Thermal barrier

Abstract

Described herein is a thermal barrier comprising (i) a layer of a nonwoven fibrous thermal insulation comprising a fiber matrix of inorganic long fibers; (ii) a binder dispersed within the fiber matrix so as to hold together the fiber matrix; (iii) first particles dispersed within the fiber matrix, wherein the first particles are fumed silica; second particles dispersed within the fiber matrix, wherein the second particles are inorganic aerogel particles and wherein the ratio of first particles to second particles is 30:70 to 60:40 based on weight. By blending the first and second particles, a thermal barrier with improved thermal and elastomeric properties can be achieved for use in automotive applications, such as a battery assembly in an electric vehicle.

Description

THERMAL BARRIERTECHNICAL FIELD

[0001] The present disclosure relates to a thermal barrier comprising a blend of fumed silica and inorganic aerogel, which has good thermal and elastic properties. Such thermal barrier materials may be used within a battery assembly, e.g., like a battery assembly used in an electric vehicle.SUMMARY

[0002] Electric motors used in electric or hybrid vehicles (e.g., automobiles) are powered, at least in part, by batteries. Lithium-ion batteries are typically used in such applications. These batteries are disposed within the vehicle compactly to save space. Typically, the lithium-ion batteries comprise a battery module or assembly of individual battery cells. In an unfortunate circumstance, these batteries may experience a thermal runaway condition, where one of the cells malfunctions due to a variety of reasons and generates a large amount of heat. The heat can get transferred to the adjoining functioning cells and make them malfunction. The heat can also start a fire. Under such circumstances, the complete battery module can ignite due to the propagation of the heat, eventually engulfing the vehicle, creating a safety hazard to the vehicle, the occupant of the vehicle, and the surroundings of the vehicle. Global regulatory bodies are moving towards enforcing a regulation that would require the battery manufacturers to isolate the malfunctioning cell, thereby avoiding spreading the heat to adjoining cells, and provide the occupants of a vehicle a certain amount of time to evacuate the vehicle. One strategy to meet these requirements is to use a thermal barrier between cells that can delay the thermal runaway propagation.

[0003] In addition to being thermally insulating, a thermal runaway barrier also needs to provide cushioning properties. The thermal barrier needs to fit snugly between adjoining cells of the battery module and occupy the gap between the cells. The thermal barrier should be elastomeric, having the ability to compress and recover (or expand) in response to the expansion and contraction of the cells during the operation of the battery.

[0004] Thus, there is a need to identify a thermal barrier that has good insulative properties while also providing improved compression performance.

[0005] In a first aspect, the present disclosure relates to a thermal barrier for being disposed between battery cells of a battery assembly, said thermal barrier comprising: a layer of a nonwoven fibrous thermal insulation comprising a fiber matrix of inorganic long fibers; a binder dispersed within the fiber matrix so as to hold together the fiber matrix; first particles dispersed within the fiber matrix, wherein the first particles are fumed silica having a first diameter;second particles dispersed within the fiber matrix, wherein the second particles are inorganic aerogel particles having a second diameter; wherein the ratio of first particles to second particles is 30:70 to 60:40 based on weight, and wherein the first diameter is smaller than the second diameter.

[0006] In another aspect, the present disclosure also relates to a battery cell module for an electric vehicle, said battery cell module comprising: a plurality of battery cells disposed in a housing; and a plurality of thermal barriers as disclosed herein; wherein one thermal barrier is disposed between each pair of adjacent battery cells.

[0007] In yet a further aspect, the present disclosure also relates to a method of making the thermal barrier disclosed herein, the method comprising: forming a layer of nonwoven fibrous thermal insulation using a wet-laid process or dry -laid process; providing first particles, wherein the first particles are fumed silica; disposing the first particles so as to be evenly or uniformly distributed throughout or within the layer of nonwoven fibrous thermal insulation; providing second particles, wherein the second particles are inorganic aerogel particles; and disposing the second particles so as to be evenly or uniformly distributed throughout or within the layer of nonwoven fibrous thermal insulation.

[0008] The above summary is not intended to describe each embodiment. The details of one or more embodiments of the invention are also set forth in the description below. Other features, objects, and advantages will be apparent from the description and from the claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a plot of the thermal and elastomeric properties versus the percentage of fumed silica of thermal barriers according to Samples 1-5.DETAILED DESCRIPTION

[0010] As used herein, the term“a”, “an”, and “the” are used interchangeably and mean one or more; and“and / or” is used to indicate one or both stated cases may occur, for example A and / or B includes, (A and B) and (A or B).

[0011] Also herein, recitation of ranges by endpoints includes all numbers subsumed within that range (e.g., 1 to 10 includes 1.4, 1.9, 2.33, 5.75, 9.98, etc.).

[0012] Also herein, recitation of “at least one” includes all numbers of one and greater (e.g., at least 2, at least 4, at least 6, at least 8, at least 10, at least 25, at least 50, at least 100, etc.).

