Flexible inorganic coatings for impact resistant thermal barrier applications

Abstract

A coating comprising a filler, an alkali-rich silicate having the formula [Li2O]x[Na2O]y[K2O]z[SiO2], and water. The filler comprises alumina, aluminosilicate, calcium silicate, titania, silicon carbide, silicon nitride, boron nitride, hexagonal boron nitride, zircon, kaolin clay, mica, vermiculite, graphite, or combinations thereof. The sum of x, y and z in the alkali silicate is at least 0.35. The mole ratio of the water to alkali silicate in the coating is 4 to 20. Coatings and articles containing the dried coatings can be used as impact resistance thermal barriers in high temperature applications.

Description

FLEXIBLE INORGANIC COATINGS FOR IMPACT RESISTANTTHERMAL BARRIER APPLICATIONSBackground

[0001] Increasing demand for hybrid and fully electric vehicles is also increasing demand for safer, more efficient rechargeable batteries to fuel those electric vehicles. Such batteries, including the lithium-ion battery, are typically made up of several battery modules, and each battery module comprises many interconnected individual battery cells. When one cell in a battery module is damaged or faulty in its operation, the temperature within the cell may increase faster than heat can be removed. If the temperature increase remains unchecked, a phenomenon called thermal runaway can occur resulting in a fire and blasts of particles as hot as 1000°C or more. The resulting fire can spread very quickly to neighboring cells and subsequently to cells throughout the entire battery as a chain reaction. These fires can be potentially large and cause damage to the vehicle and surrounding structures.Summary

[0002] One solution to reducing the potential for a thermal runaway event is to use coatings to protect the components of a battery from the high temperatures and the high velocity particles often associated with such events. In contrast to traditional thermal insulators (e.g., mica), coatings are relatively easy to apply, conform to the substrates on which they are applied, and take up minimal space within the battery.

[0003] Ceramic inorganic coatings are currently being investigated for use in electric vehicles. However, such coatings are typically very rigid and can fracture due to conformational change, such as bending, or exposure to sudden impact.

[0004] The present disclosure describes the use of hydrated alkali -rich silicates to impart flexibility to inorganic coatings. Additionally, the coatings exhibited high impact resistance (i.e., resistance to damage due to particle impact) and high thermal transfer resistance at elevated temperatures (e.g., up to 1800°C). Such coatings and the substrates to which they are applied may be used, for example, as impact resistant thermal barriers in the construction of battery components to isolate fires and reduce the chance for a catastrophic thermal runaway.

[0005] In one embodiment, the present disclosure provides a coating comprising a filler, an alkali silicate having the formula [Li2O]x[Na2O]y[K2O]z[SiO2], and water. The filler comprises alumina, aluminosilicate, calcium silicate, titania, silicon carbide, silicon nitride, boron nitride, hexagonal boron nitride, zircon, kaolin clay, mica, vermiculite, graphite, or combinations thereof. The sum of x, y and z in the alkali silicate is at least 0.35. The mole ratio of the water to alkali silicate in the coating is 4 to 20.

[0006] In another embodiment, the present disclosure provides an article comprising a substrate having a first major surface and a second major surface opposite the first major surface, and a dried coating described above on at least the first major surface of the substrate. The molar ratio of water to alkali silicate in the dried coating is 1 to 5.

[0007] In a further embodiment, the present disclosure provides a method of making the article comprising applying the above described coating to a substrate, and drying the coating to reduce the amount of water, wherein the molar ratio of water to alkali silicate after drying is 1 to 5.

[0008] In yet another embodiment, the present disclosure provides a battery pack comprising a plurality of modules. Each module comprises a plurality of cells. Gaps exist between adjacent cells and between adjacent modules. The above article is disposed between at least one of the gaps between adjacent cells, at least one of the gaps between adjacent modules, or combinations thereof.

[0009] In a further embodiment, the present disclosure provide a battery pack comprising a casing having an inner and outer surface. The inner surface of the casing encompasses a plurality of battery modules. The above article is disposed on at least a portion of the inner surface of the casing.

