Flame resistant shield for a battery module for a battery electric vehicle

Abstract

Flame resistant shield blank for covering more than one side of a battery pack or battery module, comprising a main plate and at least one flap cut from the same material blank and whereby the main plate and the at least one flap are adjacent and connected to each other, and whereby the connection comprises at least one bridging element, which at least partly breaks or deforms upon folding the flame resistant shield blank into its final shape.

Description

DescriptionFlame resistant shield for a battery module for a battery electric vehicleTechnical Field

[0001] Flame resistant shield blank and a flame resistant shield formed from the flame resistant shield blank as well as a process of making both.Background Art

[0002] Flame resistant shield for covering battery modules or full battery packs inside a traction battery box are known in the industry. They are needed to prevent any debris, fire, or smoke from escaping the battery box in the case of a battery thermal runaway event. In a thermal runaway event, a fault in the battery may cause contact between the chemical phases within the battery cumulating in a chemical fire that produces its own oxygen and is difficult to stop. Not only the overall temperature increases to a high level very rapidly, also internal explosive reactions may catapult material to the walls of the enclosure. Hence, the main reason for a full enclosure and an internal flame resistant shield is to prevent further damage to the surrounding by flying objects, flames, fumes or debris.

[0003] Related to the severity of such a thermal runaway event, the materials used are highly impact resistant and should not cause any cracks or breakage during a thermal event, that may cause additional damage. Hence the materials used are all in the form of highly rigid plates with a high inert fiber filler content, preferably composites with glass fibers or endless filaments. Although these materials can be formed in a 3 D structure, the limited space provided inside a battery box around the battery modules or battery pack as well as the resulting lack of draft angle of the materials makes it difficult to obtain a good fitting structure. So today these materials are mainly used as a flat top cover on top of the battery cells, modules or full pack within the battery box. Often under the actual battery box lid. While the battery box is made of thick metal, the main purpose of the flame resistant shield is to ward of any flames, impacting debris and the heat itself.

[0004] The current material used for creating flame resistant shields is very rigid and standard folding techniques cannot be used, as the occurrence of fold lines cannot be predicted and any fold line may cause a weakness of the material. Unpredictable weakness areas can cause the part to fail at an early state during a thermal runaway event.

[0005] Finished 3D structures are furthermore expensive in logistics and transport as a high volume per part is transported, making efficient stacking difficult or expensive. While a breakage or damage to the formed parts may impair the final fit as a cover.

[0006] Related to the actual nature of a thermal runaway event, there is still a need for a more 3 dimensional covering option, that is able to fit in a tight space as well as optimises transport. Hence, It is a goal to provide for an alternative solution, that maintains the level of protection on the material level but makes it possible to extend the coverage to multiple sides of the battery module or pack.Summary of invention

[0007] The object of the invention is achieved by a flame resistant shield blank for covering more than one side of a battery pack or battery module, a flame resistant shield produced using such a flame resistant shield blank and a method of producing the flame resistant shield blank and the flame resistant shield.

[0008] In particular, a flame resistant shield blank comprising a main panel and at least one flap cut from one material blank, and whereby the main plate and the at least one flap are adjacent and connected to each other, and whereby the connection comprises at least one bridging element, which at least partly breaks or deforms upon folding the flame resistant shield blank into its final shape.

[0009] Surprisingly, it is possible to create a flame resistant shield blank comprising multiple plates whereby adjacent plates maintain connected to each other with bridging elements.

[0010]

[0011] For the sake of clarity, flaps and main panel are all made of the same material and may be overall being perceived as plates being connected toadjacent plates by connecting bridges forming together one flame resistant shield blank in a distinct pattern that may be folded into a flame resistant shield with a desired 3D shape. The use of main panel and flaps enables the folding and forming process by defining a base or reference surface from which the folding proceeds to create the final form. However, one flame resistant shield form may have different possibilities for the flame resistant shield blank and an optimised cutting and folding process, may provide one or more option or combined options to achieve the same form. For instance a nesting of two forms to achieve the same final flame resistant shield may be used to achieve an optimised material utilisation.

[0012]

[0013] Preferably, the material blank comprises at least one rigid flame resistant layer. The rigid flame resistant layer may consist of a fibrous material, like a textile or nonwoven, impregnated with a thermoplastic or thermoset material such that the final layer has a flame resistance up to temperatures of at least 1100°C.

