Composite for battery compression pad

Abstract

The present invention relates to a composite for use in a battery assembly comprising: • 35 to 95 wt% silicone resin, which forms at least part of a silicone resin matrix; • 0 to 40 wt% optional additives • 5 to 65 wt% granules comprising fumed silica and an IR opacifier, said granules dispersed within the silicone resin matrix; one or both of said silicone resin matrix and said granules further comprise the optional additives. The granules comprise pores filled with the silicone resin to form impregnated granules.

Description

[0001] COMPOSITE FOR BATTERY COMPRESSION PAD

[0002] FIELD

[0003] The present invention relates to a composite for battery compression pads with good insulative properties at high temperatures; battery compression pads thereof and a method for making said composite.

[0004] BACKGROUND

[0005] When a lithium-ion battery cell malfunctions (for whatever reason) the cell typically overheats and / or becomes over charged which may consequently lead to a fire and / or explosion. Such malfunctions might be caused, for the sake of example, by short circuiting, by being physically damaged i.e. being crushed, or by being subjected to a higher electrical load without having overcharge protection. If present in a multi-cell module of lithium-ion batteries, the overheating of a first cell is likely to propagate similar occurrences in adjacent cells resulting in multiple cells in a battery module overheating and failing potentially leading to a “thermal runaway” and cell rupture.

[0006] A thermal runaway is usually initiated by the malfunction of one of the battery cells in a battery module leading to that cell releasing heat abnormally and to a sudden increase in the battery cell’s temperature. Once the temperature exceeds a threshold of e.g. about 150° C. or thereabouts, the constituents in the malfunctioning cell initiate a self-heating, autocatalytic, thermal decomposition exothermic reaction, where the temperature of the battery increases rapidly, e.g. at a rate of more than 20° C. per minute, with the temperature of the battery potentially reaching 500°C. or even 1000° C. In the absence of good insulation and heat dissipation structures in the battery module in which the malfunctioning battery is housed, the thermal energy released consequently heats up neighboring battery cells, resulting in a “thermal runaway” within the battery module. When thermal runaway has commenced inside the battery module it cannot be controlled effectively, potentially resulting in combustive exothermic reactions followed by the release of large amounts of flammable electrolyte gas and battery material decomposition gas (e.g. CO2, CO, and H2) and possible explosions.

[0007] In a quest for increased energy densities in battery packs, prismatic and pouch batteries have been gaining popularity. The prevention of thermal runway events within these batteries is further complicated due to the they tend to be constructed of materials that allow for the expansion and contraction of the cell surfaces during normal charge and discharge cycles, and the cell's planar surfaces tend to expand during a cell runaway event. Thus, thermal runaway prevention measures between cells, such as battery compression pads, needs to withstand cyclic expansion and contractions as well as potentially high temperatures. Ideally, this functionality is provided in a single layered solution, rather than a multilayered solution in which one layer provides good insulative properties and another layer good compression properties.

[0008] US2023 / 0231232 addresses this problem through providing a battery compression pad comprising aerogel particles coated with a polymer to mechanically strengthen the particles before the particles are dispersed into a liquid silicon rubber which is then vulcanized. Whilst the battery compression pad comprises acceptable insulative properties, the stiffness of the composite structure to protect the insulative properties of the aerogel particles resulted in the batteries having limited scope to expand the contract during the charging cycle. This results in increased internal stresses and charge degradation thereby reducing the life and performance of the battery through charging cycles. Thus, battery compression pads with good compression characteristics and heat insulation properties at high temperatures are still needed within industry.

[0009] SUMMARY OF THE INVENTION

[0010] In a first aspect of the present invention, there is provided a composite comprising:

[0011] • 35 to 95 wt% silicone resin, which forms at least part of a silicone resin matrix;

[0012] • 0 to 40 wt% optional additives;

[0013] • 5 to 65 wt% granules comprising fumed silica and an IR opacifier, said granules dispersed within the silicone resin matrix; one or both of said resin matrix and said granules further comprise the optional additives (if present), wherein the granules comprise pores impregnated with the silicone resin. The granule pores impregnated with silicone resin (or the silicone resin matrix) may be referred to as impregnated granules.

[0014] The composite may be used for battery compression pads or other applications requiring insulation, prevention of thermal runaway or fire retardant properties.

[0015] The sum of silicone resin, additives and granules is preferably greater than 90 wt% or greater than 95 wt% or 100 wt%.

[0016] Against conventional wisdom which teaches against the filling of granule pores due to a loss in thermal insulative properties (see US2023 / 0002627 paragraph 4), the applicants have found that through at least partially filling the granule pores, an advantageous combination of mechanical, compression and thermal runaway properties may be achieved by the composite of the present invention.

[0017] In one embodiment, the silicone resin matrix comprises at least 50 wt% or at least 60 wt% or at least 70 wt% or at least 80 wt% or at least 90 wt% or 100 wt% of the optional additives, when present. The remainder of the additives, not forming part of the silicone resin matrix, preferably form part of the granules, when present.

[0018] In one embodiment, the composite comprises:

[0019] • 70 to 95 wt% silicone resin matrix; and

[0020] • 5 to 30 wt% granules.

[0021] In one embodiment, the silicone resin matrix and the granules comprise at least 80 wt% or at least 90 wt% or 100 wt% of the composite.

[0022] In one embodiment, relative to the total weight of the composite, the silicone resin matrix comprises 35 to 95 wt% silicone resin and 0 to 35 wt% optional additives (e.g. MgSO4.7H2O) and the granules comprise 5 to 25 wt% fumed silica and IR opacifiers (combined); and 0 to 10 wt% optional additives (e.g. fluxing agents, fillers, organic or inorganic binders).

[0023] In an alternative aspect of the present invention, there is provided a composite comprising:

[0024] • 35 to 95 wt% silicone resin, which forms at least part of a silicone resin matrix;

[0025] • 0 to 40 wt% optional additives

[0026] • 5 to 65 wt% granules comprising fumed silica and an IR opacifier, said granules dispersed within the silicone resin matrix; one or both of said resin matrix and said granules further comprise the optional additives (if present), wherein in the range of 20% to 80% of a cross-sectional area of the composite comprises granules or impregnated granules and the apparent density of the composite is greater than 950 g / L (preferably on a silicon resin matrix void free basis).

[0027] A silicon resin matrix void free basis means that apparent density of the silicon resin matrix is determined on the basis that there is no void space in the silicone resin matrix.

[0028] The cross-sectional area of the composite may comprise at least 30% or at least 40% granules / impregnated granules (i.e. surface area occupied by granules or impregnated granules) as a lower proportion of granules / impregnated granules may be detrimental to the insulative properties of the ceramified product of the battery compression pad after being exposed to a thermal runaway event. The cross-sectional area of the composite may comprise no more than 75% or no more than 70% or no more than 65% or no more than 60% granules or impregnated granules as a higher proportion of granules / impregnated granules may be detrimental to the compression properties of the composite.

[0029] The cross-sectional area of the components may be determined via optical images or SEM images using Imaged™ image analysis software. The size of the images should be at least 100 mm2or at least 250 mm2or at least 500 mm2or sufficiently large to obtain a representative cross-section of the composite.

[0030] In one embodiment, the apparent density of the composite is greater than Z, where

[0031] Z = (X1 x X2) + (Y1 x Y2) wherein

[0032] X1 = wt% of silicone resin matrix and X2 - apparent density of silicone resin matrix

[0033] Y1 = wt% of granules and Y2 - apparent density of granules wherein the apparent density of the granules is no more than 1000g / L or no more than 800g / L or no more than 600g / L or no more than 500g / L or no more than 400g / L or no more than 450g / L or no more than 400g / L or no more than 350g / L or no more than 300g / L or no more than 250g / L.

[0034] In some embodiments, the apparent density of the silicone resin matrix is determined on a void or bubble free basis.

[0035] Z may be taken as the apparent density of the composite in which the granules are deemed not to be filled with silicone resin.

