Battery module

Abstract

Battery module (1) with a plurality of individual battery cells (3) in a housing (2), with an integrated module heater (60), wherein the module heater (60) is formed by an electrically conductive, resistive material (6) which is arranged in an electrical circuit together with a switching element (9), characterized in that the module heater (60) is formed from a foamed material (6) which fixes the individual battery cells (3) in the housing (2).

Description

[0001] The invention relates to a battery module with a plurality of individual battery cells in a housing according to the type defined in more detail in the preamble of claim 1 and to a method for heating a battery with such battery modules.

[0002] Battery modules, especially those based on lithium-ion battery cells, must be operated within a specific temperature range if possible to achieve optimal performance and the longest service life. In cold ambient temperatures, it is therefore necessary to heat the individual battery cells of the battery module; at high temperatures, they must be cooled. This serves to prevent so-called "lithium plating" in battery cells with liquid electrolyte. Furthermore, very strong temperature gradients in the active material of the individual battery cells have a negative impact on the service life of the individual battery cells.

[0003] It is known from the general state of the art that a cooling medium, which is typically in thermally conductive contact with the individual battery cells via a heat exchanger, can be used both to heat the individual battery cells and to cool them. For this purpose, the cooling medium is heated accordingly at cold ambient temperatures using an electrical resistance heating element, for example, in order to indirectly temperature-control the individual battery cells via the cooling medium in the desired manner. However, the high temperature gradients that occur when the cooling medium is used both to cool and to heat the individual battery cells can damage the coolant. For example, gelling can occur, meaning that the coolant then has to be completely replaced to ensure continued functionality.

[0004] Furthermore, when the individual battery cells are heated via the cooling medium, the use of various components and the required heat transfer from the heating element to the coolant on the one hand and from the coolant to the individual battery cells on the other hand results in a comparatively slow and inefficient process in which far more energy is required to temper the individual battery cells than is absolutely necessary.

[0005] In addition, flat heating foils are known that can be integrated into the battery module. However, these are comparatively expensive and require additional installation space. Nevertheless, they are frequently used, for example, in the field of solid-state batteries, for which reference can be made to DE 10 2016 214 337 A1.

[0006] DE 10 2017 206 080 A1 describes a battery module in which an elastically and / or plastically deformable compensating element is arranged between the individual battery cells. An electric heating element in the form of a heating foil can be positioned within this compensating element. This element is then surrounded on both sides by the elastic material and can heat the individual battery cells as needed through this elastically and / or plastically deformable material of the compensating element.

[0007] A similar structure with a porous and flexible compensating element, which can also be used to control the temperature of the cells, is described in DE 10 2009 052 508 A1. While it is mentioned that the material can be both thermally and electrically conductive, electrical heating is not mentioned. Rather, only the thermal conductivity of the compensating element is addressed, which can then transfer heat from a connected heating or cooling device to the cells.

[0008] Finally, DE 10 2016 214 640 A1 also describes a battery module in which an electrically insulating potting compound is used to secure the individual battery cells. This electrically insulating potting compound can be coated with silver particles or similar to improve thermal conductivity.

[0009] The object of the present invention is to create an improved battery module with multiple individual battery cells and an integrated module heater, which avoids the aforementioned disadvantages and enables simple, efficient, and cost-effective heating of the battery module when needed. Furthermore, the object is to provide a method for heating a battery with multiple such battery modules.

[0010] According to the invention, this object is achieved by a battery module with a plurality of individual battery cells and the features in claim 1, and in particular with the features in the characterizing part of claim 1. Advantageous embodiments and further developments of the battery module according to the invention emerge from the dependent subclaims. Furthermore, the object is achieved by a method for heating a battery with a plurality of such battery modules according to claim 9. Here, too, an advantageous embodiment of the method according to the invention emerges from the dependent subclaim.

