Laminated barrier having ceramic or aerogel layers defining a cavity containing a heat absorbing material - Patent Application 20070233633

Abstract

The article includes a multilayer laminate having: (a) a first surface layer having opposing major surfaces, the first surface layer comprising a crosslinked polysiloxane matrix having a flame retardant additive dispersed therein; (b) a central layer having opposing major surfaces, one major surface adhered to a major surface of the first surface layer, the central layer being selected from a ceramic fiber sheet and an aerogel sheet defining one or more voids; and (c) a second surface layer having opposing major surfaces, one major surface adhered to a major surface of the central layer opposite the major surface adhered to the first surface layer, the second surface layer having a composition as described for the first surface layer, although the first and second surface layers need not have the same composition, the article comprising a heat sink occupying the void defined by the central layer.

Description

[Technical field]

[0001] The present invention relates to a laminated article comprising a central layer of ceramic or aerogel material defining a void containing a heat absorbing material, the article being useful as a barrier material for electric vehicle battery packs. [Background technology]

[0002] Introduction Electric vehicle (EV) technology is becoming increasingly popular. EV technology utilizes battery packs to store energy and power the vehicle. The energy demands of the vehicles are high, especially as the desire and demand for EVs that can travel longer distances on each charge increases. Uncontrolled release of energy in a battery pack for an EV can be catastrophic due to the enormous heat release. Therefore, it is desirable to design a battery pack with protection against uncontrolled release of energy from the battery pack.

[0003] A battery pack for an EV typically includes multiple battery cells that are electrically connected together and assembled to form a battery pack directly or to form a module, and then multiple modules are stacked to form a battery pack. An EV may contain up to several thousand battery cells. A single cell failure may result in the release of enough energy to heat adjacent cells, resulting in the failure of these adjacent cells with the release of more energy, leading to thermal runaway and heat propagation. Therefore, it is desirable to identify barrier materials that can be present between the cells and modules of a battery pack and can insulate the adjacent cells from thermal energy release in the event of a cell failure.

[0004] Prefabricated ceramic sheets, such as ceramic fiber sheets, are commonly used as thermal insulation layers between cells in battery packs for EVs. However, ceramic sheets alone or even laminated ceramic sheets are often insufficient to prevent heat propagation and thermal runaway in battery packs. Although aerogel blankets may have better thermal insulation than prefabricated ceramic sheets, their performance may still be insufficient by themselves. Therefore, it is desirable to identify articles that provide flame retardancy and higher thermal insulation than simple ceramic sheets or simple aerogel sheets. Summary of the Invention

[0005] The present invention provides an article that provides flame retardancy and higher thermal insulation than simple ceramic or aerogel sheets. The invention is the result of the discovery of a multi-layer laminate comprising a ceramic or aerogel layer between two silicone layers, the ceramic or aerogel layer defining a cavity filled with a heat-absorbing agent. The silicone layer includes a flame-retardant additive and provides thermal insulation and flame-retardant barrier properties. The ceramic layer provides additional flame retardancy, while the cavity filled with the heat-absorbing agent provides even higher thermal barrier properties by absorbing heat and, at least in some cases, releasing the heat in heated gases to remove heat from areas of the battery pack experiencing exothermic failure. This combination of elements surprisingly works together to provide particularly desirable thermal and flame barrier properties for a laminate structure that may be present between cells of a battery pack.

[0006] The multi-layer laminate can achieve a "time to 180°C per millimeter of thickness" result of 20 seconds or more, even 25 seconds or more, or even 40 seconds or more in the thermal insulation test described herein. At the same time, the multi-layer laminate is flame-resistant as shown by the absence of flame when directly compressed against a hot plate at a temperature of at least 650°C in the flame resistance test method described herein. The multi-layer laminate can achieve these properties even at a thickness of 10 millimeters (mm) or less, or even 5 mm or less. Thus, the multi-layer laminate achieves the desired properties of functioning as a barrier material for use in EV battery packs.