[0010] The above summary of the present disclosure is not intended to describe each disclosed embodiment or every implementation of the present disclosure. The description that follows more particularly exemplifies illustrative embodiments.Brief Description of Drawings

[0011] FIG. 1 is a schematic drawing of the Bend Test Method in the Examples;

[0012] FIG. 2 is a photograph of coatings from Example 23 after having been immersed in deionized water for 24 hours at 80°C (Example 23A); 100°C (Example 23B); 120°C (Example 23C); and 140°C (Example 23D); and

[0013] FIG. 3 is a photograph of coatings from Comparative Example 5 after having been immersed in deionized water for 24 hours at 80°C (Example 5A); 100°C (Example 5B); 120°C (Example 5C); and 140°C (Example 5D).Detailed Description

[0014] The following is a description of exemplary embodiments. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention.

[0015] As used herein:

[0016] The term “comprises” and variations thereof do not have a limiting meaning where these terms appear in the description and claims. Such terms will be understood to imply the inclusion of a stated step or element or group of steps or elements but not the exclusion of any other step or element or group of steps or elements. By “consisting of’ is meant including, and limited to, whatever follows the phrase “consisting of.” Thus, the phrase “consisting of’ indicates that the listed elementsare required or mandatory, and that no other elements may be present. By “consisting essentially of’ is meant including any elements listed after the phrase, and limited to other elements that do not interfere with or contribute to the activity or action specified in the disclosure for the listed elements. Thus, the phrase “consisting essentially of’ indicates that the listed elements are required or mandatory, but that other elements are optional and may or may not be present depending upon whether or not they materially affect the activity or action of the listed elements.

[0017] The terms “a,” “an,” and “the” are used interchangeably with “at least one” to mean one or more of the components being described.

[0018] The term “and / or” means one or all of the listed elements or a combination of any two or more of the listed elements.

[0019] The term “some embodiments” means that a particular feature, configuration, composition, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure. Thus, the appearances of such phrases in various places throughout this specification are not necessarily referring to the same embodiment of the disclosure. Furthermore, the particular features, configurations, compositions, or characteristics may be combined in any suitable manner in one or more embodiments.

[0020] The terms “preferred” and “preferably” refer to embodiments of the disclosure that may afford certain benefits, under certain circumstances; however, other embodiments may also be preferred, under the same or other 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 disclosure.

[0021] All numbers are assumed to be modified by the term “about”. As used herein in connection with a measured quantity, the term “about” refers to that variation in the measured quantity as would be expected by the skilled artisan making the measurement and exercising a level of care commensurate with the objective of the measurement and the precision of the measuring equipment used.

[0022] The recitations of numerical ranges by endpoints include all numbers subsumed within that range as well as the endpoints (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.). The phrase “up to” a number (e.g., up to 50) includes the number (e.g., 50).

[0023] General

[0024] The coatings of the present disclosure generally comprise a filler and a hydrated alkali- rich silicate. The filler comprises alumina, aluminosilicate, calcium silicate, titania, silicon carbide, silicon nitride, boron nitride, hexagonal boron nitride, zircon, kaolin clay, mica, vermiculite, graphite, or combinations thereof. The alkali silicate has the formula [Li2O]x[Na2O]y[K2O]z[SiO2] where the sum of x, y and z is at least 0.35. Water is present in an amount where the mole ratio of water to alkali silicate is 4 to 20. The coatings are typically applied to one or more surfaces of a substrate and hardened by drying. The resultant article can be used to create a high impact resistantthermal barrier that operates at temperatures as high as 1800°C. In some embodiments, the article can be used as a thermal barrier between cells in a battery module within a battery pack, and / or as a thermal barrier between battery modules within a battery pack to reduce the potential for catastrophic thermal runaway events. Additionally, or alternatively, the article can be used as a protective inner surface of a battery pack casing (e.g., inner surface of lid). Although the coatings and articles disclosed herein are discussed in the context of electric vehicle battery applications, it should be understood that the coatings and articles can be used in other applications desiring impact resistance and / or thermal transfer resistance at elevated temperatures.

[0025] Coating Composition

[0026] The alkali-rich silicates for the coatings disclosed herein have the formula [Li2O]x[Na2O]y[K2O]z[SiO2]. Alkali-rich refers to the sum of x, y and z being at least 0.35. In some embodiments of the present disclosure, the sum of x, y and z is at least 0.35, at least 0.40, at least 0.45, at least 0.50, at least 0.55, at least 0.60, at least 0.65, at least 0.70, at least 0.75, at least 0.80, at least 0.85, at least 0.90, at least 0.95, or at least 1.00. In some embodiments, the sum of x, y and z is 0.35 to 1, more particularly 0.35 to 0.70. The terms “alkali-rich silicates” and “alkali silicates” are used interchangeable herein. The alkali silicates can be made up of only one alkali metal (e.g., sodium silicate, lithium silicate or potassium silicate). Alternatively, the alkali silicates can be made up of two or three alkali metals in silicate form. In some embodiments, x and z are each zero. In some other embodiments, x is zero. In yet some other embodiments, z is zero.

