a sample. [Figure 9] FIG. 13 is a schematic diagram showing a heating test using a heater. [Figure 10] FIG. 10A is a photograph showing the ashed area of ​​the sample after the heating test, and FIG. 10B is a photograph showing the carbonized area. [Figure 11] FIG. 11A is a photograph of the burned surface of the sample according to Example 1, and FIG. 11B is a photograph of the back surface. [Figure 12] FIG. 12A is a photograph of the burned surface of the sample according to Example 2, and FIG. 12B is a photograph of the back surface. [Figure 13] FIG. 13A is a photograph of the burned surface of the sample according to Example 3, and FIG. 13B is a photograph of the back surface. [Figure 14] FIG. 14A is a photograph of the burned surface of the sample according to Comparative Example 1, and FIG. 14B is a photograph of the back surface. [Figure 15] FIG. 15A is a photograph of the burned surface of the sample according to Comparative Example 2, and FIG. 15B is a photograph of the back surface. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Hereinafter, the embodiments of the present invention will be described with reference to the drawings. However, the embodiments shown below are merely examples for embodying the technical idea of ​​the present invention, and the present invention is not limited to the following. In addition, this specification does not specify the members shown in the claims as the members of the embodiments. In particular, the dimensions, materials, shapes, and relative positions of the components described in the embodiments are merely explanatory examples, and are not intended to limit the scope of the present invention, unless otherwise specified. Note that the size and positional relationship of the members shown in each drawing may be exaggerated to clarify the explanation. Furthermore, in the following explanation, the same name and symbol indicate the same or similar members, and detailed explanation will be omitted as appropriate. Furthermore, each element constituting the present invention may be configured as a form in which multiple elements are composed of the same member, and one member serves multiple elements, or conversely, the function of one member can be shared by multiple members. [Embodiment 1]

[0024] The thermal diffusion sheet according to the embodiment of the present invention can be appropriately used in applications where heat insulation is required and where fire spread is avoided. For example, it is suitable for applications such as lithium ion secondary batteries, which require heat dissipation during normal use, but require fire spread prevention from the perspective of safety when high temperatures are reached during thermal runaway. Here, an example is described in which a thermal diffusion sheet is used as a spacer interposed between adjacent secondary battery cells in a power supply device in which a large number of rectangular secondary battery cells are stacked and connected in series or parallel. Such a power supply device is used as a driving power source for electric vehicles such as electric cars, hybrid cars, electric buses, trains, and electric carts, or as a backup power source for factories and base stations, or as a storage battery for home use. It can be preferably used as a thermal diffusion sheet that is sandwiched between objects that repeatedly expand and contract.

[0025] The power supply device according to the first embodiment is shown in an exploded perspective view in FIG. 1. The power supply device 100 shown in this figure includes a plurality of secondary battery cells 20 and a thermal diffusion sheet 10 interposed between the secondary battery cells 20. The secondary battery cells 20 have an outer can 21 in a rectangular shape with a bottom, and a plurality of the secondary battery cells 20 are stacked with their main surfaces facing each other. The stacking is performed, for example, by covering both end faces of a battery stack 25 in which the secondary battery cells 20 are stacked with end plates 30, and fastening the end plates 30 together with fastening members. The battery stack 25 is fixed onto a base plate 40 as necessary. The base plate 40 can function as a cooling plate, for example, by circulating a refrigerant inside.

[0026] Each secondary battery cell 20 has an electrode body housed inside an outer can 21, and the open end is sealed with a sealing plate 22. A pair of electrodes 23 and an explosion-proof valve 24 are provided on the sealing plate 22 located on the top surface of the outer can 21 in FIG. 1. The electrodes 23 of the multiple secondary battery cells 20 are connected to each other electrically in series and / or in parallel by connecting the electrodes 23 with a bus bar. The explosion-proof valve 24 is a member that opens when it detects an increase in the internal pressure of the outer can 21, and discharges high-pressure gas from inside the outer can 21. Each explosion-proof valve 24 is connected to a gas duct for guiding the high-pressure gas to the outside as necessary. (Thermal diffusion sheet 10)

[0027] A thermal diffusion sheet 10 is interposed between adjacent secondary battery cells 20. The thermal diffusion sheet 10 is also called a spacer or separator, and provides insulation between adjacent secondary battery cells 20 to prevent the exterior cans 21 from shorting out.

[0028] A cross-sectional view of the thermal diffusion sheet 10 is shown in Fig. 2. The thermal diffusion sheet 10 shown in this figure is composed of an intermediate layer 11 and surface layers 12 laminated on both sides of the intermediate layer 11. Here, the intermediate layer constitutes the first heat insulating layer, and the surface layer constitutes the first heat transfer layer. The sheet-shaped thermal diffusion sheet is composed of a three-layer laminate with the surface layer / intermediate layer / surface layer being the first heat transfer layer / first heat insulating layer / first heat transfer layer.

