Thermal barrier with glass fibers

Abstract

Described herein is a thermal barrier comprising a layer of a nonwoven fibrous thermal insulation comprising (i) a fiber matrix comprising a plurality of inorganic fibers, wherein at least 30 % of the inorganic fibers are glass fibers free of shot; (ii) an organic binder dispersed within the fiber matrix so as to hold together the fiber matrix; and (iii) a plurality of inorganic particles dispersed within the fiber matrix. Also disclosed are methods of making such a barrier and using it in automotive applications, such as a battery assembly in an electric vehicle.

Description

PA103142W003THERMAL BARRIER WITH GLASS FIBERS TECHNICAL FIELD

[0001] The present disclosure relates to a thermal barrier comprising glass fibers. 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 the generation of heat during a thermal runaway event, the battery can explode, releasing gases that can rupture (or erode) the thermal barrier material compromising the material. Thus, it is desirable to identify thermal barrier materials that have better erosion resistance.

[0004] In one aspect, a thermal barrier for being disposed between battery cells of a battery assembly is disclosed. The thermal barrier comprising: a layer of a nonwoven fibrous thermal insulation comprising (i) a fiber matrix comprising a plurality of inorganic fibers, wherein at least 30 % by weight of the inorganic fibers are glass fibers free of shot; (ii) an organic binder dispersed within the fiber matrix so as to hold together the fiber matrix; and (iii) a plurality of inorganic particles dispersed within the fiber matrix.

[0005] In another aspect, a method of making the thermal barrier is disclosed. The method comprising:forming a layer of nonwoven fibrous thermal insulation using a wet-laid process or dry-laid process, wherein the nonwoven fibrous thermal insulation comprises (i) a fiber matrix comprising a plurality of inorganic fibers, wherein at least 30 % by weight of the inorganic fibers are glass fibers free of shot; (ii) an organic binder dispersed within the fiber matrix so as to hold together the fiber matrix; and (iii) a plurality of inorganic particles dispersed within the fiber matrix; and disposing the plurality of particles so as to be evenly or uniformly distributed throughout or within the layer of nonwoven fibrous thermal insulation.

[0006] In yet another aspect, a battery cell module for an electric vehicle is disclosed. The battery cell module comprising:a plurality of battery cells disposed in a housing; anda plurality of thermal barriers, wherein the thermal barriers comprise: a layer of a nonwoven fibrous thermal insulation comprising (i) a fiber matrix comprising a plurality of inorganic fibers, wherein at least 30 % by weight of the inorganic fibers are glass fibers free of shot; (ii) an organic binder dispersed within the fiber matrix so as to hold together the fiber matrix; and (iii) a plurality of inorganic particles dispersed within the fiber matrix; andwherein one thermal barrier is disposed between each pair of adjacent battery cells

[0007] 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.DETAILED DESCRIPTION

[0008] 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).

[0009] 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.).

[0010] 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.).

[0011] 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.

[0012] The thermal barrier disclosed herein comprises a layer of a nonwoven fibrous thermal insulation comprising a fiber matrix of inorganic fibers, wherein at least a portion of the inorganic fibers are glass fibers free of shot. In the present disclosure, it has been found that effective thermal barrier materials can be made with glass fibers free of shot.

[0013] As used herein, glass fibers refer to amorphous, inorganic material. As used herein, the term “amorphous” refers to a material that lacks crystallinity. As used herein, the term “inorganic” refers to a material free of carbon-hydrogen bonds. Often, glass fibers are derived from metal oxides, such as SiO2, Na2O, AI2O3, MgO, and / or CaO.

[0014] The glass fibers of the present disclosure are free of shot, which means no shot is observed or substantially no shot is observed (i.e., the glass fibers have less than 2, 1, 0.5, 0.1, or even 0.05 wt% of shot) in the glass fibers. “Shot” is a globule of material (often spherical in shape, but not always) that results from the incomplete fiberization of the molten glass as it is formed into a fiber. Shot in the glass fiber can be observed visually with the unaided eye or by microscopy. The shot can have a wide size distribution with the average diameter being from about 10 micrometers up to about 1 millimeter.

