Microsphere-containing silicone foam composites and methods of making them

Abstract

A foamed silicone comprising hollow inorganic microspheres and a plurality of gas fdled cavities surrounded by a cured silicone resin is described. The foamed silicone is the addition-cured product of at least one first poly(organosiloxane) having a plurality of alkenyl groups and at least one second poly(organosiloxane) having a plurality of Si-H groups. Methods of making such microsphere-containing silicone foam composites are also described.

Description

MICROSPHERE-CONTAINING SILICONE FOAM COMPOSITES AND METHODS OF MAKING THEM FIELD

[0001] The present disclosure relates to silicone foams containing both gas-filled cavities and hollow inorganic microspheres. Methods of making such microsphere-containing silicone foam composites and their uses are also described. SUMMARY

[0002] Briefly, in one aspect, the present disclosure provides methods of making a microsphere- containing silicone foam composite. The methods comprise blending a component A with a component B to a form a blend, wherein component A comprises at least one first poly(organosiloxane) having a plurality of alkenyl groups and component B comprises at least one second poly(organosiloxane) having a plurality of Si-H groups, wherein at least one of component A and component B further comprises a plurality of hollow inorganic microspheres; foaming the blend by a reaction between Si-H groups of the second poly(organosiloxane) and a compound comprising at least one hydroxyl containing moiety; and addition curing the first poly(organosiloxane) and the second poly(organosiloxane) in the presence of a catalyst to form a cured silicone foam comprising a plurality of gas filled cavities surrounded by a cured silicone resin. The cured silicone foam comprises from 10 to 50 volume percent of the hollow inorganic microspheres based on the total volume of the microsphere-containing silicone foam composite.

[0003] In another aspect, the present disclosure provides microsphere-containing silicone foam composites. The microsphere-containing silicone foam composites comprise a foamed silicone comprising the reaction product of at least one first poly(organosiloxane) having a plurality of alkenyl groups and at least one second poly(organosiloxane) having a plurality of Si-H groups, wherein the foamed silicone comprises a plurality of gas filled cavities surrounded by a cured silicone resin and 10 to 50 volume percent of hollow inorganic microspheres based on the total volume of the microsphere- containing silicone foam composite. BRIEF DESCRIPTION OF THE DRAWINGS

[0004] FIG.1 illustrates an exemplary battery module assembly according to one aspect of the present disclosure.

[0005] FIGS.2A-D are optical microscope images of cross sections of various microsphere- containing silicone foam composites.

[0006] FIG.3A illustrates an exemplary battery module with vent seals prior to rupture.

[0007] FIG.3B illustrates the battery module of FIG.3A after rupture DETAILED DESCRIPTION

[0008] Batteries can be broadly classified into primary and secondary batteries. Primary batteries are intended to be used until depleted, after which they are simply replaced with one or more new batteries. Secondary batteries, more commonly referred to as rechargeable batteries, are capable of being repeatedly recharged and reused. Examples of secondary batteries include nickel-cadmium batteries, nickel-metal hybrid batteries, nickel-hydrogen batteries, and lithium batteries.

[0009] Due to their high potential, high energy, power densities, and good lifetimes, secondary batteries are now the preferred battery technology. For example, in the automotive industry different sizes and shapes of lithium-ion battery cells are being manufactured and are subsequently assembled into modules (or packs) of different configurations. An automotive secondary battery module typically consists of many battery cells, sometimes several hundreds or even thousands, to meet desired power and capacity needs.

[0010] In general, the chemistries used in rechargeable batteries are less stable than those used in primary cells. For example, lithium-ion cells are susceptible to thermal run-away which can occur when elevated temperatures trigger exothermic reactions, raising the temperature even further. In some cases, large amounts of thermal energy rapidly released from one cell can lead to increased temperatures of adjacent cells ultimately propagating the effect throughout the battery module. This can disrupt battery performance and, left unimpeded, result in significant damage including combustion of the battery and extensive damage to the surrounding area. Thermal barriers positioned between and around cells can help inhibit the rate and extent of thermal transfer from one cell to the next.

[0011] During a thermal runaway event, the highest temperatures and abrasive wear may be experienced around vent ports within the cell because they represent areas with a decreased resistance to gas flow that allows overheated gases to converge to that location. Typically, the vent port gives the runaway cell a controllable direction to discharge its pressure, heat, and debris during failure. Nonetheless, thermally stable, durable materials are still needed to protect the adjacent cells in a battery module during a thermal runaway event. Silicone-based foams with functional fillers, in particular thermally-insulating polymeric foam layers, are described for use as a venting sealant in automotive battery modules. The polymeric foam layers are intended to provide good compressibility and thermal insulation during normal use and controllably fail in one uncompressed direction (e.g., its thickness or z- direction) while providing a high degree of thermal insulation and structural support in the other xy- directions. These polymeric foam layers allow for easier cell assembly over liquid sealants because they do not require application equipment. At the same time, these polymeric foam layers provide another barrier between neighboring battery cells and can be placed over venting ports, which experience thehighest temperature and pressure during battery cell failure, so that the polymeric foam layer ruptures easily in the thickness direction and allows gases to escape without additional weakening of the material (such as slits, and cuts), reducing internal pressure within the cell and / or module.

[0012] Secondary battery cells also change dimensions (expand and contract) during charging and discharging cycles and swell over the lifetime of the battery. It has been noted that if these batteries swell unconstrained, the lifetime of the battery is shortened. By providing resistance to swelling in the form of a cushioning pad between battery cells, the battery lifetime can be improved.

[0013] U.S. Patent Number 10,501,597 B2 (“Secondary Battery Pack with Improved Thermal Management”) describes the drawbacks of using chemically or physically foamed materials in battery pack applications. Instead, this patent describes the use of silicone rubber syntactic foams comprising a liquid silicone rubber binder and hollow glass beads. The stiffness and resilience of syntactic foams may be dominated by the mechanical properties of the silicone rubber binder. In fact, the addition of rigid glass microspheres may lead to increases in syntactic foam rigidity at higher compressive strains.

[0014] U.S. Patent Number 5,162,397 (“Silicone Foams”) describes the need for foams having a low density and good mechanical properties for applications where fire resistance is desirable. The patent describes the incorporation of chemically treated hollow glass spheres in a foamed silicone. The resulting foams are described as “rather rigid” and are said to “display a good resistance to compression, tension and deflection.” The rigid hollow glass spheres are said to contribute to the strength of the cured foam. For example, glass bubbles are taught to contribute to Young’s compressive modulus in proportion to their volume fraction in the composite.

[0015] There is still a need for foams with improved thermal barrier properties while providing softer foams with the desired compression performance, e.g., for use in secondary battery packs in automotive applications.