[0029] The thermal conductivity of the first heat transfer layer in the surface direction is preferably 10 times or more the thermal conductivity of the first heat insulating layer in the surface direction. Specifically, the thermal conductivity of the first heat insulating layer is preferably 0.14 W / m·K or less in the surface direction and 1.7 W / m·K or less in the thickness direction. The thermal conductivity of the first heat transfer layer is preferably 19 W / m·K or more in the surface direction and 1.7 W / m·K or less in the thickness direction. This configuration has the advantage that the back surface temperature does not change over time.

[0030] Furthermore, the thermal diffusion sheet has insulating properties. Specifically, the volume resistance of the entire laminate is set to 1×10 12 In conclusion, the dielectric breakdown voltage for AC is 2.5 kV or more, and the dielectric breakdown voltage for DC is 4.5 kV or more.

[0031] Each layer contains at least 80% of inorganic fiber or inorganic filler. This suppresses volumetric changes at high temperatures. It also prevents the material from melting at high temperatures and losing its insulating properties. Resin fibers such as PET and aramid are added as needed.

[0032] Conventionally, in power supply devices in which multiple lithium-ion secondary battery cells are stacked, separators made of resins such as polyolefin resin, phenolic resin, epoxy resin, etc. have been used to insulate the secondary battery cells from each other. However, such separators do not have sufficient heat resistance, and cannot cope with a situation in which, if any secondary battery cell becomes hot due to some abnormality, the high temperature propagates to the other secondary battery cells, causing fire.

[0033] On the other hand, even under normal use conditions, lithium-ion secondary batteries generate heat due to rapid charging and discharging, so they need heat dissipation properties to release the generated heat to the outside. Thus, the separators interposed between the secondary battery cells are required to have the contradictory properties of thermal conductivity at normal temperatures and insulation at high temperatures, and it has been difficult to achieve these contradictory properties.

[0034] Therefore, the thermal diffusion sheet according to the present embodiment realizes a characteristic of suppressing the spread of fire at high temperatures by being made of a material with excellent flame retardancy while exhibiting heat dissipation at normal temperatures. Specifically, the thermal diffusion sheet shown in Fig. 2 has a three-layer structure of a first heat transfer layer / a first heat insulating layer / a first heat transfer layer, and is made of a material with excellent flame retardancy and flame resistance. Specifically, it is made of inorganic fillers such as silicate minerals, metal oxides, and graphite, inorganic fibers such as glass fibers, organic fibers with excellent flame retardancy such as aramid, and organic fibers containing a flame retardant.

[0035] As an index of the thermal diffusion property of a thermal diffusion sheet, when the thermal diffusion sheet is heated at 40°C for 15 minutes, the temperature difference per unit thickness between the front and back sides is preferably 3°C or less. In addition, when the thermal diffusion sheet is heated for 10 minutes in accordance with the JIS L 1091 A-1 method (1999) test, the temperature difference per unit thickness between the flame-contacting part and the back side is preferably 200°C / mm or more. Furthermore, when the thermal diffusion sheet is exposed to a flame from a burner for 10 minutes, the area of ​​the back side that is incinerated is preferably 500mm2 or more. 2 Furthermore, when heated for 10 minutes in accordance with the JIS L 1091 A-1 method (1999) test, the temperature difference between the back surface side and a distance of 50 mm therebelow is preferably 250° C. or less.

[0036] Meanwhile, the thermal conductivity in the plane direction of the first heat transfer layer is set to be 10 times or more the thermal conductivity in the plane direction of the first insulation layer. In this way, by forming a multi-layer structure with a heat transfer layer that exhibits heat dissipation on the surface and an insulation layer in the middle, it is possible to ensure heat dissipation performance by the first heat transfer layer on the surface at room temperature, while at the same time providing insulation by the first insulation layer at abnormally high temperatures such as during thermal runaway, thereby improving safety.

[0037] In addition, the thermal diffusion sheet according to the embodiment preferably has a thickness change of 18% or less at 150°C, based on 15°C. This allows it to be applied to thermally expanding objects such as secondary battery cells. Among conventional thermal diffusion sheets, a laminated structure has been proposed in which an intermediate layer that undergoes a phase change, expansion, or foaming at high temperatures is interposed to prevent fire spreading, and the intermediate layer behaves as a thermal diffusion material at low temperatures, while at high temperatures the intermediate layer undergoes a phase change, expansion, or foaming to provide thermal insulation through an air layer. However, there was a problem in that the volume of the intermediate layer increases due to the phase change, expansion, or foaming, resulting in a thick thermal diffusion sheet. For this reason, in order to allow the thermal diffusion sheet interposed between the exterior cans that have expanded during thermal runaway to further expand, it is necessary to ensure a suitable space and flexibility of the bind bar that fastens the secondary battery cells in a stacked state, which has been extremely difficult to achieve. In contrast, the thermal diffusion sheet according to the present embodiment can avoid such problems by suppressing the change in volume even at high temperatures, making it possible to ensure highly practical heat dissipation and insulation performance. [Embodiment 2]

