Protective Structures for Battery Enclosures

Abstract

A protective structure for protecting a battery enclosure, the protective structure including a functional layer and a reinforcing layer, the functional layer including a flame retardant and fire resistant material, or an expansion additive.

Description

[Technical field]

[0001] SUMMARY OF THE DISCLOSURE Embodiments of the present disclosure relate to protective structures for battery enclosures, battery enclosures including protective structures, vehicles including battery enclosures, methods of forming protective structures, and methods of protecting battery enclosures. [Background technology]

[0002] Battery packs have many applications, for example, in electric vehicles, aerospace, and for use as storage in power grids. A battery pack includes multiple battery cells within an enclosure. The enclosure separates the battery cells from the surrounding area, which could be, for example, the chassis of an electric vehicle.

[0003] Batteries, typically lithium-ion batteries, are susceptible to thermal runaway events. These events may be caused by overheating, short circuits, or mechanical damage to the battery cells. Some battery cells may even have minor manufacturing defects. These defects may cause a thermal runaway event during a normal charge or discharge cycle.

[0004] A thermal runaway event is often accompanied by the release of combustion gases at high pressure and temperatures of approximately 1200° C., which can propagate between cells in the battery pack and lead to chain reactions. The walls of the enclosure often do not provide sufficient protection from such events. Thus, energy from the runaway event can escape from the enclosure, creating safety hazards and causing damage to the surrounding area. Therefore, it is desirable to provide a protective structure to protect the battery enclosure. Summary of the Invention [Means for solving the problem]

[0005] According to various, but not necessarily all, embodiments, a protective structure for protecting a battery enclosure includes: a functional layer comprising a cured polymer, the functional layer comprising a flame retardant and a fire resistant material dispersed in the cured polymer, or a functional layer comprising an expansion additive dispersed in the cured polymer; Reinforcement layer and A protective structure is provided that includes:

[0006] In some cases, during use, the functional layer of the protective structure is the outermost layer of the protective structure that defines the exposed surface.In some cases, during use, the reinforcing layer of the protective structure is the outermost layer of the protective structure that defines the exposed surface.

[0007] In some cases, the protective structure is for protecting an interior surface of a battery enclosure. In some cases, during use, the functional layer of the protective structure is the outermost layer of the protective structure and is exposed to the interior environment of the battery enclosure. In some cases, during use, the reinforcing layer of the protective structure is the outermost layer of the protective structure and is exposed to the interior environment of the battery enclosure.

[0008] In some cases, the reinforcing layer is in the form of a reinforcing sheet comprising a fabric or mesh, which may be at least partially made of fiberglass, basalt fiber, mineral fiber, ceramic fiber, carbon fiber, or steel.

[0009] The reinforced sheet may comprise a fabric weighing from 50 to 1600 gsm. The reinforced sheet may comprise a fabric weighing from 50 to 250 gsm. Alternatively, the reinforced sheet may comprise a fabric weighing from 200 to 1600 gsm.

[0010] The cured polymer may include silicone polymers, epoxy resins, silane terminated polymer resins, acrylic resins, alkyd resins, vinyl acetate copolymers, or combinations thereof.

[0011] The flame retardant may include an endothermic additive. The endothermic additive may include an inorganic salt. The inorganic salt may be aluminum trihydroxide, magnesium dihydroxide, or ammonium polyphosphate.

[0012] The refractory material may include mica, clay, organoclay, talc, ceramic fibers, or borates.

[0013] The expansion additive may include a phosphorus-containing compound, a gas source, and a carbon source. In some cases, the phosphorus-containing compound includes ammonium polyphosphate, triphenyl phosphate, or aluminum phosphinate, the gas source includes melamine or boric acid, and the carbon source includes pentaerythritol or tris-(2-hydroxyethyl)isocyanurate. In some embodiments, tris-(2-hydroxyethyl)isocyanurate can be used as the gas source. Thus, tris-(2-hydroxyethyl)isocyanurate may be the carbon source and / or the gas source.

[0014] The functional layer may include a vitrifiable additive dispersed in the cured polymer. The vitrifiable additive may include a glass frit or a ceramifying agent.

[0015] The functional layer may have a thickness of from 50 to 1000 microns.

[0016] The protective structure may further include an adhesive layer for attaching the protective structure to a surface of the battery enclosure. The adhesive layer may include a double-sided adhesive film or a wet contact adhesive.

[0017] The protective structure may be flexible. The protective structure may have a thickness of 50 to 5000 microns.

[0018] According to various, but not necessarily all, embodiments, a battery enclosure is provided that includes a protective structure as described in any of the preceding paragraphs.

[0019] In some cases, the battery enclosure includes at least a first wall, with the reinforcing layer disposed at least partially between the first wall and the functional layer.

[0020] In some cases, the battery enclosure includes at least a first wall, with the functional layer disposed at least partially between the first wall and the reinforcing layer.

[0021] According to various, but not necessarily all, embodiments, a vehicle is provided that includes a battery enclosure as described in the above paragraph.

[0022] According to various, but not necessarily all, embodiments, a method for protecting a battery enclosure is provided, the method including attaching a protective structure according to any of the above paragraphs to a surface of the battery enclosure.

[0023] In some cases, the method includes attaching a protective structure to an interior surface of the battery enclosure.

[0024] Various, but not necessarily all, embodiments provide implementations as claimed in the following claims.

[0025] In order to better understand various embodiments which are beneficial for understanding the detailed description, reference will now be made, by way of example only, to the following embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] The present disclosure provides a protective structure for protecting a battery enclosure. In some embodiments, the protective structure is for protecting an interior surface of the battery enclosure.

[0027] The protective structure includes a functional layer and a toughening layer. The functional layer includes a curable polymer and one or more additives (as described below) dispersed in the curable polymer. The curable polymer and additives are selected according to the desired performance of the functional layer during a thermal runaway event.

