Partially calcined silica particles

Abstract

The present invention relates to partially calcined mesoporous silica particles comprising calcined mesoporous silica particles and volatile materials embedded therein. The partially calcined silica particles are useful as an additive for crosslinked polyorganosiloxanes and polyorganosiloxane foams. This combination provides a heat-insulating spacer, preferably a compressible heat-insulating spacer, in a rechargeable battery module.

Description

[0001] Partially Calcined Silica Particles

[0002] Background of the Invention

[0003] The present invention relates to partially calcined silica particles useful as fillers for polyorganosiloxanes, which provide thermal barriers to improve thermal insulation for lithium-ion batteries.

[0004] 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. Although LiBs have the desirable properties of high energy density and stability, safety concerns currently limit their usefulness. First, failure of an LiB cell can be triggered due to a manufacturing defect, an internal short circuit, overheating, overcharging, or mechanical impact; second, the heat generated from the failing cell may propagate, thereby causing a thermal runaway in adjacent cells. The rapid pressure build-up arising from these thermal events increases the risks of fire and explosion.

[0005] Thermal runaway can be mitigated by placing a thermal barrier between cells in an LiB module, which provides heat insulation and flame resistance. Commonly used thermal barriers such as aerogel, ceramic fiber, and mica board provide such properties; however, aerogel and ceramic fiber suffer poor mechanical resilience, while mica board suffers from poor compressibility. On the other hand, although silicone blown foam provides adequate compressibility and, therefore, suitable for batteries of low and moderate energy density, it suffers from insufficient heat insulation to prevent thermal runaway for the very high energy density battery packs. Accordingly, it would be desirable in the field of thermal barriers for rechargeable batteries to create a barrier that provides heat insulation, flame resistance, and satisfactory compressibility.

[0006] Summary of the Invention

[0007] The present invention addresses a need in the art by providing partially calcined mesoporous silica particles comprising calcined mesoporous silica particles and volatile materials embedded therein. The partially calcined silica particles are useful as an additive for crosslinked polyorganosiloxanes and polyorganosiloxane foams. This combination provides a heatinsulating spacer, preferably a compressible heat-insulating spacer, in a rechargeable battery module. Detailed Description of the Invention

[0008] The present invention relates to partially calcined silica particles comprising calcined mesoporous cellular silica particles and volatile materials embedded therein.

[0009] The term “partially calcined” refers to mesoporous silica (SiCh) particles that have been subjected to a sufficiently elevated temperature and for a sufficient time to partially remove volatile materials contained in the silica particles with concomitant formation of mesopores in the silica particles. The term “volatile materials” refers to a combination of one or more oils, one or more templates, and volatile silicon-containing materials that are removed (volatized) from the mesoporous cellular silica particles under conditions described in the Example section hereinbelow. Volatile materials do not include water, which is removed prior to the temperature ramping starting from 110 °C.

[0010] The word “template” refers to a micelle-forming organic molecule that provides architecture for growing a silica scaffold, and that is removable at elevated temperatures. Examples of suitable templates include surfactants. Nonionic surfactants include secondary alcohol ethoxylates and nonionic block copolymers. Commercial examples of secondary alcohol ethoxylates include TERGITOL™ 15-S-30 Secondary Alcohol Ethoxylate, TERGITOL™ 15-S-5 Secondary Alcohol Ethoxylate, and TERGITOL™ 15-S-9 Secondary Alcohol Ethoxylate. (TERGITOL is a trademark of The Dow Chemical Company or its Affiliates). A commercial example of a nonionic block copolymer is Pluronic Pl 23 PEO-PPO-PEO triblock copolymer. Anionic surfactants include Ci2-Cis-alkyl phosphates, carboxylates, sulfates, and sulfonates; and cationic surfactants include Ci2-Ci8-alkyl quaternary ammonium salts.

[0011] The mesoporous silica may be in the form of unagglomerated or agglomerated particles. The morphology of the calcined silica ranges from mesoporous cellular silica particles to hexagonal silica particles. Mesoporous cellular silica particles are cage-like particles with interconnecting spherical pores, wherein at least 90% of the pores have a pore size diameter in the range of from 2 nm to 50 nm (mesopores), as determined by Brunauer-Emmett-Teller (BET) Nitrogen Adsorption-Desorption Analysis. Hexagonal silica particles are characterized by a rod-like one-dimensional structure with hexagonal packing of the rods.

[0012] Mesoporous cellular silica particles can be prepared by first dissolving the template in a strong acid such as HC1. Then, an oil, for example a non-polar aprotic solvent such as mesitylene is added to the acidified solution under mild heating conditions. The weight-to-weight ratio of the oil to the template that is conducive to mesoporous cellular silica particle formation is in the range of from 0.5:1, preferably from 1:1, to 3:1 or to 2:1. Preferably at least 90% of the pores have a pore size diameter in the range of from 2 nm to 25 nm, more preferably to 15 nm.

