Insulation sheet

Abstract

Provided is a thermal insulation sheet with increased followability to deformation. The thermal insulation sheet 10 comprises: an intermediate layer 11 containing inorganic fibers; and paper superficial layers 12 that are stacked on both surfaces of the intermediate layer 11 so as to have said intermediate layer 11 sandwiched therebetween. When the thermal insulation sheet is subjected to five rounds of repeated compression test in which FS load is measured by pressing said sheet to a depth of 0-1.5 mm under a temperature range from -40°C to 60°C, the test shows an FS load of 1000-6000 N at a depth of 1.5 mm. With this configuration, this thermal insulation sheet is able to achieve the property that undergoes little stress variation during a compression-restoration test where the sheet is subjected to iterations of stress variation over a wide temperature range.

Description

Technical Field

[0001] The present invention relates to a heat insulating sheet.

Background Art

[0002] Sheet materials having heat insulating properties are used in various applications, such as spacers for heat insulation and insulation of secondary battery cells, explosion-proof sheets, or sheet materials for covering members with temperature differences such as refrigerators. As an example, the heat insulating spacer for secondary battery cells will be described. A power supply device in which a plurality of rectangular secondary battery cells are stacked is used as a driving power supply for electric vehicles such as electric cars, hybrid cars, electric buses, and trains, or as a backup power supply for factories and base stations, and further as a household storage battery. In recent years, there has been a demand for weight reduction and high capacity of power supply devices, and high-capacity types such as lithium-ion secondary batteries are used for secondary battery cells.

[0003] On the other hand, when a large number of high-capacity secondary battery cells such as lithium-ion secondary battery cells are used, there is a concern that one secondary battery cell may become hot and thermally runaway for some reason, which may have an adverse effect on other adjacent secondary battery cells. Therefore, it is required to thermally insulate adjacent secondary battery cells from each other.

[0004] Conventionally, between secondary battery cells, a plate material obtained by solidifying inorganic powders such as sepiolite and mica, called spacers and separators, or an insulating resin plate, etc. have been arranged to achieve insulation and heat insulation between adjacent secondary battery cells. However, since these plate materials are hard and hardly deform, there is a problem that they cannot follow the deformation of secondary battery cells. That is, it is known that the exterior cans of rectangular secondary battery cells expand and contract due to charge and discharge. In particular, the plate material inserted between secondary battery cells needs to individually follow the deformation on both sides because the secondary battery cells arranged on both sides deform, and it is also required to restore to the original shape. In addition, due to the high capacity of secondary battery cells, the amount of deformation of each exterior can tends to increase.

Prior Art Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2018-204708 [Patent Document 2] Patent No. 6506942 [Overview of the project] [Problems that the invention aims to solve]

[0006] This invention was made in view of the above background, and one of its objectives is to provide a heat insulating sheet with improved conformability to deformation. Means for solving the problem and effects of the invention

[0007] According to the first embodiment of the present invention, the heat insulating sheet comprises an intermediate layer having inorganic fibers and a paper surface layer laminated on both sides so as to sandwich the intermediate layer. In a repeated compression test performed five times in an environment with a temperature of -40°C to 60°C, the FS load measured by pressing to a depth of 0 to 1.5 mm is 1000 N or more and 6000 N or less. With the above configuration, it is possible to achieve the characteristic of small stress change in compression recovery tests over a wide temperature range in response to repeated stress changes.

[0008] Furthermore, according to the second embodiment of the heat insulating sheet, it comprises a paper surface layer laminated on both sides so as to sandwich the intermediate layer, and when a repeated compression test is performed five times in an environment with a temperature of -40°C to 60°C, pressing to a depth of 0 to 1.5 mm and measuring the FS load, the stress of the fifth measurement is 80% or more, with the stress of the first measurement being taken as 100%.

[0009] Furthermore, according to the third embodiment of the heat insulating sheet, in addition to the above configuration, the inorganic fibers are long fibers with an average fiber diameter of 6 μm or more and 40 μm or less, and an average fiber length of 13 mm or more.

[0010] Furthermore, according to the fourth embodiment of the heat-insulating sheet, in addition to any of the above configurations, the inorganic fibers are one of glass fibers, ceramic fibers, carbon fibers, basalt fibers, silica fibers, or rock wool. With the above configuration, flame retardancy and compression recovery properties can be achieved.