[0016] Thermal Barrier Performance. As discussed above, an individual cell of a secondary battery such as lithium-ion battery can reach an elevated temperature triggering an exothermic reaction. The heat generated can be transferred to adjacent cells leading to a cascading effect where the temperature increase initiated within a single cell propagates throughout the entire battery module resulting in extensive damage. The microsphere-containing silicone foam composites of the present invention can be used as thermal barriers, inhibiting the rate of heat transfer between adjacent cells.

[0017] The following Hot-Side Cold-Side test method (“HSCS” described in more detail in the Examples) can be used to determine the thermal barrier performance of the composites. In this test method, heat is applied to one side of the composite (i.e., the hot side) at a reference temperature, e.g., 600 °C. Then, the temperature of the opposing side (i.e., cold side) of the composite is measured for a given length of time, e.g., after 300 seconds or after 600 seconds. Because the thickness of the sample canimpact the measured cold side temperature, the measured temperature is normalized for thickness by multiplying the temperature after a given amount of time by the thickness of the sample. For example, if the measured cold side temperature was 100 °C and the thickness of the sample was 5 millimeters, then the reported normalized value would be 100 °C x 5 mm = 500 °C ● mm.

[0018] Generally, for a hot side reference temperature of 600 °C, the silicone foam composites of the present disclosure have a thermal barrier performance on the hot-side cold-side test at 300 seconds of no greater than 600 °C ● mm when measured according to the HSCS test (i.e., TBP @ Tref 600 °C and 300 s of 600 °C ● mm or less). In some cases, the silicone foam composite of the present disclosure has a TBP @ Tref 600 °C and 300 s of 500 °C ● mm or less. In some cases, a test time of 600 seconds may be used for a more challenging thermal barrier target. Generally, for a hot side reference temperature of 600 °C, the silicone foam composites of the present disclosure have a thermal barrier performance on the hot- side cold-side test at 600 seconds of no greater than 850 °C ● mm when measured according to HSCS- test (i.e., TBP @ Tref 600 °C and 600 s of 850 °C ● mm or less). In some cases, the silicone foam composite of the present disclosure has a TBP @ Tref 600 °C and 600 s of no greater than 800, 700, 600, or even 550 °C ● mm.

[0019] Based on the measured thermal barrier performance (TBP) value, the thickness of the composite may be selected to increase the time provided by the composite to maintain a temperature below a target cold side temperature, e.g., 150 °C. Alternatively, for a desired maximum composite thickness, a target TBP value may be identified to increase the time provided by the composite to maintain a temperature below a target cold side temperature, e.g., 150 °C. Generally, for a reference temperature of 600 °C, the thickness and TBP may be selected to provide at least 400 seconds before the cold side temperature reaches 150 °C as measured according to the HSCS test. In some cases, the thickness and TBP may be selected to provide at least 500, at least 600, at least 700 or even at least 800 seconds before the cold side temperature reaches 150 °C.

[0020] In addition to these tests, the thermal conductivity of the composites may be useful in identifying suitable composites. However, the thermal conductivity should be measured under compressed conditions comparable to what might occur in a battery cell application. In some cases, the thermal conductivity of the composites when measured according to ASTM D5470 at 100 kPa is no greater than 0.15 W / m ● K, e.g., no greater than 0.12, 0.1, 0.095 or even no greater than 0.08 W / m ● K. In some cases, the thermal conductivity of the composites when measured according to ASTM D5470 at 100 kPa is from 0.04 to 0.12 W / m ● K, e.g., 0.04 to 0.1, 0.05 to 0.095, or even 0.05 to 0.08 W / m ● K.

[0021] Compression Performance. In addition to thermal barrier properties, the microsphere- containing silicone foam composites of the present invention provide mechanical properties adapted to accommodate changes in dimensions of the cells during charging and discharging cycles and swell over the lifetime of the battery. Generally, there is a desire to have “soft” foams, i.e., foams that exhibit lowcompressive forces at high compressive strains. For example, in some cases, the composites of the present disclosure have a compressive force of no greater than 250 kPa at compressive strains of up to 50%. In some cases, the compressive force is no greater than 200, no greater than 100 kPa, or even no greater than 50 kPa at 50% compressive strain.

[0022] While 50% compressive strain may be adequate in some applications, others may require low compressive forces at even higher strains, e.g., at compressive strains of 75%. In some cases, the composites of the present disclosure have a compressive force of no greater than 800 kPa at compressive strains of up to 75%. In some cases, the compressive force is no greater than 500, or even no greater than 300 kPa at 75% compressive strain. In addition to the low compression forces at high compressive strains, the foam composites should have good resilience as indicated by a low compression set.

[0023] In the present disclosure, it has been found that the addition of hollow glass microspheres to a foamed silicone matrix can enable improved thermal barrier properties in combination with low compression forces at high compressive strains.

[0024] Generally, the microsphere-containing silicone foam composites of the present disclosure are based on a foamed silicone matrix derived from a curable composition comprising poly(organosiloxane)s. Generally, a poly(organosiloxane) is an oligomer or polymer having a plurality of repeating groups represented by the general formula herein: each R6w independently represents or R7independently represents alkyl, aryl, orH; p is an integer greater than or equal to 2; and each asterisk indicates the connection site of the repeat unit to another group.

[0025] The foamed silicone matrix is derived from (A) at least one poly(organosiloxane) having a plurality of alkenyl groups, (B) at least one poly(organosiloxane) having a plurality of Si-H groups, (C) at least one hydroxyl containing compound, and (D) an effective amount of curing catalyst. The poly(organosiloxane)s are cured via an addition cure reaction as well as a condensation cure reaction to generate a silicone foam.

[0026] Component A. Exemplary poly(organosiloxane)s having a plurality of alkenyl groups can be represented bywherein each R3represents an alkenyl group having from 1 to 20, preferably from 1 to 5, carbon atoms.Examples of suitable alkenyl groups include vinyl, allyl, hexenyl, decenyl, or tetradecenyl. In someembodiments, R3represents a vinyl group.

[0027] Each R4independently represents an alkyl or fluoroalkyl group having from 1 to 30 carbonatoms or phenyl. Examples of suitable alkyl groups include methyl, ethyl, propyl, trifluoropropyl, butyl,pentyl, hexyl, heptyl, octyl, decyl, dodecyl, hexadecyl, and octadecyl. In some embodiments, each R4independently represents an alkyl group having from 1 to 8 carbon atoms, or an alkyl group having from 1 to 4 carbon atoms, or phenyl. Methyl and ethyl groups may be preferred.

[0028] The subscript d represents an integer greater than or equal to zero, e.g., in some cases at least 5, at least 10, at least 20, at least 30, or even at least 40). The subscript d should not be so large as to inhibit the handling (for example, mixing) of the components.

[0029] The subscript e represents an integer greater than or equal to zero. In some cases, e is zero. In some cases, the subscript e may be selected to introduce additional alkenyl (e.g., vinyl) functional groups in the backbone to control reactivity or adjust physical properties.