[0014]

[0015] A preferred flame resistant shield blank according to the invention may have each flap separated from the main plate by a partial cut through the at least rigid layer while leaving bridging elements in the rigid layer as connecting elements. These partial cut lines will function in a second stage as fold lines for forming the final flame resistant shield shape.

[0016] In a preferred embodiment additional flaps or tabs maybe placed adjacent and connected to the flaps. These maybe smaller flaps that overlap with the adjacent plate to form an overlapping joint or it may form further walls either as an outside structure of the flame resistant shield or as an internal separation wall for the flame resistant shield, to be able to further separate battery units or auxiliary appliances within the battery module or pack.

[0017] Preferably the plate or flaps, preferably along the edges being in contact with other flaps, may further have notches, slots or other design elements to aid either the folding or the connection between the adjacent and contacting plates or flaps. The flame resistant shield blank may have other cut outs to aid the coverage or to function as pass through enablingappliances reaching the battery cell, module or pack covered by the formed flame resistant shield.

[0018] A preferred flame resistant shield blank comprises at least a main plate and at least 4 flaps arranged along the sites of the main plate such that upon folding, the plate and flaps form a shape that fits over a battery module or battery pack to be covered.

[0019] In an alternative embodiment a flame resistant shield may comprise at least one or more flame resistant shield blanks whereby some of the main plate or flaps may be folded to become an inside wall or divider within the final formed flame resistant shield.

[0020] Most folds formed will create an angle of between 60 and 120°, preferably close to 90° between the two surfaces of the adjacent plates or flap in the inside corner.

[0021] The flame resistant shield blank according to the invention may further comprise an at least partial coverage of at least one surface with a flexible flame resistant layer, preferably at least one of a flexible tape, sealant, film or foil. This at least partial coverage is preferably at least over the area flanking a folding line with a flexible flame resistant layer, preferably a tape, sealant, film or foil, such that the flexible layer provides the connection between the main plate and the at least one flap when folded in the final shape and the bridging elements are at least partly broken or deformed. The flexible layer may be flexible during folding and may be cured into a rigid bond after forming the final flame resistant shield form. This curing may be aided with thermal treatment, UV treatment or applying a pressure on the area or full part.

[0022]

[0023] The flame resistant shield blank is made of one material blank comprising at least one flame-resistant layer. The flame resistant layer may consist of a composite comprising a reinforcing fiber or filament, preferably a fibrous material like a nonwoven or a textile impregnated with a matrix material chosen from at least one of polyurethane, polyisocyanurate, epoxy or silicon, and wherein the composite material has a flame resistance of up to at least 1100°C and wherein the matrix material impregnates the fibrousmaterial in such a way that the flame-resistant layer is impervious to airflow.

[0024] Preferably the flame resistant is further optimised by ensuring that all fibrous material is covered such that no fiber ends are sticking out of the surface of the flame resistant shield blank facing the possible source of ignition, like the battery cells. Preferably an addition coat of preferably the same matrix material or a similar material is applied on top of the flame resistant shield blank.

[0025]

[0026] In one preferred embodiment the fibers or filaments used, for instance in the form of a nonwoven web, are bonded by means of a thermoset binder before being impregnated with the final matrix material like for instance polyurethane. Preferably a water based acrylic binder is used for the prebonding step.

[0027] The thickness of the flame-resistant layer may comprise between 0.5 mm and 7mm, preferably between 0.5mm and 5mm and more preferably between 0.7mm and 3mm.

[0028] The density of the flame-resistant layer may comprise between 800kg / m3and 2500kg / m3, preferably between 1000kg / m3and 1800kg / m3.

[0029] The weight of the fibrous material within the flame resistant layer may be between 40% and 80% of the total weight of the flame-resistant layer, preferably between 50% and 70%. The flame resistant layer may comprise of multiple layer together forming the flame resistant layer, for instance including organo sheets or unidirectional tapes to further increase the impact performance of the sheets.

[0030] Alternatively, the material blank for the flame resistant shield blank is a mica based material, for instance the rigid flame resistant layer may comprise of mica platelets and a binder forming a plate-like structure such that the rigid flame resistant layer has a flame resistance up to at least 1100°C.

[0031]

[0032] In an alternative embodiment the flame resistant shield blank is covered at least on one side of the blank with an additional flame resistant layer overthe full plate including the cut areas comprising the bridging elements according to the invention. Upon folding the flame resistant shield blank in the final form the bridges are broken or deformed to enable the folding, while the film follows the new shape to close and seal the folded structure. The film or foil applied may partly cut larger than the flame resistant shield blank to form overlapping areas that may be used to sealing and closing the new formed corners where edges of adjacent flaps meet during folding and shaping the final structure.

