Expansive sheet used in an electric vehicle battery for thermal runaway management

Abstract

An expandable sheet used in an electric vehicle battery for thermal runaway management, wherein in 100 weight percent (wt%) of the expandable sheet, the expandable sheet comprises: 5 to 20 wt% of a nonwoven fiber mat; 60 to 95 wt% of an alkali silicate-based binder; and 0.5 to 10 wt% of a microporous and / or mesoporous and / or nanoporous additive, and the alkali silicate-based binder is injected into the nonwoven fiber mat by impregnating the nonwoven fiber mat with an alkali silicate-based solution.

Description

Technical Field

[0001] Field The present invention relates to an expandable sheet used in an electric vehicle (EV) battery for thermal runaway management, and a method for manufacturing the expandable sheet. In particular, it can provide passive thermal runaway management and fire protection for EV batteries. One or more of the above expandable sheets can be used in EV batteries at various levels, for example, in the spaces between cells and as linings on the inner walls of modules or battery packs.

Background Art

[0002] Background The global electric vehicle (EV) market has seen very significant growth over the past decade, reaching $163.01 billion in 2020 and is expected to reach $823.75 billion by 2030. Factors such as climate change mitigation and efforts towards net-zero carbon emissions, as well as the increasing number of countries involved in rising fuel prices, have been the driving forces behind this growth. However, despite its reputation, the fire protection issue regarding lithium-ion batteries (LiBs) used in EVs has become a major obstacle to reaching a much wider adoption. A number of fire incidents related to EV batteries have been reported, and in 2020, Hyundai and General Motors recalled over 100,000 vehicles each due to such incidents. This clearly demonstrates the importance of improved fire protection to mitigate these problems.

[0003] Referring to FIG. 1, the EV LiB is composed of three hierarchies, namely cells (104), modules (102), and battery packs (100). The arrangement of cells (104) constitutes modules (102), and a group of modules (102) constitutes battery packs (100). The maximum operating temperature range of the LiB is typically 150°C or lower. When the temperature of the cell exceeds this operating temperature limit, it may cause a heat generation chain reaction that accelerates uncontrollably, which may cause the temperature to rise up to 900°C, and in the process called "thermal runaway", a large amount of smoke, fragments, and other fine particles may be released in an explosive manner. The high temperature and pressure generated from one cell due to thermal runaway may induce thermal runaway of adjacent cells that are not confined. Subsequently, a "domino effect" of thermal runaway may occur in all the cells in the module and ultimately in the entire battery pack in a very short time, which may pose a risk of a large explosive fire to the EV.

[0004] To prevent thermal runaway of multiple cells, generally, two types of thermal runaway management systems are used. First, it is ensured that the temperature of each cell does not exceed the maximum operating temperature. Second, when thermal runaway occurs in one cell, it is ensured that the occurrence of thermal runaway in adjacent cells is prevented.

[0005] The first type of thermal runaway management system includes an active monitoring system in which sensors are used to detect in real time whether the temperature or voltage has reached an unsafe level, such as that described in U.S. Patent No. 7433794B1 of the U.S. Patent. However, such a system may not be economically feasible in some cases.

[0006] The first type of thermal runaway management system also includes passive systems such as fluid cooling based on the principle of heat exchange, in which the modules are immersed in a circulating coolant (i.e., refrigerant) or air, such as those described in U.S. Patent Application Publication No. 20200112073A1 or Japanese Patent No. 6331017B2, respectively.

[0007] Furthermore, in order to evenly disperse heat among the cells within the module and release heat to the surroundings by radiation, a heat spreader, which is a high thermal conductivity and radioactive sheet, can be used as a spacer between the cells, thereby reducing the risk of thermal runaway occurring in any of the cells. As an example, in Korean Patent No. 200479471Y1, a compression sheet made of expanded graphite particles or a graphitized polyimide sheet having an in-plane thermal conductivity of 300 W / mK is used. However, if thermal runaway occurs in one cell, such a heat spreader may increase the likelihood of thermal runaway occurring in all cells due to its high thermal conductivity. Furthermore, such a heat spreader may not have the insulation resistance to prevent a rapid voltage increase from moving from one cell to adjacent cells and causing thermal runaway.

[0008] Finally, in order to reduce the temperature rise of any of the cells and reduce the risk of thermal runaway occurring in any of the cells, a sheet made of a phase change material can also be used between the cells. This example is described in Chinese Patent No. 105742755B of a Chinese patent document where a paraffin-expanded graphite composite material is used as the phase change material. The drawback of using such a phase change sheet is that there is a limit to the amount of heat that such a sheet can absorb, that is, when the phase transition of all molecules progresses, the sheet cannot be used to absorb further heat. Furthermore, such a phase change sheet may accelerate the thermal runaway of adjacent cells if a flammable phase change material such as paraffin has already been used when thermal runaway occurs in one cell. As can be seen in Chinese Patent No. 107887671B of a Chinese patent document, a combination of a phase change sheet and a heat spreader as a composite laminate is also used, but the drawbacks of the phase change sheet still exist.

[0009] The second type of thermal runaway management involves the use of a heat-resistant insulating foam, sheet, or expandable sheet, or a combination thereof, as a spacer between cells, as a means to prevent the occurrence of thermal runaway in adjacent cells when thermal runaway occurs in one cell. Due to its low thermal conductivity, the foam is a common choice as a spacer for this technology. However, the drawback of the foam is that its principle of action is contrary to the principle of heat diffusion during normal battery operation, i.e., when the cell is heated, the foam prevents heat diffusion, thereby increasing the risk of thermal runaway occurring in that cell.

[0010] An example of a foam spacer is described in International Publication No. WO 2021 / 019495 A1 of the International Patent Publication, which uses a flexible flame-retardant polymer foam used together with an aqueous fire-resistant silicone elastomer and an inorganic fiber layer. During thermal runaway, the integrity of such a polymer foam cannot be maintained, and therefore, an expandable coating of the polymer is required in this patent document. However, the expanded fluffy carbonaceous char obtained by the expansion of the expandable coating has a low insulation resistance and insufficient ability to withstand high-pressure smoke and debris.

[0011] Another example of a foam is the flexible silica aerogel sheet used in Chinese Patent No. CN 108862286 B of the Chinese Patent Document. Although it has fire resistance and heat resistance, due to the lack of porosity and mechanical strength, its ability to prevent the movement of high-pressure smoke and debris is questionable.

[0012] Canadian Patent No. 3008606C describes a composite laminate in which a low melting point thermally conductive polymer sheet is laminated with an expandable layer. During normal operation, due to heat diffusion, the risk of thermal runaway of each cell is reduced. When one cell undergoes thermal runaway, the thermally conductive polymer layer in the adjacent spacer melts, enabling the expandable layer to easily expand and form a low thermal conductivity carbonaceous char across the involved cell and adjacent cells. However, the dielectric strength of the resulting carbonaceous char and the mechanical strength to withstand the pressure from smoke and debris are important issues.

