Organopolysiloxane foams containing ceramic microspheres

Abstract

A thermally insulating, compressible, and flame resistant foam material comprising a polyorganosiloxane foam, a flame retardant, and micron-sized hollow ceramic particles. The foam material is useful for providing thermal insulation, flame resistance, and compressibility for applications such as lithium ion batteries.

Description

[Technical field]

[0001] The present invention relates to organopolysiloxane foams containing micron-sized ceramic particles. [Background technology]

[0002] Rechargeable batteries such as lithium-ion batteries (LiBs) are commonly used in a variety of applications, including electric vehicles (EVs) and grid energy storage systems. LiBs have desirable properties of high energy density and stability, but safety concerns currently limit their practical use. First, failure of LiB cells can be caused by manufacturing defects, internal short circuits, overheating, overcharging, or mechanical shock, and second, heat generated from a failed cell can propagate, thereby causing thermal runaway in adjacent cells. The rapid pressure rise resulting from these thermal events increases the risk of fire and explosion.

[0003] Thermal runaway can be mitigated by placing thermal barriers between cells in a LiB module that provide thermal insulation and flame resistance. Commonly used thermal barriers such as aerogel, ceramic fiber, and mica board provide such properties, but aerogel and ceramic fiber have poor mechanical resilience, while mica board has poor compressibility. Silicone blown foam, on the other hand, provides adequate compressibility and is therefore suitable for low and medium energy density batteries, but suffers from insufficient insulation to prevent thermal runaway in very high energy density battery packs. Therefore, in the field of thermal barriers for rechargeable batteries, it is desirable to create a barrier that provides thermal insulation, flame resistance, and satisfactory compressibility. Summary of the Invention

[0004] The present invention provides a thermally insulating, compressible, and flame resistant foam material, comprising 35 to 95 weight percent of a polyorganosiloxane foam, 1 to 30 weight percent of a flame retardant, and 1 to 35 weight percent of hollow ceramic particles having a volume average particle size in the range of 25 μm to 300 μm, based on the weight of the foam material, and having a density of 0.10 to 0.90 g / cm. 3 The present invention addresses a need in the art by providing a foam material having a density in the range of 0.1 to 1.0 MPa. The foam material of the present invention is useful in providing one or more spacers in lithium ion batteries that are thermally insulating, flame resistant, and compressible. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0005] The present invention provides a thermally insulating, compressible, and flame resistant foam material, comprising, based on the volume of the article, 35 to 95 weight percent of a polyorganosiloxane foam, 1 to 30 weight percent of a flame retardant, and 1 to 35 weight percent of hollow ceramic particles having a volume average particle size in the range of 25 μm to 300 μm, and having a mass per unit area of ​​0.10 to 0.90 g / cm. 3 The present invention addresses a need in the art by providing a foam material having a density in the range of

[0006] The polyorganosiloxane foam material of the present invention can be prepared by modifying the method as described in U.S. Patent No. 5,358,975. For example, a polydimethylsiloxane (a) functionalized with at least two, preferably at least three, Si-H groups is contacted with one or more hydroxyl-containing compounds (b), which are advantageously water, alcohols, diols, polyols, or compounds containing at least one silanol group, a divinyl-functionalized polydimethylsiloxane (c), a hydrosilylation catalyst, such as a platinum-based catalyst (d), a flame retardant (e), and hollow ceramic particles (f) to form -Si-CH 2 -CH 2They form a crosslinked network of insulating, compressible, and flame resistant foamed materials having -Si and -Si-OR groups, where R is H or structural units (i.e., reaction products) of alcohols, diols, polyols, or silanols. The sum of components (a), (b), and (c) ranges from 35 or 40 weight percent to 80 or 70 weight percent of the polyorganosiloxane foam.