[0036] In an alternative aspect there is provided a composite comprising:

[0037] • 35 to 95 wt% silicone resin, which forms at least part of a silicone resin matrix;

[0038] • 0 to 40 wt% optional additives

[0039] • 5 to 65 wt% granules comprising fumed silica and an IR opacifier, said granules dispersed within the silicone resin matrix; one or both of said resin matrix and said granules further comprise the optional additives (if present), wherein the apparent density of the composite is greater than Z, where

[0040] Z = (X1 x X2) + (Y1 x Y2) wherein

[0041] X1 = wt% of silicone resin matrix and X2 - apparent density of silicone resin matrix

[0042] Y1 = wt% of granules and Y2 - apparent density of granules. wherein the apparent density of the granules is no more than 1000g / L or no more than 800g / L or no more than 600g / L or no more than 500g / L or no more than 400g / L or no more than 450g / L or no more than 400g / L or no more than 350g / L or no more than 300g / L or no more than 250g / L.

[0043] In some embodiments, the apparent density of the silicone resin matrix is determined on a void or bubble free basis.

[0044] For a composite comprising 87.5 wt% silicone resin and 12.5 wt% granules, the apparent density of the composite with the apparent density of the granule of 500g / L would be

[0045] (0.875 x 0.9864) + (0.125 x 0.500) = 0.926 g / cc.

[0046] Prior art granules not filled with silicone resin would have an apparent density lower than 500 g / L. Indeed, the prior art composites are better characterised as insulation pads which are focused on insulation properties of the composite and, as such, teach towards lower density composites.

[0047] The granules are typically dispersed within the silicone resin, with the silicone resin forming part or all of a silicon resin matrix in which the granules are disperse or embedded.

[0048] The pores of the impregnated granules may be partially filled or completely filled with the silicone resin.

[0049] In some embodiments, greater than 20% or greater than 35% or greater than 50% or greater than 60% or greater than 70% of the pore volume in the impregnated granules is filled with the silicone resin.

[0050] In some embodiments, the impregnated granules comprise greater than 10 wt% or greater than 15 wt% or greater than 20 wt% or greater than 25 wt% or greater than 30 wt% or greater than 40 wt% or greater than 50 wt% or greater than 60 wt% or greater than 70 wt % of silicone resin, relative to the total weight of the impregnated granules.

[0051] In some embodiments, the majority of all granules (e.g. > 50%) are impregnated granules, i.e. are at least partially filled or impregnated with the silicone resin. A peripheral portion of the impregnated granules is preferably filled with the silicon resin. It is apparent from the total porosity of the composite compared to the proportion of highly porous granular material, that at least a portion of the granular material has been penetrated by the uncured silicone resin during the dispersal of the granules within the silicone resin to form the composite.

[0052] The battery compression pads comprising the composite have been found to provide beneficial compression characteristics when used in a battery pack comprising prismatic or pouch batteries, wherein the battery compression pads are able to endure cyclic compression forces as battery cells expand and contract during the charging cycles. Further, the battery compression pad has been found to have excellent heat insulation properties at high temperatures (e.g. 800°C).

[0053] While not wanting to be bound by theory it is thought that the at least partial penetration of the silicone resin into the pores of the impregnated granules comprising fumed silica facilitates a ceramification product with excellent insulative properties. In particular, the high surface area of the fumed silica facilitates ceramification reactions which result in a large volume of gases including CO2 and H2O, thereby forming a highly porous ceramified structure derived from the impregnated granules.

[0054] Additionally, it is also thought that the formation of impregnated granules with silicone resin located in at least the peripheral portion of the granule is able to strengthen the granules making the composite sufficiently robust to withstand cyclic compression and decompression forces over the battery’s lifetime.

[0055] The ability of the silicone resin to penetrate the granules without detrimentally compromising the mechanical integrity of granules is unexpected, as is the combination of excellent compression properties of the composite during normal operation; and excellent insulative properties at high temperatures during a thermal runaway event. Such a combination of properties would typically only be available from a multi-layered structure with one layer providing the compression properties and a different layer providing the heat insulative properties.

[0056] Fumed silica

[0057] Fumed silica is a porous structure typically produced by the hydrolysis of volatile chlorosilanes in an oxyhydrogen flame. It typically consists of a highly pure amorphous silicon dioxide which is fluffy in texture. The primary particle may be in the range of 5 to The BET surface area is typically in the range of 50 to 600 m2 / g preferably 80 to 350 m2 / g and more preferably 170 to 230 m2 / g, measured in accordance with DIN EN ISO 9277 / DI N 66132. The bulk density of the fumed silica is typically in the range of 20 to 80 g / litre and preferably 30 to 60 g / litre measured in accordance with DIN EN ISO 787 / 11.

[0058] Fumed silicas are generally in aggregated form. “Aggregated” is understood to mean that what are called primary particles, which are formed at first in the genesis, become firmly bonded to one another later in the reaction to form a three-dimensional network. The primary particles are substantially free of pores and have free hydroxyl (silanol-) groups on their surface. The silica thus obtained may be modified with some surface-treatment agents, e.g. silanes to convert at least a part of free hydroxyl groups on their surface to substituted with silanes hydroxyl groups and impart hydrophobic properties to silica.

[0059] In some embodiments, the unmodified hydrophilic fumed silica is used as it has good wettability with the uncured silicone resin solution, thereby facilitating the penetration of the silicone into the granules.

[0060] Examples of suitable fumed silica (also known as pyrogenic silica) is HDK® available at Wacker Chemie AG; Aerosil® available at Evonik or Cab-O-Sil® available at Cabot Corporation.

[0061] IR Opacifiers

[0062] An IR-opacifier reduces the infrared transmittance of a heat-insulating material and thus minimizes the heat transfer due to radiation. Preferably, the IR-opacifier is selected from the group consisting of silicon carbide, titanium dioxide, zirconium dioxide, ilmenites, iron titanates, iron oxides, zirconium silicates, manganese oxides, graphites, carbon blacks and mixtures thereof. The particle size of the IR-opacifiers is generally between 0.1 and 25 pm.

[0063] Granules

[0064] The granules may comprise fumed silica and IR opacifiers and optionally a proportion or all of the optional additives. In one embodiment, the granules consist or essentially consist of fumed silica and IR opacifiers.

[0065] The fumed silica and IR opacifiers particles are mixed and mechanically compressed to densify the components into granules. If required, commercial granules may be further densified to improve their mechanical properties. For example, the granules may be densified with a Grenzebach densifying roll (Vacupress VP 160 / 220). The tamped density of the granular material obtained may be adjusted via the contact pressure, the roll speed and the reduced pressure applied. The vacuum applied was less than 300 mbar, absolute. The roll speed was about 5 rpm, and the pressure was 1500 to 2500 N. The obtained particles may optionally be processed in an oscillating sieve mill with for example a mesh size of 355 pm (manufacturer: FREWITT), in order to establish an upper particle limit and hence remove the particles larger than this upper limit.

[0066] The granules are porous and typically comprise a void volume of up to 95% of the total value of the granules, making the granules highly insulative. The fumed silica and IR opacifiers particles may be compressed, such that the apparent density of the granules compared to the granule powder mixture (before being formed into a granule) is increased in the range of 100 to 1000% or in the range of 200 to 600%. Too low a compression results in a mechanical unstable granule.

[0067] The granules may comprise pores sizes in a range between 1nm to 100pm or more. The pore size distribution may have a D50 of between 1 nm and 1 pm and more preferably between 1 nm and 50 nm.

[0068] The composite may comprise less than 50 wt% granules or less than 40 wt% granules or less than 30 wt% granules or less than 25 wt% granules. In some embodiments, the composite comprises, >0 to 15 wt% additives as part of the granules and preferably no more than 10 wt% or no more than 5 wt% of the total weight of the composite.

[0069] The composite may comprise between 5 wt% and 25 wt% granules or in the range of 6 wt % and 20 wt% granules or in the range of 7 wt% and 18 wt% granules or in the range of 8 wt% and 15 wt% granules. Higher proportions of granules may detrimentally affect the compression properties of the battery compression pad. Lower proportions of granules may be detrimental to the insulative performance of the composite at high temperatures (e.g. 800°C).

[0070] The granules may comprise

[0071] • 50 to 95 (or 50 to 80) parts by weight fumed silica;

[0072] • 5 to 50 (or 20 to 40) parts by weight IR opacifiers; and

[0073] • 0 to 20 (or 0.2 to 10) parts by weight additives.

