EP4725073A2

EP4725073A2 - A separator for separating adjacent battery cells

Info

Publication number: EP4725073A2
Application number: EP24746790.5A
Authority: EP
Inventors: Yiran XIE; Simon Harry Shepherd
Original assignee: Advanced Innergy Ltd
Current assignee: Advanced Innergy Ltd
Priority date: 2023-07-26
Filing date: 2024-07-16
Publication date: 2026-04-15
Also published as: WO2025022088A3; GB202311454D0; WO2025022088A2; CN121569400A; MX2026000896A; KR20260041806A

Abstract

A separator for separating adjacent battery cells in a prismatic battery module. The separator comprises a cured foamed material, and the cured foamed material comprises a cured silicone polymer.

Description

TITLE

A Separator for Separating Adjacent Battery Cells

TECHNOLOGICAL FIELD

Embodiments of the present disclosure relate to a separator for separating adjacent battery cells, and in particular to a separator for separating adjacent battery cells in a prismatic battery module.

BACKGROUND

Prismatic battery modules have a number of applications, for instance in electric vehicles and in the aerospace industry. Prismatic battery modules comprise a plurality of individual battery cells enclosed within a casing. The individual battery cells are commonly lithium-ion batteries.

Prismatic battery modules are susceptible to thermal runaway events. A thermal runaway event often involves the release of burning gas at high pressure and temperatures of around 1200°C.

A thermal runaway event in a prismatic battery module can be caused by overheating, a short-circuit or mechanical damage to a battery cell leading to a chain reaction which propagates between the battery cells. Some battery cells also have minor manufacturing defects, which can cause a thermal runaway event during normal charge or discharge cycles.

It is known to provide separators, i.e., cell dividers, between adjacent battery cells in a battery module to prevent or limit a thermal runaway event by minimizing heat transfer between neighboring battery cells. Known separators typically comprise Aerogel or ceramic fibre wool. Aerogel is a class of synthetic porous ultralight materials derived from a gel, in which the liquid component for the gel has been replaced with a gas, without significant collapse of the gel structure. Such known separator materials can be fibrous or dusty in nature, can disintegrate, deteriorate, or slump in use compromising performance, and/or can contaminate the inside of a battery module.

There is, therefore, a need to mitigate these drawbacks.

BRIEF SUMMARY

According to various, but not necessarily all, embodiments there is provided a separator for separating adjacent battery cells in a prismatic battery module, wherein the separator comprises a cured foamed material, and the cured foamed material comprises a cured silicone polymer.

The cured foamed material may comprise a fire retardant. The fire retardant may comprise aluminium trihydrate (ATH). The fire retardant may comprise calcium carbonate. The fire retardant may comprise aluminium trihydrate and calcium carbonate. Accordingly, the cured foamed material may comprise at least two different fire retardants. The cured foamed material may comprise from 10 to 75 wt.% of the fire retardant. Preferably, the cured foamed material may comprise from 30 to 60 wt.% of the fire retardant. Preferably, the cured foam material may comprise 20 to 40 wt.% of the fire retardant. The cured foamed material may comprise from 10 to 60 wt.% of the aluminium trihydrate. Preferably, the cured foamed material may comprise from 20 to 50 wt.% of the aluminium trihydrate. Preferably, the cured foamed material may comprise from 20 to 40 wt.% of the aluminium trihydrate. The cured foamed material may comprise up to 30 wt.% of the calcium carbonate. Preferably, the cured foamed material may comprise from 10 to 25 wt.% of the calcium carbonate.

In some examples, possibly the cured foamed material is a cured reaction product of a mixture comprising silanol fluid, a hydride functional silicone polymer, a fire retardant, and a hydrosilylation catalyst.

The mixture may comprise from 0.2 to 10 wt.% of the hydride functional silicone polymer. Preferably, the mixture may comprise 1 to 6 wt.% of the hydride functional silicone polymer. The mixture may comprise 0.25 to 6 wt.% of the hydride functional silicone polymer. The hydride functional silicone polymer may have a mol % of hydride greater than 80%. The hydride functional silicone polymer may have a mol % of hydride greater than 90%. The hydride functional silicone polymer may have a mol % of hydride greater than 95%.

The mixture may further comprise a fire retardant. The mixture may comprise from 10 to 75 wt.% of the fire retardant. The fire retardant may comprise aluminium trihydrate (ATH). The fire retardant may comprise calcium carbonate. The fire retardant may comprise aluminium trihydrate and calcium carbonate. Accordingly, the mixture may comprise at least two different fire retardants. Preferably, the mixture may comprise from 30 to 60 wt.% of the fire retardant. The mixture may comprise from 10 to 60 wt.% of the aluminium trihydrate. Preferably, the mixture may comprise from 20 to 50 wt.% of the aluminium trihydrate. Preferably, the mixture may comprise from 20 to 40 wt.% of the aluminium trihydrate. The mixture may comprise up to 30 wt.% of the calcium carbonate. Preferably, the mixture may comprise from 10 to 25 wt.% of the calcium carbonate.

The mixture may further comprise a vitrifying filler. The mixture may comprise up to 50 wt.% of the vitrifying filler. Preferably, the mixture may comprise from 10 to 50 wt.% of the vitrifying filler. Preferably, the mixture may comprise from 15 to 30 wt.% of the vitrifying filler. The vitrifying filler may be a glass frit.

The mixture may further comprise a vinyl functional silicone polymer. The mixture may comprise from 10 to 60 wt.% of the vinyl functional silicone polymer. Preferably, the mixture may comprise 15 to 30 wt.% of the vinyl functional silicone polymer. The vinyl functional silicone polymer may have a viscosity of about 5000 cPs. The vinyl functional silicone polymer may have a % vinyl of 0.115.

The mixture may comprise from 10 to 60 wt.% of the silanol fluid. In some embodiments, preferably, the mixture may comprise 40 to 55 wt.% of the silanol fluid. In some embodiments, preferably, the mixture may comprise 15 to 30 wt.% of the silanol fluid. In some embodiments, the silanol fluid may have a viscosity of about 80,000 cPs. In some embodiments, the silanol fluid may have a viscosity of about 5,000 cPs. In some embodiments, the silanol fluid may have a molecular weight of about 70,000 g/mol. In some embodiments, the silanol fluid may have a molecular weight of about 20,000 g/mol. The mixture may further comprise a blowing agent. The mixture may comprise from 0.05 to 1.5 wt.% of the blowing agent. Preferably, the mixture may comprise from 0.15 to 1.0 wt.% of the blowing agent. The blowing agent may be a chemical blowing agent. The blowing agent may comprise hydroxy functional groups. The blowing agent may comprise isopropyl alcohol.

