A battery module for a battery pack, a battery pack, and a method for producing said battery module

Abstract

A battery module 10 for a battery pack comprising a plurality of battery cells 12 arranged in a volume space 14 which is only partially filled with the cells such that there is a free space 18 which i

Description

FIELD OF THE INVENTION

[0001] The present invention relates to the field of battery modules for a battery. More specifically, the present invention relates to a battery pack, in particular a battery pack configured as a traction battery for a motor vehicle, and therefore the present invention also relates to the field of automobiles. Furthermore, the present invention relates to a method for producing said battery module. BACKGROUND INFORMATION

[0002] In the case of a thermal runaway of a battery cell, which is part of a battery module, for example of a traction battery, the surroundings of the battery cell should be built in such a way that the thermal runaway does not spread to the surrounding battery cells and mitigates the thermal propagation.

[0003] A typical cell pack consists of cooling packs or base cooling to mitigate the cell temperature in an event of thermal runaway. Non-flammable materials are used around an individual battery cell or cell to slow down the thermal propagation. These include for example the covering of thermal insulating material on metallic pipes that are carrying a water-glycol mixture. Different wrapping designs exist for maximizing the cell contact area to improve heat transfer. Currently mica is used as a high-temperature incombustible barrier for electrically isolating battery packs.

[0004] However, increasing demand for high-energy battery cells, with which a longer driving range per charge is possible, requires much more efficient thermal shielding and thermal isolators. In addition, an active mechanism to minimize the cell-to-cell thermal propagation would be desirable.

[0005] Existing materials are inefficient in mitigating thermal runaway, especially in high energy density cells or battery cells. SUMMARY OF THE INVENTION

[0006] It is an object of the present invention to provide a battery module, a battery pack, and a method of producing that battery module, by which a thermal runaway of a dysfunctional battery cell, which spreads to neighboring battery cells, could be very efficiently limited.

[0007] A battery module, a battery pack, and a method according to the invention solve this object. Advantageous embodiments are presented in the dependent claims, the description, and the drawings.

[0008] One aspect of the present invention relates to a battery module for a battery pack. The battery module comprises a plurality of battery cells arranged in a volume space, which is built or surrounded in particular by a frame or housing, said volume space being only partially filled by the battery cells, in particular due to their shape, which is for example cylindrical, so that a free space is formed between and / or around the battery cells in the volume space, and said free space being filled with a composite material formed by an in particular wax-like polymer material which is solid at operating temperature, has a predetermined melting temperature and is mixed with a boron-containing compound and / or a layer compound. The boron-containing compound is also a layered compound so that therefore the layered compound could be seen as a further layer compound, which may be part of the composite material.

[0009] In other words, the present invention addresses the need for high-performance thermal insulating non-flammable medium within a battery pack or the battery module in particular for an electronic vehicle battery, by leveraging a boron-containing compound polymeric wax composite. Therefore, in case of a failure of one of the battery cells spreading of the failure may be stopped or at least slowed down.

[0010] The fault that can cause a battery cell to thermally runaway can be a cell defect or external mechanical damage that shorts out the cell, raising the temperature enough to cause it to self-ignite.

[0011] Boron compounds are being used as a multifunctional flame-retardant additive. In particular, by mixing hexagonal boron nitride in a wax or wax-like polymer medium, a fire resistance compound or medium is produced. This medium may be introduced during the manufacturing process as a filler within the entire space between individual battery cells by heating the medium just above the melting point of the wax or polymer.

[0012] In particular, the composite material is a boron wax medium that can act as an effective non-combustible thermal barrier in two ways: The decomposition of boron nitride is an endothermic reaction and releases water and / or steam. Some organoboron compounds release free radicals that serve as radical scavengers for flame retardancy.

[0013] An advantage of the present invention is that as the battery cells high-energy density battery cells could be safely used for batteries in electric vehicles to achieve high performance while maintaining high safety ratings. The battery module according to the invention is capable of stopping or reducing the thermal propagation or thermal runaway of the battery cells, which are in particular lithium-ion-cells, in particular on a cell-to-cell level. Therefore, another advantage is that the safety of the battery could be significantly improved. Furthermore, boron nitride is an inexpensive material, in particular, compared to other expensive polymer systems, which contributes to achieve high safety levels of the cell packs.