[0074] In some embodiments, the granules comprise 60 to 80 wt% fumed silica and 20 to 40 wt% silicon carbide. The apparent density of the granule will vary depending upon the degree of densification and the proportion of fumed silica and specific IR-opacifier used, however a range of between 60 and 500 kg / m3or in the range of 80 to 350 kg / m3or in the range of 120 to 350 kg / m3or in the range 150 to 300 kg / m3may be regarded as typical.

[0075] The particle size distribution of the granules is preferably such that no more than 1 .0 wt% or no more than 5.0 wt% or no more than 10 wt% or no more than 20 wt% or no more than 30 wt% or more than 40 wt% of the granules pass through a mesh size of 150 pm. In some embodiments, at least 20 wt% or at least 30 wt% or at least 40 wt% or at least 50 wt % or at least 60 wt% of the granules pass through a 355 pm sieve, but not a 150 pm sieve. In some embodiments, no more than 40 wt% or no more than 30 wt% or no more than 20 wt% or no more than 10 wt% of the granules do not pass through a 355 pm sieve.

[0076] In another embodiment, at least 70 wt% or at least 80 wt% or at least 90 wt% or at least 95 wt% of the granules comprise sizes in the range of 150 pm to 6000 pm. In some embodiments, some granules are greater than 2000 pm (e.g. in the range of 10 to 40 wt% or 15 to 30 wt%). Unless otherwise specified, the size of the granule is taken as the maximum distance of a line passing through the centre of a granule.

[0077] An example of suitable fumed silica - IR opacifier granules are WDS® available from Morgan Advanced Materials, which has a composition of approximately 70 wt% fumed silica and 30 wt% silicon carbide and a bulk density (i.e. of loose filled granulate) of about 120 to 180 kg / m3.

[0078] The granules (and silicone resin) are preferably chosen such that there is sufficient wettability with the silicone resin to enable the silicone resin to penetrate the granules. Functional groups on the granules may be selected to achieve this objective (i.e. hydrophilic granules and hydrophilic uncured silicone resin solution; or hydrophobic granules and hydrophobic uncured silicone resin solution). In some embodiments, the granules may be hydrophilic and in other embodiments, the granules may be hydrophobic, dependent upon any optional solvent that the uncured silicone resin may be carried in. In some embodiments, the granules are hydrophilic and the uncured silicon resin is hydrophobic (or vice versa). To determine the suitability of the uncured silicon resin to penetrate into the granules, a wettability test may be used. For example a drop of uncured silicon resin solution may be placed on a board pressed with granules to a density of 240 kg / m3. The contact angle and height of the drop is observed over 300 seconds. If the height of the drop reduces to less than 80% of the original height after 60 seconds and / or to less than 40% of the original height after 300 seconds, then the uncured silicon resin may be considered suitable for penetrating the granules.

[0079] The skilled artisan would also understand that other factors may determine the selection of the silicone resin including durable, heat resistance and crack resistance.

[0080] The impregnated granules preferably comprise at least 5 wt% or at least 10 wt% or at least 20 wt% or at least 30 wt% or at least 40 wt% or at least 50 wt% or at least 60 wt% silicone resin relative to the total weight of the impregnated granules.

[0081] The BET surface area of the granules may be in the range of 100 to 200 m2 / g and typically in the range of 120 to 170 m2 / g.

[0082] A hydrophilic granule is deemed to be a granule with a hydroxyl group content of greater than 0.12 mmol OH / g or a surface concentration of greater than 1.0 OH / nm2. A hydrophobic granule is deemed to be a granule with a hydroxyl group content of no greater than 0.12 mmol OH / g or a surface concentration of no greater than 1 .0 OH / nm2.

[0083] The free hydroxyl group content of silica or a material comprising silica can be determined by the method published by J. Mathias and G. Wannemacher in Journal of Colloid and Interface Science 125 (1988), pp 61-68 “Basic characteristics and applications of Aerosil: 30. The chemistry and physics of the Aerosil surface” by reaction with lithium aluminium hydride. Using the corresponding BET surface area of the used material, the free hydroxyl group content in mmol OH / g can be easily converted in number of hydroxyl groups per surface area [OH / nm2].

[0084] Additives

[0085] The additives are optional and may not be present or may make up to 40 wt% of the total weight of the composite. Preferably the composition comprises no more than 35 wt% or no more than 30 wt% additive or no more than 25 wt% additive or no more than 20 wt% additive or no more than 15 wt% additive or no more than 10 wt% additive or no more than 5.0 wt% additive or no more than 3.0 wt% additive. Too high the proportion of additives may detrimentally affect the compression properties of the composite. In some embodiments, the additive content is at least 0.20 wt% or at least 0.5 wt% or at least 1 .0 wt% of the total weight of the composite.

[0086] In one embodiment, the sum of fire retardants, smoke suppressants and fire ignition inhibitors (e.g. MgSO4.7H2O) comprise up to 40 wt% or up to 35 wt% or up to 30 wt% or up to 25 wt% or up to 20 wt% of the total weight of the composite. The sum of the fire retardants, smoke suppressants and fire ignition inhibitors preferably form part of the silicone resin matrix.

[0087] Other additives may include conductors, inorganic or organic fibres, fluxing agents and / or filler materials which may further facilitate the ceram ification of the composite, including silicates (including alkali metal silicate alkaline earth silicates) or ammonium polyphosphate. In one embodiment, the additives comprise one or more of magnesium silicate, aluminum silicate, and calcium silicate, silicon dioxide, titanium dioxide, and aluminum oxide.

[0088] The fluxing agents may form part of the granules. Blow or foaming agents may form part of the silicone resin matrix.

[0089] The additives may form part of one or both of the granules and the silicone resin.

[0090] Silicone Resin Matrix

[0091] The silicone resin matrix may comprise a cured silicone resin and a proportion or all of the additives. In some embodiments, the silicone resin matrix consists of a cured silicone resin.

[0092] Any suitable silicone resin and precursors thereof may be used. Silicone resins, often referred to as silicone elastomers, are typically composed of at least two, three or four ingredients. These ingredients are (i) one or more reactive silicone polymer, (ii) a crosslinking agent, (iii) a catalyst, and (iv) a diluents (e.g. aliphatic or aromatic solvents). Generally, there exists two main types of silicone rubber compositions which are heat vulcanized, (HTV) silicone rubber and room temperature vulcanizing (RTV) silicone rubber. Heat vulcanized or high temperature vulcanizing

[0093] (HTV) silicone rubber compositions are often further differentiated as high consistency rubber (HCR) or liquid silicone rubber (LSR) depending on uncured viscosity of the composition. The terms “room temperature vulcanizing” (RTV) silicone rubber compositions, however may be misleading as some RTV compositions can require a modicum of heat to progress the reaction at a reasonable rate.

[0094] The silicone resin is preferably a ceramifiable silicone resin. Suitable ceramifiable silicone resins may include hydroxy or alkyl terminated (and / or grafted) polydimethylsiloxane (“PDMS”) and polyalkyl siloxane resins.

[0095] The silicone resin in which the granules of the invention are dispersed may be obtained by curing either an addition curing type organopolysiloxane composition, a peroxide curing type organopolysiloxane composition or a condensation type organopolysiloxane composition. The silicone resin may be formed from a one or two part condensation or addition type organopolysiloxane.

[0096] Such silicone compositions are well known by those skilled in the art of the silicone field. The addition curing type organopolysiloxane composition is preferably defined as primarily comprising (1) 100 parts by weight of an organopolysiloxane having at least two alkenyl groups attached to silicon atoms in a molecule, (2) 0.1 to 50 parts by weight of an organo- hydrogenpolysiloxane having at least two, preferably at least three hydrogen atoms attached to silicon atoms (i.e. , SiH groups) in a molecule, and (3) a catalytic amount of an addition reaction catalyst. The peroxide curing type organopolysiloxane composition is preferably defined as primarily comprising (1) 100 parts by weight of an organopolysiloxane having at least two alkenyl groups attached to silicon atoms in a molecule, and (2) a catalytic amount of an organic peroxide. The condensation type organopolysiloxane compositions that crosslink via polycondensation generally involve a silicone oil, generally a polydimethylsiloxane, with hydroxyl end groups, optionally prefunctionalized with a silane so as to have hydrolyzable and condensable ends and a crosslinking agent, a polycondensation catalyst, conventionally a tin salt or an alkyl titanate.

