JP7837862B2 - Insulation sheet - Google Patents

Description

This invention relates to an insulating sheet.

Sheet materials with thermal insulation properties are used in a variety of applications, such as spacers for insulating and insulating secondary battery cells, explosion-proof sheets, and sheets for covering components with temperature differences, such as refrigerators. As an example, we will explain spacers for insulating secondary battery cells. Power supply units, which consist of multiple stacked rectangular secondary battery cells, are used as power sources for electric vehicles such as electric cars, hybrid cars, electric buses, and trains, as backup power sources for factories and base stations, and even as home storage batteries. In recent years, there has been a demand for lighter and higher-capacity power supply units, and high-capacity types such as lithium-ion secondary batteries are being used for secondary battery cells.

On the other hand, when using a large number of high-capacity secondary battery cells, such as lithium-ion secondary batteries, there is a concern that one secondary battery cell may overheat and undergo thermal runaway for some reason, adversely affecting other adjacent secondary battery cells. Therefore, thermal insulation between adjacent secondary battery cells is required.

Conventionally, spacers or separators, such as plates made of solidified inorganic powders like sepiolite or mica, or insulating resin plates, have been placed between secondary battery cells to provide insulation and heat retention. However, these plates are rigid and hardly deform, which poses a problem as they cannot follow the deformation of the secondary battery cells. Specifically, it is known that the outer casing of prismatic secondary battery cells expands and contracts due to charging and discharging. In particular, the plates inserted between secondary battery cells need to individually follow the deformation of the secondary battery cells on both sides, as each cell deforms, and also need to be able to return to its original shape. Furthermore, as the capacity of secondary battery cells increases, the amount of deformation of each outer casing tends to increase as well.

Japanese Patent Publication No. 2018-204708 Patent No. 6506942

This invention was made in view of the above background, and one of its objectives is to provide a thermal insulation sheet with improved conformability to deformation.

Means for solving the problem and the effects of the invention

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.

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%.

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.

Furthermore, according to the fourth embodiment of the heat-insulating sheet, in addition to any of the above configurations, the inorganic fiber is one of glass fiber, ceramic fiber, carbon fiber, basalt fiber, silica fiber, or rock wool. This configuration allows for flame retardancy and compression recovery.

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: an acrylic adhesive, a vinyl chloride adhesive, a vinyl acetate adhesive, a phenolic resin, or a hot melt adhesive.

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.

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.

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

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.
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Furthermore, according to the tenth embodiment of the heat-insulating sheet, in addition to any of the above configurations, the initial thickness of the heat-insulating sheet before the compression test can be set to 3 mm to 6 mm.

This is an exploded perspective view showing a power supply device according to Embodiment 1 of the present invention. This is a schematic cross-sectional view of an insulating sheet. This is an exploded perspective view showing a power supply device according to Embodiment 2 of the present invention. This is an exploded perspective view showing a power supply device according to Embodiment 3 of the present invention. This is a perspective view showing a power supply device according to Embodiment 4 of the present invention. Figure 6A is a perspective view showing a power supply device according to Embodiment 5 of the present invention, and Figure 6B is a perspective view showing a power supply device with a secondary battery cell positioned horizontally. This graph shows the results of repeated compression tests performed at -30°C on the heat insulating sheet according to Example 1. This graph shows the results of repeated compression tests performed at 0°C on the heat insulating sheet according to Example 1. This graph shows the results of repeated compression tests performed at 23°C on the heat insulating sheet according to Example 1. This graph shows the results of repeated compression tests performed at 60°C on the heat insulating sheet according to Example 1. This graph shows the results of repeated compression tests performed on the thermal insulation sheet according to Comparative Example 1. This graph shows the results of repeated compression tests performed on the thermal insulation sheet according to Comparative Example 2. This graph shows the creep characteristics of the heat insulating sheet according to Example 1. This graph shows the rate of change in stress when the thermal insulation sheet according to Example 1 is subjected to repeated compression tests at -30°C. This graph shows the rate of change in stress when a repeated compression test is performed at 0°C on the heat insulating sheet according to Example 1. This graph shows the stress change rate when the thermal insulation sheet according to Example 1 is subjected to repeated compression tests at 23°C. This graph shows the rate of change in stress when the thermal insulation sheet according to Example 1 is subjected to repeated compression tests at 60°C. This graph shows the stress change rate when the thermal insulation sheet according to Comparative Example 1 is subjected to five repeated compression tests at 23°C. This graph shows the stress change rate when the thermal insulation sheet according to Comparative Example 2 was subjected to five repeated compression tests at 23°C.

Embodiments of the present invention will be described below with reference to the drawings. However, the embodiments shown below are illustrative examples for realizing the technical concept of the present invention, and the present invention is not limited to these. Furthermore, this specification does not limit the members shown in the claims to 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 to those, unless otherwise specified, but are merely illustrative examples. Note that the size and positional relationships of the members shown in each drawing may be exaggerated for clarity of explanation. Furthermore, in the following description, the same name and reference numerals indicate the same or similar members, and detailed explanations are omitted as appropriate. Furthermore, each element constituting the present invention may be configured such that multiple elements are made of the same material, with one material serving multiple elements, or conversely, the function of one material can be shared among multiple materials.
[Embodiment 1]

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, and also as a storage battery for homes.

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 position where 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.

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 upper 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)

An insulating sheet 10 is interposed 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.

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.

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.