[0013] As used herein, “comprises at least one of’ A, B, and C refers to element A by itself, element B by itself, element C by itself, A and B, A and C, B and C, or a combination of all three.

[0014] In the present disclosure, it has been found that by blending fumed silica with inorganic aerogel particles, a thermal barrier material can be achieved that has both good thermal and elastomeric properties.

[0015] The thermal barrier disclosed herein comprises a layer of a nonwoven fibrous thermal insulation comprising a fiber matrix of inorganic fibers. The thermal barrier may comprise of one or more layers of a nonwoven fibrous thermal insulation comprising a fiber matrix of inorganic fibers. The nonwoven fibrous thermal insulation may be dry -laid or wet-laid. The nonwoven fibrous thermal insulation may be in the form of a mat, sheet, strip, or three-dimensional thin-walled structure.

[0016] As used herein, the term “inorganic” refers to ceramic or otherwise nonmetallic (i.e., not a metal, metal alloy, or metal composite) inorganic material.

[0017] The inorganic fibers typically have a mean aspect ratio, i.e., a mean length to diameter ratio, of greater than 1000. In some embodiments, the mean aspect ratio of the inorganic long fibers may be from at least 1000, 1500, 2000, 2500, 3000, 4000, 5000, or even 8000. In some embodiments, the mean aspect ratio of the inorganic long fibers may be from at most 70000, 60000, 50000, or even 40000. The mean aspect ratio of the inorganic fibers may also be greater than 70000. The mean aspect ratio is measured by measuring length and diameter of individual fibers using for example a light microscope or calibrated ruler and calculating the aspect ratio, i.e., the length to diameter ratio. The aspect ratio of 50 individual fibers is determined and the average value is calculated. The diameter of the inorganic fibers may be from 1 to 20 pm. The length of the inorganic fibers may be from 1 mm to 400 mm, or more.

[0018] The inorganic fibers of the fiber matrix may be selected from the group of fibers consisting of alkaline earth silicate fibers, refractory ceramic fibers (RCF), polycrystalline wool (PCW) fibers, basalt fibers, glass fibers, silica fibers, and combinations thereof. Glass fibers and silica fibers typically do not contain any or only nominal shot particles. PCW typically contains a maximum of 5% shot particles, while alkaline earth silicate (AES) fibers contain up to 60% shot particles when uncleaned and as low as 10% - 30% minimum shot particles when cleaned. Shot particles consist of globular grains that were not turned into fiber during the manufacturing process.

[0019] The layer of nonwoven fibrous thermal insulation may comprise an amount of inorganic fibers in the range of from at least 15, 20 or even 25 percent by weight and at most 90, 80, 70, or even 60 percent by weight, based on the total weight of the nonwoven fibrous thermal insulation.

[0020] The layer of nonwoven fibrous thermal insulation of the thermal barrier disclosed herein comprises first particles and second particles dispersed within the fiber matrix. The first particles are fumed silica particles, while the second particles are an inorganic aerogel.

[0021] The first and second particles may be dispersed evenly, uniformly, generally or otherwise throughout or to the extent permitted by the manufacturing process (e.g., there can be a little sedimentation of the particles on the bottom of the mat in both the dry laid and wet laid processes) within the fiber matrix.

[0022] Fumed silica are silica materials known to those of skill in the art as being comprised of primary particles that are essentially irreversibly bonded together in the form of aggregates, in the absence ofhigh-shear mixing. These fumed silica particles have an average size greater than 100 nm (e.g., typically of at least 200 nanometers) and from which it is not possible to straightforwardly extract individual primary particles. The aggregates can form larger accumulations through entanglement and electrostatic interactions. These agglomerates have a size of up to 300 pm (e.g. typically of about 100 micrometers) and can be easily reduced by shear forces.

[0023] In some embodiments, the surface of the fumed silica is unmodified. In some embodiments, the fumed silica is hydrophilic in nature. For example, having mainly (>50, or even 60%) hydrophilic silanol groups Si-OH) on the surface. In some embodiments, the hydrophilic silica has a methanol number of less than 35, 32, or even 30, for example, wherein the fumed silica is titrated with methanol and measured with a wettability tester to determine wetting.

[0024] Examples of useful commercially available hydrophilic, silica include those available from Cabot Corp. (Boston, MA) under the trade designation “CAB-O-SIL H-5” and “CAB-O-SIL EH-5” or “AEROSIL 200” and “AEROSIL 300” available from Evonik, Essen, Germany.

[0025] The particles of fumed silica may have a specific surface area in the range of from about 100 m2 / g up to about 400 m2 / g as measured by Brunauer-Emmett-Teller (BET) analysis with nitrogen gas.