[0027] The alkali silicates are hydrated, which means water is present in both the coating and hardened coating formed by drying. The molar ratio of water to alkali silicate in the coating (i.e., prior to drying) is at least 4 but no greater than 20. In some embodiments, the hydration value is at least 4, at least 5, at least 6, at least 7, at least 8, at least 9, at least 10, at least 11, at least 12, at least 13, at least 14, at least 15, at least 16, at least 17, at least 18, or at least 19 up to 20. In some embodiments, the hydration value is no greater than 20, no greater than 19, no greater than 18, no greater than 17, no greater than 16, no greater than 15, no greater than 14, no greater than 13, no greater than 12, no greater than 11, no greater than 10, no greater than 9, no greater than 8, no greater than 7, no greater than 6, or no greater than 5 down to 4. If the hydration values are less than 4, the coating is typically not spreadable, making application to a substrate difficult. If the hydration values are greater than 20, the components of the coating can separate out to form a nonuniform mixture, which can negatively impact the properties of the dried coating. In some embodiments, the hydration value is 4 to 20, more particularly 5 to 15, and even more particularly 6 to 9.

[0028] The hydrated alkali silicates can be made, for example, by combining a silicate solution with an alkali hydroxide in the proper proportions. The term “silicate”, as used herein, means a salt in which the anion contains both silicon and oxygen. Silicates include metasilicates (SiCE2) and orthosilicate (SiO / ). Exemplary alkali silicates for use in the silicate solution include sodium silicate, potassium silicate, lithium silicate, or combinations thereof. In some embodiments, thesilicate solution comprises sodium silicate or potassium silicate. The alkali hydroxide comprises sodium hydroxide, potassium hydroxide, lithium hydroxide, or combinations thereof.

[0029] In some embodiments, the coating comprises 20 wt.% to 80 wt.% alkali silicate based upon the percentage of solids in the coating. The term “solids”, as used herein in the context of percentage of solids in the coating, means the components that remain in the coating after drying, excluding any remaining water. Solvents driven off during formation of the dried coating are not considered solids. Since any solvents and remaining water do not form part of the solids in the coating, the solids content will be approximately the same before and after a coating is dried. In some embodiments, the coating comprises at least 20 wt.%, at least 25 wt.%, at least 30 wt.%, at least 35 wt.%, at least 40 wt.%, at least 50 wt.%, at least 60 wt.%, or at least 70 wt.% alkali silicate based upon the percentage of solids in the coating. In some embodiments, the coating comprises up to 80 wt.%, up to 75 wt.%, up to 70 wt.%, up to 65 wt.%, up to 60 wt.%, up to 50 wt.%, or up to 40 wt.% alkali silicate based upon the percentage of solids in the coating. In some embodiments, the coating comprises 20 wt.% to 80 wt.%, more particularly 20 wt.% to 60 wt.%, even more particularly 30 or wt.% to 40 wt.% alkali silicate based upon the percentage of solids in the coating.

[0030] Fillers

[0031] The coatings further comprises fillers. Fillers can be used to enhance the mechanical properties of the dried coating. Suitable fillers include alumina, aluminosilicate, calcium silicate, titania, silicon carbide, silicon nitride, boron nitride, hexagonal boron nitride, zircon, kaolin clay, mica, vermiculite, graphite, or combinations thereof. In some embodiments, the coating comprises kaolin clay, mica or combinations thereof. In some embodiments, the coating comprises at least 20 wt.%, at least 25 wt.%, at least 30 wt.%, at least 35 wt.%, at least 40 wt.%, at least 50 wt.%, at least 60 wt.%, or at least 70 wt.% filler based upon the percentage of solids in the coating. In some embodiments, the coating comprises up to 80 wt.%, up to 75 wt.%, up to 70 wt.%, up to 65 wt.%, up to 60 wt.%, up to 50 wt.%, or up to 40 wt.% filler based upon the percentage of solids in the coating. In some embodiments, the coating comprises 20 wt.% to 80 wt.%, more particularly 40 wt.% to 80 wt.%, even more particularly 60 wt.% to 70 wt.% filler based upon the percentage of solids in the coating.