[0028] In some cases, the cured polymer is a resin. For the avoidance of doubt, resins referred to herein are cured resins, not resin precursors, unless otherwise specified. A resin may also be considered a polymeric material.

[0029] In some embodiments, the functional layer includes a flame retardant and a fire resistant material dispersed in the cured polymer. In such embodiments, the flame retardant and the fire resistant material are additives contained in the functional layer. In other embodiments, the functional layer includes an expansion additive dispersed in the cured polymer. In such embodiments, the expansion additive is an additive contained in the functional layer.

[0030] The present disclosure also provides a battery enclosure including the protective structure, and a vehicle including the battery enclosure.The present disclosure also provides a method for protecting a battery enclosure, the method including attaching a protective structure to a surface of the battery enclosure.

[0031] The protective structure protects the battery enclosure from thermal runaway events.

[0032] The battery enclosure houses one or more battery cells. The battery enclosure includes a number of walls for enclosing the battery cells. The walls of the battery enclosure define a cavity for placing the battery cells. In some embodiments, the battery enclosure has six walls forming a cubical shape. That is, the battery enclosure includes a top wall, a bottom wall, and four side walls. In other embodiments, the battery enclosure may have a more complex shape, for example including one or more curved walls. One or more of the walls of the battery enclosure may act as a lid to allow access into the battery enclosure. Preferably, the battery enclosure is moisture sealed to prevent the ingress of water into the cavity. The battery enclosure may also include one or more brackets for holding the battery cells in place within the enclosure. The battery enclosure also contains a battery cooling device in some embodiments. The battery cooling device may be an air cooling system or a fluid cooling system.

[0033] The walls of the battery enclosure are preferably made of a rigid material such as steel, aluminum, a rigid polymeric material, or a composite material. The composite material may be a sheet laminate compound (SMC), also known as sheet laminate composite. Sheet laminate compounds are made by dispersing strands of chopped fiber (such as glass or carbon fiber) in a thermosetting resin.

[0034] In some embodiments, the battery enclosure forms part of a vehicle, such as an electric car. The battery enclosure may be secured to a frame of the vehicle, such as below the floor of the vehicle, typically between the axles.

[0035] The interior surface of the battery enclosure protected by the protective structure could be, for example, the interior face of a wall of the battery enclosure (i.e., the surface of the wall facing into the cavity of the battery enclosure). The protective structure may cover some or substantially all of the inner surface of the wall to inhibit the energy of a thermal runaway event from escaping the enclosure.

[0036] In some embodiments, the protective structure has a thickness between 50 microns and 5000 microns. Preferably, the protective structure has a thickness between 200 microns and 2000 microns.

[0037] In some embodiments, the cured polymer is flexible. In some embodiments, the cured polymer has a Shore A hardness of up to 80. The cured polymer may be a silicone polymer, an epoxy resin, a silane terminated polymer resin, an acrylic resin, an alkyd resin, a vinyl acetate copolymer, or a combination thereof. The cured polymer may be a copolymer, such as a copolymer resin.

[0038] Other components (ie, additives) contained in the functional layer are dispersed in the cured polymer. Preferably, the functional layer has a thickness of 50 microns to 1000 microns.

[0039] In some embodiments, the reinforcing layer is in the form of a reinforcing sheet. The reinforcing layer may be considered an enhancing member. The reinforcing layer has a higher tensile strength and / or tear strength than the functional layer, thus improving the tensile strength and / or tear strength of the protective structure.

[0040] The reinforcing sheet may include a fabric or mesh that may be partially or entirely made of fiberglass (such as high silica glass), basalt fiber, mineral fiber, ceramic fiber, carbon fiber, steel, or a combination of any of these materials. The fabric may be woven or non-woven.

[0041] In some embodiments, the fabric has a weight of 50 to 1600 gsm. Preferably, the fabric has a weight of 300 to 900 gsm. In one preferred embodiment, the fabric is a woven glass fabric weighing 600 gsm. In some embodiments, the reinforced sheet comprises a fabric weighing 50 to 250 gsm. In other embodiments, the reinforced sheet comprises a fabric weighing 200 to 1600 gsm.

[0042] In some embodiments, reinforcing fibers may be dispersed in the cured polymer of the functional layer. The reinforcing fibers may be basalt fibers, glass fibers, ceramic fibers, carbon fibers, and / or mineral fibers.

[0043] In embodiments where the functional layer comprises a flame retardant and fire resistant material dispersed in the cured polymer, the flame retardant inhibits ignition of the functional layer during a thermal runaway event. Preferably, the flame retardant comprises an endothermic additive such as an inorganic salt.

[0044] The endothermic additive acts to cool the functional layer in the presence of heat by an endothermic reaction. The inorganic salt generates a non-flammable gas, such as water or carbon dioxide, at elevated temperatures, which can remove heat from the functional layer.

[0045] The inorganic salt may be aluminum trihydroxide, magnesium dihydroxide, or ammonium polyphosphate. In some embodiments, the flame retardant comprises an additional endothermic additive. The additional endothermic additive could be, for example, a different inorganic salt.

[0046] In such embodiments, the refractory material is removed or destroyed (e.g., by erosion or charring) in the presence of flame. The refractory material is capable of blocking flame or heat for a limited period of time until the refractory material is completely depleted. In some embodiments, the refractory material comprises a mineral or ceramic. Preferably, the refractory material comprises mica, clay, organoclay, talc, ceramic fiber, or borate. The refractory material is an abrasive or abrasive additive.

[0047] In embodiments where the functional layer includes an expansion additive dispersed in the cured polymer, the expansion additive expands upon exposure to heat, thereby providing a foam-like protective layer that is low density and insulates the substrate.

[0048] In some embodiments, the expansion additive includes a phosphorus-containing compound, a gas source, and a carbon source. The phosphorus-containing compound could be, for example, ammonium polyphosphate, triphenyl phosphate, or aluminum phosphinate. The gas source could be, for example, melamine or boric acid. The carbon source could be, for example, pentaerythritol or tris-(2-hydroxyethyl)isocyanurate.