[0013] A silica precursor such as tetraethylorthosilicate (TEOS) or silicic acid is then added, and the sample is aged at about 100 °C then dried: the aged sample is then partially calcined, that is, heated to a sufficiently elevated temperature and for a sufficient time to partially remove the volatiles from the consequent mesoporous cellular silica particles. The aged silica particles are preferably calcined at a temperature in the range of from 200 °C to 450 °C for a time sufficient to remove from 80 or from 85 weight percent, to 97 or to 95 weight percent of volatile materials present in the aged and non-calcined heat-aged particles.

[0014] When the mesoporous cellular silica particles are partially calcined, that is, when the volatile materials are not substantially completely removed, the concentration of residual volatile materials is in the range of from 3 or from 3.5, or from 4 weight percent, to 15 or to 10 or to 7 weight percent, based on the weight of the mesoporous silica particles and the volatile materials. The residual amount of the volatile material is determined as described in the Examples section, hereinbelow. As used herein, the term “substantially completely removed” means that less than 3 weight percent volatile materials remain in the silica particles after the calcination step. Thus, a calcined mesoporous silica sample that experiences less than a 3% weight loss after being heated to 1000 °C is considered completely calcined, not partially calcined.

[0015] The partially calcined mesoporous cellular silica particles preferably have a Dvyo volume particle diameter by dynamic light scattering in the range of 30 pm to 50 pm, and a pore volume in the range of from 0.25 cm3 / g or from or from 0.70 cm3 / g or from 1.00 cm3 / g, to 2.00 cm3 / g or to 1.50 cm3 / g; fully calcined mesoporous cellular silica particles preferably have a Dv$io volume particle diameter in the range of from 30 pm to 50 pm, and a pore volume typically in the range of from 0.50 cm3 / g or from 1.00 cm3 / g or from 1.50 cm3 / g or from 1.70 cm3 / g, to 4.00 cm3 / g or to 3.00 cm3 / g or to 2.50 cm3 / g.

[0016] When the ratio of the oil to the template is from 0:1 to 0.4:1, the resulting morphology of the partially calcined silica is hexagonal. The partially calcined hexagonal silica has a pore volume in the range of from 0.25 cm3 / g to 3.00 cm3 / g. Preferably, at least 90% of the pores have a pore size diameter in the range of 1 nm to 10 nm, as determined by Brunauer-Emmett- Teller (BET) Nitrogen Adsorption-Desorption Analysis. The partially calcined mesoporous particles can be used in combination with a first polyorganosiloxane functionalized with at least three Si-H groups and having a degree of polymerization in the range of from 5 to 1000 or to 500 or to 200, a second polyorganosiloxane functionalized with terminal divinyl groups; and a hydrosilylation catalyst such as a platinumbased catalyst, to form a crosslinked network of an insulating and compressible material. The resultant crosslinked polyorganosiloxane article embedded with the partially calcined mesoporous particles, which is preferably a crosslinked foam embedded with the particles, possesses excellent insulation properties, as demonstrated in the Examples Section hereinbelow.

[0017] Examples

[0018] Measurement of Residual Volatiles in Mesoporous Silica Particles

[0019] The concentration of volatiles in non-calcined, fully calcined, and partially calcined mesoporous cellular silica particles was determined using a TGA Q5000 Thermal Analysis Instrument in N2 (flow rate of 25 mL / min). The temperature was ramped from room temperature to 1000 °C at a ramp rate of 10 C° / min using platinum high temperature pans. Particles (~3 mg) were placed in the tared pans. The weight loss of non-calcined and calcined materials between 110 °C and 1000 °C was measured by weighing the difference (w) of the weight of the sample at 110 °C and at 1000 °C, as illustrated in Table 1. The oils, templates, and volatile silicon-containing materials were substantially completely removed; that is, less than 3 weight percent volatiles remained after a sample was subjected to the temperature ramping under the conditions described above.

[0020] Table 1 - Percent Loss of Volatiles in non-Calcined and Calcined Mesoporous Cellular Silica

[0021] Particles

[0022] In the following examples, Mwand Mnof the ViMezSiOi / r CHs^Si-O SiCL / z resin was determined by gel permeation chromatography using a gpc column packed with 5 -mm diameter sized divinyl benzene crosslinked polystyrene beads pore type Mixed-C (Polymer Laboratory).

[0023] Tetrahydrofuran was used as the mobile phase and detection was carried out by a refractive index detector.