[0013] In Japanese Patent Application Publication No. 2013-528911A, a heat-absorbing refractory coating such as gypsum is used to cover a part or the entire exterior of the cell array and individual cells in the module. The char generated during a thermal runaway event is expected to have a higher dielectric strength and mechanical strength than carbonaceous char, but the mechanical strength may still not be sufficient to withstand the pressure caused by smoke and debris. Furthermore, the thermal conductivity of the generated char is expected to be much higher than that of carbonaceous char.

SUMMARY OF THE INVENTION

MEANS FOR SOLVING THE PROBLEM

[0014] Overview According to an example of the present disclosure, an expandable sheet claimed in the independent claims is provided. Some optional features are defined in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Brief Description of the Drawings

Figure 1

MODE FOR CARRYING OUT THE INVENTION

[0016] Detailed Description Examples of the present disclosure include an expandable sheet having a thickness of less than 2 mm that expands to produce a mechanically robust inorganic char having good thermal insulation and dielectric strength. "Char" means a carbonized or burned material. The expandable sheet may or may not be made of an inorganic material. The expandable sheet may be as thin as 1 mm or less or may have a thickness greater than 1 mm, depending on the application. One or more expandable sheets can be used as spacers in an electric vehicle (EV) battery. These spacers can be present between cells and between the inner wall linings within the casings of modules and battery packs. This prevents the occurrence of thermal runaway in a plurality of cells and confines a flame within the module / battery pack if thermal runaway occurs. The plurality of expandable sheets can be stacked layer by layer to form one or more laminates having the thickness required by the application. The one or more laminates can be laminated or coated into the walls of the cells, modules, and / or casings of an EV battery.

[0017] In the present disclosure, an electric vehicle (EV) means a vehicle that uses one or more electric motors for propulsion and is typically powered by a battery. Examples of EVs include, but are not limited to, road and rail vehicles (such as electric scooters, electric bicycles, electric cars, space exploration vehicles, etc.), water and underwater vessels, electric aircraft (such as manned / unmanned airplanes and drones, etc.), and electric spacecraft.

[0018] Space constraints are an important factor for EV battery manufacturers, so thin spacers with a thickness of 2 mm or less are highly desirable. Various methods have been adopted to manage thermal runaway in EV lithium batteries (LiBs), but there is still a shortage of thin inter-cell spacers, module linings, and battery pack linings that can achieve relatively good thermal conductivity during normal operating conditions and very low thermal conductivity with excellent mechanical strength and insulation resistance when thermal runaway occurs in one or more cells. Examples of the present disclosure provide one or more expandable sheets to address these issues. In particular, expandable sheets with a thickness of 1 mm or less are proposed in the present disclosure.

[0019] Compared with the use of foams, expandable coatings or sheets have the advantage of having a higher thermal conductivity before thermal runaway of the cells (i.e., during normal operating conditions). This allows for heat dissipation, and when the first cell undergoes thermal runaway, they expand to form a low-thermal-conductivity char, preventing thermal runaway of adjacent cells.

[0020] In one example of the present disclosure, an inorganic expandable sheet is provided, which in its most basic form includes a non-woven inorganic fiber mat impregnated with an aqueous and alkali silicate-based solution. In this example, the impregnating solution includes an alkali silicate-based binder, a porous heat-insulating additive, a char strength additive, one or more surfactants, water, one or more curing agents, and other additives such as organic additives. The expandable sheet has an alkali silicate-based coating containing these additives after drying and / or curing.

[0021] The alkali silicate binder can mean lithium silicate, potassium silicate, and sodium silicate, or a mixture thereof. Since lithium silicate is much more expensive, potassium silicate and / or sodium silicate are preferred. Such alkali silicates are expandable to produce inorganic expandable char at high temperatures. Sodium silicate has lower stability than potassium silicate and requires a lower temperature for expansion, and thus can be activated earlier in the case of thermal runaway of one cell. Therefore, between potassium silicate and sodium silicate, when faster activation is required, sodium silicate is the preferred choice.

[0022] The "silicon dioxide:alkali oxide" molar ratio of the alkali silicate binder determines properties such as the curing rate, the flexibility of the cured sheet, and the expansion and mechanical robustness of the char when the cured sheet is exposed to high temperatures. The "cured sheet" means the inorganic expandable sheet of the above example after it is made. At a small ratio, large expansion of the char, low mechanical robustness, high flexibility of the cured sheet, and a slow curing rate are obtained, and the opposite is true for a large ratio. Considering the best compromise among multiple factors, the above molar ratio is preferably in the range of 2.5 to 4, more preferably in the range of 3 to 3.3. For a good balance between the expandability and mechanical robustness of the char, the alkali silicate content should be between 60 and 95 weight percent (wt%) of the expandable sheet, more preferably between 75 and 85 wt% of the expandable sheet.

[0023] As a substance that has a dense network and enables the formation of char having a typical high pore volume fraction in a uniformly distributed microporous and / or mesoporous and / or nanoporous network, a microporous and / or mesoporous and / or nanoporous additive is added to the expandable sheet. The microporous and / or mesoporous and / or nanoporous additive is a heat-insulating additive. This depends on the miscibility with the impregnating solution of the heat-insulating additive (i.e., aqueous and alkali silicate-based solutions), and it can be added within the range of 0.5 to 10% by weight of the expandable sheet. The microporous and / or mesoporous and / or nanoporous additive can densify the expandable sheet. Further, the microporous and / or mesoporous and / or nanoporous additive may be of the nature of silica and / or silicate.

[0024] Examples of the microporous and / or mesoporous and / or nanoporous additive include, but are not limited to, hollow microglass spheres, fumed silica, cenospheres, and aerogel particles. It has been confirmed that adding aerogel particles having a hydrophobic surface group shows good performance for the formation of char having a dense network and a large pore volume fraction in micropores and / or mesopores. More preferably, aerogel particles having a particle size of 10 to 60 μm, a pore diameter of 5 to 50 nm, a porosity > 90%, a bulk density of 0.02 to 0.1 g / cm 3 and a surface area of 500 to 900 m 2 / g can be selected. The aerogel content should be between 0.5 and 10% by weight of the expandable sheet, preferably between 1 and 5% by weight of the expandable sheet. Above the recommended range, dispersion becomes a problem, while below the above range, the improvement of the heat insulation of the char is not sufficient enough.

[0025] Without the addition of microporous and / or mesoporous and / or nanoporous additives, the char obtained from an expandable sheet having only an alkali silicate binder can be a loosely connected network with a broad pore size distribution.