[0026] In some embodiments, the fumed silica has an d50 (median) particle size of at most 10 mm and may be from 1 pm to 1 mm, or from 10 pm to 1 mm, or from 100 pm to 1mm. The particle size of the fumed silica can be determined based on techniques known in the art, for example, microscopy, electrical impedance, or light scattering techniques. A particle size distribution can be obtained by scattering techniques, reporting dlO, d50 and d90 values. In some embodiments, the fumed silica has a d50 when measured using a light scattering technique as disclosed herein of at least at least 10, 25, 40, 50, 60, 75, 90, 100, 150, or even 200 micrometers. In some embodiments, the fumed silica has a d50 of at most 1, 0.75, 0.5, 0.2, or even 0.1 micrometers. The d50 measurement, or median, is where 50 percent by volume of particles in the distribution are smaller than the indicated size diameter. In some embodiments, the dlO (where 10 percent by volume of particles fall below this diameter value) of the particle size distribution, can be at least 1, 2, 5, 8, 10, 15, 20, or even 25 micrometers. In some embodiments, the d90 (where 90 percent by volume of particles fall below this diameter value) of the particle size distribution is no greater than 500, 400, 300, 200, or even 150 micrometers.

[0027] The shape of the fumed silica particles may be spherical, irregular, platelet-shaped, or any other shape.

[0028] The inorganic aerogel particles are solid, amorphous materials composed of silica. Silica aerogels are typically highly porous material (e.g., greater than 60%, even 80 to 99.8%). Exemplary surface areas of aerogels are 500 to 1200 m2 / g or even 30 to 550 m2 / g as measured by techniques known in the art, such as BET analysis with nitrogen gas.

[0029] In some embodiments, the surface of the inorganic aerogel particles is modified. Examples of useful commercially available hydrophobically modified aerogel particles include those available from Cabot Corp, under the trade designation “ENTERA” such as “ENTERA EV5200” or “ENTERA EV5400”.

[0030] The inorganic aerogel particles are used as received and may comprise particles composed of primary particles that are essentially irreversibly bonded together in the form of aggregates in the absence of high-shear mixing, crushing, grinding, etc. In some embodiments, the inorganic aerogel particles have a d50 (median) particle size of at most 10 mm and may be from 1 pm to 10 mm, or from 10 pm to 10 mm, or from 100 pm to 10 mm, or from 1 mm to 10 mm. The particle size of the inorganic aerogel particles can be determined based on techniques known in the art. In some embodiments, the inorganic aerogel particles have a d50 when measured using a light scattering technique as disclosed herein of at least at least 10, 25, 50, 100, 250, 300, 400, or even 500 micrometers. In some embodiments, the inorganic aerogel particles have a d50 of at most 10, 5, 2, 1.5, 1, 0.8, 0.6, or even 0.5 millimeter (mm). In some embodiments, the dlO of the particle size distribution, can be at least 50, 100, 150, or even 200 micrometers. In some embodiments, the d90 of the particle size distribution is no greater than 2, 1.5, 1, 0.9, or even 0.8 mm.

[0031] The shape of the inorganic aerogel particles may be spherical, irregular, platelet-shaped, or any other shape.

[0032] The layer of nonwoven fibrous thermal insulation may comprise the first and second particles in a total amount of at least 10, 15, 20, 25, 30, or even 35% by weight, based on the total weight of the nonwoven fibrous thermal insulation. The layer of nonwoven fibrous thermal insulation may comprise the first and second particles in a total amount of up to 40, 45, 50, 55, or even 60% by weight, based on the total weight of the nonwoven fibrous thermal insulation. For example, a particle content as high as 60% by weight can be achieved using a dry -laid process, and as high as 50% by weight using a wet-laid process. The layer of nonwoven fibrous thermal insulation may comprise the first particles in an amount of at least 5, 10, 20, or even 25 percent by weight and at most 30, 35, 40, 45, or even 50 percent by weight, based on the total weight of the nonwoven fibrous thermal insulation. The layer of nonwoven fibrous thermal insulation may comprise the second particles in an amount of at least 5, 10, 15, or even 20 percent by weight and at most 25, 30, 35, 40, or even 50 percent by weight, based on the total weight of the nonwoven fibrous thermal insulation. In some embodiments, the layer of nonwoven fibrous thermal insulation comprises more second particles than first particles.

[0033] The layer of nonwoven thermal insulation of the thermal barrier disclosed herein comprises a binder dispersed within the fiber matrix so as to hold together the fiber matrix. The binder may be an organic or inorganic binder, e.g., an organic or inorganic adhesive binder, organic or inorganic binder fibers that are stitched or otherwise mechanically entangled into the fiber matrix so as to hold together the fiber matrix. The binder may be dispersed evenly, uniformly, generally or otherwise throughout or to the extent permitted by the manufacturing process within the fiber matrix so as to bond together the inorganic long fibers and first and second particles or otherwise hold together the fiber matrix for as long as needed to at least survive the degree of handling required (e.g., during the encapsulation process) before being installed between battery cells.

