Heat transfer suppression sheet and secondary battery

Abstract

The present invention provides a heat transfer suppression sheet that can effectively suppress heat transfer and reduce secondary damage during thermal runaway of battery cells in a secondary battery, and a secondary battery including the heat transfer suppression sheet. [Solution] The heat transfer suppression sheet is a heat transfer suppression sheet for a secondary battery that contains inorganic fibers and inorganic particles, wherein the inorganic fibers include a first inorganic fiber which is a ceramic fiber and a second inorganic fiber which is a ceramic fiber and has a smaller average fiber diameter than the first inorganic fiber, and the inorganic particles include a first inorganic particle which is made of a metal hydroxide.

Description

Technical Field

[0001] The present disclosure relates to a heat transfer suppression sheet and a secondary battery including the heat transfer suppression sheet.

Background Art

[0002] Conventionally, in order to suppress secondary damage during abnormal heat generation or ignition (thermal runaway) of a secondary battery, a heat transfer suppression sheet has been provided inside the secondary battery or the like.

[0003] For example, Patent Document 1 discloses a heat transfer suppression sheet composed of two types of inorganic fibers having different glass transition points and two types of inorganic particles having different glass transition points.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the technique of Patent Document 1, when an inorganic fiber having a low glass transition point is selected as a material, it may be difficult to maintain the skeletal strength of the sheet when exposed to high temperatures. In addition, when an inorganic fiber having a low glass transition point melts, voids are generated between the fibers, and heat transfer due to the movement of air and penetration of flames may occur, resulting in a loss of heat insulation performance.

[0006] Therefore, the present disclosure provides a heat transfer suppression sheet that can effectively suppress heat transfer and suppress secondary damage during thermal runaway of a battery cell in a secondary battery, and a secondary battery including the heat transfer suppression sheet.

Means for Solving the Problems

[0007] In order to solve the above problems, one aspect of the heat transfer suppression sheet disclosed herein is A heat transfer suppression sheet for secondary batteries containing inorganic fibers and inorganic particles, The inorganic fiber is The first inorganic fiber is a ceramic fiber, The present invention comprises a ceramic fiber and a second inorganic fiber having a smaller average fiber diameter than the first inorganic fiber, The inorganic particles are a heat transfer suppression sheet containing first inorganic particles made of metal hydroxide.

[0008] According to this configuration, by including ceramic fibers with a high heat resistance temperature as inorganic fibers, the structure of the heat transfer suppression sheet can be maintained even when exposed to high temperatures such as approximately 1000°C or higher during thermal runaway of battery cells. Furthermore, the sheet structure is maintained by the first inorganic fibers with a large average fiber diameter, and the gaps between the first inorganic fibers are filled by the second inorganic fibers with a small average fiber diameter, thereby suppressing gas heat transfer and radiant heat transfer in the heat transfer suppression sheet. In addition, by including metal hydroxides, when exposed to high temperatures during thermal runaway, structural water can be released to extinguish fires, lower temperatures, or slow down temperature increases. In this way, when a battery cell of a secondary battery experiences thermal runaway, heat transfer can be effectively suppressed, and secondary damage due to high temperatures and ignition can be suppressed.

[0009] The first inorganic fiber and the second inorganic fiber are preferably at least one selected from the group consisting of alumina fiber, mullite fiber, zirconia fiber, alkali earth silicate fiber, and magnesium silicate fiber.

[0010] These ceramic fibers have high heat resistance and are effective in ensuring sufficient thermal insulation performance in heat transfer suppression sheets.

[0011] The first inorganic fiber is preferably an alumina fiber.

[0012] Alumina fibers are among the most heat-resistant ceramic fibers and have a low thermal shrinkage rate, making them advantageous for maintaining the sheet structure.

[0013] The average fiber diameter of the first inorganic fiber is preferably 5 μm or more and 7 μm or less.

[0014] According to this configuration, since the fiber is thick and rigid, high skeleton maintainability can be ensured.

[0015] The average fiber diameter of the second inorganic fiber is preferably 4 μm or less.

[0016] Since the fiber diameter is smaller than that of the first inorganic fiber, it exhibits the effect of a filler, improving the molding density.

[0017] Also, since the fiber length is longer than that of inorganic particles, it is difficult to fall off and has high papermaking (molding) property.

[0018] The decomposition temperature of the metal hydroxide is preferably 150°C or higher.

