Pleated thermal insultative layer

Abstract

Described herein is a pleated thermal insulative layer comprising a layer of a nonwoven comprising (i) a fiber matrix of inorganic fibers; (ii) a 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; wherein the layer comprises plurality of regular parallel folds. The pleating of the layer of nonwoven has been shown to improve pressure management of the thermal insulative layer which may be useful in automotive applications, such as a battery assembly in an electric vehicle.

Description

PA102809W002PLEATED THERMAL INSULTATIVE LAYERTECHNICAL FIELD

[0001] A pleated thermal insulative layer comprising a fiber matrix of inorganic fibers, insulative particles and a binder is described. Such layers may be used as a thermal barrier 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 barrier also needs to provide pressure management of the cell stack. 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 have the ability to compress, recover, and provide appropriate mechanical pressure levels 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 insulative layer that has good insulative properties while also providing pressure management of a cell stack.

[0005] In a first aspect, the present disclosure provides a pleated thermal insulative layer comprising: a layer of a nonwoven comprising(i) a fiber matrix of inorganic fibers;(ii) a 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; wherein the layer comprises a plurality of regular parallel folds.

[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; anda plurality of pleated thermal insulative layers as disclosed herein; wherein one thermal insulative layer is disposed between a pair of adjacent battery cells.

[0007] In yet a further aspect, the present disclosure also relates to a method of making a pleated thermal insulative layer, the method comprising: forming a layer of nonwoven fibrous thermal insulation using a wet-laid process or dry -laid process; disposing a plurality of inorganic particles so as to be evenly or uniformly distributed throughout or within the layer of nonwoven fibrous thermal insulation; and folding the layer of nonwoven fibrous thermal insulation to form a plurality of regular parallel folds.

[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] Fig. 1 is a cross-sectional view of an exemplary embodiment of a pleated thermal insulative layer of the present disclosure;

[0010] Figs. 2A-2C are cross-sectional views of exemplary embodiments of a pleated thermal insulative layer of the present disclosure;

[0011] Fig. 3 is a schematic end view of a battery cell module as disclosed herein, with thermal insulative layers as disclosed herein disposed between adjacent battery cells;

[0012] Fig. 4 is a cross-sectional view of a plate used for holding the pleated thermal insulative layer for compression testing;

[0013] Fig. 5 is a perspective view of an exemplary pleated thermal insulative layer of the present disclosure held between plates for compression testing;

[0014] Fig. 6 is a plot of the stress versus gap size for pleated Nonwoven 1 and a comparative planar web; and

[0015] Fig. 7 is a plot of the stress versus gap size for pleated Nonwoven 2 and a comparative planar web.

[0016] It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of the principles of the disclosure. The figures may not be drawn to scale.DETAILED DESCRIPTION

[0017] 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).

[0018] 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.).

[0019] 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.).

[0020] 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.

[0021] The thermal insulative layer disclosed herein comprises a nonwoven fibrous thermal insulation. The nonwoven fibrous thermal insulation comprises a fiber matrix of inorganic fibers and a plurality of inorganic particles. The thermal insulative layer may comprise of one or more layers of the nonwoven fibrous thermal insulation. In the present disclosure, the nonwoven fibrous thermal insulation is formed into a three-dimensional, pleated sheet having a plurality of regular parallel folds.

[0022] As used herein, the term “inorganic” refers to ceramic or otherwise nonmetallic (i.e., not a metal, metal alloy, or metal composite) inorganic material.

[0023] The inorganic fibers typically have a mean aspect ratio, i.e., a mean length to diameter ratio, of greater than 50. In some embodiments, the mean aspect ratio of the inorganic fibers may be from at least 50, 100, 500, 1000, 1500, 2000, 2500, 3000, 4000, 5000, or even 8000. In some embodiments, the mean aspect ratio of the inorganic fibers may be 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 the 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.

[0024] The inorganic fibers of the fiber matrix may be selected from alkaline earth silicate fibers, refractory ceramic fibers (RCF), polycrystalline wool (PCW) fibers, basalt fibers, glass fibers, silica fibers, or 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.

[0025] 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 to at most 90, 80, 70, or even 60 percent by weight, based on the total weight of the nonwoven fibrous thermal insulation.

[0026] The layer of nonwoven fibrous thermal insulation disclosed herein comprises inorganic particles dispersed within the fiber matrix. The inorganic particles are thermally insulative inorganic particles. 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.

[0027] 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.

[0028] Intumescent particles (e.g., vermiculite particles) can be permanently expanded 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.