The mixture may comprise from 0.0001 to 1 wt.% of the hydrosilylation catalyst. In some embodiments, preferably the mixture may comprise from 0.001 to 0.3 wt.% of the hydrosilylation catalyst. In some embodiments, preferably the mixture may comprise from 0.001 to 0.01 wt.% of the hydrosilylation catalyst. The hydrosilylation catalyst may comprise a platinum catalyst. The hydrosilylation catalyst may comprise a Karstedt catalyst.

The mixture may comprise an inhibitor. The mixture may comprise from 0.001 to 1 wt.% of the inhibitor. In some embodiments, preferably the mixture may comprise from 0.001 to 0.3 wt.% of the inhibitor. In some embodiments, preferably the mixture may comprise from 0.0001 to 0.7 wt.% of the inhibitor. Preferably, the mixture may comprise from 0.001 to 0.15 wt.% of the inhibitor. The inhibitor may comprise methyl vinyl cyclosiloxane.

The mixture may further comprise a filler. The filler may be a light-weight filler. The filler may be a porous filler. The filler may be an expandable filler. The filler may be an inert insulating filler. The filler may be a porous and/or expandable filler. The filler may comprise microspheres, which may be expandable microspheres such as Expancel®. The filler may comprise microporous silica. The filler may comprise vermiculite. The mixture may comprise up 25 wt.% of the filler. The mixture may comprise from 0.2 to 25 wt.% of the filler. In some embodiments, preferably the mixture may comprise from 1 to 15 wt.% of the filler. In some embodiments, preferably the mixture may comprise from 1 to 8 wt.% of the filler.

The mixture may further comprise a reinforcing filler. The reinforcing filler may also act as a rheological modifier. The filler may comprise fumed silica. The filler may have a coating that makes it compatible for use with silicone polymers. The coating may be hexamethyldisilazane. The mixture may comprise up to 5 wt.% of the reinforcing filler. Preferably, the mixture may comprise up to 2 wt.% of the reinforcing filler.

The cured foamed material may be syntactic. The cured foamed material may comprise hollow microspheres. The hollow microspheres may comprise thermoplastic microspheres. The cured foamed material may comprise from 0.1 to 10 wt.% of the hollow microspheres. Preferably, the cured foamed material may comprise from 0.5 to 2.0 wt.% of the hollow microspheres.

Possibly the cured foamed material is a cured reaction product of a mixture comprising a vinyl functional silicone polymer, a hydride functional silicone polymer, hollow microspheres, and a hydrosilylation catalyst.

The mixture may comprise from 20 to 60 wt.% of the vinyl functional silicone polymer. Preferably, the mixture may comprise from 30 to 40 wt.% of the vinyl functional silicone polymer. The vinyl functional silicone polymer may have a viscosity of about 1000 cPs. The vinyl functional silicone polymer may have a % vinyl of 0.311.

The mixture may comprise from 2 to 6 wt.% of the hydride functional silicone polymer. Preferably, the mixture may comprise from 3 to 4 wt.% of the hydride functional silicone polymer. The hydride functional silicone polymer may have a molecular weight of about 2100.

The mixture may further comprise a fire retardant. The mixture may comprise at least two different fire retardants. The mixture may comprise from 20 to 70 wt.% of the fire retardant. Preferably, the mixture may comprise from 30 to 65 wt.% of the fire retardant. The fire retardant may comprise aluminium trihydrate (ATH) and/or calcium carbonate. The mixture may comprise from 20 to 70 wt.% of the aluminium trihydrate. Preferably, the mixture may comprise from 30 to 55 wt.% of the aluminium trihydrate. The mixture may comprise up to 30 wt.% of the calcium carbonate. Preferably, the mixture may comprise from 10 to 20 wt.% of the calcium carbonate.

The mixture may comprise from 0.1 to 10 wt.% of the hollow microspheres. Preferably, the mixture may comprise from 0.5 to 2.0 wt.% of the hollow microspheres. The hollow microspheres may comprise thermoplastic microspheres. The mixture may comprise from 0.0001 to 0.1 wt.% of the hydrosilylation catalyst. In some embodiments, preferably the mixture may comprise from 0.0005 to 0.01 wt.% of the hydrosilylation catalyst. The hydrosilylation catalyst may comprise a platinum catalyst. The hydrosilylation catalyst may comprise a Karstedt catalyst.

The mixture may comprise an inhibitor. The mixture may comprise from 0.0001 to 0.5 wt.% of the inhibitor. Preferably, the mixture may comprise from 0.001 to 0.1 wt.% of the inhibitor. The inhibitor may comprise methyl vinyl cyclosiloxane.

The mixture may comprise a non-reactive diluent. The mixture may comprise up to 20 wt.% of the non-reactive diluent. Preferably, the mixture may comprise from 10 to 13 wt.% of the non-reactive diluent. The non-reactive diluent may have a viscosity of from 50 to 500 cPs.

Possibly, the separator comprises an inner layer and two outer layers, wherein the inner layer is sandwiched by the two outer layers, wherein the inner layer comprises the cured foamed material, and wherein each of the two outer layers comprises a cured silicone resin and glass fibres.

Possibly, the cured silicone resin comprises a plurality of T groups and/or a plurality of Q groups, wherein the T groups and the Q groups are respectively:

CH₃ OR

RO - S Ii - OR RO - S Ii - OR

OR OR

T Q wherein R is any organic group.

Possibly, the cured silicone resin of each of the two outer layers is the cured reaction product of a mixture comprising silicone resin, the glass fibres, and a solvent.

The mixture may comprise from 10 to 90 wt.% of the silicone resin. Preferably, the mixture may comprise from 20 to 75 wt.% of the silicone resin. The silicone resin may be powdered. Possibly, the silicone resin comprises a plurality of T groups and/or a plurality of Q groups, wherein the T groups and the Q groups are:

CH₃ OR

RO - S Ii - OR RO - S Ii - OR

OR OR

T Q wherein R is any organic group.

The mixture may comprise from 10 to 90 wt.% of the solvent. Preferably, the mixture may comprise from 20 to 75 wt.% of the solvent. The solvent may comprise toluene or dimethyl carbonate.

The mixture may comprise a catalyst. The mixture may comprise up to 5 wt.% of the catalyst. Preferably, the mixture may comprise from 0.5 to 2 5 wt.% of the catalyst. The catalyst may comprise amino silane. The catalyst may comprise a Wacker catalyst.

According to various, but not necessarily all, embodiments there is provided a method of forming a separator for separating adjacent battery cells in a prismatic battery module, the method comprising: curing a mixture to provide a cured foamed material, wherein the mixture comprises a silanol fluid, a hydride functional silicone polymer and a hydrosilylation catalyst.

The mixture may further comprise a vinyl functional polymer. The mixture may further comprise a blowing agent. The mixture may further comprise a fire retardant.