[0097] The viscosity of the silicone composition in uncured form is preferably sufficient for the silicone composition to penetrate at least a peripheral portion of the granules at the mixing temperature. Elevated mixing temperatures (e.g. greater than 50°C or greater than 100°C) may be used to lower the viscosity of an uncured silicone resin to assist in the penetration of the uncured silicone resin into the granules.

[0098] The viscosity of the uncured silicone resin may be no more than 10,000 mPas or no more than 5,000 mPas or no more than 3,000 at 23°C measured in accordance with ISO 2555:2018. Typically, the viscosity is at least 200 mPas or at least 500 mPas or at least 740 mPas.

[0099] The viscosity of the uncured silicone resin may be adjusted, for example, by adding different amounts of thickeners and / or crosslinkers in the two resin components. Furthermore, it is also possible to adjust the physical and / or chemical properties of the two resin components by using different polymer chain lengths. Longer-chain polymers are typically more viscous than shorter-chain ones.

[0100] The pot life may be influenced by the atmospheric conditions under which the silicone resins components are combined as well as the proportion of reactive side chains groups, catalysts and inhibitors which influence the curing rate of the silicone resin components. The silicone resin may further comprise an inhibitor to control the pot life and curing rate of the composition. The inhibitor can be a variety of inhibitors used in the art, for example alkynol such as 1-ethynyl-1 -cyclohexanol, 2-methyl-3-butyn-2-ol; polymethylvinylcyclosiloxanes, such as 1,3,5,7-tetravinyltetramethyltetracyclo-siloxane, alkyl maleate. The amount of the inhibitor can be selected according to its chemical structure and the desired curing rate. Generally, the weight of inhibitor in the composition is from 1 to 50,000 ppm, for example from 10 to 10,000 ppm.

[0101] The uncured silicone resin viscosity may be lowered by the inclusions of aliphatic or aromatic solvents, such as xylene. In one embodiment the solvent is selected from the group consisting of water, alcohols, aliphatic and aromatic hydrocarbons, ethers, esters, aldehydes, ketones and the mixtures thereof. For example, the solvent used can be water, methanol, ethanol, propanol, butanol, pentane, hexane, benzene, toluene, xylene, diethyl ether, methyl tert-butyl ether, ethyl acetate, acetone. Particularly preferably, the solvents used in the thermal insulating composition have a boiling point of less than 300° C., particularly preferably less than 200° C. Such relatively volatile solvents can be easily evaporated or vaporized during the curing of the thermal insulating composition according to the invention.

[0102] The silicone resin is preferably chosen such that there is sufficient wettability with the granules to enable the silicone resin to penetrate the granules. Functional groups on the silicone resin may be selected to achieve this objective. In some embodiments, the silicone resin may be hydrophilic and in other embodiments, the silicone resin may be hydrophobic.

[0103] According to one embodiment, the silicone resin is an in-situ foamable composition, meaning that the foaming of the silicone resin occurs upon combining of the two precursor components without requiring any additional compound, in particular external compound.

[0104] According to another embodiment, the foaming of the silicone resin is performed with a gaseous compound, e.g. via gas generation (e.g. blowing agent) or gas injection (e.g. N2or H2).

[0105] In one embodiment, the chemical blowing agent comprises one or more hydroxylcontaining blowing agents, blowing agent may be a suitable alcohol. These may be select ed from aliphatic organic alcohols having from 1 to 12 carbon atoms such as low molecula r weight alcohols including, but are not limited to, methanol, ethanol, propanol, isopropanol , and the like or alternatively, benzyl alcohol. In embodiments comprising a foamed silicone resin, the proportion of voids on a volume basis within the foamed silicone resin may be in the range of 5-90 %, 5-50 %, 5-40 %, 5- 30 %, 5-20 %, 5-10 %, 10-60 %, 10-50 %, 10-40 %, 10-30 %, 10-20 %, 20-60 %, 20-50 %, 20-40 %, 20-30 %, 30-60 %, 30-50 %, 30-40 %, 40-60 %, 40-50 % or 50-90%, based on the total volume of the composite.

[0106] The silicone resin foam may comprise a gas bubble size d5o of 10-1000 microns, 10- 800 microns, 10-600 microns, 10-400 microns, 10-200 microns, 10-100 microns, 10-50 mi crons, 50-1000 microns, 50-800 microns, 50-600 microns, 50-400 microns, 50-200 micron s, 50-100 microns, 100-1000 microns, 100-800 microns, 100-600 microns, 100-400 micro ns, 100-200 microns, 200-1000 microns, 200-800 microns, 200-600 microns, 200-400 mic rons, 400-1000 microns, 400-800 microns, 400-600 microns, 600-1000 microns, 600-800 microns or 80-1000 microns.

[0107] The composite of the present invention is light, insulative and possesses a desirable compression force deflection curve.

[0108] Shore A hardness

[0109] The Shore A hardness of the silicone composite (including granules) is preferably no more than 25 or no more than 20 or no more than 15 or no more than 10 when measured post cure in accordance with ASTM D2240-15. Higher Shore A hardness may result in excessive pressures being placed upon the expanding batteries during charging. A minimum Shore A hardness is typically at least 0.5 or at least 1.0 or at least 2.0 or at least 3.0 or at least 4.0 or at least 5.0.

[0110] Density

[0111] The apparent density of the composite is preferably in the range of 0.3 g / cc to 1.5 g / cc or 0.4 g / cc to 1.4 g / cc or 0.80 g / cc to 1.30 g / cc or in the range of 0.90 to 1.20 g / cc. Obtaining the low end of the apparent density range may require the foaming agents or the like.

[0112] Preferably, the density of the composite is no more than 1.20 g / cc or 1.10 g / cc, with lighter weight battery compression pads preferred due to the industry objective of increasing the power density of battery packs.

[0113] The apparent density of the composite will be dependent upon the apparent density of the silicone resin and the apparent density of the granules. Due to the void space between the granules in the bulk density measurement, the apparent density of a single granule (mass / volume) will be higher compared with the bulk density. In any event, the apparent density of the composite will be dependent upon the proportion of the silicon resin which has penetrated the granules, thereby decreasing the porosity of the composite.

[0114] The total porosity of the composite may be as low as 0% v / v, although due to manufacturing conditions a minimum total porosity is typically at least 1.0 %v / v or at least 2.0% v / v or 4.0% v / v if the silicone resin effectively fully penetrates almost all of the granules. In some embodiments, the total porosity of the composite is between 4 and 40% v / v or 5 and 25% v / v or 8 to 18% v / v without generating a foamed silicone resin composite. In embodiments comprising a foamed composite the total porosity of the composite may reach 80% v / v. However, the upper limit of the porosity is preferably no more than 60% v / v or 50% v / v or 45% v / v as too high a porosity content may result in the mechanical integrity of any ceramified product of the battery compression pad being compromised, thereby detrimentally affecting the insulative properties of the battery compression pad at high temperature (e.g. 800°C).

[0115] In some embodiments, the silicone resin occupies pores of one or more impregnated granules from at least 20 pm or at least 50 pm or at least 100 pm or at least 200 pm or at least 300 pm from the outer surface to a core of the impregnated granule.

[0116] Insulative properties

[0117] The composite’s insulative properties may be measured in accordance with the “hotplate test” which is conducted at 800°C. Preferably, the composite has a hotplate test result with a cold face temperature of no more than 180°C or no more than 170°C or no more than 160°C for a 5 mm composite sample after 15 minutes exposure.

[0118] In one embodiment, the battery compression pad according comprises a compressive pressure in the range of 100 to 1600 kPa at 50% compressive stain. A sample thickness of approximately 4 to 5 mm is preferably used.

[0119] Compression force deflection characteristics

[0120] To accommodation for the batteries cyclically expanding and contracting, the composite is preferably able to be compressed and decompressed when the battery expands and contracts during the life of the battery.