[0015] The presence of shot depends on how the inorganic fibers are made. For example, glass free of shot can be made by drawing down molten glass and winding on a spool. Glass fiber made in this controlled process is free (or virtually free) of shot and results in long, continuous lengths of fiber with a more uniform diameter. For example, the fibers have an average standard deviation of diameter of less than ± 2, 1, or even 0.5 micrometers. In some embodiments, the glass fiber has an average diameter of at least 3, 4, 5, or even 6 micrometers. In some embodiments, the glass fiber has an average diameter of at most 20, 15, 12, 10, 9, 8, 7, or even 6 micrometers. The diameter of the glass fibers may be determined by techniques known in the art such as microscopy. Exemplary types of shot-free (or substantially shot-free) glass include: A-glass, C-glass, D-glass, S-glass, E-glass, H-glass, HR-glass, R-glass, ECR-glass, AR-glass, and silica-glass (i.e., silica fiber free of boron and comprising less than 1, 0.5, 0.1 or even 0.05 wt% or even no amount of alkaline and alkaline earth elements, typically silica-glass comprises 96 wt % of SiC>2 and 4 wt % AI2O3).

[0016] In some embodiments, the only fibers used to make the nonwoven fibrous thermal insultation are glass fibers free of shot. In some embodiments, a blend of inorganic fibers is used, wherein at least a portion of the inorganic fibers are the shot-free glass fibers disclosed herein. In some embodiments, at least 30, 40, 50, or even 60 % of the inorganic fibers used to make the nonwoven fibrous thermal insultation are shot-free glass fibers. In some embodiments, at most 60, 70, 80, 90, 95, or even 100% of the inorganic fibers used to make the nonwoven fibrous thermal insultation are glass fibers free of shot. Other fibers that may be used in addition to the glass fibers free of shot include glass fibers that comprise shot and crystalline fibers.

[0017] The inorganic fibers comprising shot are made with a less controlled process. Such processes include wherein the molten glass is melt spun or melt blown resulting in generally less controlled fiber diameters (e.g., the fibers have an average standard deviation of diameter of more than ± 3 micrometers), shorter lengths of fibers, and the presence of substantial shot.

[0018] The glass fibers free of shot 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 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 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.

[0019] In addition to the glass fibers free of shot, other inorganic fibers may used. These other inorganic fiber may be selected from the group of fibers consisting of alkaline earth silicate fibers, refractory ceramic fibers (RCF), polycrystalline wool (PCW) fibers, basalt fibers, silica fibers, and combinations thereof.

[0020] 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.

[0021] The layer of nonwoven fibrous thermal insulation of the thermal barrier disclosed herein comprises a plurality of inorganic particles dispersed within the fiber matrix.

[0022] The layer of nonwoven fibrous thermal insulation disclosed herein comprises inorganic particles dispersed within the fiber matrix. Exemplary particles include inorganic aerogel, xerogel, hollow or porous ceramic microspheres, unexpanded vermiculite, irreversibly or permanently expanded vermiculite, fumed silica, otherwise porous silica, irreversibly or permanently expanded or unexpanded perlite, pumicite, irreversibly or permanently expanded clay, diatomaceous earth, titania, zirconia, or combinations thereof.

[0023] As used herein, an irreversibly or permanently expanded expandable particle (e.g., particle of an intumescent material such as vermiculite or perlite mineral) refers to a particle that has been heated to a temperature and for a time that causes the particle to irreversibly or permanently expand to at least 10% and up to 100% of its expandability, either by being pre-expanded before being used to form the thermal insulative layer, or post-expanded after it is incorporated into the nonwoven fibrous thermal insulation.

[0024] Intumescent particles (e.g., vermiculite particles) can be permanently expanded as known in the art by overheating the particles to beyond the point of reversibility (e.g., in the range of from about 350 °C up to about 1000 °C for vermiculite). Such a permanently expanded intumescent particle (e.g., vermiculite particle) can have an expanded accordion or worm-like structure that is easier to break apart into smaller particles, compared to the same particle in its unexpanded state, because of its elongated geometry, lower density and lower mechanical stability. As the heating temperature increases, the degree of permanent expansion of the particle increases (i.e., the particles can get larger and / or longer). It may also be desirable to use vermiculite that has been permanently expanded by a chemical treatment method as known in the art.