[0026] For comparison purposes, (a) samples of chars having only an alkali silicate binder were magnified 100-fold and 1000-fold, and (b) samples of chars from expandable sheets having 1 wt% of the aforementioned aerogel particles added to the alkali silicate binder were magnified 100-fold, 1000-fold, and 5000-fold. The char of (a) shows a loosely connected network with a broad pore size distribution. The pore sizes are non-uniform, and the walls forming the pores appear weak and brittle. In contrast, the char of (b) shows a very dense network with a very high pore volume fraction typical of a uniformly distributed microporous and / or mesoporous and / or nanoporous network. At 100-fold magnification, in the case of the char of (a), almost all pores can be seen and seem large, but in the case of the char of (b), very few pores are of the same size appearance, and most pores cannot be seen. Even at a magnification as large as 5000-fold, the pore volume of the char of (b) still appears very high, and the pore distribution still seems to be uniformly distributed. At 1000-fold magnification, in the case of the char of (a), only the walls of very few pores can be seen. However, the pores and their walls of the char of (b) can hardly be seen even at 5000-fold magnification. From this comparison, it is clear that the char obtained from an example of an alkali silicate - aerogel combination shows excellent performance in terms of the insulation and strength of the char. The above-mentioned char thus has such a dense network, high pore volume, and distribution. Such microporous and / or mesoporous and / or nanoporous additives do not cause or affect the degree or effect of expansion, which should be noted is mainly caused by the decomposition of the alkali silicate binder. By having such additives, the strength of the char increases, and its ability to reduce the moving speed of the heat flux improves.

[0027] Optionally, in order to further improve the mechanical robustness, insulation, and flame retardancy of the char, a char strength improving additive can be included in the expandable sheet of the foregoing example. The char strength improving additive includes, but is not limited to, one or more metal salts such as metal oxides, for example magnesium oxide, aluminum oxide, calcium oxide, and zinc oxide, metal hydroxides, for example aluminum trihydrate and magnesium dihydroxide, metal carbonates, for example calcium carbonate and zinc carbonate, and silicates, for example mica and talc, and metal powders, for example iron, zinc, and aluminum, individually or in any combination thereof. The above metal hydroxides and carbonates can further function as endothermic additives capable of obtaining further fire resistance by endothermic cooling at higher temperatures (i.e., above 200 °C). For an optimal balance between the expandability and mechanical robustness of the char, the total amount of such char strength improving additive added should be between 1 and 10 wt% of the expandable sheet, or preferably between 3 and 8 wt% of the expandable sheet.

[0028] Optionally, 1 to 10 wt% of an opacifier such as iron oxide, silicon carbide, and titania can be added to the expandable sheet. The opacifier imparts high temperature heat insulation and functions to reflect and thereby reduce heat transfer by radiation at high temperatures.

[0029] Optionally, a surfactant can be added to the impregnating solution (i.e., an aqueous and alkali silicate-based solution) used during the production of the expandable sheet in the above example. By adding a surfactant, the dispersion of the additive is improved, and the ability of the impregnating solution to diffuse and wet the nonwoven fiber mat is improved. Since the impregnating solution is alkaline, the surfactant should be selected to be stable within the pH range of 2 to 12. Preferably, the surfactant or its mixture is selected from the group including amine oxide, alkyl carbohydrate ester, alkoxylated polysiloxane, and alkyl polyacrylate. The amount of the surfactant used can be between 0.05 and 2% by weight of the impregnating solution, preferably between 0.2 and 0.5% by weight of the impregnating solution. The reason is that with a higher amount of surfactant used, undesirable changes in flame retardancy may occur, while with a lower amount used, the uniformity and the ability to sufficiently wet the nonwoven fabric may not be improved.

[0030] Optionally, a curing agent can be added to the impregnation solution (i.e., an aqueous and alkali silicate-based solution) used during the production of the expandable sheet in the aforementioned examples. By adding the curing agent, the drying and curing time of the impregnated nonwoven fiber mat is improved. Such a curing agent facilitates the mass production of the expandable sheet, especially in the case of a conveyor belt type continuous production line, and such a curing agent can be broadly classified into acid-based or alkali-based curing agents. Examples of acid-based curing agents include, but are not limited to, hydrochloric acid, sulfuric acid, phosphoric acid, formic acid, aluminum phosphate, and sodium fluorosilicate. On the other hand, the most commonly used alkali-based curing agent is potassium methyl silicate. An acid in the form of a solid powder with the property of dissolving slowly is preferred so as to prevent aggregation during working hours (i.e., during the impregnation of the nonwoven fiber mat). Therefore, among the acid curing agents, preferably sodium fluorosilicate is selected. Among the alkali curing agents, potassium methyl silicate is a preferred choice. Furthermore, the curing agent improves the water resistance of the produced impregnated and cured expandable sheet, thereby reducing the risk of damage during storage. The amount of the curing agent used is determined particularly by the production method and requirements. However, at high usage levels, the flexibility tends to decrease significantly. Therefore, it is preferable that less than 10% by weight of the expandable sheet constitutes such a curing agent.

[0031] Optionally, organic additives can be added to improve the flexibility and water resistance of the expandable sheet in the aforementioned example. For this purpose, a number of organic additives and their combinations can be added. For example, these can be obtained in the form of latex, emulsion, suspension, solution, or solid powder. Examples of organic additives include thermoplastic or thermosetting polymers such as polymethyl methacrylae, polyacrylic acid, polyvinyl alcohol, polyvinyl acetate, polyvinyl acrylate, polyvinyl pyrrolidine, poly(ethyl-vinyl acetate), styrene-butadiene rubber, polyethylene glycol, polyurethane, polyester, and epoxy, as well as organic molecules or polymers such as ethylene glycol, pentaerythritol, glycerol, starch, mannitol, carboxymethyl cellulose, but are not limited thereto. Aqueous organic additives are preferred because they can be stably added to the impregnating solution without forming aggregates during the working time. Among these, in particular, glycerol and polyvinyl alcohol show good miscibility and improved flexibility when added in appropriate amounts without impairing the fireproof performance, and thus they are preferred choices. The addition of a high amount of such organic additives may significantly reduce the fireproof performance. Therefore, preferably, the addition of such organic additives should be less than 10% by weight of the expandable sheet.

[0032] The inorganic nonwoven fiber mat of the expandable sheet in the aforementioned example has two important functions. This increases the flexibility of the expandable sheet and ensures higher mechanical robustness of the char formed during a thermal runaway event in the EV battery. A nonwoven fiber mat based on glass fiber is preferred. This depends on the type, diameter, and length of the fibers used, the type and amount of the binder used, and the areal density (i.e., g / m 2) is defined by. Suitable choices of mats or fabrics of non-woven glass fibers for producing the expandable sheet include types E, S, C, R, T, and A. Types E and S are preferred choices. The fiber diameter and length can be between 8 and 18 μm and between 10 and 75 mm, respectively, preferably between 10 and 15 μm and between 15 and 60 mm. The type of binder selected should be stable in the alkaline environment and any coolant to which the expandable sheet is exposed inside the EV battery. The amount of binder should be sufficient to impart flexibility but should not be so high as to adversely affect the fireproof performance. For example, a polymer binder can be used. In particular, an acrylic resin can be selected as the binder, and the binder content is between 5 and 20% by weight of the non-woven fiber mat, and preferably between 8 and 15% by weight of the non-woven fiber mat. The areal density is less than 400 g / m 2 and preferably between 30 and 280 g / m 2 . The non-woven fiber mat can constitute 5 to 20% by weight, preferably 8 to 16% by weight of the expandable sheet composition.