[0032] Additives

[0033] Coatings of the present disclosure may, optionally, include additives. Exemplary additives include defoamers, surfactants, rheological modifiers, forming aids, pH-adjusting materials, plasticizers, or combinations thereof. In some embodiments, the coating comprises 0 wt.%, at least 0.5 wt.%, at least 1 wt.%, at least 1.5 wt.%, at least 2 wt.%, at least 2.5 wt.%, at least 3 wt.%, at least 3.5 wt.%, at least 4 wt.%, at least 4.5 wt.%, or at least 5 wt.% additives based upon the percentage of solids in the coating. In some embodiments, the coating comprises up to 10 wt.%, up to 9 wt.%, up to 8 wt.%, up to 7 wt.%, up to 6 wt.%, up to 5 wt.% , up to 4 wt.%, or up to 3 wt.% additives based upon the percentage of solids in the coating. In some embodiments, the coating comprises 0 wt.% to10 wt.%, more particularly 0.5 wt.% to 10 wt.%, even more particularly 0.5 wt.% to 5 wt.%, and further 1 wt.% to 3 wt.% additives based upon the percentage of solids in the coating.

[0034] In some preferred embodiments, the additive includes sodium tetraborate. The presence of water in the dried coatings can make the coatings more susceptible to moisture uptake and, in extreme cases, cause dissolution of the coating. Chemical hardeners, such as aluminum-based hardeners and zinc borate, can stabilize the coatings by crosslinking the silicate network. However, such hardeners often lead to premature crosslinking that reduces shelf life of the coatings, necessitating a less favorable two-component application. Further, borates can decompose to boric acid when hydrated, which acid can also decrease the shelf life of the coating. However, it was found that in some instances sodium tetraborate can improve moisture sensitivity of the dried coatings. The sodium ion does not lead to premature crosslinking like the previously mentioned aluminum and zinc ions. Further, by adding alkali hydroxides during formation of the coating, the alkalinity of the coating neutralizes the acidity of the boric acid, thus maintaining shelflife of the coating slurry and reducing moisture sensitivity of the dried coating.

[0035] In the coatings of the present application, the above described water can provide the proper consistency for the coating. Therefore, in some preferable embodiments, the coating does not include additional solvents (i.e., the only solvent is water).

[0036] Substrates

[0037] The above coatings can be applied to a substrate to create articles exhibiting high impact and high thermal transfer resistance in high temperature applications. The substrates are typically flame resistant and may include flame resistant paper (e.g., inorganic paper or mica based paper), an inorganic fabric, or flame resistant boards (e.g., inorganic fiber boards or mica boards or sheets). Inorganic fabrics may comprise E-glass fibers, R-glass fibers, ECR-glass fibers, basalt fibers, ceramic fibers, silicate fibers, Nextel™ fibers, steel filaments, or combinations thereof. The fibers in the inorganic fabric may be chemically treated. The fabrics may, for example, be a woven or nonwoven mat, a felt, a cloth, a knitted fabric, a stitch bonded fabric, a crocheted fabric, an interlaced fabric, or combinations thereof. Substrates may also include flame resistant polymers, including thermoplastic resins, thermosetting resins, or glass-fiber reinforced resins (e.g., polyester).Substrates may further include metals or metal alloys, including aluminum, steel, or stainless steel. Substrates may comprise a single layer structure (e.g., sheets or foils) or a multi-layered structure comprising one or more of the forementioned materials. In some embodiments involving battery application, is it preferably that the substrate by non-conductive and light weight (e.g., nonmetals).

[0038] Method of Making Solution

[0039] In one method, the articles are made by applying the coatings described herein to a substrate and drying the coating by reducing the amount of water present. The coating can be applied to the substrate by conventional techniques, including by dispensing (e.g., flat streamcoating), spraying, brushing, knife coating, nip coating, or dip coating, to a thickness, for example, of at least 0.5 mm.