According to various, but not necessarily all, embodiments there is provided a method of forming a separator for separating adjacent battery cells in a prismatic battery module, the method comprising: curing a mixture to provide a cured foamed material, wherein the mixture comprises a vinyl functional silicone polymer, a hydride functional silicone polymer, hollow microspheres, and a hydrosilylation catalyst.

The mixture may further comprise a fire retardant. Possibly, the method further comprises: curing a mixture comprising silicone resin, glass fibres, and a solvent to provide a cured silicone resin comprising the glass fibres; and curing the mixture to provide the cured foamed material of the separator under compression between two layers of the cured silicone resin comprising the glass fibres to provide an inner layer comprising the cured foamed material sandwiched by the two layers.

According to various, but not necessarily all, embodiments there is provided a prismatic battery module comprising: a first battery cell, wherein the first battery cell has a length, a width and a depth, the length being greater than the depth and the width being greater that the depth, a face of the first battery cell being defined by the length and the width; a second battery cell, wherein the second battery cell has a length, a width and a depth, the length being greater than the depth and the width being greater that the depth, a face of the second battery cell being defined by the length and the width; and a separator disposed between (i) the face of the first battery cell that is defined by the length and the width of the first battery cell and (ii) the face of the second battery cell that is defined by the length and width of the second battery cell, wherein the separator comprises a cured foamed material.

The face of the first battery cell that is defined by the length and the width of the first battery cell may be substantially planar. The face of the second battery cell that is defined by the length and the width of the second battery cell may be substantially planar. The face of the first battery cell that is defined by the length and the width of the first battery cell may be substantially rectangular. The face of the second battery cell that is defined by the length and the width of the second battery cell may be substantially rectangular.

The first battery cell may have a first battery housing. The second battery cell may have a second battery housing. The separator may be disposed between the first battery housing and the second battery housing.

The first and second battery cells may have a substantially prismatic shape. The first and second battery cells may have a substantially rectangular cross section. The prismatic battery module may further comprise a casing. The first battery cell, the second battery cell and the separator may be disposed in the casing. The casing may have a substantially rectangular cross section. The casing may be formed from at least one metal. The casing may be formed substantially of metal.

The cured foamed material may comprise a cured silicone polymer.

According to various, but not necessarily all, embodiments there is provided a separator for separating adjacent battery cells in a prismatic battery module, wherein the separator comprises a cured foamed material.

According to various, but not necessarily all, embodiments there is provided a method of forming the separator, the method comprising: curing a mixture to provide a cured foamed material of the separator, wherein the mixture comprises: (i) silanol fluid, a vinyl functional silicone polymer, a hydride functional silicone polymer, a blowing agent, a fire retardant, and a hydrosilylation catalyst; or (ii) a vinyl functional silicone polymer, a hydride functional silicone polymer, a fire retardant, hollow microspheres, and a hydrosilylation catalyst.

According to various, but not necessarily all, embodiments there is provided a prismatic battery module comprising: a first battery cell, a second battery cell, and a separator, wherein the separator is disposed between the first battery cell and the second battery cell, wherein the separator comprises a cured foamed material.

According to various, but not necessarily all, embodiments there are provided examples as claimed in the appended claims.

BRIEF DESCRIPTION

For a better understanding of various examples that are useful for understanding the detailed description, reference will now be made by way of example only and with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE FIGURES Figure 1 illustrates a front view of an individual battery cell.

Figure 2 illustrates a front view of a prismatic battery module containing a plurality of individual battery cells.

Figure 3 illustrates a front view of a prismatic battery pack containing a plurality of prismatic battery modules.

Figure 4 illustrates a system with a cavity that is designed to receive a prismatic battery module.

Figure 5 illustrates the system of figure 4 with a plurality of prismatic battery modules located within the cavity.

Figure 6 illustrates a graph displaying the thermal insulation properties (i.e., the ability to limit heat transfer therethrough) of different separators according to examples of the disclosure compared to known separators.

DETAILED DESCRIPTION

Prismatic battery modules comprise a plurality of individual battery cells enclosed within a casing, for instance, an aluminium casing. Accordingly, prismatic battery modules comprise at least a first battery cell and a second battery cell.

Figure 1 shows an example individual battery cell 100. The cell 100 has a length L, a width W and a depth D. Each of the length L, the width W and the depth D represent a different dimension of the cell 100. Each of the dimensions L, W, D may be orthogonal to each of the other dimensions, L, W, D The length L is greater than the depth D, and may be greater than the width W. The width W is greater than the depth D. A set of two (orthogonal) dimensions defines a face of the cell 100. For example, the length L and the width W define a face labelled with the reference numeral 102 in figure 1. There is another face of the cell 100 that is defined by the length L and the width W which cannot be seen in figure 1 . Those two faces are separated by the depth D of the cell 100. The faces 102 defined by the length and width W may be substantially planar. For example, the faces 102 may be substantially rectangular. The individual battery cell 100 may have a substantially prismatic shape. For example, the individual battery cell 100 may have a substantially cuboidal shape. The individual battery cell 100 may have a substantially rectangular cross section. The individual battery cell may be a lithium-ion battery.

Each individual battery cell 100 may comprise an anode, a cathode and a separator enclosed in a housing 101. The separator may be considered an internal separator in that it is enclosed within the battery housing 101 of the cell 100. The internal separator may be located between the anode and the cathode of the cell 100. The internal separator may be exposed to or be in contact with the electrolyte of the cell 100. Accordingly, the internal separator may be chemically and electrochemically stable when it is exposed to or is in contact with the electrolyte. The internal separator may allow ionic charge carriers that are present in the electrolyte to migrate freely between the anode and cathode. Accordingly, the internal separator may be considered permeable to the ionic charge carriers in the electrolyte. The internal separator may have a thickness of less than around 100 pm.

Figure 2 shows an example prismatic battery module 200 comprising a plurality of individual battery cells 100. Each cell 100 in figure 2 may be as described in figure 1. The number of cells 100 in the module 200 may be greater or fewer than that shown in figure 2. In some examples, the module 200 may comprise many cells 100, for instance, tens or hundreds of cells 100. All of the cells 100 in the module 200 may be wired in series or in parallel. Alternatively, some of the cells 100 may be wired in series and some in parallel.

The prismatic battery module 200 may have a substantially prismatic shape. For example, the prismatic battery module 200 may have a substantially cuboidal shape. Accordingly, the prismatic battery module 200 may have a substantially rectangular cross-section.

The prismatic battery module 200 also comprises at least one separator 210 for separating adjacent battery cells 100 in a prismatic battery module 200. The separator 210 is therefore a battery cell divider. The separator 210 may be disposed between a first individual battery cell 100 and a second individual battery cell 100, such as between a face 102 of the first cell 100 that is defined by the length and the width of the first cell 100 and a face 102 of the second cell 100 that is defined by the length and width of the second cell 100. Accordingly in some examples, the separator 210 is disposed between respective largest faces of the first and second battery cells 100.