[0011] Furthermore, according to the fifth embodiment of the heat insulating sheet, in addition to any of the above configurations, the adhesive layer that bonds the intermediate layer and the surface layer is one of the following: acrylic adhesive, vinyl chloride adhesive, vinyl acetate adhesive, phenolic resin, or hot melt.

[0012] Furthermore, according to the sixth embodiment of the heat insulating sheet, in addition to any of the above configurations, the intermediate layer is constructed by laminating multiple layers of inorganic fibers.

[0013] Furthermore, according to the seventh embodiment of the heat insulating sheet, in addition to any of the above configurations, the surface layer contains inorganic powder or inorganic fibers.

[0014] Furthermore, according to the eighth embodiment of the heat insulating sheet, in addition to any of the above configurations, the heat insulating sheet is used by being sandwiched between objects that repeatedly expand and contract. As a result, even when the object to be insulated deforms, the sheet can follow the deformation and adhere tightly, thus reliably exhibiting heat insulating performance.

[0015] Furthermore, according to the ninth embodiment of the heat insulating sheet, in addition to any of the above configurations, the heat insulating sheet is for insulating between a plurality of secondary battery cells that are connected in series and / or parallel and stacked together, and comprises an intermediate layer containing inorganic fibers and surface layers stacked on both sides so as to sandwich the intermediate layer, and when a repeated compression test is performed five times in an environment with a temperature of -40°C to 60°C, pressing to a depth of 0 to 1.5 mm and measuring the FS load, the FS load at 1.5 mm is 1000 N or more and 6000 N or less. ru.

[0016] Furthermore, according to the heat insulation sheet according to the tenth aspect, in addition to any of the above configurations, the initial thickness of the heat insulation sheet before the compression test can be set to 3 mm to 6 mm.

Brief Description of the Drawings

[0017] [Figure 1] It is an exploded perspective view showing a power supply device according to Embodiment 1 of the present invention. [Figure 2] It is a schematic cross-sectional view of a heat insulation sheet. [Figure 3] It is an exploded perspective view showing a power supply device according to Embodiment 2 of the present invention. [Figure 4] It is an exploded perspective view showing a power supply device according to Embodiment 3 of the present invention. [Figure 5] It is a perspective view showing a power supply device according to Embodiment 4 of the present invention. [Figure 6] FIG. 6A is a perspective view showing a power supply device according to Embodiment 5 of the present invention, and FIG. 6B is a perspective view showing a power supply device with a secondary battery cell in a horizontal posture. [Figure 7] It is a graph showing the results of repeatedly performing a compression test on the heat insulation sheet according to Example 1 at -30°C. [Figure 8] It is a graph showing the results of repeatedly performing a compression test on the heat insulation sheet according to Example 1 at 0°C. [Figure 9] It is a graph showing the results of repeatedly performing a compression test on the heat insulation sheet according to Example 1 at 23°C. [Figure 10] It is a graph showing the results of repeatedly performing a compression test on the heat insulation sheet according to Example 1 at 60°C. [Figure 11] It is a graph showing the results of repeatedly performing a compression test on the heat insulation sheet according to Comparative Example 1. <于 [Figure 12] It is a graph showing the results of repeatedly performing a compression test on the heat insulation sheet according to Comparative Example 2. [Figure 13] It is a graph showing the creep characteristics of the heat insulation sheet according to Example 1. [Figure 14]It is a graph showing the stress change rate when a repeated compression test is performed at -30°C on the heat insulation sheet according to Example 1. [Figure 15] It is a graph showing the stress change rate when a repeated compression test is performed at 0°C on the heat insulation sheet according to Example 1. [Figure 16] It is a graph showing the stress change rate when a repeated compression test is performed at 23°C on the heat insulation sheet according to Example 1. [Figure 17] It is a graph showing the stress change rate when a repeated compression test is performed at 60°C on the heat insulation sheet according to Example 1. [Figure 18] It is a graph showing the stress change rate when a repeated compression test is performed 5 times at 23°C on the heat insulation sheet according to Comparative Example 1. [Figure 19] It is a graph showing the stress change rate when a repeated compression test is performed 5 times at 23°C on the heat insulation sheet according to Comparative Example 2.