[0034] Inorganic binders, organic binders, or a combination of both can be useful according to the present disclosure and may include, e.g., those disclosed in US 8,834,759 (Liu et. al). An example of aninorganic binder useful in both dry -laid or wet-laid fiber processing can include particles of silicone that convert to fusible silica when heated. An organic-inorganic hybrid binder may also be useful such as, those available under the trade designation “WACKER MQ 803 TF”, which is a co-hydro lysis product of tetra-alkoxy silane (Q unit) and trimethyl-alkoxy silane (M unit). The chemical structure of “WACKER MQ 803 TF” can be seen as a three dimensional network of poly silicic acid units which are end-blocked with trimethylsilyl groups. Some residual ethoxy and hydroxy functions are present. The average molecular weight can be exactly controlled by the ratio of M and Q units. This ratio approximately is 0.67 for “WACKER MQ 803 TF”.

[0035] The binder dispersed within the fiber matrix may be in the form of polymer fibers. Advantageously, the binder may be in the form of bicomponent core-sheath polymer fibers, such as coresheath polyester / polyethylene fibers, wherein the sheath melts and holds the nonwoven fibrous thermal insulation together while the core provides mechanical support.

[0036] Exemplary binder fibers include the use of bicomponent core-sheath polymeric fibers in a dry- laid process. In a wet-laid process, ethylene vinyl acetate latex dispersion binder, bicomponent coresheath polymeric fibers, or a combination of both can be used. When a polymeric binder fiber is used, the binder can be activated by heating and compressing the nonwoven fibrous thermal insulation material. A combination of organic and inorganic binder can also be used.

[0037] The organic binders as used for the thermal barrier disclosed herein may be in the form of polymer fibers (e.g., PE / PET, PET, FRPET), dry polymer powder (e.g., LDPE, polyamide, epoxy resin powder (e.g., available under the trade designation “3M SCOTCHCAST 265”, “3M SCOTCHKOTE 6258”)), or a liquid binder (e.g., acylic latex, ethylene vinyl acetate (e.g., EAF68) latex, silicone, polyurethane etc.).

[0038] The layer of nonwoven fibrous thermal insulation may comprise the binder in an amount of at least 2.5, 3, 4, 4.5, 5, 5.5, 6, or even 6.5% by weight, based on the total weight of the nonwoven fibrous thermal insulation. The layer of nonwoven fibrous thermal insulation may comprise the binder in an amount of up to 7, 7.5, 8, 8.5, 9, 9.5, 10, 15, or even 20% by weight, based on the total weight of the nonwoven fibrous thermal insulation.

[0039] The thermal barrier disclosed herein is compressible, meaning that the thermal barrier has elastomeric properties. In some embodiments, the thermal barrier material when tested with a single compression test, such as ASTM D3574-17 or the Single Compression Test disclosed herein, has a normalized hysteresis loss of at most 78, or even 79%. In some embodiments, the thermal barrier material can be tested under repeated compression cycles such as the Cyclic Compression Test disclosed herein, to understand the performance of the thermal barrier material when tested under repeated compression cycles. In some embodiments, the thermal barrier material has minimum peak pressure of at least 22, 23, 24, 25, or even 26 kPa (kiloPascals). In some embodiments, the thermal barrier material has minimum peak pressure of at least 22, 23, 24, 25, or even 26 kPa at the 1199 cycle. In some embodiments, the thermal barrier material has maximum peak pressure of at least 1000, 900, 800, or even 700 kPa at the1199 cycle. In some embodiments, the thermal barrier material has an amplitude (maximum peak pressure - minimum peak pressure) of at most 1000, 900, 800, or even 700 kPa.

[0040] The thermal barrier disclosed herein not only is compressible, but also retains its thermal properties. In some embodiments, the thermal barrier material takes at least 330, 350, or even 375 seconds to reach 120°C when heated to 700°C in the Hot-side / Cold-side test described below.Advantageously, the thermal barriers of the present disclosure have an optimum range of fumed silica and aerogel to balance the thermal and compressive properties of the particles. As shown in the samples below, there is a tradeoff between an increase in pressure and an increase in time to reach 120°C in the hot-side / cold-side test. The increases were not linear and there appears to be an optimum range for the first and second particles. It has been discovered that the fumed silica provides better thermal properties to the thermal barrier as compared to the inorganic aerogel. However, the inorganic aerogel tends to provide better compression resistance or elasticity. Thus, by blending the fumed silica with inorganic aerogel particles in a ratio of 60:40 to 30:70 the thermal and elastomeric properties can be balanced as will be disclosed herein. In one embodiment, the thermal barrier comprises a ratio of first particles (or fumed silica) to second particles (or inorganic aerogel) of at least 60:40, 55:45, or even 50:50. In one embodiment, the thermal barrier comprises a ratio of first particles (or fumed silica) to second particles (or inorganic aerogel) of at most 30:70, 35:65, 40:60, 45:55, or even 50:50.

[0041] In some embodiments, the thermal barrier of the present disclosure has a thermal conductivity at 25 °C of at least 25, 30, 35, or even 40 milliWatts per meter Kelvin (mW / m K) at a thickness of 10 mm.

[0042] The thermal barrier exerts a pressure in an installed (i.e., compressed) condition on an adjacent battery cell.