In some examples, a separator 210 is disposed between each pair of adjacent battery cells of the plurality of individual battery cells 100. Accordingly, in some examples the prismatic battery module 200 comprises a plurality of individual battery cells 100, where respective separators 210 are disposed between adjacent battery cells 100. A possible arrangement in the prismatic battery module 200 is alternating battery cell 100-separator 210-battery cell 100-separator 210.

The prismatic battery module 200 may comprise a casing 201. The plurality of battery cells 100 and the respective separators 210 may be disposed within the casing 201. The casing 201 may have a substantially rectangular cross section. The casing 201 may be formed from at least one metal. The casing 201 may be formed at least in part from aluminium. In some examples, a separator 210 may also be disposed between a terminal battery cell and an inner wall of the prismatic battery module casing 201. A terminal battery cell is a battery cell 100 which has one of its faces 102 that is defined by its length and width adjacent an inner wall of the prismatic battery module casing 201 rather than another battery cell.

Each separator 210 may be considered an external separator in that it is located outside of the housing 101 of the individual battery cells 100 that it separates. Accordingly, each separator 210 may be disposed between the housing 101 of a first cell 100 and the housing 101 of a second cell 100. Each separator 210 is not exposed to or in contact with the electrolyte of the individual battery cells 100. Accordingly, each separator 210 may not be chemically and/or electrochemically stable to electrolyte. Moreover, each separator 210 may be less permeable to ions such as the charge carriers in the electrolyte than the internal separator in each of the cells 100. Each separator 210 may be substantially impermeable to the charge carriers in the electrolyte. Each separator 210 may have a greater thickness than that of the internal separator within each battery cell 100. The thickness of a separator 210 is considered to be the extent of the separator 210 in the dimension aligned with the depth of the battery cells 100. The thickness may, for example, be in the range 1 mm to 20 mm. Preferably, the thickness may be in the range of 1 mm to 8 mm.

Each separator 210 may be considered to be a thermal insulator. For example, each separator 210 may have a thermal conductivity of less than 0.5 W/mk.

Each separator 210 comprises a cured foamed material. In this specification, a “foamed material” is a material having a cellular nature or structure resulting from introduction of gas bubbles and/or hollow spheres during manufacture. The gas bubbles may be introduced as a result of the reaction of between a polymer precursor and a cross-linker. In other words, the gas bubbles may be a by-product of the reaction between a polymer precursor and a cross linker that are incorporated into the crosslinked polymer to form a foamed material. Alternatively or additionally, the gas bubbles may be introduced through the use of a blowing agent. A “blowing agent” may be defined as a substance that has the capability of producing a cellular structure through a foaming process. Blowing agents may include physical blowing agents or chemical blowing agents. In this specification, “a chemical blowing agent” means a blowing agent which undergoes a chemical reaction in situ to generate gas bubbles.

In this specification, “cured” (as in a “cured foamed material”) means a chemical process that produces the toughening or hardening of a polymer material by crosslinking of polymer chains.

Separators 210 according to examples of the disclosure prevent or limit a thermal runaway event by minimizing heat transfer between adjacent, i.e., neighboring, battery cells 100. Furthermore, separators 210 according to examples of the disclosure are not fibrous or dusty in nature, can withstand vibrational disturbance and do not disintegrate, deteriorate, or slump in use (which would otherwise compromise performance), and do not contaminate the inside of battery modules 200.

In some examples, each separator 210 may comprises an inner layer and two outer layers. The outer layers provide a skin. The inner layer is sandwiched by the two outer layers. The inner layer comprises the cured foamed material. Each of the two outer layers comprises a cured silicone resin and glass fibres. Accordingly, the two outer layers each comprise cured silicone resin and glass fibres. In the described examples, the two outer layers are identical and therefore have identical compositions, properties, and characteristics. The outer layers, i.e., skins, improve fire resistance of each separator 210.

A plurality of prismatic battery modules 200 may be located together to form a battery pack. Figure 3 shows an example battery pack 300. The plurality of prismatic battery modules 200 may be wired together in series and/or in parallel. The battery pack 300 may have a prismatic shape. The battery pack 300 may have a substantially rectangular cross section. The battery pack 300 may comprise a casing 301. The casing 301 may have a substantially rectangular cross section. The casing 301 may be formed, at least in part, from at least one metal.

A prismatic battery module 200 may form part of a (wider) system such as an electric vehicle or an energy storage system. Figure 4 illustrates an example system 400. The system 400 may comprise a cavity 500 into which a battery module 200 may be located. Figure 5 illustrates the system 400 with a plurality of battery modules 200 located within the cavity 500. In some embodiments, the plurality of battery modules 200 may be located within a battery pack 300 and the battery pack 300 may be located within the cavity 500. In embodiments where the system 400 is an electric vehicle, the cavity 500 may be located under the cabin floor of the electric vehicle and between its front axle and rear axle, for example. The cavity 500 may alternatively be located under the bonnet/hood of the vehicle for example.

Cured foamed material of the (external) separator

As described above, each separator 210 comprises a cured foamed material. In some examples, the cured foamed material provides an inner layer of each separator 210.

In some examples, the cured foamed material comprises cured silicone polymer. The cured foamed material may comprise a fire retardant, such as aluminium trihydrate (ATH) and/or calcium carbonate. The cured foamed material may comprise from 10 to 75 wt.% of the fire retardant. The cured foam material may preferably may comprise from 30 to 60 wt.% of the fire retardant or from 20 to 40 wt.% of the fire retardant. The cured foamed material may comprise from 10 to 60 wt.% of the aluminium trihydrate, or preferably may comprise from 20 to 50 wt.% of the aluminium trihydrate or from 20 to 40 wt.% of the aluminium trihydrate. The cured foamed material may comprise up to 30 wt.% of the calcium carbonate, or preferably may comprise from 10 to 25 wt.% of the calcium carbonate.

In some examples, the cured foamed material is syntactic on account of it comprising hollow microspheres, such as thermoplastic microspheres. The cured foamed material may comprise from 0.1 to 10 wt.% of the hollow microspheres, or preferably may comprise from 0.5 to 2.0 wt.% of the hollow microspheres.

As described below, the disclosure exemplifies two chemically distinct types of cured foamed material.

First type of cured foamed material

In some examples, the cured foamed material is a cured reaction product of a mixture comprising silanol fluid, a hydride functional silicone polymer, a fire retardant, and a hydrosilylation catalyst.

Table 1 provides examples E1 , E2, E3 and E4 of such mixtures.