[0049] In some embodiments, tris-(2-hydroxyethyl)isocyanurate can be used as a gas source. Thus, tris-(2-hydroxyethyl)isocyanurate can be a carbon source and / or a gas source.

[0050] In some embodiments, the functional layer includes a vitrifiable additive dispersed in the cured polymer. The vitrifiable additive vitrifies / ceramizes upon exposure to heat, thereby forming a solid or glass-like layer that is resistant to high pressures and erosion. Preferably, the vitrifiable additive includes a glass frit or ceramifier. Exemplary glass frits include Ferro®'s 14019 frit, and exemplary ceramifiers include Ceepree®'s CGB 3BAM additive, and Johnson Matthey®'s XF®T inorganic additive.

[0051] In some embodiments, the protective structure further comprises an adhesive layer for attaching the protective structure to a surface of the battery enclosure. Preferably, the adhesive layer comprises a double-sided adhesive tape, such as a double-sided acrylic adhesive tape. In other embodiments, the adhesive layer can be applied as a liquid (e.g., via spraying or using a brush), for example, using a liquid polymer adhesive, such as a liquid acrylic adhesive, a liquid neoprene adhesive, a liquid silicone adhesive, a liquid polyurethane adhesive, or a liquid epoxy adhesive.

[0052] As an alternative or in addition to using an adhesive to attach the protective structure to the surface of the battery enclosure, the protective structure can be mechanically attached to the surface of the battery enclosure. This can be accomplished using fasteners such as staples or rivets, or by providing holes in the surface of the battery enclosure that are positioned to allow at least a portion of the protective structure to be inserted.

[0053] In some embodiments, a reinforcing layer is disposed between the adhesive layer and the functional layer, so that the reinforcing layer can act as an adhesion promoter between the functional layer and the adhesive layer.

[0054] In some embodiments, in use, the functional layer of the protective structure is the outermost layer of the protective structure. In other embodiments, in use, the reinforcing layer of the protective structure is the outermost layer of the protective structure. The outermost layer of the protective structure is the layer of the protective structure that is furthest from the surface of the battery enclosure to which the protective structure is attached. In use, the outermost layer of the protective structure defines an exposed surface. In such embodiments, the surface of the battery enclosure to which the protective structure is attached may be an interior surface or an exterior surface of the battery enclosure.

[0055] In some embodiments, where the protective structure is for protecting an internal surface of a battery enclosure, during use, the functional layer of the protective structure is the outermost layer of the protective structure and is exposed to the internal environment of the battery enclosure. The functional layer is therefore an exposed surface layer on the inside of the battery enclosure. The reinforcing layer is therefore located, at least in part, between the first wall of the battery enclosure and the functional layer.

[0056] In another embodiment, where the protective structure is for protecting an internal surface of a battery enclosure, in use, the reinforcing layer of the protective structure is the outermost layer of the protective structure and is exposed to the internal environment of the battery enclosure. The reinforcing layer is therefore an exposed surface layer on the inside of the battery enclosure. The functional layer is therefore at least partially located between the first wall of the battery enclosure and the reinforcing layer.

[0057] The outermost layer of the protective structure, in use, provides the innermost surface of the battery enclosure to be protected and is therefore exposed to the internal environment of the battery enclosure, in use.

[0058] The "in use" status of the protective structure means that the protective structure is attached to a surface of the battery enclosure.

[0059] Exemplary protective structures are described below.

[0060] [Protective Structure (Example 1)] A first embodiment of a protective structure was comprised of a functional layer, a reinforcing layer, and optionally an adhesive layer for attaching the protective structure to the interior surface of the battery enclosure.

[0061] In this embodiment, the functional layer provides the outermost layer of the protective structure during use and is exposed to the internal environment of the battery enclosure.

[0062] The adhesive layer, if present, provides the innermost layer during use and may include a contact adhesive film with a protective film (i.e. a double-sided adhesive film) to allow easy bonding to the surface to be protected, this effect can also be achieved by mechanical fastening or application of a wet contact adhesive.

[0063] [Functional Layer] The functional layer is the cured reaction product of a mixture having the components listed below: In Example 1, the functional layer includes flame retardants and fire resistant materials dispersed in the cured polymer.

[0064] [Table 1]

[0065] [Reinforcement layer] The reinforcing layer is in the form of a reinforcing sheet comprising a fabric. In this embodiment, the fabric is made of fiberglass, typically high silica glass. The fabric has a weight of 200-1600 gsm, and may have a weight of 600 gsm. The fabric is a high temperature fabric or felt of sufficient thickness to withstand a 1200°C gas jet without melting.

[0066] Example 1 provides resistance to penetration during a thermal runaway event. As detailed above, Example 1 is comprised of an exterior / exposed surface functional layer. Fire retardants and fire resistant materials are added to the functional layer to form a hard, resistant char. The functional layer is the primary layer of defense against erosion. The functional layer is applied to the reinforcing layer to provide structure, resistance to the pressure of gas jets, and additional resistance to penetration and erosion.

[0067] [Protection structure (Example 2)] A second embodiment of the protective structure was comprised of a functional layer, a reinforcing layer, and optionally an adhesive layer for attaching the protective structure to the interior surface of the battery enclosure.

[0068] In this embodiment, the functional layer provides the outermost layer of the protective structure during use and is exposed to the internal environment of the battery enclosure.

[0069] The adhesive layer, if present, provides the innermost layer during use and may include a contact adhesive film with a protective film (i.e. a double-sided adhesive film) to allow easy bonding to the surface to be protected, this effect can also be achieved by mechanical fastening or application of a wet contact adhesive.

[0070] [Functional Layer] The functional layer is the cured reaction product of a mixture having the components listed below: In Example 2, the functional layer includes flame retardants and fire resistant materials dispersed in the cured polymer.