[0033] The fibrous material may comprise fibers and or endless filaments.

[0034] The fibers or filaments may be at least one of ceramic fibers, glass fibers, carbon fibers, mineral-based fibers, oxidized poly-acrylo-nitrile fibers.

[0035] In case staple fibers are used, an average length for at least 80% of the fibers is preferably between 20mm and 150mm, more preferably between 30mm and 80mm and even more preferably comprised between 40mm and 60mm.

[0036] The fibrous material may comprise fibers bonded by means of a thermoset binder before being impregnated with the matrix material, preferably the prebonding may be done with a thermoset binder.

[0037] Polyurethane or polyisocyanurate may be preferably used as a possible matrix and or pre-binder may be obtained from the reaction of a polyurethane-forming-mixture or a polyisocyanurate-forming mixture, preferably without any blowing agent. The polyurethane or polyisocyanurate may be applied as an in-mould reacting mixture, impregnating the fibrous material and forming the flame resistant shield blank in an one step process. Preferably the mould used may incorporate the final form and may apply an in-mould cutting for the folding lines and or the outline of the flame resistant shield, leaving the bridging elements uncut.

[0038] The pre-bonding material as well as the matrix material may further comprise flame retarding agents or additives.

[0039] Optionally a mica layer may be placed between at least two fibrous layer before the impregnation with the matrix material. The mica enhances the flame resistant properties of the rigid flame resistant layer.

[0040]

[0041] A process for making a flame resistant shield blank according to the invention comprising at least the following steps:- providing a fibrous material wherein the fibers and or filaments comprised in the fibrous material, preferably in the form of a web, nonwoven or fabric;- spreading a matrix forming mixture onto the fibrous material;- thermally compressing the thus formed stack such that the matrix is impregnating the fibrous material and fully engulfs the fibers and or filaments, while most gas bubbles may be compressed out of the layer forming a impervious rigid flame resistant layer having a flame resistance up to at least 1100°C;- cutting the thus formed rigid flame resistant layer into flame resistant shield blanks comprising multiple plates, with at least one plate forming a panel and at least one plate forming a flap, whereby additional folding lines are cut between plates and adjacent flaps leaving bridging elements uncut to maintain the integrity of the flame resistant shield blank formed.

[0042] The process may further comprise the step of applying a tape, film, sealant or foil on at least one side of the flame resistant shield blank at least over and aside folding lines including the bridging element, at least such that upon folding adjacent plates are still connected by the tape, sealant, film or foil after breaking and or deforming the bridging element. The step may be applied before or after the flame resistant shield blank cutting step. Preferably after the cutting step to prevent any damage to the foil. A second cutting step to cut off any unwanted tape, foil or film or sealant. Alternatively a flexible flame resistant coating may be applied before or after the cutting of the flame resistant shield blank.

[0043] A possible example of a flame resistant tape or foil may be a mica paper material combined with organic and / or inorganic film, preferably with the mica paper forming the outer layer.

[0044] Method of folding a flame resistant shield blank according to the invention comprising the steps of folding a flame resistant shield blank into its final shape, and closing any gap between plates touching each other after folding with an flame resistant adhesive and whereby the final shaperepresents a box shape with at least one open side such that it can be placed or slide over a battery unit, cell, module or pack or any other unit that needs severe flame protection.

[0045] After folding the flame resistant shield blank into the final shape, additional sealant may be applied to close any remaining gaps between plates, preferably at least on any side facing the battery pack or module to be covered.

[0046] The production of the flame resistant shield in a two step process enables the possibility to store and ship the flame resistant shield blanks in a flat pack status, due to the placement of the bridging elements the flame resistant shield maintains its integrity, depending on the shape design and the flame resistant shield blank it is possible to optimise the material utilisation while also multiple designs may be formed from one flame resistant shield blank by snapping of or combining different blanks.

[0047] The impregnation of the fibrous layer or layers may occur in a spray or flow process before entering a compression step for instance in a continuous belt press or in a mold. Alternatively the matrix material may be applied to the reinforcement fibrous material inside a mold, either just before the mold is fully closed or when the mold is fully closed. The binder or matrix element can consist of any thermosetting polymer including polyurethane, polyisocyanurate, epoxy, phenolic or acrylic based resins. In general, thermosetting polymers are preferred due to their liquid state before curing but thermoplastic polymers may also be considered. Compression of the thus impregnated material is preferred to press out any air and obtain an airtight layer.