[0007] In a first aspect, the invention provides an article comprising a multi-layer laminate, the multi-layer laminate comprising: (a) a first surface layer having opposing major surfaces, the first surface layer comprising a crosslinked polysiloxane matrix having a flame retardant additive dispersed therein at a concentration in the range of 5 to 95 weight percent based on the weight of the first surface layer; (b) a central layer having opposing major surfaces, one major surface adhered to a major surface of the first surface layer, the central layer being selected from a ceramic fiber sheet and an aerogel sheet; and (c) a second surface having opposing major surfaces. and a second surface layer having one major surface adhered to a major surface of the central layer opposite the major surface adhered to the first surface layer, the second surface layer having a composition as described for the first surface layer, although the first and second surface layers need not have the same composition, the central layer defining one or more voids such that a total volume of the voids defined in the central layer is within the range of 5 to 95 volume percent of the volume defined by the central layer, and the article including a heat sink occupying the voids defined by the central layer. The article may further comprise battery cells, the battery cells being electrically connected to each other with the multilayer stack present between the battery cells.

[0008] The laminates of the present invention are useful as thermal and flame barrier materials in battery packs, such as battery packs in EVs. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Test methods refer to the test method most recent to the priority date of this document unless a date is given with the test method number. Reference to a test method includes both a reference to the testing society and the test method number. The following test method abbreviations and identifiers apply herein: ASTM refers to ASTM International Method, END refers to European Norm, DIN refers to Deutsches Institut fur Normung, ISO refers to the International Organization for Standards, and UL refers to the Underwriters Laboratory.

[0010] Products identified by trade names refer to compositions available under those trade names as of the priority date of this document.

[0011] "Plurality" means two or more. "And / or" means "and, or alternatively." All ranges are inclusive of the endpoints unless otherwise indicated.

[0012] "Sheet" refers to an article having opposed major surfaces separated by a thickness that is less than 1 / 10th the length or width dimension defining the major surfaces.

[0013] Width, length, and thickness are mutually perpendicular dimensions of an object.

[0014] "Major surface" refers to the surface of an object having the largest planar surface area as well as the surface opposing that surface. Planar surface area refers to the surface area projected onto a plane to eliminate contributions to the surface area from contours on the surface. Opposing major surfaces are separated by the thickness dimension of the object.

[0015] The present invention is an article that includes a multi-layer laminate. The article can consist of the multi-layer laminate or can include components in addition to the multi-layer laminate. For example, the article can include battery cells with the multi-layer laminate present between the battery cells.

[0016] A multi-layer laminate comprises a first surface layer, a central layer, and a second surface layer, in that order relative to each other. "Laminate" means that the layers are on top of each other and are adhered to each other. Typically, the major surfaces of the adhered layers are adhered to each other. "Adhered to" means either directly attached with direct contact between the adhered layers, or attached via an adhesive, with adhesive present between the adhered layers. The adhesive can be a layer covering the entirety of the adhered surfaces, or it can be present over only a portion of the adhered surfaces.

[0017] The first and second surface layers may be the same or different in composition and / or size, but each is selected from materials having a similar composition and size description. The first and second surface layers each have opposing major surfaces and include a crosslinked polysiloxane matrix and a flame retardant.

[0018] The crosslinked polysiloxane matrix desirably has a 10 percent strain modulus of at least 100 Pascals (Pascal, Pa), and preferably has a 10 percent strain modulus of at least 200 Pa, at least 300 Pa, at least 400 Pa, at least 500 Pa, at least 600 Pa, at least 700 Pa, at least 800 Pa, at least 850 Pa, at least 900 Pa, at least 1000 Pa, at least 2000 Pa, at least 4000 Pa, at least 6000 Pa, at least 8000 Pa, at least 10 kiloPascals (kPa), at least 100 kPa, at least 500 kPa, at least 800 kPa, or even at least 870 kPa. Although there is no technical upper limit to the 10 percent strain modulus value of the crosslinked polysiloxane matrix, the crosslinked polysiloxane matrix often has an upper limit of its 10 percent strain modulus of 1 GigaPascal (GPa) or less, 0.5 GPa or less, 100 MegaPascal (MPa) or less, 50 MPa or less, 25 MPa or less, 15 MPa or less, 100 MPa or less, 5 MPa or less, 1 MPa or less, or even 900 kPa or less, while having a lower limit as mentioned above. The 10 percent strain modulus is the tensile stress of the material at 10 percent elongation, determined according to ASTM D412. Desirably, the crosslinked polysiloxane matrix is ​​flexible.