[0121] In some embodiments (e.g. where the battery is near the beginning of life (BOL)), the compressive force required to produce a 50% compressive strain is in the range of 50kPa to 1200kPa and preferably no more than 1000 kPa or 900 kPa or 800 kPa or 700 kPa or 600 kPa. In some embodiments (e.g. where the battery is nearing its end of life (EOL)), the compressive force required to produce a 80% compressive strain is in the range of 500kPa to 5000kPa and preferably no more than 4000 kPa or 3500 kPa or 3200 kPa or 3000 kPa or 2800 kPa.

[0122] In some embodiments, the composite may be delivered to uncured or semi-cured form. This may be achieved with the use of inhibitors. For example, an injectable form of the composite may be used to inject an uncured or partially uncured composite into the space between the battery cells. Alternatively, a two-component silicone resin formulation, with each component housed in a separate compartment may be injected via a mixing operation (e.g. static mixer) into a space between cells within a battery pack. The granules may be pre-dispersed in one or both of the silicone resin precursor components.

[0123] In one embodiment, the battery compression pad comprises a cold face temperature of less than 180°C after 15 minutes of the battery compression pad of dimension 150mm x 150mm x 5mm being placed on a hot plate set at 800°C, with the cold face temperature measured on a 1.0 mm aluminium sheet on the cold face surface, with a thermocouple attached to the centre of an external side of the aluminium sheet.

[0124] In a second aspect of the present invention, there is provided a battery compression pad comprising the composite of the first aspect of the invention.

[0125] The compression pad comprises a sheet of the composite material of the required dimensions to fit between the battery cells in the battery pack. The compression pad may further comprise additional layers, such as one or more heat spreading layers. The heat spreading layers may comprise copper, aluminum, silver, a copper alloy, an aluminum alloy, a silver alloy, boron nitride, aluminum nitride, silicon carbide, beryllium oxide, carbon fibers, carbon nanotubes, graphene, graphite, or a combination thereof.

[0126] The battery compression pad is typically a rectangular shaped sheet Width (W) Length (L) x Thickness (T). The planar surface area of the W x L dimensions is typically in the range of 2,000 mm2to 250,000 mm2. The volume of the battery compression pad is typically in the range of 25 cm3to 2,500 cm3.

[0127] In some embodiments, the thickness of the battery compression pad is from 1 mm to 10 mm, optionally from 1 mm to 8 mm, from 1.5 mm to 5 mm, from 2 mm to 6 mm, or from 2 mm to 4 mm, or the like. A battery compression pad having a thickness within the appropriate ranges can effectively block the heat and buffer the expansion stress, and meanwhile allows the battery assembly to have a smaller volume or weight, thereby obtaining a battery having higher safety performance and higher volume energy density or gravimetric energy density.

[0128] In some embodiments, the battery compression pad is a monolithic sheet consisting of a single layer of the composite. In other embodiments, the compression pad comprises a single layer of the composite at least partially enclosed in a covering (e.g. polymeric foil or aluminum foil). In one embodiment, each side of the battery compression pad is covered by a covering, to prevent the composition from adhering to the processing equipment during the manufacture of the process as well as facilitating the insertion of the battery compression pad within the battery pack. By keeping a minor dimensional plane uncovered, gases and associated heat generated during the ceramification process during thermal runaway may escape from the vicinity of the compression pad, in embodiments (e.g. polyethylene foil) in which the covering has not already “burnt off’ in the thermal runaway event.

[0129] In one embodiment, the battery compression pad comprises a metallic or polymeric covering on the major dimensional planes (i.e. L x W) interfacing with a battery cell. The minor dimensional plane(s) (i.e. T x W and / or T x L) are preferably left uncovered.

[0130] In other embodiments, the battery compression pad is formed from direct injection of the composite, not yet fully cured, into the space between the battery cells.

[0131] As an alternative producing the granules, they may be commercially acquired. Suitable granules include WDS® granules available form Morgan Advanced Materials PLC.

[0132] Prior to curing, the uncured composite may be formed into a target shape, through casting or moulding techniques.

[0133] Preferably, the granules are gradually added to the silicone resin. The suitable intensity of mixing, e.g. the rate and the duration of stirring is preferably selected so as to ensure well mixing of the thermal insulation composition, but to avoid the mechanical attrition granules. In some embodiments, the method of mixing is such that the incorporation of void space (e.g. bubbles) is minimized or avoided.

[0134] In some embodiments, the viscosity of the uncured silicone resin liquid is in the range of 100 mPas to 2000 mPas measured according to ISO 2555:2018 determined using the recommended spindle and rotational speed (Annexure A) at room temperature (23±2)°C. Preferably, the uncured silicone resin liquid has a viscosity of no more than 1500 mPas or no more than 1200 mPas or no more than 1050 mPas. Too high a viscosity may result in no penetration of the resin into the granules.

[0135] The pot life (i.e. the time for the silicone resin to double in viscosity) of the silicone resin is preferably at least 10 minutes or at least 20 minutes or at least 30 minutes. The silicone resin requires a sufficient pot life to enable the granules to be disperse into the silicone resin and for the silicone resin to penetrate the granules. Too low a pot life may result in the silicone resin not being able to penetrate the granules.

[0136] Unless otherwise stated, parameters, such as density have been measured at ambient temperature (22±2°C).

[0137] As used herein, the term “D5o” means median particle / pore size, which can be measured b y sieving method, for example, the expression “D5o of 200 pm” means that 50% of the particles / pores have a particle / pore size of 200 pm or more, and 50% the particles / pores have a particle / pore size of less than 200 pm.

[0138] In a third aspect of the present invention, there is provided a process for producing a composite comprising:

[0139] • blending 5.0 to 65 wt% of a combination of fumed silica, IR opacifiers particles and optional additives (if present) together to form a powder mixture;

[0140] • densifying the powder mixture to form granules comprising an apparent density in the range of 60 to 500 g / L;

[0141] • mixing 35 to 95 wt% of an uncured silicone resin liquid / solution and further optional additives (if present) with the granules to form an uncured composite comprising said granules disperse within a silicone resin matrix; and

[0142] • allowing the uncured composite to cure, wherein the granules and uncured resin solution are selected such that the uncured resin solution is able to impregnate into pores of the granules; and the composite optionally comprises up to 40 wt% additives in one or both of the granules and silicone resin matrix and wherein the granules preferably have been at least partially filled with the silicone resin. The optional additives are preferably either combined in with the powder mixture of fumed silica and IR opacifiers prior to the formation of the granules. Alternatively, or in addition to, the additives and disperse into the uncured silicone resin liquid either prior to; afterwards; or at the same time as the granules.

[0143] The resultant composites may be the composites of the first aspect of the present invention.

[0144] The apparent density of the composite may be at least 900 g / L or at least 950g / L or at least 960 g / L or at least 970g / L or at least 980 g / L or at least 990g / L or at least 1000 g / L or at least 1010 g / L. The maximum value is typically no more than 1300 g / L or no more than 1250 g / L or no more than 1200 g / L or no more than 1150 g / L.

[0145] Composites with lower apparent densities (e.g. 400 g / L or 500 g / L or 600 g / L or higher) may be achieved through using a foamable silicone resin liquid formulation or the addition of blowing agents or the injection of gases into the silicone resin liquid.

[0146] In one embodiment, the apparent density of the composite is greater than the apparent density of the silicone resin liquid, free of fugitive solvents. Due to the silicone resin filling the pores of the granules, the apparent density of the granules may increase to greater than that of the silicone resin. Whilst the increase in apparent density of the composite may adversely affect the insulative properties of the composite during the normal operating temperature of a battery pack, the ceramifiable nature of the composite enables the composite to provide excellent insulative properties when the composite is exposed to a thermal runaway event with temperatures in excess of 700°C or more.

[0147] As understood by the skilled artisan, the viscosity of the uncured silicone resin liquid may be appropriately adjusted to ensure that the silicone resin penetrates the granules, with through increasing the blending temperature or selecting a lower viscosity silicone resin or a silicone resin with a longer pot time.