[0014] According to an embodiment of the invention, the polymer material comprises polyethylene, polymethylpentene, polypropylene, and / or polyimide. In other words, the wax-like material is a polymer that is. in particular, solid at room temperature and becomes fluidized at elevated temperatures. Use of a polyimide-type polymer may for example provide high thermal stability compared to the polyethylene-type of polymers. Therefore, an advantage is that producing the battery cell is easy and a distribution into the defective cell or battery cell is easy.

[0015] In another embodiment of the present invention, the boron-containing compound comprises boron nitride and / or an inorganic boron-containing material. In other words, the boron compound is not only limited to boron nitride but also includes inorganic boron-type materials. Furthermore, boron nitride may be replaced with other layered compounds that can remove thermal energy from the heat source. An advantage thereof is that the battery module could be built very cost-efficient. Another advantage is that decomposing of boron nitride is for example endothermic.

[0016] In still another embodiment of the present invention, a surface of the boron nitride is functionalized for miscibility with the polymer material. In other words, the surface of the boron nitride may be functionalized to achieve improved miscibility of the boron nitride in the polymer / way media. Therefore, another advantage is that the composite material may be very homogeneous and therefore have a very clear thermal characteristic.

[0017] In yet another embodiment of the present invention, a thermal property and / or a mechanical property is predetermined by a ratio of the polymer material to the boron-containing compound and / or the layer compound. In other words, this ratio controls the thermal and / or mechanical properties of the medium. For example, higher boron-containing amounts may increase the strength while more polymers may introduce an elastic nature to the composite material or medium. Therefore, the battery module could be specifically designed for its use-case or, in particular, for the operating temperature. Additionally, the present invention may help to facilitate the change in cell volume of the cells during the operation.

[0018] A second aspect of the present invention relates to a battery pack comprising at least one battery module according to the first aspect of the present invention.

[0019] Advantageous embodiments of the battery module are to be regarded as advantageous embodiments of the battery pack and vice versa.

[0020] According to an embodiment of the invention, the battery pack is configured as a traction battery for a motor vehicle. In other words, the battery pack is used to provide energy for an electric drive train of an electric vehicle. An advantage is that the vehicle may be built very safe in case of a malfunction of the battery cell.

[0021] A third aspect of the present invention relates to a method for producing a battery module according to the first aspect of the present invention, wherein the composite material is produced by liquefying a polymer material and introducing therein a powder of a boron-containing compound and / or a layered compound until a predetermined ratio of polymer material to boron-containing compound and / or layered compound is achieved.

[0022] Advantageous embodiments of the battery module and the battery pack are to be regarded as advantageous embodiments of the method for producing the battery module and vice versa.

[0023] According to an embodiment of the invention while the production of the battery module mixing of the polymer material comprising the boron-containing compound and / or the layered compound is affected by mechanical mixing and / or sonication, and the composite material, which is heated slightly above its melting temperature, is poured into a free space of the battery module.

[0024] In other words, producing the battery module and the polymer compound can first take place at a solid state at room temperature and then at increased temperature to amend the polymer compound. Boron, in particular boron nitride powder, is dispersed to the medium at a controlled rate to achieve the desired ratio. Because boron nitride is a layered material it may be dispersed in the polymer medium via mechanical mixing or sonication for having a uniform composite material. After the battery, cells are assembled in particular within the frame or housing of the battery module in the volume space the composite material solution is brought to a slightly higher temperature than the melting point of the composite material. Then the liquefied composite material may be poured to the void space or free space between the battery cells and the enclosure and / or housing. An advantage is that the free space could be filled very efficiently.

[0025] In another embodiment of the present invention, the composite material is cast in a mold to form a sheet, and the solidified sheet is pressed to produce dense spacer sheets used as spacers between battery cells within a volume space and in particular a free space of the volume space.

[0026] In other words, after the polymer compound and the boron-containing compound are mixed together to produce the composite material, the composite material may be poured into a mold to obtain a sheet structure, in particular, with desired dimensions. Once solidified, the sheet may be pressed to make dense thick spacer sheets that may be used as spacers between the battery cells within the cell module and the pack level. An advantage is that the production process is very efficiently performable.

[0027] Further advantages, features, and details of the present invention derive from the following description of preferred embodiments as well as from the drawings. The features and feature combinations previously mentioned in the description as well as the features and feature combinations mentioned in the following description of the figures and / or shown in the figures alone can be employed not only in the respectively indicated combination but also in any other combination or taken alone without leaving the scope of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The novel features and characteristic of the disclosure are set forth in the appended claims. The accompanying drawings, which are incorporated in and constitute a part of this disclosure, illustrate exemplary embodiments and together with the description, serve to explain the disclosed principles. The same numbers are used throughout the figures to reference like features and components. Some embodiments of system and / or methods in accordance with embodiments of the present subject matter are now described below, by way of example only, and with reference to the accompanying figures.

