Patent Description:
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, and they are available in three forms: prismatic cells, pouch cells or cylindrical-shaped cells. These batteries are disposed within the vehicle compactly to save space. Sometimes one or more of the battery cells or battery modules experience a thermal runaway event, which can result in many if not all of the battery cells or battery modules overheating and being destroyed.

<CIT> describes in its Example <NUM>, a porous body containing vermiculite paper (height <NUM>, width <NUM>, thickness <NUM>, density <NUM>/cm<NUM>, vermiculite (powdery inorganic substance) and glass fiber (fibrous inorganic substance) as an heat insulating material.

There is a desire in the industry to prevent, stop or at least significantly slowing down such a thermal runaway event. The present invention is a contribution to that effort.

In one aspect of the present invention, a thermal runaway barrier operatively adapted for being disposed between battery cells of a battery assembly and for at least significantly slowing down a thermal runaway event within the battery assembly is provided which comprises a layer of a nonwoven fibrous thermal insulation comprising a fiber matrix of inorganic fibers, thermally insulative inorganic particles comprising fumed silica and inorganic aerogel particles dispersed within the fiber matrix, and a binder dispersed within the fiber matrix so as to hold together the fiber matrix, and an organic encapsulation layer enclosing the layer of nonwoven fibrous thermal insulation.

In another aspect of the present invention, a battery cell module or assembly for an electric vehicle is provided. The battery cell module or assembly comprises a plurality of battery cells disposed in a housing, and a plurality of thermal runaway barriers according to the present invention. The battery cells are lined up in a row or stack, with one thermal runaway barrier being disposed between each pair of adjacent battery cells.

A thermal runaway barrier according to the present invention can be made in a method comprising forming the layer of nonwoven fibrous thermal insulation using a wet-laid process or dry-laid process.

The above summary of the present invention is not intended to describe each disclosed embodiment or every implementation of the present invention.

Descriptions corresponding to the included figures can be within this description.

In describing preferred embodiments of the invention, specific terminology is used for the sake of clarity. The invention, however, is not intended to be limited to the specific terms so selected, and each term so selected includes all technical equivalents that operate similarly.

As used herein, the terms "preferred" and "preferably" refer to embodiments described herein that can afford certain benefits, under certain circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful and is not intended to exclude other embodiments from the scope of the invention.

As used herein and in the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a" or "the" component may include one or more of the components and equivalents thereof known to those skilled in the art. Further, the term "and/or" means one or all the listed elements or a combination of any two or more of the listed elements.

It is noted that the term "comprises" and variations thereof do not have a limiting meaning where these terms appear in the accompanying description. Moreover, "a," "an," "the," "at least one," and "one or more" are used interchangeably herein. Relative terms such as left, right, forward, rearward, top, bottom, side, upper, lower, horizontal, vertical, and the like may be used herein and, if so, are from the perspective observed in the drawing. These terms are used only to simplify the description, however, and not to limit the scope of the invention in any way.

Reference throughout this specification to "one embodiment," "certain embodiments," "one or more embodiments" or "an embodiment" means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Thus, the appearances of the phrases such as "in one or more embodiments," "in certain embodiments," "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily referring to the same embodiment of the invention. Where applicable, trade designations are set out in all uppercase letters.

The term "and/or" means one or all of the listed elements or a combination of any two or more of the listed elements (e.g., preventing and/or treating an affliction means preventing, treating, or both treating and preventing further afflictions).

As used herein, the term "or" is generally employed in its sense including "and/or" unless the content clearly dictates otherwise.

Also herein, the recitations of numerical ranges by endpoints include all numbers subsumed within that range (e.g., <NUM> to <NUM> includes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, etc.).

"Ambient conditions" means at <NUM> and <NUM> kPa pressure.

"Average" means number average, unless otherwise specified.

"Substantially" means to a significant degree, as in an amount of at least <NUM>%, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>%, or <NUM>%.

"Thickness" means the distance between opposing sides of a layer or multilayered article.

The recitation of numerical ranges by endpoints includes all numbers subsumed within that range in increments commensurate with the degree of accuracy indicated by the end points of the specified range (e.g., for a range of from <NUM> to <NUM>, the increments will be <NUM>, and the range will include <NUM>, <NUM>, <NUM>, etc., <NUM>, <NUM>, <NUM>, etc., <NUM>, <NUM>, <NUM>, etc., <NUM>, <NUM>, <NUM>, etc., <NUM>, <NUM>, <NUM>, etc., <NUM>, <NUM>, <NUM>, etc., <NUM>, <NUM>, <NUM>, etc., <NUM>, <NUM>, <NUM>, etc., <NUM>, <NUM>, <NUM>, etc. up to <NUM>) and any range within that range, unless expressly indicated otherwise.

The term "polymer" will be understood to include polymers, copolymers (e.g., polymers formed using two or more different monomers), oligomers and combinations thereof, as well as polymers, oligomers, or copolymers that can be formed in a miscible blend.

The following Examples have been selected merely to further illustrate features, advantages, and other details of the invention. It is to be expressly understood, however, that while the Examples serve this purpose, the particular ingredients and amounts used as well as other conditions and details are not to be construed in a manner that would unduly limit the scope of this invention.

Referring to <FIG>, a fiber matrix layer <NUM> useful in a thermal runaway barrier application contains nonwoven inorganic (i.e., nonmetallic) or otherwise heat resistant fibrous insulation material, thermally insulative ceramic or otherwise nonmetallic inorganic particles, and an organic or inorganic binder. As used herein, nonmetallic means it is not a metal or metal alloy. The fiber matrix layer <NUM> is encapsulated with an organic polymeric layer <NUM>.

