Low density organopolysiloxane foam with filler

Abstract

The present invention relates to a composition comprising a polyorganosiloxane foam interspersed with from 30% to 50% by weight of a filler wherein the foam has a density in the range of from 0.20 g / cm3 to 0.60 g / cm3. The composition of the present invention is useful as a thermal barrier for a battery module.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a low density organopolysiloxane foam having a relatively high filler content.

[0002] Polydimethylsiloxane (PDMS) foams offer lower density and higher compressibility than the corresponding rigid materials. Filled PDMS foams can provide additional beneficial effects such as flame retardancy, targeted (high or low) thermal conductivity, and more robust mechanical properties. The filled foams can be used as thermal barriers for rechargeable batteries such as lithium ion batteries (LiBs), which are commonly used in various applications including electric vehicles (EVs). Although LiBs have desirable properties of high energy density and cycle stability, safety issues currently limit their usefulness. First, failures in LiB batteries can be triggered by manufacturing defects, internal short circuits, overheating, overcharging, or mechanical shock; second, heat generated from a failed battery can spread, leading to thermal runaway in adjacent batteries. The rapid pressure buildup caused by these thermal events increases the risk of fire and explosion.

[0003] Thermal events can be mitigated by placing thermal barriers between the batteries in a battery module, which provide thermal insulation and flame retardancy. Commonly used thermal barriers such as aerogels, ceramic fibers, and mica sheets provide such properties; however, aerogels and ceramic fibers have poor mechanical resilience, while mica sheets are incompressible. On the other hand, although silicone foamed foams provide sufficient compressibility and are thus suitable for low energy density and medium energy density batteries, their thermal insulation is insufficient to prevent thermal events for very high energy density battery packs. Adding filler particles to the foam would overcome this defect; however, the presence of the available levels of filler unfavorably increases the density of the foam.

[0004] Therefore, in the field of thermal barriers, it would be advantageous to find a low density insulating barrier having desired thermal properties, flame retardancy, and other mechanical properties such as high modulus and greater mechanical strength. SUMMARY OF THE INVENTION

[0005] In one aspect, the present invention addresses the needs in the art by providing a composition comprising a polyorganosiloxane foam dispersed with 30 wt% to 50 wt% of one or more fillers, based on the weight of the composition, the fillers being selected from the group consisting of metals, metal oxides, metal hydroxides, metal acetates, metal carbides, metal oxycarbides, metal carbonates and bicarbonates, metal hydroxycarbonates, metal nitrides, metal nitrates, metal sulfates, metal chlorides, metal silicides, metal silicates; wherein the foam has a density of 0.20 g / cm 3 to 0.60 g / cm 3a density in the range of, and the foam comprises Si - O - R′ groups and Si - X - R″ groups, with the Si - O - R′:Si - X - R″ ratio in the range of 0.4:1 to 7:1, where each X is independently O or CH₂CH₂, O - R′ is the remainder of the blowing agent, and X - R″ is the remainder of a vinyl - substituted or OH - substituted polyorganosiloxane.

[0006] The present invention addresses the needs in the art by providing a method for preparing a polyorganosiloxane foam having a relatively low density and a relatively high filler content. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 is an illustration of a battery module containing a polyorganosiloxane foam material. DETAILED DESCRIPTION

[0008] In one aspect, the present invention is a composition comprising a polyorganosiloxane foam, the polyorganosiloxane foam being dispersed with 30 wt% to 50 wt% of one or more fillers, based on the weight of the composition, the fillers being selected from the group consisting of: metals, metal oxides, metal hydroxides, metal carbides, metal carbon oxides, metal acetates, metal carbonates and bicarbonates, metal hydroxycarbonates, metal nitrides, metal nitrates, metal sulfates, metal chlorides, metal silicides, and metal silicates; wherein the foam has a density in the range of 0.20 g / cm 3 to 0.60 g / cm 3 and the foam comprises Si - O - R′ groups and Si - X - R″ groups, with the Si - O - R′:Si - X - R″ ratio in the range of 0.4:1 to 7:1, where each X is independently O or CH₂CH₂, O - R′ is the remainder of the blowing agent, and X - R″ is the remainder of a vinyl - substituted or OH - substituted polyorganosiloxane.