[0007] It may be advantageous to prepare the foamed material using a two-part approach as follows: In a first container, a first portion of the divinyl-functionalized polydimethylsiloxane, a first portion of the flame retardant, a hydrosilylation catalyst, a hydroxyl-containing compound, and a first portion of the hollow ceramic particles are blended to form a part A composition; In a second container, the remaining portion of the divinyl-functionalized polydimethylsiloxane, a polymer resin blend that is a mixture of divinyl-functionalized polydimethylsiloxane and crosslinked organopolysiloxane resin, the remaining portion of the flame retardant, a polydimethylsiloxane functionalized with at least three Si-H groups, and the remaining portion of the hollow ceramic particles are blended to form a part B composition; Parts A and B are then combined, mixed, and then poured between two release film sheets to form the foamed material of the present invention.

[0008] Flame retardants produce CO when heated. 2 Examples of flame retardants are metal hydroxides, carbonates, hydroxide-carbonates, or hydrates that release oxygen, water, or both. 3 , Mg(OH) 2 , Ca(OH) 2 MgCO 3 3H 2 O (Nesquehonite), Mg 5 (CO 3 ) 4 (OH) 2 4H 2 O(hydromagnesite), MgCa(CO 3 ) 2 (huntite), AlO(OH) (boemite), NaHCO 3, and hydrated MgSO 4 (Epsomite). The polyorganosiloxane foam material includes from 1 or 2 or 3 weight percent to 30 or 20 or 15 weight percent of a flame retardant, based on the weight of the foam material.

[0009] The composition further comprises from 1 or 5 or 10 weight percent to 35 or 30-25 weight percent of hollow, air-filled, or inert gas-filled ceramic particles. As used herein, "ceramic" refers to aluminum (e.g., crystalline or semi-crystalline Al 2 O 3 ), silicon (e.g., crystalline or semi-crystalline SiO 2 "Semicrystalline" refers to a crystalline or semicrystalline inorganic oxide, nitride, carbide, oxynitride, or oxycarbide of metals such as zinc (e.g., crystalline or semicrystalline CaO), or calcium (e.g., crystalline or semicrystalline CaO), or combinations thereof. Crystallinity can be measured by X-ray powder diffraction. As used herein, the term "semicrystalline" refers to a ceramic material having amorphous and crystalline regions. The hollow ceramic particles have an average volume particle size of from 25 μm, or from 50 μm, or from 70 μm to 300 μm, or to 200 μm, or to 150 μm, as measured using a dynamic light scattering analyzer, such as a Beckman Coulter LS 130 Particle Size Analyzer. The resulting article has a weight average of 0.10 or 0.15 g / cm. 3 to 0.90 or 0.50 g / cm 3 The densities range from

[0010] In another aspect, the present invention is a composition comprising, based on the weight of the composition, a) 2 to 50 weight percent of a polysiloxane functionalized with at least two Si-H groups and having a degree of polymerization in the range of 5 to 1000; b) 1 to 50 weight percent of water, alcohol, diol, polyol, or a compound containing one or more silanol groups; c) 10 to 90 weight percent of a polysiloxane functionalized with at least one ethylenically unsaturated group and having a degree of polymerization in the range of 20 to 2000; (the total concentration of components a, b, and c is in the range of 35 to 95 weight percent based on the weight of the composition); d) a catalytic amount of a hydrosilylation catalyst; e) 1 to 30 weight percent of a flame retardant; and f) 1 to 35 weight percent of hollow ceramic particles having a volume average particle size in the range of 25 μm to 300 μm.

[0011] In yet another aspect, the invention is a battery module including a shell containing an array of spatially separated battery cells and a polyorganosiloxane foam material in contact with adjacent battery cells. The polyorganosiloxane foam may contact the battery cells by filling the space between adjacent battery cells with the foam and / or by covering the battery cells with the foam. The battery module may further include end plates on the inner edge of the shell that directly or indirectly contact the battery cells closest to the edge. The foam material may be inserted into the cavities between adjacent battery cells and between the cells and the end plates, or a foam precursor may be applied onto the cells and into the cavities and then cured to form the foam material.

[0012] The foam material of the present invention has been found to provide the desired properties of insulation, flame resistance, and compressibility in LiB thermal barrier applications.