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 preferable from the viewpoint of compression recovery. More preferably, they should be 40 mm or longer, and even more preferably, uncut long fibers.
(Surface layer 12)

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)

The intermediate layer 11 and the surface layer 12 are bonded together with an adhesive. The cured adhesive layer 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.

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.

The thickness of the heat-insulating sheet 10 is preferably thin. In particular, miniaturization and weight reduction are strongly desired in power supply devices. Here, the thickness of the heat-insulating sheet 10 is preferably 3 mm to 6 mm.

The heat insulating 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 heat insulating sheet to deform in accordance with the deformation of the objects, such as secondary battery cells, when used in applications where the heat insulating sheet is sandwiched between objects that repeatedly expand and contract. Thus, it is possible to exhibit suitable heat insulating performance even for such deforming objects. During the compression test, the heat insulating sheet is set to be compressed to approximately 25% to 50% of its initial thickness.

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 maintains a stress of 80% or more even on the fifth test, thus maintaining its conformability. Therefore, it can effectively provide thermal insulation performance when used in applications where the thermal insulation sheet is sandwiched between objects that repeatedly expand and contract.

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.

The heat-insulating sheet 10 has a low thermal conductivity, which prevents heat from spreading to secondary battery cells 20 on the opposite side, even if a secondary battery cell 20 in close contact with one side of the heat-insulating sheet 10 experiences thermal runaway. 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.

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.

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 suitably used as the natural pulp.

The blending ratio of hemp pulp is, for example, 5% to 20% by weight, preferably 10% by weight. Inorganic fibers may also be included as a 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 inorganic fiber.

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 exhibits effects such as shape retention and improved heat insulation under high-temperature atmospheres. In Embodiment 1, highly flexible talc was used. The amount of filler added to the heat 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.

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 a rubber composition is used as a binder, the amount of rubber added to the heat insulating sheet is preferably 2.0 to 30% by weight. In this case, 6.0% by weight of Nipol 1562, an NBR (Non-British Rubber) from Nippon Zeon Co., Ltd., is added.

Furthermore, chemicals such as paper strength agents, fixatives, and defoamers are added as additives. In this case, 0.5% by weight of WS4030 from Seikoh PMC is added as a paper strength agent, 0.3% by weight of Kogum 15H from Showa Denko 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 KM-70 from Shin-Etsu Silicone is added as an defoamer.
[Embodiment 2]

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 material 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 material 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 from 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. 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.

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 the explosion-proof valve 24 formed in the sealing plate of each secondary battery cell 20. This protects the circuit board 60 from high-temperature and high-pressure gas.

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 in which multiple secondary battery cells 20 are stacked. By providing heat insulating material 10X between these battery modules, heat transfer between adjacent battery modules can be suppressed.

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, although 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]

Next, a heat insulating sheet according to Example 1 was prepared and its properties were measured. The heat insulating 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 used a paper sheet made by papermaking with 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 as an 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)

Repeated compression tests were performed on the created 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 a predetermined compression depth was reached. Details are provided below.

First, before 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 restoration position 0). After this pre-compression, the repeated compression test was performed. The measurement started from the pre-compression restoration position 0 described above. The measuring device and load area were the same as in the pre-compression test. 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.

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.

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 cannot follow the deformation of the secondary battery cell.

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)

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 performed.

The graph in Figure 13 shows that plastic deformation does not occur even under sustained pressure, and good creep characteristics are obtained. In this way, by adding a fibrous intermediate layer 11 in addition to the paper sheet, it is possible to realize a heat insulating sheet with enhanced creep resistance, and in particular, it can be used as a spacer for secondary battery cells that are exposed to compressive pressure for a long period of time, as it can recover and conform to the shape even if it deforms.
(Stress change rate)

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 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 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 insulation board according to Comparative Example 2 was subjected to 5 repeated compression tests at 23°C, respectively. In Figure 18, the rate of change in stress when the glass wool according to Comparative Example 1 was used was subjected to 5 repeated compression tests at 23°C, and Figure 19 shows the rate of change in stress when the insulation board according to Comparative Example 2 was similarly subjected to 5 repeated compression tests at 23°C. 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.

As shown in these figures, in 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 example using glass wool according to Comparative Example 1, 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 example at -30°C 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 compression deformation and filled the gaps in the inorganic fibers. Also, in the environment of 60°C 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 placing the adhesive in a 60°C environment caused a slight cross-linking reaction, resulting in a slight increase in its elastic modulus.

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 on-board 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, as secondary battery cells repeatedly expand and contract due to charging and discharging, 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 restorative force during compression and exhibits stability that allows it to return to its original shape even when deformed by compressed 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.

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.

100, 200, 300, 400, 500A, 500B... Power supply unit 10, 10X, 10A, 10B... Insulation sheet 11... Intermediate layer 12... Surface layer 20, 20B... Secondary battery cell 21... Outer casing 22... Sealing plate 23... Electrode 24... Explosion-proof valve 25... Battery stack 30... End plate 32... Cushioning sheet 40... Base plate 50... Gas duct 60... Circuit board

Claims (8)

An insulating sheet interposed between secondary battery cells or between secondary battery cell modules,
An intermediate layer having inorganic fibers (excluding biodegradable fibers),
The system comprises a paper surface layer laminated on both sides, sandwiching the aforementioned intermediate layer.
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%) . 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. 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. 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. 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. 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. 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. 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.