[0009] The term "remainder of the blowing agent" refers to the repeating unit generated by the reaction of the blowing agent with the Si - H groups from the first polyorganosiloxane, the first polyorganosiloxane having a degree of polymerization in the range of 5 to 200 and a D concentration in the range of 60 mol% to 100 mol%. H The blowing agent is a C₁ - C₈ - alcohol, a C₁ - C₈ - diol, benzyl alcohol, or HO - (CH₂CHRO) z -H or water, where R is H, methyl, or ethyl, and z is 2 to 5. Examples of blowing agents include benzyl alcohol, ethanol, propanol, and 1,4 - butanediol.

[0010] The first polyorganosiloxane is represented by Structure I:

[0011]

[0012] where m is from 0 to 80, and n is from 5 to 200 or to 100, provided that the ratio of m:n is in the range of 0:100 to 40:60, preferably to 36:64. Thus, D H concentration is in the range of 60 mol% or 64 mol% to 100 mol%. It should be understood that the first polyorganosiloxane can be a weighted average D H concentration is one or more polyorganosiloxanes in the range of 60 mol% or 64 mol% to 100 mol%. It should also be understood that the D and D H groups are distributed randomly, in blocks or alternately.

[0013] Thus, the remainder of the blowing agent is produced by the following reaction:

[0014]

[0015] where R-Si-H is the first organopolysiloxane and R′-OH is the blowing agent.

[0016] Similarly, the remainder of the vinyl-substituted polyorganosiloxane is produced by the reaction of the Si-H groups of the first polyorganosiloxane with a second polyorganosiloxane functionalized with one or more vinyl groups. The second polyorganosiloxane has a degree of polymerization in the range of 50 or 100 to 2000 or to 1000.

[0017] Thus, the remainder of the vinyl-substituted polyorganosiloxane is produced by the following reaction:

[0018]

[0019] where =-R″ is the vinyl-substituted second polyorganosiloxane.

[0020] The remainder of the OH-substituted polyorganosiloxane is produced by the following reaction:

[0021]

[0022] where HO-R″ is the OH-substituted second polyorganosiloxane.

[0023] The polyorganosiloxane foam has 0.20 g / cm 3 or 0.25 g / cm 3 to 0.60 g / cm 3 or to 0.52 g / cm 3 or to 0.40 g / cm 3The density within the range. The Si-O-R′:Si-X-R″ ratio, preferably the Si-O-R′:Si-CH2CH2-R″ ratio, is in the range of 0.4:1 or 0.6:1 or 0.8:1 or 1:1 to 7:1 or to 5:1 or to 3:1. As used herein, the term "Si-O-R′:Si-X-R″ ratio" refers to the ratio determined by the area under the curve measured by 13 13C NMR spectroscopy as described in the Examples section.

[0024] The filler is a metal, metal oxide, metal hydroxide, metal acetate, metal carbide, metal carbon oxide, metal carbonate and bicarbonate, metal hydroxycarbonate, metal nitride, metal nitrate, metal sulfate, metal chloride, metal silicide and metal silicate, as well as their hydrates, and mixtures thereof. The filler is in particulate form, and its average volume particle size is generally in the range of 0.1 μm or 0.5 μm or 1 μm to 1000 μm or to 500 μm or to 200 μm or to 100 μm or to 50 μm, as determined using a dynamic light scattering analyzer such as a Beckman Coulter LS130 particle size analyzer.

[0025] Examples of suitable fillers include aluminum hydroxide, hydromagnesite, epsomite, nesquihonite, boehmite, calciummagnesium carbonate, magnesium hydroxide, silica, silica flour, alumina, calcium sulfate, copper acetate, magnesium chloride, sodium sulfate, aluminosilicate, boron nitride, aluminum nitride, mica, wollastonite, calcium silicate, basalt, clay (including calcined clay), zeolite, hollow fillers (such as hollow glass spheres and hollow ceramics), expanded perlite, calcium carbonate, cerium oxide, iron oxide, titanium oxide, zinc oxide, and glass fiber, as well as hydrates of these fillers.