[0030] Component B. Exemplary poly(organosiloxane)s having a plurality of Si-H groups, can be represented by the formula 1wherein each R independently represents an group 1 to 18 carbon atoms or phenyl. Insome embodiments, each R1independently represents an alkyl group having from 1 to 8 carbon atoms, orfrom 1 to 4 carbon atoms, or a phenyl. Methyl and ethyl groups may be preferred.

[0031] Each X independently represents hydrogen (i.e., H) or R1wherein R1is as previously defined.

[0032] The subscript a represents an integer greater than or equal to zero. In some cases, subscript a is zero, in which case both X groups represent H. If only one X is H then a is at least one, and if neither X is H then a is at least two. In some cases, subscript a is at least 5, at least 10, at least 20, at least 30, or even at least 40. Typically, a is less than 100, e.g., less than 50, although this is not a requirement.

[0033] The subscript b represents an integer greater than or equal to two. In some cases, subscript b is at least 5, at least 10, at least 20, at least 30, or even at least 40. Typically, b is less than 100, e.g., less than 50, although this is not a requirement.

[0034] Examples of such poly(organosiloxane)s include trimethylsilyl-terminated methylhydrosiloxane-dimethylsiloxane copolymers marketed, for example, by: Gelest Inc., Morrisville, Pennsylvania (e.g., product codes: HMS-013, HMS-031, HMS-053, HMS-064, HMS-071, HMS-082, HMS-151, HMS-301, HMS-501, HMS-993); SiSiB Silanes and Silicones, Nanjing, China (e.g., under the trade designations SISIB HF2050 in grades 100H75, 15H75, 55H55, 22H55, 60H36, 15H36, 15H100, 60H120,15H43, 115H41, 21H20, 70H18, 20H11, and HF2050); and Dow Corning, Midland, Michigan (e.g., under the trade designation SYL-OFF 7678).

[0035] Examples of such poly(organosiloxane)s also include: trimethylsilyl-terminated poly(methylhydrosiloxane), for example, as marketed by Genesee Polymers Corp., Burton, Michigan, under the trade designations GP-499, GP-535, GP-536, and GP-678 and from SiSiB Silanes and Silicones, Hanjing, China under the trade designation PF2020; trimethylsilyl-terminated poly(ethylhydrosiloxane), for example, as marketed by SiSiB Silanes and Silicones under the trade designation HF2025; hydrogen-terminated polydimethylsiloxane as marketed by SiSiB Silanes and Silicones under the trade designation HF2030 in grades M134, M400, M1250, M200, M400, M7500, M10000, M17500, M28000, and M62000; hydrogen terminated-polydiphenylsiloxane, for example, as marketed by SiSiB Silanes and Silicones under the trade designation HF2038; hydride-terminated methylhydrosiloxane dimethylsiloxane copolymer, for example, as marketed by SiSiB Silanes and Silicones under the trade designation HF2060; hydride-terminated phenylhydrosiloxane dimethylsiloxane copolymer, for example, as marketed by SiSiB Silanes and Silicones under the trade designation HF2068; and hydride-terminated poly(methylphenylsiloxane), for example, as marketed by SiSiB Silanes and Silicones under the trade designation HF2080.

[0036] In some cases, suitable poly(organosiloxane)s having a plurality of Si-H groups have a number average molecular weight (Mn) of 400 to 100,000 grams / mole, often 500 to 50,000 grams / mole or even 600 to 10,000 grams / mole, although higher and lower molecular weights may also be used.

[0037] Component C. Generally, when combined, the poly(organosiloxane) having a plurality of Si-H groups (Component B) and the at least one hydroxyl containing compound (Component C) undergo a condensation reaction leading to the generation of a gas (e.g., hydrogen gas) and the formation of a plurality of cavities in the silicone resin. Thus, the result is a chemically foamed silicone matrix.

[0038] The hydroxyl containing compound comprises at least one hydroxyl group, e.g., at least two hydroxyl groups. Exemplary compounds containing at least one hydroxyl group include alcohols (e.g., C1 to C12 organic alcohols), polyols (in particular polyols having 3 to 12 carbon atoms and having anaverage of at least two hydroxyl groups per molecule), silanols, silanol containing poly(organosiloxane)s, silanol containing silanes, water, and any combinations or mixtures thereof.

[0039] In some cases, the hydroxyl containing compound is a poly(organosiloxane) having a plurality of Si-OH groups represented by the formulawherein each R2independently represents an group 1 to 18 carbon atoms or phenyl.Examples of suitable alkyl groups include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, decyl,dodecyl, hexadecyl, and octadecyl. In some cases, each R2independently represents an alkyl grouphaving from 1 to 8 carbon atoms, or an alkyl group having from 1 to 4 carbon atoms, or phenyl. Methyl and ethyl groups may be preferred.

[0040] The subscript c represents an integer greater than or equal to two. In some cases, the subscript c is at least 5, at least 10, at least 20, at least 30, or even at least 40. Typically, c is less than 100, e.g., less than 50, although this is not a requirement.

[0041] Examples of suitable poly(organosiloxane)s that include hydroxy-terminated poly(dimethylsiloxane)s are marketed, for example, by Gelest under the product numbers of DMS-S31, DMS-S32, DMS-S35, DMS-S42, DMS-S45, and DMS-S51; by Dow Corning under the trade designation OHX4070; by Genesee Polymer Corp. under the trade designation GP-426 ; by MilliporeSigma, Saint Louis, Missouri, under the product numbers 481939, 481955, 432997, 432989, 481963, 482005, 482161; and from SiSiB Silanes and Silicones under the trade designation OF0025.

[0042] Component D. In addition to the condensation reaction between Components B and C, the components of the silicone resin matrix undergo an addition-curing reaction. A curing catalyst is selected to facilitate the addition cure of the poly(organosiloxane)s. Generally, any known addition cure catalysts may be used. The curing catalyst is preferably a hydrosilylation catalyst. Suitable hydrosilylation catalysts can contain at least one of the following elements: Pt, Rh, Ru, Pd, Ni (e.g., Raney Nickel), and their combinations. Exemplary catalysts include Karstedt’s catalyst shown in U.S. Pat. No.3,715,334 (Karstedt) or other platinum or rhodium catalysts known to those in the art. Suitable catalysts also include microencapsulated hydrosilylation catalysts for example those known in the art such as seen in U.S. Pat. No.5,009,957 (Lee et al.). Optionally, the catalyst may be coupled to an inert or active support. Examples of preferred catalysts which can be used include platinum type catalysts such as chloroplatinic acid, alcohol solutions of chloroplatinic acid, complexes of platinum and olefins, complexes of platinum and 1,3-divinyl-1,1,3,3-tetramethyldisiloxane and powders on which platinum is supported. The platinum catalysts are fully described in the literature. Mention may in particular be made of the complexes ofplatinum and of an organic product described in U.S. Pat. Nos.3,159,601; 3,159,602; and 3,220,972 and European Patents EP-A-057,459, EP-188,978 and EP-A-190,530 and the complexes of platinum and of vinylated organopolysiloxane described in U.S. Pat. Nos.3,419,593; 3,715,334; 3,377,432; 3,814,730; and 3,775,452, to Karstedt. In some cases, platinum type catalysts are especially desirable.