Mode for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present invention will be described based on the drawings. However, the embodiments shown below are examples for embodying the technical idea of the present invention, and the present invention is not limited to the following. Also, this specification does not in any way specify the members shown in the claims as the members of the embodiments. In particular, the dimensions, materials, shapes, relative arrangements, etc. of the components described in the embodiments are not intended to limit the scope of the present invention only to those, unless specifically described, but are merely illustrative examples. Note that the sizes and positional relationships of the members shown in each drawing may be exaggerated for clarity of explanation. Further, in the following description, the same names and reference numerals indicate the same or similar members, and detailed descriptions will be omitted as appropriate. Furthermore, each element constituting the present invention may be configured such that a plurality of elements are constituted by the same member and one member serves as a plurality of elements, or conversely, the function of one member may be shared by a plurality of members and realized. [Embodiment 1]

[0019] The heat insulating sheet according to the embodiment of the present invention can be used as appropriate for applications requiring heat insulating properties. For example, it can be used as an insulating material for insulating refrigerators and freezers, or as an insulating sheet for building materials. Here, we will describe an example in which the heat insulating sheet is used as a spacer interposed between adjacent secondary battery cells in a power supply device in which many rectangular secondary battery cells are stacked and connected in series or parallel. Such a power supply device is used as a 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.

[0020] A power supply device according to Embodiment 1 is shown in the exploded perspective view of Figure 1. The power supply device 100 shown in this figure comprises a plurality of secondary battery cells 20 and an insulating sheet 10 interposed between the secondary battery cells 20. The secondary battery cells 20 have a bottomed cylindrical rectangular outer casing 21, and a plurality of them are stacked in a manner in which their main surfaces face each other. The stacking is done, for example, by covering both ends of the battery stack 25, which is made up of stacked secondary battery cells 20, with end plates 30, and fastening the end plates 30 together with fastening members. The battery stack 25 is also fixed on a base plate 40 as needed. The base plate 40 can function as a cooling plate by circulating a refrigerant inside, for example.

[0021] Each secondary battery cell 20 houses its electrode body inside the outer casing 21, and its open end is sealed with a sealing plate 22. In Figure 1, the sealing plate 22 located on the top surface of the outer casing 21 is provided with a pair of electrodes 23 and an explosion-proof valve 24. Multiple secondary battery cells 20 are electrically connected to each other in series and / or parallel by connecting the electrodes 23 with busbars. The explosion-proof valve 24 is a component that opens when it detects an increase in the internal pressure of the outer casing 21, and is used to discharge the high-pressure gas inside the outer casing 21. Each explosion-proof valve 24 is connected to a gas duct to guide the high-pressure gas to the outside as needed. (Insulation sheet 10)

[0022] An insulating sheet 10 is placed between adjacent secondary battery cells 20. The insulating sheet 10, also known as a spacer or separator, insulates the outer casing 21 from short-circuiting between adjacent secondary battery cells 20.

[0023] A cross-sectional view of the insulation sheet 10 is shown in Figure 2. The insulation sheet 10 shown in this figure consists of an intermediate layer 11 and surface layers 12 laminated on both sides, sandwiching the intermediate layer 11.

[0024] The intermediate layer 11 contains inorganic fibers. Suitable inorganic fibers include glass fibers, ceramic fibers, carbon fibers, basalt fibers, silica fibers, and rock wool. Among these, glass fibers and ceramic fibers are preferred from the viewpoint of heat resistance and insulation. Carbon fibers can be used in applications where thermal insulation and insulation are not required. This results in a thermal insulation sheet with excellent flame retardancy.

[0025] This intermediate layer 11 may consist of a single layer, or it may be constructed by laminating multiple layers of glass fiber or ceramic fiber. Furthermore, inorganic fibers with a fiber length of 13 mm or more are preferably used from the viewpoint of compression recovery. More preferably, they are 40 mm or longer, and even more preferably, they are uncut long fibers. (Surface layer 12)

[0026] The surface layer 12 is made of an insulating paper sheet material. Suitable materials for such a surface layer 12 include paper sheets made from natural pulp, synthetic pulp, inorganic fibers, and inorganic powders. The surface layer 12 may also contain inorganic powders or inorganic fibers. Suitable inorganic powders include silicate minerals such as sepiolite, talc, kaolin, mica, and sericite, 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. Suitable inorganic fibers include glass fibers, microglass, ceramic fibers, rock wool, basalt fibers, and carbon fibers. (adhesive layer)