[0033] To produce the expandable sheet of the foregoing example, the non-woven fiber mat is first stacked on a non-sticky polymer sheet and an aqueous alkali silicate-based solution (also known in the present disclosure as the "impregnation solution"), for example, in a 100% by weight alkali silicate-based solution, a. 70 to 95% by weight of sodium silicate aqueous solution; b. 0.5 to 10% by weight of the aforementioned microporous and / or mesoporous and / or nanoporous additive; c. Optionally, 1 to 10% by weight of the aforementioned char strength-imparting ceramic additive; d. Optionally, less than 10% by weight of the aforementioned curing agent; e. Optionally, less than 10% by weight of the aforementioned organic additive; f. Optionally, 0.05 to 2% by weight of the aforementioned surfactant; g. Optionally, 2 to 10% by weight of water to reduce viscosity, Impregnate with an aqueous alkali silicate-based solution.

[0034] Various impregnation methods such as spraying, brush coating, and / or doctor blading can be employed. Preferably, doctor blading is employed for better thickness control and feasibility in mass production. Next, drying is carried out at an appropriate temperature (e.g., room temperature) to remove water without causing results such as warping. This purpose is to sufficiently dry the sheet to make the non-stick polymer sheet easily peelable. Optionally, drying can be carried out at a higher temperature (e.g., 60 °C) to speed up the process. Drying and / or curing can be carried out by using hot air, microwave heating, infrared heating, etc. The drying and / or curing temperature should not be too high as defects such as cracks and warping of the expandable sheet may occur. The conditions of drying and / or curing (e.g., temperature and time) are determined by many factors such as the thickness of the expandable sheet to be manufactured and further the type of oven used, and should be adjusted accordingly to obtain the best results. Optionally, the aforementioned curing agent can be added to accelerate the drying and / or curing process of the expandable sheet to be manufactured, which is particularly feasible in the case of a continuous manufacturing line.

[0035] According to an example of the present disclosure, an expandable sheet is provided. Its composition and related properties before and after being exposed to high temperature are summarized in Tables 1 and 2 respectively. Tables 1 and 2 are shown below. A non-woven glass fiber mat having a thickness of 0.5 mm before impregnation is used. The thickness of the cured expandable sheet is 0.4 mm. The expandable sheet can be used as a single sheet, or the same impregnation solution described above (i.e., an alkali silicate-based solution) can be applied between the layers and assembled and stacked layer by layer. In particular, this assembly includes stacking a plurality of non-woven fiber mats layer by layer and applying an impregnation solution between the layers to impregnate each layer of the non-woven fiber mat with the impregnation solution. A cold press is performed on the plurality of stacked layers to form a multi-layer laminate. The single sheet or the multi-layer laminate is used as a spacer between cells in an electric vehicle (EV) battery, for example. These can be made to have the same surface area as the cells, or they can be made slightly larger, i.e., up to 2 - 3 cm larger around all sides of the cells. When thermal runaway occurs in one cell, as soon as the temperature reaches 200°C, the adjacent expandable sheet spacer rapidly undergoes endothermic decomposition and expansion, forming a mechanically robust char, and good heat insulation and dielectric insulation are formed. Thereby, the heat flux can be greatly reduced, and high-pressure smoke and fragments can be prevented from moving to adjacent cells, thereby preventing the occurrence of thermal runaway in adjacent cells. As described above, when the area of the expandable sheet or laminate used is slightly larger than the cells, the adjacent cells are further protected from the lateral transfer of heat, i.e., it becomes more difficult for heat to move laterally around the spacer. Depending on the type of cell used, such as a prismatic cell, when thermal runaway occurs, the involved cell may cave in inward. Due to the properties of the expandable sheet, when activated at a higher temperature, this softens during expansion and solidifies after expansion to become a hard char. Thereby, the char can expand to fit precisely into the shape of the depression, thereby providing a high degree of protection against thermal runaway to adjacent cells.

[0036]

Table 1

[0037]

Table 2

[0038] Some of the selected properties of the expandable sheets in Table 2 are obtained by the following methods.

[0039] The expansion ratio is determined by placing each of a plurality of expandable sheets on a hot plate preheated to 300 °C for 10 minutes by a "slap-on" procedure to form a completely expanded char. The range of the expansion ratio is obtained by calculating the ratio between the thickness of the completely expanded char of the expandable sheet and the original thickness of the expandable sheet before expansion. The original thickness of the expandable sheet tested to obtain the range of the expansion ratio was between 0.4 and 1 mm.

[0040] In the case of thermal conductivity, the expandable sheet (or laminate) is placed in a sealed jig having spacers, and the sheet can expand to form a char. The sealed jig ensures that the surface of the char is smoothed for an accurate test of thermal conductivity. Next, the set of jigs is placed on a hot plate at 300 °C for 30 minutes. The dimensions of the expandable sheet were approximately 20 cm × 20 cm. Next, measurements were performed on the obtained char using a hot flow meter (HFM) at room temperature and 50 °C, and their thermal conductivities were determined.

[0041] Regarding the compressive strength, an expandable sheet having dimensions of 5 cm × 5 cm was placed on a hot plate at 300 °C for 10 minutes by a "slap-on" procedure to ensure the formation of a completely expanded char. After cooling the char, the compressive stress-strain relationship of the char was tested by an Instron mechanical tester equipped with a 5 kN load cell.

[0042] Regarding the aforementioned "slap-on" procedure, in particular, the expandable sheet is slapped onto the hot plate so as to ensure that the sheet is placed flat on the hot plate. This purpose is to evenly apply heat to the entire area of the expandable sheet and at the same time ensure the formation of a char that expands uniformly.

[0043] In an example of the present disclosure, the aforementioned expandable sheet or laminate can be arranged in contact with (e.g., sandwiched between) a compressible material. By assembling each layer, the compressible material can be joined to the expandable sheet or laminate to each other. Next, these are used as spacers between cells in an EV battery. Examples of the compressible material include, but are not limited to, polymer foams such as polyurethane foam and silica-aerogel foam. This is one of the feasible options for meeting the requirements of compressibility and thickness under compression at the beginning of life (BOL) and end of life (EOL) by EV battery manufacturers.