Table 1

Some further examples of the mixture may further comprise a vinyl functional silicone polymer. Table 2 provides examples, E1 , E2, E3, E4 and E5 of such mixtures.

Table 2

A fire retardant may otherwise be referred to as an endothermic filler.

In examples E1 to E4 of table 1 and E1 to E5 of Table 2, the cured foamed material comprises cured silicone polymer. Cured silicone polymers are flexible, making them suitable for use as an external separator 210 for a prismatic battery module 200. Moreover, silicone polymers are inherently fire resistant and do not release toxic smoke when they are burnt. The cured foamed material of examples E1 to E4 and E1 to E5 of Table 2 also comprise a fire retardant. The fire retardant may comprise aluminium trihydrate (ATH) and/or calcium carbonate. The silanol fluid in examples E1 to E4 of Table 1 may have a viscosity of about 80,000 cPs. The silanol fluid in examples E1 to E4 of Table 1 may have a molecular weight of 70, 000 g/mol. The silanol fluid in examples E1 to E5 of Table 2 may have a viscosity of about 5000 cPs. The silanol fluid in examples E1 to E5 of Table 2 may have a molecular weight of about 20,000 g/mol. The use of a silanol fluid with a higher viscosity, such as in examples E1 to E4 in Table 1 , provides a foamed material with a more uniform cell structure. This may provide improved insulative properties.

The vinyl functional silicone polymer may have a viscosity of about 5000 cPs. The vinyl functional silicone polymer may have a % vinyl of 0.115.

The hydride functional silicone polymer in examples E1 to E4 of Table 1 and examples E1 to E5 of Table 1 may have a high mol % of hydride, for instance greater than 80%, greater than 90%, or greater than 95%.

In the examples above, the cured foamed material has a cellular nature or structure resulting from introduction of gas bubbles during its manufacture. The gas bubbles may be hydrogen gas that is formed as a by-product of the reaction of the silanol fluid and the hydride functional silicone polymer cross-linker. In some examples, gas bubbles may be introduced through the use of a blowing agent. Accordingly, in examples such as E1 to E5 in Table 2 a blowing agent may be added to the mixture. The additional blowing agent may be a chemical blowing agent which undergoes a chemical reaction in situ to generate gas bubbles. In examples E1 to E5 of Table 2, the blowing agent is isopropyl alcohol which comprises hydroxy (-OH) functional groups that react with the hydride functional silicone polymer in situ to produce hydrogen gas. The hydrogen gas produced is then incorporated into the cured foam material.

In the examples above, the catalyst is a Karstedt catalyst, which is a platinum based hydrosilylation catalyst.

In some examples, the mixture may optionally comprise an inhibitor such as methyl vinyl cyclosiloxane. The mixture may comprise from 0.0001 to 1 wt.% of the inhibitor. In some embodiments, preferably the mixture may comprise from 0.0001 to 0.7 wt.% of the inhibitor or from 0.001 to 0.15 wt.% of the inhibitor. In other embodiments, preferably the mixture may comprise from 0.001 to 0.3 wt.% of the inhibitor.

In examples of the disclosure, the amount of silanol fluid, vinyl functional silicone polymer, blowing agent and hydride functional silicone polymer are selected to provide optimum compressibility and surface properties.

In some examples, the mixture may optionally comprise a vitrifying filler. A vitrifying filler may partially or fully transform the cured foamed material into a glass. The vitrifying filler may be a glass frit. The mixture may comprise up to 50 wt.% of the vitrifying filler. Preferably, the mixture may comprise from 10 to 50 wt.% of the vitrifying filler. Preferably, the mixture may comprise from 15 to 30 wt.% of the vitrifying filler. The presence of a vitrifying filler in the mixture may allow the cured silicone polymer to harden when exposed to heat and prevent the cured silicone polymer in the cured foamed material from turning dusty.

In some examples, the mixture may optionally comprise a filler. The filler may be lightweight and/or porous and/or expandable. The filler may be an inert insulating filler. The filler may comprise microspheres, which may be expandable microspheres such as Expancel®. The filler may comprise microporous silica. In this regard, the pores in the silica may each have a diameter of less than 2 nm. The presence of a microporous silica filler may improve the fire resistance of the cured foamed material. The filler may comprise vermiculite. The mixture may comprise up 25 wt.% of the filler. The mixture may comprise from 0.2 to 25 wt.% of the filler. In some embodiments, preferably the mixture may comprise from 1 to 15 wt.% of the filler. In some embodiments, preferably the mixture may comprise from 1 to 8 wt.% of the filler.

Second type of cured foamed material

In other examples, the cured foamed material is a cured reaction product of a mixture comprising a vinyl functional silicone polymer, a hydride functional silicone polymer, hollow microspheres, and a hydrosilylation catalyst. Table 3 provides examples, E1 and E2, of such mixtures. In such examples, the cured foamed material may be classified as a ‘syntactic foam’, given the presence of hollow microspheres. Table 3

A fire retardant may otherwise be referred to as an endothermic filler. In examples E1 and E2 of Table 3, the cured foamed material comprises cured silicone polymer. The cured foamed material may also comprise a fire retardant. The fire retardant may comprise aluminium trihydrate (ATH) and/or calcium carbonate. The cured foamed material comprises hollow microspheres in the form of thermoplastic microspheres. The cured foamed material is therefore syntactic.

Syntactic foam is a class of material created using pre-formed hollow spheres (commonly made of glass, ceramic, polymer or even metal) bound together with a polymer. The “syntactic” term refers to the ordered structure provided by the hollow spheres. The “foam” term relates to the cellular nature or structure of the material.

In example E2 of Table 3, the mixture comprises a non-reactive diluent, which can be present in an amount up to one third of the overall polymer content. The non-reactive diluent may have a viscosity of from 50 to 500 cPs.

In examples E1 and E2 of Table 3, the amount of hydride functional silicone polymer is 10% that of the vinyl functional silicone polymer content.

The vinyl functional silicone polymer may have a viscosity of from 50 to 100,000 cPs. Preferably, the vinyl functional silicone polymer may have a viscosity of about 1000 cPs. The vinyl functional silicone polymer may have a % vinyl of 0.311.

The hydride functional silicone polymer may have a molecular weight of about 2100.

In some examples, for example E1 and E2 of Table 3, the mixture comprises an inhibitor such as methyl vinyl cyclosiloxane. The mixture may comprise from 0.0001 to 0.5 wt.% of the inhibitor, or preferably from 0.001 to 0.1 wt.% of the inhibitor.

Optional outer layers (i.e., skin)

As described above, optionally each separator 210 has a sandwich structure in which the cured foamed material provides an inner layer which is sandwiched by two outer layers. Each of the two outer layers comprises a cured silicone resin and glass fibres.