[0019] Since the decomposition temperature of the metal hydroxide is high, it does not decompose within the normal operating temperature range of the secondary battery, and a sufficient fire extinguishing / temperature reduction effect can be ensured in case of an abnormality.

[0020] The content of the inorganic particles is preferably larger than the content of the inorganic fiber in terms of mass ratio.

[0021] According to this configuration, by increasing the content of the inorganic particles, the heat transfer suppression sheet can be densified, and heat conduction due to flame penetration and air movement can be effectively suppressed.

[0022] The heat transfer suppression sheet further contains organic fibers, The organic fiber is preferably an aramid fiber.

[0023] By including organic fibers, the capture property of inorganic particles during the production of the heat transfer suppression sheet is improved. Also, aramid fiber is a flame-retardant fiber and does not ignite but only burns out even when exposed to high temperatures, so the safety of the secondary battery can be enhanced.

[0024] The content of the organic fiber is preferably 10% by mass or less.

[0025] Since the heat resistance temperature of aramid fiber is lower than that of ceramic fiber, from the viewpoint of ensuring sufficient heat resistance of the heat transfer suppression sheet, the content of aramid fiber is preferably within the above range.

[0026] One aspect of the secondary battery disclosed herein is a battery pack formed by connecting a plurality of battery cells in series or in parallel, and the above heat transfer suppression sheet disposed on at least one of the outer periphery of the plurality of battery cells and between each battery cell, and is a secondary battery.

[0027] According to this configuration, secondary damage due to high temperature and ignition during thermal runaway of the battery cell can be sufficiently suppressed.

Effect of the Invention

[0028] As described above, according to the present disclosure, when the battery cell of the secondary battery undergoes thermal runaway, heat transfer can be effectively suppressed, and secondary damage due to high temperature and ignition can be suppressed.

Brief Description of the Drawings

[0029] [Figure 1] Perspective view showing an example of the secondary battery according to the present disclosure. [Figure 2] Cross-sectional view taken along line II-II of FIG. 1. [Figure 3] View corresponding to FIG. 2 showing another example of the secondary battery according to the present disclosure. [Figure 4] Photograph showing the evaluation test results of the sample of the example. [Figure 5] Photograph showing the evaluation test results of the sample of the comparative example.

Modes for Carrying Out the Invention

[0030] Embodiments of the present disclosure will be described in detail below with reference to the drawings. The following description of preferred embodiments is illustrative in nature and is not intended to limit the present disclosure, its applications, or its uses in any way.

[0031] <Secondary battery> As shown in Figures 1 and 2, a battery 10, which is an example of a secondary battery according to this disclosure, includes a housing 12, a plurality of battery cells 14, and a heat transfer suppression sheet 16.

[0032] The housing 12 is positioned on the outer periphery of the structure consisting of the battery cell 14 and the heat transfer suppression sheet 16. For ease of understanding, the housing 12 is shown as a dashed line in Figures 1 and 2, and in Figure 3, which will be described later.

[0033] Multiple battery cells 14, although not shown in the diagram, are connected in series or parallel to form a single battery pack.

[0034] The configuration of the housing 12 and the battery cell 14 is not particularly limited as long as it is a configuration of housing and battery cell used in generally known secondary batteries such as lithium-ion secondary batteries, nickel-metal hydride storage batteries, lead-acid batteries, and NAS batteries. A detailed explanation of the configuration of the housing 12 and the battery cell 14 is omitted.

[0035] The heat transfer suppression sheet 16 is a heat transfer suppression sheet according to the present disclosure, and in the example shown in Figures 1 and 2, it is also placed between each battery cell 14 and on the outside of the battery cells 14, i.e., between the battery cells 14 and the housing 12.

[0036] With this configuration, even if the battery cell 14 experiences thermal runaway, the heat transfer suppression sheet 16 suppresses heat transfer between the battery cells 14 and from the battery cells 14 to the housing 12, thereby sufficiently suppressing secondary damage caused by high temperatures or ignition of the battery cells 14.

[0037] Furthermore, Figure 3 is a diagram corresponding to Figure 2 in another example of the secondary battery according to this disclosure. As shown in Figure 3, the heat transfer suppression sheet 16 may be placed on the outer periphery of the multiple battery cells 14, that is, between the upper ends of the four battery cells 14 and the housing 12. As a result, even if the battery cells 14 experience thermal runaway, the heat transfer suppression sheet 16 suppresses heat transfer from the battery cells 14 to the housing 12, thereby sufficiently suppressing secondary damage caused by high temperatures and ignition of the battery cells 14.