[0025] Because they are easier to break apart in their expanded state, it can be desirable to post-expand the intumescent particles, after the unexpanded intumescent particles have been incorporated into the nonwoven fibrous thermal insulation. Even if gentle processing is employed so as not to substantially break them apart, it is believed that incorporating pre-expanded intumescent particles into the nonwoven fibrous thermal insulation can still result in the expanded particles becoming oriented into the plane (i.e., x-axis, y-axis, and / or therebetween) of the insulation. For example, with pre-expanded vermiculite particles, the elongated particles can become generally aligned with the fibers in the longitudinal or downstream direction (i.e., y-axis), rather than in the thickness direction (i.e., z-axis), of the nonwoven fibrous thermal insulation.

[0026] In contrast, when the intumescent particles are post-expanded (i.e., after the nonwoven fibrous thermal insulation is made with unexpanded intumescent particles), the expanded intumescent particles are not oriented primarily in the plane of the insulation. Unexpanded intumescent particles typically have a more uniform structural geometry (i.e., have an aspect ratio closer to 1) compared to the same particlesin their expanded state. It is believed that this more uniform structural geometry is less likely to be influenced by the alignment of the inorganic fibers during the formation of the nonwoven fibrous thermal insulation. As a result, the post-expanded intumescent particles are more likely to be oriented isotropically within the nonwoven fibrous thermal insulation. For example, with post-expanded vermiculite particles, the elongated particles can become aligned in the thickness direction (i.e., z-axis), in plane (i.e., x-axis, y-axis, and / or therebetween), or off-axis thereof. It is believed this difference between the orientation of pre-expanded particles versus post-expanded particles is caused by the unexpanded particles having a more uniform structural geometry than that exhibited while in their expanded state.

[0027] The 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.

[0028] 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 of high-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.

[0029] 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 (greater than 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.

[0030] Examples of useful commercially available 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 and “HDK T30 from Wacker Chemical Corp, Ann Arbor, ML

[0031] 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.

[0032] 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 of at least 0.1, 0.5, 1, 5, 10, 25, 40, 50, 60, 75, 90, 100, 150, or even 200 pm. In some embodiments, the fumed silica has a d50 of at most 1, 0.75, 0.5, 0.2, or even 0.1 mm. 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 pm. In some embodiments, the d90 (where 90 percent byvolume of particles fall below this diameter value) of the particle size distribution is no greater than 500, 400, 300, 200, or even 150 pm.

[0033] The shape of the fumed silica particles may be spherical, irregular, platelet-shaped, or any other shape.

[0034] 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.

[0035] In some embodiments, the surface of the inorganic aerogel particles is modified. Examples of useful commercially available modified aerogel particles include those available from Cabot Corp., Boston, MA under the trade designation “ENTERA” such as “ENTERA EV5200” or “ENTERA EV5400”.

[0036] 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 10, 25, 50, 100, 250, 300, 400, or even 500 pm. 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 pm. 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.

[0037] The shape of the inorganic aerogel particles may be spherical, irregular, platelet-shaped, or any other shape.

[0038] The layer of nonwoven fibrous thermal insulation may comprise the inorganic 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 may comprise the inorganic 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 may comprise the inorganic 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.

[0039] In some embodiments, the layer of nonwoven fibrous thermal insulation comprises more than one type of inorganic particle. For example, fumed silica and inorganic aerogel may be used together as taught in U.S. Provisional Pat. Appl. No. 63 / 672409 (Middendorf, et al.) to balance the thermal and compressive properties. In some embodiments, the weight ratio of fumed silica to inorganic aerogel particles is at least 1:99, 2:98, 4:96, 5:95, 10:90, 20:80, 25:75, 30:70, or even 40:60. In someembodiments, the weight ratio of fumed silica to inorganic aerogel particles is at most 99:1, 95:5, 90:10, 80:29, 70:30, 60:40, 50:50, 45:55, 40:60, 35:65, 30:70, 25:75, 20:80, or even 15:95. The ratio of fumed silica to inorganic aerogel particles may be adjusted to optimize the compression and / or thermal properties of the layer.

[0040] Generally, if both the inorganic aerogel and fumed silica particles are used, the nonwoven fibrous thermal insulation comprises a total amount of inorganic particles of at least 10, 15, 20, 25, 30, or even 35% by weight and at most 40, 45, 50, 55, or even 60% by weight based on the weight of the nonwoven fibrous thermal insulation.