[0043] An effective amount of the catalyst is used, typically 2 to 20 parts per million by weight of the cure catalyst based on the silicone resin, e.g., 5 to 15 parts per million of the cure catalyst based on the silicone resin.

[0044] In some cases, an inhibitor may be added to the curable silicone composition to slow the cure of the compounded silicone matrix if needed. Cure rate controllers are well known in the art. For example, U.S. Pat. No.3,923,705 refers to the use of vinyl contained cyclic siloxanes. U.S. Pat. No. 3,445,420 describes the use of acetylenic alcohols. U.S. Pat. No.3,188,299 shows the effectiveness of heterocyclic amines. U.S. Pat. No.4,256,870 describes alkyl maleates used to control cure. Olefinic siloxanes can also be used as described in U.S. Pat. No.3,989,667. Polydiorganosiloxanes containing vinyl radicals have also been used and this art can be seen in U.S. Pat. Nos.3,498,945, 4,256,870, and 4,347, 346. Preferred inhibitors for this composition are methylvinylcyclosiloxanes, 3-methyl-1-butyn-3- ol, and 1-ethynyl-1-cyclohexanol with the most preferred being the 1,3,5,7-tetramethyl-1,3,5,7-tetravinyl- cyclotetrasiloxane in amounts from 0.002% to 1.00% of the silicone compound depending on the cure rate desired. The preferred inhibitors include: 1,3,5,7-tetramethyl-1,3,5,7-tetravinyl-cyclotetrasiloxane; 3- methyl-1-butyn-3-ol; and 1-ethynyl-1-cyclohexanol.

[0045] In making the cured silicone foams of the present disclosure, the silicon-bonded hydrogen groups (Si-H) of Component B undergo a condensation reaction with the hydroxyl groups of Component C to generate a gas creating gas-filled cavities and the resulting silicone foam. Also, in the presence of the catalyst (Component D), the silicon-bonded hydrogen groups of Component B undergo an addition reaction with the alkenyl groups (C=C) of Component A.

[0046] To ensure sufficient Si-H groups remain available to achieve the desired addition cure with the competing condensation reactions, an excess of Si-H can be used. In some cases, the molar ratio of the silicon-bonded hydrogen groups (Si-H) to alkenyl groups (C=C) is from 15:1 to 2:1. For example, in some cases, the molar ratio Si-H:C=C is from 10:1 to 2:1, 7:1 to 2:1, or even 7:1 to 2.5:1.

[0047] Generally, the amount of Si-H groups can also be selected based on the combined amounts of alkenyl groups (C=C) and hydroxyl groups (OH). In some cases, the molar ratio of Si-H groups to the total amount of C=C + OH groups is from 10:1 to 1:1. For example, in some cases, the molar ratio of Si- H:(C=C + OH) is from 7:1 to 1:1, 7:1 to 1.5:1, 7:1 to 2:1 or even 6:1 to 2:1.

[0048] Suitable curable silicone foam resins include room temperature vulcanizing (RTV) silicones that are sold in a 2-part format that, upon mixing, cure to form the silicone foam resin. Part A contains thepoly(organosiloxane)s having a plurality of alkenyl groups (Component A) as well as the hydroxyl containing compound (Component C) and an addition cure catalyst (Component D). Part B contains the poly(organosiloxane)s having a plurality of Si-H groups (Component B). In some cases, Part B may also contain poly(organosiloxane)s having a plurality of alkenyl groups such that a portion of Component A may be present in both parts of the two part system. Exemplary 2-part silicone foam kits are available commercially and are sold under the trade designation RTF 8510 by Momentive Performance Materials Inc. Niskayuna, NY, “SILBIONE RT FOAM 4230”, “BLUESIL RT FOAM 3244” and “BLUESIL RT FOAM 3242” by Elkem Silicones France SAS, Lyon, France and “DOWSIL 3-8209”, “DOWSIL 3- 6548”, “DOWSIL 3-8259”, and “SILASTIC 8257” from the Dow Chemical Company, Midland, M

[0049] Hollow Microspheres. The foam composites of the present disclosure also include a plurality of hollow inorganic microspheres sometimes referred to as bubbles. Generally, these hollow microspheres comprise a thin inorganic shell surrounding a hollow core. Suitable inorganic microspheres include hollow glass microspheres and hollow ceramic microspheres.

[0050] Microspheres have been treated with, e.g., silanes and polysiloxanes to introduce reactive functional groups at their surfaces. As used herein, the term “reactive functional group” refers to moieties reactive with one or more of the poly(organosiloxane)s, e.g., vinyl groups and silicon-bonded hydrogen atoms. Generally, there is no requirement to pretreat the hollow inorganic microspheres of the present disclosure to provide such reactive groups. In fact, the presence of such reactive functional groups could lead to additional crosslinking and an undesirable increase in the modulus and compressive force required for a given compressive strain. Therefore, in some cases, no greater than 10% by weight of the hollow inorganic microspheres are pretreated to provide reactive functional groups. In some cases, no greater than 5 wt.%, no greater than 1 wt.% or even 0 wt.% of the of the microspheres are pretreated with reactive functional groups.

[0051] It is also known to pretreat microspheres with, e.g., silanes, to introduce non-reactive functional groups at their surfaces, i.e., moieties that do not react with the poly(organosiloxane)s, e.g., alkyl groups. Generally, there is no requirement to pretreat the hollow inorganic microspheres of the present disclosure to provide such non-reactive groups. However, the introduction of such groups may improve compatibility of the microspheres with the selected resins.

[0052] Exemplary hollow glass microspheres (“HGM”) include those marketed by 3M Co. (St. Paul, MN) under the trade designation “3M GLASS BUBBLES” (e.g., grades – K1, K15, S32, K37, S38, S38HS, S38XHS, K46, D32 / 4500, H50 / 10000, S60, S60HS, and iM30K); glass bubbles marketed by Potters Industries, Valley Forge, PA, (an affiliate of PQ Corporation) under the trade designations “Q- CEL HOLLOW SPHERES” and “SPHERICEL HOLLOW GLASS SPHERES” and hollow glass particles marketed by Silbrico Corp., Hodgkins, IL under the trade designation “SIL-CELL”.