[0029] 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.

[0030] 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 particles in its expanded state. It is believed that this more uniform structural geometry is less likely to be influenced by the alignment of the inorganic long 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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 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 pm.

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

[0038] 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.

[0039] 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, under the trade designation “ENTERA” such as “ENTERA EV5200” or “ENTERA EV5400”.

[0040] 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.

[0041] The shape of the inorganic aerogel particles may be spherical, irregular, platelet-shaped, or any other shape.

[0042] 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. 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.

[0043] The layer of nonwoven thermal insulation of the thermal insulative layer 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 fibers and 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.

[0044] 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 an inorganic 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 “WACKERMQ 803 TF” can be seen as a three-dimensional network of poly silicic acid units that 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”.

[0045] 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.

[0046] 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.

[0047] The organic binders as used for the thermal insulative layer disclosed herein may be in the form of polymer fibers (e.g., polyethylene / polyethylene terephthalate, polyethylene terephthalate, flame 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”)), or a liquid binder (e.g., acrylic latex, ethylene vinyl acetate (e.g., EAF68) latex, silicone, polyurethane etc.).

[0048] 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.

[0049] The nonwoven fibrous thermal insulation of the present disclosure is pleated. The layer of nonwoven fibrous thermal insulation of the present disclosure is folded into rows of generally parallel fold-lines that provide alternating peaks and valleys on both sides of the nonwoven with the fold-lines parallel to one another across the layer. The folds are regular, meaning that there is a repeated pattern to the folding with a similar spacing between the pattern.

[0050] In the present disclosure, the thermal insulative material is configured into a pleated structure having alternating ribs and flanges. An exemplary pleated thermal insulative layer is shown in Fig. 1, where a is the thickness of the nonwoven layer. Pleated thermal insulative layer 10, comprises a base 12 with a plurality of ribs 11 extending therefrom. The base, or bottom of the pleat, has a width b with distance c between adjacent ribs (mid base to adjacent mid base). Flange 13, or top of pleat, has a width d with distance e between adjacent flanges (mid flange to adjacent mid flange). The height of the pleated thermal insulative layer, f, is the distance from the top of the flange to the base.

[0051] Alternative embodiments for the pleated thermal insulative layer include those shown in Figs. 2A to 2C. In Fig. 2A, the pleated thermal insulative layer is not stretched a lot, so the width of the base andflange is about twice the thickness of the nonwoven layer, a. In Fig. 2B, the pleated thermal insulative layer is stretched out more, leading to a larger peak-to-peak distance. In Fig. 2C, the pleated thermal insulative layer comprises bases with substantially no width, but flanges which have a measurable width. The rib sidewalls may be tapered as shown in Fig. 1, or more perpendicular to the base as shown in Fig. 2 A, or a combination of tapered and perpendicular.

[0052] In some embodiments, the flanges have an average width, d, double the thickness of the web. In some embodiments, the flanges have an average width, d, of at least double the thickness of the web. In some embodiments, the flanges have an average width, d, of at least 1, 1.5, 2, 4, 5, 10, 12, 15, or even 20 mm; and at most 13, 12, 10, 8, 5, 1, 0.5, 0.2, 0.1, or even 0.05 cm. In another embodiment, the flanges (or bases) do not have a substantial width, for example where the flange is represented by an angular point or an apex of a curve as shown in Fig. 2A. The base width, b, may have the same or different value as the flange width d. In some embodiments, the average width of the flanges and the bases are the same (in other words, d=g). In some embodiments, the base width has an average width of at least 1, 2, 4, 5, 10, 12, 15, or even 20 mm; and at most 13, 12, 10, 8, 5, 1, 0.5, 0.2, 0.1, or even 0.05 cm. In some embodiments, the average height f of the pleated thermal insulative layer is at least 2.0, 2.5, 3.0, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, 6, or even 8 mm; and at most 10, 9, or even 8.5 mm.

[0053] In some embodiments, the average thickness of the nonwoven layer, a, is at least 0.75, 1, 1.25, 1.5, 1.75, or even 2 mm thick and at most 4, 3.5, 3, 2.5, or even 2.25 mm thick.

[0054] The pleated thermal insulative layer of the present disclosure comprises a plurality of flanges and ribs across the width of the structure, which typically extend down the entire length of the structure.