[0040] The composition of the dried coating typically comprises less water but is not completely dehydrated. Typically, the molar ratio of water to alkali silicate in the dried coating is at least 1.0, at least 1.5, at least 2.0, at least 2.5, at least 3.0, at least 3.5, at least 4.0, at least 4.5 up to 5 in the dried coating. In some embodiments, the hydration value is no greater than 5.0, no greater than 4.5, no greater than 4.0, no greater than 3.5, no greater than 3.0, no greater than 2.5, no greater than 2.0, or no greater than 1.5 down to 1.0 in the dried coating. If the molar ratio of water to alkali silicate in the dried coating is less than 1.0, the coating loses its flexibility and can fracture due to conformation changes (e.g., bending) or exposure upon high impact particles. If the hydration values are greater than 5, the coating is not sufficiently hard to provide the desired mechanical properties. In some embodiments, the molar ratio of water to alkali silicate is 1 to 5, more particularly 1 to 3, and even more particularly 2 to 3. Therefore, the term “dried” as applied to the finished coating does not involve driving off all the water but, instead, refers to removing solvent (if present) and reducing, but not eliminating, the water in the dried coating.

[0041] The thickness of the dried coating will depend upon the desired application. For example, thinner coatings can be used for applications involving lower temperatures and / or lower potential particle blast forces. Thicker coatings would be used for higher temperature applications and / or higher potential particle blast forces. In some embodiments, the dried coating has a thickness in the range of 0. 1 mm to 6 mm.

[0042] Properties of Coating

[0043] In some embodiments, the dried coating of the present disclosure can survive at least 1, at least 2, least 3, at least 4, at least 5, at least 6, at least 7, at least 8, at least 9, at least 10, at least 11, at least 12, at least 13, at least 14, at least 15, or at least 16 blasts of abrasive media at 1200°C, as determined by the Torch and Grit Test in the Examples. In some embodiments, the dried coating can survive at least 8, more preferably at least 12, and even more preferably at least 16 blasts of abrasive media at 1200°C, as determined by the Torch and Grit Test in the Examples.

[0044] In some embodiments, the dried coating of the present disclosure exhibits a bend angle (6) of at least 10°, or more preferably 20° when subject to the Bend Test Method in the Examples.

[0045] Applications

[0046] Articles of the present application may be used in a variety of high impact, high temperature applications. For example, articles of the present disclosure may be used as impact resistant thermal barriers disposed in the gap between battery cells in an electric vehicle battery (e.g., in a battery module or a batter pack) and / or between individual battery modules in a battery pack. In addition, or alternatively, the coatings or articles of the present disclosure may be disposed on the inner surface of the casing of a battery pack (e.g., a battery module or a battery pack), including the inner surface of a compartment lid or the inner surface of vent passages for exhaust gas. Further, thecoatings and articles of the present disclosure may be used to protect a wide variety of components used in high voltage equipment, such as busbars used for high current power distribution.Examples

[0047] Objects and advantages of this invention are further illustrated by the following examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this invention. These examples are merely for illustrative purposes only and are not meant to be limiting on the scope of the appended claims.

[0048] Unless otherwise noted or readily apparent from the context, all parts, percentages, ratios, etc. in the Examples and the rest of the specification are by weight. The following abbreviations are used throughout: wt.% = percent by weight; g = gram; mm = millimeter; cm = centimeter; and °C = degrees Celsius.

[0049] Table 1. Materials Used in the Examples

[0050] Torch and Grit Test Method

[0051] A hydrogen / oxygen torch (a customized hydrogen / oxygen burner obtained from Bethlehem Apparatus, Hellertown, PA having a central channel for particulates and a ring of outer ports for fuel and oxidizer feeds) was first equilibrated to a designed flame temperature of 1200°C, as measured by a thermocouple inserted into the flame cone one inch (2.54 cm) from the face of the torch (i.e. tip of the nozzle). A test panel was prepared with a sample coating on one side of the panel and a high temperature black paint on the other side of the panel. The panel was oriented so that the side with the sample coating faced the torch flame. A FLIR IR camera, Model T440, was set up to monitor the backside panel temperature, and the temperature was recorded once the backside panel temperature exceeded 200°C. The test panel was place at a distance of 2.38 inches (6.03 cm) from the face of the torch and simultaneously subjected to the torch flame, at a temperature of 1200°C, and a series of blasts from a stream of 120Grit AL Oxide Media. The blasts were powered by a 25 psi (241.32 KPa) compressed air source aligned along the same axis as the torch. The series of blasts cycled between 10 seconds of grit exposure (on) followed by a 10 seconds of no grit exposure (off) while maintaining the hot flame temperature throughout. This on / off cycle was continued until either penetration of the coating or 16 on / off cycles were completed, whichever came first. The backside temperature and the number of cycles for each sample were recorded. The results of the Torch and Grit Test Method are provided in Table 5.