[0053] Exemplary hollow ceramic particles include aluminosilicate particles extracted from pulverized fuel ash collected from coal-fired power stations (i.e., cenospheres). Useful cenospheres include those marketed by Sphere One, Inc., Chattanooga, TN, under the trade designation “EXTENDOSPHERES HOLLOW SPHERES” (e.g., grades SG, MG, CG, TG, HA, SLG, SL-150, 300 / 600, 350 and FM-1); and those marketed by 3M Company under the trade designation “3M HOLLOW CERAMIC MICROSPHERES” (e.g., grades G-3125, G-3150, and G-3500).

[0054] Generally, thinner walled, lower density hollow inorganic microspheres will result in lower thermal conductivities and better thermal barrier properties. The thickness of the shells may vary as suppliers try to balance low density (typically provided by thinner walls) with high crush strength as may be required to provide the desired compression performance, especially resilience (typically provided by thicker walls). In some cases, the core of the hollow microspheres comprises at least 50, 60, 70, 80, or even 90% of the diameter of the hollow microspheres.

[0055] Generally, the hollow inorganic microspheres have an average diameter of no greater than 500 micrometers, e.g., no greater than 400 micrometers. Surprisingly, the present inventors discovered that low compressive forces at high compressive strains could be provided by using smaller bubbles. For example, in some cases, the microspheres have an average diameter of no greater than 250 micrometers, for example, no greater than 150, no greater than 100 micrometers, or even no greater than 50 micrometers. Typically, the microspheres have an average diameter of at least 10 or 20 micrometers. For example, in some cases, the microspheres have an average diameter of 10 to 400 micrometers, e.g., 10- 300, 20 to 250, 20 to 150 or even 20 to 70 micrometers.

[0056] For some applications, lower density hollow microspheres may be selected to lower the thermal conductivity and improve the thermal barrier properties pf the foam composites. Generally, the microspheres have an average true density of no greater than 1 gram per cubic centimeter. However, even lower densities are preferred, for example, no greater than 0.8, 0.6 or even no greater than 0.4 grams per cubic centimeter. Exemplary hollow glass microspheres have an average true density of 0.1 to 0.8, 0.1 to 0.6, 0.1 to 0.5 or 0.2 to 0.5 grams per cubic centimeter.

[0057] It is important to distinguish the average true density from the bulk density, as bulk density includes air between the microspheres and provides an artificially lower value. The term "average true density" is the quotient obtained by dividing the mass of a sample of hollow particles by the true volume of that mass of hollow particles as measured by a gas pycnometer. The "true volume" is the aggregate total volume of the hollow particles, not the bulk volume. The average true density may be measured using a pycnometer according to ASTM D2840- 69, "Average True Particle Density of Hollow Microspheres”. The pycnometer may be obtained, for example, under the trade designation "ACCUPYC 1330 PYCNOMETER" from Micromeritics, Norcross, Georgia. Average true density can typically be measured with an accuracy of 0.001 g / cc.

[0058] Generally, the microsphere-containing silicone composites contain at least 10 vol.%, e.g., at least 15 vol.% of the hollow inorganic microspheres based on the total volume of the foam. For example, in some cases, the microsphere-containing silicone composites comprises 10 to 50 vol.%, 15 to 45 wt.%, or even 25 to 35 vol.% of the hollow inorganic microspheres based on the total volume of the foam.

[0059] In some cases, the hollow inorganic microspheres are at least partially embedded in the silicone foam matrix. That is, the microspheres are located in the silicone resin walls surrounding the gas- filled cavities as opposed to being located within the cavities themselves. Depending on the size of the microspheres and the thickness of the cavity walls, the microspheres may be partially or fully embedded in the silicone. For example, some of the microspheres will be minimally embedded, for example attached to the walls. In other cases, a larger portion of the microspheres may be surrounded by the silicone, up to and including the microspheres fully surrounded by the silicone. In some cases, at least 70 wt.% of the hollow inorganic microspheres are at least partially embedded in the silicone foam matrix. In some cases, at least 80 wt.%, at least 90 wt.% or even at least 95 wt.% of the hollow inorganic microspheres are at least partially embedded in the silicone foam matrix.

[0060] In addition to the silicone foam matrix and the hollow inorganic microspheres, additional additives may be incorporated into the composite. Such additives include, e.g., pigments, dyes, clays, surfactants, non-reactive diluents, flame retardants, expandable organic microspheres, and solid fillers such as solid microspheres or beads, ceramics, and silica particles.

[0061] The hollow inorganic microsphere-containing silicone foam composites of the present disclosure may be used as a thermal barrier in industrial applications, including, e.g., the automotive industry. For example, the silicone foam composites can be used a thermal barrier (e.g., a thermal runaway barrier) in a rechargeable electrical energy storage system, e.g., a battery module. In some cases, the silicone composites disclosed herein can be used as a thermal barrier spacer (e.g., a thermal runaway barrier spacer) between the battery cells in a rechargeable electrical energy storage system. For example, the composites may be placed between adjacent cells in lithium ion battery.

[0062] An exemplary assembled battery module according to one aspect of the present disclosure is illustrated in FIG.1. Battery module 15 comprises a plurality of adjacent battery cells 16 separated from each other by a gap. Silicone foam composite 17 is positioned in the gap between adjacent battery cells 16. In some cases, battery module 15 may include base plate 19 upon which is positioned thermally conductive gap filler 18. Exemplary battery modules, battery subunits and methods of manufacturing thereof for use herein are known and include those described in U.S. Pat. No.11,171,370 (Goeb et al.).

[0063] One method of manufacturing such a battery module comprises the steps of: (a) providing a plurality of battery cells separated from each other by a gap; and (b) positioning a microsphere-containing silicone foam composite of the present disclosure in the gap between the battery cells. In some cases, thebattery cells may be held in fixtures during assembly to maintain gaps between the cells to aid in positioning the microsphere-containing silicone foam composites. During later assembly, the gaps may be reduced under a compressive force to place at least parts of the microsphere-containing silicone foam composites into compressive strain.

[0064] Another exemplary assembled battery module according to one aspect of the present disclosure is illustrated in FIG.3A. As shown in this cross section, battery module 300 has cell walls 310 and a variety of battery cells (320(a), 320(b), and 320(c). Each battery cell has at least one corresponding vent port 330. Thermally-insulating polymeric foam layer 340 is between the venting ports and the adjacent cell wall. The silicone foam can be immediately adjacent with the venting ports or can include an adhesive layer to enhance the adhesion between the foam and the battery.

[0065] Battery module 300 is illustrated in FIG.3B after cell 320(b) suffered an adverse event and hot gases 350 were released through the venting port 330 and through the seal provided by the polymeric foam layer 340 in that region, which has ruptured in the thickness direction, z, but which has maintained structural integrity in the x-y plane, thereby protecting neighboring cells 320(a) and 320(c).

[0066] Generally, the microsphere containing silicone foam composites may be shaped to the desired size prior to inserting them between the battery cells. In addition, it may be desirable to enclose the composites partially or fully with a covering to aid in handling or to contain debris that might shed from the composites during use, e.g., repeated compressive loading and unloading.