[0148] In some embodiments, the uncured silicone resin liquid and the granules are mixed, so to avoid the entrainment of gas within the silicon resin liquid or the break-up of the granules.

[0149] In a fourth aspect of the present invention, there is provided a prismatic or pouch battery pack comprising a plurality of prismatic or pouch cells, wherein the battery compression pad according to the second aspect of the invention is disposed between adjacent prismatic or pouch cells.

[0150] In a fifth aspect of the present invention, there is provided the use of a battery compression pad according to the second aspect of the present invention to delay or prevent thermal runaway of a battery pack. The thermal runaway event may reach a temperature above the ceramification temperature of the battery compression pad. The thermal runaway event may reach of a temperature of at least 700°C or at least 750°C or at least 800°C.

[0151] In a sixth aspect of the present invention, there is provided the use of a composite of the first aspect of the present invention for fire protection.

[0152] In one embodiment, the battery compression pad comprises a hot face exposed to a heat source and a cold face separated from the hot face by a thickness of 5 mm. In one embodiment, the cold face temperature is less than 200°C (and preferably less than 190°C or less than 180°C or less than 170°C) after 15 minutes of the hot face of the battery compression pad of dimension 150mm x 150mm x 5mm being placed on a hot plate set at 800°C, with the cold face temperature measured on a 1 .0 mm aluminium sheet on the cold face, with a thermocouple attached to the centre of the external side of the aluminium sheet.

[0153] In a seventh aspect of the prevent invention, there is provide a ceramified battery compression pad formed from the battery compression pad of the second aspect of the present invention.

[0154] For clarity, the apparent density of a granule or granules relates to the mass of the granule or granules divided by the total volume of the granule or granules including the pores (open and closed) therein. In comparison, the bulk density of the granules would be the mass of granules divided by the volume of the granules, including the void space between the granules.

[0155] Reference to granules, unless otherwise indicated or implied, is reference to the granules in their raw material form prior to disperse into a silicone resin matrix. Therefore, reference to the granules is made in their unimpregnated state. It will be appreciated that the process of the silicon resin impregnating the unfilled granules may result in a concentration of additives within the silicone resin matrix, as some or all of the additives may not impregnate the granule.

[0156] The terms filled, impregnated or absorbed may be interchangeable used to describe the process of impregnating the granule or the state of the granule.

[0157] The terms silicone and silicone resin may be interchangeably used in the specification. Brief Description of the Figures

[0158] Figure 1 is a schematic diagram illustrating a composite comprising granules dispersed within a silicone resin matrix.

[0159] Figure 2 is an optical image of Sample 5 comprising granules within a silicone resin matrix.

[0160] Figure 3a is a CT scan image of the composite illustrating the silicon resin matrix, voids and granule components.

[0161] Figure 3b is a CT scan image illustrating the void component.

[0162] Figure 3c is a CT scan image illustrating the granule component.

[0163] Figure 4 is a diagram of a battery pack comprising the compression pad of the present invention.

[0164] Detailed Description of a Preferred Embodiment

[0165] The present invention is further illustrated by the following examples but is not limited to the scope thereof. Any experimental methods with no conditions specified in the following examples are selected according to the conventional methods and conditions, or product specifications.

[0166] With reference to Figure 1 , there is provided a composite comprising granules 100, 110, 120, 130, 140 dispersed within a silicone resin matrix 150. Some of the granules 100, 110, 120 have a central core region 105 which comprises a mix of void space, fumed silica and silicon carbide particles. The periphery of these granules 100, 110, 120 comprise silicone resin contained within the pore structure of the granules. Other granules 130, 140 may have the granules fully impregnated by the silicone resin. Additional void spaces may be present between the granules 160, 170 or within the silicon resin matrix 180, 190.

[0167] Figure 2 provides an optical image of the composite 200 of Sample 5. The surface of the composite 210 (as annotated with a dash white line) is not flat, hence the need to apply pressure to the composite sheet to flatten the surface when determining the apparent density of the composite. The composite comprises granules 220, 230 dispersed within a silicone resin matrix. Granules 240 and 250 have been highlight with a black line to define the outer surface of the granule. The granules 230 and 240 are further annotated to highlight a lighter internal ring represented by a dash black line 205. It is thought that this lighter internal ring is the impregnation front of the silicone resin, with the core regions 205 of these granules not fully impregnated with silicone resin. These granules also appear to have the largest minimum diameter, suggestive that the other smaller granules are more fully impregnated with silicone resin.

[0168] A silicone resin matrix 260, which encompasses the particles comprises a number of bubbles 270, 280, 290, which have a darker colour on the image. Some of the smaller voids or bubbles appear to be located between granules (e.g. 300).

[0169] Figures 3a-3c are a CT scan images of the composite of the present invention illustrating the distribution of voids 310, granules 320 and the silicone resin matrix 330. Figures 3b & 3c provides images of the void and granule distribution in the composite respectively.

[0170] Figure 4 illustrates a battery pack 4 in a housing 1. In the example shown, the battery pack 4 has three battery cells 2, each of which is separated from one another by a compression pad 3 according to the invention. In addition, such a compression pad 3 is provided at each end of the battery pack 4. Since the compression pads 3 are in the assembled state, i.e. in the non-expanded state, the battery pack 4 is undersized and can be inserted relatively easily into the housing 1 without any special measures.

[0171] Experiments

[0172] Granules:

[0173] WDS® granules comprising approximately 70 wt% fumed silica and 30 wt% SiC available from Morgan Advanced Materials PLC. The granules are hydrophilic and have been formed from compressing a powder mix of fumed silica and SiC into granules with an apparent density of 245 kg / m3. The BET surface area of fumed silica was determined to be 200 m2 / g. The BET surface area of the granules was determined to be 145 m2 / g. The BET surface area is determined in accordance with DIN9277:2014 / DIN 66132.

[0174] Silicone resin:

[0175] Jumbo Gel 2000: two component hydrophobic silicone resin derived from polydimethylsiloxane with a pot life of 17 minutes measured in accordance with I EC 60684-2 and a viscosity of 1000 mPa-s measured in accordance with ISO 2555:2018 using a No.3 spindle and a rotation speed of 50 rpm as recommended. The wettability of the silicon resin and granules resulted in a drop of uncured resin absorbing into the granule with the height of the dropping by a half in 60 seconds and by 90% (10% of original height) after 300 seconds. Similar wettability and compression deflection force results were obtained when Jumbo Gel 2000 was replaced with Elastosil® RT 745 “S” A & B available form Wacker Chemie AG.

[0176] Sample preparation: The two-component silicone resin formulation was initially mixed together to achieve homogeneity, with granules immediately blended into the uncured silicon resin mixture, using gentle mixing, unless otherwise indicated, (e.g. A Hobart planet mixer type HSM 10 with a Dough Hook ED was used at a speed in the range of 50 to 200 rpm for 30 to 300 seconds) to disperse the granules to form a homogeneous mixture. The battery compression pads were made using a plate roller to obtain uniform thickness with a thin foil (e.g. 20 pm polyethylene film) covering each surface to prevent sticking to testing equipment.

[0177] Sample 7 was prepared using more aggressive mixing (50 rpm for 180 seconds) with the higher granular loading resulting in a higher viscosity. The effect of this more aggressive mixing compared to sample 8 (hand mixing (i.e. < 50 rpm for 90 seconds) was that the granules fragmented in sample 7 but stayed intact in sample 8.

[0178] Table 1

[0179] Granule Size The WDS® granule particle size range was determined via sieving techniques, with the results provided in Table 2. Of the WDS® granules which passed through a 355 pm sieve they were further sieved through a 150 pm mesh sieve, with 24 wt% passing through this sieve.

[0180] Table 2

[0181] Skeletal density, Apparent density, Theoretical Density, Total Porosity and Calculated Porosity

[0182] Bulk density (mass / volume) is determined by measuring the density of loosely packed granules or particles with the volume including the void space between the particles or granules.

[0183] Apparent density (mass / volume) is determined by measuring the volume of an article (e.g. granule or composite sheet), which includes both the open and closes pores therein.