[0027] The intermediate layer 11 and the surface layer 12 are bonded together with an adhesive. The bonded layer, formed by curing the adhesive, is interposed between the intermediate layer 11 and the surface layer 12. The adhesive is preferably made of a material with excellent heat resistance. Suitable adhesives include acrylic adhesives, vinyl chloride adhesives, vinyl acetate adhesives, phenolic resins, and hot melt adhesives.

[0028] By constructing the intermediate layer 11 with fibers in this way, the insulation sheet can be made lighter than if it were made of thick paper. For example, while the specific gravity of a paper insulation sheet is about 1, the specific gravity of the insulation sheet 10 according to Embodiment 1 can be suppressed to 0.3 or less.

[0029] The thickness of the insulation sheet 10 is preferably thin. In particular, there is a strong demand for miniaturization and weight reduction in power supply devices. Here, the thickness of the insulation sheet 10 is preferably 3 mm to 6 mm.

[0030] The thermal insulation sheet 10 according to Embodiment 1 is subjected to five repeated compression tests in an environment of -40°C to 60°C, where it is pressed to a depth of 0 to 1.5 mm and the FS load is measured. The FS load at 1.5 mm is set to be between 1000 N and 6000 N. This allows the thermal insulation sheet to deform in accordance with the deformation of the objects, such as secondary battery cells, when used in applications where the thermal insulation sheet is sandwiched between objects that repeatedly expand and contract. Thus, it is possible to exhibit suitable thermal insulation performance even for such deforming objects. During the compression test, the thermal insulation sheet is set to be compressed to approximately 25% to 50% of its initial thickness.

[0031] Furthermore, when the thermal insulation sheet 10 underwent five repeated compression tests in an environment with a temperature of -40°C to 60°C, where it was pressed to a depth of 0 to 1.5 mm and the FS load was measured, the stress on the fifth test was 80% or more, compared to the stress on the first test which was set to 100%. This means that, while normally the stress decreases and the conformability deteriorates with each repetition, the thermal insulation sheet according to this embodiment can maintain conformability by exhibiting a stress of 80% or more even on the fifth test. Therefore, it can effectively exhibit thermal insulation performance in applications where the thermal insulation sheet is sandwiched between objects that repeatedly expand and contract.

[0032] Furthermore, it is desirable that the heat-insulating sheet 10 has heat resistance. By using a material that is resistant to deformation and melting even when the secondary battery cell 20 reaches high temperatures, it is possible to maintain the heat-insulating performance. Preferably, the melting temperature of the heat-insulating sheet 10 is 400°C or higher. More preferably, it is 600°C or higher.

[0033] The heat insulating sheet 10 has a low thermal conductivity, so that even if a secondary battery cell 20 in close contact with one side of the heat insulating sheet 10 experiences thermal runaway, the heat generated will not spread to the secondary battery cell 20 on the opposite side. The thermal conductivity of the heat insulating sheet 10 is preferably 0.03 to 0.30 W / mK. More preferably, the thermal conductivity is 0.05 to 0.25 W / mK.

[0034] To satisfy the above characteristics, the surface layer 12 of the heat insulating sheet 10 includes a fibrous base material, a filler, and a binder. Preferably, natural pulp and inorganic fibers can be used as the fibrous base material, silicate minerals as the filler, and a rubber composition as the binder. Specifically, the heat insulating sheet 10 according to Embodiment 1 includes hemp pulp and microglass as the fibrous base material, talc and sepiolite as the filler, and NBR as the binder.

[0035] The fibrous base material (also called the base fiber) can be inorganic fibers such as glass fibers, carbon fibers, or ceramic fibers, or organic fibers such as aromatic polyamide fibers or polyethylene fibers. Here, natural pulp of organic fibers is used as the fibrous base material. Hemp pulp is preferably used as the natural pulp.

[0036] The blending ratio of hemp pulp is, for example, 5% to 20% by weight, preferably 10% by weight. In addition, inorganic fibers may be included as the fibrous base material. The blending ratio of inorganic fibers is 5% to 20% by weight, preferably 8% to 15% by weight. In Embodiment 1, 12% by weight of microglass is added as the inorganic fiber.