[0041] The layer of nonwoven thermal insulation of the thermal barrier disclosed herein comprises an organic binder dispersed within the fiber matrix so as to hold together the fiber matrix. The binder may be an organic adhesive binder or organic 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 plurality of inorganic fibers and plurality of inorganic 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.

[0042] Organic binders useful to the present disclosure may include, e.g., those disclosed in US 8,834,759 (Liu et. al). An organic -inorganic hybrid binder may be useful such as, those available under the trade designation “WACKER MQ 803 TF”, which is a co-hydrolysis 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 is approximately 0.67 for “WACKER MQ 803 TF”.

[0043] 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.

[0044] 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.

[0045] The organic binders as used for the thermal barrier disclosed herein may be in the form of polymer fibers (e.g., polyethylene / polyethylene terephthalate, polyethylene, fire retardant polyethylene terephthalate), dry polymer powder (e.g., low density polyethylene, polyamide, epoxy resin powder (e.g., available under the trade designation “3M SCOTCHCAST 265”, “3M SCOTCHKOTE 6258” from 3M Co., St. Paul, MN)), or a liquid binder (e.g., acrylic latex, ethylene vinyl acetate (e.g., EAF68) latex, silicone, polyurethane etc.).

[0046] The layer of nonwoven fibrous thermal insulation may comprise the binder in an amount of at least 2.5, 3, 3.5, 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.

[0047] The nonwoven fibrous thermal insulation of the present disclosure may be made by a dry -laid or wet-laid process as known in the art, by combining the plurality of inorganic fibers, the plurality of inorganic particles, a binder, and any additional optional components. 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 including glass fibers;providing a binder;providing inorganic particles; andmixing the inorganic fibers, the binder, and the inorganic particles to homogeneously disperse.

[0048] 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 inorganic fibers, binder, and the inorganic 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.

[0049] 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 can be subsequently applied to each adhesive surface.

[0050] 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 the plurality of inorganic fibers, binder, and inorganic 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.

[0051] The nonwoven fibrous thermal insulation may be in the form of a mat, sheet, strip, or three-dimensional thin-walled structure. The thermal barrier may comprise one or more layers of a nonwoven fibrous thermal insulation comprising a fiber matrix of inorganic fibers.

[0052] In some embodiments, the layer of nonwoven fibrous thermal insulation may have a thickness in the range of at least 1, 1.2, 1.4, 1.5, 2, 2.5, or even 2.8 mm and at most 20, 15, 12, 10, 8, 6, 5, 4, 3, 2.5, 2, 1.5, or even 1.2 mm.

[0053] 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, 850 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, 2100 g / m2, 2200 g / m2, 2400 g / m2, 2600 g / m2, 2800 g / m2, or even 3000 g / m2,).

[0054] The thermal barrier disclosed herein is compressible, meaning that the thermal barrier has elastomeric properties. 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 30, 32, 34, 36, 38, 40, or even 45 kPa (kiloPascals). In some embodiments, the thermal barrier material has maximum relax pressure (P relax max) of no more than 2000, 1500, 1000, 900, 800, or even 700 kPa. 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. In some embodiments, Pmin should be at least 30, 35, 40, 45, 50, or even 60 kPa; and at most 100, 150, 200, or even 300 kPa.

[0055] As gas is released during a thermal event out of a battery cell, it is important that the thermal barrier material remain intact over the course of use. Erosion can be used to examine the loss of the thermal barrier over time. In some embodiments, the thermal barrier disclosed herein may have an erosion of less than 10, 9, 8, 6, 4, or even 2 % after 4 hours as described in Erosion Test I. In some embodiments, the thermal barrier when tested according to Erosion Test II will not exhibit breakthrough until after 10, 12, or even 14 cycles. As shown in the example section, there appears to be a correlation between the diameter of the glass fibers free of shot and the resistance to breakthrough, wherein the smaller the diameter the glass fiber free of shot, the longer it takes for breakthrough to occur.

[0056] 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, organicfibrous 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.

[0057] 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 to 80 g / m2or 150 to 400 g / m2.

[0058] 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.