[0038] The above-mentioned heat transfer layer is an example, and other heat transfer layers can be appropriately adopted. As an example, a heat diffusion sheet according to the second embodiment is shown in the cross-sectional view of FIG. 3. The heat diffusion sheet 10' shown in this figure has a three-layer structure in which a second heat transfer layer 12B is disposed on both sides of a first heat insulation layer 11B. The first heat insulation layer 11B can adopt the same material and thermal conductivity as the first embodiment. On the other hand, the thermal conductivity of the second heat transfer layer 12B is 120 W / m·K or more in the surface direction and 3 W / m·K or less in the thickness direction. Even with such a configuration, the advantage of diffusing heat from a heat source without transmitting it can be obtained. [Embodiment 3]

[0039] Furthermore, in the above example, the thermal diffusion sheet of the multi-layer structure is laminated in the order of the thermal conductive layer / thermal insulating layer / thermal conductive layer, but the present invention is not limited to this configuration, and the multi-layer structure may be laminated in the order of the thermal insulating layer / thermal conductive layer / thermal insulating layer. Such an example is shown in the cross-sectional view of FIG. 4 as the thermal diffusion sheet 10C according to the third embodiment. The thermal diffusion sheet 10C shown in this figure has a three-layer structure in which the first thermal insulating layer 12C is arranged on both sides of the second thermal conductive layer 11C. The second thermal conductive layer 11C and the first thermal insulating layer 12C can be selected from the same materials and thermal conductivities as those of the second embodiment. With this configuration, it becomes easier to make the surface of the thermal diffusion sheet exhibit electrical insulation, and the thermal diffusion sheet can be suitably used for applications requiring insulation. For example, when the thermal diffusion sheet is applied to the power supply device shown in FIG. 1, the surface layer is generally conductive when it is composed of a thermal conductive layer, so that it is necessary to insulate the surface of the secondary battery cell in order to prevent a short circuit between the exterior cans of adjacent secondary battery cells. For example, when the exterior can of the secondary battery cell is made of aluminum, it is necessary to cover it with a shrink tube such as PET resin. In contrast, the thermal diffusion sheet according to the third embodiment has a first insulating layer on the surface, which makes it easier to achieve insulation, and therefore makes it unnecessary to insulate the exterior can of the secondary battery cell. Note that if the exterior can of the secondary battery cell is insulating, such as in the case of a pouch battery, it goes without saying that insulation is essentially unnecessary.

[0040] In the above example, the thermal diffusion sheet has been described as having a three-layer structure, but it goes without saying that the present invention does not limit the number of layers of the thermal diffusion sheet composed of the laminate to three, and it may have four or more layers. (First insulation layer)

[0041] The first heat insulating layer of the thermal diffusion sheet 10 described above includes a fiber base material, a filler, and a binder. Preferably, natural pulp and inorganic fiber are used as the fiber base material, silicate mineral is used as the filler, and a rubber composition is used as the binder. Specifically, the first heat insulating layer according to the first embodiment includes hemp pulp and micro glass as the fiber base material, talc and sepiolite as the filler, and NBR as the binder.

[0042] The fiber substrate (also called substrate fiber) can be inorganic fibers such as glass fiber, carbon fiber, ceramic fiber, or organic fibers such as aromatic polyamide fiber, PET fiber. Here, natural pulp, which is an organic fiber, is used as the fiber substrate. Hemp pulp is preferably used as the natural pulp. The blending ratio of hemp pulp is, for example, 5% by weight to 20% by weight, and preferably 10% by weight.

[0043] The fiber base material may contain inorganic fibers. The blending ratio of the inorganic fibers is 5% by weight to 20% by weight, preferably 8% by weight to 15% by weight. In the first embodiment, 12% by weight of microglass is added as the inorganic fibers.

[0044] The filler may be an inorganic filler. Examples of the inorganic filler include silicate minerals such as sepiolite, talc, kaolin, mica, sericite, zeolite, and bentonite, magnesium carbonate, calcium carbonate, hard clay, calcined clay, barium sulfate, calcium silicate, wollastonite, sodium bicarbonate, synthetic silica such as white carbon and fused silica, natural silica such as diatomaceous earth, aluminum hydroxide, magnesium hydroxide, and glass beads, which may be used alone or in combination. The addition of these inorganic fillers shows effects such as maintaining the shape in a high-temperature atmosphere and improving heat insulation. In the first embodiment, talc, which has high flexibility, is used. The amount of the filler to be mixed in the thermal diffusion sheet is preferably 5% by weight to 65% by weight. In the first embodiment, magnesium silicate is used as the filler, and 58% by weight of talc and 14% by weight of sepiolite are added.