[0011] The battery module according to the invention is provided with an integrated module heater, which is formed from an electrically conductive, resistive material. According to the invention, the material of the module heater is designed as a foamed material and secures the individual battery cells in the housing. The material thus serves, on the one hand, to position and secure the individual battery cells in the housing and, for this purpose, surrounds the individual battery cells over a large portion of their respective outer surfaces. The material is designed as an electrically conductive thermal foam, which is also flame-retardant, in particular, by adding a flame retardant.This electrically conductive thermal foam, together with a switching element, then forms part of the circuit. When the switching element is switched on, an electrical current flows through the thermal foam, heating it accordingly due to the electrical resistance of the current in the thermal foam. The thermal foam can then transfer the heat energy directly to the individual battery cells in direct contact with it, enabling extremely efficient heating. Since the thermal foam simultaneously secures the individual battery cells in the housing, no additional installation space is required for it, as it would already be available for securing the individual battery cells and now simply takes on the additional task of heating the module.

[0012] According to an exceptionally advantageous development of the battery module according to the invention, the thermal foam can be constructed as a polyurethane foam with electrically conductive additives, for example based on carbon or aluminum, in particular based on graphite and / or aluminum oxide. Other electrically conductive additives would, however, also be conceivable. Such a PU foam, thanks to the electrically conductive additives and preferably an additional flame retardant, is therefore an ideal thermal foam for securing the battery cells in the housing on the one hand and for forming a module heater on the other. The flame retardant also allows for a high level of safety in the event of a thermal runaway of the battery module.

[0013] According to a very advantageous development of the battery module according to the invention, the circuit itself can connect the poles of the battery module via the switching element and the module heater. The energy for the module heater is thus provided within the module itself by using part of the energy content of the battery module for the module heater. This enables very efficient heating of the respective battery module.

[0014] By creating an electrical circuit between the battery module's terminals, each individual module can be heated specifically, even in cases where a battery is made up of multiple battery modules, as is common practice with traction batteries in electric vehicles, for example. Module-specific heating then allows for very efficient heating of the entire battery, since only those modules actually need to be supplied with the amount of heating energy that is currently required for that specific module.

[0015] If the battery module or the battery comprising the battery module is connected to a charger, the charger's power is also applied, at least indirectly, to the terminals of the respective battery module. If the battery module is heated in this situation, the circuit design described above allows the energy to be provided directly via the charger without first having to be stored in the battery module, thus increasing energy efficiency.

[0016] According to a very advantageous embodiment of the battery module according to the invention, the switching element can be designed as an insulated-gate bipolar transistor (IGBT). Using a corresponding control voltage at the gate electrode, the current flow through the switching element and thus through the module heating of the battery module can then be easily and efficiently controlled or regulated, for example, by pulse-width modulation.

[0017] A very advantageous embodiment of the battery module according to the invention can also provide for the electrical contacting of the module heating material to be realized via a first electrode at a first end of the battery module and via a second electrode at a second, opposite end of the battery module. These electrodes can be integrated into the foamed material of the module heating or arranged adjacent to it. They can then be connected directly to the terminals of the battery module to form the electrical circuit. The switching element can then be integrated into one of these connections, for example, between the first electrode and the positive terminal of the battery module.

[0018] It is particularly advantageous if, as is provided in an advantageous development of this concept, the electrodes each have projections or hooks that extend toward the other electrode. Such projections or hooks can facilitate the positioning of the electrodes relative to the individual battery cells and, on the other hand, improve electrical contact by increasing the contact area between the foamed material of the module heater and the electrode.

[0019] Another very advantageous embodiment can provide for the individual battery cells to be arranged in a heat-conducting connection with a heat exchanger. The module heater can take over the temperature control of the individual battery cells to the extent that heating of the individual battery cells is necessary. A heat exchanger known per se can also be provided, which, for example, is in a heat-conducting connection with the elements of the individual battery cells that protrude beyond the foamed fixing. Such a heat exchanger can, for example, be a cooling plate through which a fluid flows and which, in the battery module, is in contact with the individual battery cells, for example from above and / or below.One or both cooling plates can then be used to cool the individual battery cells in the conventional manner, without the need to heat the individual battery cells via the coolant, as this heating can be done directly via the module heater. This protects the coolant accordingly and achieves a long service life with good coolant quality and thus good cooling efficiency.