[0013] In the following examples, ViMe 2 SiO 1 / 2 / (CH 3 ) 3 Si-O 1 / 2 / SiO 4 / 2 Resin M w and M nwas determined by gel permeation chromatography using a gpc column packed with 5 mm diameter divinylbenzene cross-linked polystyrene beads, pore type Mixed-C (Polymer Laboratory). THF was used as the mobile phase, and detection was performed with a refractive index detector.

[0014] Example 1 - Preparation of a foamed organopolysiloxane article with ceramic particles Using a Flacktek Speed ​​Mixer, a dimethylvinylsiloxy endblocked polydimethylsiloxane (Polymer 1, 11.3 pbw) having a viscosity of about 40,000 mPa s was mixed with 1) a dimethylvinylsiloxy endblocked polydimethylsiloxane having a viscosity of about 1,900 mPa s and about 0.22 wt% Vi and 2) a 5:40:55 ViMe 2 SiO 1 / 2 :(CH 3 ) 3 Si-O 1 / 2 :SiO 4 / 2 Structural unit ratio: 5000 m n , and 21,400 M w ViMe with 2 SiO 1 / 2 / (CH 3 ) 3 Si-O 1 / 2 / SiO 4 / 2 The first component (Part A) was prepared by mixing together a 64:36 w / w blend with resin (polymer-resin blend, 64.9 pbw), and Micral 855 aluminum hydroxide (15.2 pbw). The contents were stirred at 2000 rpm for 30 seconds, after which Pt(0) divinyltetramethyldisiloxane complex (0.93 pbw, 0.62 wt% Pt), 1,4-butanediol (2.6 pbw), and benzyl alcohol (3.3 pbw) were added to the mixture and the contents were stirred at 2000 rpm for 30 seconds. Finally, Elminas Spheres HCMS-W150 hollow ceramic particles (100 μm average volume particle size; 20 pbw) were added to the mixture and the contents were stirred at 2000 rpm for 30 seconds.

[0015] A second composition (Part B) was similarly prepared by mixing together Polymer 1 (8.9 pbw), polymer resin blend (51 pbw), and Hymod M855 aluminum hydroxide (26.4 pbw). The contents were stirred at 2000 rpm for 30 seconds, after which a linear organohydrogenpolysiloxane having a viscosity of 30 mPa·s and a SiH content of 1.6 wt% (6.7 pbw) and a polydimethylorganohydrogensiloxane having a viscosity of 5 mPa·s and a SiH content of 0.7 wt% (5.1 pbw) were added to the mixture, and the contents were stirred at 2000 rpm for 30 seconds. Elminas Spherers HCMS-W150 hollow ceramic particles (20 pbw) were then added to the mixture, and the contents were stirred at 2000 rpm for 30 seconds.

[0016] Equal amounts of parts A and B were then mixed and the mixture was poured between two release film sheets (matte Mylar film). The initial (pre-foaming) thickness was controlled at 0.045 inches using nip rollers. The samples were cured at 70°C for 5 minutes and then at 100°C for 15 minutes to produce foam sheets used for further testing. (Density = 0.31 g / cm 3 )

[0017] Example 2 - Preparation of a foamed organopolysiloxane article with ceramic particles Substantially the same process was followed to prepare the foam article of Example 1, except that Elminas Spheres HCMS THERMO-W75 hollow ceramic particles (80 μm average volume diameter, 20 pbw) were used in parts A and B. (Density=0.31 g / cm 3 )

[0018] Example 3 - Preparation of foamed organopolysiloxane article with ceramic particles Substantially the same process was followed to prepare the foam article of Example 1, except that Elminas Spheres-W300 hollow ceramic particles (180 μm average volume diameter, 20 pbw) were used in parts A and B. (Density=0.34 g / cm 3 )

[0019] Insulation and flammability The foams prepared as described in the examples were tested for thermal insulation and flammability using a hot plate mounted on a hydraulic press. The hot plate was set to 600°C and the insulator was placed on the surface. Four thermocouples (Type K) were secured onto an aluminum heat sink (4" x 4" x 0.47") using Kapton tape. The sample (4" x 4") was then placed and secured onto the heat sink using Kapton tape. An additional thermocouple (Type K) was attached to the sample surface using Kapton tape. The insulator was removed from the hot surface and the heat sink mounted sample was quickly placed onto the hot surface with the sample surface facing the hot plate surface and the Al heat sink facing the opposite side. The pressure was rapidly increased to 355 kPa. The interface temperatures between the hot plate surface and the sample surface and between the sample surface and the heat sink were recorded using a data logger. Once the time reached 300 seconds, the pressure was released and the test was terminated. Temperatures below 300°C on the sample surface were considered acceptable. No observable flame throughout the test is deemed to be acceptable flame resistance.