[0045] As the binder, in addition to synthetic resins such as vinyl chloride resin, vinylidene chloride resin, acrylic acid resin, urethane resin, vinyl acetate resin, polyethylene resin, polystyrene resin, acrylobutadiene styrene resin, acrylonitrile styrene resin, fluororesin, silicone resin, epoxy resin, and phenol resin, acrylonitrile butadiene rubber, hydrogenated acrylonitrile butadiene rubber, acrylic rubber, acrylonitrile rubber, ethylene propylene rubber, styrene butadiene rubber, chloroprene rubber, butadiene rubber, butyl rubber, fluororubber, silicone rubber, fluorinated silicone rubber, chlorosulfonated rubber, ethylene vinyl acetate rubber, chlorinated polyethylene, chlorinated butyl rubber, epichlorohydrin rubber, nitrile isoprene rubber, natural rubber, and isoprene rubber can be used. Among them, acrylonitrile butadiene rubber (NBR) is preferable in terms of high water resistance and oil resistance. These rubbers can be used alone or in combination of two or more. In addition, for the purpose of higher water resistance and oil resistance, sizing agents such as alkyl ketene dimer and fluorine-based and silicone-based water repellents can be used in combination. When a rubber composition is used as the binder, the amount of rubber in the thermal diffusion sheet is preferably 0 to 40% by weight, more preferably 3 to 10% by weight. Here, 6.0% by weight of Nipol 1562, which is NBR, is added.

[0046] The first heat insulating layer has a thickness of 0.03 mm to 5.5 mm, preferably 0.05 mm to 2 mm, and more preferably 0.07 mm to 1 mm. The first heat transfer layer may be formed of a single layer or may be formed by laminating a plurality of inorganic fiber layers, such as glass fiber layers or ceramic fiber layers, arranged in layers. (First heat transfer layer)

[0047] The first heat transfer layer has a thermal conductivity in the thickness direction of 1.00 W / m·K or more, preferably 1.30 W / m·K to 20.00 W / m·K, and more preferably 1.70 W / m·K to 15.00 W / m·K. Alternatively, the thermal conductivity in the thickness direction of the first heat insulating layer may be 3.00 W / m·K or less. The thermal conductivity in the plane direction of the first heat insulating layer is preferably 1000 W / m·K or less. With this configuration, when the power supply device 100 is provided with a gas exhaust device such as an explosion-proof valve, it is possible to ensure a time lag for the thermal decomposition gas of the electrolyte to be exhausted and the power supply device 100 to be cooled before the high heat is transmitted to another secondary battery cell through the outer can during the process of thermal runaway of any of the secondary battery cells 1.

[0048] In order to provide sufficient thermal conductivity, the first heat transfer layer preferably contains organic fibers and thermally conductive fillers. The organic fibers can be any one or more of para-aramid fibers, para-aramid pulp, meta-aramid pulp, polyphenylene sulfide fibers, PET fibers, flame-retardant PET fibers, and flame-retardant rayon fibers. The thermally conductive filler can be magnesium oxide, aluminum oxide, boron nitride, aluminum nitride, or the like. The first heat transfer layer may also contain inorganic fibers. The inorganic fibers can be glass fibers, ceramic fibers, or the like. The intermediate sheet made of a paper sheet may be subjected to a heating and pressurizing process using a hot calendar roll or the like. This can densify the inside and increase the thermal conductivity. (Second heat transfer layer)

[0049] The second heat transfer layer may contain, in addition to the components of the first heat transfer layer, heat conductive fillers such as aluminum, copper, graphite, carbon nanotubes, etc., and inorganic fibers such as carbon fibers.

[0050] The first heat transfer layer and the second heat transfer layer have a thickness of 0.02 mm to 0.8 mm, preferably 0.03 mm to 0.6 mm, and more preferably 0.03 mm to 0.3 mm.

[0051] In addition, the first heat insulating layer, the first heat transfer layer and the second heat transfer layer preferably have an air resistance of 3000 sec / ml or more when measured with a Gurley standard densometer conforming to the JIS P 8117 (2009) test. This provides a layer with little powder falling off, and has the advantage of making it easy and inexpensive to manufacture without the need to seal the thermal diffusion sheet 10. (adhesive layer)

[0052] The first heat transfer layer and the first heat insulating layer are bonded with an adhesive. An adhesive layer formed by curing the adhesive is interposed between the first heat transfer layer and the first heat insulating layer. The adhesive is preferably made of a material having excellent heat resistance. Examples of such adhesives include acrylic adhesives, vinyl chloride adhesives, vinyl acetate adhesives, hot melts, etc. The adhesive may be in the form of a liquid or slurry, or a heat-sealed sheet formed by molding the hot melt adhesive into a nonwoven fabric or a mesh.

[0053] The overall thickness of the thermal diffusion sheet 10 is set to 0.2 mm to 6.0 mm, preferably 0.2 mm to 4.0 mm, and more preferably 0.3 mm to 2.0 mm.