[0071] [Table 2]

[0072] [Reinforcement layer] The reinforcing layer is in the form of a reinforcing sheet comprising a fabric. In this embodiment, the fabric is made of fiberglass, typically high silica glass. The fabric has a weight of 200-1600 gsm, and may have a weight of 600 gsm. The fabric is a high temperature fabric or felt of sufficient thickness to withstand a 1200°C gas jet without melting.

[0073] Example 2 provides resistance to penetration during a thermal runaway event. As detailed above, Example 2 is comprised of an exterior / exposed surface functional layer. Fire retardants and fire resistant materials are added to the functional layer to form a hard, resistant char. The functional layer is the primary layer of defense against erosion. The functional layer is applied to the reinforcing layer to provide structure, resistance to the pressure of gas jets, and additional resistance to penetration and erosion.

[0074] [Protective Structure (Example 3)] A third embodiment of the protective structure was comprised of a functional layer, a reinforcing layer, and optionally an adhesive layer for attaching the protective structure to the interior surface of the battery enclosure.

[0075] In this embodiment, the functional layer provides the outermost layer of the protective structure during use and is exposed to the internal environment of the battery enclosure.

[0076] The adhesive layer, if present, provides the innermost layer during use and may include a contact adhesive film with a protective film (i.e. a double-sided adhesive film) to allow easy bonding to the surface to be protected, this effect can also be achieved by mechanical fastening or application of a wet contact adhesive.

[0077] [Functional Layer] The functional layer is the cured reaction product of a mixture having the components listed below: In Example 3, the functional layer includes an expanding additive dispersed in the cured polymer.

[0078] [Table 3]

[0079] [Reinforcement layer] The reinforcing layer is in the form of a reinforcing sheet comprising a substrate, in this embodiment the substrate is glass paper, the substrate having a weight of 50 to 250 gsm.

[0080] Example 3 provides thermal insulation and heat absorption during a thermal runaway event.

[0081] In this example, the outermost layer of the protective structure in use is a functional layer containing an intumescent additive that expands by more than three times and provides a low density char. This functional layer is very insulating but vulnerable to erosion and therefore not suitable for areas close to the first vent where gas velocities are high.

[0082] The reinforcing layer here is not so important since it is not intended to resist penetration. The reinforcing layer is usually a thinner and cheaper layer (compared to Examples 1 and 2 above), such as glass paper. The function of the reinforcing layer is mainly to provide a substrate on which the functional layer (i.e. the intumescent membrane) rests, and also to provide a key layer for the adhesive membrane (if present).

[0083] [Protective Structure (Example 4)] A fourth embodiment of the protective structure was comprised of a functional layer, a reinforcing layer, and optionally an adhesive layer for attaching the protective structure to the interior surface of the battery enclosure.

[0084] In this embodiment, the functional layer provides the outermost layer of the protective structure during use and is exposed to the internal environment of the battery enclosure.

[0085] The adhesive layer, if present, provides the innermost layer during use and may include a contact adhesive film with a protective film (i.e. a double-sided adhesive film) to allow easy bonding to the surface to be protected, this effect can also be achieved by mechanical fastening or application of a wet contact adhesive.

[0086] [Functional Layer] The functional layer is the cured reaction product of a mixture having the components listed below: In Example 4, the functional layer includes an expanding additive dispersed in the cured polymer.

[0087] [Table 4]

[0088] [Reinforcement layer] The reinforcing layer is in the form of a reinforcing sheet comprising a substrate, in this embodiment the substrate is glass paper, the substrate having a weight of 50 to 250 gsm.

[0089] Example 4 provides thermal insulation and heat absorption during a thermal runaway event.

[0090] In this example, the outermost layer of the protective structure in use is a functional layer containing an intumescent additive that expands by more than three times and provides a low density char. This functional layer is very insulating but vulnerable to erosion and therefore not suitable for areas close to the first vent where gas velocities are high.

[0091] The reinforcing layer here is not so important since it is not intended to resist penetration. The reinforcing layer is usually a thinner and cheaper layer (compared to Examples 1 and 2 above), such as glass paper. The function of the reinforcing layer is mainly to provide a substrate on which the functional layer (i.e. the intumescent membrane) rests, and also to provide a key layer for the adhesive membrane (if present).

[0092] [Protection structure (Example 5)] A fifth embodiment of the protective structure was comprised of a functional layer, a reinforcing layer, and optionally an adhesive layer for attaching the protective structure to the interior surface of the battery enclosure.

[0093] In this embodiment, the reinforcing layer provides the outermost layer of the protective structure, in use, and is exposed to the internal environment of the battery enclosure.

[0094] The adhesive layer, if present, provides the innermost layer during use and may include a contact adhesive film with a protective film (i.e. a double-sided adhesive film) to allow easy bonding to the surface to be protected, this effect can also be achieved by mechanical fastening or application of a wet contact adhesive.

[0095] [Functional Layer] The functional layer is the cured reaction product of a mixture having the components listed below: In Example 5, the functional layer includes an expanding additive dispersed in the cured polymer.

[0096] [Table 5]

[0097] [Reinforcement layer] The reinforcing layer is in the form of a reinforcing sheet comprising a fabric. In this embodiment, the fabric is made of fiberglass, typically high silica glass. The fabric has a weight of 200-1600 gsm, and may have a weight of 600 gsm. The fabric is a high temperature fabric or felt of sufficient thickness to withstand a 1200°C gas jet without melting.

[0098] Example 5 combines the functional layers of Examples 3 and 4 with the reinforcing layers of Examples 1 and 2, except that in Example 5, the reinforcing layer is the outermost layer of the protective structure during use that is exposed to the internal environment of the battery enclosure.

