Battery module and method for operating

Abstract

The invention relates to a battery module (1) with a plurality of individual battery cells (2) stacked to form a cell stack (4), with an actuator (8) for actively compensating cell thickness growth, with a receptacle (3) for each of the individual battery cells (2), and with guide rails (6) in the stacking direction (S), on which guide rails the receptacles (3) are movably guided in the stacking direction (S). The battery module according to the invention is characterized in that expansion elements (10) are arranged between the receptacles (3), which expand at least in the stacking direction (S) when subjected to a pressurized medium (p). The invention also relates to a method for operating such a battery module (1) in the event of a thermal event (E) in one of its individual battery cells (2), for which purpose the expansion elements (10) are pressurized.

Description

[0001] The invention relates to a battery module according to the type defined in more detail in the preamble of claim 1. Furthermore, the invention relates to a method for operating such a battery module in the event of a thermal event in one of its individual battery cells.

[0002] Battery modules with individual battery cells are generally known from the state of the art. They can be designed, for example, as so-called high-voltage or HV batteries, which are used in vehicles, for example, to store drive energy. The term "high-voltage" refers to the definition according to ECE 100R.

[0003] The individual battery cells of such battery modules can have various designs, for example, they can be lithium-ion cells with a liquid electrolyte or so-called solid-state cells. What all of these individual battery cells have in common is that they experience a change in volume during charging and discharging, as well as over time as the individual battery cells age. For some battery types, it is crucial that this volume change is compensated for while maintaining a largely constant pressure on the individual battery cells. This is particularly true for so-called solid-electrolyte or solid-state cells, which experience a relatively large change in volume during charging and discharging.

[0004] In this context, it is known from the applicant's unpublished German patent application with the file number 10 2023 004 322 to support the individual battery cells of a battery module within a battery housing with active volume compensation, which can be achieved, for example, via hydraulic or pneumatic cylinders. Three hydraulic or pneumatic cylinders are arranged in a module housing, which are supplied with pressurized medium, for example, from an external compressed gas reservoir, in order to implement the active volume and / or pressure compensation. This allows length changes due to cell thickness growth to be compensated for, and a constantly high pressure can be exerted on the cell stack of the individual battery cells, regardless of the current cell volume.

[0005] Especially with individual battery cells, which must be compressed very tightly during operation to maintain full performance, the problem arises that in the event of a failure in which one of the individual battery cells experiences thermal runaway, this severe compression of the individual battery cells within the battery module poses a hazard. The higher the compression, the better the heat transfer between the individual battery cells and the faster the thermal event spreads to the neighboring cells. If this leads to thermal runaway of the entire battery module, this can be safety-critical.

[0006] Active compensation of cell thickness growth is also known in principle at the level of each individual battery cell. For this, reference can be made to DE 10 2021005 257 A1.

[0007] Furthermore, DE 10 2020 003 892 B4 describes a cell holder for holding each individual battery cell of a cell stack. The cell holder is guided in a module frame via guide devices in the stacking direction and is movable relative to the frame in the stacking direction.

[0008] The object of the present invention is to provide an improved battery module that reduces the risk of thermal runaway of neighboring cells of a single battery cell affected by a thermal event. Furthermore, the object of the present invention is to provide a suitable operating method for such a battery module in the event of a thermal event involving one of its single battery cells.

[0009] According to the invention, this object is achieved by a battery module having the features of claim 1, and in particular in the characterizing part of claim 1. Advantageous embodiments and further developments emerge from the dependent subclaims. Furthermore, a method for operating this battery according to claim 7 solves the problem. Here, too, advantageous further developments emerge from the dependent subclaims.

[0010] The battery module according to the invention comprises several individual battery cells stacked to form a cell stack. Each of these cells is held in a holder. These holders are movably guided on guide rails in the stacking direction. An actuator actively compensates for cell thickness growth, ensuring that the individual battery cells are subjected to as uniform a pressure as possible in all states of charge and aging. A sufficiently high pressure is beneficial for performance, especially in so-called anodeless solid electrolyte cells.

[0011] According to the invention, expansion elements are arranged between the receptacles, which expand at least in the stacking direction when subjected to a pressurized medium.

[0012] If a thermal event occurs within the battery module, the expansion elements can be subjected to a pressurized medium, e.g., a liquid or gas. The expansion elements then expand accordingly, and the receptacles and the individual battery cells held within them move away from each other. The increased distance between the individual battery cells reduces heat transfer between the individual battery cells by creating an insulating layer of air in the gap. Ultimately, this minimizes the risk of the thermal event spreading to neighboring individual battery cells. This significantly reduces the risk of thermal propagation resulting from a single thermal event in one of the individual battery cells.

[0013] According to a highly advantageous development of the battery module according to the invention, all expansion elements can be connected to a common pressure source. This allows for a sufficiently uniform application of pressure to all expansion elements from a single pressure source in a very simple and efficient manner, which, on the one hand, minimizes the design and control complexity and, on the other hand, ensures the activation of all expansion elements in the battery module.