[0019] The crosslinked polysiloxane matrix can be a crosslinked liquid polysiloxane elastomer or a crosslinked polysiloxane gum. A "crosslinked liquid polysiloxane elastomer" is a polysiloxane elastomer made by crosslinking a liquid polysiloxane. Crosslinked liquid polysiloxane elastomers and crosslinked gums are well known and can be made by any known process. Desirably, the crosslinked liquid polysiloxane elastomer comprises 50 mole percent (mol%) or more, 60 mole% or more, 70 mole% or more, 80 mole% or more, 90 mole% or more, based on the total siloxane units, and is RSiO 3 / 2 and RSiO 2 / 2 The polysiloxane unit may contain 95 mol % or more of polysiloxane units selected from RSiO units. 1 / 2("M" type units), R2SiO 2 / 2 ("D" type units), RSiO 3 / 2 ("T" type units), and SiO 4 / 2 ("Q" type units), where each R is independently selected from hydrocarbyl and substituted hydrocarbyl groups, the oxygen atoms recited in the units refer to the oxygens bonded to silicon atoms of two different siloxane units, and the subscript on the oxygen refers to the number of shared oxygens in the molecule, dividing the molecule by two indicates that the oxygen atom is shared with another siloxane unit. Examples of polysiloxane elastomers suitable for use as the polysiloxane matrix include, for example, crosslinked dimethylvinyl terminated dimethyl, methylvinyl siloxane gums, and / or crosslinked dimethlyvinyl terminated dimethyl siloxane gums, each having a Williams plasticity of 154-155 millimeters per 100 millimeters (Williams Plasticity is determined according to ASTM D926).

[0020] Curing of the liquid siloxane and / or polysiloxane gum can be achieved, for example, by free radical, hydrosilylation, and / or condensation reactions. Free radical polymerization can be catalyzed, for example, by peroxide. The hydrosilylation curable silicone composition comprises one or more vinyl-containing siloxane polymers and one or more silicon hydride functional siloxanes. At least one of the vinyl-containing siloxane polymers and the silicon hydride functional siloxanes contains two or more of the specific functional groups to act as a crosslinker. Typically, a hydrosilylation catalyst, such as a platinum compound, is present to promote the hydrosilylation reaction. The condensation reaction curable silicone composition comprises a siloxane having a condensation curable functional group, such as any one or more selected from hydroxyl functional groups and hydrolyzable functional groups, such as alkoxy, carboxy, amido, enoxy, amino, oximo, and amoxy groups. Condensation reaction curable silicone compositions typically further comprise crosslinkers such as silanes with hydrolyzable groups, water scavengers such as vinyltrimethoxysilane and methyltrimethoxysilane, and curing catalysts such as titanium and tin compounds, and may be formulated to tailor the curing behavior, shelf life, and other properties after curing. Condensation reaction curable silicone compositions may be cured at room temperature or at elevated temperatures, with or without artificially added moisture in addition to that available from the atmosphere as it cures.

[0021] Desirably, the polysiloxane matrix is ​​a continuous non-porous sheet.

[0022] The first and second surface layers further comprise a flame retardant additive dispersed within the crosslinked polysiloxane matrix. Suitable flame retardant additives include any one or any combination of two or more selected from the group consisting of metal hydroxides, mixed metal hydroxides, hydrated metal salts, and combinations thereof. Desirably, the flame retardant additive is aluminum trihydrate, and any one or any combination of additives, or any combination of additives, or two or more additives in the group consisting of magnesium hydroxide, calcium hydroxide, magnesium carbonate hydroxide, aluminum carbonate hydroxide, boehmite, hydrated magnesium sulfate, magnesium carbonate trihydrate, and magnesium carbonate hydroxide tetrahydrate. Optionally, the polysiloxane layer may further comprise metal carbonates and bicarbonates in combination with the metal hydroxides, metal salts, mixed metal hydroxides, and / or hydrated metal salts to further improve flame retardancy. Examples of metal carbonates and bicarbonates include magnesium carbonate, calcium magnesium carbonate (e.g., commercially available as huntite), and sodium bicarbonate. The flame retardant additive may optionally be surface treated.