[0099] The functional layer containing the intumescent additive is applied to the inner surface of the reinforcement layer fabric. The char formed from the functional layer, while still vulnerable to erosion, is protected by the outer reinforcement layer during initial exposure to vent gases, and can then safely react to prolonged heat to insulate the substrate.

[0100] In the above embodiments 1-5, the functional layer comprises a cured polymer formed from a mixture comprising one or more curable polymers and a crosslinker. The crosslinker comprises a crosslinkable functional group and the curable polymer comprises a crosslinkable functional group. In the above embodiments, the functional layer can be formed by combining a first portion of the mixture with a second portion of the mixture. The first portion comprises a curable polymer for forming a cured polymer and the second portion comprises a crosslinker. The second portion may also optionally comprise a catalyst. The remaining components (i.e., additives) are provided to either the first portion and / or the second portion. The first portion and / or the second portion may also comprise additional components (i.e., additives), such as wetting agents, dispersants, surfactants, solvents, or rheology modifiers, as is conventional.

[0101] The reaction to form the functional layer may be initiated by combining the first and second portions. The curable polymer reacts with the crosslinker to form a cured polymer. Thus, an example functional layer includes a cured polymer with the remaining ingredients (i.e., additives) dispersed in the cured polymer.

[0102] In other examples, the functional layer may be formed from a one-part mixture that cures in response to exposure to an environmental stimulus, for example. The environmental stimulus may be UV light, or alternatively, the presence of moisture and / or oxygen upon exposure to the atmosphere. The curable polymer and crosslinker may be exposed to the atmosphere following evaporation of an organic solvent in the mixture, or by opening a container holding the mixture. The environmental stimulus activates the crosslinker that includes a crosslinkable functional group and / or the curable polymer that includes a crosslinkable functional group, allowing the curing reaction to proceed. When the functional layer is formed from a one-part mixture, in some examples, the crosslinker may be integrated into the curable polymer molecule such that the polymer is self-crosslinking (i.e., the crosslinker that includes a crosslinkable functional group and the curable polymer that includes a crosslinkable functional group are present in the same molecule). Exemplary cured polymers formed from one-part mixtures include drying oils or alkyd resins.

[0103] In some embodiments, the mixture comprises 10-50 wt.% of the curable polymer and crosslinker. Preferably, the mixture comprises 20-40 wt.% of the curable polymer and crosslinker.

[0104] In some embodiments, the curable polymer comprises a silicone polymer and the cross-linking agent comprises a silicone cross-linking agent, which upon curing forms a cured silicone polymer. Silicone polymers are particularly flexible, imparting this property to the functional layer. The resulting flexibility of the functional layer allows the protective structure to easily conform to curved surfaces within the battery enclosure.

[0105] A catalyst, such as a hydrosilylation catalyst, may also be added to the mixture to accelerate the curing process. Alternatively or additionally, the curable polymer could include an epoxy and / or silane terminated polymer with a corresponding crosslinker, as illustrated above in Examples 2 and 4. In Examples 2 and 4, the mixture includes a curable polymer that is bisphenol A and a silane terminated polyether, along with a crosslinker that is isophorone diamine and aminopropyltrimethoxysilane.

[0106] In some embodiments, the functional layer comprises 3-40 wt.% of the flame retardant. Preferably, the functional layer comprises 5-30 wt.% of the flame retardant. Most preferably, the functional layer comprises 15-25 wt.% of the flame retardant.

[0107] Preferably, the flame retardant comprises an endothermic additive, such as an inorganic salt. The inorganic salt may be aluminum trihydroxide, magnesium dihydroxide, or ammonium polyphosphate. In some embodiments, the flame retardant comprises a further endothermic additive. The further endothermic additive could be, for example, a different inorganic salt. In the above examples 1 and 2, the flame retardant comprises aluminum trihydroxide and ammonium polyphosphate.

[0108] In some embodiments, the functional layer comprises 3-45 wt.% of the fire-resistant material. Preferably, the functional layer comprises 5-22 wt.% of the fire-resistant material.

[0109] In some embodiments, the refractory material comprises a mineral or ceramic. Preferably, the refractory material comprises mica, clay, organoclay, talc, ceramic fiber, or borate. The functional layer may comprise 3-40 wt.% mica powder. Preferably, the functional layer comprises 5-20 wt.% mica powder. In some embodiments, the functional layer also comprises up to 5 wt.% organoclay, which is also a refractory material. Preferably, the functional layer comprises 0.5-2 wt.% organoclay. In the above examples 1 and 2, the organoclay is Addins® Clay 20 by Tolsa®.

[0110] In some embodiments, the functional layer comprises a vitrifiable additive dispersed in the cured polymer. Preferably, the vitrifiable additive comprises a glass frit or a ceramifying agent. The functional layer may comprise 5-35 wt.% of the vitrifiable additive. Preferably, the functional layer comprises 15-25 wt.% of the vitrifiable additive.

[0111] The functional layer may contain 1 to 75 wt.% of the expansion additive, preferably 10 to 60 wt.% of the expansion additive.

[0112] In some embodiments, the expansion additive includes a phosphorus-containing compound, a gas source, and a carbon source. The phosphorus-containing compound could be, for example, ammonium polyphosphate, triphenyl phosphate, or aluminum phosphinate. The gas source could be, for example, melamine or boric acid. The carbon source could be, for example, pentaerythritol or tris-(2-hydroxyethyl)isocyanurate.

[0113] The expanding additive may comprise 10 to 40 wt.% ammonium polyphosphate. Preferably, the expanding additive may comprise 20 to 35 wt.% ammonium polyphosphate. The expanding additive may comprise 5 to 25 wt.% melamine. Preferably, the expanding additive may comprise 7 to 15 wt.% melamine. The expanding additive may comprise 2 to 25 wt.% pentaerythritol. Preferably, the expanding additive may comprise 2 to 12 wt.% pentaerythritol. The expanding additive may comprise 2 to 25 wt.% titanium dioxide. Preferably, the expanding additive may comprise 2 to 12 wt.% titanium dioxide. The expanding additive may comprise 0.5 to 10 wt.% zinc borate. Preferably, the expanding additive may comprise 0.5 to 5 wt.% zinc borate.