[0048] The use of an airtight flame resistant layer increases the overall flame resistance.Brief description of drawings

[0049] Figure 1 A and B example of the flame resistant shield blank and the flame resistant shield according to the invention.

[0050] Figure 2 A and B is an example of an alternative embodiment for the flame resistant shield corner joints

[0051] Figure 3 is an example of the flame resistant shield according to the invention applied to traction battery for an electric vehicle.

[0052] Figure 1A is showing an example of a flame resistant shield blank 1 according to the invention with a main panel 2 and flaps 3a, 3b and 3c. The whole blank is cut from the same material blank, whereby the main panel and the adjacent flaps are having a cutting line for forming the fold line. However at least on the unfolded blank, the main plate and adjacent flap are connected to each with at least one bridging element 4. These bridging elements are formed by areas on the fold line that are not cut yet.

[0053] Although the material used for the flame resistant shield blank is a rigid flame resistant composite, it is possible to break or snap small areas between plates. Furthermore the snapped or broken ends of the bridging element are not able to punch or damage surrounding parts or materials. Depending on the size of the flap the bridging element may be wider or smaller. On larger flaps there may be more than one bridging element per side. The size of the bridging element should be chosen such that the breaking or snapping of the element may be done without much force needed upon folding the flame resistant shield blank into its final shape, while it is strong enough to hold during transport of the flame resistant shield blanks.

[0054] Additionally the size of the bridging element should be chosen such that it is strong enough to remain rigid during gripping and transportation by robotic gripper elements during packing, unpacking and assembly.

[0055] The use of a substantial flat flame resistant shield blank during production and logistics has the advantage that the transport is more economical and ecological as there is less "air" or volume per part as would have been the case when fully formed boxes would have been transported or stored for the same reason. Furthermore the boxes may be adapted with the amount of sides used when forming and placing the flame resistant shields into the battery box. The flame resistant shield thus formed may be placed over battery modules, cells or packs. The shape may be adapted and a design for the necessary blank may be created. Although a square box is shown and might be the preferred solution for most of the current battery modulesor packs. Also other shapes may be formed in a substantial flat configuration that may be folded into the final structure following the teaching of this disclosure.

[0056] Figure 1 B shows the same configuration as figure 1 A however for the sake of clarity the numbering was omitted in favour of a folding scheme.

[0057] The produced flame resistant shield blank may be formed into its final shape by folding, shown with arrows f over the folding lines 5 in figure 1 A. For instance the folding is such that the edges of adjacent flaps, for example 3c and 3b, indicated with a and a' are touching each other. The new formed shape may be further stabilised with an adhesive bead of glue or with a strip of sealing tape along the new formed corner. The adhesive or sealing tape used should be flame resistant to close and seal the box at the fold lines. In the example of figure 1A and B the use of sealing strips at the inside is indicated with dotted lines on both sides of the fold line. The sealing strip or tape is at least used at the inside of the formed shape but may be used on both sides of the fold line without hampering the folding of the flame resistant shield into the final shape. Preferably a tape is used that is flexible to form the folding and has a slight stretch to get a nice sealing around the corners of the folded structure.

[0058] Figure 2 is showing an alternative embodiment for the connection of two adjacent flaps upon folding, the flaps may include additional dovetail joints. Preferably the bridging elements are placed within the dove tail joint and the height t of the joining area is slightly larger than the thickness of the material such that the snapped or broken end of the bridge and the thickness of the counter flap are forming a substantial flat surface.

[0059] Figure 3 is showing a battery box 10 with a lower tray 12 and a lid 11. In the box are placed battery cells or modules 13 which may be each covered with a folded flame resistant shield according to the invention. Alternately the flame resistant shield blank incorporates a design that upon folding encompasses additional combined walls between modules as shown in flame resistant shield 1b.

[0060] To achieve more intrigued designs additional flaps adjacent flaps may be used. This may also be smaller flaps that may overlap upon folding otherflaps to obtain a more stable closure of corners or fold lines. Such overlapping flaps may be dedicated to adhering and sealing overlapping areas and may have already an adhesive applied on the flame resistant shield blank that is activated later during folding the final shape for instance by thermal or pressure or UV curing.

[0061] Additional adhesive layers may be applied to the edges to connect the thus formed flame resistant shield to the unit to be covered.