Each of the two outer layers is the cured reaction product of a mixture comprising silicone resin, the glass fibres and a solvent. In some examples, the mixture also comprises a catalyst. In the described examples, the two outer layers are identical and therefore have identical compositions, properties, and characteristics.

Table 4 provides examples, E1 to E7, of such mixtures.

Table 4

Example catalysts include Wacker catalyst F and Geniosil GF 91 , which may be referred to as Geniosil DAPM N-(2-Aminoethyl)-3-aminopropyltrimethoxysilane.

In examples of the disclosure, the glass fibres, which may take the form of a glass veil, are impregnated with the mixture, the mixture for instance being according to examples E1 to E7 of Table 4. A glass veil is a matt of glass fibres. Accordingly, a glass veil is impregnated with the described mixture, e.g., a mixture according to examples E1 to E7 of Table 4.

The glass veil may be lightweight. The glass veil may have a weight from 8 to 200 GSM, or preferably from 25 to 70 GSM, or most preferably from 25 to 35 GSM. In some examples, the glass veil has a weight of 30 GSM or 34 GSM.

In other examples, the glass fibres may be in the form of a randomly oriented, chemically bonded mat, a woven fabric, or as discreet fibres dispersed in a solvent or resin mixture.

Silicone resins (whether cured or uncured) have a branched structure including T and Q groups and may also include M and/or D groups, as detailed below. Q (RsSiO^), T (RsSiOs^), D (RsSiO2/2), and M (RsSiOi^) indicate the number of attached oxygen atoms on each silicon atom, where Q, T, D, and M, respectively, refer to four, three, two, and one oxygen atoms, regardless of the attached organic groups. As would be understood by one skilled in the art, the abbreviation for a CH3 group is Me, i.e. , methyl group.

Q T D M

R is any organic group, which includes a continuation of the polymer chain.

A silicone resin (whether cured or uncured) according to examples of the disclosure comprises a plurality of T groups and/or a plurality of Q groups. Accordingly, such silicone resins are typically highly cross-linked. Consequently, silicone resins can be brittle solids. The use of silicone resins in the amounts described above provides a material for the outer layers with the required properties in terms of limiting the flexibility and/or rubberiness of the material. Silicone resins are inherently fire resistant.

Example method

Examples of the disclosure also provide a method of forming a separator 210. The method comprises curing a mixture to provide the cured foamed material of the separator 210.

In some examples, the mixture comprises a silanol fluid, a hydride functional silicone polymer, and a hydrosilylation catalyst. Examples of such mixtures are provided in Table 1 and Table 2 above. In some examples, the mixture may further comprise a vinyl functional silicone polymer. In some examples, the mixture may further comprise a blowing agent. In some examples, the mixture may further comprise a fire retardant.

In other examples, the mixture comprises a vinyl functional silicone polymer, a hydride functional silicone polymer, hollow microspheres, and a hydrosilylation catalyst. Examples of such mixtures are provided in Table 2 above. In some examples, the mixture may further comprise a fire retardant.

In examples in which the separator 210 has a sandwich structure in which the cured foamed material provides an inner layer which is sandwiched by two outer layers, the method comprises curing a mixture comprising silicone resin, glass fibres, and a solvent to provide a cured silicone resin comprising the glass fibres. Examples of such mixtures are provided in Table 4 above. The method subsequently comprises curing the mixture to provide the cured foamed material (for example mixtures detailed in Table 1 , Table 2 or Table 3 above) under compression between two layers of the cured silicone resin comprising the glass fibres to provide an inner layer comprising the cured foamed material sandwiched by the two layers. The two layers provide respective outer layers (i.e., skins) of the separator 210.

In some examples, to make the outer layers powdered silicone resin is dissolved or suspended in solvent (e.g., toluene) to provide a mixture (for example as per E1 to E7 of Table 4). A glass veil is impregnated with this mixture. The resulting composite is gently heated to evaporate the solvent (e.g., the temperature may be below 100°C if toluene is the solvent). Subsequently, the composite is placed in an oven and heated to about 200°C for an hour to cure the mixture thus consolidating the glass veil within the cured material resulting in a composite. Optionally, a catalyst can be included in the mixture to reduce the cure time. The resulting cured material is a sheet material which can be cut to required lengths to provide a number of layers which can then be used as outer layers in a sandwich structure of the separator 210.

The ingredients required to make the cured foamed material, which is the inner layer in some examples, (for example, as per E1 to E4 of T able 1 , E1 to E5 of T able 2 or E1 and E2 of Table 3) are mixed to provide a mixture. This mixture is pressed (i.e., compressed) between two outer layers to a desired thickness. As the mixture is being pressed it is cured to provide the cured foamed material of the inner layer sandwiched by the two outer layers.

The resulting composite is then cut to a required size and shape for use, for example, in a prismatic battery module 200 as described above. Test data

Figure 6 provides a graph 600 displaying the thermal insulation properties (i.e., the ability to limit heat transfer therethrough) of different separators 210 according to examples of the disclosure compared to known separators comprising Aerogel or ceramic fibre wool.

In each case, samples were placed on a hot plate set to 800°C and heat transfer through the samples over time was measured.

With reference to Figure 6, samples A and B are examples of known prior art separators. Samples C to H are separators 210 according to examples of the disclosure.

Sample A is Aerogel. Sample B is ceramic fibre wool.

Sample C is a cured foamed material corresponding to mixture E1 of Table 2.

Sample D is a sandwich structure in which the inner layer comprises a cured foamed material corresponding to mixture E1 of Table 2 and the two outer layers each comprise a cured silicone resin and glass fibres corresponding to mixture E1 of Table 4.

Sample E is a cured foamed material corresponding to mixture E5 of Table 2.

Sample F is a cured foamed material corresponding to mixture E4 of Table 2.

Sample G is a sandwich structure in which the inner layer comprises a cured foamed material corresponding to mixture E1 of Table 3 and the two outer layers each comprise a cured silicone resin and glass fibres corresponding to mixture E1 of Table 4.

Sample H is a cured foamed material corresponding to mixture E1 of Table 1. It is apparent from the graph 600 of Figure 6, that the thermal insulation properties of separators 210 according to examples of the disclosure (samples C to H) are at least comparable with known prior art separators (A and B). Over the time period measured, samples C to H are better thermal insulators than sample B (ceramic fibre wool) because the peak temperature of samples C to H is lower than the peak temperature of sample B, and samples E and F are better thermal insulators than sample A (Aerogel) because the peak temperature of samples E and F is lower than the peak temperature of sample A.

Separators 210 according to examples of the disclosure can therefore prevent or limit a thermal runaway event by minimizing heat transfer between neighboring, i.e., adjacent, battery cells 100 at least as well if not better than these known prior art materials. However, separators 210 according to examples of the disclosure are not fibrous or dusty in nature, can withstand vibrational disturbance and do not disintegrate, deteriorate, or slump in use (which would otherwise compromise performance), and do not contaminate the inside of a battery module 200. Aerogel and ceramic fibre wool, along with other known separator materials, can suffer from one or more of these drawbacks.