[0038] <Heat transfer suppression sheet> The heat transfer suppression sheet described herein is a heat transfer suppression sheet for secondary batteries that has excellent heat resistance and fire resistance. When a battery cell of a secondary battery experiences thermal runaway, this heat transfer suppression sheet can effectively suppress heat transfer and prevent secondary damage caused by high temperatures and ignition.

[0039] The heat transfer suppression sheet according to this disclosure contains inorganic fibers and inorganic particles. The heat transfer suppression sheet may also contain any organic fibers and any other components as needed.

[0040] In this specification, the first inorganic fiber, the second inorganic fiber, and the organic fiber may be collectively referred to as "fibers."

[0041] Furthermore, in this specification, the average fiber diameter and average fiber length of the fibers, and the average particle diameter of the inorganic particles are values ​​obtained by the measurement methods described in the examples below.

[0042] [Inorganic Fibers] The inorganic fiber includes a first inorganic fiber and a second inorganic fiber.

[0043] -Materials of the first and second inorganic fibers- The first and second inorganic fibers are ceramic fibers. By including ceramic fibers with high heat resistance, the structure of the heat transfer suppression sheet can be maintained even when exposed to high temperatures, such as 1000°C or higher.

[0044] In this specification, "ceramic fiber" includes oxide-based ceramic fibers mainly composed of alumina, silica, zirconia, etc., and non-oxide-based ceramic fibers mainly composed of silicon carbide, silicon nitride, etc. Specific examples of ceramic fibers, though not intended to be limiting, include alumina fibers, mullite fibers, zirconia fibers, alkali earth silicate fibers, magnesium silicate fibers, silica fibers, glass fibers, silicon carbide fibers, silicon nitride fibers, etc. The first inorganic fiber and the second inorganic fiber can each be one of these types alone or in combination of two or more types.

[0045] The first inorganic fiber and the second inorganic fiber are preferably at least one selected from the group consisting of alumina fiber, mullite fiber, zirconia fiber, alkali earth silicate fiber, and magnesium silicate fiber. These ceramic fibers have high heat resistance and are effective in ensuring sufficient thermal insulation performance in the heat transfer suppression sheet.

[0046] It is preferable to use ceramic fibers as the first inorganic fiber and the second inorganic fiber, each having at least one of the following: a melting point of 1500°C or higher and a maximum operating temperature of 900°C or higher. This ensures sufficient heat resistance of the heat transfer suppression sheet. Examples of such ceramic fibers include alumina fibers (melting point: 2050°C, maximum operating temperature: 1300-1600°C), mullite fibers (melting point: 1850°C, maximum operating temperature: 1200°C), and zirconia fibers (melting point: 2700°C, maximum operating temperature: 1000-1250°C).

[0047] The first inorganic fiber and the second inorganic fiber may be ceramic fibers of the same material, or they may be ceramic fibers of different materials. Preferably, the second inorganic fiber is a ceramic fiber of a different material than the first inorganic fiber.

[0048] The first inorganic fiber is more preferably an alumina fiber. Alumina fibers are among the most heat-resistant ceramic fibers and have a low thermal shrinkage rate, which is advantageous for maintaining the sheet structure.

[0049] Furthermore, it is more preferable that the second inorganic fiber be a mullite fiber. Since mullite fibers are also high heat-resistant fibers, they can effectively suppress gas heat transfer and radiant heat transfer even at high temperatures.

[0050] -Average fiber diameter and average fiber length of the first and second inorganic fibers- The average fiber diameter of the second inorganic fiber is smaller than that of the first inorganic fiber. The first inorganic fiber, with its larger average fiber diameter, maintains the sheet structure, while the second inorganic fiber, with its smaller average fiber diameter, fills the gaps between the first inorganic fibers. This suppresses gas heat transfer and radiant heat transfer in the heat transfer suppression sheet.

[0051] The average fiber diameter of the first inorganic fiber is preferably 5 μm to 7 μm, and more preferably 5.2 μm to 6.5 μm. Even ceramic fibers shrink slightly at high temperatures. Therefore, if the average fiber diameter is too small, it may become difficult to maintain the skeletal strength. If the diameter is within the above range, the fibers are thick and rigid, which improves the skeletal structure retention.