[0020] hardness Hardness was measured using a Shore 00 durometer. The test specimen was placed on a hard, flat surface. The Shore 00 durometer indenter was then pressed against the specimen, ensuring that the indenter was parallel to the surface. The hardness was read while in firm contact with the specimen. A hardness of less than 80 was considered acceptable.

[0021] Compression force Compressive forces were measured using a TA.HDplus texture analyzer equipped with a 100 kg load cell, a 40 mm diameter aluminum probe, and a flat heavy duty aluminum substrate. Silicone foam samples were cut into circles using a 1 inch diameter die cut and placed between the substrate and the probe. The probe was initially placed at the same height as the sample thickness and lowered at a rate of 1 mm / sec until the pressure reached its highest point. The sample thickness and pressure were recorded as a compression force curve. The pressure at 30% of the original sample thickness was recorded. Compressive forces below 500 kPa were considered acceptable.

[0022] Foam Density Foam density was calculated based on the average thickness and weight of two 1 inch diameter foam samples.

[0023] The properties of the ceramic-filled organopolysiloxane articles were compared to a commercially available organopolysiloxane article (COHRlastic Silicone Foam, available from Stockwell Elastomerics) that is similar in structure to the example foams except that it does not contain hollow ceramic particles.

[0024] Table 1 summarizes the performance properties of the foams of Examples 1-3 and a commercially available comparison foam. Density is in g / cm 3 Hardness was measured in Shore 00 units. Compressive force (Force) was measured in kPa at 30% compression. Temperature at 600°C (T after 300 seconds) refers to the sample surface temperature after 300 seconds, and flammability refers to the observability of flame during the insulation test.

[0025] [Table 1]

[0026] Table 1 shows that the foams of the present invention pass all tests, while the commercial examples fail the insulation test. Surprisingly, hollow ceramic particles were found to reduce the surface temperature in 300 seconds without adversely affecting other important properties of the foam. Furthermore, hollow ceramic particle sizes in the range of 50 μm to 150 μm were found to be particularly effective in reducing the surface temperature.

Claims

1. A thermally insulating, compressible, and flame resistant foam material, comprising, based on the volume of the foam material, 35 to 95 weight percent of a polyorganosiloxane foam, 1 to 30 weight percent of a flame retardant, and 1 to 35 weight percent of hollow ceramic particles having a volume average particle size in the range of 25 μm to 300 μm. 0.10 to 0.90 g / cm ３ A foam material having a density in the range of

2. 10. The foam material of claim 1, wherein the foam material comprises 50 to 80 weight percent of the polyorganosiloxane foam and 2 to 20 weight percent of the flame retardant.

3. The flame retardant is Al(OH) ３ , Mg(OH) ２ , MgCO ３ ・3H ２ O or Mg ５ (CO ３ ) ４ (OH) ２ ・4H ２ O, MgCa(CO ３ ) ２ , AlO(OH), NaHCO ３ , or hydrated MgSO ４ or a combination thereof.

4. 0.15~0.50g / cm ３ The foam material according to any one of claims 1 to 3, having a density in the range of

5. 5. The foam material of claim 4, wherein the hollow ceramic particles have an average volume particle size by dynamic light scattering in the range of 25 μm to 200 μm.

6. 5. The foam material of claim 4, wherein the hollow ceramic particles have an average volume particle size by dynamic light scattering in the range of 50 μm to 150 μm.

7. The hollow ceramic particles are crystalline or semi-crystalline Al ２ O ３ Particulate, crystalline or semi-crystalline SiO ２ 7. The foam material according to claim 5 or 6, which is a crystalline or semi-crystalline Al / Mg / Ca silicate.

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