[0023] The flame retardant additives are present in each of the first and second surface layers in a concentration of 5 weight percent (wt%) or more, 10 wt% or more, 15 wt% or more, 20 wt% or more, 25 wt% or more, 30 wt% or more, and may be present in a concentration of 35 wt% or more, 40 wt% or more, 45 wt% or more, 50 wt% or more, 55 wt% or more, 60 wt% or more, 65 wt% or more, 70 wt% or more, 75 wt% or more, or even 80 wt% or more, while at the same time typically being present in a concentration of 95 wt% or less, and may be present in a concentration of 90 wt% or less, 85 wt% or less, 80 wt% or less, 75 wt% or less, 70 wt% or less, 65 wt% or less, 60 wt% or less, 55 wt% or less, or even 50 wt% or less, 45 wt% or less, 40 wt% or less, or 35 wt% or less.

[0024] The first and / or second surface layer may or may not include any one additional additive, or any combination of two or more additional additives. "Additional additives" are additives that are included in addition to the flame retardant additives already mentioned above. For example, the polysiloxane layer may include silica, calcium silicate, calcium metasilicate, fumed silica, precipitated silica, ground quartz, precipitated and ground calcium carbonate, calcium sulfate, magnesium sulfate, barium sulfate, zeolites, TiO2, ZnO, magnesium oxide, iron oxide, boron oxide, wollastonite, perlite, vermiculite, mica, kaolin, glass, glass bubbles, aerogel particles, diatomaceous earth, halloysite, magnetite, hematite; benzotriazole, ammonium polyphosphate, ammonium or aluminum alkyl phosphinate, melamine polyphosphate, organic phosphates, halogenated organic phosphates, other halogen-containing additives with or without antimony oxide. The composition may include any one additional additive, or any combination of two or more additional additives, selected from the group consisting of flame retardants, dihydrooxaphosphaphenanthrene, zinc stannate, zinc hydroxostannate, platinum metal and platinum metal compositions, colorants, e.g., carbon black and pigments (e.g., ultramarine pigment, and / or Yellow 109), stabilizers, e.g., other flame retardant additives, such as cerium hydroxide; curing catalysts, such as peroxides, organic stannates or titanates, platinum; curing reaction accelerators or retarders, such as amines, acetylenic alcohols, organic phosphines; rheology modifiers, such as diluents and thickeners; and / or density reducing additives, such as hollow glass or ceramic additives.

[0025] The combined concentration of the flame retardant additive and the additional additives in the surface layer is 95% by weight or less, and can be 90% by weight or less, 85% by weight or less, 80% by weight or less, 75% by weight or less, 70% by weight or less, 65% by weight or less, 60% by weight or less, 55% by weight or less, or even 50% by weight or less, 45% by weight or less, 40% by weight or less, or 35% by weight or less, based on the weight of the surface layer, provided that the amount of the flame retardant additive is within the range specified above for the flame retardant additive.

[0026] Typically, each surface layer has a thickness of 0.1 millimeter (mm) or more, and typically is 0.2 mm or more, 0.3 mm or more, 0.4 mm or more, 0.5 mm or more, 0.6 mm or more, 0.7 mm or more, 0.8 mm or more, 0.9 mm or more, 1.0 mm or more, 1.2 mm or more, 1.2 mm or more, 1.4 mm or more, 1.6 mm or more, 1.8 mm or more, or even 2.0 mm or more thick. There is no technical limit on the upper limit of how thick the polysiloxane layer can be. However, typically, in combination with any of the lower limits, the polysiloxane can be 10 mm or less, 5.0 mm or less, 3.0 mm or less, 1.0 mm or less, 0.8 mm or less, 0.7 mm or less, 0.6 mm or less thick, and 0.5 mm or less, 0.4 mm or less, or even 0.2 mm or less thick.

[0027] The central layer has opposed major surfaces, one major surface adhered to a major surface of the first surface layer and the opposing major surface adhered to a major surface of the second surface layer, The central layer is selected from the group consisting of a ceramic fiber sheet and an aerogel sheet.

[0028] Ceramic fiber sheets are non-woven or woven sheets containing a wide range of amorphous or crystalline mineral fibers, such as aluminosilicates, metal oxides (e.g., alumina, silica, zirconia), non-oxide materials (e.g., silicon carbide, silicon nitride, boron nitride), etc. Suitable ceramic fiber sheets are commercially available under the names CeraTex® Ceramic Fiber Paper, CeraTex® Ceramic Fiber Blanket, Fiberfrax® Ceramic Fiber Papers, Isofrax® 1260C Paper. (CeraTex is a trademark of Mineral Seal Corporation. Fiberfrax and Isofrax are trademarks of Unifrax I LLC). A desirable property of ceramic fiber sheets is flame retardancy above 100°C, more preferably above 650°C.