Referring to <FIG>, an exemplary battery module <NUM> includes an assembly of battery cells <NUM> and a plurality of thermal runaway barriers <NUM>. Each thermal runaway barrier <NUM> can be in the form of one or more fiber matrix layers <NUM>, with an encapsulation <NUM>, and that can be made from the exemplary materials described herein. A thermal runaway barrier <NUM> can be disposed between adjacent battery cells <NUM>, between groups of cells <NUM>, or both, at one or more locations throughout the battery module <NUM>. Typically, the battery module <NUM> rests above a cooling plate <NUM> and a tray <NUM>.

Referring to <FIG>, an exemplary battery pack <NUM> includes a plurality of battery modules <NUM>, which may each have its own cooling plate <NUM> and tray <NUM> or all of the modules <NUM> may share the same cooling plate <NUM> and tray <NUM>. A thermal runaway barrier <NUM>, formed from the exemplary materials described herein, can be disposed between one or more or all adjacent battery modules <NUM>, on the top of one or more or all of the battery modules <NUM> (see reference number <NUM>'), or any combination of both. A single or multiple thermal runaway barriers <NUM> may also be dimensioned so as to cover the tops of all of the battery modules <NUM>.

Referring to <FIG>, an exemplary thermal runaway barrier <NUM> includes one or more fiber matrix layers (not shown) encapsulated with an organic polymeric layer <NUM> that covers both sides and the peripheral edge of the one or more fiber matrix layers. In one embodiment, the major opposite faces of the encapsulating layer <NUM> are coated with an adhesive (e.g., a pressure sensitive adhesive) protected by corresponding release liners <NUM> and <NUM>. It is preferable for the encapsulating layer <NUM> to include one or more outlets or openings <NUM> (e.g., in the form of a notch) that allows air (e.g., hot air) or other gases to escape from inside the encapsulation <NUM>, rather than cause the encapsulation <NUM> to swell and expand like a balloon, e.g., when the air trapped in the encapsulation <NUM> is heated to an elevated temperature (e.g., when the temperature of one or more of the adjacent battery cells <NUM> increases).

Referring to <FIG>, a conventional dry-laid manufacturing equipment and processes can be used to manufacture thermal runaway barriers <NUM> according to the invention. Examples of such equipment and processes can be found described in <CIT>), <CIT>), <CIT>), and <CIT>). Such equipment can include a chamber or forming box <NUM> with multiple feeder inlets, including an inlet <NUM> for feeding any desired combination of fibers, binder and particles into the box <NUM>, and multiple inlets <NUM>, <NUM>' and <NUM>" for feeding any desired number or type of filler materials into the box <NUM>. After the fibers are combined and mixed together with the other ingredients, the resulting nonwoven fibrous material <NUM> is deposited onto a belt <NUM> that conveys the material <NUM> into, through and out of a baking oven <NUM> where the binder is cured at least so that the fibrous material <NUM> can be further processed. The resulting cured nonwoven fibrous material <NUM>' is then die-cut, laser-cut, water-jet cut, or otherwise processed into individual nonwoven fiber layers <NUM> (not shown), which are then processed at an encapsulation station <NUM>, e.g., by having a polymeric film <NUM> (not shown) laminated to opposite sides of a single layer <NUM> or a stack of two or more layers <NUM>. An optional hot melt adhesive or pressure sensitive adhesive can be applied to one or both sides of the encapsulate <NUM> at corresponding spray stations <NUM> and <NUM>'. A protective release liner (not shown) can be subsequently applied to each adhesive surface.

Referring to <FIG>, one preferred embodiment of a thermal runaway barrier <NUM> according to the invention includes one or more vent holes <NUM> formed through one or both layers of the encapsulating film <NUM>. The vent holes <NUM> can have any desired shape (e.g., circular, rectangular, oval, etc.), and preferably the vent holes <NUM> are formed through a portion of the film <NUM> located beyond the periphery of the encapsulated fibrous layer(s) <NUM> and still within the periphery of the encapsulation <NUM>, while also providing a path for expanding gases (e.g., air) to escape out of the space containing the fibrous layer(s) <NUM>. The number, size and location of these vent holes <NUM> can vary as desired.

Referring to <FIG>, another preferred embodiment of a thermal runaway barrier <NUM> according to the invention includes two vent holes <NUM>, each in the form of a notch formed through the encapsulating film <NUM>. The vent holes <NUM> can have any desired shape (e.g., semicircular, rectangular, semioval, etc.), and preferably the notches <NUM> are formed through a portion of the film <NUM> located beyond the periphery of the encapsulated fibrous layer(s) <NUM> and past the periphery of the encapsulation <NUM>, while also providing a path for expanding gases (e.g., air) to escape out of the space containing the fibrous layer(s) <NUM>. The number, size and location of these notches <NUM> can vary as desired.

Referring to <FIG>, an additional preferred embodiment of a thermal runaway barrier <NUM> according to the invention includes two different types of vent holes <NUM> and <NUM> formed through the encapsulation <NUM>, like those described above relative to <FIG>.

In an MTS Insight <NUM> kN tensile test machine (obtained from MTS Insight of Eden Prairie, MN, United States), a bottom platen was heated to <NUM>, and a sample was placed on top of it. The upper platen, with a thermocouple embedded, was lowered such that the distance between the two platens was at <NUM>. The temperature increase at the cold-side was recorded with respect to time (continuously) until it reached <NUM> seconds (<NUM> minutes).