[0026] It may be desirable to use a combination of fillers at a high loading to achieve desired properties such as improved fire resistance and mechanical strength at high temperatures. A particularly desirable filler combination is aluminum hydroxide and wollastonite. Based on the weight of the composition, the concentration of the filler is in the range of 30 wt%, preferably 35 wt% to 50 wt%, preferably to 45 wt%.

[0027] The composition is advantageously prepared as a two - part system. More specifically, the catalyst, preferably a Pt catalyst, is separated from the first polyorganosiloxane to prevent premature reaction of the first polyorganosiloxane with the second polyorganosiloxane and the blowing agent. In a preferred method of preparing the composition of the present invention, a first part of the second polyorganosiloxane, the catalyst, and the blowing agent are mixed in a first chamber. Then, with further mixing, a first part of the filler is added to the contents of the first chamber. In a second container, the first polyorganosiloxane is mixed with a second part of the second polyorganosiloxane, and then a second part of the filler is added and further mixed. Advantageously, a filler is included in each chamber to enhance the mixing of the two parts. The two parts are each dispensed through a dispenser, which is typically a dual - cartridge equipped with a static mixer, and then dispensed onto the desired substrate or target area. After the first polyorganosiloxane contacts the second polyorganosiloxane and the blowing agent, the reaction caused by the release of hydrogen and the accompanying foaming begin. The foam advantageously cures at an elevated temperature, preferably at least 80 °C or at least 100 °C, and preferably up to 200 °C or up to 150 °C.

[0028] The foam can be used as a barrier material in battery module applications. Thus, in another aspect, the present invention is a battery module that includes a housing containing an array of spatially separated battery cells and the composition of the present invention in contact with adjacent battery cells.

[0029] Figure 1 Shows this embodiment of the present invention. The battery module includes a housing (20) containing an array of spatially separated battery cells (30 and 30a) and a barrier material (40) in contact with adjacent battery cells, thereby creating an insulating barrier between the battery cells (30 and 30a). In this embodiment, the barrier material is positioned between adjacent battery cells (30 and 30a); in another embodiment, the barrier material covers the battery cells. The battery module may also include end plates (50) at the inner edges of the housing that are in direct contact with the battery cells (not shown) or indirectly in contact with the battery cells (30a) through the barrier material (40). The barrier material can be inserted into the spaces between adjacent battery cells and into the spaces between the cells and the end plates; alternatively, a foam precursor can be applied to the cells and into the spaces between the battery cells and then cured to form the barrier material. Examples of suitable battery cell designs include cylindrical, pouch, and prismatic cells.

[0030] Example

[0031] In the following examples, pbw refers to parts by weight. All components were mixed at 2000 rpm using a Flacktex Speed Mixer.

[0032] Comparative Intermediate Example 1 - Preparation of a 2 - part composition without filler

[0033] The first component (Part A) was prepared by mixing the following substances, blended at 64:36 w / w, for 30 seconds: 1) dimethylvinylsilanyloxy-terminated polydimethylsiloxane, having a viscosity of ~1,900 mPa·s and 0.22 wt% vinyl groups; and 2) ViMe2SiO 1 / 2 / (CH3)3Si-O 1 / 2 / SiO 4 / 2 resin, ViMe2SiO 1 / 2 :(CH3)3Si-O 1 / 2 :SiO 4 / 2 with a structural unit ratio of 5:40:55, M n being 5000 and M w being 21,400 (polymer-resin blend, 78.11 pbw); and b) dimethylvinylsilanyloxy-terminated polydimethylsiloxane having a viscosity of 40,000 mPa·s (Polymer 1, 13.63 pbw). A complex of Pt(0) and divinyltetramethyldisiloxane (1.13 pbw, 0.62 pbw Pt), 1,4-butanediol (3.14 pbw), and benzyl alcohol (4 pbw) were added to the mixture and mixing was continued for an additional 30 seconds.