[0029] Aerogel sheets are sheets made of aerogel materials. In the broad scope of the present invention, the aerogel materials may include or consist of any aerogel material, such as silica aerogels, metal oxide aerogels, mixed metal oxide aerogels, organic or carbon aerogels, semiconducting metal aerogels, chalcogenide aerogels, metal aerogels, silane and siloxane modified aerogels, and reinforced forms of any of these aerogels. "Aerogels" include those known as "xerogels", which are porous structures typically formed by drying a wet gel, resulting in a volumetric shrinkage greater than 10% of the more traditionally known supercritically dried aerogels. The aerogel material may be a reinforced aerogel. Reinforced aerogels include aerogels with fiber reinforcement materials such as glass fibers and / or carbon fibers. Fiber reinforced aerogels may have fiber mats, meshes, or battings within the aerogel material. Such materials are commercially available and can be prepared by placing an aerogel precursor sol in or around a fiber mat, mesh, or batting and then converting the sol to an aerogel with the fiber mat, mesh, or batting bearing the aerogel. Fiber-reinforced silica aerogel is particularly desirable for use as the aerogel layer.

[0030] The central layer typically has an average thickness of 0.5 mm or more, and can have a thickness of 1.0 mm or more, 1.5 mm or more, 2.0 mm or more, 2.5 mm or more, 3.0 mm or more, 4.0 mm or more, 5.0 mm or more, 10 mm or more, 20 mm or more, 30 mm or more, or even 40 mm or more, while at the same time generally having a thickness of 50 mm or less, and can have a thickness of 40 mm or less, 30 mm or less, 20 mm or less, 10 mm or less, 5.0 mm or less, 4 mm or less, or even 3.0 mm or less.

[0031] The central layer defines one or more voids that can extend partially or entirely through the thickness of the central layer, and each void can have a volume of 5 volume percent or more, or even 10 volume % or more, or even 20 volume % or more of the total volume of the central layer. The total volume of void space defined by the central layer is 5 vol.% or more, and can be 10 vol.% or more, 15 vol.% or more, 20 vol.% or more, 25 vol.% or more, 30 vol.% or more, 35 vol.% or more, 40 vol.% or more, 45 vol.% or more, 50 vol.% or more, 55 vol.% or more, 60 vol.% or more, 65 vol.% or more, 70 vol.% or more, 75 vol.% or more, 80 vol.% or more, 85 vol.% or more, or even 90 vol.% or more of the total volume of the central layer, while at the same time it is typically 95 vol.% or less, and can be 90 vol.% or less, 85 vol.% or less, 80 vol.% or less, 75 vol.% or less, 70 vol.% or less, 65 vol.% or less, 60 vol.% or less, 55 vol.% or less, 50 vol.% or less, 45 vol.% or less, 40 vol.% or less, 35 vol.% or less, 30 vol.% or less, or even 25 vol.% or less.

[0032] The multi-layer laminate further includes a heat absorbing agent occupying the void defined by the central layer. The heat absorbing agent is typically in particulate form, with numerous particles of the heat absorbing agent occupying a given void. The heat absorbing agent is a material that absorbs heat when it decomposes to produce carbon dioxide and / or water at temperatures ranging from 80° C. to 550° C. The heat absorbing agents can all be the same or can be a combination of multiple different heat absorbing agents. Examples of heat absorbing agents that absorb heat and produce water when they decompose include metal hydroxides and hydrates of metal salts, such as aluminum hydroxide, magnesium hydroxide, calcium hydroxide, calcium-magnesium hydroxide, hydrotalcite, boehmite, talc, calcium sulfate hydrate, magnesium hydroxide, and zinc borate. Specific examples include hydrated magnesium sulfate minerals (e.g., epsomite), aluminum trihydrate, and magnesium hydroxide. Examples of endothermic agents that absorb heat and produce carbon dioxide upon decomposition include magnesium carbonate, calcium carbonate, magnesium calcium carbonate, sodium bicarbonate, lithium carbonate, magnesium bicarbonate, and potassium bicarbonate. Examples of endothermic materials that absorb heat and release both water and carbon dioxide while decomposing include hydrated magnesium carbonate minerals such as hydromagnesite. The endothermic agent can fully or partially occupy the void space defined within the central layer. Desirably, the void space and the endothermic agent are located throughout the central layer, rather than being concentrated in a small portion of the central layer. The role of the endothermic agent is to absorb heat and release water or carbon dioxide, thereby reducing heat transfer through the multi-layer stack, and therefore it is optimal to distribute the endothermic agent widely throughout the central layer. In this regard, it is desirable for the central layer to define voids widely distributed throughout the central layer, and for the endothermic agent to occupy these voids.