In a <NUM> kN tensile test machine (obtained from ZWICKROELL of Ulm, Germany), a top platen was heated to <NUM> and a sample was placed on a bottom platen with a thermocouple embedded set at ambient temperature. A heat shield was used to cover the sample to ensure that it stayed at ambient temperature. The heat shield was then removed, and the upper platen was lowered with pressure held at <NUM> MPa. The time the sample took reach a temperature of <NUM> (<NUM>°F), designated t(<NUM>), was recorded.

The methods of ASTM273C <NUM> were followed. A five-minute shear speed was used.

Thermal conductivity measurements values were obtained using a Thermal Constants Analyzer, Model TPS <NUM> obtained from Hot Disk® AB of Goteborg, Sweden. Measurements were taken by choosing the Isotropic/Bulk (Type I) module within the software. The measurements were run using a Kapton <NUM> sensor (Hot Disk®) having a diameter of <NUM>. As specified by the manual, the samples should have a lateral dimension that is <NUM> to <NUM> times the radius of the sensor. The sample thickness should also be equivalent or greater than the radius of the sensor. To ensure that the thickness was sufficiently greater than the radius of the sensor, three to four layers of a sample were stacked on each side of the sensor and a small pressure was applied to ensure that layers were all in contact with one another.

Specified parameters were <NUM>) measurement time in seconds and <NUM>) heating power in mW. The sample temperature was inputted as the ambient room temperature. The measurement was then executed as defined in the TPS Manual.

The results were analyzed by clicking on "Calculate" within the software and selecting the "Standard Analysis" option. After the measurement, several graphs were presented by the software, including the "Transient" graph and the "Residual" graph. The transient graph displays the temperature increase of the sensor during the heating of the sample up to <NUM> points. The first pass at analyzing the results will start at point <NUM> and include everything up to point <NUM> on the transient. If the residual graph does not look like a random scatter of points, a smaller subset of datapoints was used for the analysis. This was done by trimming points from the beginning and end of the measurement. As a rule, the result was not reliable if less than <NUM> points are used in the analysis. In addition to satisfying the quality of the residual plot, several other numerical requirements were defined including "probing depth (PD)", "temperature increase (TI)", "total to characteristic time (TCT)", and "mean deviation (MD)" as specified in the manual. For these specifications: the PD must be less than the thickness of the sample, the TI must be between <NUM> and <NUM>, the TCT must be between <NUM> and <NUM>, and the MD must be a magnitude of <NUM>-<NUM> or better. If these five criteria were not met, the heating power and measurement times were adjusted. The settings were iterated until an accurate measurement was made, where accuracy was defined by satisfying all the numerical requirements laid out in the manual. Thermal conductivity values in W/m·K were measured and recorded for tested samples.

For Examples <NUM>, <NUM>, and <NUM>-<NUM>, combinations of staple fibers by weight percent (as identified in Table <NUM>) were weighed and premixed by hand before placing on top of a feeding belt. The fiber material was processed (i.e., fed from the top) through an air-laid processer, like that disclosed in <CIT>, 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 <CIT>), <CIT>. ), <CIT>), and <CIT>. Fillers by weight percent (as identified in Table <NUM>) 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 fillers into the web uniformly. The sample was then sent through a forced-air convection oven at <NUM> (<NUM>°F) at a speed of <NUM>/min.

For Examples <NUM> and <NUM>, the process described in Example <NUM> of <CIT>) was followed. Samples were assembled containing fibers and fillers by weight percent as identified in Table <NUM> rather than the materials identified in <CIT>.

For Example <NUM>, Example A of <CIT>) was followed with noted modifications. An aerogel slurry was prepared by adding <NUM> grams of Barlox <NUM> (obtained from Lonza Group of Basel, Switzerland) to <NUM> liters (<NUM> gallons) of water at <NUM> (<NUM>°F). The slurry was mixed. <NUM> grams of Foamaster <NUM> (obtained from BASF Group of Ludwigshafen, Germany) was added and the slurry was mixed. EAF68 by weight percent (as identified in Table <NUM>) was added and mixed. AG by weight percent (as identified in Table <NUM>) was then added and mixed. The slurry was mixed for fifteen minutes and <NUM> grams of MOJO MP 9307C was added and mixed. A fiber slurry was prepared by adding <NUM> grams of Microstrand 110X-<NUM> (obtained from John Manville of Denver, CO, United States) to <NUM> liters (<NUM> gallons) of water. The slurry was pulped for <NUM> seconds at <NUM> rpm. T255 by weight percent (as identified in Table <NUM>) was added and the slurry was pulped for <NUM> seconds at <NUM> rpm. Another <NUM> liters (<NUM> gallons) of water was added to the slurry. <NUM> liters (<NUM> gallons) of the fiber slurry was mixed with <NUM> liters (<NUM> gallons) of the aerogel slurry and SW+ by weight percent (as identified in Table <NUM>) was mixed in. The combined slurry was processed on a papermaking machine.

The samples underwent HCST1 testing and the results are represented in Table <NUM>.