[0054] Furthermore, the thermal diffusion sheet 10 has flexibility and pliability. As a result, when the secondary battery cell 1 expands, the thermal diffusion sheet 10 follows the deformation of the secondary battery cell 1, maintaining a close contact state, and avoiding a situation in which thermal conductivity is reduced due to the formation of voids. In particular, many conventional thermal diffusion sheets are hard and have low followability to deformation, so that voids are formed on the contact surface and thermal conductivity is reduced due to the insulating effect of the air layer. When the thermal diffusion sheet is intended to exhibit insulating performance to prevent fire from spreading, a hard thermal diffusion sheet is actually preferable because the insulating performance is further improved by the air layer. In contrast, as in the thermal diffusion sheet 10 according to this embodiment, in order to exhibit heat dissipation performance, the first insulating layer is made of a thermal diffusion sheet 10 having flexibility and pliability rather than such a hard material, so that the heat conductivity can be maintained high and heat dissipation performance can be exhibited.

[0055] Furthermore, by providing the thermal diffusion sheet 10 with flexibility, it can be wound around a roll material such as a roll material, and can be stored and transported in a rolled form, improving handleability. In order to provide flexibility, for example, when one side of the thermal diffusion sheet 10 is placed against a cylinder with an outer diameter of 110 mm and folded 90°, no wrinkles or cracks are generated.

[0056] Furthermore, it is desirable that the thermal diffusion sheet 10 has heat resistance and flame retardancy. By using a material that is unlikely to deform or melt even when the secondary battery cells 1 become hot, it is possible to maintain the heat insulating performance. Preferably, the heat resistance temperature of the thermal diffusion sheet 10 is set to 300 to 600°C. In the thermal diffusion sheet according to this embodiment, the surface layer is made of fibers, a filler, and a binding material (binder), thereby achieving a high heat resistance temperature and maintaining insulation even in a high temperature environment. Furthermore, the ashing area of ​​the back surface when heated for 10 minutes in accordance with the JIS L 1091 A-1 method (1999) test is set to 500 mm 2 It is preferable to keep it below this value.

[0057] In addition, in the thermal diffusion sheet 10 according to this embodiment, the smoothness of the entire thermal diffusion sheet is preferably set to 15 to 150 sec. This provides the advantage that sealing of the thermal diffusion sheet is not required, making production easy and inexpensive.

[0058] The thermal diffusion sheet according to the present embodiment can be flexible enough to be deformed. Preferably, the sheet has flexibility enough not to break even when wrapped around a paper tube with a curvature radius of 55 mm. This allows the sheet to follow the deformation and maintain a tight contact state even if the object with which the sheet is in contact expands or deforms, and prevents the formation of voids that reduce thermal conductivity. (Method of manufacturing the thermal diffusion sheet 10)

[0059] Here, the thermal diffusion sheet 10 can be manufactured in a roll-to-roll manner by sandwiching a heat-sealing sheet between the first heat transfer layer and the first heat insulating layer, which are rolled, and passing them between two heat pressing rolls to bond them together. Alternatively, a liquid adhesive may be applied to one or both sides of the first heat transfer layer or the first heat insulating layer, and they may be bonded together. In Examples 1 to 3 and Comparative Examples 1 and 2 described below, a polyethylene heat-sealing sheet is sandwiched between the first heat transfer layer and the first heat insulating layer, and they are bonded together by applying pressure of 50 kPa for 20 seconds using a hot press at 150°C.

[0060] In the above example, the thermal diffusion sheet 10 has been described as having a three-layer structure in which both sides of the first heat transfer layer are covered with a single first heat insulating layer. However, the present invention is not limited to such a three-layer structure, and may have a multi-layer structure of four or more layers, for example, a multi-layer surface layer or a multi-layer intermediate layer. Alternatively, depending on the application, a two-layer structure may be used in which a surface layer is provided on only one side of the intermediate layer.

[0061] Furthermore, in the example of FIG. 1, the secondary battery cell 1 is placed vertically, but it goes without saying that the thermal diffusion sheet can also be similarly applied to a power supply device in which the secondary battery cell is placed horizontally.

[0062] Furthermore, the thermal diffusion sheet 10 can be used not only for thermal insulation between secondary battery cells, but also for thermal insulation between battery modules each composed of a plurality of secondary battery cells. [Embodiment 4]

[0063] In the above example, the heat insulating material is applied to a secondary battery cell using a rectangular exterior can as the secondary battery cell. However, the present invention is not limited to a rectangular shape of the secondary battery cell, and can be applied to secondary battery cells of other shapes such as a cylindrical shape or a pouch shape. As an example, FIG. 5A shows an example of application to a cylindrical secondary battery cell as a power supply device according to embodiment 5. In the power supply device 500A shown in this figure, a thermal diffusion sheet 10 is interposed between adjacent secondary battery cells in a state where a plurality of cylindrical secondary battery cells 20B are arranged side by side. As a result, even if any of the secondary battery cells 20B becomes hot, the thermal diffusion sheet 10 can suppress heat propagation. In this example, in order to separate the secondary battery cells 20B, a cut is formed from one end of one thermal diffusion sheet 10A, and a cut is formed from the other end of another thermal diffusion sheet 10B, and these cuts are combined so that the thermal diffusion sheets cross each other. Furthermore, in the example of FIG. 5A, the secondary battery cell 20B is placed vertically, but it goes without saying that it may be placed horizontally as shown in FIG. 5B. [Examples 1 to 3]

[0064] Next, the thermal diffusion sheets according to Examples 1 to 3 and Comparative Examples 1 and 2 were produced, and the characteristics of each sample were examined. The thickness and thermal conductivity of the intermediate layer and surface layer used in each sample are shown in Table 1.