[0020] In principle, the battery module can be constructed with any desired individual battery cells. It is particularly preferred to use lithium-ion cells, with the cells being designed as individual battery cells with liquid electrolyte, as provided for in a very advantageous embodiment of the battery module according to the invention.

[0021] The inventive method for heating a battery with battery modules according to one of the preceding claims provides that the switching units of the battery modules are controlled in a pulse-width modulated manner according to the required thermal energy. In the preferred embodiment as an insulated gate bipolar transistor (IGBT), this can preferably be achieved by appropriately controlling the gate voltage. The pulse-width modulated control thus allows for comparatively good control of the introduced thermal energy in a simple and efficient manner. In particular, the required amount of heat for each individual battery module can be provided by the module heater integrated into the respective module according to a temperature measured in the respective module as a controlled variable.Such temperature control now makes it possible to easily and effortlessly control each individual battery module within a larger battery with multiple battery modules with regard to its required thermal energy. Since the control is part of the modules themselves, virtually no additional effort is required, especially if each module includes an integrated temperature sensor and control electronics that provides the gate voltage for the IGBT using pulse-width modulation.

[0022] According to a very advantageous development of the method according to the invention, it can be provided that the module heating is only enabled when the charge level of the corresponding battery module is within predetermined limits. Such enablement can, for example, occur in such a way that the charge level does not fall below a predetermined limit, in order to ensure, for example, that a vehicle using the battery can always achieve the required remaining range with the amount of energy stored in the respective battery module. Furthermore, such activation of the basic option of module heating, controlled according to the charge level, can prevent deep discharge of the module, which has a positive effect on its service life.

[0023] Further advantageous embodiments of the battery module according to the invention and of the method according to the invention also emerge from the exemplary embodiment, which is described in more detail below with reference to the figures.

[0024] Showing: Fig. 1 is a schematic plan view of a battery module in an embodiment according to the invention; and Fig. 2 a side view of the battery module according to Fig. 1.

[0025] In the presentation of the Fig. 1 shows a plan view of a battery module, designated as a whole by 1. It consists of a housing, designated 2, and a plurality of individual battery cells 3, which here are exemplary in the form of round cells. These individual battery cells 3 are arranged upright in the housing 2. Only a few of them are provided with a reference symbol. The battery poles 4, 5, designated plus and minus, of the battery module 1 can be seen at the top left and bottom right, the individual battery cells 3 of which are connected in a conventional manner, for example electrically in series. To fix the individual battery cells 3 in the housing 2, the latter is filled with a material designated 6. The individual battery cells 3 can therefore be positioned in the housing 2, which is open at the top, for example, and are then fixed in the housing by the foamed material 6, a thermal foam.This thermal foam 6 ensures the mechanical integrity of the cell assembly by reliably filling the spaces between the individual battery cells 3. This increases the robustness and the compressive, tensile, and shear strength of the cell assembly of the battery module 1. The thermal foam 6 used can, for example, be a polyurethane foam, which is flame-retardant due to the use of flame retardants. In addition, electrically conductive particles are added to the thermal foam 6, which can, for example, contain a combination of carbon or graphite and / or aluminum oxide, for example Al2O3. These particles can be arranged as powder or fibers in the thermal foam 6. The thermal foam 6 thus becomes electrically conductive and acquires improved thermal conduction properties.