[0055] In some embodiments, the pleated thermal insulative layer of the present disclosure has an average peak-to-peak distance (represented by distance e and / or distance b) versus height (represented by f) of no more than 5, 4, 3, 2, 1, 0.9, 0.8, 0.7, or even 0.6. In some embodiments, the pleated thermal insulative layer of the present disclosure has an average peak-to-peak distance versus height of more 0.02, 0.03, 0.04, 0.5, 0.7, or even 1. As will be shown in the data below, for a given height, the smaller the average peak-to-peak distance versus height, the higher the stress value of the plateau when compression tested.

[0056] In some embodiments, the pleated thermal insulative layer of the present disclosure has an average peak-to-peak distance (represented by distance e and / or b) of at least 2.0, 2.5, 3.0, 3.5, or even 4.0 times the thickness of the nonwoven layer (represented by a in Fig. 1) and at most 10, 9, 8, 7, or even 6 times the average thickness of the nonwoven layer.

[0057] The thermal insulative material can be shaped to form the pleated structure using techniques known in the art, for example, by bending, pressing, twisting, roll forming, stamping, and other alterations. The configuration of the thermal insulative pleated stmcture is thus made without breaking or unduly cracking the layer. The thermal insulative layer may have sufficient flexibility that bends or folds of up to 180° may be achieved without causing undue defects.

[0058] Although not wanting to be limited by theory, it is believed that the pleating of the nonwoven fibrous thermal insulation layer as disclosure herein enables pressure management of the thermal insulative layer between cells.

[0059] Referring to Fig. 3, an exemplary battery cell module 35 includes a plurality of battery cells 36 and a plurality of thermal insulative layers 30. Each thermal insulative layer 30 can be in the form of one or more layers of a nonwoven fibrous thermal insulation. Thermal insulative layer 30 can be disposed between adjacent battery cells 36, between groups of cells 36, or both, at one or more locations throughout battery cell module 35. Typically, battery cell module 35 rests above cooling plate 37 and tray 38.

[0060] Planar thermal insulative materials when compressed have an exponential increase in stress, as shown for the comparative example in Fig. 6. Also shown in Fig. 6, is the response of the pleated thermal insulative layer of the present disclosure, which appears to have a plateaued region, where the stress is maintained while pressure is applied. This plateauing is thought to be desirable when developing a thermal barrier material for a battery stack, which not only can provide protection against thermal runaway events, but can also provide pressure management of the battery stack. In some embodiments, this plateau occurs at a stress of at least 0.02, 0.025, 0.03, 0.04, or even 0.05 MPa (megapascal).

[0061] Generally, a nonwoven comprising a fiber matrix of inorganic fibers; a plurality of insulative inorganic particles dispersed within the fiber matrix; and a binder dispersed within the fiber matrix so as to hold together the fiber matrix are known in the art for their ability to act as a thermal barrier and prevent thermal runaways of battery cells. In some embodiments, the thermal barrier of the present disclosure has a thermal conductivity at 25 °C of at least 25, 30, 35, 40, or even 50 milliWatts per meter Kelvin (mW / m K) at a thickness of 10 mm. An exemplary thermal conductivity test is described in U.S. Pat. Publ. No. 20230238600 (Rathod et al.)

[0062] In some embodiments, the layer of pleated nonwoven fibrous thermal insulation has a weight per square meter in the range of from 100, 200, 300, or even 400 grams per square meter (gsm); and at most 1000, 900, 800, 700, 600, or even 500 gsm

[0063] The thermal insulative layer may be provided as a thermal barrier assembly comprising a plurality of the thermal insulative layers as disclosed herein, wherein the plurality of thermal insulative layers 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 insulative layer being adhered onto a major adhesive surface of a length of single-sided 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 insulative layer 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.).

[0064] Further disclosed herein is a method of making the thermal insulative layer disclosed herein, the method comprising:forming a layer of nonwoven fibrous thermal insulation using a wet-laid process or dry-laid process; disposing a plurality of inorganic particles so as to be evenly or uniformly distributed throughout or within the layer of nonwoven fibrous thermal insulation; and folding the layer of nonwoven fibrous thermal insulation to form a plurality of regular parallel folds.

[0065] 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 a plurality of inorganic particles; and mixing the inorganic fibers, the binder, the inorganic particles.

[0066] The inorganic fibers, the binder, and the inorganic particles as described above for the thermal insulative layer may be used for making the thermal insulative layer disclosed herein.

[0067] The thermal insulative layer 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 insulative layer or a stack of two or more layers of thermal insulative layer. 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.

[0068] An example of a “wet laid” process that may be used to manufacture thermal insulative layers 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 insulative layer 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 insulative layer is then fully dried with heated rollers.