There is thus described a separator 210, a method of forming a separator 210, and a prismatic battery module 200 with a number of advantages as detailed above.

Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed. For example, in some examples the inner layer is sandwiched by the two outer layers, and this may enclose the inner layer such that no portion of the inner layer is exposed. In other examples, the inner layer is sandwiched by the two outer layers but is not enclosed such that a minor portion of the inner layer, for instance the respective end portions, is exposed.

The term ‘comprise’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising Y indicates that X may comprise only one Y or may comprise more than one Y. If it is intended to use ‘comprise’ with an exclusive meaning then it will be made clear in the context by referring to “comprising only one” or by using “consisting”.

In this description, reference has been made to various examples. The description of features or functions in relation to an example indicates that those features or functions are present in that example. The use of the term ‘example’ or ‘for example’ or ‘can’ or ‘may’ in the text denotes, whether explicitly stated or not, that such features or functions are present in at least the described example, whether described as an example or not, and that they can be, but are not necessarily, present in some of or all other examples. Thus ‘example’, ‘for example’, ‘can’ or ‘may’ refers to a particular instance in a class of examples. A property of the instance can be a property of only that instance or a property of the class or a property of a sub-class of the class that includes some but not all of the instances in the class. It is therefore implicitly disclosed that a feature described with reference to one example but not with reference to another example, can where possible be used in that other example as part of a working combination but does not necessarily have to be used in that other example.

Features described in the preceding description may be used in combinations other than the combinations explicitly described above.

Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

Although features have been described with reference to certain examples, those features may also be present in other examples whether described or not.

The term ‘a’ or ‘the’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising a/the Y indicates that X may comprise only one Y or may comprise more than one Y unless the context clearly indicates the contrary. If it is intended to use ‘a’ or ‘the’ with an exclusive meaning, then it will be made clear in the context. In some circumstances the use of ‘at least one’ or ‘one or more’ may be used to emphasis an inclusive meaning but the absence of these terms should not be taken to infer any exclusive meaning. The presence of a feature (or combination of features) in a claim is a reference to that feature or (combination of features) itself and also to features that achieve substantially the same technical effect (equivalent features). The equivalent features include, for example, features that are variants and achieve substantially the same result in substantially the same way. The equivalent features include, for example, features that perform substantially the same function, in substantially the same way to achieve substantially the same result.

In this description, reference has been made to various examples using adjectives or adjectival phrases to describe characteristics of the examples. Such a description of a characteristic in relation to an example indicates that the characteristic is present in some examples exactly as described and is present in other examples substantially as described.

Whilst endeavoring in the foregoing specification to draw attention to those features believed to be of importance it should be understood that the applicant may seek protection via the claims in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not emphasis has been placed thereon.

Claims

1. A separator for separating adjacent battery cells in a prismatic battery module, wherein the separator comprises a cured foamed material, and the cured foamed material comprises a cured silicone polymer.

2. A separator according to claim 1 , wherein the cured foamed material comprises a fire retardant.

3. The separator according to claim 2, wherein the cured foamed material comprises from 10 to 75 wt.% of the fire retardant.

4. The separator according to any of the preceding claims, wherein the cured foamed material is a cured reaction product of a mixture comprising a silanol fluid, a hydride functional silicone polymer and a hydrosilylation catalyst.

5. The separator according to claim 4, wherein the mixture comprises from 0.2 to 10 wt.% of the hydride functional silicone polymer.

6. The separator according to claim 4 or 5, wherein the mixture further comprises a fire retardant.

7. The separator according to claim 6, wherein the mixture comprises from 10 to 75 wt.% of the fire retardant.

8. The separator according to any of claims 4 to 7, wherein the mixture further comprises a vitrifying filler.

9. The separator according to claim 8, wherein the mixture comprises from 10 to 50 wt.% of the vitrifying filler.

10. The separator according to any of claims 4 to 9, wherein the mixture further comprises a vinyl functional silicone polymer.

11 . The separator according to claim 10, wherein the mixture comprises from 10 to 60 wt.% of the vinyl functional silicone polymer.

12. The separator according to any of claims 4 to 11 , wherein the mixture comprises from 10 to 60 wt.% of the silanol fluid.

13. The separator according to any of claims 4 to 9 wherein the mixture comprises from 40 to 55 wt.% of the silanol fluid.

14. The separator according to claim 10 or 11 , wherein the mixture comprises from 15 to 30 wt.% of the silanol fluid.

15. The separator of according to any of claims 4 to 14 wherein the mixture further comprises a blowing agent.

16. The separator according to claim 15, wherein the mixture comprises from 0.05 to 1 .5 wt.% of the blowing agent.

17. The separator according to any of claims 1 to 3, wherein the cured foamed material is syntactic.

18. The separator according to any of claim 17, wherein the cured foamed material is a cured reaction product of a mixture comprising a vinyl functional silicone polymer, a hydride functional silicone polymer, hollow microspheres, and a hydrosilylation catalyst.

19. The separator according to claim 18, wherein the mixture comprises from 20 to 60 wt.% of the vinyl functional silicone polymer.

20. The separator according to claim 18 or 19, wherein the mixture comprises from 2 to 6 wt.% of the hydride functional silicone polymer.

21. The separator according to any of claims 18 to 20, wherein the mixture further comprises a fire retardant.

22. The separator according to claim 21 , wherein the mixture comprises from 20 to 70 wt.% of the fire retardant.

23. The separator according to any of claims 18 to 22, wherein the mixture comprises from 0.1 to 10 wt.% of the hollow microspheres.

24. The separator according to any of the preceding claims, wherein the separator comprises an inner layer and two outer layers, wherein the inner layer is sandwiched by the two outer layers, wherein the inner layer comprises the cured foamed material, and wherein each of the two outer layers comprises a cured silicone resin and glass fibres.

25. The separator according claim 24, wherein the cured silicone resin comprises a plurality of T groups and/or a plurality of Q groups, wherein the T groups and the Q groups are respectively:

CH₃ OR

RO - S Ii - OR RO - S Ii - OR

OR OR

T Q wherein R is any organic group.

26. The separator according to claim 24 or 25, wherein the cured silicone resin of each of the two outer layers is the cured reaction product of a mixture comprising silicone resin, the glass fibres, and a solvent.

27. The separator according to claim 26, wherein the mixture comprises from 10 to 90 wt.% of the silicone resin.

28. The separator according to claim 26 or 27, wherein the mixture comprises from 10 to 90 wt.% of the solvent.

29. A method of forming a separator for separating adjacent battery cells in a prismatic battery module, the method comprising: curing a mixture to provide a cured foamed material, wherein the mixture comprises a silanol fluid, a hydride functional silicone polymer and a hydrosilylation catalyst.