[0043] In some embodiments, the layer of nonwoven fibrous thermal insulation may have an installed thickness in the range of at least 0.5, 0.6, 0.8, 1, 1.2, 1.4, or even 1.5 mm and at most 10, 8, 6, 5, 3, 2.5, 2, 1.5, 1.4, 1.2 or even 0.1 mm. In some embodiments, the layer of nonwoven fibrous thermal insulation may have an installed (i.e., compressed) thickness in the range of at least 2.6, 2.7, 2.8, 2.9, 3, 3.1, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, 6, or even 8 mm.

[0044] The layer of nonwoven fibrous thermal insulation has a weight per square meter in the range of from 200 g / m2up to 2000 g / m2. Depending on the composition of the thermal barrier, it can be desirable for the weight per square meter to be in the range of from about 200 g / m2to about 400 g / m2(e.g., 250 g / m2, 300 g / m2, 350 g / m2) for a gap between adjacent battery cells in the range of from about 0.75 mm up to about 1.25 mm. Depending on the composition of the thermal barrier, it can also be desirable for the weight per square meter to be in the range of from about 300 g / m2up to about 550 g / m2for a gap between adjacent battery cells in the range of from about 0.75 mm up to about 2.5 mm. For gaps between adjacent battery cells in the range of from about 2.5 mm up to 5.0 mm, it can be desirable for the weight per square meter to be in the range of from about 600 g / m2up to about 2000 g / m2(e.g., 650 g / m2, 700 g / m2, 750 g / m2, 800 g / m2, 900 g / m2, 950 g / m2, 1000 g / m2, 1050 g / m2, 1100 g / m2, 1150 g / m2, 1200 g / m2, 1250 g / m2, 1300 g / m2, 1350 g / m2, 1400 g / m2, 1450 g / m2, 1500 g / m2, 1550 g / m2, 1600 g / m2, 1650 g / m2, 1700 g / m2, 1750 g / m2, 1800 g / m2, 1850 g / m2, 1900 g / m2, 1950 g / m2, 2000 g / m2).

[0045] The thermal barrier disclosed herein may optionally further comprise an organic encapsulation layer encapsulating the layer of nonwoven fibrous thermal insulation. The optional organic encapsulation layer may be a polymeric layer or a paper layer. The organic encapsulation layer may be, e.g., one layer or multiple opposing sandwiching layers, with each layer being in the form of a film, coating, organic fibrous nonwoven or woven fabric. The organic encapsulation layer may enclose or otherwise encapsulate all of, a majority of or a portion of at least one or both major faces and preferably also all of, a majority of or a portion of the peripheral edge of the layer of nonwoven fibrous thermal insulation so as to prevent or significantly reduce the shedding or loss of fibers or particles from the encapsulated layer of nonwoven fibrous thermal insulation.

[0046] The thermal barrier disclosed herein may optionally further comprise an inorganic encapsulation layer encapsulating the layer of nonwoven fibrous thermal insulation. The optional inorganic encapsulation layer may be, e.g., glass fiber woven fabric of 25 - 80 g / m2or 150 - 400 g / m2.

[0047] The inorganic encapsulation layer may be, e.g., one layer or multiple opposing sandwiching layers, with each layer being in the form of an inorganic coating or fibrous nonwoven or woven fabric. The inorganic encapsulation layer may enclose or otherwise encapsulate all of, a majority of or a portion of at least one or both major faces and preferably also all of, a majority of or a portion of the peripheral edge of the layer of nonwoven fibrous thermal insulation so as to prevent or significantly reduce the shedding or loss of fibers or particles from the encapsulated layer of nonwoven fibrous thermal insulation.

[0048] The reduction of inorganic fiber or particle shedding is significant, when the number of inorganic fibers or particles loss is less than 10, 5, or 1% by weight percent of the original fiber or particle content of the layer of nonwoven fibrous thermal insulation. The thinner the organic encapsulation layer (i.e., the lower the organic content of the barrier) the better the hot / cold test results.

[0049] The thermal barrier may be provided as a thermal barrier assembly comprising a plurality of the thermal barriers as disclosed herein, wherein the plurality of thermal barriers are provided (a) in a container (e.g., a cardboard or other box) in the form of a stack, (b) disposed end-to-end in series, with one major face of each thermal barrier being adhered onto a major adhesive surface of a length of singlesided or double-sided adhesive tape (when a double-sided adhesive tape is used, the opposite major adhesive surface of the tape can be protected by a release liner), or (c) disposed end-to-end in series in the form of a tape, with the one or more layers of nonwoven fibrous thermal insulation of each thermal barrier being disposed end-to-end and sandwiched or otherwise encapsulated between two opposing lengths of organic (e.g., polymeric) encapsulation layers (e.g., in the form of two opposing films, coatings, fibrous fabrics, etc.).