[0037] Inorganic fillers can be used. Examples of inorganic fillers include silicate minerals such as sepiolite, talc, kaolin, mica, and sericite; 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. These can be used individually or in combination. The addition of these inorganic fillers has effects such as maintaining shape under high-temperature atmospheres and improving thermal insulation. In Embodiment 1, highly flexible talc was used. The amount of filler added to the thermal insulation sheet is preferably 10% to 75% by weight. In Embodiment 1, magnesium silicate was used as the filler, with 58% by weight of talc and 14% by weight of sepiolite added.

[0038] As binders, synthetic resins such as polyvinyl 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 phenolic resin can be used, as well as 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, polyethylene chloride, butyl chloride rubber, epichlorohydrin rubber, nitrile isoprene rubber, natural rubber, and isoprene rubber can be used. Among these, acrylonitrile butadiene rubber (NBR) is preferred due to its high water and oil resistance. These rubbers can be used individually or in combination of two or more. Furthermore, sizing agents such as alkyl ketene dimers and fluorine-based or silicone-based water repellents can be used in combination for even higher water and oil resistance. When using a rubber composition as a binder, the amount of rubber added to the heat insulating sheet is preferably 2.0 to 30% by weight. Here, 6.0% by weight of Nipol 1562, an NBR (non-woven rubber) from Zeon Corporation, is added.

[0039] Furthermore, chemicals such as paper strength agents, fixatives, and defoamers are added as additives. In this case, 0.5% by weight of Seikoh PMC's WS4030 is added as a paper strength agent, 0.3% by weight of Showa Denko's Kogum 15H is added as a paper strength agent, 1.9% by weight of aluminum sulfate manufactured in-house is added as a fixative, and an appropriate amount of Shin-Etsu Silicone's KM-70 is added as an defoamer. [Embodiment 2]

[0040] The above describes an example of using a heat-resistant sheet as a spacer between lithium-ion secondary battery cells. However, the present invention does not limit the use of the heat-insulating sheet to spacers for insulating batteries, but can be used for other purposes as well. The present invention has heat resistance and its characteristic of having little fluctuation in thermal conductivity, making it suitable for applications where reliability is required. Furthermore, because of its low compressive modulus, it can be suitable for applications where deformation is required. For example, it can be used as a buffer between the explosion-proof valve and gas duct of a secondary battery cell, as a protective insulation material for circuit boards, and as insulation material between modules. As an example, an example in which a heat-insulating sheet is used as a buffer between the explosion-proof valve and gas duct of a secondary battery cell is shown in the exploded perspective view of Figure 3 as a power supply device according to Embodiment 2. In the power supply device 200 shown in this figure, a gas duct 50 is provided on the upper surface of a battery stack 25 in which a plurality of secondary battery cells 20 are stacked. The gas duct 50 is in communication with the explosion-proof valve 24 of each secondary battery cell 20. A buffer sheet 32 ​​is interposed to airtightly connect each explosion-proof valve 24 to the gas duct 50. The heat insulating sheet 10 according to the embodiment is used as this buffer sheet 32. In Figure 3, the same reference numerals are used for the same components as those described in Embodiment 1 above, and detailed descriptions are omitted as appropriate. The heat insulating sheet 10, which functions as a buffer sheet 32, connects to the connection holes of each explosion-proof valve 24 and the gas duct 50. In the event of thermal runaway, the heat insulating sheet 10 can be used to airtightly connect the explosion-proof valve 24 and the gas duct 50 to prevent high-pressure gas from leaking between them. In particular, the heat insulating sheet 10 according to the embodiment can be appropriately deformed due to its high compressive modulus. In addition, it has high heat resistance that can withstand high temperature and high pressure gas, and can be suitably used in such applications. Even in the event of thermal runaway, it can stably guide the high-pressure gas into the gas duct 50 and discharge it to the outside of the power supply unit, thereby enhancing safety.