[0065] In Examples 1 to 3 and Comparative Example 1, the heat insulation layer was made of the same sheet made of natural pulp, microglass, silicate mineral powder, and rubber-based resin as a binder. To prepare the heat insulation layer, first, disintegrated natural pulp was prepared, and microglass and silicate mineral powder were uniformly dispersed. Rubber-based resin was added to the pulp to obtain a papermaking slurry, which was then made into a paper by a wet papermaking method to obtain a heat insulation layer base sheet with a thickness of about 0.70 mm. The heat insulation layer base sheet had a thermal conductivity (thickness direction) of 0.14 W / m·K, a thermal conductivity (plane direction) of 1.7 W / m·K, a smoothness of 46.8 sec, and an air resistance of 30 sec / 100 ml. Both sides of the heat insulation layer base sheet were covered with different heat transfer layers, respectively, to prepare the samples of Examples 1 and 2. Example 1

[0066] A papermaking sheet containing 80% boron nitride powder was used as the heat transfer layer of Example 1. Specifically, a papermaking slurry was prepared by dispersing a mixture of boron nitride powder with an average particle size of 200 μm, scaly boron nitride with an average particle size of 40 μm, and organic fibers in water at a weight ratio of 80:20, and the sheet obtained by the wet papermaking method was subjected to heat and pressure processing to obtain a surface layer base sheet. The thickness was 0.20 mm.

[0067] A surface layer base sheet was laminated on both sides of the aforementioned heat insulation layer base sheet, and a polyethylene heat-sealing sheet was sandwiched between the surface layer and the intermediate layer. The sheets were then bonded together using a hot press at 150°C under pressure of 50 kPa for 20 seconds to obtain a thermal diffusion sheet according to Example 1. Example 2

[0068] A papermaking sheet containing 90% graphite powder was used as the heat transfer layer of Example 2. Specifically, graphite powder and organic fibers were dispersed in water in a weight ratio of 90:10 to prepare a papermaking slurry, and the sheet obtained by the wet papermaking method was subjected to heat and pressure processing to obtain a surface layer base sheet. The thickness was 0.23 mm. Surface layer base sheets were attached to both sides of the above-mentioned heat insulating layer base sheet in the same manner as in Example 1 to obtain a thermal diffusion sheet according to Example 2. Example 3

[0069] The intermediate layer of Example 3 was the same sheet as that used for the heat transfer layer of Example 2. The above-mentioned heat insulating layer base sheet was attached to each side of this intermediate layer base sheet to obtain a thermal diffusion sheet according to Example 3. Comparative Example 1

[0070] As the thermal diffusion sheet 10D according to Comparative Example 1, as shown in the cross-sectional view of FIG. 6, a three-layer structure of a heat insulating layer 12D / heat insulating layer 11D / heat insulating layer 12D was used. As the surface layer, a heat insulating papermaking sheet was used as the intermediate layer. Specifically, a papermaking slurry obtained by mixing raw materials in the same weight ratio as in Example 1 was made into paper by a wet papermaking method to obtain a surface layer base sheet with a thickness of about 0.3 mm. The obtained surface layer base sheet was bonded to both sides of the heat insulating layer base sheet in the same manner as in Example 1, etc., to obtain a thermal diffusion sheet according to Comparative Example 1. Comparative Example 2

[0071] As a thermal diffusion sheet 10E according to Comparative Example 2, six heat dissipation layers 11E were laminated as shown in the cross-sectional view of Fig. 7. For each heat dissipation layer, a papermaking slurry obtained by mixing raw materials in the same weight ratio as the heat transfer layer of Example 2 was made into a paper by a wet papermaking method to obtain a heat transfer layer base sheet having a thickness of about 0.3 mm. Six of the obtained heat transfer layer base sheets were laminated, and the same heat fusion sheets as those of Example 1 were attached between the layers, respectively, and hot pressing was performed to obtain a thermal diffusion sheet according to Comparative Example 2.

[0072] The layer structure, thickness of the surface layer, thickness of the intermediate layer, thickness of the entire thermal diffusion sheet, and thermal conductivity (thickness direction and surface direction) of the surface layer and intermediate layer of the thermal diffusion sheets of Examples 1 to 3 and Comparative Examples 1 and 2 are shown in Table 1.