The 'General Procedure for Preparing Fibrous Sheet' as described in <CIT> with material substitution as identified in Table <NUM> was followed. Tap water (<NUM> liters, <NUM>° C. ) and <NUM> grams (g) of inorganic fibers and cleaned to a shot content of less than <NUM> percent by weight) were added to a GT800 Classic blender (obtained from Rotor Lips Ltd, Uetendorf, Switzerland). The blender was operated on low speed for five seconds. The resultant slurry was rinsed into a RW16 mixing container equipped with a paddle mixer (obtained from IKA-Werke GmbH, Staufen, Germany) using one liter of tap water (<NUM>° C. The slurry was diluted with an additional one liter of tap water (<NUM>° C. The diluted slurry was mixed at medium speed to keep solids suspended. Defoaming agent (obtained under the trade designation "FOAMASTER <NUM>" (<NUM>) from Henkel, Edison, N. ) and ethylene-vinyl acetate terpolymer latex (obtained under the trade designation "AIRFLEX 600BP" (<NUM>, <NUM> percent by weight solids) from Air Products were added. Flocculent is added dropwise in amounts as indicated in Table <NUM>. Thermally insulative particles were then added as indicated in Table <NUM>. The mixer speed was increased and mixing continued for from <NUM> to <NUM> minutes. The paddle mixer was removed, and the slurry was poured into a <NUM> x <NUM> (<NUM> inches x <NUM> inches) sheet former (obtained from Williams Apparatus Co, Watertown, NY, United States) and drained. The surface of the drained sheet was rolled with a rolling pin to remove excess water. Then, the sheet was pressed between blotter papers at a surface pressure of <NUM>-<NUM> kPa (<NUM>-<NUM> psi) for five minutes. The sheet was then dried at <NUM>° C. in a forced air oven for <NUM>-<NUM> minutes and allowed to equilibrate overnight while exposed to the ambient atmosphere. The thickness and basis weight of the samples were measured at a constant pressure of <NUM> kPa, and are recorded in Table <NUM>. For Examples <NUM> - <NUM> (EX15-EX25) the vermiculite material used in these samples were either pre-heated to permanently pre-expand the vermiculite, before being used to make the samples, or post-heated to permanently post-expand the vermiculite, after the samples were made, at specific time and temperature conditions. For EX21, the vermiculite was pre-heated at <NUM> for <NUM> hours before sample assembly. For EX22 and EX23, the vermiculite was heated at <NUM> for <NUM> minutes after sample assembly. For EX24, the vermiculite was pre-heated at <NUM> for <NUM> minutes before sample assembly. For EX25, EX33, and EX34. the vermiculite in the sample was pre-heated at <NUM> for <NUM> minutes before sample assembly.

The samples underwent HCST2 testing, and the results are represented in Table <NUM>.

PP was laminated onto a sample as assembled in Example <NUM>. Hand samples were hot pressed at <NUM> (<NUM>°F) and <NUM> kPa on both sides. The edges were manually sealed using an impulse sealer which was at <NUM> (<NUM>°F), and heated for <NUM> seconds, cooled for <NUM> seconds, with all the steps being conducted under a compressive force of <NUM> kPa (<NUM> psi) pressure. The PP film thickness was <NUM> (<NUM> mil). The <NUM> gsm sample underwent Shear Strength testing and the results are represented in Table <NUM>.

Hot melt adhesive H2345 was applied to the sample in Example <NUM> using a Nordson Altablue Gridmelter with a <NUM> (<NUM> inch) melt blown adhesive die. The adhesive was heated at <NUM> (<NUM>°F) and sprayed on to the web at <NUM> kPa (<NUM> psi) air pressure and <NUM> RPM pump rate. The <NUM> gsm sample underwent Shear Strength testing and the results are represented in Table <NUM>.

FB was spray coated onto a sample as assembled in Example <NUM> using a ACCUSPRAY ONE Spray Gun System with PPS obtained from <NUM> Company of St. Paul, MN, United States. Hand samples were spray coated on one side and then flipped to coat the other side. The <NUM> gsm sample underwent Shear Strength testing and the results are represented in Table <NUM>.

PKHH Phenoxy Resin obtained from Gabriel Performance Products of Akron, OH, United States was dissolved in a <NUM>% solution of methyl ethyl ketone (MEK) to create an adhesive. The MEK was evaporated at room temperature for <NUM> minutes. Two coatings of the adhesive were applied onto one side of a <NUM> (<NUM> mil) PET film obtained from Dupont of Wilmington, DE, United States. Two coatings of the adhesive were applied onto a side of another <NUM> (<NUM> mil) PET film. The thickness of the adhesive coating was <NUM> (<NUM> mil). The adhesive coated PET sample films were placed onto the top and bottom side of a sample as assembled in Example <NUM>. The <NUM> gsm sample underwent Shear Strength testing and the results are represented in Table <NUM>.

Samples were assembled using procedures described in Examples <NUM>-<NUM> with the materials identified in Table <NUM>. The thickness and basis weight of the samples were measured at a constant pressure of <NUM> kPa and are recorded in Table <NUM>. The samples underwent HCST2 testing and the results are represented in Table <NUM>.

Combinations of staple fibers by basis weight (as identified in Table <NUM>) were weighed and processed through an air-laid processer. Details of the apparatus and methods of using the apparatus in forming air-laid webs are described in <CIT>), <CIT>), <CIT>), and <CIT>). The combined staple fibers were then processed again by the air-laid processor and a fumed silica filler was directly fed into the chamber of the air-laid processor by basis weight (as identified in Table <NUM>). A screw feeder was used to distribute the fillers into the web uniformly. The web was sent through a forced-air convection oven at <NUM> (<NUM>°F) at a speed between <NUM>/min and <NUM>/min. The thickness of the samples was between <NUM> to <NUM>.