[0052] The average fiber diameter of the second inorganic fiber is preferably 4 μm or less, more preferably 0.1 μm to 4 μm, and even more preferably 1 μm to 3 μm. Because its fiber diameter is smaller than that of the first inorganic fiber, when combined with the first inorganic fiber, it exhibits a filler-like effect, improving the molding density and enhancing the suppression of gas heat transfer and radiant heat transfer.

[0053] The average fiber length of the first inorganic fiber and the second inorganic fiber is preferably 0.05 mm or more and 2.0 mm or less, and more preferably 0.1 mm or more and 1.0 mm or less. If the average fiber length of the first inorganic fiber and the second inorganic fiber is too short, the papermaking performance in the papermaking process described later will decrease, meaning that it may become like a clump of powder and not be able to be formed into a sheet. Also, if the average fiber length is too long, the flexibility of the heat transfer suppression sheet may decrease. Furthermore, because the average fiber length of the first inorganic fiber and the second inorganic fiber is longer than the average particle diameter of the first inorganic particles and the second inorganic particles, the inorganic particles are less likely to fall off, and the papermaking (forming) performance is improved.

[0054] The ratio of the average fiber length to the average fiber diameter of the first inorganic fiber and the second inorganic fiber is preferably 10 or more, and more preferably 20 or more.

[0055] The average fiber length of the second inorganic fiber is preferably shorter than the average fiber length of the first inorganic fiber. This is advantageous for improving molding density and suppressing gas heat transfer and radiant heat transfer.

[0056] -Other inorganic fibers- The inorganic fibers may include other inorganic fibers besides the first and second inorganic fibers, but it is preferable that they are not included. In other words, it is preferable that the inorganic fibers consist of the first inorganic fibers and the second inorganic fibers.

[0057] Other inorganic fibers include, for example, aerogel composite materials.

[0058] The average fiber diameter and average fiber length of the other inorganic fibers are not limited and may be similar to the average fiber diameter and average fiber length of the first and second inorganic fibers.

[0059] -Inorganic fiber content- The inorganic fiber content in the heat transfer suppression sheet is preferably 20% by mass or more and 40% by mass or less, and more preferably 25% by mass or more and 38% by mass or less. If the content is less than 20% by mass, it may become difficult to maintain the sheet structure, and if it exceeds 40% by mass, the air layer may increase and the heat insulation performance may decrease.

[0060] Furthermore, the content of the first inorganic fiber in the heat transfer suppression sheet is preferably 15% by mass or more and 30% by mass or less, and more preferably 20% by mass or more and 25% by mass or less, from the viewpoint of maintaining the skeletal strength of the heat transfer suppression sheet at high temperatures.

[0061] The content of the second inorganic fiber in the heat transfer suppression sheet is preferably 5% by mass or more and 20% by mass or less, and more preferably 10% by mass or more and 15% by mass or less, from the viewpoint of effectively suppressing gas heat transfer and radiant heat transfer.

[0062] The content of the second inorganic fiber is preferably less than the content of the first inorganic fiber. The ratio of the content of the second inorganic fiber to the total content of the first and second inorganic fibers is preferably 30% by mass or more and 40% by mass or less. This is advantageous in achieving both sufficient skeletal strength at high temperatures and suppression of gas heat transfer and radiant heat transfer.

[0063] When inorganic fibers include other inorganic fibers, the content of other inorganic fibers in the heat transfer suppression sheet is, for example, 5% by mass or less.

[0064] [Organic Fibers] The heat transfer suppression sheet preferably contains organic fibers from the viewpoint of improving the capture of inorganic particles in the papermaking process described later. Examples of organic fibers, though not limited to them, include aramid fibers, PBO (poly(p-phenylene)benzobis(oxazole)) fibers, nylon fibers, polyester fibers, pulp fibers, and cellulose fibers. One of these organic fibers can be used alone or in combination of two or more.

[0065] The organic fiber is preferably an aramid fiber, and more preferably a para-aramid fiber. Aramid fibers are flame-retardant fibers and will only burn up without igniting even when exposed to high temperatures, thus enhancing the safety of secondary batteries.

[0066] The average fiber diameter of the organic fibers is not particularly limited, but can be, for example, 1 μm to 40 μm, preferably 3 μm to 10 μm.

[0067] The average fiber length of organic fibers is not particularly limited, but can be, for example, between 0.1 mm and 3.0 mm.

[0068] The ratio of the average fiber length to the average fiber diameter of the organic fibers is preferably 10 or more.