[0052] Bend Test Method

[0053] Referring to FIG. 1, a sample coating 10 was bent down over a cylinder spacer 12 located on a flat surface 14. The cylinder spacer 12 had a diameter “h” The sample coating extended a length “1” across the flat surface 14. The bend angle “6” was determined according to the following equation: Bend Angel (6) = ATAN (2h / l). Results of the Bend Test Method are provided in Table 4.

[0054] Examples 1A - 12A: Synthesis of Alkali Rich Silicates

[0055] Alkali rich silicates were made by dissolving alkali metal hydroxide(s) in a silicate solution using the reagents and quantities provided in Table 2.

[0056] Examples 1B-12B: Preparation of Coating

[0057] Coatings were made by adding fdler to each of the alkali rich silicates in Examples 1 A- 12A using the reagents and quantities provided in Table 3. The solutions were mixed by a high shear mixer (Speedmixer DAC 600 from Flack Tek Inc.).

[0058] Examples 1C-12C: Dried Coatings

[0059] The dried coatings were made by drying each of the coatings in Examples 1B-12B. The coating was spread onto a release liner using a round 3 / 8” outer diameter (OD) steel tube and 2.29 mm coating gap. The coating was then either (1) air dried in a convection oven at 50°C for 24 hours followed by exposure to room air at 21°C for 24 hours (Exs. 1B-3B and 6B-12B), or (2) air dried at room temperature (21-22°C) for 4 weeks (Exs. 4B and 5B). A free-standing coating was obtained by removing the release liner and cutting the dried coating into pieces for flexibility evaluation, e.g., 2.54 cm (1 inch) wide and 12.7 cm (5 inches) long. The thickness of the dried coatings and results of the 20° Bend Test are provided in Table 4.

[0060] Example 13: Dried Coating Subjected to Torch and Grit Test

[0061] The coating of Example IB was spread onto an aluminum panel (6” x 6” x 0.05”) using a round 3 / 8” OD steel tube and a coating gap of 2.29 mm. The coating was then air dried in a convection oven at 50°C for 24 hours followed by exposure to room air at 21 °C for 24 hours. The dried coating was 62% Kaolin and 38% Na-rich sodium silicate. The coating thickness and results from the Torch and Grit Test are provided in Table 5.

[0062] Examples 14-22: Dried Coatings Subjected to Torch and Grit Test

[0063] The dried coatings in Examples 14-22 were prepared and tested in the same manner asExample 13 using the reagents and conditions provided in Table 5. The coating thickness and results from the Torch and Grit Test are also provided in Table 5.

[0064] Comparative Examples (CE) 1B-4B: Preparation of Coatings

[0065] Coatings were made by adding fdler to silicate solutions using the reagents and quantities provided in Table 3. The solutions were mixed by a high shear mixer (Speedmixer DAC 600 from Flack Tek Inc.).

[0066] Comparative Examples (CE) 1C-4C: Dried Coatings

[0067] The dried coatings in Comparative Examples 1C-4C were made by drying each of the coatings in Comparative Examples 1B-4B. The coatings was spread onto a release liner using a round 3 / 8” outer diameter (OD) steel tube and 2.29 mm coating gap. The coating was then air dried in a convection oven at 50°C for 24 hours followed by exposure to room air at 21 °C for 24 hours. A free-standing coating was obtained by removing the release liner and cutting the dried coating intopieces for flexibility evaluation, e.g., 2.54 cm (1 inch) wide and 12.7 cm (5 inches) long. The thickness of the dried coating and results of the 20° Bend Test are provided in Table 4.

[0068] Examples 23A-D: Coating with Sodium Tetraborate

[0069] 10 g of sodium tetraborate were added to 90 g of coating solution 3B and applied to fourG10-FR4 panels using a round 3 / 8” outer diameter (OD) steel tube and 2.29 mm coating gap. The panels were dried for 24 hours, each at a different temperature: 80°C (Example 23A); 100°C (Example 23B); 120°C (Example 23C); and 140°C (Example 23D). Pieces of dried coating were broken off and immersed in deionized water in closed vials for 24 hours at ambient temperature Sample dissolution in the deionized water is indicated by cloudiness. Results are shown in FIG. 2.