[0033] The heat absorbing agent occupies the void volume defined within the central layer, and therefore can occupy anywhere within the range of 5 to 95% by volume of the volume defined by the central layer. Desirably, the heat absorbing agent occupies 40% by volume or more, preferably 45% by volume or more, 50% by volume or more, or even 55% by volume or more of the volume defined by the central layer, and at the same time, typically 95% by volume or less, 90% by volume or less, 85% by volume or less, 80% by volume or less, 75% by volume or less, 70% by volume or less, 65% by volume or less, 60% by volume or less, or even 55% by volume or less, 50% by volume or less, or even 45% by volume or less.

[0034] One example of a desirable void orientation in the central layer is to have one large void space defined by the perimeter of the central layer material such that the heat absorbing material in the void space occupies a majority of the volume of the central layer space in a continuous manner. Another example of a desirable void orientation is to have multiple void spaces defined and occupied by heat absorbing material throughout the central layer to effectively provide a wide distribution of the heat absorbing material throughout the central layer.

[0035] The heat sink agents are typically sealed within the void they occupy by the central layer and the first and second surface layers.

[0036] The multi-layer laminate can be made by any conceivable means, for example, a first surface layer can be adhered to a central layer, then a heat absorbing agent can be disposed in the void defined by the central layer, and then a second surface layer can be adhered onto the central layer, sandwiching the central layer and the heat absorbing agent between the first and second surface layers.

[0037] One or both of the surface layers may be directly adhered to the central layer, or neither may be directly adhered to the central layer. To achieve direct adhesion between the surface layer and the central layer, the surface layer may be cured to form a crosslinked polysiloxane matrix while in contact with the central layer.

[0038] One or both surface layers may be adhered to the central layer using an adhesive, or neither may be adhered. The adhesive may be between the surface layer and the central layer and adhere the two layers together. The adhesive may completely cover the surfaces that are adhered to each other, forming a film between the two layers. Alternatively, the adhesive may only cover a portion of the surfaces that are adhered to each other. The adhesive may be continuous, such as a film or bead, or discontinuous, such as a series of dots, unconnected beads, or a combination of beads and dots. The adhesive may be in any pattern that adheres the surface layer to the central layer.

[0039] The adhesive, if used, can be a silicone adhesive. The adhesive can be a one-part or two-part adhesive. The adhesive desirably contains a flame retardant additive. For example, the adhesive can be a silicone foam adhesive, such as that available from The Dow Chemical Company under the name DOWSIL™ 3-8235 Silicone Parts A and B. DOWSIL is a trademark of The Dow Chemical Company. Desirably, the adhesive is suitable for high temperature applications.

[0040] The multi-layer laminate is particularly useful as an insulator between cells of a battery module for an electric vehicle. In this regard, the article of the present invention can further include a plurality of battery cells having the multi-layer laminate present between the battery cells. The article can be a battery module, which can be in a vehicle, including a housing in which a plurality of battery cells are present having the multi-layer laminate present between the battery cells. EXAMPLES

[0041] Table 1 lists the materials for use in the examples below.

[0042] [Table 1] XIAMETER is a trademark of Dow Corning Corporation. DOWSIL is a trademark of The Dow Chemical Company. HALTEX is a trademark of TOR Minerals International. ZEROGEN is a trademark of JM Huber Corporation. WOLLASTOCOAT is a trademark of NYCO Minerals, Inc. CAB-O-SIL is a trademark of Cabot Corporation. CeraTex is a trademark of Mineral Seal Corporation.

[0043] Preparation of Additive A2. Prepare A2 as described in WO2020131985 using the standard mixing procedure described in ASTM D3182. A2 consists of 7 wt% magnesium ferrite, 23 wt% ultramarine pigment, 23 wt% titanium dioxide, 6 wt% chromium oxide green, and 41 wt% G1.