[0069] The organic fiber content is preferably 10% by mass or less, more preferably 2% by mass or more and 8% by mass or less, and even more preferably 3% by mass or more and 5% by mass or less. Since organic fibers have a lower heat resistance temperature than ceramic fibers, the above range of organic fiber content is preferred from the viewpoint of ensuring sufficient heat resistance of the heat transfer suppression sheet.

[0070] [Inorganic particles] The inorganic particles include at least the first inorganic particle.

[0071] The inorganic particles may optionally include a second inorganic particle of an optional component. Preferably, the inorganic particles consist of a first inorganic particle and a second inorganic particle.

[0072] The inorganic particles may consist of a first inorganic particle, a second inorganic particle, and other inorganic particles of any optional component.

[0073] By incorporating inorganic particles, the gaps between fibers can be filled, increasing the density of the heat transfer suppression sheet and effectively suppressing heat conduction through flame penetration and air movement.

[0074] -The first inorganic particle- The first inorganic particles consist of metal hydroxides. When exposed to high temperatures during thermal runaway, metal hydroxides release structured water, which has the effect of extinguishing fires, reducing temperature, and delaying temperature rise, thus being advantageous in suppressing heat transfer.

[0075] The metal hydroxide is not particularly limited, but specific examples include aluminum hydroxide, magnesium hydroxide, calcium hydroxide, zinc hydroxide, iron hydroxide, manganese hydroxide, zirconium hydroxide, and gallium hydroxide. One of these metal hydroxides can be used alone or in combination of two or more. Preferably, the metal hydroxide is at least one selected from the group consisting of aluminum hydroxide, magnesium hydroxide, calcium hydroxide, zinc hydroxide, iron hydroxide, manganese hydroxide, zirconium hydroxide, and gallium hydroxide.

[0076] The temperature at which metal hydroxides release structured water through thermal decomposition, i.e., the decomposition temperature of metal hydroxides, is preferably 150°C or higher, and more preferably 300°C or higher. Because the decomposition temperature of metal hydroxides is high, they do not decompose within the normal operating temperature range of secondary batteries (e.g., -20°C to 60°C), ensuring sufficient fire extinguishing / temperature reduction effects in abnormal situations. Specific examples of such metal hydroxides include magnesium hydroxide (decomposition temperature: 330-430°C), calcium hydroxide (decomposition temperature: 580°C), and iron hydroxide (decomposition temperature: 180°C or higher).

[0077] The average particle size of the first inorganic particles is preferably 0.01 μm to 50 μm, and more preferably 1 μm to 30 μm, from the viewpoint of filling the gaps between fibers and increasing the density of the heat transfer suppression sheet. If the average particle size is below the lower limit, it may lead to a decrease in the handlingability of the first inorganic particles and an increase in cost. If the average particle size exceeds the upper limit, it may become difficult to fill the gaps between fibers. Furthermore, it is preferable that the maximum particle size of the first inorganic particles is 100 μm or less in the particle size distribution obtained when measuring the average particle size as described in the examples below.

[0078] -The second inorganic particle- The second type of inorganic particle consists of a material primarily composed of SiO2, and is an optional component added as needed. Examples of materials primarily composed of SiO2 include silica and diatomaceous earth. Such materials have low solid thermal conductivity and can contribute to improving the thermal insulation performance of the heat transfer suppression sheet.

[0079] The average particle size of the second inorganic particles is preferably 0.01 μm to 50 μm, and more preferably 1 μm to 30 μm, from the viewpoint of filling the gaps between fibers and increasing the density of the heat transfer suppression sheet. If the average particle size is below the lower limit, it may lead to a decrease in the handlingability of the second inorganic particles and an increase in cost. If the average particle size exceeds the upper limit, it may become difficult to fill the gaps between fibers. Furthermore, it is preferable that the maximum particle size of the second inorganic particles is 500 μm or less in the particle size distribution obtained when measuring the average particle size as described in the examples below.

[0080] -Other inorganic particles- Other inorganic particles are not particularly limited, but specifically include, for example, alumina particles, zirconia particles, and other oxide-based ceramic particles. These particles have excellent heat resistance and can contribute to increasing the density of the heat transfer suppression sheet.

[0081] - Inorganic particle content - The inorganic particle content in the heat transfer suppression sheet is preferably 40% by mass or more and 70% by mass or less, and preferably 45% by mass or more and 60% by mass or less. If the inorganic particle content is below the lower limit, the voids between fibers will increase, increasing the air layer and potentially reducing the heat insulation performance. If it exceeds the upper limit, the papermaking performance may decrease.