[0041] Furthermore, the power supply device 300 according to Embodiment 3 shown in Figure 4 shows an example in which the heat insulating sheet 10 is used as a protective heat insulating material for the circuit board. In the power supply device 300 shown in this figure, a circuit board 60 is provided on the upper surface of a battery stack 25 in which a plurality of secondary battery cells 20 are stacked. A heat insulating sheet 10 is interposed between the circuit board 60 and the battery stack 25 to protect the circuit board 60 from the scattering of high-temperature gas and electrolyte released from explosion-proof valves 24 formed in the sealing plates of each secondary battery cell 20. This protects the circuit board 60 from high-temperature and high-pressure gases.

[0042] Furthermore, the heat insulating sheet can be used not only for insulating between secondary battery cells, but also for insulating between battery modules composed of multiple secondary battery cells. An example of this is shown in Figure 5 as a power supply device according to Embodiment 4. The power supply device 400 shown in this figure has a battery module composed of a battery stack 25 made up of multiple secondary battery cells 20 stacked on top of each other. By providing heat insulating material 10X between these battery modules, heat transfer between adjacent battery modules can be suppressed.

[0043] The above examples describe the application of the thermal insulation material to secondary battery cells using a rectangular outer casing. However, the present invention is not limited to the rectangular shape of secondary battery cells and can be applied to secondary battery cells of other shapes, such as cylindrical or pouch-type cells. As an example, an example of application to cylindrical secondary battery cells is shown in Figure 6A as a power supply device according to Embodiment 5. In the power supply device 500A shown in this figure, multiple cylindrical secondary battery cells 20B are arranged side by side, with thermal insulation sheets 10 interposed between adjacent secondary battery cells. As a result, even if any of the secondary battery cells 20B become hot, heat transfer can be suppressed by the thermal insulation sheets 10. In this example, in order to partition each secondary battery cell 20B, a cut is formed from one end of one thermal insulation sheet 10A and a cut is formed from the other end of another thermal insulation sheet 10B, and these cuts are combined so that the thermal insulation sheets intersect. Furthermore, while the secondary battery cell 20B is positioned vertically in the example shown in Figure 6A, it goes without saying that it can also be positioned horizontally, as shown in Figure 6B. [Example 1]

[0044] Next, a thermal insulation sheet according to Example 1 was prepared and its properties were measured. The thermal insulation sheet 10 according to Example 1 used glass fibers with an average fiber diameter of 30 μm and an average fiber length of 13 mm as the intermediate layer 11. The surface layer 12 was made of a paper sheet formed by papermaking using natural pulp, microglass, silicate mineral powder, and a rubber-based resin as a binder. To prepare the surface layer 12, first, disintegrated natural pulp was prepared, and microglass and silicate mineral powder were uniformly dispersed in it. A rubber-based resin was added to this, and papermaking was carried out using a wet papermaking method to create a surface layer 12 with a thickness of approximately 0.3 mm. On the other hand, the intermediate layer 11 was made by laminating six sheets of glass fiber paper to a thickness of approximately 4.0 mm. The surface layer 12 was bonded to both sides of the intermediate layer 11 obtained in this way using an acrylic adhesive and then cured. The obtained sheet was cut to a size of 70 mm x 70 mm. The thickness was approximately 5.0 mm. (Repeated compression test)

[0045] Repeated compression tests were performed on the prepared insulation sheet samples under different temperatures. In the repeated compression tests, the sample was compressed at a constant speed, and the pressure on the sample at each compression depth, i.e., the rebound force, was measured as the FS (Force-Strain) load until the compression depth reached a predetermined depth. Details are described below.

[0046] First, before measuring the repeated compression test, the sample was pre-compressed. For the pre-compression, an Instron 5985 universal material testing machine was used, with a load area of ​​50 mmφ. First, the sample was compressed at a speed of 0.1 mm / min until it reached a load of 3.9 kN. After reaching a load of 3.9 kN, it was returned to a load of 0 at a speed of 0.1 mm / min. The device was then stopped at the load of 0 (this is designated as the pre-compression recovery position 0). After this pre-compression, the repeated compression test was performed. Measurement began from the pre-compression recovery position 0 described above. The measuring device and load area were the same as for the pre-compression. First, the sample was compressed at a speed of 0.1 mm / min until it reached a displacement of 1.5 mm. Next, it was returned from a displacement of 1.5 mm to a displacement of 0 mm at a speed of 0.5 mm / min. This procedure was repeated 20 times.