[0024] Intermediate Example 1 - Preparation of Fully Calcined Mesoporous Cellular Silica Particles

[0025] Pluronic P123 PEO-PPO-PEO triblock copolymer (EO20-PO70-EO20, MW -5800 Daltons, 10 g) was dissolved in 1.6 M HC1 (375 mL). Mesitylene (15 g) was slowly added to the solution, and the mixture was heated with stirring to 40 °C for 1 h. Tetraethyl orthosilicate (22 g) was then added, and heating is continued at 40 °C for 24 h. The mixture was then transferred to an vessel, and the sample was aged at 100 °C for an additional 24 h. Solids were filtered and washed with DI water, then dried at room temperature for 24 h, then heated in a dish at 550 °C for 8 h under air flow.

[0026] Intermediate Example 2 - Preparation of Partially Calcined Mesoporous Cellular Silica Particles The preparation of silica particles was carried out substantially as described in Intermediate Example 1, except that in the final step, the sample was heated in an dish at 400 °C for 8 h. Examples 1-3 - Preparation of Organopoly siloxane Foam Articles with Fully Calcined Mesoporous Cellular Silica Particles

[0027] A master batch of a first component (Part A) was prepared by mixing together, using a Flacktek Speed Mixer, a dimethylvinylsiloxy end-capped polydimethylsiloxane having a viscosity of -40,000 mPa s (Polymer 1, 89.2 g), a 64:36 w / w blend of 1) a dimethylvinylsiloxy-terminated poly dimethylsiloxane, having a viscosity of -1,900 mPa s, and -0.22 wt.% of Vi; and 2) a ViMe2SiOi / 2 / (CH3)3Si-Oi / 2 / SiO4 / 2 resin, having a ViMe2SiOi / 2:(CH3)3Si-Oi / 2:SiO4 / 2 structural unit ratio of 5:40:55, a Mnof 5000 and a Mwof 21,400 (Polymer-Resin Blend, 186.2 g). The contents were mixed at 2000 rpm for 30 s, after which time, a complex of Pt(O) and divinyltetramethyldisiloxane (2.7 g, 0.62 wt% Pt), 1 ,4-butanediol (5.4 g), and benzyl alcohol (13.4 g) were added to the mixture and the contents were mixed at 2000 rpm for 30 s. A portion of the master batch (20 g) was placed in a separate vessel, and Intermediate Example 1 mesoporous cellular particles (1.33 g for Example 1, 2. 14 g for Example 2, and 3.22 g for Example 3) were added to the mixture and the contents were mixed at 800 rpm for 10 s, then 2000 rpm for 30 s.

[0028] A master batch of a second composition (Part B) was similarly prepared by mixing together Polymer 1 (121.8 g), Polymer Resin Blend (122.5 g), and a dimethylvinylsiloxy end-capped poly dimethylsiloxane having a viscosity of -1,950 mPa s (Polymer 2, 17.5 g). The contents were mixed at 2000 rpm for 30 s, after which time a linear organohydrogenpolysiloxane having a viscosity of 30 mPa s and 1.6 wt% SiH content (Polymer 3, 20.2 g), and a polydimethylorganohydrogensiloxane with viscosity’ of 5 mPa s and 0.7 wt% SiH content (Polymer 4, 15.5 g) were added to the mixture and the contents were mixed at 2000 rpm for 30 s. A portion of the master batch (20 g) was placed in a separate vessel, and Intermediate Example 1 mesoporous cellular particles (1.33 g for Example 1, 2.14 g for Example 2, and 3.22 g for Example 3) were added to the mixture. The contents were mixed at 800 rpm for 10 s, then 2000 rpm for 30 s.

[0029] Equal amounts of Parts A and B were mixed, and the mixture was poured between two release film sheets (matte mylar film). The initial (before foaming) thickness was controlled at 0.045” using a nip roller. The sample was cured at 60 °C for 10 min, then 100 °C for 10 min, producing a foam sheet that was used for further testing.

[0030] Example 4 - Preparation of Organopolysiloxane Foam Articles with Partially Calcined Mesoporous Cellular Silica Particles The preparation was carried out substantially as described for Example 2, except that Intermediate Example 2 was used as the filler material.

[0031] Comparative Example 2 - Preparation of Foamed Organopolysiloxane Article with Aerogel Particles

[0032] The foamed article was prepared substantially as described in Example 1 , except that the mesoporous cellular particles were replaced with Aerogel TLD203 Matting Agent (Aerogel, 1.06 g) for Parts A and B.

[0033] Measurements of Surface Area, Pores Size, and Pore Volume

[0034] The surface area, pore size and pore volumes of the silica mesoporous materials were measured by nitrogen adsorption at 77.4 K using the conventional technique on a Micromeritics ASAP 2420 apparatus. Prior to the adsorption measurements, the fully calcined samples were degassed in vacuum at 300 °C for at least 3 hours. The pore size distributions, average pore diameter and pore volumes were determined from the adsorption branch of isotherms using the Barret-Joyner-Halenda (BJH) procedure. The surface area was calculated using BET method.