[0067] Examples. Table 1: Summary of materials used in the preparation of the examples. Name Description Trade Name and Source SIL-I-A Part A of a 2-part silicone foam kitBLUESIL 3242A and BLUESIL 3242B(foam Shore 00 hardness of 40) SIL-I-B Part B of a 2-part silicone foam kitfrom Elkem ASA, Norway.SIL-II-A Part A of a 2-part silicone foam kitSILASTIC 8257A and SILASTIC 8257B(foam Shore 00 hardness of 25) SIL-II-B Part B of a 2-part silicone foam kitfrom Dow Chemical Co., USAGlass bubbles (average particle obtained under the trade designation HGM-1 diameter of 40 micrometers, density “3M Glass Bubbles S38” of 0.38 g / cc). from 3M Company, St. Paul, MN Glass bubbles (average particle obtained under the trade designation HGM-2 diameter of 35 micrometers, density “3M Glass Bubbles S22” of 0.22 g / cc) from 3M Company, St. Paul, MN 90-180 micron diameter hollow glass obtained under the trade designation microspheres (average particle “poraSpheres” hollow glass microspheres HGM-3 diameter of 135 micrometers, density from PORAVER GMBH (Innisfil, Ont. of 0.63 g / cc). Canada) 180-300 micron diameter hollow obtained under the trade designation glass microspheres (average particle “poraSpheres” hollow glass microspheres HGM-4 diameter of 240 micrometers, density from PORAVER GMBH (Innisfil, Ont. of 0.52 g / cc). Canada)Name Description Trade Name and Source 300-500 micron diameter hollow obtained under the trade designation glass microspheres (average particle “poraSpheres” hollow glass microspheres HGM-5 diameter of 344 micrometers, density from PORAVER GMBH (Innisfil, Ont. of 0.49 g / cc). Canada) Vermiculite Filler with an average commercially available from Xinjiang Yuli VM-1 particle diameter of 757 Xinlong Vermiculite Co., Ltd. (China) micrometers. Vermiculite Filler generated by reduction of the particle size of VM1 by a hammer VM-2 milling process, followed by separation by sieving using an ASTM E11 No.50 Sieve. The resultant average particle diameter was 261 micrometers. Vermiculite Filler generated by reduction of the particle size of VM1 by a hammer VM-3 milling process, followed by separation by sieving using an ASTM E11 No.100 Sieve. The resultant average particle diameter was 65 micrometers.

[0068] Both SIL-I and SIL-II are two-part silicone foam kits. In each case, Part A comprises Component A (at least one poly(organosiloxane) having a plurality of alkenyl groups, which are vinyl groups) as well as Components C (at least one hydroxyl containing compound) and D (an effective amount of curing catalyst). In each case, Part B comprises Component B (at least one poly(organosiloxane) having a plurality of Si-H groups) and is also believed to contain at least one poly(organosiloxane) having a plurality of alkenyl groups (i.e., an additional portion of Component A).

[0069] Test methods used.

[0070] CFD Test Method. Compression Force Displacement (CFD) was measured as follows. Samples 50.8 mm in diameter were prepared. A single layer of samples was loaded between parallel platens in an Instron Model 5581 with a 5kN load cell. The test followed ASTM D3574 (2017) with a modified preload of 725 Pa. Compressive load was recorded for three consecutive compressions from 0- 80% with a constant displacement of 1 mm / minute. The results of the 3rd cycle were used for evaluation.

[0071] Density Measurements. The densities in g / cm3of the silicone foam layers were calculated bydividing the coating weight of the foam layers in g / cm2by their thickness in cm.

[0072] Thermal Conductivity. Thermal conductivity was measured on 50.0 mm diameter foam disks with an upper platen temperature of 75 °C, and lower platen temperature of 45 °C, and 100 kPa using a TA instruments DTC 300 thermal conductivity tester according to the ASTM E1530 Standard. Thermal conductivity results are generally reported as an average of the platen temperatures, so 60 °C in the case of an upper platen temperature of 75 °C and a lower platen temperature of 45 °C.

[0073] Compression Set. Compressions et was determined according to ASTM D3547-17, Test D. The test specimens were compressed by 50% and held at 70 °C for twenty-two hours.

[0074] Hot-side Cold-Side Test (HSCS). A hot-side cold-side test was performed using a tensile / compression tester from Zwick in a compression mode. The compression tester was equipped with two plates: a cold (room temperature) bottom plate equipped with a thermocouple to record temperatureand a hot upper plate heated to maintain a constant temperature of 600 °C. At the beginning of the test a heat shield was between the two plates. The sample was placed on the bottom cold plate, then the heat shield was removed, and the upper plate was moved to the desired gap between the two plates (constant thickness) or to the desired compression force (constant force). The temperature of the cold side as a function of time was recorded.

[0075] Preparation of Part A and Part B including fillers. Various fillers were independently compounded into Parts A and B of the 2- part silicone foam kits using a DAC 600 SpeedMixer (Flacktek, Landrum, S.C.) at 2000 rpm for 1-2 minutes to provide a well-dispersed resin blend. The fillers were weighed into the speedmix cup and wetted by the silicone fluid prior to mixing. Table 2: Compositions of samples of Part A and Part B with fillers. Sample Silicone filler Wt. % Wt.% silicone filler A0 SIL-II-A -- 100 0 B0 SIL-II-B -- 100 0 A1 SIL-II-A HGM-1 85 15 B1 SIL-II-B HGM-1 85 15 A2 SIL-II-A HGM-3 77 23 B2 SIL-II-B HGM-3 77 23 A3 SIL-II-A HGM-4 80 20 B3 SIL-II-B HGM-4 80 20 A4 SIL-II-A HGM-5 81 19 B4 SIL-II-B HGM-5 81 19 A5 SIL-II-A HGM-1 80 20 B5 SIL-II-B HGM-1 80 20 A6 SIL-I-A -- 100 0 B6 SIL-I-B -- 100 0 A7 SIL-I-A HGM-1 85 15 B7 SIL-I-B HGM-1 85 15 A8 SIL-I-A HGM-2 85 15 B8 SIL-I-B HGM-2 85 15 A9 SIL-I-A HGM-3 77 23 B9 SIL-I-B HGM-3 77 23 A10 SIL-I-B HGM-4 80 20 B10 SIL-I-B HGM-4 80 20 A11 SIL-I-A VM-1 60 40 B11 SIL-I-B VM-1 60 40 A12 SIL-I-A VM-2 60 40 B12 SIL-I-B VM-2 60 40 A13 SIL-I-A VM-3 60 40 B13 SIL-I-B VM-3 60 40

[0076] Microsphere-containing silicone foam composite samples were prepared by mixing Sample A and Sample B (pre-compounded with their respective fillers, if present) at various weight ratios in a speedmixer for 30 seconds at 1200 rpm. The resulting mixture was poured between two liners and coated through a knife coater with a gap of 600 micrometers. The resulting coating was placed in an oven at 90 °C for 15 minutes to form the samples for testing.