[0044] Preparation of the polysiloxane layer. The polysiloxane layer is prepared as described in WO2020131985 using the standard mixing procedure described in ASTM D3182. The polysiloxane layer is composed of 17.19 wt% B1, 13.45 wt% G1, 33.52 wt% alumina trihydrate, 20.12 wt% magnesium hydroxide, 0.8 wt% magnesium silicate, 8.05 wt% calcium metasilicate, 2.68 wt% A1, 1.07 wt% P1, 0.24 wt% F1, and 2.88 wt% A2. The polysiloxane layer is prepared to a thickness of 0.6 mm by calendaring the composition using a two-roll mill. The sheet is cured at 120 degrees Celsius (°C) for 15 minutes in a hot press under 30 tons of pressure on the sample within a 30.5 centimeter wide by 30.5 centimeter long metal chase with a thickness of 0.6 mm to form a sample with dimensions of 30.5 centimeters by 30.5 centimeters by 0.6 mm thick. The polysiloxane layer has a 10 percent elastic modulus of 0.87 megapascals determined according to ASTM D412.

[0045] Sample characterization The samples are characterized using the following insulation and flame resistance tests.

[0046] Insulation Test. A hot plate is placed in a hydraulically enclosed space vented from one side of the hot plate, with the vent port directly adjacent to the specimen. A porous ceramic refractory insulator is placed on the top surface of the hot plate and the hot plate is heated to 710°C. Four thermocouple probes are attached onto an aluminum heat sink using Kapton tape. The specimen is placed on the aluminum heat sink and secured to the aluminum heat sink using Kapton tape. Another thermocouple is secured onto the specimen surface using Kapton tape. The insulator is removed from the heated surface of the hot plate and the specimen is rapidly placed onto the heated surface of the hot plate with the aluminum heat sink on the opposite side of the specimen from the hot plate. A pressure of 355 kilopascals is rapidly applied to compress the specimen against the hot plate. The temperature of the hot plate surface and the specimen are monitored using a data logger. When the temperature of the specimen side opposite the hot plate reaches 180°C, the pressure is released and the test is terminated. The time required for the specimen side opposite the hot plate to reach 180°C is recorded as the insulation time in seconds. The insulation time is divided by the thickness of the sample to provide the "time to 180°C per millimeter" in seconds per millimeter (s / mm). Longer times correspond to better insulation.

[0047] Flame Resistance Test. During the insulation test, the specimen is observed to see if it ignites. If flames are observed, note if they self-extinguish within the test time (the time required to reach 180°C). General observation indicates that specimens that ignite generally do so within the first 5 seconds after contact with the hot plate. If the specimen ignites during the test time, it fails the flame resistance test.

[0048] sample Comparative Example (Comp Ex) A. Comp Ex A is a 10 centimeter (cm) by 10 cm square piece of ceramic sheet. Characterization results: Sample thickness: 3 mm. Insulation test: Time to 180° C. per mm of thickness: 0.63 s / mm. Flame resistance test: No flames.

[0049] Comp Ex B. Comp Ex B is prepared as a laminate using two 10 cm x 10 cm square pieces of polysiloxane layer and one 10 cm x 10 cm square piece of ceramic sheet. 2 grams (grams, g) of silicone adhesive is applied on both opposing major surfaces of the ceramic sheet by dispensing part A and part B of the silicone adhesive through a static mixture and mixing the parts together as they are dispensed. The silicone adhesive is applied as a bead about 3 millimeters in diameter on the major surface of the center layer around the void. A sheet of polysiloxane layer is adhered to each side of the ceramic sheet to form a prelaminate. The prelaminate is placed in a chaise that is 25.4 cm x 25.4 cm x 4 mm and a 10 ton weight is applied on the laminated layers to press them together. The compressed laminate layers are cured at 25°C for 24 hours or to 60°C for 10 minutes to achieve Comp Ex B. Comp Ex B has a final thickness of 4.5 mm. Characterization results: Sample thickness: 4.5mm. Thermal insulation test: Time to 180℃ per mm of thickness 18s / mm. Flame resistance test: No flames.

[0050] Example (Ex) 1. Prepare Ex1 similarly to Comp Ex B, except that nine circular voids with a diameter of 2.54 cm are defined in the ceramic sheet, distributed uniformly throughout the thickness of the ceramic sheet. Prior to forming the laminate, 3 grams of hydrated magnesium carbonate mineral is distributed evenly into the nine voids to provide 44% by volume of heat sink in the ceramic sheet layer (center layer of the laminate). Characterization results: Sample thickness: 4.5 mm. Thermal insulation test: Time to 180° C. per mm of thickness 24 s / mm. Flame resistance test: No flame.