[0014] According to a very advantageous embodiment of the battery module, the pressure source can comprise a pressure accumulator, for example, with a valve device. This allows the use of a dedicated pressure accumulator or one already present in a pneumatic system, for example, of a vehicle incorporating the battery module, to move the individual battery cells apart when necessary. Instead of the valve device, a mechanical or pyrotechnic trigger could also be used, which, upon activation, opens a suitable flow path.

[0015] Alternatively, the pressure source can also comprise a gas generator. Such a gas generator, within the meaning of the invention, is a system that can be activated when needed to produce a sufficient amount of gas to actuate the expansion elements. Such gas generators are already used today, for example, in the deployment of airbags. They are usually activated pyrotechnically.

[0016] The expansion elements themselves can take various conceivable forms. For example, bellows could be conceivable, which extend in the stacking direction when pressure is applied. According to a very advantageous development of the battery module according to the invention, the expansion elements can be at least partially integrated into the receptacles. This allows for savings in material and installation space. In particular, the expansion elements can be formed integrally with the receptacles.

[0017] Preferably, the expansion elements can comprise interlocking pistons and cylinders, with the pistons being arranged on the respective first side of the receptacles and the corresponding cylinders on the respective opposite side of the receptacles. The individual battery cells held in the receptacles can thus be efficiently stacked, with the pistons engaging the respective cylinders of the adjacent receptacle. This has the positive side effect of facilitating the alignment and positioning of the receptacles during stacking.

[0018] An extremely advantageous further development of this battery module design can then provide for all receptacles, with the exception of one of the two receptacles closing off the cell stack or a corresponding pressure plate, to have a connecting bore between their cylinder and a piston surface located in the adjacent cylinder, whereby the connecting bore in the receptacle closing off the cell stack is connected or connectable to the connecting bore with the pressure source. With the exception of one end receptacle or pressure plate without a connecting bore, the respective pistons are therefore provided with connecting bores, e.g. between the piston surface and the cylinder base. If the pressurised medium is now introduced into one of the cylinders, it spreads through the connecting bores across all cylinders and ensures movement of the pistons in the cylinders.The holders, and thus the individual battery cells contained within them, are thus moved away from each other. This creates the insulating air gaps.

[0019] The inventive method for operating such a battery module in the event of a thermal event in one of its individual battery cells provides for the expansion elements to be pressurized as soon as a thermal event is detected in one of the individual battery cells. This then moves the individual battery cells of the battery module away from each other to prevent the thermal event from spreading to neighboring individual battery cells and thus thermal runaway of the entire battery module.

[0020] An exceptionally advantageous development of the method according to the invention can provide for the active compensation of cell thickness growth to be deactivated. Even though the force of the expansion elements could, in principle, be set so high that it would be greater than the forces of the active compensation of cell thickness growth, it is nevertheless advantageous if the active compensation of cell thickness growth is deactivated in order to implement the movement of the individual battery cells away from each other as simply as possible.

[0021] According to another very advantageous embodiment of the method according to the invention, it can further be provided that the pressure is applied by establishing a fluid connection to a pressure accumulator. In this case, a switching valve can be opened electromagnetically or pyrotechnically, for example. Bursting a membrane or a barrier body, which then opens the flow path, would also be conceivable.

[0022] According to an alternative, very advantageous development of the method according to the invention, it can be provided that the pressurization takes place by activating a gas generator in the sense described above.

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

[0024] Showing: Fig. 1 is a schematic view of a battery module according to the invention in regular operation; Fig. 2 the view according to Fig. 1 in the event of a thermal event in one of the battery cells; Fig. 3 an excerpt from the recordings Fig. 1 in a schematic sectional view; and Fig. 4 the view according to Fig. 3 in the event of a thermal event, as in Fig. 2.

[0025] In Fig. 1 shows an example battery module 1. In the illustration chosen here, it comprises five individual battery cells, each designated 2. These are held at the top and bottom in receptacles 3 and stacked in a stacking direction S to form a cell stack 4. In the illustration in the figure, the cell stack 4 is bordered on the right by an end plate 5. Two guide rails 6, indicated here only by the dash-dotted line, are connected to this end plate 5. The other end of the cell stack 4 forms a pressure plate 7. Both the pressure plate 7 and the receptacles 3 are displaceable relative to the guide rails 6 in the stacking direction S.

[0026] In the battery module 1 shown here, whose individual battery cells 2 are designed, for example, as anode-less solid electrolyte cells, the displaceability of the pressure plate 7 and the receptacles 3 serves to actively compensate for the cell thickness growth and to continuously exert a predetermined pressure on the individual battery cells 2. For this purpose, an actuator designated 8 is used, which exerts a force F on the cell stack 4 similar to the one in the aforementioned unpublished German patent application of the applicant with the file number 10 2023 004 322. In regular operation, as shown in the illustration of the Fig. 1 should be visible, this increases the service life and performance of the battery module 1.