[0077] The samples were tested for density and compression force displacement according to the methods described above. The modulus at 50% compression (E @ 50%) was calculated from the CFD at 50% compression where E = CFD / strain, i.e., E @ 50% = CFD @ 50% / 0.5.

[0078] Various samples and comparative examples were prepared using the SIL-II silicone foam kit and 40 micron hollow glass microspheres (HGM-1). Generally, the addition of the HGM reduced the density of the foam, although the impact was reduced at higher A:B ratios. At A:B weight ratios of 1:1 and 2:1, the addition of up 40 vol% hollow glass microspheres had little or no impact on the CFD @ 50% and the corresponding elastic modulus. At higher A:B ratios, the foam without HGM became stiffer (higher CFD and modulus at 50% compression). As HGM were added at amounts the CFD and elastic modulus increased, but only by about 3x (A:B ratio of 2.5:1) and 10x (A:B of 3:1). Table 3: Samples prepared from SIL-II-A and SIL-II B with 40 micron hollow glass microspheres. Example SIL-II SIL-II A:B HGM-1 Density CFD @ 50% E @ 50% Part A Part B wt. ratio Vol% (g / cc) (kPa) (MPa) CE-1 A0 B0 1 0 0.28 6 0.03 EX-1 A1 B1 1 32 0.17 18 0.04 CE-2 A0 B0 2 0 0.25 15 0.03 EX-2 A1 B0 2 19 0.21 43 0.09 EX-3 A1 B1 2 32 0.18 18 0.04 EX-4 A5 B5 2 40 0.22 58 0.12 EX-5 A1 B1 2.5 32 0.19 64 0.13 EX-6 A5 B5 2.5 40 0.23 144 0.29 CE-3 A0 B0 3 0 0.27 14 0.03 EX-7 A1 B1 3 32 0.23 135 0.27 EX-8 A5 B5 3 40 0.23 152 0.30

[0079] Additional samples and comparative examples were prepared using the SIL-I silicone foam kit and 40 micron hollow glass microspheres (HGM-1). Again, the addition of the HGM reduced the density, but had little impact on the CFD and modulus at 50% compression. Table 4: Samples prepared from SIL-I-A and SIL-I B with 40 micron hollow glass microspheres. Example SIL-I SIL-I A:B HGM-1 Density CFD @ 50% E @ 50% Part A Part B wt. ratio Vol% (g / cc) (kPa) (MPa) CE-4 A6 B6 1 0 0.28 64 0.13 EX-9 A7 B6 1 19 0.19 19 0.04 EX-10 A7 B7 1 32 0.18 55 0.11Example SIL-I SIL-I A:B HGM-1 Density CFD @ 50% E @ 50% Part A Part B wt. ratio Vol% (g / cc) (kPa) (MPa) EX-11 A7 B7 1.5 32 0.19 78 0.16 EX-12 A7 B6 2 24 0.19 46 0.09 EX-13 A7 B7 2 32 0.22 158 0.32 EX-14 A7 B6 3 26 0.23 128 0.26

[0080] The impact of bubble size on the CFD is shown in Table 5 (SIL-II) and Table 6 (SIL-II). As shown in Table 5, in silicone system SIL-II, increasing the average diameter of the HGM from 40 to 365 microns had little or no effect on the compression force, even at strains of up to 70%. At 77% stain there was about a 5x increase in the compressive force as the HGM size increased to 365 microns. As shown in Table 6, varying the HGM diameters from 35 to 240 microns had no significant impact on the compressive force at 50% compressive strain. Table 5: Samples prepared from SIL-II at an A:B weight ratio of 2:1 with various diameter (micron) hollow glass microspheres. SIL-II Hollow Glass MicrospheresCFD (kPa) @ % strainPart Part Avg. Vol. Example A B Type Diam. % 20% 50% 70% 77% EX-3 A1 B1 HGM-1 40 32 6 18 90 280 EX-15 A2 B2 HGM-3 135 32 4 20 88 436 EX-16 A3 B3 HGM-4 240 32 3 14 91 680 EX-17 A4 B4 HGM-5 365 32 7 22 140 1130 Table 6: Samples prepared from SIL-I with various diameter (micron) hollow glass microspheres. SIL-I Hollow Glass Microspheres Ex. Part Part A:B Avg. CFD @ wTypeVol. % A Bt. ratioDiam. 50% (kPa) EX-18 A8 B8 1.5:1 HGM-2 35 32 207 EX-13 A7 B7 2:1 HGM-1 40 32 158 EX-19 A9 B9 2:1 HGM-3 135 32 148 EX-20 A10 B10 2:1 HGM-4 240 32 165

[0081] These results demonstrate that very small diameter hollow inorganic microspheres can be added at high loadings, with little or no detrimental impact on the mechanical properties. In fact, the decrease in modulus with decreasing diameter observed at 77% compression is contrary to expectations based on more traditional thermal insulating fillers such as vermiculite.

[0082] When vermiculite filler was added, the compression force increased as the particle diameter decreased. For example, a 20x increase was observed even at low compressive strains of 20% and 50%. At higher strains, the compressive force exceeded 1800 Kpa.Table 7: Samples prepared from SIL-II with various diameter (micron) vermiculite particles. CFD (kPa) @ % strainEx. Part Part Filler Avg. Vol. % 20% 50% 70% 77% A B Diam. Filler CE-5 A13 B13 VM-3 65 21 87 1010 > 1800 > 1800 CE-6 A12 B12 VM-2 261 21 25 306 1280 > 1800 CE-7 A11 B11 VM-1 727 21 4 56 360 600

[0083] The microsphere-containing silicone foams of the present disclosure also exhibit superior thermal barrier properties compared to available alternatives. As shown in Table 8, the examples with hollow inorganic microspheres (EX-2, EX-3, EX-4, and EX-15) provided significantly reduced thermal conductivity with no loss of compression properties compared to samples with no filler (CE-2) or with a vermiculite filler (CE-7). Table 8: Thermal conductivity of samples prepared with SIL-II. Diameter Thermal Conductivity CFD (kPa) Ex. Filler Vol% (microns) (W / m●K) @ 50% strain CE-2 None -- -- 0.2 15 EX-2 HGM-1 19 40 0.068 43 EX-3 HGM-1 32 40 0.097 18 EX-15 HGM-3 32 135 0.088 20 EX-4 HGM-1 40 40 0.094 58 CE-7 VM-1 21 727 0.15 56

[0084] A Keyence Model VHX-1000 digital optical microscope was used to take cross section images of foam samples. FIG.2A is a cross section of Example 3 (32 Vol.% HGM-1 (40 micron) in SIL-II.); FIG.2B is a cross section of Example 15 (32 Vol.% HGM-3 (135 micron) in SIL-II.); FIG.2C is a cross section of Example 16 (32 Vol.% HGM-4 (240 micron) in SIL-II.); and FIG.2D is a cross section of Example 17 (32 Vol.% HGM-5 (365 micron) in SIL-II.). In each case, the foams comprise gas filled cavities surrounded by the cured silicone resin.