[0034] The second component (Part B) was prepared by mixing the polymer-resin blend (64.36 pbw) and Polymer 1 (11.23 pbw) for 30 seconds. MD H 79.31 linear organohydrogenpolysiloxane of MD 3.2 D H 5.8 M (Polymer 2, 17.95 pbw) and polydimethylorganohydrogensiloxane of MD

[0035] Comparative Intermediate Example 2 - Preparation of a Filled Intermediate with a Si-H:Vinyl Ratio of 6.23:1 and a D H mole % of 31.8% of the 2 - part composition

[0036] D M (Polymer 3, 6.46 pbw) were added to the mixture and mixing was continued for an additional 30 seconds.

[0037] Part B is prepared by mixing a polymer resin blend (48.27 pbw), Polymer 1 (3.91 pbw), and Hymod M855 aluminum hydroxide (10.41 pbw) for 30 seconds, then adding Polymer 3 (2.02 pbw) and MD 8.7 D H 3.7 M linear organohydrogensiloxane (Polymer 4, 33.72 pbw). Mixing is continued for 30 seconds, after which Imerys Nyad G wollastonite (31.03 pbw) is added to the mixture and mixing is continued for an additional 30 seconds.

[0038] Comparative Intermediate Example 3 - Preparation of a Filled Intermediate with an Si-H:Vinyl Ratio of 1.48:1 and a D H of 21.5% of the 2 - part composition 。

[0039] The first component (Part A) is prepared by mixing a polymer-resin blend (18.75 pbw) and dimethylvinylsiloxy-terminated polydimethylsiloxane with a viscosity of ~2,200 mPa·s (Polymer 5, 50.9 pbw) for 30 seconds. A complex of Pt(0) and divinyltetramethyldisiloxane (0.64 pbw, 0.62 pbw Pt) and benzyl alcohol (7.72 pbw) are added to the mixture. The contents are mixed for 30 seconds, after which Imerys Nyad G wollastonite (14.39 pbw) and Minusil 5 silica (5 μm, 7.6 pbw) are added to the mixture and mixing is continued for an additional 30 seconds.

[0040] Part B is prepared by mixing a polymer resin blend (18.75 pbw) and Polymer 5 (47.58 pbw) for 30 seconds. Polymer 4 (6.68 pbw) and MD 60 D H 7M linear organohydrogensiloxane (Polymer 6, 5 wt%) is added to the mixture and the contents are mixed at 2000 rpm for 30 seconds. Then, Imerys Nyad G wollastonite (14.39 wt%) and Minusil 5 silica (5 μm, 7.6 wt%) are added to the mixture and mixing is continued for an additional 30 seconds.

[0041] Intermediate Example 1 - Preparation of a filler-containing product with an Si-H:vinyl ratio of 1.94:1 and a D H of 90.6% of 2 Part composition

[0042] The first composition (Part A) was prepared by mixing a polymer-resin blend (45.53 pbw), Polymer 1 (7.94 pbw), and Micral 855 aluminum hydroxide (10.68 pbw) for 30 seconds. Then a complex of Pt(0) and divinyltetramethyldisiloxane (0.66 pbw, 0.62 pbw Pt), 1,4-butanediol (1.82 pbw), and benzyl alcohol (2.33 pbw) were added to the mixture and mixing was continued for 30 seconds. Imerys Nyad G wollastonite (31.03 pbw) was added to the mixture and mixing was continued for an additional 30 seconds.

[0043] The second composition (Part B) was prepared by mixing a polymer resin blend (48.27 pbw), Polymer 1 (3.91 pbw), and Hymod M855 aluminum hydroxide (11.59 pbw) for 30 seconds. Then Polymer 2 (2.93 pbw) and Polymer 3 (2.25 pbw) were added to the mixture and the contents were mixed for 30 seconds. Imerys Nyad G wollastonite (31.03 pbw) was added to the mixture and mixing was continued for an additional 30 seconds.