[0059] 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 thermal test results, e.g., measured by a hot-side cold-side test procedure or thermal conductivity test procedure.

[0060] 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.).

[0061] 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; anda 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

[0062] 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, Saint Louis, Missouri, or may be synthesized by conventional methods.

[0063] These abbreviations are used in the following examples: °C = degree Celsius, g = gram, gsm = grams per square meter, in = inch, pm= micrometer, m = meter, min = minute, mm = millimeter, N = Newton, s = second, and wt = weight.TABLE 1. Materials List

[0064] Particle Size

[0065] A sample of each of 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 below.Aerogel: dlO =155 pm, d50 = 424 pm, and d90 = 934 pmFumed Silica: dlO =12.8 pm, d50 = 54.5 pm, and d90 = 179 pm

[0066] Cyclic Compression Test

[0067] The compression test is performed using a tensile tester (obtained from ZwickRoell Ulm, Germany) in compression mode.

[0068] The sample has a diameter of 50.8 mm or square sample of 50x50mm 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.

[0069] 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.

[0070] 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).

[0071] 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.

[0072] 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.

[0073] Cycle 201 to 1200 follows the same procedure until the full cell thickening after 12 times 100 cycles has been reached.

[0074] 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 relax start is the pressure at the start of the test, the maximum relaxed pressure of the entire test is reported as maximum relax pressure P relax max and the lowest pressure of the entire test is reported as minimum pressure peak P min.

[0075] Erosion Test I

[0076] The samples are mounted between two steel plates. The test assembly was heated to bum out the organic binder and the burned mat was weighed (initial weight). The burned mat was placed back into the assembly and exposed to a pulsating cold airflow (Pressure: 3.5 bar Motor revolution: 666rpm) for 4 hours. The mat was removed from the assembly and reweighed (final weight). The amount of weight loss calculated as I (final weight - initial weight)! x 100% / final weight which was considered the erosion rate.

[0077] Erosion Test II

[0078] Samples were subjected to a closely controlled hydrogen-fueled flame set at target temperature (700 °C) and set a defined distance (2.375 inches or 60 mm) away from the torch face. The flame was constantly applied to the sample, while blasts of grit were intermittently applied to the sample surface. The grit, alumina-oxide particles (120 grit, 70-270 mesh size), were introduced into the flow of the flame by a venturi block using compressed air (25 psi (172 kPa), 50 standard liters per minute). The gritwas heated by the flame during the blast. Samples were sandwiched between 2 stainless steel plates with 6 mm spacers. Thermocouples were affixed to the back stainless steel plate in 2 locations (center and north edge). The front stainless steel plate was machined to include a 0.5 inch (13 mm) wide slot starting from the north edge down to the center of the plate to simulate a rupture point in a battery cell. The flame targeted the machined center of the front plate so that the nonwoven sample was exposed to the flame and grit. The grit was cycled on and off. A cycle is 10 seconds of the combination of flame and grit followed by 5 seconds of flame. During the testing, the exposed nonwoven sample was visually observed for erosion. When the black plate is observed, the sample was said to have break through and the number of cycles it took to reach break through was recorded.

[0079] Preparation of Nonwoven Fibrous Webs for Examples 1 and 2 (Ex 1 and 2)

[0080] An air-laying forming apparatus was used to prepare nonwoven fibrous webs having the compositions and basis weight as shown in Table 2 below.Table 2

[0081] The designated amount of Fibers and Binder were weighed and premixed by hand. The mixture was processed (i.e., fed from the top) through an air-laid processer, like that disclosed in US Patent No.7,491,354, where the fibers were opened and dispersed into an air stream, then collected on a screen belt. Details of such air-laid processing apparatus and methods of using such apparatus in forming air-laid webs can be found 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.). The designated amounts of Aerogel and Fumed Silica by weight percent were top or side fed into the chamber or forming box of the air-laid processor. A volumetric feeder coupled with an air-driven horn was used to distribute the particles into the web uniformly.

[0082] 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 m 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.

[0083] 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 7 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 7 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. 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.).