[0044] A thermal runaway (TR) comparison test was conducted between a polyurethane foam (PUF), which is a widely adopted inter-cell spacer by EV manufacturers, and a combination of an expandable sheet-PUF of the same thickness. The expandable sheet combined with the PUF is the same as that described in the previous example. The entire structure was compressed at 100 kPa for the TR test on two inter-cell spacers assembled between three prismatic cells of an EV battery. In the case of the first spacer, 1.7 mm of PUF was used (1.7 mm is the thickness of the PUF after compression), and in the case of the second spacer, a 0.5 mm expandable sheet was combined with 1.2 mm of polyurethane foam (1.2 mm is the thickness of the PUF after compression). When thermal runaway was forcibly initiated in the first cell of the three prismatic cells, the PUF in the first spacer immediately melted, and thermal runaway occurred in the adjacent second cell of the three prismatic cells in 73 seconds. However, during the thermal runaway of the second cell, the PUF in the second spacer melted simultaneously, and the expandable sheet expanded to fill the entire space (left by the melting of the PUF), thereby obtaining an excellent heat insulation barrier, which enabled heat protection for approximately 16 minutes until thermal runaway occurred in the adjacent third cell of the three prismatic cells. This test shows that it is possible to obtain excellent thermal runaway protection in EV batteries by combining a compressible material with an expandable sheet or laminate.

[0045] In one example of the present disclosure, the expandable sheet or laminate described in the previous example can be used as an inner wall lining for an electric vehicle (EV) module and a battery pack casing. In the case of an inner wall having a complex shape, a thinner non-woven fiber mat can be used, and / or an organic additive can be added to the impregnating solution to improve the flexibility of the expandable sheet or laminate used. A layer-by-layer method can be employed, whereby individual expandable sheet layers (each including a non-woven fiber mat) are arranged (i.e., laminated) on the inner wall of the EV module and / or the battery pack casing. The impregnating solution can be applied between the layers to function as an adhesive between the layers. In this case, there are multiple layers of non-woven fiber mats, thereby increasing the heat insulation and mechanical strength of the inner wall. Therefore, the inner wall and its lining can confine the highly pressurized smoke and debris generated by multiple cells in which thermal runaway has occurred. Preferably, such a laminated inner wall lining has a minimum thickness of 1 mm (estimated as about two layers of expandable sheet layers), preferably at least 2 mm (estimated as about four layers of expandable sheet layers) to obtain the desired performance.

[0046] In another example of the present disclosure, an expandable tape can be manufactured from the expandable sheet or laminate described in the previous example. An adhesive backing is attached onto the expandable sheet or laminate to form the expandable tape. This facilitates layer-by-layer assembly with another material such as a foam combined with the expandable sheet or laminate, or the expandable tape can be attached as a single layer or multiple layers on the inner wall of an EV battery module or an EV battery pack casing.

[0047] In summary, the examples of the present disclosure relate to thermal runaway management of electric vehicle (EV) batteries by using one or more thin inorganic expandable sheets or laminates used as spacers between cells. In line with the importance of optimizing the space for EV battery manufacturers, the flame-retardant expandable one or more sheets or laminates of the examples of the present disclosure can obtain the necessary thermal runaway protection at a thickness of 1 mm or less.

[0048] In another aspect, examples of the present disclosure relate to fire protection of an electric vehicle when thermal runaway occurs in a plurality of cells in a battery for an EV. This is done by using one or more expandable sheets or laminates of the examples of the present disclosure as an inner wall lining of a battery module and / or pack to confine a flame within each battery module and / or pack.

[0049] One or more expandable sheets or laminates of the examples of the present disclosure are produced by impregnating a non-woven fiber mat with an alkali silicate-based solution containing a small amount of microporous and / or mesoporous and / or nanoporous additives that may be aerogel particles, and optionally a small amount of another char strength-imparting additive such as ceramic powder. When cured, the impregnated non-woven fiber mat sheet maintains a significant degree of flexibility, which is important for preventing cracks (i.e., due to vibration / pressure between cells) during operation of the EV battery.

[0050] During normal operating conditions, the thermal conductivity of one or more expandable sheets or laminates of the examples of the present disclosure is relatively high, and heat diffusion can reduce the risk of thermal runaway occurring in any particular cell. When thermal runaway occurs in one cell of an EV battery, adjacent spacers containing one or more expandable sheets or laminates can activate and expand in an endothermic manner, for example, when reaching 200°C. The resulting char can be a mechanically robust inorganic char further supported by the impregnated non-woven fibers, which can withstand high-pressure smoke and debris. Further, this char has a high electrical insulation resistance and a low thermal conductivity due to the presence of a microporous and / or mesoporous and / or nanoporous network, thereby forming an effective barrier for preventing the occurrence of thermal runaway in adjacent cells.

[0051] An example of the expandable sheet or laminate described in the previous example can be referred to as an FR Blade (or "FR-Blade"). The FR-Blade means an expandable sheet for thermal runaway management of an electric vehicle battery. The thickness of this sheet is less than 2 mm, preferably 1 mm or less. For example, the expandable sheet is formed by impregnating non-woven inorganic fibers with an alkali silicate-based solution (hereinafter referred to as "impregnating solution"). The impregnating solution may be an aqueous expandable coating containing an aerogel. The impregnating solution can contain additives, and after drying and / or curing thereof, the expandable sheet has an alkali silicate-based coating containing additives.

[0052] The composition of the expandable sheet (after drying) and the composition of the impregnating solution for an example of the FR Blade will be described below.

[0053] The expandable sheet can include a mat (or cloth) of non-woven inorganic fibers, for example, ECR-50 (a type of E-glass) from Owen’s Corning. The impregnating solution used for this product contains a sodium silicate-based binder and aerogel microparticles having a hydrophobic surface group. The particle size of the aerogel particles is between 10 and 60 μm, and its porosity exceeds 90%. In order to improve the mechanical robustness, insulation, and flame retardancy of the char formed from the FR Blade under heat exposure, alumina (a type of metal oxide) and metal dihydroxide (a type of metal hydroxide) are added as additives to the impregnating solution.

[0054] Tables 3 and 4 below show examples of the composition of the FR Blade after drying and the composition of the impregnating solution.

[0055]

Table 3

[0056]

Table 4

[0057] In the above example, in order to improve the ability to disperse and wet the non-woven inorganic fiber mat, a surfactant stable within the range of pH 2 to 12 is added to the impregnating solution. Preferably, the surfactant is selected from the group including amine oxide, alkyl carbohydrate ester, alkoxylated polysiloxane, and alkyl polyacrylate. The amount of the surfactant used is between 0.2 and 0.5% by weight of the impregnating solution, while the preferred amount used is 0.2 to 1.2% by weight of the expandable sheet.