[0044] Table 1 is a summary of the Part A and Part B formulations, in pbw. PRB refers to the polymer-resin blend; P1-P6 refer to Polymers 1-6; BDO refers to 1,4-butanediol; BzOH refers to benzyl alcohol; Pt refers to the Pt(0) complex; F1 refers to the Micral855 ATH filler; F2 refers to the Hymod M855-SP filler; F3 refers to the Nyad G wollastonite filler; F4 refers to Minusil 5 silica.

[0045] Table 1 - Part A and Part B formulations

[0046]

[0047] Table 2 shows additional Part A and Part B formulations for preparing the compositions of the present invention. F5 refers to Mica WG-325 Muscovite mica.

[0048] Table 2 - Part A and Part B formulations (continued)

[0049]

[0050] Manufacture of foam sheet

[0051] All foam sheets were manufactured using the following procedure. Parts A and B were mixed thoroughly for 15 seconds. The mixture was then poured between two matte polyester film sheets. The initial (pre-foamed) thickness was controlled at 0.045" using a roller. The sample was then transferred to an oven set at 120 °C. After 2 minutes, the release film sheets were removed, and the sample was cured continuously at 120 °C. The foam density was calculated based on the average thickness and weight of two foam samples with a diameter of 1 inch (2.54 cm).

[0052] By 13 Calculating the Si-O-R′:Si-X-R″ ratio by 13C NMR spectroscopy

[0053] Crosslinked silicone foam samples were cryogenically ground with liquid nitrogen in a SPEX SamplePrep 6875 freezer / mill. The resulting powder was loaded into a 4-mm zirconia rotor for solid-state 13 13C NMR (ssCNMR) spectroscopic analysis. The ssCNMR experiments were performed using a Bruker AVIII 400 MHz spectrometer with a 4-mm CP / MAS probe. All experiments were conducted at room temperature (∼20 °C) without additional heating or cooling of the samples. The spinning rate was fixed at 13,000 Hz. Spectra were acquired using a standard hpdec pulse sequence with a recycle delay time of 60 seconds and 4096 scans. All spectra were acquired using Bruker Topspin 3.2 software and processed using MestReNova 12.004 software. In the 13 13C spectrum, the Si-CH3 peak was adjusted to 1.25 ppm. For the Si-CH2CH2-Si group (Si-X-R″ group), the peak at 9 ppm was integrated, and for the Si-O-CH2- group (Si-O-R′ group), the peaks between 58 ppm and 67 ppm were integrated. The area under the peak at 9 ppm was divided by 2 to account for each vinyl group. For the foams formed from the compositions of Example 1 and Example 3, the ratios of the resonances associated with Si-O-R′ and the resonances associated with the Si-X-R″ group were 0.5:1 and 2:1, respectively. Table 3 shows the calculated D H mole % (D H % = D H m / (D H m + D n )), the ratio of the D H groups to vinyl groups at the time of blending of the blend of parts A and B (i.e., pre-foam) (D H :vinyl), the filler concentration (filler %), the foam density in g / cm 3 3 (density), and the uniformity of the foam (foam). U refers to a uniform foam, and NU refers to a non-uniform foam.

[0054] Table 3-D H mol% and D H : Vinyl ratio

[0055] Example number <![CDATA[D H %]]> <![CDATA[D H : vinyl]]> Filler % Density Foam C1 90.6 6.13 0 0.15 NU C2 31.8 6.23 40.83 1.04 U C3 21.5 1.48 21.99 1.03 U Example 1 84.6 1.94 42.17 0.52 U Example 2 96.4 14.93 42.33 0.39 U Example 3 100 6.61 45.07 0.31 U Example 4 64.4 10.00 41.81 0.48 U Example 5 90.6 6.13 44.34 0.27 U Example 6 90.6 6.13 44.34 0.49 U

[0056] Table 3 shows that by adjusting D H : vinyl ratio and D H concentration, foams with a density < 0.6 g / cm 3 and a filler concentration higher than 30% can be obtained from the polyorganosiloxane composition. The data also show that low-density, high-filler-concentration foams can be achieved with a variety of filler materials. It was also surprisingly found that the foam without filler (C1) was non-uniform, resulting in poor thickness control and poor compressibility.