[0085] The hollow glass microspheres are primarily present in the silicone walls surrounding these cavities. Depending on their size, a high percentage of the glass microsphere are partially or fully embedded in the silicone resin. Although not wishing to be bound by theory, it is thought that the location of the microspheres in the walls rather than in the cavities contributes to the surprising combination of properties provided by the claimed compositions. For example, the location of the microspheres in the walls is believed to contribute to the reduction in both the density and thermal conductivity, and the independence of compression force from bubble size, especially at high compressive strains.

Claims

What is Claimed is:

1. A method of making a microsphere-containing silicone foam composite, the method comprising: blending a component A with a component B to a form a blend, wherein component A comprises at least one first poly(organosiloxane) having a plurality of alkenyl groups and component B comprises at least one second poly(organosiloxane) having a plurality of Si-H groups, wherein at least one of component A and component B further comprises a plurality of hollow inorganic microspheres; foaming the blend by a reaction between Si-H groups of the second poly(organosiloxane) and a compound comprising at least one hydroxyl group; and addition curing the first poly(organosiloxane) and the second poly(organosiloxane) in the presence of a catalyst to form a cured silicone foam comprising a plurality of gas-filled cavities surrounded by a cured silicone resin; wherein the cured silicone foam comprises from 10 to 50 volume percent of the hollow inorganic microspheres based on the total volume of the microsphere-containing silicone foam composite.

2. The method of claim 1, wherein both the first component and the second component comprise a plurality of the hollow inorganic microspheres.

3. The method of claim 1 or 2, wherein the plurality of hollow inorganic microspheres comprises hollow glass microspheres.

4. The method according to any one of the preceding claims, wherein the hollow inorganic microspheres have an average diameter of from 20 to 250 micrometers.

5. The method according to any one of the preceding claims, wherein no greater than 5 percent by weight of the hollow inorganic microspheres are treated to provide reactive groups.

6. The method according to any one of the preceding claims, wherein at least one of the first poly(organosiloxane)s comprises vinyl groups.

7. The method according to any one of the preceding claims, wherein at least one of the second poly(organosiloxane)s is selected from the group consisting of trimethylsilyl-terminated methylhydrosiloxane-dimethylsiloxane copolymers and trimethylsilyl-terminated poly(methylhydrosiloxane)s.

8. The method according to any one of the preceding claims, wherein the compound comprising at least one hydroxyl group is a poly(organosiloxane) having a plurality of Si-OH groups.

9. The method according to any one of claims 1 to 7, wherein the compound comprising at least one hydroxyl group is selected from the groups consisting of water, alcohol, and combinations thereof.

10. The method according to any one of the preceding claims, wherein the catalyst is a hydrosilylation catalyst containing at least one of the following: platinum, palladium, rhodium, ruthenium, and nickel.

11. The method according to any one of the preceding claims, wherein the cured silicone foam comprises from 15 to 45 volume percent of the hollow inorganic microspheres based on the total volume of the microsphere-containing silicone foam composite.

12. The method according to any one of the preceding claims, wherein a molar ratio of silicon-bonded hydrogen groups to alkenyl groups in the blend is from 8:1 to 2:

1.

13. The method according to any one of the preceding claims, wherein a molar ratio of silicon-bonded hydrogen groups to the combined amounts of alkenyl groups and hydroxyl groups in the blend is from 7:1 to 1.5:

1.

14. A microsphere-containing silicone foam composite prepared by the method according to any one of claims 1 to 13.

15. A microsphere-containing silicone foam composite comprising a foamed silicone comprising the reaction product of a blend of at least one first poly(organosiloxane) having a plurality of alkenyl groups, at least one second poly(organosiloxane) having a plurality of Si-H groups, and at least one compound comprising at least one hydroxyl group, wherein the foamed silicone comprises a plurality of gas filled cavities surrounded by a cured silicone resin and 10 to 50 volume percent of hollow inorganic microspheres based on the total volume of the microsphere-containing silicone foam composite.

16. The microsphere-containing silicone foam composite of claim 15, wherein the plurality of hollow inorganic microspheres comprises a plurality of hollow glass microspheres.

17. The microsphere-containing silicone foam composite of claim 15 or 16, wherein the hollow inorganic microspheres have an average diameter of from 20 to 250 micrometers.

18. The microsphere-containing silicone foam composite of claim 17, wherein the hollow inorganic microspheres have an average diameter of from 20 to 70 micrometers.

19. The microsphere-containing silicone foam composite according to any one of claims 15 to 18, wherein no greater than 5 percent by weight of the hollow inorganic microspheres are treated to provide reactive groups.

20. The microsphere-containing silicone foam composite according to any one of claims 15 to 19, wherein the foamed silicone comprises 15 to 45 volume percent of hollow inorganic microspheres based on the total volume of the microsphere-containing silicone foam composite.

21. The microsphere-containing silicone foam composite according to any one of claims 14 to 20, wherein at least 80 wt.% of the hollow inorganic microspheres are at least partially embedded in the cured silicone resin.

22. The microsphere-containing silicone foam composite according to any one of claims 13 to 21, wherein the microsphere-containing silicone foam composite can be compressed to 50% compressive strain with a compressive force of no greater than 200 kPa, as measured according to compressive force displacement test ASTM D3574 (2017) with a modified preload of 725 Pa.

23. The microsphere-containing silicone foam composite according to any one of claims 13 to 21, wherein the microsphere-containing silicone foam composite can be compressed to 70% compressive strain with a compressive force of no greater than 300 kPa, as measured according to compressive force displacement test ASTM D3574 (2017) with a modified preload of 725 Pa.

24. The microsphere-containing silicone foam composite according to any one of claims 13 to 23, wherein the microsphere-containing silicone foam composite has a thermal conductivity of no greater than 0.1 W / m ● K as measured according to ASTM E1530 with an upper platen temperature of 75 °C, a lower platen temperature of 45 °C, and a compressive load of 100 kPa.

25. A battery comprising at least two secondary battery cells and the microsphere-containing silicone foam composite according to any one of claims 13 to 24 between the two secondary battery cells.

26. A battery comprising cell walls surrounding a plurality of secondary battery cells, wherein each secondary battery cell comprises a vent port; and the microsphere-containing silicone foam composite according to any one of claims 13 to 24 between the vent port and one of the cell walls.

27. The battery of claim 25 or 26, wherein the secondary battery cells are lithium battery cells.

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