[0069] 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 pleated thermal insulative layers as disclosed herein, wherein one thermal insulative layer is disposed between each pair of adjacent battery cells.

[0070] In some embodiments, a plurality of battery cell modules may be included in a battery pack.EXAMPLES

[0071] 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.

[0072] These abbreviations are used in the following examples: cm = centimeter, °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

[0073] Test Methods

[0074] Basis Weight Measurement

[0075] A given sample was measured to determine area and weighed on a scale (Mettler Toledo XS4002S, available from Mettler-Toledo International Inc., Greifensee, Switzerland). The weight was divided by the area to calculate the basis weight.

[0076] Preparation of Nonwoven Webs

[0077] An air-laying forming apparatus was used to prepare nonwoven fibrous webs as follows. The binder and the fibers were fed into a blending chamber with a conveyor belt with a width of 0.6 m at a velocity 0.7 m / min at various mass flow rates and to achieve the grams per square meter (gsm) of web and percentage of web weights shown in Table 2. Thereafter, the blend of materials was fed into the top of the forming chamber.

[0078] 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.

[0079] The fumed silica particulates in this silica-containing fibrous web were fed to the lower end of the forming chamber to achieve the gsm of web and percentage of web weights shown in Table 2. A particle feeder, type STS-2 (commercially available from The Young Industries Inc. in Muncy, Pennsylvania, United State of America), was used to deliver these fumed silica particulates.

[0080] 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.

[0081] A 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 containing the silica particulates supported by the support layer underneath.

[0082] The web was then conveyed into an electric oven with a line speed of 1.0 m / min, which melted 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). It had one heating chamber of 5.5 meters in length; the main source of heat was air blowing in the chamber from the top. The circulation was set so that 60% of the blown air was evacuated and 40% was re-circulated. The temperature was 160°C in the chambers. The sample was passed once in the chamber.

[0083] The resulting three-dimensional fiber nonwoven fibrous web was an open, lofty web and was visually observed to have silica particulates homogenously distributed within the obtained three- dimensional fiber nonwoven fibrous web.

[0084] The web was then conveyed into a dual belt compression oven. The oven (Glenro HPH-32HC.5 dual belt compression oven from Glenro Inc., Maysville Ky). The web was fed into a 1 mm wide gap between the two belts. 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 0 mm wide. The nip also had a maximum force set point of 30000 N. The belt then passed through a l m cooling zone set to 10°C. The line speed was 1.0 m / min. The sample passed through the oven one 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.), herein incorporated by reference.Table 2

[0085] Initial Pleating:

[0086] A roll of the nonwoven web (either Nonwoven 1 or 2) was placed on an unwind and fed into a blade pleater (JCEM P3-Digital-CNC blade pleater from JCEM Group (Fulenbach, Switzerland)). The web was guided into the blade pleater by a series of 5 infeed rollers. The web was rested on a heated infeed platform set to 22°C to heat the web prior to pleating. The pleater had two main heated platforms, top and bottom, that were heated to 149°C. The upper platform was raised using a pneumatic cylinder creating a 75 mm gap. The web was placed in this gap on the lower platform. A copper plate 60 cm x 30 cm x 0.16 cm was then place on top of the web on the lower platform. A felt mat 60 cm x 30 cm xlO cm was then placed on top of the copper plate. The upper platform was then lowered by the pneumatics. A 10 mm gap between the two platforms was fine-tuned using a servo motor. The gap caused the platforms to come in contact with the felt mat and created friction between the felt mat and the two platforms. This friction provided the back pressure needed for the blade pleating process. The size of the gap also determined the height of the pleats. Once the platforms were in place, the blades were engaged. The bottom blade raised and intersected the web perpendicular to the machine direction. Then the upper blade was lowered in front of the lower blade folding the web between the back of the upper blade and then the front of the lower blade. The lower blade then retracted and shifted forward in front of the upper blade and raised again. This folded the web between the two blades again creating a pleat. This process was repeated each cycle creating a new pleat. The blades were moved by servo motors at 15% of their maximum speed. This process continued until the desired amount of material was pleated. The pleater was then stopped and the pleated web was left in between the heated platforms for 5 minutes. After 5 minutes, the felt and copper plate were removed, and the pleated material was allowed to relax. The upper platform was lifted, and the pleated web comprising a regular, alternating fold was collected.