[0073] [Table 1]

[0074] The insulation properties of the thus obtained Examples 1 to 3 and Comparative Examples 1 to 2 were measured. The insulation volume resistivity was measured in accordance with JIS K6911 "General test method for thermosetting plastics" using an ultra-super insulation meter SM-10E manufactured by DKK-TOA under an environment of 23°C. The dielectric strength (AC voltage) was measured in accordance with JIS C2110-1 "Solid electrical insulating material-Test method for dielectric breakdown strength-Part 1: Test by application of commercial frequency AC voltage" using a voltage tester TW-5110ADL manufactured by Tokyo Seiden under an environment of 23°C. The dielectric strength (DC voltage) was measured in accordance with JIS C2110-2 "Solid electrical insulating material-Test method for dielectric breakdown strength-Part 2: Test by application of DC voltage" using a voltage tester TW-5110ADL manufactured by Tokyo Seiden under an environment of 23°C. The voltage rise rate was 100V / min for both AC and DC. The results are shown in Table 2.

[0075] [Table 2]

[0076] (40℃ heating test) In order to confirm the performance of the thermal diffusion sheet at normal use temperature, a heating test using a heater was performed. Here, for the samples SM of Comparative Examples 1-2 and Examples 1-3, a 25 mm square micro ceramic heater CH was installed on the sample SM cut to 100 mm x 80 mm as shown in FIG. 9. Heat dissipation grease HG was applied to the contact surface. Thermocouples TC4 and TC5 were installed on the heater CH and on the back surface of the sample SM directly below the heater CH, and electricity was applied to the heater SH, and the output was adjusted so that the thermocouple TC4 was stable at about 40°C. The temperatures of the thermocouples TC4 and TC5 at this time were read, and the temperature difference between the front and back was divided by the sheet thickness to calculate the temperature difference per unit thickness. The above results are shown in Table 3.

[0077] [Table 3]

[0078] All of Examples 1 to 3 show a temperature difference per unit thickness of 3°C / mm or more, suggesting that heat diffusion in the in-plane direction is possible while suppressing heat transmission to the back surface of the sheet. Comparative Example 1 has low thermal conductivity in both the thickness direction and the in-plane direction, and it is believed that the temperature difference is small as a result of heat transmission concentrating at one point. Comparative Example 2 has only a layer with high thermal conductivity, so the amount of heat transmitted in the thickness direction is also large, and as a result, it is believed that the temperature difference is small. (600℃ heating test)

[0079] In order to confirm the heat insulating properties of the thermal diffusion sheets according to the examples and comparative examples prepared as described above, a heating test using a gas burner was carried out. Here, the samples of comparative examples 1-2 and examples 1-3 were heated with a flame of a gas burner according to the JIS L 1091 A-1 method (1999) test (45° microburner method), and the temperature change after 10 minutes from the start of heating the samples was measured.

[0080] As in the 45° microburner method, each sample SM was attached to the jig at a 45° angle as shown in Figure 8. Thermocouples TC1 and TC2 were attached to the flame contact part and back side of gas burner GB, and TC3 was attached 50 mm below TC2. The flame from gas burner GB was applied to the sample, and the temperatures of thermocouples TC1, TC2, and TC3 were measured 10 minutes after the start of heating when the temperature change stabilized. To evaluate the thermal barrier properties, the temperature difference between the front and back of the sheet was calculated using the difference between TC1 and TC2, and this was divided by the sheet thickness to calculate the temperature difference per unit thickness. To evaluate the thermal diffusivity within the surface, the temperature difference between TC2 and TC3 was calculated and evaluated according to the following criteria. ◎: Temperature difference is 200℃ or less ○: Temperature difference is 300℃ or less △: Temperature difference is 400℃ or less The above results are shown in Table 4.

[0081] [Table 4]

[0082] In Comparative Example 1, even though only the heat insulating sheets were laminated, the temperature difference was smaller than in the Examples. This is presumably because the thermal diffusivity in the in-plane direction was low, and heat was transmitted only intensively to the burner flame contact area. In Comparative Example 2, the thermal diffusivity was high overall, and the temperature difference was the smallest. On the other hand, in all of Examples 1 to 3, a temperature difference of 200°C or more per mm of thickness was maintained, and the effect of suppressing heat transmission in the thickness direction while diffusing heat in the in-plane direction was confirmed.

[0083] Furthermore, without attaching a thermocouple, the flame of a gas burner GB was applied to the sample to observe whether it burned or not, and the state of both sides of the sample after the test was photographed. This state is shown in Fig. 10A to Fig. 10B. In these figures, Fig. 10A shows the ashed area of ​​the sample, and Fig. 14B shows the carbonized area. When the organic components were burned and turned white, the area was measured using the image processing software "leafareacounter_plus3_3". Using this image processing software, the ashed area was measured by measuring the area where the organic components had disappeared due to burning and only the inorganic components remained and turned white, as surrounded by the dashed line in Fig. 10A. Similarly, the carbonized area was measured by measuring the area that was blackened including the ashed area, as surrounded by the red line in Fig. 10B. In this way, the combustion test results of the samples of Examples 1 to 3 and Comparative Examples 1 and 2 are shown in Figs. 11A to 15B. In these figures, Figure 11A shows a photograph of the burnt surface of a sample according to Example 1, Figure 11B shows a photograph of the back side, Figure 12A shows a photograph of the burnt surface of a sample according to Example 2, Figure 12B shows a photograph of the back side, Figure 13A shows a photograph of the burnt surface of a sample according to Example 3, Figure 13B shows a photograph of the back side, Figure 14A shows a photograph of the burnt surface of a sample according to Comparative Example 1, Figure 14B shows a photograph of the back side, Figure 15A shows a photograph of the burnt surface of a sample according to Comparative Example 2, and Figure 15B shows a photograph of the back side.