[0050] Further disclosed herein is a method of making the thermal barrier disclosed herein, the method comprising: forming a layer of nonwoven fibrous thermal insulation using a wet-laid process or dry-laid process; providing first particles, wherein the first particles are fumed silica;disposing the first particles so as to be evenly or uniformly distributed throughout or within the layer of nonwoven fibrous thermal insulation; providing second particles, wherein the second particles are inorganic aerogel particles; and disposing the second particles so as to be evenly or uniformly distributed throughout or within the layer of nonwoven fibrous thermal insulation.

[0051] The process step of forming a layer of nonwoven fibrous thermal insulation using a wet-laid process or dry -laid process comprises providing inorganic fibers; providing a binder; providing fumed silica and inorganic aerogel particles; and mixing the inorganic fibers, the binder, the fumed silica, and the inorganic aerogel particles.

[0052] The inorganic long fibers, the binder, the first particles and the second particles as described above for the thermal barrier may be used for making the thermal barrier disclosed herein.

[0053] The thermal barrier may be made using conventional dry -laid manufacturing equipment and processes such as described in U.S. Pat. Nos. 9,580,848 (Henderson et al.), 9,475,034 (Vincent et al.), 7,491,354 (Anderson), and 6,808,664 (Falk et al.), herein incorporated by reference. Such equipment can include a chamber or forming box with multiple feeder inlets, for feeding any desired combination of matrix fibers, binder, and first and second particles into the forming box. After the fibers are combined and mixed together with the other ingredients, the resulting nonwoven fibrous material is deposited onto a belt that conveys the material into, through and out of a baking oven where the binder is cured at least so that the fibrous material can be further processed. The resulting cured nonwoven fibrous material is then die-cut, laser-cut, water-jet cut, or otherwise processed into individual nonwoven fiber layers, which are then processed at an encapsulation station, e.g., by having a polymeric film laminated to opposite sides of a single layer of thermal barrier or a stack of two or more layers of thermal barrier. An optional hot melt adhesive or pressure sensitive adhesive can be applied to one or both sides of the encapsulate. A protective release liner (not shown) can be subsequently applied to each adhesive surface.

[0054] An example of a “wet laid” process that may be used to manufacture thermal barriers as disclosed herein is described in the Examples of U.S. Pat. No. 6,458,418 (Langer et al.), which is incorporated herein by reference in its entirety. In such a wet laid process, a thermal barrier can be made using at least one dilute (desirably, not over 5 percent solids by weight) aqueous slurry containing inorganic long fibers, binder and first and second particles, by depositing the aqueous slurry onto a permeable substrate, such as a screen or a “wire” of a paper making machine, partially dewatering the slurry by gravity and / or vacuum and then pressing to increase the density (e.g., with pressure rollers). The thermal barrier is then fully dried with heated rollers.

[0055] Further disclosed herein is a battery cell module for an electric vehicle, the battery cell module comprising: a plurality of battery cells disposed in a housing; and a plurality of thermal barriers as disclosed herein,wherein one thermal barrier is disposed between each pair of adjacent battery cells. In some embodiments, a plurality of battery cell modules may be included in a battery pack.EXAMPLES

[0056] Unless otherwise noted, all parts, percentages, ratios, etc. in the examples and the rest of the specification are by weight, and all reagents used in the examples were obtained, or are available, from general chemical suppliers such as, for example, Sigma-Aldrich Company, Burlington, MA, or may be synthesized by conventional methods.

[0057] These abbreviations are used in the following examples: °C = degree Celsius, g = gram, gsm = grams per square meter, in = inch, kPa = kilopascal, pm= micrometer, m = meter, min = minute, MPa = megapascal, mm = millimeter, rpm = revolutions per minute, psi = pounds per square inch, s = second, and wt = weight.TABLE 1. Materials List

[0058] Particle Size

[0059] A sample of each of the Aerogel and Fumed Silica, as received, was measured for particle size using a particle size analyzer (Horiba Ltd., Horiba Scientific, Piscataway, NJ) following the manufacturer’s directions. The dlO, d50, and d90 values are reported belowAerogel: dlO =155 pm, d50 = 424 pm, and d90 = 934 pmFumed Silica: dlO =12.8 pm, d50 = 54.5 pm, and d90 = 179 pm

[0060] Basis Weight Measurement

[0061] A given sample was measured to determine area and weighed on a scale (Mettler-Toledo International Inc., Greifensee, Switzerland). The weight was divided by the area to calculate the basis weight.

[0062] Elastomeric Property: Single Compression Test

[0063] The compression test is performed using a tensile tester (ZwickRoell Ulm, Germany) in compression mode.

[0064] The sample has a diameter of 50.8 mm and a thickness greater than 3 millimeters. The test was performed at about 23 °C. The upper plate of the compression tester was moved with a speed of 20 mm / min until a load of 4.9 kPa was reached and the thickness was determined after applying a contact load of 4.9 kPa to the specimen area for 20 s.

[0065] Immediately, the upper plate was further moved down with a speed of 1 mm / min until a maximum force of 1.5 MPa was reached. Immediately, the gap was opened to unload the force completely. Two specimens were run for each sample and the average hysteresis loss is reported.