[0082] Furthermore, the content of the first inorganic particles in the heat transfer suppression sheet is preferably 20% by mass or more and 60% by mass or less, and preferably 25% by mass or more and 40% by mass or less, from the viewpoint of obtaining sufficient fire extinguishing, temperature reduction, and temperature rise delay effects by metal hydroxides.

[0083] Furthermore, the content of the second inorganic particles in the heat transfer suppression sheet is preferably 40% by mass or less, and more preferably 20% by mass or more and 30% by mass or less, from the viewpoint of ensuring sufficient papermaking properties during the manufacture of the heat transfer suppression sheet.

[0084] The content of other inorganic particles in the heat transfer suppression sheet can be, for example, 10% by mass or less.

[0085] In a heat transfer suppression sheet, it is preferable that the inorganic particle content is greater than the inorganic fiber content by mass ratio. A higher inorganic particle content is advantageous for increasing the density of the heat transfer suppression sheet.

[0086] [Other ingredients] The heat transfer suppression sheet may contain other components such as organic binders (resin binders) or inorganic binders, as needed.

[0087] For example, including organic or inorganic binders improves the capture of inorganic particles and thus improves papermaking performance. Specific examples of organic binders, though not intended to be limiting, include polyvinyl alcohol, acrylic resin, starch, and methylcellulose. Specific examples of inorganic binders, though not intended to be limiting, include alumina sol and silica sol.

[0088] The content of the organic binder in the heat transfer suppression sheet can be, for example, 3% by mass or less, although this is not intended to be limiting.

[0089] The inorganic binder content in the heat transfer suppression sheet can be, for example, 5% by mass or less, although this is not intended to be a limitation.

[0090] [Sheet material thickness] The thickness of the sheet material is not particularly limited, but it is preferable to adjust it to, for example, between 0.1 mm and 5 mm. If the sheet material is too thin, sufficient heat insulation performance may not be obtained. Also, if the thickness is too thick, it will take up space, which may make it difficult to apply to secondary batteries according to their specifications. The thickness of the sheet material can be adjusted, for example, during the drying process described later.

[0091] <Method for manufacturing a heat transfer suppression sheet> The method for manufacturing the heat transfer suppression sheet is not particularly limited, and generally known methods can be employed, preferably a wet papermaking method. When using a wet papermaking method, the method for manufacturing the heat transfer suppression sheet may include, for example, a material mixing step, a papermaking step, a drying step, and a slitting step.

[0092] In detail, first, the material for the heat transfer suppression sheet is placed in water and stirred to obtain a slurry (material mixing step). To the slurry described above, flocculants and pH adjusters, which are optional components as needed, are added, and the mixture is dewatered using a 50-100 mesh screen, for example. This process yields a sheet material of any size (papermaking process). The resulting sheet material is sandwiched between filter paper and dewatered under pressure using a press to adjust its thickness. Then, it is dried using a hot plate, dryer, etc. (drying process). Then, the dried sheet material is cut to the desired size to obtain a heat transfer suppression sheet (slitting process). By manufacturing using a wet papermaking method, ceramic fibers with different average fiber diameters are uniformly dispersed, and the filling of inorganic particles into the voids between fibers is promoted. This is advantageous for increasing the density of the heat transfer suppression sheet. [Examples]

[0093] Next, we will describe specific examples of the implementations. Heat transfer suppression sheet samples were prepared for the examples and comparative examples, and their respective heat transfer suppression effects were evaluated. The materials and formulations used in the examples and comparative examples are shown in Table 1.

[0094] [Table 1]

[0095] <Material> As the first inorganic fiber, alumina fiber (Al2O3:SiO2 = 7:3 (mass ratio)) was used. As the second inorganic fiber, mullite fiber (main component 3Al2O3·2SiO2) or glass fiber was used. As the organic fiber, aramid fiber (para-aramid fiber) was used. The average fiber diameter and average fiber length of each fiber are shown in Table 1. Magnesium hydroxide was used as the first inorganic particle. Diatomaceous earth was used as the second inorganic particle. The average particle size of each particle is shown in Table 1. Other components used included polyvinyl alcohol, an organic binder, and alumina sol, an inorganic binder.