[0084] In addition, the dimensional change rate in the thickness direction was measured when Examples 1 to 3 and Comparative Examples 1 to 2 were heated to 150°C. Specifically, each sample was cut into 10 cm x 10 cm, and left to stand in a dryer set to 150°C for 1 hour. The thickness was measured immediately after removal and before heating (15°C) in accordance with JIS P 8118 (2014), and the increase in thickness relative to the thickness before heating was calculated as a percentage. The results are shown in Table 5.

[0085] [Table 5] [Industrial Applicability]

[0086] The thermal diffusion sheet of the present invention can be used as a thermal diffusion sheet sandwiched between objects that repeatedly expand and contract. For example, it can be used as a heat insulating spacer interposed between secondary battery cells or secondary battery cell modules, a buffer sheet interposed between an explosion-proof valve and a gas duct, or a heat insulating material for protecting a drive circuit of an ECU or the like. [Explanation of symbols]

[0087] 100, 500A, 500B…Power supply device 10, 10', 10A, 10B, 10C, 10D, 10E...Heat diffusion sheet 11. Middle class 12…Surface layer 11B…First insulation layer 12B: Second heat transfer layer 11C…Second heat transfer layer 12C…First insulation layer 11D…Thermal insulation layer 12D…Thermal insulation layer 11E…Heat dissipation layer 20, 20B…Secondary battery cell 21...Outer can 22...Sealing plate 23...Electrode 24...Explosion-proof valve 25...Battery stack 30...End plate 40...Foundation plate TC1, TC2, TC3, TC4, TC5... Thermocouples SM…Sample GB…Gas burner CH...Micro ceramic heater HG…Thermal grease

Claims

1. A second heat transfer layer; A first heat insulating layer is disposed on each side of the second heat transfer layer; A sheet-shaped thermal diffusion sheet comprising: The thermal conductivity of the first insulation layer is 1.7 W / m K or less in the surface direction and 0.14 W / m K or less in the thickness direction; The thermal conductivity of the second heat transfer layer is 120 W / m K or more in the surface direction and 3 W / m K or less in the thickness direction; A thermal diffusion sheet with electrical insulation properties.

2. The thermal diffusion sheet according to claim 1 , A thermal diffusion sheet containing at least 80% of at least one of inorganic fibers and inorganic fillers.

3. The thermal diffusion sheet according to claim 1 or 2, A thermal diffusion sheet that, when heated from one side at 40°C for 15 minutes, has a temperature difference per unit thickness between the reverse side and one side of 3°C / mm or more.

4. The thermal diffusion sheet according to any one of claims 1 to 3, A thermal diffusion sheet in which the temperature difference per unit thickness between the flame-contacting part and the back surface is 200° C. / mm or more when heated for 10 minutes in accordance with the JIS L 1091 A-1 (1999) test.

5. The thermal diffusion sheet according to any one of claims 1 to 4, When heated for 10 minutes according to the JIS L 1091 A-1 (1999) test, the area of ​​the backside that is incinerated is 500 mm 2 The thermal diffusion sheet is shown below.

6. The thermal diffusion sheet according to any one of claims 1 to 5, A thermal diffusion sheet in which the temperature difference between the back surface and a distance of 50 mm therebelow is 250° C. or less when heated for 10 minutes in accordance with the JIS L 1091 A-1 (1999) test.

7. The thermal diffusion sheet according to any one of claims 1 to 6, A thermal diffusion sheet in which the change in thickness in the thickness direction at 150°C is 18% or less with respect to 15°C as the standard.

8. The thermal diffusion sheet according to any one of claims 1 to 7, The volume resistance of the entire laminate is 1×10 12 A thermal diffusion sheet having a dielectric strength of Ω·cm or more, an AC breakdown voltage of 2.5 kV or more, and a DC breakdown voltage of 4.5 kV or more.

9. The thermal diffusion sheet according to any one of claims 1 to 8, A thermal diffusion sheet is used by being sandwiched between objects that repeatedly expand and contract.

10. A thermal diffusion sheet for insulating between a plurality of secondary battery cells that are stacked and connected in series and / or parallel to each other, An intermediate layer including inorganic fibers; surface layers laminated on both sides of the intermediate layer so as to sandwich the intermediate layer; Equipped with The thermal conductivity of the intermediate layer is 1.7 W / m K or less in the surface direction and 0.14 W / m K or less in the thickness direction, A thermal diffusion sheet, wherein the thermal conductivity of the surface layer is 120 W / m·K or more in the surface direction and 3 W / m·K or less in the thickness direction.

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