[0114] In some embodiments, the functional layer may include reinforcing fibers dispersed in the cured polymer. The reinforcing fibers act as strength members. The reinforcing fibers may be basalt fibers, glass fibers, ceramic fibers, carbon fibers, and / or mineral fibers.

[0115] In some examples, the mixture for forming the functional layer may include one or more processing aids. The one or more processing aids may include at least one of a solvent, a rheology modifier, or a dispersant. The mixture may include up to 20 wt.% of a solvent, preferably the mixture includes 5-11 wt.% of a solvent. The mixture may include up to 2 wt.% of a rheology modifier, preferably the mixture includes up to 0.7 wt.% of a rheology modifier. The mixture may include up to 5 wt.% of a dispersant, preferably the mixture includes up to 1.5 wt.% of a dispersant. Example 1 and Example 2 each include a dimethyl carbonate solvent. Example 2 includes a 7420ES rheology modifier from REOVIK® and a BS1316 dispersant from ZILRES®.

[0116] In the embodiments described above, the functional layer is formed by curing a mixture that includes at least one curable polymer to form a cured polymer, a crosslinker to form a cured polymer, and either a flame retardant and fire resistant material or an intumescent additive. The mixture may include additional components as set forth above in connection with Examples 1-5.

[0117] In other embodiments, the functional layer may be formed by drying a mixture including cured polymer particles dispersed in a solvent and either a flame retardant and fire resistant material or an intumescent additive. The mixture may include additional components as set forth above in connection with Examples 1-5. The functional layer is formed once the solvent has evaporated. The solvent may be a volatile organic solvent (such as hexane or xylene) or water. The cured polymer particles could be made of, for example, an acrylic resin.

[0118] [Example method] An embodiment of the present disclosure also provides a method of forming a protective structure according to an embodiment of the present disclosure. The method includes mixing the components of any of the mixtures described herein, for example to form a functional layer. The mixture includes at least one curable polymer and a crosslinker to form a cured polymer. The method further includes allowing the mixture to cure in the presence of a reinforcing layer to provide the protective structure. If the mixture includes cured polymer particles dispersed in a solvent, the method further includes allowing the mixture to dry in the presence of a reinforcing layer to provide the protective structure.

[0119] In a first embodiment of the method, the method includes applying a mixture for forming a functional layer to a first side of a reinforced sheet as described herein and allowing the mixture to dry or cure. The mixture may be smoothed once applied to the reinforced sheet to ensure a uniform thickness of the mixture on the reinforced sheet before the mixture dries or cures.

[0120] In some examples of the first embodiment, the mixture is manually applied to the reinforced sheet and then manually smoothed using a film casting knife. In other examples, the reinforced sheet is fed over one or more rollers and the mixture is applied via one or more nozzles positioned above the reinforced sheet passing over the rollers. The sheet may be fed between the rollers and a blade that smoothes the mixture on the sheet once the mixture has been applied. This is known as a "knife-over-roll" process. To ensure that the coating of the mixture on the sheet is uniform, the blade may be positioned a predetermined distance away from the roller. The coated sheet is then optionally moved to an oven for accelerated curing and / or drying. The oven may be at a temperature of 100°C to 200°C, for example 160°C.

[0121] In a second embodiment of the method, the method includes the step of adding reinforcing fibers to the mixture. In the second embodiment, the mixture for forming the functional layer may be applied to a sheet / layer and allowed to cure / dry using the same example steps as described above in relation to the first embodiment. However, in the second example, the mixture is applied to a removable backing sheet or adhesive layer rather than directly to the reinforcing sheet as described in the first embodiment. After the mixture has cured and / or dried, the resulting functional layer may be applied to the reinforcing sheet to provide a protective structure. In such an example, the reinforcing members are also dispersed in the cured polymer of the functional layer.

[0122] In some embodiments, an adhesive layer may be added to the protective structure after the curable polymer has cured and / or dried. In one embodiment, a double-sided adhesive tape is applied to one side of the protective structure. The double-sided adhesive tape is often provided with a non-adhesive film that protects each side of the adhesive tape. When applying the tape to the protective structure, the non-adhesive film on only one side of the tape may be removed, and the other side of the tape remains non-adhesive, which allows for easy transportation. The non-adhesive film on the other side of the tape can then be removed when the protective structure is being applied to the surface of the battery enclosure. In another embodiment, instead of the adhesive tape, an adhesive spray is applied to the protective structure. In some embodiments, the adhesive is preferably applied to the reinforcement layer rather than the functional layer.

[0123] In embodiments where the protective structure is for protecting an interior surface of a battery enclosure, the protective structure may be provided in the form of a rolled sheet and then cut to fit an interior surface of the battery enclosure, such as the inner surface of a wall of the battery enclosure. Alternatively, the protective structure may be provided as a pre-cut piece to fit the wall of the battery enclosure. The protective structure could be cut into multiple pieces to cover complex shapes.

[0124] The protective structure is then attached to an interior surface of the battery enclosure, such as a wall of the battery enclosure. The protective structure may be applied to the interior surface of the wall of the battery enclosure, and in some embodiments the protective structure covers substantially the entire surface of the wall. In other embodiments the protective structure covers only a portion of the wall. This portion could be a weak portion of the wall. This weak portion of the wall may be located such that it will be directly affected by venting gases from a thermal runaway event. The battery enclosure may form part of a vehicle, such as an electric car.