[0029] The drawings show in:

[0030] Fig. 1 a schematic perspective view of a battery module comprising a plurality of battery cells; and

[0031] Fig. 2 a sequence showing the characteristics of a composite material which is placed between the battery cells in case of a thermal runaway of one of the battery cells.

[0032] In the figures, the same elements or elements having the same function are indicated by the same reference signs. DETAILED DESCRIPTION

[0033] In the present document, the word “exemplary” is used herein to mean “serving as an example, instance, or illustration”. Any embodiment or implementation of the present subject matter described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments.

[0034] While the disclosure is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawing and will be described in detail below. It should be understood, however, that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternatives falling within the scope of the disclosure.

[0035] The terms “comprises”, “comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusion so that a setup, device or method that comprises a list of components or steps does not include only those components or steps but may include other components or steps not expressly listed or inherent to such setup or device or method. In other words, one or more elements in a system or apparatus preceded by “comprises” or “comprise” does not or do not, without more constraints, preclude the existence of other elements or additional elements in the system or method.

[0036] In the following detailed description of the embodiment of the disclosure, reference is made to the accompanying drawing that forms part hereof, and in which is shown by way of illustration a specific embodiment in which the disclosure may be practiced. This embodiment is described in sufficient detail to enable those skilled in the art to practice the disclosure, and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present disclosure. The following description is, therefore, not to be taken in a limiting sense.

[0037] Fig. 1 shows a perspective view of a battery module 10 for a battery pack, in particular a traction battery of an electric vehicle. Besides the battery module 10, the battery pack should also be introduced here. The battery pack comprises at least one of the shown battery module 10.

[0038] The battery module 10 comprises a plurality of battery cells 12 arranged in a volume space 14, which is surrounded and therefore in particular built by a frame or housing 16. That said volume space 14 is due to the form of the battery cells 12, which is for example cylindrical, only partially filled by the battery cell 12 so that a free space 18 is formed between and / or around the battery cells 12 in the volume space 14. The free space 18 is filled with a composite material 20 formed by an, in particular, wax-like polymer material, which is solid at operation temperature of the battery. The wax-like polymer material has a predetermined melting temperature, which is in particular slightly above the operating TP and is mixed with a boron-containing compound, which is, in particular, a layered compound and / or another layered compound.

[0039] The battery module 10 could be manufactured by a process in which the composite material 20 is affected by mechanical mixing and / or sonication. The composite material 20 may be mixed by liquefying the polymer material, which is liquefied, in particular, by heating above its melting point, and the composite material 20 may be mixed with a powder comprising the boron-containing compound and / or the layered compound. The powder is added until a predetermined ratio of polymer material to boron-containing compound and layer compound is achieved. In some embodiments, the layered compound may be a standalone casted sheet or shaped composite material.

[0040] When mixing the powder with the polymeric material, the thermal property and / or the mechanical property of the composite material 20 can be affected by the predetermined ratio and therefore can be customized for the application.

[0041] With the battery module 10 and the corresponding battery pack, in which the composite material 20 is used, a high-performance thermally insulating, non-combustible medium can be provided within a battery pack or the battery module 10 for batteries for an electric vehicle.

[0042] In one embodiment of the method for producing the battery module 10, the polymer material comprising the boron-containing compound or the layer compound is mixed for a homogenous composite material 20, for example, by mechanically mixing and / or sonication. The composite material 20, which has a temperature slightly above its melting point, is poured into the free space 18 of the battery module 10.

[0043] In another embodiment of the method for producing the battery module 10, the composite material 20 is cast in a mold to form a sheet, and the solidified sheet is pressed to produce dense spacer sheets used as spacers between battery cells 12 within the volume space and, in particular, a free space 18 of the volume space 14. In some embodiments, the method may be applied to the module level by introducing the sheets between battery modules 10 when manufacturing a battery pack.

[0044] The boron-containing compound comprises, in particular, boron nitride and / or an inorganic boron containing material. The polymer material comprises, in particular, polyethylene, polymethylpentene, polypropylene, polyimide, other polymer classes, and / or other functional group baring polymer classes. A surface of the boron nitride may be functionalized to mix well with the polymer material.