30. The method according to claim 29, wherein the mixture further comprises a vinyl functional silicone polymer.

31. The method according to claim 29 or 30, wherein the mixture further comprises a blowing agent.

32. The method according to any of claims 29 to 31 , wherein the mixture further comprises a fire retardant.

33. A method of forming a separator for separating adjacent battery cells in a prismatic battery module, the method comprising: curing a mixture to provide a cured foamed material, wherein the mixture comprises a vinyl functional silicone polymer, a hydride functional silicone polymer, hollow microspheres, and a hydrosilylation catalyst.

34. The method according to claim 33, wherein the mixture further comprises a fire retardant.

35. A prismatic battery module, comprising: a first battery cell, wherein the first battery cell has a length, a width and a depth, the length being greater than the depth and the width being greater that the depth, a face of the first battery cell being defined by the length and the width; a second battery cell, wherein the second battery cell has a length, a width and a depth, the length being greater than the depth and the width being greater that the depth, a face of the second battery cell being defined by the length and the width; and a separator disposed between (i) the face of the first battery cell that is defined by the length and the width of the first battery cell and (ii) the face of the second battery cell that is defined by the length and the width of the second battery cell, wherein the separator comprises a cured foamed material.

36. The prismatic battery module according to claim 35, wherein the face of the first battery cell that is defined by the length and the width of the first battery cell is substantially planar and the face of the second battery cell that is defined by the length and the width of the second battery cell is substantially planar.

37. The prismatic battery module according to claim 36, wherein the face of the first battery cell that is defined by the length and the width of the first battery cell is substantially rectangular and the face of the second battery cell that is defined by the length and the width of the second battery cell is substantially rectangular.

38. The prismatic battery module according to any of claims 35 to 37, wherein the first battery cell has a first battery housing, the second battery cell has a second battery housing, and the separator is disposed between the first battery housing and the second battery housing.

39. The prismatic battery module according to any of claims 35 to 38, wherein the first and second battery cells have a substantially prismatic shape.

40. The prismatic battery module according to claim 39, wherein the first and second battery cells have a substantially rectangular cross section.

41. The prismatic battery module according to any of claims 35 to 40, wherein the prismatic battery module further comprises a casing and the first battery cell, the second battery cell and the separator are disposed in the casing.

42. The prismatic battery module according to claim 41 , wherein the casing has a substantially rectangular cross section.

43. The prismatic battery module according to claim 41 or 42, wherein the casing is formed from at least one metal.

44. The prismatic battery module according to any of claims 35 to 43, wherein the cured foam material comprises a cured silicone polymer.

45. A separator for separating adjacent battery cells in a prismatic battery module, wherein the separator comprises a cured foamed material.

46. The separator according to claim 45, wherein the cured foamed material comprises cured silicone polymer.

47. The separator according to claim 45 or 46, wherein the cured foamed material comprises a fire retardant.

48. The separator according to claim 47, wherein the cured foamed material comprises from 10 to 75 wt.% of the fire retardant.

49. The separator according to any claims 45 to 48 wherein the cured foamed material is syntactic.

50. The separator according to any of claims 45 to 48, wherein the cured foamed material is a cured reaction product of a mixture comprising silanol fluid, a vinyl functional silicone polymer, a hydride functional silicone polymer, a blowing agent, a fire retardant, and a hydrosilylation catalyst.

51 . The separator according to claim 50, wherein the mixture comprises from 10 to 60 wt.% of the silanol fluid.

52. The separator according to claim 50 or 51 , wherein the mixture comprises from 10 to 60 wt.% of the vinyl functional silicone polymer.

53. The separator according to any of claims 50 to 52, wherein the mixture comprises from 0.2 to 10 wt.% of the hydride functional silicone polymer.

54. The separator according to any of claims 50 to 53, wherein the mixture comprises from 0.05 to 1 .5 wt.% of the blowing agent.

55. The separator according to any of claims 50 to 54, wherein the mixture comprises from 10 to 75 wt.% of the fire retardant.

56. The separator according to any of claims 45 to 49, wherein the cured foamed material is a cured reaction product of a mixture comprising a vinyl functional silicone polymer, a hydride functional silicone polymer, a fire retardant, hollow microspheres, and a hydrosilylation catalyst.

57. The separator according to claim 56, wherein the mixture comprises from 20 to 60 wt.% of the vinyl functional silicone polymer.

58. The separator according to claim 56 or 57, wherein the mixture comprises from 2 to 6 wt.% of the hydride functional silicone polymer.

59. The separator according to any of claims 56 to 58, wherein the mixture comprises from 20 to 70 wt.% of the fire retardant.

60. The separator according to any of claims 56 to 59, wherein the mixture comprises from 0.1 to 10 wt.% of the hollow microspheres.

61 . The separator according to any of claims 45 to 60, wherein the separator comprises an inner layer and two outer layers, wherein the inner layer is sandwiched by the two outer layers, wherein the inner layer comprises the cured foamed material, and wherein each of the two outer layers comprises a cured silicone resin and glass fibres.

62. The separator according claim 61 , wherein the cured silicone resin comprises a plurality of T groups and/or a plurality of Q groups, wherein the T groups and the Q groups are respectively:

CH₃ OR

RO - S Ii - OR RO - S Ii - OR

OR OR

T Q wherein R is any organic group.

63. The separator according to claim 61 or 62, wherein the cured silicone resin of each of the two outer layers is the cured reaction product of a mixture comprising silicone resin, the glass fibres, and a solvent.

64. The separator according to claim 63, wherein the mixture comprises from 10 to 90 wt.% of the silicone resin.

65. The separator according to claim 63 or 64, wherein the mixture comprises from 10 to 90 wt.% of the solvent.

66. A method of forming the separator according to any of claims 45 to 65, the method comprising: curing a mixture to provide a cured foamed material of the separator, wherein the mixture comprises: silanol fluid, a vinyl functional silicone polymer, a hydride functional silicone polymer, a blowing agent, a fire retardant, and a hydrosilylation catalyst; or a vinyl functional silicone polymer, a hydride functional silicone polymer, a fire retardant, hollow microspheres, and a hydrosilylation catalyst.

67. A prismatic battery module comprising: a first battery cell, a second battery cell, and a separator, wherein the separator is disposed between the first battery cell and the second battery cell, wherein the separator comprises a cured foamed material.

68. The prismatic battery module according to claim 67, wherein the separator is disposed between respective larger faces of the first and second battery cells.

69. The prismatic battery module according to claim 67 or 68, wherein the first and second battery cells have a substantially prismatic shape.