The webs were then densified to a specified gap thickness using a hot press. Polytetrafluoroethylene (PTFE) coated fiberglass fabric sheets (obtained from McMaster-Carr of Elmhurst, IL. United States) were placed on both sides of the samples and the samples were placed between two hot plates maintained at a temperature of <NUM> (<NUM>°F). Pressure was applied for <NUM> to <NUM> seconds to activate the bi-component fibers (T255). The densified sample was then immediately placed between two plates maintained at room temperature under a pressure for <NUM> to <NUM> seconds, to set the web to the desired thickness.

The samples underwent HCST2 testing, and the results are represented in Table <NUM>. The actual thickness of the samples was measured by ASTM D5736-<NUM> with the fiberglass fabric sheets removed. The plate pressure was calibrated at <NUM> psi (<NUM> Pascal).

Densities of <NUM> gsm samples containing <NUM>% fumed silica (represented in EX48 - EX53) were computed by dividing the actual basis weight (gsm) by the actual thickness (mm). Density and the cold side temperature recorded after <NUM> seconds of HCST2 testing for EX48 - EX53 is represented in Table <NUM>. The table is organized in descending order by measured cold side temperatures.

Thermal conductivity testing was performed, and the results are represented in Table <NUM>.

Surprisingly, it has been found that fumed silica has a higher thermal conductivity than silica aerogel. It is believed that the thermal conductivity of the nonwoven fibrous thermal insulation without the fumed silica particles (i.e., the fiber matrix) is lower than the same fiber matrix with the fumed silica particles.

As described above, the present invention provides, a thermal runaway barrier operatively adapted for being disposed between battery cells of a battery assembly and for at least significantly slowing down a thermal runaway event within the battery assembly is provided which comprises a layer of a nonwoven fibrous thermal insulation comprising a fiber matrix of inorganic fibers, thermally insulative inorganic particles comprising fumed silica and inorganic aerogel particles dispersed within the fiber matrix, and a binder dispersed within the fiber matrix so as to hold together the fiber matrix, and an organic encapsulation layer enclosing the layer of nonwoven fibrous thermal insulation.

In particular, the thermal runaway barrier is operatively adapted (i.e., designed, configured, shaped and/or dimensioned) or otherwise suitable for being disposed between adjacent battery cells (e.g., prismatic- or pouch-type battery cells) of a battery module or assembly (i.e., a series of battery cells stacked together in a row) such as that used to power an electric motor (e.g., like that used in an electric or hybrid vehicle) and for preventing, stopping or at least significantly slowing down a thermal runaway event within the battery module or assembly or between adjacent battery modules or assemblies. Favorably the thermal runaway barrier comprises:.

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

The present thermal runaway barrier may also be used between battery modules or assemblies.

Inorganic binders, organic binders, or a combination of both can be useful according to the present invention and may include, e.g., those disclosed in <CIT>. 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, e.g., WACKER® MQ <NUM> 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 <NUM> TF can be seen as a three dimensional network of polysilicic 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 approx. is <NUM> for WACKER® MQ <NUM> TF.

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 core-sheath 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 binders can also be used.

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

A "thermal runaway" is when a battery cell experiences an exothermic chain reaction causing the phenomenon of an uncontrollable temperature rise of the battery cell. The exothermic chain reaction may be caused, for example, by over-heating of the battery cell, over-voltage of the battery cell, and mechanical puncture of the battery cell, among other reasons.

A "thermal propagation" is when a battery cell thermal runaway causes the remaining battery cells in a battery pack or system to undergo the thermal runaway phenomenon.

A "thermal runaway event" refers to the overheating of one battery cell, in a container of battery cells, causing a chain reaction of adjacent battery cells overheating, and potentially exploding or catching fire, until the number of overheated battery cells reaches a critical point of propagation resulting in all or more than half of the battery cells in the module or assembly of modules being destroyed. Factors that can cause a battery cell to overheat include: physical damage, applying over voltage, overheating (internal battery cell shorting).

As the energy density of a battery cell increases, the temperature at which the battery cell starts to malfunction (e.g., from at least losing its efficiency or failing to function up to igniting, burning or exploding) decreases. Likewise, as the energy density of the battery cell decreases, the temperature at which the battery cell starts to malfunction increases. For example, with a controlled ramping up of the temperature, NMC811 type battery cells tend to start malfunctioning or even blow up when the temperature reaches around <NUM> to <NUM>, while NMC622 type battery cells start to malfunction or even blow up when they reach a temperature of around <NUM>. The corresponding temperature is higher for battery cells with lower energy densities (e.g., NMC532 and NMC433 type battery cells). With physically larger battery cells or when the temperature is rapidly increased, thermal diffusion through the battery cell can result in the localized temperature taking longer to get up to the critical point. It is believed that this thermal diffusion effect can cause the actual temperature at which the battery cell starts to malfunction or blow up to be somewhat higher. It can be desirable for the thermal runaway barrier of the present invention to prevent an adjacent battery from reaching a temperature in the range of from about <NUM> up to about <NUM>.

As used herein, "preventing" a thermal runaway event refers to preventing the overheating of a single battery cell from causing the overheating of battery cells that are adjacent to the single battery cell. The barrier is considered to prevent a thermal runaway event, when adjacent battery cells do not reach above <NUM>, <NUM>, <NUM>, <NUM> or <NUM>.

As used herein, "stopping" a thermal runaway event refers to the overheating of a battery cell only causing adjacent battery cells (i.e., three, two or even only one battery cell away on either side of the overheating battery cell) to overheat and the remaining battery cells in the battery module or assembly do not overheat.