[0184] Apparent density of the composite sheet was determined using standard practice of collecting the mass and volume of a sample (size: 4” x 4” x 5mm). The composite thickness for this calculation was measured with 2 kPa of pressure on the sample surface to level out surface imperfections of composite sheet.

[0185] Apparent density of the granule was measured in accordance with solid displacement methodology and was determined using a Micromeritics® using Geopyc® 1365 envelope density analyser.

[0186] Skeletal density of the composite was determined by helium autopycnometer, in which the volume included the volume of the mass and the closed porosity.

[0187] Total porosity was determined by calculating the theoretical density (i.e. zero porosity) of the raw materials (from manufacturer of raw materials) using relative weight percentages of components and comparing that to the apparent density of the end article.

[0188] Relative closed porosity was determined by comparing the open porosity, determined by comparing the apparent density to the skeletal density, to the total porosity. Open and closed porosity may be determined indirectly with a helium pycnometer. The porosity of the system will contribute both to the compressive properties and thermal properties.

[0189] Based upon the skeletal density of the granule, the total porosity within the granules was determined to be approximately 90% v / v.

[0190] Therefore, the density of the composite (Example 5), if there was no penetration of silicone resin into the granules, would be (0.875 x 0.9864) + (0.125 x 0.245) = 0.894 g / cc. This compares with the actual density of the composite (Example 5) of 1.162 g / cc.

[0191] Table 3

[0192] The volume from 12.5 grams of granules is 51.02 cc. The volume of 87.5 grams of silicone resin is 88.71 cc. Therefore, the granules represent 36.51 %v / v of the composite if there is no silicone resin penetration of the granules. Given that the granules are about 90% v / v voids, then the minimum porosity of the composite (i.e. with no bubbles in the silicone resin and no silicone resin penetration into the granules), is about 33% v / v compared to about 12% v / v in the actual Example 5 composite. Therefore, it can be established that the silicone resin fills a significant portion of the granule’s pores.

[0193] Determination that the granules are filled with silicone resin.

[0194] Inspection of optical images of a cross-section of the composite may be used to establish that the granules are at least partially filled with silicone resin. The extent that the granules are filled with silicone resin may be determined by extracting one or more granules from the composite. The mass of the granules is determined before dissolving the silicone resin component with a hydrocarbon solvent such as toluene, xylene, ligroin, and mineral spirits. The granules, or remnants thereof, are re-weighed, and the difference determined to be the weight of the silicone resin. The extracted granules may be first treated with the hydrocarbon solvent to first remove any excessive silicone resin on the outside of the granules.

[0195] Alternatively, the volume of the silicon resin, granules and voids may be determined via CT scanning, with the volume silicon resin extracted via solvent extraction techniques compared to the volume of silicon resin determined by CT scanning. If the volume determined by CT scanning is less than determined by solvent extraction techniques, then the excess silicone silicon can be deduced as being extracted from the volume of granules.

[0196] SEM imaging using backscattered electrons may be utilized to highlight void space within the granules. Additionally, MRI or CT technology may be used to generate a 3D scan from which the volume components and location can be determined.

[0197] CT scan determination of silicon penetration into the granules

[0198] A Nikon Xtek High Flux Bay CT scanner was used under the following settings:

[0199] • X-ray source energy: 120 kV / 92 mA

[0200] • Resolution: 11 micron

[0201] • Distance x-ray source to object: 48 mm

[0202] • Distance x-ray source to detector: 875 mm

[0203] • Detector pixels: 2024 x 2024 (2x2 pixel binning)

[0204] Image and statistical analysis were performed using Avizo™ (developed by Thermo Fisher Scientific) software.

[0205] The samples had a dimension of 300 x 300 x 3.8 mm resulting in a volume of 342 cm3with a weight of about 350 grams. As the samples are 87.5 wt% silicone and 12.5 wt% WDS granules, then the weight of silicone and granules is 306.25 grams and 33.75 grams respectively. An example of the CT images for analysis is provided in Figures 3a-3c, illustrating globular voids 310; granules (dark shading) 320; and a silicon resin matrix (light shading) 330. Sample sizes for analysis are preferably at least 200 cm3or at least 300 cm3. Table 4

[0206] Sample calculation:

[0207] According to the actual amount of silicone resin in the composition, the silicone resin volume should be:

[0208] (wt% of silicone: 87.5) x (volume of sample: 342 cm3) x (density of silicone: 0.9864 g / cm3)

[0209] = 295.2 cm3. Therefore, the unaccounted silicon is 97.48 cm3or 96.5 grams of silicone.

[0210] Therefore in Sample 1 , the impregnated granules are composed of 96.51 (96.5 + 33.75) = 74 wt% silicone resin. As indicated in Table 4, the proportion of silicone impregnated into the granules is 74%.

[0211] Viscosity:

[0212] The viscosities of the uncured silicone resins were measured according to ISO 2555:2018 (3rdedition) determined using a Brookfield viscometer using No. 3 spindle at a speed of 50 rpm at room temperature (23±2)°C. Rotational speed and spindle number were chosen with reference to Annexure A ISO 2555:2018 (3rdedition).

[0213] Shore A hardness

[0214] Shore A hardness was measured on post cure state samples in accordance with ASTM D2240 for compositions with differing amount of WDS® granules. A Zwick Durometer was used on 6.0 mm thick samples of 300 x 150 mm dimensions at 20 equally spaced points. As indicated in Table 5, samples containing 5 and 12.5 wt% WDS® granules had a Shore hardness A reading which could not be measured, with the equipment only able to measure down to a Shore A hardness of 10. Therefore, these samples were deemed to have a Shore A hardness of less than 10. The 20 wt% WDS® granules sample had a Shore A hardness of 13.4, indicating that Shore A hardness increases with the % wt increase in granules in the composite. Table 5

[0215] Hot Plate test

[0216] A hot plate was set at 800°C. Samples (dimensions: 150mm x 150mm x 5mm) were prepared with a 1.0 mm aluminium sheet on the cold face surface, with a thermocouple attached to the centre of the aluminium sheet.

[0217] Samples were placed on the hot plate at 800°C and the temperature of the cold face recorded after 15 minutes in Table 6.

[0218] Table 6

[0219] Compression Force Deflection

[0220] Pouch and prismatic cells require a set amount of pressure on the cell exterior to maintain cell health over the lifetime of the application. Cell health may be determined by charge retention over lifetime cycling (charge and discharge) of the cell. The specific compression force deflection (CFD) curve for an application is defined by the manufacturer. The preferred CFD may be fully defined or may be defined by a series of critical points such as Beginning of Life (BOL), End of Warranty (EOW), or End of Life (EOL). A typical BOL pressure ranges from 5-150 kPa while a typical EOL pressure ranges from 1000-3000 kPa. The typical BOL compression strain is typically 0 to 30%, whilst the EOL compression strain is typically in the 50 to 80% range.

[0221] Pressures on the pouch or prismatic cells largest surface area (typically perpendicular to the internal construction) is essential in ensuring maximum charge retention over cycling as well as ensuring safety of the cell. Both pouch and prismatic cells swell during charge / discharge cycles. If allowed to swell freely without resistance, there is potential for over expansion to occur, thus allowing defects to present themselves in the cell and potentially cause self-discharge, reduction in charge capacity, or in worst cases thermal runaway. If a cell is too restricted and not allowed to swell while cycling there is potential for internal stress to build which can lead to defects and potentially cause self-discharge, reduction in charge capacity, or in worst cases thermal runaway.

[0222] Compression Set test

[0223] Compression set refers to the permanent deformation of a material. This is ideally as close to 0% as possible. A target application range, for the test conditions described below, is 0-3.5% and preferably 0-2.5% indicating a preferable rebound of 96.5-100% or

[0224] 97.5 to 100%.

[0225] 28.5 mm x 28.5 mm samples were prepared with the initial thickness recorded (approx.4 to 5mm)

[0226] Samples are compressed at a rate of 2.0 mm / min from 0% to 80% compression under ambient conditions (22±2°C, relative humidity of 40 to 60%). Compression force was recorded for every 5% compression, with selected resulted recorded in Table 7.

[0227] Samples were held at 50% compression for 24 hours with the compression force removed and the samples allowed to rest for 1 hour before the final thickness measured and the % change in thickness recorded in Table 7.