[0125] In embodiments where the protective structure is for protecting an internal surface of a battery enclosure and the protective structure includes an adhesive layer, the protective structure may be attached to the internal surface of the battery enclosure using an adhesive. Alternatively or additionally, the protective structure may be mechanically attached to the internal surface. Mechanical attachment could include fastening the protective structure to the wall using one or more fasteners, such as staples or rivets. Alternatively, holes could be provided in the wall of the enclosure to insert at least a portion of the protective structure. In other embodiments, the protective structure may be overmolded with the battery enclosure. In the case of overmolding, the material forming the protective structure is placed into a tool and a liquid resin (or polymer melt, or SMC / DMC preform) that constitutes the structure or part of the battery enclosure is injected or placed. The tool is compressed, or the resin is cured, melted and cooled, etc. The structure or part associated with the battery enclosure is then removed from the tool, and the protective structure becomes a permanent layer of the structure or part of the battery enclosure.

[0126] Thus, a protective structure having many advantages as described above and in more detail below, a battery enclosure including the protective structure, a vehicle including the battery enclosure, a method of forming the protective structure, and a method of protecting a battery enclosure are described.

[0127] The battery enclosure is provided with the described protective structure and is resistant to high heat, high pressure and high mechanical stresses caused within the enclosure by a thermal runaway event. The protective structure can be easily applied to the surface of the battery enclosure. For example, a single user can manually apply the protective structure without the need for complex equipment. Furthermore, the protective structure is less expensive, less bulky and lighter than known solutions to suppress thermal runaway in battery enclosures. By using a functional layer, the thickness of the protective structure can be tightly controlled across its width to maintain consistent protection and avoid weak spots. The functional layer of the protective structure also prevents fibers from falling into, for example, the battery enclosure.

[0128] Therefore, embodiments of the present disclosure protect the battery pack casing (i.e., the battery enclosure) from either internal thermal runaway or external fire attack that would lead to thermal runaway. Battery pack casings are typically made of sheet steel, aluminum, SMC / DMC, composites, or even thermoplastics.

[0129] Thermal runaway usually starts in a single cell, but can progress to include most or all of the cells in the pack. When the lead cell is triggered (by heat, overcharging, internal short circuit, external short circuit, or mechanical damage), very hot gases and molten metal (about 1200C) will be ejected very quickly. This jet can sever the internal partitions in the battery pack and trigger other cells, or it can sever the external casing and cause an uncontained fire. If battery pack elements are directly exposed to the vent jet, they need to be protected from penetration or destruction by a protective layer. Even in the case of steel, which the jet will not penetrate, the heating effect will make the opposite side of the partition or casing hot enough to ignite materials outside the pack.

[0130] Protection against penetration must be provided by a material that has good resistance to the abrasive effects of hot gas jets, usually very high temperatures, resistance to the formation of hard glassy carbides, resistance to wear, and some degree of thermal insulation to protect the substrate. This is achieved at least by Examples 1 and 2 above.

[0131] Some distance from the direct gas jet, there may still be very high temperatures and turbulent flames as the released energy and material spreads through the open space in the pack and escapes through the pressure relief device. This is known as the vent path. Typically, there will be vulnerable materials in the vent path, such as insulating bus bars, wiring and circuits / electronics, cooling pipes, electrical insulation layers, and even the material of the battery casing or partitions in the vent path may be vulnerable. This application does not require the same degree of resistance to penetration or erosion, but it is important that a good level of insulation and / or heat absorption is provided, as materials may be more vulnerable to temperature increases. This is achieved by at least Example 3 and Example 4 above.

[0132] Further applications are found where a high degree of insulation is required along with a high degree of resistance to erosion. Erosion can occur when weak members are located very close to the point of initial venting and also when the internal temperature rise can become very high and last for a long time as multiple cells propagate within the pack. This means that not only must the pack casing withstand initial damage from direct exhaust, but the pack casing material must be insulated to prevent melting of the pack casing material (in the case of aluminum) or burning of the resin (in the case of SMC / DMC, composites or polymeric materials) or excessive heat transfer (especially in the case of steel). This is a longer term failure mode, but again, it can result in structural failure of the pack and uncontained fire. This is achieved at least by Example 5 above.

[0133] In the preceding paragraphs, embodiments of the invention have been described with reference to various examples, but it should be recognized that a given example can be modified without departing from the scope of the invention as claimed. For example, the ratio of each component of the mixture for forming the functional layers can be varied to provide a required degree of protection of the battery enclosure or to vary the flexibility of the protective structure. For example, different numbers or thicknesses of functional layers may be provided to provide different levels of protection. The protective structure could be provided in a number of shapes. The protective structure would not have to be applied directly to the walls of the battery enclosure. For example, the protective structure could be applied to a coating on the walls, such as a corrosion resistant coating. The protective structure could also be applied to an electromagnetic compatibility shield provided on the inside of the walls, rather than directly on the walls. The battery enclosure may contain lithium ion cells or other types of battery cells. The battery enclosure could be used in a variety of applications, such as electric vehicles, household, aerospace equipment, or marine equipment.

[0134] Each of the additives described herein may include a single composition or multiple compositions. For example, an expansion additive may include multiple components in the form of a phosphorus-containing compound, a gas source, and a carbon source.

[0135] In this document, the term "comprise" is used in an inclusive sense, not a limiting sense, i.e., any reference to X containing Y indicates that X may contain only one Y or may contain two or more Y. If it is intended to use "comprise" in a limiting sense, this will be made clear in the context by mentioning "containing only one" or by using "consisting of".

[0136] Various embodiments have been referenced in this description. The description of features or functions in relation to an embodiment indicates that the features or functions are present in that embodiment. Use of the terms "embodiment" or "for example" or "can" or "may" in this text indicates that such features or functions are present in at least the described embodiment, whether or not they are described as an embodiment, whether or not they are explicitly stated, and that these features or functions may, but are not necessarily, present in some or all other embodiments. Thus, "embodiment", "for example", "can" or "may" refers to a particular instance in a class of embodiments. The characteristics of that instance may be characteristics of that instance only, or of the class, or of a subclass of that class that includes some, but not all, instances in the class. Thus, it is implicitly disclosed that a feature described with reference to one embodiment but not to another embodiment can be used in that other embodiment as part of a practical combination, where possible, but not necessarily in that other embodiment.