As used herein, "slowing down" a thermal runaway event refers to the thermal runaway event being slowed down at least long enough to allow personnel adjacent to the battery module or assembly (e.g., an occupant inside of an electric vehicle passenger compartment) to escape to a safe distance away from the battery module or assembly, before being injured by the thermal runaway event. Once a battery cell malfunctions (e.g., is on fire or overheats to the point of not functioning) and a thermal barrier is in place between battery cells, the time for any adjacent battery cells to propagate the malfunction (e.g., catching fire or overheating) is at least more than <NUM> minutes, and preferably more than <NUM> minutes or even <NUM> minutes.

In preferred embodiments of the thermal runaway barrier the particles of fumed silica have a surface area in the range of from about <NUM><NUM>/g up to about <NUM><NUM>/g.

The inorganic particles can include, e.g., particles of irreversibly or permanently expanded intumescent material, irreversibly or permanently expanded perlite mineral, etc. Such inorganic particles that contain voids such as, e.g., those found in irreversibly or permanently expanded vermiculite are particularly desirable. Particles of irreversibly or permanently expanded perlite mineral also contain voids, but perlite mineral is harder and less compressible than vermiculite mineral.

As used herein, an irreversibly or permanently expanded expandable particle (e.g., particle of an intumescent material such as vermiculite and 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 <NUM>% and up to <NUM>% of its expandability, either by being pre-expanded before being used to form the thermal runaway barrier, or post-expanded after it is incorporated into the nonwoven fibrous thermal insulation.

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 <NUM> up to about <NUM> 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 (see, e.g., "<NPL>).

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.

In contrast, when they 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 <NUM>) 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 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.

In preferred embodiments of the thermal runaway barrier, the layer of nonwoven fibrous thermal insulation contains an amount of inorganic fibers in the range of from as low as about <NUM> to <NUM>% up to as high as about <NUM>, <NUM>, <NUM>, <NUM> or <NUM>%, by weight of the layer of nonwoven fibrous thermal insulation.

In preferred embodiments of the thermal runaway barrier, the layer of nonwoven fibrous thermal insulation contains an amount of fiber shot in the range of from about <NUM>% up to about <NUM>% by weight of the amount of inorganic fibers in the layer of nonwoven fibrous thermal insulation.

Generally if no insulative particles were added, then inorganic fiber content is <NUM> % by weight in dry-laid and <NUM> % by weight in wet-laid. At the lowest level of insulative particle (e.g., aerogel particle) loading, the inorganic fiber content is <NUM>% by weight for dry-laid and wet-laid. For dry laid nonwoven fibrous thermal insulation, the fibers are opened (i.e., the bulk fibers are separated, made less dense), which may remove some shot. For wet laid nonwoven fibrous thermal insulation, the fibers are wet cleaned, which removes more shot than is removed by the dry laid opening process. There is about <NUM>% shot in uncleaned SuperWool Plus from Morgan, actual fibrous material content is <NUM>-<NUM>% in the nonwoven fibrous thermal insulation. It can be desirable for the nonwoven fibrous thermal insulation to have a fiber content in the range of from about <NUM>% up to about <NUM>%. The lower amount of fiber would require a higher amount of organic binder. Other additives (e.g., flame retardant materials, endothermic materials, infra-red reflective materials, etc.) may be included.

In preferred embodiments of the thermal runaway barrier, the layer of nonwoven fibrous thermal insulation contains an amount of the thermally insulative inorganic particles in the range of from as low as about <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>% or <NUM>% up to as high as about <NUM>%, <NUM>%, <NUM>%, <NUM>% or <NUM>%, by weight of the layer of nonwoven fibrous thermal insulation. For example, a particle content as high as <NUM>% can be achieved using a dry-laid process, and as high as <NUM>% using a wet laid process.

In preferred embodiments of the thermal runaway barrier, the layer of nonwoven fibrous thermal insulation contains an amount of organic binder in the range of from as low as about <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>% or <NUM>% up to as high as about <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, or <NUM>%, by weight of the layer of nonwoven fibrous thermal insulation.

In preferred embodiments of the thermal runaway barrier, the layer of nonwoven fibrous thermal insulation has an installed (i.e., compressed) thickness in the range of from about <NUM> up to less than <NUM>. In particular, the installed (i.e., compressed) thickness in the range of from about <NUM> up to about <NUM>, where the lower limit can be about <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and the upper limit can be about <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM>. In some applications, the installed thickness may even be as high as about <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or less than <NUM>. The installed thickness of the layer of nonwoven fibrous thermal insulation is almost always less than its uninstalled (i.e., uncompressed) thickness. The performance of the thermal runaway barrier is measured when it is in its installed (i.e., compressed) condition.

In preferred embodiments of the thermal runaway barrier, the layer of nonwoven fibrous thermal insulation has an uninstalled (i.e., uncompressed) thickness in the range of from about <NUM> up to less than <NUM>, where the lower limit can be about <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>, and the upper limit can be about <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>. The uncompressed thickness of the layer of nonwoven fibrous thermal insulation is always greater than its installed thickness.