[0035] Calculation of Mesoporous Cellular Silica Particle Size

[0036] Median particle size (DV9o) measured by volume and particle size distribution (differential volume curves) of all the fillers reported in this study were measured using a Coulter LSI 3 320 Particle Size Analyzer.

[0037] Measurement of Thermal Insulation

[0038] Thermal insulation was performed using a hot plate placed on a hydraulic press. The hot plate was set at 600 °C with an insulator on the top of the surface. Four K-type thermocouples were fixed onto an aluminum heat sink (10 cm x 10 cm x 2 cm thickness) using Kapton tape. A foam (10 cm x 10 cm x 0.4 cm thickness) was then placed and fixed onto the heat sink using Kapton tape. An additional thermocouple was attached onto the sample surface using Kapton tape. The insulator was removed from the hot surface and the sample attached to the heat sink was rapidly placed onto the hot surface with the sample surface facing the hot plate surface, and the heat sink facing the opposite side. The pressure was quickly increased to 355 kPa. The interfacial temperature between the hot plate surface and the sample surface, and the interfacial temperature between the sample surface and the heat sink were recorded using a data logger. Pressure was released after 300 s, and the test was ended. The lower heat-sink side temperature is a measure of better heat insulating property.

[0039] Measurement of Foam Density

[0040] Foam density was calculated based on the average thickness and weight of two l”-diameter foam samples. The height of the 25 mm diameter (2r) foam pucks was measured using a Mitutoyo Dial Indicator. The height (h) (cm) was measured for all 4 foam pucks for each foam sample. The mass (m) in grams (g) of each puck was measured using a balance. The density (p, in g / cm3) was calculated for each foam disk using the formula: p = m / jihr2

[0041] The properties of mesoporous cellular particle filled organosiloxane foams were compared to two other cured foams: Comparative Example 1 (CE1), which is a commercial organopolysiloxane article (COHRlastic Silicone Foam, available from Stockwell Elastomerics), which was similar in construction to the example foams except it did not contain any filler; and Comparative Example 2 (CE2), which is an aerogel particle filled organosiloxane foam.

[0042] Table 2 is a summary of performance properties for completely ceramified mesoporous cellular particles of the Examples 1-4, the commercial comparative foam (CE1), and the foam containing aerogel particles (CE2). MCf refers to a fully calcined mesoporous cellular particles, and MCPrefers to partially calcined mesoporous cellular particles. VporeFiller refers to the pore volume of the filler.

[0043] Table 2 - Properties of Organopolysiloxane Article

[0044] Table 2 illustrates improvement in thermal insulation of the tested articles, which is predictive of improved battery performance during thermal runaway events for organosiloxane articles containing mesoporous cellular silica particles. It has been discovered that excellent thermal insulation can be achieved in polyorganosiloxane articles containing either completely or partially calcined mesoporous cellular silica particles. Surprisingly, the organopolysiloxane foam article containing partially calcined mesoporous cellular silica particles exhibited thermal insulation properties far superior to any other samples.

Claims

Claims:

1. Partially calcined mesoporous silica particles comprising calcined mesoporous silica particles and volatile materials embedded therein.

2. The partially calcined mesoporous silica particles of Claim 1 wherein the volatile materials comprise from 3.5 to 15 weight percent of one or more oils, one or more templates, and silica materials.

3. The partially calcined mesoporous silica particles of Claim 2 wherein the volatile materials comprise from 3.5 to 10 weight percent of the one or more oils, the one or more templates, and the silica materials.

4. The partially calcined mesoporous silica particles of Claim 3 which are partially calcined mesoporous cellular silica particles; wherein at least 90% of the pores of the partially calcined mesoporous cellular silica particles have a pore size diameter in the range of from 2 nm to25 nm.

5. The partially calcined mesoporous cellular silica particles of Claim 4 which have a Dvgo volume particle diameter in the range of 30 pm to 50 pm, and a pore volume in the range of from 0.7 cm3 / g to 2.00 cm3 / g.

6. The partially calcined mesoporous cellular silica particles of Claim 5 wherein the one or more oils comprises a nonpolar aprotic solvent; and the one or more templates comprises a nonionic surfactant.

7. The partially calcined mesoporous cellular silica particles of Claim 6 wherein the nonionic surfactant is a EO-PO-EO triblock copolymer or a secondary alcohol ethoxylate.

8. The partially calcined mesoporous silica particles of Claim 3 having hexagonal morphology.

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