[0084] Examples 3-10 (Ex 3-10) and Comparative Examples A-D (CE A- D)

[0085] Samples were made following the same procedure as described above for Examples 1 and 2 to prepare nonwoven fibrous webs having the compositions and basis weight as shown in Table 3 below, except that the samples were densified to 6 mm thickness.Table 3

[0086] Examples 3-10 and Comparative Examples A-D were tested following the Cyclic Compression Test. The results for the Pmin and P relax max are reported in Table 4 below. Erosion % was determined for Examples 3-7 and Comparative Examples A-D.Table 4NM= not measured

[0087] As shown in Table 4, the P relax start force is relatively the same between the various samples, however, the Pmin values are lower and the percentage of erosion is worse for the comparative examples relative to their example counterparts.

[0088] Examples 11-13 (Ex 11-13)

[0089] Samples were made following the same procedure as described above for Examples 1 and 2 to prepare nonwoven fibrous webs having the compositions and basis weight as shown in Table 5 below, except that the samples were densified to 6 mm thickness.Table 5

[0090] 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 (i) a fiber matrix comprising a plurality of inorganic fibers, wherein at least 30 % by weight of the inorganic fibers are glass fibers free of shot; (ii) an organic binder dispersed within the fiber matrix so as to hold together the fiber matrix; and (iii) a plurality of inorganic particles dispersed within the fiber matrix.

2. The thermal barrier of claim 1, wherein at least 60 % by weight of the inorganic fibers are glass fibers free of shot.

3. The thermal barrier of any one of the previous claims, wherein the glass fibers free of shot have a fiber diameter of at least 4 micrometers.

4. The thermal barrier of any one of the previous claims, wherein the glass fibers free of shot have a fiber diameter of at least 5 micrometers.

5. The thermal barrier of any one of the previous claims, wherein the glass fibers free of shot have a fiber diameter of at most 7 micrometers.

6. The thermal barrier of any one of the previous claims, wherein the glass fibers free of shot have a fiber diameter of at most 6 micrometers.

7. The thermal barrier of any one of the previous claims, wherein the glass fibers free of shot comprise S-glass, E-glass, H-glass, HR-glass, R-glass, ECR-glass, silica-glass, or combinations thereof.

8. The thermal barrier of any one of the previous claims, wherein the fiber matrix further comprises ceramic fibers, refractory ceramic fibers, polycrystalline wool fibers, basalt fibers, silicate fibers, or combinations thereof.

9. The thermal barrier of any one of the previous claims, wherein the inorganic particles comprise inorganic aerogel, xerogel, hollow or porous ceramic microspheres, unexpanded vermiculite, irreversibly or permanently expanded vermiculite, fumed silica, otherwise porous silica, irreversibly or permanently expanded or unexpanded perlite, pumicite, irreversibly or permanently expanded clay, diatomaceous earth, titania, zirconia, or combinations thereof.

10. The thermal barrier of any one of the previous claims, wherein the layer comprises 15 to 50 % by weight of the plurality of inorganic particles.

11. The thermal barrier of any one of the previous claims, wherein the layer of a nonwoven fibrous thermal insulation comprises at least two different types of inorganic particles.

12. The thermal barrier of any of the previous claims, wherein the plurality of particles comprises a blend of aerogel and fumed silica.

13. The thermal barrier of any of the previous claims, wherein the binder dispersed within the fiber matrix is a polymer fiber.

14. The thermal barrier of claim 13, wherein the polymeric fiber is a bicomponent core-sheath polymer fibers.

15. The thermal barrier of any of the previous claims, wherein 100 % of the plurality of inorganic fibers are glass fibers free of shot.

16. The thermal barrier of any of the previous claims, wherein the thermal barrier has an erosion of less than 10% after 4 hours.

17. The thermal barrier of any of the previous claims, wherein the thermal barrier when tested according to Erosion Test II does not exhibit breakthrough until after 10 cycles.

18. A method of making the thermal barrier according to any one of claims 1 to 17, the method comprising:forming a layer of nonwoven fibrous thermal insulation using a wet-laid process or dry-laid process;disposing the plurality of particles so as to be evenly or uniformly distributed throughout or within the layer of nonwoven fibrous thermal insulation.

19. A battery cell module for an electric vehicle, the battery cell module comprising:a plurality of battery cells disposed in a housing; anda plurality of thermal barriers according to any one of claims 1 to 17,wherein one thermal barrier is disposed between each pair of adjacent battery cells.

Images