[0026] The electrical conductivity of the thermal foam 6 is utilized by integrating an electrode 7, 8 into the housing 2 at the left and right ends of the illustrated embodiment, which electrodes are intimately connected to the thermal foam 6. The electrode 8 shown on the left is electrically connected to the positive pole 4 of the battery module 1 via a switching element 9, which is preferably designed as an IGBT, and the electrode 7 shown on the right is electrically connected directly to the negative pole 5 of the battery module 1. The two electrodes 7, 8 are connected to the electrically conductive, resistive thermal foam 6.The electrodes 7, 8 may have projections 10, hooks, or the like facing the respective other electrode 8, 7, which, on the one hand, facilitate their positioning relative to the individual battery cells 3 during assembly and, on the other hand, correspondingly increase the surface area of ​​the electrodes 7, 8 that are in contact with the thermal foam 6. During assembly, these electrodes 7, 8 are positioned together with the individual battery cells 3 in the housing 2 before the remaining empty spaces are filled with the thermal foam 6.

[0027] The thermal foam 6 now takes on the additional functionality of a module heater 60 by connecting the first electrode 8 to the positive terminal 4 of the battery module 1 via the switching element 9, and by permanently connecting the other of the electrodes 7 to the negative terminal 5 of the battery module 1. This causes a current to flow through the thermal foam 6 as a module heater 60, as indicated by the arrows in Fig. 1 is indicated according to the technical current direction. The thermal foam 6 heats up and heats the individual battery cells 3 as a module heater 60.

[0028] As indicated by the arrow labeled 11, the switching element 9, especially if it is designed as an IGBT, can now be controlled accordingly via its gate voltage. This can preferably be used to implement a pulse-width modulated control, in which a measured value of a voltage shown in the diagram below is used as the controlled variable. Fig. 2 indicated temperature sensor 12 is used to regulate a desired target temperature of the battery module 1.

[0029] In the presentation of the Fig.2 that in the exemplary embodiment shown here, the housing 2 is closed by a type of "cover." This cover is to be designed as a heat exchanger 13, which is known per se. It serves as a cover and cooling plate, which is in thermally conductive connection to the individual battery cells 3 and cools them as needed, for example by a coolant flowing through the heat exchanger 13. This conventional type of cooling is now efficiently supplemented in the structure of the battery module 1 by the use of the thermal foam 6, which serves on the one hand to fix the individual battery cells 3 and on the other hand as a module heater 60, in order to be able to temperature the battery module 1 in any desired way, for example by heating it accordingly via the module heater 60 or cooling it accordingly via the heat exchanger 13.

Claims

[1] Battery module (1) with several individual battery cells (3) in a housing (2), with an integrated module heater (60), wherein the module heater (60) is formed by an electrically conductive resistive material (6) which is arranged together with a switching element (9) in an electrical circuit, characterized by that the module heater (60) is formed from a foamed material (6) which fixes the individual battery cells (3) in the housing (2). [2] Battery module (1) according to claim 1, characterized by that the foamed material (6) is designed as polyurethane foam with electrically conductive additives. [3] Battery module (1) according to claim 1 or 2, characterized by that the circuit connects the poles (4, 5) of the battery module (1) via the switching element (9) and the module heater (60). [4] Battery module (1) according to one of claims 1, 2 or 3, characterized bythat the switching element (9) is designed as a bipolar transistor with an insulated gate electrode. [5] Battery module (1) according to one of claims 1 to 4, characterized by that an electrical contact of the foamed material (6) is realized via a first electrode (7) at a first end of the battery module (1) and a second electrode (8) at a second opposite end of the battery module (1) within the housing (2). [6] Battery module (1) according to claim 5, characterized by that the electrodes (7, 8) each have projections (10) or hooks projecting in the direction of the other electrode (8, 7). [7] Battery module (1) according to one of claims 1 to 6, characterized by that the individual battery cells (3) are arranged in a heat-conducting connection with a heat exchanger (13). [8] Battery module (1) according to one of claims 1 to 7, characterized bythat the individual battery cells (3) are designed as lithium-ion cells with liquid electrolyte. [9] Method for heating a battery with battery modules (1) according to one of claims 1 to 8, characterized by that the switching elements (9) of the respective battery modules (1) are controlled in a pulse-width modulated manner according to the required thermal energy. [10] Method according to claim 9, characterized by that the heating of the respective battery module (1) is only enabled if its state of charge is within predetermined limits, in particular above a predetermined threshold.

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