[0137] The features described in the preceding description may be used in combinations other than those explicitly described above. For example, the layers may be provided in a different order. A single protective structure may be applied to a single wall of the enclosure. Multiple protective structures may be applied to a single wall, or a single protective structure may be applied to multiple walls. A protective structure may cover one, some or all of the interior surfaces of the walls of the battery enclosure.

[0138] Although functions have been described with reference to particular features, those functions may be implemented with other features whether or not described.

[0139] Although features have been described with reference to particular embodiments, those features may be present in other embodiments whether or not they are described.

[0140] In this document, the terms "a" or "the" are used in an inclusive sense, not a limiting sense. That is, unless the context clearly indicates the contrary, any reference to X including a / the Y indicates that X may include only one Y or may include two or more Y. If "a" or "the" is intended to be used in a limiting sense, this will be clear in the context. In some situations, the use of "at least one" or "one or more" may be used to emphasize an inclusive sense, but without these terms, no limiting sense should be construed as being implied.

[0141] The presence of a feature (or combination of features) in a claim refers to the feature or (combination of features) per se, and also to features that achieve substantially the same technical effect (equivalent features). Equivalent features include, for example, features that are modifications and achieve substantially the same result in substantially the same way. Equivalent features include, for example, features that perform substantially the same function in substantially the same way to achieve substantially the same result.

[0142] In this description, adjectives or adjectival phrases have been used to refer to various embodiments and to describe features of the embodiments. Such a description of a feature in connection with an embodiment indicates that in some embodiments the feature is present exactly as described and in other embodiments the feature is present generally as described.

[0143] Although an effort has been made in the foregoing specification to draw attention to the features which are believed to be important, it should be understood that applicant may seek protection through the claims with respect to any patentable feature or combination of features previously referenced and / or shown in the drawings, whether emphasized or not.

Claims

1. 1. A protective structure for protecting a battery enclosure, comprising: a functional layer comprising a cured silicone polymer, the functional layer comprising a flame retardant and a fire resistant material dispersed in the cured silicone polymer, or a functional layer comprising an expansion additive dispersed in the cured silicone polymer; Reinforcement layer and 1. A protective structure comprising:

2. 10. The protective structure of claim 1 for protecting an interior surface of the battery enclosure.

3. 3. The protective structure of claim 2, wherein, during use, the functional layer of the protective structure is the outermost layer of the protective structure and is exposed to the internal environment of the battery enclosure.

4. 3. The protective structure of claim 2, wherein, in use, the reinforcing layer of the protective structure is the outermost layer of the protective structure and is exposed to the internal environment of the battery enclosure.

5. 10. The protective structure of claim 1, wherein the reinforcing layer is in the form of a reinforcing sheet comprising fabric or mesh.

6. 6. The protective structure of claim 5, wherein the fabric or mesh is at least partially made from fiberglass, basalt, mineral, ceramic, carbon, or steel.

7. 6. A protective structure according to claim 5, wherein the reinforcing sheet comprises a fabric having a weight of between 50 and 1600 gsm.

8. 6. A protective structure according to claim 5, wherein the reinforcing sheet comprises a fabric having a weight of 50 to 250 gsm.

9. 6. A protective structure according to claim 5, wherein the reinforcing sheet comprises a fabric having a weight of between 200 and 1600 gsm.

10. 10. The protective structure of any one of claims 1 to 9, wherein the flame retardant comprises an endothermic additive.

11. 11. The protective structure of claim 10, wherein the endothermic additive comprises an inorganic salt.

12. 12. The protective structure of claim 11, wherein the inorganic salt is aluminum trihydroxide, magnesium dihydroxide, or ammonium polyphosphate.

13. The protective structure of any one of claims 1 to 9, wherein the refractory material comprises mica, clay, organoclay, talc, ceramic fiber, or borate.

14. The protective structure of any one of claims 1 to 9, wherein the expansion additive comprises a phosphorus-containing compound, a gas source, and a carbon source.

15. 15. The protective structure of claim 14, wherein the phosphorus-containing compound comprises ammonium polyphosphate, triphenyl phosphate, or aluminum phosphinate, the gas source comprises melamine or boric acid, and the carbon source comprises pentaerythritol or tris-(2-hydroxyethyl)isocyanurate.

16. 10. The protective structure of claim 1, wherein the functional layer comprises a vitrifiable additive dispersed in the cured silicone polymer, the vitrifiable additive comprising a glass frit or a ceramifying agent.

17. 10. The protective structure according to any one of claims 1 to 9, wherein the functional layer has a thickness of 50 to 1000 microns.

18. The protective structure according to any one of claims 1 to 9, further comprising an adhesive layer for attaching the protective structure to a surface of a battery enclosure.

19. 20. The protective structure of claim 18, wherein the adhesive layer comprises a double-sided adhesive film.

20. A protective structure according to any one of claims 1 to 9, which is flexible.

21. The protective structure of any one of claims 1 to 9, wherein the protective structure has a thickness of 50 to 5000 microns.

22. A battery enclosure comprising a protective structure according to any one of claims 1 to 9.

23. 23. The battery enclosure of claim 22, including at least a first wall, the reinforcement layer being disposed at least partially between the first wall and the functional layer.

24. 23. The battery enclosure of claim 22, including at least a first wall, the functional layer being disposed at least partially between the first wall and the reinforcing layer.

25. A vehicle comprising a battery enclosure according to any one of claims 22 to 24.

26. A method for protecting a battery enclosure, comprising the step of attaching a protective structure according to any one of claims 1 to 9 to a surface of the battery enclosure.

27. 27. The method of claim 26, including attaching the protective structure to an interior surface of a battery enclosure.