[0047] The results of the repeated compression tests conducted in this manner are shown in Figures 7 to 10. In these figures, Figure 7 was conducted at -30°C, Figure 8 at 0°C, Figure 9 at 23°C (corresponding to room temperature), and Figure 10 at 60°C.

[0048] Furthermore, Figure 11 shows an example of using a single layer of glass wool as the insulation sheet for Comparative Example 1, and Figure 12 shows an example of using a single layer of insulation board for Comparative Example 2. In Comparative Example 1, a 10 mm thick Glasslon Wool manufactured by Asahi Fiber Glass Co., Ltd., which is commercially available as an insulation material using glass wool, was used. In Comparative Example 2, a 3.1 mm thick insulation material manufactured by Promat Co., Ltd., which is made by forming inorganic fibers and powder into a board with a binder, was used. Measurements were taken at 23°C in each comparative example. In Comparative Example 2 shown in Figure 12, an overload occurred before the compressive deformation reached 1.5 mm, and the safety device of the device activated, stopping the measurement. This confirms that the insulation board in this comparative example could not follow the deformation of the secondary battery cell.

[0049] The graphs in Figures 7 to 10 confirm that the load increase is small even in regions with large displacement, and that a heat-insulating sheet with minimal stress change in repeated compression tests is obtained. In particular, Comparative Examples 1 and 2 showed a tendency for the FS load to increase sharply, indicating that it was difficult to exert a stable compressive force. In contrast, the heat-insulating sheet according to Example 1 was able to exert a resilient force. Furthermore, it showed particularly stable characteristics at low temperatures, and although it deteriorated somewhat at high temperatures, it was confirmed that stress changes could be suppressed over a wide temperature range in general. (Creep characteristics)

[0050] Furthermore, Figure 13 shows the results of measuring the creep characteristics of the thermal insulation sheet according to Example 1. Prior to the creep characteristic test, a preliminary compression of the sample was performed in the same manner as in the repeated compression test described above. After the preliminary compression, the creep characteristic test measurement was started from the preliminary compression recovery position 0. The evaluation device and load area used were the same as in the repeated compression test. The measurement temperature environment was 23°C. First, the sheet was compressed at a speed of 0.1 mm / min until the displacement reached 1.5 mm. Then, at a displacement of 1.5 mm, the speed was changed to 0 mm / min (stopped) and the measurement was taken.

[0051] The graph in Figure 13 shows that the sheet does not undergo plastic deformation even under sustained pressure, and good creep properties are achieved. Thus, by adding a fibrous intermediate layer 11 in addition to the paper sheet, it is possible to realize a thermal insulation sheet with enhanced creep resistance. In particular, it can be used as a spacer for secondary battery cells that are subjected to compressive pressure for long periods of time, as it can recover and conform to the shape even if it deforms. (Stress change rate)

[0052] Furthermore, in the repeated compression test described above, the change in stress with increasing number of repetitions was measured as the rate of change in stress. Here, under the same conditions as described above, Figures 14 to 19 show the results of 20 repeated compression tests for each case where the indentation depth was 1.5 mm and 1.0 mm. In these figures, Figure 14 shows the rate of change in stress when the thermal insulation sheet according to Example 1 was subjected to 20 repeated compression tests at -30°C, Figure 15 shows the rate of change in stress when the thermal insulation sheet according to Example 1 was subjected to 20 repeated compression tests at 0°C, Figure 16 shows the rate of change at 23°C, and Figure 17 shows the rate of change when the thermal insulation board according to Comparative Example 2 was subjected to 5 repeated compression tests at 23°C, respectively. In each graph, the stress of the first test is set to 100%, and the rate of change in stress at each number of compression tests is shown.

[0053] As shown in these figures, in the case of the thermal insulation sheet according to Example 1, it was confirmed that the stress remained at approximately 90% or higher after 20 repeated compression tests in an environment of -30°C to 60°C, where the sheet was pressed to a depth of 0 to 1.5 mm. On the other hand, in the case of Comparative Example 1, which used glass wool, the stress fell to less than 80% after 5 repetitions. This confirms that, unlike Comparative Example 1, where the stress gradually decreased and the conformability deteriorated with increasing repetitions, the thermal insulation sheet according to Example 1 maintained high stress and conformability even after 20 repetitions. In the -30°C example shown in Figure 14, the stress change rate exceeded 100% from around the 12th repetition. This is presumed to be because the adhesive, which became brittle and glassy at low temperatures, cracked due to compressive deformation and filled the gaps in the inorganic fibers. Also, in the 60°C environment shown in Figure 17, the stress exceeded 100% from the 2nd to the 6th repetition. Although the reason for this is unverified, it is presumed that a slight cross-linking reaction occurred in the adhesive when placed in a 60°C environment, causing a slight increase in the elastic modulus.