[0070] Comparative Examples 5A-D: Coating without Sodium Tetraborate

[0071] Coating solution 3B was applied to four G10-FR4 panels using a round 3 / 8” outer diameter (OD) steel tube and 2.29 mm coating gap. The panels were dried for 24 hours, each at a different temperature: 80°C (Example 5 A); 100°C (Example 5B); 120°C (Example 5C); and 140°C (Example 5D). Pieces of dried coating were broken off and immersed in deionized water in closed vials for 24 hours at ambient temperature. Sample dissolution in the deionized water is indicated by cloudiness. Results are shown in FIG. 3.

[0072] Thus, the present disclosure provides, among other things, flexible coatings and articles containing the flexible coatings that can be used in high temperature applications where impact resistance and / or thermal transfer resistance are desired. Various features and advantages of the present disclosure are set forth in the following claims.Table 2. Preparation of Alkali Rich Silicate Solutions’ Molar ratio of water to alkali silicate.Table 3. Coating’ Molar ratio of water to alkali silicate.2Based upon total solid content in coating.Table 4. Dried Coatings, Coating Thickness and Bend Test Results’ Molar ratio of water to alkali silicate.2Based upon total solid content in coating.Table 5. Dried Coatings, Coating Thickness, and Torch and Grit Test Results’ Molar ratio of water to alkali silicate.2Based upon total solid content in coating.

Claims

What is claimed is:

1. A coating comprising: a filler comprising alumina, aluminosilicate, calcium silicate, titania, silicon carbide, silicon nitride, boron nitride, hexagonal boron nitride, zircon, kaolin clay, mica, vermiculite, graphite, or combinations thereof; and an alkali silicate having the formula [Li2O]x[Na2O]y[K2O]z[SiO2]; water, wherein the sum of x, y and z is at least 0.35, and wherein the molar ratio of water to alkali silicate is 4 to 20.

2. The coating of claim 1, wherein the filler comprises kaolin clay, mica or combination thereof.

3. The coating of claim 1 or claim 2, wherein the sum of x, y and z is 0.35 to 1.

4. The coating of any one of claims 1 to 3, wherein x and z are each zero.

5. The coating of any one of claims 1 to 3, wherein x is zero.

6. The coating of any one of claims 1 to 3, wherein z is zero.

7. The coating of any one of the preceding claims, further comprising defoamers, surfactants, rheological modifiers, forming aids, pH-adjusting materials, plasticizers, or combinations thereof.

8. The coating of any one of the preceding claims, further comprising sodium tetraborate.

9. An article comprising: a substrate having a first major surface and a second major surface opposite the first major surface; and a dried coating of any one of the preceding claims on at least the first major surface of the substrate, wherein the molar ratio of water to alkali silicate in the dried coating is 1 to 5.

10. The article of claim 9, wherein the substrate comprises flame resistant paper, an inorganic fabric, flame resistant boards, flame resistant polymers, metals, metal alloys, or combinations thereof.

11. The article of claim 8 or claim 10, wherein the molar ratio of water to alkali silicate in the dried coating is 2 to 3.

912. The article of any one of claims 9 to 11, wherein the dried coating exhibits a bend angle (0) of at least 10°.

13. The article of any one of claims 9 to 12, wherein the dried coating survives at least 8 cycles of the Torch and Grit Test as described herein.

14. A method of making an article, the method comprising: applying the coating of any one of claims 1 to 8 to a substrate; and drying the coating to reduce the amount of water, wherein the molar ratio of water to alkali silicate after drying is 1 to 5.

15. The method of claim 14, where the coating is applied to the substrate by dispensing, spraying, brushing, knife coating, nip coating, or dip coating.

16. A battery pack comprising : a plurality of modules, each module comprising a plurality of cells; gaps between adjacent cells; gaps between adjacent modules, and the article of any one of claims 9 to 13 disposed between at least one of the gaps between adjacent cells, at least one of the gaps between adjacent modules, or combinations thereof.

17. A battery pack comprising : a casing having an inner and outer surface, the inner surface encompassing a plurality of battery modules; and the article of any one of claims 9 to 13 disposed on at least a portion of the inner surface of the casing.

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