[0058] Regarding the non-woven inorganic fiber mat of this example, in addition to E-type glass, S-type is another preferred option. When E-type glass is used, E-type glass from which the boron oxide element has been removed is most preferred. The diameter and length of the fiber should be between 10 and 15 μm and between 15 and 60 mm.

[0059] Microporous heat-insulating additives such as fumed silica and hollow micro glass spheres (i.e., substances capable of forming a char having a dense network) can be added. Appropriate char strength-imparting ceramic additives, such as combinations of metal oxides, metal hydroxides, metal carbonates, metal silicates, and / or metal powders, can be added.

[0060] In addition to the aforementioned components, optionally, 1 to 10% by weight of an opacifier such as iron oxide, silicon carbide, and / or titania can be added to the expandable sheet of this example. The opacifier functions to impart high-temperature heat insulation and reflect and thereby reduce heat transfer by radiation at high temperatures.

[0061] In order to improve the flexibility and water resistance of the expandable sheet, an organic additive can be added at the impregnation station (the place where the non-woven inorganic fiber mat and the impregnating solution are impregnated). Glycerol and polyvinyl alcohol are preferred examples of the organic additive.

[0062] The production of the impregnating solution involves sequentially adding an alkali silicate solution and one or more surfactants, followed by an insulating agent, a char strength agent, and another additive, and finally adding the required amount of water while stirring and mixing for less than 30 minutes (e.g., 15 minutes) after each step (i.e., after the sequential addition of each component), and finally stirring and mixing the solution with all components added for an additional 2 - 3 hours. The curing agent is the last component added to the impregnating solution and is added immediately before impregnating the non-woven inorganic fiber mat. The viscosity is preferably between 200 and 500 centipoises (cps).

[0063] The curing agent is preferably sodium fluorosilicate or potassium methyl silicate (most preferred).

[0064] When an opacifier, a curing agent, and water are added, the composition of the impregnating solution is shown in Table 5 below.

[0065]

Table 5

[0066] By applying the impregnating solution between layers and cold pressing a plurality of expandable sheets, a plurality of sheets of the expandable sheet can be stacked to form a laminate with each other.

[0067] In one of the usage plans of the product in an electric vehicle (EV) battery, the aforementioned expandable sheet or laminate is placed in contact with a polymeric foam, which is a compressible material such as polyurethane form (PUF), used as a cell spacer. To further protect adjacent cells from the lateral transfer of heat, the area of the expandable sheet / laminate is larger than the surface area of the cell to cover all sides of the cell by 2 - 3 cm.

[0068] When one cell in an EV battery undergoes thermal runaway, simultaneously the PUF in the spacer melts and the expandable sheet expands to fill the entire space (left by the melting of the PUF), thereby obtaining a heat insulation barrier to prevent the occurrence of thermal runaway in adjacent cells of the battery module.

[0069] In another usage plan of the product in the EV battery, an adhesive backing is attached onto the expandable sheet or laminate as described above to form an expandable tape. This facilitates layer-by-layer assembly with other materials such as aerogel foams, mica sheets, etc., i.e., the expandable sheet or laminate in the form of a tape can adhere to these other materials to be disposed in the EV battery for thermal runaway management. Further, the expandable tape can be attached as a single layer or multiple layers on the inner wall of the EV battery module or the EV battery pack casing.

[0070] To manufacture the expandable sheet, a non-woven inorganic fiber mat is first laid on a non-sticky polymer sheet and impregnated with an aqueous alkali silicate-based solution (i.e., the impregnation solution).

[0071] Various impregnation methods such as spraying, brushing, and / or doctor blading can be employed. Preferably, doctor blading is adopted for better thickness control and feasibility in mass production. Next, drying is performed at an appropriate temperature (e.g., room temperature) to remove water without causing defects such as warping. Optionally, curing can be performed at a higher temperature (e.g., by microwave heating) to speed up the process.

[0072] Other char strength enhancing additives that can be added include zirconium oxide and colloidal silica. Sodium silicate is defined by the molar ratio between silica: sodium oxide. Increasing the ratio of silica can form a stronger char, and this increase can be adjusted by adding colloidal silica.

[0073] Another example of the aforementioned FR-blade can have the following properties: Expansion characteristics: · React rapidly at a temperature >175°C · Expand to 5 times the original thickness · Form an insulating foam that fills the voids to reduce heat transfer. · A non-combustible inorganic formulation.

[0074] The FR-blade may be a flexible sheet material manufactured from bulk roll for lamination and die-cut. The FR-blade is available in a standard thickness of 0.4 mm to 1.0 mm. See Table 6 (i.e., 6(A) and 6(B)) below for details.

[0075]

Table 6

[0076]

Table 7

[0077] In one example, the FR-blade may be a generally square or rectangular sheet that is suitable in shape for most EV batteries.

[0078] The FR-blade can be used alone or inserted as a layer having one or more layers of another material (e.g., PUF, another thermal insulation material, etc.).

[0079] The FR-blade can be supplied from bulk roll. A die-cut process can be used to cut the FR-blade to the exact size.

[0080] The FR-blade can be supplied from two or more FR-blades stacked on top of each other. In this case, a release liner can be provided between the layers of two or more FR-blades.

[0081] Examples of the present disclosure can have the following features.

[0082] An expandable sheet used in an electric vehicle battery for thermal runaway management, wherein in 100 weight percent (wt%) of the expandable sheet, the expandable sheet is: 5 to 20% by weight of a non-woven fiber mat; 60 to 95% by weight of an alkali silicate binder; 0.5 to 10% by weight of a microporous and / or mesoporous and / or nanoporous additive and comprising an expandable sheet in which the non-woven fiber mat is impregnated with an alkali silicate solution so that the alkali silicate binder is injected into the non-woven fiber mat.

[0083] The expandable sheet can have a thickness of 1 mm or less.

[0084] The alkali silicate binder can have a silicon dioxide:alkali oxide molar ratio in the range of 2.5 to 4.

[0085] The alkali silicate binder can have a silicon dioxide:alkali oxide molar ratio in the range of 3 to 3.3.

[0086] The expandable sheet can contain 75 to 85% by weight of an alkali silicate binder.

[0087] The microporous and / or mesoporous and / or nanoporous additive can include aerogel particles having a hydrophobic surface group.

[0088] The aerogel particles can have a particle size of 10 to 60 μm, a pore diameter of 5 to 50 nm, a porosity of more than 90%, a bulk density of 0.02 to 0.1 g / cm 3 and a surface area of 500 to 900 m 2 / g.

[0089] The microporous and / or mesoporous and / or nanoporous additive can include hollow microglass spheres, fumed silica, and / or cenospheres.

[0090] The expandable sheet can contain 1 to 10% by weight of an opacifier containing any one of iron oxide, silicon carbide, and titania, or a combination thereof.

[0091] The expandable sheet can contain 1 to 10% by weight of a char strength-imparting ceramic additive containing any one of metal oxides, metal hydroxides, metal carbonates, metal silicates, and metal powders, or a combination thereof.