[0027] However, if one of the individual battery cells 2 experiences a Fig. 2, then the force F acting on the individual battery cells 2 can be a disadvantage. The individual battery cells 2 pressed together with the force F transfer thermal energy from cell to cell much more easily than individual battery cells 2 that are not pressed together. With individual battery cells 2 that are pressed together, the risk increases that the thermal event E will spread and that a chain reaction-like thermal runaway of all individual battery cells 2 occurs.

[0028] In order to at least minimize this risk, it is now intended that the individual battery cells 2 are pushed away from each other in the event of a thermal event E in one of the individual battery cells 2. This state is shown in the illustration of the Fig. 2. This creates air gaps 9 between the individual battery cells 2, which act as thermal insulation. To achieve this, hydraulic or pneumatic expansion elements 10 are arranged between the receptacles 3, which can be actively pressurized in order to push apart the receptacles 3 and thus the individual battery cells 2 held therein through a longitudinal expansion in the stacking direction S. In the illustration, the expansion elements 10 are shown below purely as an example, with only one being provided with a reference symbol. They could just as easily be arranged laterally, at the top, or in separate positions simultaneously.

[0029] In the Fig. 3 and Fig. 4, this is shown using a possible embodiment of the expansion elements 10 in the operating states analogous to the representations in the Fig. 1 and Fig. 2. Shown are only the receptacles 3 stacked in the stacking direction S on one of the guide rails 6, which is also connected to the end plate 5. The reference symbols of the similar parts in the receptacles 3, as well as the reference symbol 3, are only found on one of the receptacles 3 in order to avoid unnecessarily confusing the figure.

[0030] The receptacles 3 are pressed together by the force F in the desired manner. The receptacles 3 arranged in the middle of the cell stack 4 each have a cylinder 11 on one side and a corresponding piston 12 on the other side. The receptacle 3 facing the end plate 5 only comprises the cylinder 11. The pressure plate 7 only comprises the piston 12. Alternatively, this could also be designed analogously in the receptacle facing the pressure plate 7. The pistons 12 are now arranged in the cylinders 11. The space of the cylinder 11 is sealed off from the piston 12 by sealing elements 14, e.g. an O-ring. A connecting bore 15 runs through the end plate 5 and through each of the receptacles 3 and connects the cylinders 11 of all receptacles 3 to one another. The connecting bore 15 is implemented here as a central bore in the preferably cylindrical piston 12 and cylinders 11.

[0031] If a thermal event E occurs in one of the individual battery cells 2, the connecting hole 15 is pressurized with a pressurized medium via a pressure source 16, as shown in the illustration of the Fig. 4. The pressure p spreads evenly through the formation bore 15 into all cylinders 11. Thus, the intermeshing pistons 12 and corresponding cylinders 11 push the receptacles 3 apart, as shown in the Fig. 2 and Fig. 4. The desired air gaps 9 are thus formed between the individual battery cells 2 in order to thermally insulate the individual battery cells 2 from one another.

Claims

[1] Battery module (1) with several individual battery cells (2) stacked to form a cell stack (4), with an actuator (8) for actively compensating the cell thickness growth, with a holder (3) for each of the individual battery cells (2), and with guide rails (6) in the stacking direction (S), on which the holders (3) are movably guided in the stacking direction (S), characterized by that expansion elements (10) are arranged between the receptacles (3), which expand at least in the stacking direction (S) when subjected to a medium under pressure (p). [2] Battery module (1) according to claim 1, characterized by that all expansion elements (10) are connected to a common pressure source (16). [3] Battery module (11) according to claim 2, characterized by that the pressure source (16) comprises a pressure accumulator or a gas generator. [4] Battery module (1) according to claim 1, 2 or 3, characterized bythat the expansion elements (10) are at least partially integrated into the receptacles (3). [5] Battery module (1) according to one of claims 2 to 4, characterized by that the expansion elements (10) have interlocking pistons (12) on the respective first side of the receptacles (3) and corresponding cylinders (11) on the respective opposite side of the receptacles (3). [6] Battery module (1) according to claim 5, characterized by that all receptacles (3), with the exception of one of the two receptacles (3) closing the cell stack (4) or a pressure plate (7), have a connecting bore (15) between their cylinders (11) and a surface of the piston (12) located in the respective adjacent cylinder (11), wherein the connecting bore (15) in the receptacle (3) adjoining the cell stack (4) is connected or connectable to the connecting bore (15) with the pressure source (16). [7] Method for operating a battery module (1) according to one of claims 1 to 6, in the event of a thermal event (E) of one of its individual battery cells (2) characterized by that the expansion elements (10) are pressurized. [8] Method according to claim 7, characterized by that the active compensation of cell thickness growth is switched off. [9] Method according to claim 7 or 8, characterized by that the pressurization occurs by establishing a fluid connection to a pressure accumulator. [10] Method according to claim 7 or 8, characterized by that the pressurization occurs by activating a gas generator.

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