In preferred embodiments of the thermal runaway barrier, the layer of nonwoven fibrous thermal insulation has a basis weight in the range of from as low as about <NUM>/m<NUM> up to as high as about <NUM>/m<NUM>. Depending on the composition of the thermal runaway barrier, it can be desirable for the basis weight to be in the range of from about <NUM>/m<NUM> to about <NUM>/m<NUM> (e.g., <NUM>/m<NUM>, <NUM>/m<NUM>) for a gap between adjacent battery cells in the range of from about <NUM> up to about <NUM>. Depending on the composition of the thermal runaway barrier, it can also be desirable for the basis weight to be in the range of from about <NUM>/m<NUM> up to about <NUM>/m<NUM> for a gap between adjacent battery cells in the range of from about <NUM> to about <NUM>. , and up to as high as about, For gaps between adjacent battery cells in the range of from about <NUM> up to less than <NUM>, it can be desirable for the basis weight to be in the range of from about <NUM>/m<NUM> up to about <NUM>/m<NUM> (e.g., about <NUM>/m<NUM>, <NUM>/m<NUM>, <NUM>/m<NUM>, <NUM>/m<NUM>, <NUM>/m<NUM>, <NUM>/m<NUM>, <NUM>/m<NUM> or <NUM>/m<NUM>). Desirable results have been achieved with thermal runaway barriers using thermally insulative inorganic particles of irreversibly or permanently expanded vermiculite, where the nonwoven fibrous thermal insulation has a basis weight of about <NUM>/m<NUM> or <NUM>/m<NUM> for a gap in the range of from about a <NUM> up to about <NUM>.

In one embodiment, the thermally insulative inorganic particles are particles of irreversibly or permanently expanded vermiculite, and the layer of nonwoven fibrous thermal insulation has a basis weight of <NUM>/m<NUM> for an installed gap between adjacent battery cells in the range of from about a <NUM> up to about <NUM>. In another embodiment, the thermally insulative inorganic particles are particles of irreversibly or permanently expanded vermiculite, and the layer of nonwoven fibrous thermal insulation has a basis weight of <NUM>/m<NUM> for an installed gap between adjacent battery cells in the range of from about a <NUM> up to about <NUM>.

In more preferred embodiments of the thermal runaway barrier, the layer of nonwoven fibrous thermal insulation has a basis weight in the range of from about <NUM>/m<NUM> up to about <NUM>/m<NUM>.

In a particular embodiment, for example, a basis weight in the range of from about <NUM>/m<NUM> up to <NUM>/m<NUM> can be desirable, when the thermally insulative inorganic particles are particles of irreversibly or permanently expanded vermiculite and the gap is about <NUM>. When the gap is about <NUM>, a basis weight in the range of from about <NUM>/m<NUM> up to about <NUM>/m<NUM> may be desirable.

In preferred embodiments of the thermal runaway barrier, the thermally insulative inorganic particles further comprise particles of one or any combination of the materials selected from the group consisting of irreversibly or permanently expanded vermiculite (i.e., vermiculite that has been heated to a temperature and for a time that causes the vermiculite particles to irreversibly or permanently expand to at least <NUM>% and up to <NUM>% of its expandability, either by being pre-expanded before being used to form the barrier, or post-expanded after it is in the nonwoven fibrous thermal insulation), irreversibly or permanently expanded perlite (i.e., perlite that has been heated to a temperature and for a time that causes the perlite particles to irreversibly or permanently expand to at least <NUM>% and up to <NUM>% of its expandability, either by being pre-expanded before being used to form the barrier, or post-expanded after it is in the nonwoven fibrous thermal insulation), and irreversibly or permanently expanded clay.

Expanded clay is a lightweight particle or aggregate, which can be made by heating clay to around <NUM>,<NUM> (<NUM>,<NUM>°F) in a rotary kiln. The yielding gases expand the clay by thousands of small bubbles forming during heating producing a honeycomb structure. Expanded clay can have an approximately round or potato shape due to circular movement in the kiln and is available in different sizes and densities. Expanded clays have been used to make lightweight concrete products (see, e.g., the website: https://www. com/architecture-design-manufacturer/expanded-clay-aggregate-concrete-<NUM>. html) and other uses. Expanded clay is most commonly known under the brand names LECA (acronym of light expanded clay aggregate) or LIAPOR (porous lias clay), also known as Hydroton and under the non-proprietary terms fired clay pebble, grow rocks, expanded clay or hydrocorns, are small globes of burnt and expanded clay (see, e.g., the website: https://www. sciencedirect. com/topics/engineering/expanded-clay-aggregate).

As described above, the thermal runaway barrier includes inorganic aerogel particles, and it can be desirable for the thermal runaway barrier to further include other thermally insulative inorganic particles such as, e.g., particles of one or any combination of the materials selected from the group consisting of xerogel, hollow or porous ceramic microspheres, unexpanded vermiculite, otherwise porous silica, unexpanded perlite, pumicite, diatomaceous earth, titania and zirconia.

In preferred embodiments of the thermal runaway barrier, 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 and silicate fiber. Glass fibers and silica fibers typically do not contain any or only nominal shot particles. PCW typically contains a max of <NUM>% shot particles, while alkaline earth silicate (AES) fibers contain up to <NUM>% shot particles when uncleaned and as low as about <NUM> - <NUM>% minimum shot particles when cleaned).

In preferred embodiments of the thermal runaway barrier, the organic binders are in the form of polymer fibers (e.g., PE/PET, PET, FRPET), dry polymer powder (e.g., LDPE, polyamide, epoxy resin powder (<NUM> SCOTCHCAST <NUM>, <NUM> SCOTCHKOTE <NUM>)) or a liquid binder (e.g., acylic latex, ethylene vinyl acetate (EAF68) latex, silicone, polyurethane etc.).

In the thermal runaway barrier, the layer of nonwoven fibrous thermal insulation is encapsulated by the organic encapsulation layer.