[0051] Ex 2. Prepare Ex 2 similarly to Comp Ex B, except that one square cavity having dimensions of 7.62 cm x 7.62 cm is defined in the center of the ceramic sheet throughout its thickness. Prior to forming the laminate, 5 grams of hydrated magnesium carbonate mineral is distributed into the cavity to provide 56% by volume of heat sink in the ceramic sheet layer (center layer of the laminate). Characterization results: Sample thickness: 4.5 mm. Thermal insulation test: Time to 180°C per mm of thickness 45 s / mm. Flame resistance test: No flame.

[0052] Ex 3. Prepare Ex 3 similarly to Comp Ex B, except that one square cavity having dimensions of 7.62 cm x 7.62 cm is defined in the center of the ceramic sheet throughout its thickness. Prior to forming the laminate, 22 grams of hydrated magnesium sulfate mineral is distributed into the cavity to provide 56% by volume of heat sink in the ceramic sheet layer (center layer of the laminate). Characterization results: Sample thickness: 4.5 mm. Thermal insulation test: Time to 180°C per mm of thickness 21 s / mm. Flame resistance test: No flame.

[0053] Ex 4. Prepare Ex 4 similarly to Comp Ex B, except define 9 circular voids in the ceramic sheet having a diameter of 2.54 cm, evenly distributed throughout the ceramic sheet throughout its thickness. Prior to forming the laminate, distribute 10 grams of sodium bicarbonate evenly into the 9 voids to provide 44% by volume of heat sink in the ceramic sheet layer (center layer of the laminate). Characterization results: Sample thickness: 4.5 mm. Thermal insulation test: Time to 180°C per mm of thickness 32 s / mm. Flame resistance test: No flame.

[0054] The results show that including a heat sink in the center layer of the laminate structure provides greater thermal insulation as evidenced by a longer time to 180°C per mm of thickness compared to similar laminate structures without the heat sink or simply the ceramic center layer.

Claims

1. 1. An article comprising a multi-layer laminate, the multi-layer laminate comprising: (a) a first surface layer having opposed major surfaces, the first surface layer comprising a crosslinked polysiloxane matrix having a flame retardant additive dispersed therein at a concentration in the range of 5 to 95 weight percent based on the weight of the first surface layer; (b) a central layer having opposing major surfaces, one major surface adhered to a major surface of the first surface layer, the central layer being selected from a ceramic fiber sheet and an aerogel sheet; (c) a second surface layer having opposing major surfaces, one major surface adhered to a major surface of the central layer opposite the major surface adhered to the first surface layer, the second surface layer having a composition as described for the first surface layer, although the first and second surface layers need not have the same composition; the central layer defines one or more voids such that the total volume of the voids defined in the central layer is in the range of 5 to 95 volume percent of the volume defined by the central layer, and the article includes a heat absorbing agent occupying the voids defined by the central layer.

2. 10. The article of claim 1, wherein the first and second surface layers each have a 10 percent strain modulus of at least 100 Pascals determined according to ASTM D412.

3. 10. The article of claim 1, wherein each of the first and second surface layers each has an average thickness in the range of 0.1 to 3.0 millimeters.

4. The article of claim 1, wherein the central layer has an average thickness of 0.5 to 50 millimeters.

5. 10. The article of claim 1, wherein the first and second surface layers each contain a flame retardant at a concentration in the range of 50 to 85 weight percent based on the weight of the layer in which it is included.

6. The article of claim 1 , wherein the heat-absorbing agent is present in a concentration ranging from 40 to 60 volume percent of the volume defined by the central layer.

7. 10. The article of claim 1, wherein the heat absorbing agent is one or more selected from the group consisting of hydrated magnesium carbonate mineral, hydrated magnesium sulfate mineral, sodium bicarbonate, aluminum trihydrate, and magnesium hydroxide.

8. The article of claim 1 , wherein the multi-layer laminate further comprises an adhesive between the central layer and each of the first and second surface layers.

9. The article of claim 8 wherein the adhesive is a silicone adhesive.

10. The article of any one of claims 1 to 9, further comprising battery cells, the battery cells being electrically connected to one another with the multi-layer stack present between the battery cells.