[0066] Hysteresis Loss is defined as the difference between the loading energy and the unloading energy, expressed as a percentage of the loading energy. This measures the loss of ability of flexible material to return to its original support characteristics after compression.

[0067] Energy is defined as the area under the force / deflection curve. Loading Energy is the energy required to compress a flexible specimen to a preset deflection (compression cycle). Unloading Energy is the energy recovered when the compression platen is retracted from the preset deflection and completely unloaded (decompression cycle).

[0068] Percent Hysteresis Loss = (Loading Energy - Unloading Energy) x 100 / Loading Energy

[0069] Elastomeric Property: Cyclic Compression Test

[0070] The compression test is performed using a tensile tester (obtained from ZwickRoell Ulm, Germany) in compression mode.

[0071] The sample has a diameter of 50.8 mm and a thickness greater than 3 mm. The test was performed at about 23 °C. The upper plate of the compression tester was moved with a speed of 25 mm / min until a maximum force of 0.15 MPa was reached. After allowing the gap to relax for 300 s at 0.15 MPa, the gap was held in the same position for 30 min. The starting thickness defined in this way applies as sample thickness. In the following, the upper plate moved 1200 cycles up and down.

[0072] The continuous thickening (irreversible swelling) of the electrodes and, therefore, the thickening of the battery cell over the full test is calculated as 34.3% of the starting gap. This is in the typical magnitude of 4 to 5 % swelling of a prismatic cell width of typically about 30 mm.

[0073] The test consists of 1200 cycles and is divided into groups of 12 times 100 cycles. Each of the 12 steps represents 1 / 12 of the continuous thickening (irreversible swelling).

[0074] The first gap cycle started with an amplitude of 14.3 % of the starting gap (cell breathing) at a speed of 1 mm / min for a full load / unload cycle. From cycle 1 to cycle 100 the gap was opened and closed 100 times with the above amplitude. After cycle 100, the gap was held in a fix position for 5 min.

[0075] Cycle 101 was closed to the original starting thickness minus 1 / 12 of the continuous cell thickening. For cycle 101 to cycle 200 the gap was opened and closed 100 times with same amplitude as for the 1stcycle, and held for 5 min at a fix gap.

[0076] Cycle 301 to 1200 follows the same procedure until the full cell thickening after 12 times 100 cycles has been reached.

[0077] The compression force (in kPa) was recorded for each maximum and minimum peak of each cycle. Two specimens were run for each sample and the average is reported. P start is the pressure at the start of the test, the maximum pressure observed at the 1199 cycle and the lowest pressure of the entire test is reported as minimum pressure peak P(min).

[0078] Thermal Property: Hot-side / Cold-side Test

[0079] In a 10 kN tensile test machine (obtained from ZwickRoell), a top platen was heated to 700°C and a sample (100 mm x 100 mm) was placed on a bottom platen with a thermocouple embedded set at ambient temperature. A heat shield was used to cover the sample to ensure that it stayed at ambient temperature. The heat shield was then removed, the sample immediately placed on the cold plate and the upper platen was lowered with a speed of 10 mm / min with pressure held at 1 MPa. The time the sample took to reach a temperature of 120°C (248°F), designated t(120°C), was recorded.

[0080] Preparation of Nonwoven Fibrous Webs

[0081] An air-laying forming apparatus was used to prepare nonwoven fibrous webs as follows. Aerogel, binder, and fibers were fed into a blending chamber with a conveyor belt having a width of 0.6 m at a velocity 0.7 m / min at various mass flow rates as detailed in Table 2 to achieve the grams per square meter (gsm) of web and percentage of web weights shown in Table 3. Thereafter, the blend was fed into the top of the forming chamber.

[0082] The fibrous materials were opened and fluffed in the top of the chamber and then fell through the upper rows of spikes rollers to the bottom of the forming chamber passing thereby the lower rows of spike rollers.

[0083] If used, the fumed silica was fed at the designated flow rate shown in Table 2 to the lower end of the forming chamber to achieve the gsm of web and percentage of web weights shown in Table 3. A particle feeder, type STS-2 (commercially available from The Young Industries Inc. in Muncy, PA), was used to deliver the fumed silica particulates.

[0084] The materials were pulled down on a porous endless belt / wire by a combination of gravity and vacuum applied to the forming chamber from the lower end of the porous forming belt / wire.

[0085] Support layer was fed into the forming chamber on the top surface of the endless forming belt / wire running at the lower end of the forming chamber moving at a speed of 1 m / min. The materials were collected on the top surface of the support layer thereby forming a three-dimensional fiber nonwoven fibrous web supported by the support layer underneath.

[0086] The web was passed one time through an electric oven at a line speed of 1.0 m / min, which melts the sheath of the bi-component fibers. Then, the web was removed immediately after the oven. The oven was an electric oven from International Thermal System, LLC (Milwaukee, WI). The oven had one heating chamber of 5.5 meters in length; the main source of heat was blown air in the chamber from the top. The circulation was set so that the air was evacuated at the 60% setting and re-circulated at 40%, the temperature was 160°C in the chamber.