[0092] The expandable sheet can contain 3 to 8% by weight of a char strength-imparting ceramic additive.

[0093] The char strength-imparting ceramic additive can contain magnesium oxide, aluminum oxide, calcium oxide, and / or zinc oxide.

[0094] The char strength-imparting ceramic additive can contain aluminum trihydrate and / or magnesium dihydroxide.

[0095] The char strength-imparting ceramic additive can contain calcium carbonate and / or zinc carbonate.

[0096] The char strength-imparting ceramic additive can contain mica and / or talc.

[0097] The char strength-imparting ceramic additive can contain metal powder, and the metal powder can contain iron, zinc, and / or aluminum.

[0098] The alkali silicate-based solution can contain 0.05 to 2% by weight of a surfactant that is stable within the range of pH 2 to 12 in a 100% by weight alkali silicate-based solution.

[0099] The alkali silicate-based solution can contain 0.2 to 0.5% by weight of a surfactant.

[0100] The expandable sheet can contain a curing agent of less than 10% by weight including sodium fluorosilicate and / or potassium dimethylsilicate.

[0101] The expandable sheet can contain an organic additive of less than 10% by weight including polyvinyl alcohol and / or glycerol.

[0102] The non-woven fiber mat can contain E and / or S type glass fibers.

[0103] The non-woven fiber mat can contain fibers having diameters and lengths between 8 to 18 μm and 10 to 75 mm, respectively.

[0104] The non-woven fiber mat can contain fibers having diameters and lengths between 10 to 15 μm and 15 to 60 mm, respectively.

[0105] The non-woven fiber mat can contain 5 to 20% by weight of an acrylic resin as a binder in 100% by weight of the non-woven fiber mat.

[0106] The non-woven fiber mat can contain 8 to 15% by weight of an acrylic resin.

[0107] The non-woven fiber mat can have a basis weight of less than 400 g / m 2 ².

[0108] The non-woven fiber mat can have a basis weight between 30 to 280 g / m 2 ².

[0109] The expandable sheet can contain 8 to 16% by weight of the non-woven fiber mat.

[0110] The expandable sheet can be manufactured to be larger than 2 to 3 cm around all sides of the cells of the EV battery.

[0111] The expandable sheet is: 8 to 16% by weight of the non-woven fiber mat; and 75 to 85% by weight of an alkali silicate binder; 1 to 5% by weight of aerogel microparticles having a hydrophobic surface group; 3 to 8% by weight of a metal oxide and / or hydroxide, and may include.

[0112] In a 100 weight percent (wt%) alkali silicate solution, the alkali silicate solution is: 92 to 97% by weight of an alkali silicate and water; 0.2 to 1% by weight of a surfactant; 0.8 to 2% by weight of aerogel microparticles having a hydrophobic surface group; 2 to 4.5% by weight of a metal oxide and / or hydroxide, and may include.

[0113] In a 100 weight percent (wt%) alkali silicate solution, the alkali silicate solution is: 70 to 95% by weight of an alkali silicate and water; 0.05 to 2% by weight of a surfactant; 0.5 to 10% by weight of aerogel microparticles having a hydrophobic surface group; 1 to 10% by weight of a metal oxide and / or hydroxide; 1 to 10% by weight of an opacifier; less than 10% by weight of an organic additive; less than 10% by weight of a curing agent; In addition to the above 70 to 95% by weight of an alkali silicate and water, 2 to 10% by weight of water, and may include.

[0114] A method for producing an expandable sheet, comprising: Impregnating a nonwoven fiber mat with an alkali silicate solution by coating the nonwoven fiber mat with the alkali silicate solution using a doctor blading technique; Drying the impregnated nonwoven fiber mat, and a method comprising.

[0115] The above method comprises: a) adding an alkali silicate in the form of a solution; b) adding one or more surfactants to the solution of step a) to form a mixture; c) adding a heat insulating agent to the above mixture; d) adding a char strength agent to the above mixture; e) adding water to the above mixture; f) adding a curing agent to the above mixture; g) stirring and mixing the above mixture for a predetermined time of less than 30 minutes after each of steps a) to f); h) stirring and mixing for about 2 to 3 hours after adding all the components to the above mixture, and can include producing an alkali silicate-based solution thereby.

[0116] A laminate comprising a plurality of stacked layers, wherein each layer is an expandable sheet.

[0117] A method for manufacturing a laminate, comprising: stacking a plurality of non-woven fiber mats layer by layer and applying an alkali silicate-based solution between the layers to impregnate each layer of the non-woven fiber mat with the alkali silicate-based solution; cold pressing the plurality of stacked layers to form a laminate, and the method.

[0118] The above expandable sheet and / or the above laminate can include an adhesive backing to facilitate attachment onto the surface of the expandable sheet and / or laminate.

[0119] An electric vehicle (EV) battery including one or more spacers disposed between cells in an EV battery to prevent thermal runaway in adjacent cells when thermal runaway occurs in one cell, wherein the one or more spacers include the above expandable sheet and / or the above laminate.

[0120] One or more spacers can include a compressible material that contacts the expandable sheet and / or laminate.

[0121] The expandable sheet and / or laminate can be a lining in the inner wall of a module formed by a plurality of cells and / or a lining in the inner wall of a battery pack casing for an EV.

[0122] As used herein and in the claims, unless the context clearly indicates otherwise, the term "comprising" has its ordinary meaning of "including at least" and not the exclusive meaning of "consisting only of". The same applies to corresponding grammatical variations of the words "comprise", "comprises", etc.

[0123] Although the invention has been described in connection with numerous embodiments and implementations, the invention is not so limited and extends to various obvious modifications and equivalent arrangements within the scope of the appended claims. The features of the invention are presented in specific combinations in the claims, but it is contemplated that these features can be arranged in any combination and sequence.

Claims

1. An expandable sheet used in an electric vehicle (EV) battery for thermal runaway management, wherein the expandable sheet comprises: a non-woven fiber mat; 60 to 95 wt% of an alkali silicate binder; and a microporous and / or mesoporous and / or nanoporous additive, The expandable sheet is formed by impregnating the non-woven fiber mat with an alkali silicate solution, thereby injecting the alkali silicate binder into the non-woven fiber mat.

2. The expandable sheet according to claim 1, having a thickness of 1 mm or less.

3. The expandable sheet according to claim 1 or 2, wherein the alkali silicate binder has a silicon dioxide:alkali oxide molar ratio in the range of 2.5 to 4.

4. The expandable sheet according to any one of claims 1, 2, or 3, wherein the alkali silicate binder has a silicon dioxide:alkali oxide molar ratio in the range of 3 to 3.

3.