[0228] Table 7

[0229] As indicated in Table 6, an increase in the proportion of granules in the silicone resin matrix results (Samples 8, 5 and 6) in an increase in thermal insulation properties of the composite, with the cold face temperature reducing as the proportion of granular material increases. The effect of the granular structure is highlighted in a comparison of Samples 4 and 5, with the disperse fumed silica and SiC having about a 30°C increase in cold face temperature compared to the sample composition in granular form.

[0230] Similarly, Sample 8, with a 23.4 wt% loading of granules has almost a 90°C decrease in cold face temperature compared to the same loaded sample, which was aggressively mixed into the silicone matrix and thereby breaking up and redispersing the fumed silica and SiC. Despite the aggressive mixing used for Sample 7, the total porosity was greater in Sample 8. It is thought that a combination of resin impregnated granules and porosity contained within the partially filled granules contributes to a highly insulative ceramified structure.

[0231] As indicated in Samples 1 and 2, the effect of fumed silica (Sample 2) has a greater effect on the thermal insulative properties than SiC (Sample 1). However, the total amount of fumed silica and SiC (in granular form or not) increases the compression pressure, with the high loading of 23.4 wt% combined fumed silica and SiC possessing unfavourable compression pressure properties for the targeted compression pad applications. Whilst Sample 6 had both acceptable compression and thermal insulation properties, it was considered that granular material below 5.0 wt% may also fall outside the targeted compression and thermal insulation properties. Therefore, the experiments support the proportion of granular material to be between 5.0 wt% and 20.0 wt% of the total weight of the composite.

[0232] As indicated in Table 7 (Samples 7 and 8), the presence of the granular form reduces the compression pressure, as well as reducing the amount of permanent deformation of the composite.

[0233] For the avoidance of doubt it should be noted that in the present specification the term “comprise” in relation to a composition is taken to have the meaning of include, contain, or embrace, and to permit other ingredients to be present. The terms “comprises” and “comprising” are to be understood in like manner. It should also be noted that no claim is made to any composition in which the sum of the components exceeds 100%.

[0234] Many variants, product forms, uses, and applications of the fibres of the present disclosure will be apparent to the person skilled in the art and are intended to be encompassed by this disclosure.

Claims

CLAIMS1 . A composite comprising:• 35 to 95 wt% silicone resin, which forms at least part of a silicone resin matrix;• 0 to 40 wt% optional additives• 5 to 65 wt% granules comprising fumed silica and an IR opacifier, said granules dispersed within the silicone resin matrix; one or both of said silicone resin matrix and said granules further comprise the optional additives, wherein the granules comprise pores impregnated with the silicone resin.

2. The composite according to claim 1, comprising• 35 to 95 wt% silicone resin;• 0 to 40 wt% optional additives; and• 5 to 25 wt% granules.

3. The composite according to claim 1, comprising• 65 to 95 wt% silicone resin;• 0 to 10 wt% optional additives; and• 5 to 25 wt% granules.

4. The composite according to claim 1, comprising• 70 to 95 wt% silicone resin• 5 to 30 wt% granules wherein the sum of the silicon resin and granules is greater than 80 wt% of the composite.

5. A composite according to any one of the preceding claims, wherein the apparent density of the composite is greater than Z, whereZ = (X1 x X2) + (Y1 x Y2) where :X1 = wt% of silicone resin matrix and X2 - apparent density of silicone resin matrixY1 = wt% of granules and Y2 - apparent density of granules. wherein the apparent density of the granules is no more than 500g / L.

6. The composite of any one of the preceding claims, wherein the composite has a Shore A hardness of no more than 25.

7. The composite of any one of the preceding claims, wherein the granules comprise:• 40 to 95 parts by weight fumed silica;• 5 to 50 parts by weight IR opacifiers; and• 0 to 10 parts by weight optional additives.

8. The composite of any one of the preceding claims, wherein the silicone resin occupies pores of one or more impregnated granules from at least 20 pm from an outer surface towards a core of the impregnated granules.

9. The composite of any one of the preceding claims, wherein the impregnated granules comprise at least 10 wt% silicone resin relative to the total weight of the impregnated granules.

10. The composite according to any one of the preceding claims, wherein the composite comprises in the range of 6 to 25 wt% granules.11 . The composite according to any one of the preceding claims, wherein the total porosity of the composite is in the range of 5 to 25 % v / v.

12. The composite according to any one of the preceding claims, wherein the composite has an apparent density in the range of 950 g / L to 1300 g / L.

13. The composite according to any one of the preceding claims, wherein the composite comprises a foamed silicone resin with the proportion of voids therein is in the range of 5-90 v / v%.

14. The composite according to any one of the preceding claims, wherein the composite comprises an apparent density in the range of 300 g / L to 950 g / L.

15. A battery compression pad comprising the composite of any one of the preceding claims.

16. A prismatic or pouch battery pack comprising a plurality of prismatic or pouch cells, comprising the battery compression pad according to claim 15 disposed between adjacent prismatic or pouch cells.

17. A process for producing a composite comprising:• blending 5.0 to 65 wt% of a combination of fumed silica, IR opacifiers particles and optional additives together to form a powder mixture;• densifying the powder mixture to form granules comprising an apparent density in the range of 60 to 500 g / L;• mixing 35 to 95 wt% of an uncured silicone resin solution and further optional additives with the granules to form an uncured composite comprising said granules disperse within a silicone resin matrix; and• allowing the uncured composite to cure wherein the granules and uncured resin solution are selected such that the uncured resin solution is able to impregnate into pores of the granules and the composite optionally comprises up to 40 wt% additives in one or both of the granules and silicone resin matrix; and wherein the granules have been at least partially filled with the silicone resin to form impregnated granules.

18. The process according to claim 17, wherein the apparent density of the composite, on a void free basis, is greater than the apparent density of the uncured silicone resin liquid, free of any fugitive solvents, if present.

19. The process according to anyone of claims 17 to 18, wherein the viscosity of the uncured resin liquid is in the range of 100 mPas to 10,000 mPas measured according to ISO 2555:2018 at room temperature (23±2)°C.

20. The process according to claim 19, wherein the viscosity of the uncured resin liquid is less than 1500 mPas measured according to ISO 2555:2018 at room temperature (23±2)°C.21 . The process according to any one of claims 17 to 20, wherein the composite comprises a total porosity less than the total porosity attributable to the granules prior to being mixed with the uncured silicone resin.

22. The process according to any one of claims 17 to 21, wherein the granules, prior to being mixed into the uncured silicone resin, comprises an apparent density in the range of 60 to 500 g / L.

23. The process according to any one of claims 17 to 22, wherein the granules are hydrophilic granules with a hydroxyl group content of greater than 0.12 mmol OH / g or a surface concentration of greater than 1.0 OH / nm2.

24. The process according to any one of claims 17 to 23, wherein the total porosity of the composite is less than 25% v / v.

25. The process according to any one of claims 17 to 24, wherein a drop of uncured silicone resin when placed on the granules which are formed into a board of 240 kg / m3density, absorb into the board such that after 60 seconds of the drop contacting the board, the height of the drop reduces to less than 80% of the original height and / or reduces to less than 40% of the original height of the board after 300 seconds.

26. Use of a battery compression pad according to claim 15, to delay thermal runaway of a battery pack.

27. Use of the composite according to any one of claims 1 to 14 for use in fire protection.

28. A ceramified battery compression pad obtainable from a battery compression pad according to claim 15 through use of the battery compression pad according to claim 26.

29. A composite comprising:• 35 to 95 wt% silicone resin, which forms at least part of a silicone resin matrix;• 0 to 40 wt% optional additives• 5 to 65 wt% granules comprising fumed silica and an IR opacifier, said granules dispersed within the silicone resin matrix; one or both of said silicone resin matrix and said granules further comprise the optional additives, wherein the apparent density of the composite is greater than Z, whereZ = (X1 x X2) + (Y1 x Y2) whereX1 = wt% of silicone resin matrix and X2 - apparent density of silicone resin matrixY1 = wt% of granules and Y2 - apparent density of granules. wherein the apparent density of the granules is no more than 500g / L.

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