[0054] As described above, the heat insulating sheet according to the embodiment of the present invention offers the advantage of being usable stably with high reliability. In particular, when used as a spacer for secondary battery cells used in automotive power supply devices, temperature characteristics that can maintain performance over a wide temperature range from low to high temperatures are required so that the vehicle itself can withstand use in cold and high temperature regions. That is, secondary battery cells repeatedly expand and contract due to charging and discharging, and when using a heat insulating sheet as a spacer interposed in the gaps between such secondary battery cells, strength and compressive recovery that can withstand such expansion and contraction of secondary battery cells are required. Furthermore, temperature characteristics that can maintain such performance from low to high temperatures are required. As described above, the heat insulating sheet according to the embodiment enhances the recovery force during compression and exhibits stability that allows it to return to its original shape even when deformed under compressive pressure. In addition, it suppresses temperature changes under load during repeated compression tests and can exhibit highly reliable heat insulating performance, thus providing the excellent advantage of being usable stably regardless of the ambient temperature. [Industrial applicability]

[0055] The heat insulating sheet of the present invention can be suitably used as a heat insulating spacer interposed between secondary battery cells or between secondary battery cell modules, as a buffer sheet interposed between an explosion-proof valve and a gas duct, or as a heat insulating material to protect drive circuits such as ECUs. [Explanation of symbols]

[0056] 100, 200, 300, 400, 500A, 500B…Power supply 10, 10X, 10A, 10B… Insulation sheets 11…Middle class 12…Surface layer 20, 20B… Secondary battery cells 21…Outer can 22...Sealing plate 23...Electrode 24… Explosion-proof valve 25…Battery stack 30…End plate 32…Cushioning sheet 40...Foundation plate 50... Gas duct 60... Circuit board

Claims

1. An insulating sheet interposed between secondary battery cells or between secondary battery cell modules, An intermediate layer having inorganic fibers (excluding biodegradable fibers), A paper surface layer is laminated on both sides, sandwiching the aforementioned intermediate layer. Equipped with, A repeated compression test is conducted in an environment with a temperature of -30°C to 60°C, where the FS load is measured by pressing to a depth of 0 to 1.5 mm. When performed five times, the FS load at 1.5 mm was between 1000 N and 6000 N. An insulating sheet in which the stress after 20 cycles remains at 90% or more of the stress after the first cycle (with the stress after the first cycle being set to 100%).

2. The heat insulating sheet according to claim 1, The aforementioned inorganic fiber is a long fiber with an average fiber diameter of 6 μm or more and an average fiber length of 13 mm or more.

3. The heat insulating sheet according to claim 1 or 2, An insulating sheet in which the inorganic fiber is one of the following: glass fiber, ceramic fiber, carbon fiber, basalt fiber, silica fiber, or rock wool.

4. An insulating sheet according to any one of claims 1 to 3, An insulating sheet in which the adhesive layer that bonds the intermediate layer and the surface layer is one of the following: an acrylic adhesive, a vinyl chloride adhesive, a vinyl acetate adhesive, a phenolic resin, or a hot melt adhesive.

5. An insulating sheet according to any one of claims 1 to 4, The aforementioned intermediate layer is a thermal insulation sheet formed by laminating multiple layers of inorganic fibers.

6. An insulating sheet according to any one of claims 1 to 5, The aforementioned surface layer is a heat insulating sheet comprising inorganic powder or inorganic fibers.

7. An insulating sheet according to any one of claims 1 to 6, An insulating sheet used by being sandwiched between objects that repeatedly expand and contract.

8. A heat insulating sheet according to any one of claims 1 to 7, The aforementioned insulation sheet has an initial thickness of 3 mm to 6 mm before the compression test.

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