5. The expandable sheet according to any one of claims 1 to 4, comprising 75 to 85 wt% of the alkali silicate binder.

6. The expandable sheet according to any one of claims 1 to 5, wherein the microporous and / or mesoporous and / or nanoporous additive comprises aerogel particles having a hydrophobic surface group.

7. The aerogel particles have a particle size of 10 to 60 μm, a pore diameter of 20 to 100 nm, a porosity exceeding 90%, a bulk density of 0.02 to 0.1 g / cm ３ , and a surface area of 500 to 900 m ２ / g, and the expandable sheet according to claim 6.

8. The expandable sheet according to any one of claims 1 to 7, wherein the microporous and / or mesoporous and / or nanoporous additive comprises hollow microglass spheres, fumed silica, and / or cenospheres.

9. The expandable sheet according to any one of claims 1 to 8, comprising 1 to 10 wt% of an opacifier comprising any one or a combination of iron oxide, silicon carbide, and titania.

10. The expandable sheet according to any one of claims 1 to 9, comprising a char strength-imparting ceramic additive comprising any one or a combination of a metal oxide, a metal hydroxide, a metal carbonate, a metal silicate, and a metal powder.

11. The expandable sheet according to claim 10, comprising 3 to 8 wt% of the char strength-imparting ceramic additive.

12. The expandable sheet according to claim 10 or 11, wherein the char strength-imparting ceramic additive contains any one of magnesium oxide, aluminum oxide, calcium oxide, and zinc oxide, or a combination thereof.

13. The expandable sheet according to any one of claims 10 to 12, wherein the char strength-imparting ceramic additive contains aluminum trihydrate and / or magnesium dihydroxide.

14. The expandable sheet according to any one of claims 10 to 13, wherein the char strength-imparting ceramic additive contains calcium carbonate and / or zinc carbonate.

15. The expandable sheet according to any one of claims 10 to 14, wherein the char strength-imparting ceramic additive contains mica and / or talc.

16. The expandable sheet according to any one of claims 10 to 15, wherein the char strength-imparting ceramic additive contains the metal powder, and the metal powder contains iron, zinc, and / or aluminum.

17. The expandable sheet according to any one of claims 1 to 16, wherein the alkali silicate-based solution contains a surfactant that is stable within a pH range of 2 to 12.

18. The expandable sheet according to claim 17, wherein the alkali silicate-based solution contains 0.2 to 0.5% by weight of the surfactant.

19. The expandable sheet according to any one of claims 1 to 18, wherein the expandable sheet contains a curing agent containing sodium fluorosilicate and / or potassium dimethylsilicate.

20. The expandable sheet according to any one of claims 1 to 19, wherein the expandable sheet contains an organic additive containing polyvinyl alcohol and / or glycerol as the organic additive.

21. The expandable sheet according to any one of claims 1 to 20, wherein the non-woven fiber mat contains E and / or S type glass fibers.

22. The expandable sheet according to any one of claims 1 to 21, wherein the non-woven fiber mat contains fibers having diameters and lengths between 8 and 18 μm and between 10 and 75 mm, respectively.

23. The expandable sheet according to claim 22, wherein the non-woven fiber mat contains fibers having diameters and lengths between 10 and 15 μm and between 15 and 60 mm, respectively.

24. The expandable sheet according to any one of claims 1 to 23, wherein the non-woven fiber mat contains 5 to 20% by weight of an acrylic resin as a binder.

25. The expandable sheet according to claim 24, wherein the nonwoven fiber mat contains 8 to 15% by weight of the acrylic resin.

26. The nonwoven fiber mat has a basis weight of less than 400 g / m ２ The expandable sheet according to any one of claims 1 to 25.

27. The nonwoven fiber mat has a basis weight between 30 and 280 g / m ２ The expandable sheet according to any one of claims 1 to 26.

28. The expandable sheet according to any one of claims 1 to 27, wherein the expandable sheet contains 8 to 16% by weight of the nonwoven fiber mat.

29. The expandable sheet according to any one of claims 1 to 28, wherein the expandable sheet is manufactured to be 2 to 3 cm larger around all sides of the cell of the EV battery.

30. The expandable sheet is: 8 to 16% by weight of a nonwoven fiber mat; 75 to 85% by weight of an alkali silicate-based binder; 1 to 5% by weight of aerogel microparticles having a hydrophobic surface group; 3 to 8% by weight of a metal oxide and / or hydroxide, and includes the expandable sheet according to any one of claims 1 to 29.

31. The alkali silicate-based solution is: 92 to 97% by weight of an alkali silicate and water; a surfactant; aerogel microparticles having a hydrophobic surface group; a metal oxide and / or hydroxide, and includes the expandable sheet according to any one of claims 1 to 30.

32. The alkali silicate-based solution is: an opacifier; an organic additive; a hardener, and further includes the expandable sheet according to any one of claims 1 to 30.

33. A method for manufacturing the expandable sheet according to any one of claims 1 to 32, comprising: impregnating the nonwoven fiber mat with the alkali silicate-based solution by coating the nonwoven fiber mat with the alkali silicate-based solution using a doctor blade technique; drying the impregnated nonwoven fiber mat and includes the method.

34. i) adding an alkali silicate in the form of a solution; j) adding one or more surfactants to the solution of step a) to form a mixture; k) adding a heat insulating agent to the mixture; l) adding a char strength agent to the mixture; m) adding water to the mixture; n) adding a hardener to the mixture; o) stirring and mixing the mixture for a predetermined time of less than 30 minutes after each of steps a) to f); p) stirring and mixing for 2 to 3 hours after adding all the components to the mixture and includes preparing the alkali silicate-based solution according to the method described in claim 33.

35. A laminate including a plurality of stacked layers, wherein each layer is an expandable sheet according to any one of claims 1 to 32.

36. A method for manufacturing the laminate according to claim 35, comprising: Stacking the plurality of nonwoven fiber mats layer by layer, applying the alkali silicate-based solution between the layers to impregnate each layer of the nonwoven fiber mat with the alkali silicate-based solution; Cold pressing the plurality of stacked layers to form the laminate; A method comprising the above steps.

37. The expandable sheet according to any one of claims 1 to 32, or the laminate according to claim 35 or 36, wherein the expandable sheet and / or the laminate includes an adhesive backing to facilitate attachment onto the surface of the expandable sheet and / or the laminate.

38. An electric vehicle (EV) battery including one or more spacers disposed between cells in an EV battery to prevent thermal runaway in adjacent cells when thermal runaway occurs in one cell, wherein the one or more spacers include the expandable sheet according to any one of claims 1 to 32 and / or the laminate according to claim 35 or 36.

39. The EV battery according to claim 38, wherein the one or more spacers include a compressible material that contacts the expandable sheet and / or the laminate.

40. The EV battery according to claim 38 or 39, wherein the expandable sheet and / or the laminate is a lining in the inner wall of a module formed by the plurality of cells and / or a lining in the inner wall of the battery pack casing of the EV battery.

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