Claims

ClaimsClaim 1. Flame resistant shield blank for covering more than one side of a battery pack or battery module, comprising a main plate and at least one flap cut from the same material blank and whereby the main plate and the at least one flap are adjacent and connected to each other, and whereby the connection comprises at least one bridging element, which at least partly breaks or deforms upon folding the flame resistant shield blank into its final shape.Claim 2. Flame resistant shield blank according to claim 1 , whereby each flap is separated from the main plate by a partial cut through at least the material blank while leaving bridging elements in the material blank as connecting elements.Claim 3. Flame resistant shield blank according to claim 1 or 2, whereby the material blank comprises at least one rigid layer, preferably a flame resistant layer.Claim 4. Flame resistant shield blank according to one of the preceding claims, whereby the material blank comprises at least one rigid flame resistant layer comprising of at least one reinforcing fibrous material, preferably a textile and or nonwoven impregnated with a matrix material such that the rigid flame resistant layer has a flame resistance up to at least 1100°C.Claim 5. Flame resistant shield blank according to one of claims 1 , 2 or 3, whereby the material blank comprises at least one rigid flame resistant layer comprising of mica platelets and a thermoset binder forming a plate-like structure such that the rigid flame resistant layer has a flame resistance up to at least 1100°C.Claim 6. Flame resistant shield blank according to one of the preceding claims further comprising an at least partial coverage of at least one side of the folding line with a flexible flame resistant layer, preferably a tape, film or foil, such that the flexible layer provides the connection between the main plate and the at least one flap when folded in the final shape and the bridging elements are at least partly broken or deformed.Claim 7. A flame resistant shield blank according to one of the preceding claims, characterized in that it comprises at least one flame-resistant layerconsisting of a fiber containing textile and or nonwoven impregnated with at least one of polyurethane, polyisocyanurate, epoxy or silicon and wherein the polyurethane impregnates the porous fibrous nonwoven in such a way that the flame-resistant layer is impervious to air-flow and has a flame resistance up to at least 1100°C.Claim 8. A flame resistant shield according to any of the preceding claims, wherein the density of the flame-resistant layer is comprised between 800kg / m3and 2500kg / m3, more preferably comprised between 1000kg / m3and 1800kg / m3.Claim 9. A flame resistant shield according to any of the preceding claims, wherein the weight of the fibrous non-woven or textile is between 40% and 80% of the total weight of the flame-resistant layer, preferably between 50% and 70%.Claim 10. A flame resistant shield according to any of the preceding claims wherein the fibrous material comprises fibers bonded by means of a thermoset binder before being impregnated with the matrix material, preferably polyurethane or polyisocyanurate, preferably the thermoset binder is an epoxy or phenolic based binder.Claim 11. A flame resistant shield according to any of the preceding claims, wherein the fibers of the fibrous material comprise at least one of ceramic fibers, glass fibers, carbon fibers, mineral-based fibers, oxidized polyacrylonitrile fibers.Claim 12. A process for making a flame resistant shield blank according to any of the preceding claims, comprising at least in the following steps:- providing a fibrous material wherein the fibers and or filaments comprised in the fibrous material have a flame resistance up to at least 1100°C, preferably in the form of a web, nonwoven or fabric;- spreading a matrix forming mixture onto the fibrous material;- thermally compressing the thus formed stack such that the matrix is impregnating the fibrous material and fully engulfs the fibers and or filaments, while most gas bubbles may be compressed out of the layer forming a impervious rigid flame resistant layer;- cutting the thus formed rigid flame resistant layer into flame resistant shieldblanks with a main panel and at least one flap, whereby additional folding lines are cut between the main panel and the adjacent flaps leaving bridging elements uncut to maintain the integrity of the flame resistant shield blank formed.Claim 13. Process according to claim 12, further comprising the step of applying a tape, film, sealant or foil on at least one side of the flame resistant shield blank at least over and aside the folding line including the bridging element, at least such that upon folding adjacent plates are still connected by the tape, sealant, film or foil after breaking and or deforming the bridging element.Claim 14. Method of folding a flame resistant shield blank according to or obtained by one of the preceding claims comprising the steps of folding a flame resistant shield blank is folded into its final shape, and closing any gap between plates touching each other after folding with an flame resistant adhesive and whereby the final shape represents a box shape with at least one open side such that it can be placed or slide over a battery unit, cell, module or pack.Claim 15. Process according to claim 14, whereby after folding the flame resistant shield blank into the final shape, additional sealant is used at least on one side to close any remaining gaps between plates, preferably at least on any side facing the battery pack or module to be covered.

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