[0045] The composite material 20 is, in particular, built with polymer material and the boron-containing compound as a boron nitride wax medium, which acts as an effective non-flammable battery in two ways. The first way is that the composite material 20may melt by absorbing the heat 22 (as shown in Fig. 2). Then, the boron nitride decomposes in an endothermic reaction and releases water, steam 26, and fluidized wax 28 (as shown in Fig. 2). Additionally, organoboron compounds may release free radicals that serve as radical scavengers for flame retardancy.

[0046] If a thermal runaway in a damaged area 24 (as shown in Fig. 2) of one of the battery cells 12 happens, for example due to a mechanical effect or short circuit of that battery cell 12, the corresponding behavior of the composite material 20 is shown in Fig. 2. The behavior is a mechanism of building an efficient thermal barrier around the battery cell 12, which is experiencing the thermal runaway. As shown, the battery cells 10 are immersed in the composite material 20, the boron wax medium. In the second part of Fig. 2, a cell failure happens which generates heat 22. The composite material 20 melts into the fluidized wax 28 and the boron nitride enters the damaged area 24. The damaged area 24 is caused by thermal runaway. The composite material 20 liquefies and fills the failed battery cell 12 providing a thermal isolation due to the boron nitride or the boron-containing compound.

[0047] As shown in the fourth part of Fig. 2, the boron-containing compound or layer compound absorbs energy to remove heat 22 from the source and the boron-containing compound may decompose and generate H2O as steam 26 and fluidized wax 28 to suppress a fire of the battery cell 12.

[0048] To sum up, the composite material 20 starts to melt at a relatively low temperature, thus becoming a fluidized boron wax 28 that may surround the source of the damaged area 24. This allows the thermal insulating medium, for example boron nitride, to flow into the defect battery cell 12 even at an early state of cell-heat-up due to a failure. This helps to migrate boron nitride, effectively thermally isolate the failed cell, and stop the thermal propagation at an early stage of the cell heating up. An endothermal nature of the decomposition of boron nitride at above 1000°C helps to remove the heat 22 from the defect cell area.

[0049] Releasing steam 26 may be favorable to suppress the fire. It can also automatically form a charcoal layer when exposed to fire which helps to obtain an oxygen isolation. Overall mechanism of mitigation of thermal propagation is via stopping the heat 22 and flammability propagation at a cell-to-cell level.

[0050] With the shown battery module 10, boron nitride wax composite material 20 is introduced as a liquefiable infill in electronic vehicle battery modules 10 to mitigate the cell thermal propagation. Signs battery module battery cell volume space housing free space composite material heat damaged area steam fluidized wax

Claims

1. A battery module (10) for a battery pack comprising a plurality of battery cells (12) arranged in a volume space (14), said volume space (14) being only partially filled by the battery cells (12) so that a free space (18) is formed between and / or around the battery cells (12) in the volume space (14), and said free space (18) being filled with a composite material (20) formed by a polymer material which is solid at operating temperature, having a predetermined melting temperature and being mixed with a boron-containing compound and / or a layer compound.

2. The battery module (10) according to claim 1, characterized in thatthe polymer material comprises polyethylene, polymethylpentene, polypropylene, and / or polyimide.

3. The battery module (10) according to claim 1 or 2, characterized in thatthe boron-containing compound comprises boron nitride and / or an inorganic boron-containing material.

4. The battery module (10) according to any one of claims 1 to 3, characterized in thata surface of the boron nitride is functionalized for miscibility with the polymer material.

5. The battery module (10) according to any one of the preceding claims, characterized in thata thermal property and / or a mechanical property is predetermined by a ratio of polymer material to boron-containing compound and / or layer compound.

6. A battery pack comprising at least one battery module (10) according to any one of the preceding claims.

7. The battery pack according to claim 6, characterized in thatthe battery pack is configured as a traction battery for a motor vehicle.

8. A method for producing a battery module (10) according to any one of claims 1 to 5, wherein the composite material (20) is produced by liquefying a polymer material and introducing therein a powder of a boron-containing compound and / or a layered compound until a predetermined ratio of polymer material to boron-containing compound and / or layered compound is achieved.

9. The method according to claim 8, characterized in thatmixing of the polymer material comprising the boron-containing compound and / or the layered compound is affected by mechanical mixing and / or sonication, and the composite material, which is heated slightly above its melting temperature, is poured into a free space (18) of the battery module (10).

10. The method according to claim 8, characterized in thatthe composite material (20) is cast in a mold to form a sheet, and the solidified sheet is pressed to produce dense spacer sheets used as spacers between battery cells (12) within a volume space (14) and a free space (18) of the volume space (14).

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