[0057] The relatively high ratio of Si-H groups to vinyl groups or SiOH groups, combined with the relatively high concentration of Si-H groups in the first polyorganosiloxane, results in a higher H2 gas yield, thus providing greater expansion, which reduces the foam density while concomitantly reducing the crosslink density. Surprisingly, despite the higher H2 gas production, the high concentration of filler helps to produce a uniform foam.

Claims

1. A composition, the composition comprising a polyorganosiloxane foam, the polyorganosiloxane foam being dispersed with 30 wt% to 50 wt% of one or more fillers based on the weight of the composition, the fillers being selected from the group consisting of: metals, metal oxides, metal hydroxides, metal acetates, metal carbides, metal oxycarbides, metal carbonates, metal bicarbonates, metal hydroxycarbonates, metal nitrides, metal nitrates, metal sulfates, metal chlorides, metal silicides, metal silicates; wherein the foam has a density in the range of 0.20 g / cm 3 to 0.60 g / cm 3 and the foam comprises Si-O-R′ groups and Si-X-R″ groups, the SiOR′:SiX-R″ ratio being in the range of 0.4:1 to 7:1, where each X is independently O or CH2CH2, O-R′ is the remainder of the blowing agent, and X-R″ is the remainder of a vinyl-substituted or OH-substituted polyorganosiloxane.

2. The composition according to claim 1, wherein the filler is one or more fillers selected from the group consisting of aluminum hydroxide, hydromagnesite, epsomite, nesquehonite, boehmite, dolomite carbonate, magnesium hydroxide, silica, quartz powder, alumina, calcium sulfate, copper acetate, magnesium chloride, sodium sulfate, aluminosilicate, boron nitride, aluminum nitride, mica, wollastonite, calcium silicate, basalt, clays including calcined clay, zeolite, hollow fillers such as hollow glass spheres and hollow ceramics, expanded perlite, calcium carbonate, cerium oxide, iron oxide, titanium oxide, zinc oxide, and glass fiber; wherein each X is CH2CH2.

3. The composition according to claim 2, wherein the foam has a density in the range of 0.25 g / cm 3 to 0.52 g / cm 3 and the foam contains Si-O-R′ groups and Si-X-R″ groups, and the Si-O-R′:Si-X-R″ ratio is in the range of 0.6:1 to 5:

1.

4. The composition according to claim 2, wherein the foam has a density in the range of 0.25 g / cm 3 to 0.40 g / cm 3 and the foam comprises Si-O-R′ groups and Si-X-R″ groups, and the Si-O-R′:Si-X-R″ ratio is in the range of 0.8:1 to 5:

1.

5. The composition according to claim 4, wherein the filler is wollastonite or aluminum hydroxide or a combination thereof, and the remainder of the blowing agent is the remainder of benzyl alcohol, ethanol, propanol, or 1,4 - butanediol or any combination thereof; and the foam contains Si - O - R′ groups and Si - X - R″ groups, and the Si - O - R′:Si - X - R″ ratio is in the range of 1:1 to 3:

1.

6. The composition according to claim 1, wherein the filler is one or more fillers selected from the group consisting of aluminum hydroxide, hydromagnesite, epsomite, nesquehonite, boehmite, dolomite carbonate, magnesium hydroxide, silica, quartz powder, alumina, calcium sulfate, copper acetate, magnesium chloride, sodium sulfate, aluminosilicate, boron nitride, aluminum nitride, mica, wollastonite, calcium silicate, basalt, clays including calcined clay, zeolite, hollow fillers such as hollow glass spheres and hollow ceramics, expanded perlite, calcium carbonate, cerium oxide, iron oxide, titanium oxide, zinc oxide, and glass fiber; wherein each X is O.

7. A battery module, the battery module comprising a housing that houses an array of battery cells separated in accommodation space and the composition according to any one of claims 1 to 6 that contacts adjacent battery cells.

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