[0087] Setting Pleat Spacing for testing

[0088] The pleated web was placed in between a clamp for testing. The clamp was 3D printed from acrylonitrile butadiene styrene plastic. The clamp comprised two 8 in x 8 in (20 x 20 cm) square plateswith a 6 in (15 cm) diameter circle cut out of the middle. The first plate comprised a plurality of teeth having various spacings as shown in Fig. 4 with the dimensions as shown Table 3 below, where w is the gap at the base, x is the width between teeth (peak-to-peak distance), y is the width of each tooth, and z is the height. The second plate opposing the first plate in the clamp was fabricated to mate with the particular first plate, holding the pleats in place. A single pleated web 50 was held between two plates 59A and 59B as shown in Fig. 5. Each pleat of the pleated web was placed between each tooth on one plate until all the teeth in the comb are filled. The second plate was then placed on top of the pleats holding them in place. The two plates were held together by four 8 mm bolts and corresponding nuts. The bolts were placed at each comer of the plate and were finger tightened to form the clamped pleated web.Table 3

[0089] Compression Test

[0090] The compression test was performed using a tensile tester (Instron, Norwood, MA) in compression mode.

[0091] The clamped pleated web was tested as follows: The lower platen of the tester was positioned under the pleated web exposed in the cut-out circle of the clamp. The upper compression platen was lowered at 8 mm / min onto the pleated web exposed in the cut-out circle at the top of the clamp until a pressure of 0.725 kPa was reached. That gap was held for 15 seconds at 0.725 kPa. The upper platen was then lowered at 1 mm / min until a pressure of 1.8 MPa was reached. The upper platen was then raised at 1 mm / min until 0% strain was reached. This loading and unloading cycle was repeated two more times.

[0092] Nonwoven 1 was placed between plate set 1 and 2 and the Compression Test was performed. Shown in Fig. 6 are the results for the first loading cycle of the Compression Test for Samples 1 and 2. Also shown in Fig. 6 are the results for the first loading cycle of the Compression Test for Sample 3. Sample 3 was a comparative nonwoven, having the same composition as Nonwoven 1, but was not pleated (in other words, it was flat). Sample 3 was made to have a similar basis weight as the pleated sample.

[0093] Nonwoven 2 was placed between plate set 2 and 3 and the Compression Test was performed. Shown in Fig. 7 are the results for the first loading cycle of the Compression Test for Samples 4 and 5. Also shown in Fig. 7 are the results for the first loading cycle of the Compression Test for Sample 6. Sample 6 was a comparative nonwoven, having the same composition as Nonwoven 2, but was not pleated and was made to have a similar basis weight as the pleated sample.

[0094] The samples are summarized in Table 3 below. The peak-to-peak distance and height (e and f in Fig. 1) was inferred from using the various plates. The reported Plateau height in Table 3 is taken from the peak height before plateauing for each sample.Table 3na = not applicable

[0095] 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 pleated thermal insulative layer comprising: a layer of a nonwoven comprising(i) a fiber matrix of inorganic fibers;(ii) a 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, wherein the layer comprises plurality of regular parallel folds.

2. The pleated thermal insulative layer of claim 1, wherein the plurality of regular parallel folds have a peak-to-peak distance and a peak height, wherein the peak-to-peak distance versus peak height of is no more than 1.0.

3. The pleated thermal insulative layer of any one of the previous claims, wherein the plurality of regular parallel folds have an average peak-to-peak distance and the layer has an average thickness, wherein the average peak-to-peak distance is at least 3.0 and at most 10 times the average thickness of the layer.

4. The pleated thermal insulative layer of any one of the previous claims, wherein the plurality of regular parallel folds have an average peak-to-peak distance of at least 2.5 mm.

5. The pleated thermal insulative layer of any one of the previous claims, wherein the inorganic fibers of the fiber matrix are selected from the group of fibers consisting of alkaline earth silicate fibers, refractory ceramic fibers (RCF), polycrystalline wool (PCW) fibers, basalt fibers, glass fibers, silicate fibers, and combinations thereof.

6. The pleated thermal insulative layer of any one of the previous claims, wherein the plurality of 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.

7. The pleated thermal insulative layer of any one 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 coresheath polymer fibers.

8. The pleated thermal insulative layer of any one of the previous claims, wherein when the layer is tested with a Compression Test, the layer exhibits a plateau in pressure response.

9. A method of making the pleated thermal insulative layer 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; disposing a plurality of inorganic particles so as to be evenly or uniformly distributed throughout or within the layer of nonwoven fibrous thermal insulation; folding the layer of nonwoven fibrous thermal insulation to form a plurality of regular parallel folds.

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 pleated thermal insulative layers according to any one of claims 1 to 8, wherein one thermal insulative layer is disposed between each pair of adjacent battery cells.

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