[0087] The resulting three-dimensional web was an open, lofty web and when fumed silica was added, the web was visually observed to have silica particulates homogenously distributed within the three- dimensional fiber nonwoven fibrous web.

[0088] The web was then conveyed into a dual belt compression oven. The oven was a Glenro HPH- 32HC.5 dual belt compression oven from Glenro Inc (Maysville, Ky). The web was fed into the gap between the two belts (1 - 50 mm), which was 6 mm wide. The belts passed over a 2 m heat zone that heated the material to 200°C. The heated web then passed through a nip roller with a set gap of 6 mm. The nip also had a maximum force set point (30000 N). The belt then passed through a l m cooling zone, which was set to 10°C. The line speed was 1.0 m / min. The sample passed through the compression oven 1 time.

[0089] Further details of the apparatus and methods of using the apparatus in forming air-laid webs is described in U.S. Pat. Nos. 9,422,653 (Wu et al.) and 9,580,848 (Henderson et al.).Table 2 Flow RatesNA = not applicableTable 3

[0090] Each of Samples 1-5 was tested for their thermal and elastomeric properties. Shown in Table 4 below are the results from the hot-side / cold-side test where the basis weight, gap distance at 120°C, and the time to reach a temperature of 120°C for each of the samples is reported. Shown in Table 5 are the results from the Cyclic Compression Test, where the pressure at the start (p start), minimum pressure (pmin) observed during the test, the minimum and maximum pressure observed during cycle 1199, and the amplitude (P max - P min) at cycle 1199 are reported. Shown in Table 6 are the weight percentage of aerogel and fumed silica added to each sample and the weight percent of fumed silica versus the total amount of particles (aerogel and fumed silica) used. Also shown in Table 6 is a summary of the hysteresis loss as determined by the Single Compression Test, the minimum pressure peak as determined by the Cyclic Compression Test and the time to reach a temperature of 120°C from the hot-side / cold-side test for each of the samples.Table 4Table 5Table 6

[0091] The results from the Cyclic Compression Test and the Hot Cold plate Test are plotted in Fig. 1 versus the percentage of fumed silica based on total particles added (i.e., aerogel and fumed silica). Asshown in Fig. 1 when a larger percentage of the total particles is fumed silica, the better the insulative properties (i.e., higher delta temperature). However, the higher the percentage of fumed silica as the total particles, the elasticity of the sample suffers.

[0092] Foreseeable modifications and alterations of this invention will be apparent to those skilled in the art without departing from the scope and spirit of this invention. This invention should not be restricted to the embodiments that are set forth in this application for illustrative purposes. To the extent that there is any conflict or discrepancy between this specification as written and the disclosure in any document mentioned or incorporated by reference herein, this specification as written will prevail.

Claims

What is claimed is:

1. A thermal barrier for being disposed between battery cells of a battery assembly, said thermal barrier comprising: a layer of a nonwoven fibrous thermal insulation comprising a fiber matrix of inorganic long fibers; a binder dispersed within the fiber matrix so as to hold together the fiber matrix; first particles dispersed within the fiber matrix, wherein the first particles are fumed silica having a first average diameter; second particles dispersed within the fiber matrix, wherein the second particles are inorganic aerogel particles having a second average diameter, wherein the ratio of first particles to second particles is 30:70 to 60:40 based on weight, wherein the first diameter is smaller than the second diameter.

2. The thermal barrier of claim 1, wherein the first particles are hydrophilic fumed silica.

3. The thermal barrier of any one of the previous claims, wherein the first particles have a d50 of at least 1 micrometer and at most 1 millimeter.

4. The thermal barrier of any one of the previous claims, wherein the second particles have a d50 of at least 10 micrometer and at most 10 millimeter.

5. The thermal barrier of any one of the previous claims, wherein thermal barrier comprises more second particles than first particles.

6. The thermal barrier of any one of the previous claims, wherein the second particles are porous.

7. The thermal barrier of any one of the previous claims, wherein the thermal barrier is compressible.

8. The thermal barrier of any of the previous claims, wherein the binder dispersed within the fiber matrix is in the form of polymer fibers, preferably in the form of bicomponent core-sheath polymer fibers.

9. A method of making the thermal barrier according to any one of claims 1 to 8, the method comprising: forming a layer of nonwoven fibrous thermal insulation using a wet-laid process or dry-laid process; providing first particles, wherein the first particles are fumed silica;disposing the first particles so as to be evenly or uniformly distributed throughout or within the layer of nonwoven fibrous thermal insulation; providing second particles, wherein the second particles are inorganic aerogel particles; and disposing the second particles so as to be evenly or uniformly distributed throughout or within the layer of nonwoven fibrous thermal insulation.

10. A battery cell module for an electric vehicle, the battery cell module comprising: a plurality of battery cells disposed in a housing; and a plurality of thermal barriers according to any one of claims 1 to 8, wherein one thermal barrier is disposed between each pair of adjacent battery cells.

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