In preferred embodiments of the thermal runaway barrier, the organic encapsulation layer has at least one vent hole formed therethrough that is located and sized to allow expanding gas (e.g., air) contained within the thermal runaway barrier to escape from the organic encapsulation, such that the structural integrity of the organic encapsulation layer is kept intact (i.e., the layer of nonwoven fibrous thermal insulation remains completely, mostly or at least significantly encapsulated by the organic encapsulation layer), when the thermal runaway barrier is compressed during the assembly of the battery cell module (e.g., a stack of battery cells) or when the thermal runaway barrier heats up (e.g., during the normal operation or overheating of the adjacent battery cells). Each vent hole can be in the shape of a rectangle (e.g., see <FIG>), circle, oval or any other shape desired or combination thereof. One or more or each vent hole can be in the form of a notch that projects from a side edge of the encapsulation towards the center of the thermal runaway barrier (e.g., see the left side vent hole <NUM> in <FIG> and the vent holes <NUM> in <FIG>). Alternatively, one or more or each vent hole can be formed interior of the side edge of the encapsulation and adjacent to the nonwoven thermal insulation (see the right side vent hole <NUM> in <FIG> and the vent holes <NUM> in <FIG>). In addition, one or more or each vent hole can be formed through the encapsulation layer on only one side (see vent hole <NUM> on the right side of <FIG>) or both sides (see vent hole <NUM> on the left side of <FIG>) of the nonwoven fibrous thermal insulation. It can also be desirable for each vent hole to be in the form of a plurality of small perforation, that are clustered together (e.g., like a screen, sieve or colander) to provide the desired exit opening area.

Preferably the thermal runaway barrier has a top edge, a bottom edge and opposite side edges, and the at least one vent hole is located along the periphery of one or both opposite side edges. More preferably, the at least one vent hole provides an exit opening through the organic encapsulation layer having an opening area in the range of from about <NUM><NUM> up to about <NUM><NUM>. It is contemplated that any particular area within this range, or any narrower range within this range, could be desirable.

In preferred embodiments of the thermal runaway barrier, the organic encapsulation layer is in the form of a continuous layer, a discontinuous layer (e.g., having perforations, through-holes, or porosity that would allow a gas to penetrate through the organic layer), or a combination of both. In addition, the organic layer can be in the form of an organic (e.g., polymeric) film, scrim, woven or nonwoven fabric, adhesive (e.g., a thermoplastic or hot-melt adhesive) layer or a combination thereof. One example of the organic layer is a polymeric film (e.g., a co-polyester polymeric film).

In preferred embodiments of the thermal runaway barrier, the organic encapsulation layer is a calendared layer, hot-melt coated layer, spray coated layer, dip coated layer, or laminated layer (e.g., with by use of a pressure sensitive adhesive or other adhesive).

In preferred embodiments of the thermal runaway barrier, the layer of nonwoven fibrous thermal insulation has a peripheral edge, and the organic encapsulation layer is sealed around the peripheral edge.

In preferred embodiments of the thermal runaway barrier, the layer of nonwoven fibrous thermal insulation passes at least the V-<NUM> or V-<NUM> level, and preferably the V-<NUM> level, of the below UL94 V0 Flammability Test.

The test was performed using the UL-<NUM> standard, the Standard for safety of Flammability of Plastic Materials for Parts in Devices and Appliances testing. The UL-<NUM> standard is a plastics flammability standard released by Underwriters Laboratories of the United States. The standard determines the material's tendency to either extinguish or spread the flame once the specimen has been ignited. The UL-<NUM> standard is harmonized with IEC <NUM>, <NUM>-<NUM>-<NUM> and <NUM>-<NUM>-<NUM> and ISO <NUM> and <NUM>. A <NUM> x <NUM> sample was exposed to a <NUM>, 50W tirrel burner flame ignition source. The test samples were placed vertically above the flame with the test flame impinging on the bottom of the sample. For each sample, the time to extinguish was measured and V ratings are assigned. V ratings are a measure to extinguish along with the sample not burning to the top clamp or dripping molten material which would ignite a cotton indicator, as shown in Table <NUM> below.

In preferred embodiments of the thermal runaway barrier, the thermally insulative inorganic particles at least comprise particles of irreversibly or permanently expanded intumescent material.

In preferred embodiments of the thermal runaway barrier, the expanded intumescent material has been irreversibly or permanently expanded in the range of from at least about <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>% or <NUM>% up to <NUM>% of its expandability.

In preferred embodiments of the thermal runaway barrier, the thermally insulative inorganic particles at least comprise particles that are irreversibly or permanently expanded vermiculite particles. More preferably, the expanded vermiculite particles have been irreversibly or permanently expanded in the range of from at least about <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>% or <NUM>% up to <NUM>% of its expandability.

A plurality of the thermal runaway barriers described herein may be provided in a thermal runaway barrier assembly, wherein the plurality of thermal runaway 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 runaway barrier 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 runaway 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.).

As described above, the present invention also provides a battery cell module or assembly for an electric vehicle, the battery cell module or assembly comprising:.

Thermal runaway barriers according to the present invention can be made by methods that comprise forming the layer of nonwoven fibrous thermal insulation using a wet-laid process or dry-laid process.

Claim 1:
A thermal runaway barrier operatively adapted for being disposed between battery cells of a battery assembly and for at least significantly slowing down a thermal runaway event within the battery assembly, said thermal runaway barrier comprising:
a layer of a nonwoven fibrous thermal insulation comprising a fiber matrix of inorganic fibers;
thermally insulative inorganic particles of fumed silica material and inorganic aerogel particles dispersed within the fiber matrix, and a binder dispersed within the fiber matrix so as to hold together the fiber matrix; and
an organic encapsulation layer enclosing the layer of nonwoven fibrous thermal insulation.