[0096] <Method for measuring average fiber diameter, average fiber length, and average particle diameter> Average fiber diameter: The diameters of 10 fibers were measured using a SEM (JSM-IT500HR manufactured by JEOL Ltd.), and the average value was defined as the average fiber diameter. Average fiber length: The length of 10 fibers was measured using a scanning electron microscope (SEM), and the average value was defined as the average fiber length. Average particle diameter: The 50% particle diameter (D50) in the volume-based particle size distribution obtained using a laser diffraction particle size distribution analyzer (Shimadzu SALD-2300) was defined as the average particle diameter.

[0097] <Manufacturing method> The materials listed in Table 1 were added to water in the proportions listed in Table 1 and stirred to obtain a slurry (material mixing step). A flocculant and a pH adjuster were added to the slurry, and the mixture was dewatered using an 80-mesh screen to obtain a sheet material measuring 400 x 400 mm (papermaking process). The sheet material was sandwiched between filter paper and dewatered under pressure using a press, and then dried using a hot plate and dryer (drying process). During the drying process, the thickness of the sheet material after drying was adjusted to 1.6 mm. The dried sheet material was cut to a size of 200mm x 200mm to obtain a sample (slitting process).

[0098] <Evaluation Method> The Torch test portion of the UL2596 standard test (UL Solutions, UL2596: Test methods for the thermal and mechanical properties of battery enclosure materials) was performed on samples of the examples and comparative examples. The results are shown in Table 1, Figure 4, and Figure 5. Test conditions: A gas burner fueled by a mixed gas containing methane and oxygen was used to apply a 1200°C flame to the sample for 200 seconds. Evaluation Method: During the test, the sample was visually assessed to determine whether or not it was damaged. After the test, if damage such as through-holes was observed in the sample, it was classified as NG (Not Good), and if no damage such as through-holes was observed, it was classified as OK (Good).

[0099] <Result> In the example sample, as shown in Figure 4, when exposed to a flame of 1200°C for 200 seconds, there was discoloration due to ceramicization, but the flame did not penetrate, and the sheet shape was maintained even after the test was completed. On the other hand, in the comparative example sample, as shown in Figure 5, through-holes formed when exposed to a flame of 1200°C for 200 seconds, allowing the flame to penetrate and resulting in a loss of thermal insulation performance. [Industrial applicability]

[0100] This disclosure is extremely useful because it can effectively suppress heat transfer when a battery cell in a secondary battery experiences thermal runaway, thereby suppressing secondary damage caused by high temperatures and ignition. [Explanation of Symbols]

[0101] 10 Secondary battery 12 cabinets 14 battery cells 16 Heat transfer suppression sheet

Claims

1. A heat transfer suppression sheet for secondary batteries containing inorganic fibers and inorganic particles, The inorganic fiber is The first inorganic fiber is a ceramic fiber, The present invention comprises a ceramic fiber and a second inorganic fiber having a smaller average fiber diameter than the first inorganic fiber, The aforementioned inorganic particles include a heat transfer suppression sheet comprising first inorganic particles made of a metal hydroxide.

2. The heat transfer suppression sheet according to claim 1, wherein the first inorganic fiber and the second inorganic fiber are each selected from the group consisting of alumina fiber, mullite fiber, zirconia fiber, alkali earth silicate fiber, and magnesium silicate fiber.

3. The heat transfer suppression sheet according to claim 1, wherein the first inorganic fiber is an alumina fiber.

4. The heat transfer suppression sheet according to claim 1, wherein the average fiber diameter of the first inorganic fiber is 5 μm or more and 7 μm or less.

5. The heat transfer suppression sheet according to claim 4, wherein the average fiber diameter of the second inorganic fiber is 4 μm or less.

6. The heat transfer suppression sheet according to claim 1, wherein the decomposition temperature of the metal hydroxide is 150°C or higher.

7. The heat transfer suppression sheet according to claim 1, wherein the content of the inorganic particles is greater by mass ratio than the content of the inorganic fibers.

8. Furthermore, it contains organic fibers, The heat transfer suppression sheet according to claim 1, wherein the organic fiber is an aramid fiber.

9. The heat transfer suppression sheet according to claim 8, wherein the content of the organic fibers is 10% by mass or less.

10. A battery pack consisting of multiple battery cells connected in series or parallel, A secondary battery comprising a heat transfer suppression sheet according to any one of claims 1 to 9, disposed on the outer periphery of the plurality of battery cells and at least one of the spaces between each battery cell.

Images