Battery module, assembly method and shutdown method

Abstract

The invention relates to a battery module (1) with at least one stack of individual battery cells (2) clamped between two end plates (5, 6), and with a flexible conductor film (9) for tapping individual cell voltages, which runs in the stacking direction (S) between the two end plates (5, 6). The battery module according to the invention is characterized in that the flexible conductor film (9), or at least a parallel section (10) of the flexible conductor film (9), which is designed for tapping the individual cell voltage of at least one of the individual battery cells (2), is mechanically fixed to the two end plates (5, 6) and has a predetermined breaking point (15) which fails when a predetermined distance between the end plates (5, 6) is exceeded and disconnects the electrical connection of the at least one individual battery cell (2) to the individual cell voltage tap. The procedure involves monitoring individual cell voltages via the flexible conductive foil (9). If this foil tears in the area of ​​the predetermined breaking point (15), at least one of the individual battery cells (2) will not provide an individual voltage value and the battery management system can switch off the battery module (1).

Description

[0001] The invention relates to a battery module of the type defined in more detail in the preamble of claim 1. The invention also relates to a method for assembling such a battery module. Furthermore, the invention relates to a method for switching off such a battery module when a critical cell thickness growth is exceeded.

[0002] Depending on their design, individual battery cells and the battery modules constructed from them can exhibit a phenomenon known as cell thickness growth, both during charging and discharging, as well as over the course of the battery module's aging. This refers to an expansion of the active materials within an individual battery cell in the stacking direction. This expansion is typically reversible during charging and discharging. However, irreversible cell thickness growth occurs over the course of the battery module's aging.

[0003] Once the cumulative cell thickness growth exceeds a certain limit, severe mechanical stresses can occur within the battery module. This can deform, for example, the end plates of stacks of individual battery cells and their connections, such as side walls, tie rods, or similar components. This can lead to mechanical damage such as cracked welds, broken bolted connections, or similar issues. Serious problems can also arise within the individual battery cells themselves, particularly if electrical components are compressed so tightly that separators rupture and the electrical components come into direct contact with each other. This can trigger short circuits, which can lead to thermal runaway of the entire battery module.

[0004] For this reason, it is standard practice to monitor at least the electrical parameters of a battery, such as voltage and current, as well as its temperature, in order to indirectly infer cell thickness growth via capacity monitoring. Typically, the underlying algorithms that establish the relationship between capacity and cell thickness growth are comparatively inaccurate, especially with changing and increasingly complex cell chemistries as batteries are developed. In practice, this necessitates a relatively high safety factor, meaning that battery modules are often shut down much earlier than necessary due to the indirectly estimated cell thickness growth. This represents a significant disadvantage.

[0005] The applicant's DE 10 2022 003 779 B3 therefore takes the approach of incorporating a sensor and implementing shutdown based on a so-called pin switch or contact pin. The operating principle relies on the installation of a switch on one of the end plates, which is connected to the electrically conductive pin screw pointing towards the end plate. The distance is designed such that, in the event of a critical increase in cell thickness due to deformation of the end plate, contact is established and an electrical circuit is closed. Consequently, a corresponding signal is triggered, which can be used to deactivate the battery module. The switch's functionality has the disadvantage of requiring a comparatively large amount of installation space and a very complex adjustment process. This limits the possible applications and reduces the energy density achievable with the battery module.Furthermore, it significantly complicates and increases the cost of assembling the battery module due to the necessary adjustment of the mandrel screw.

[0006] Another sensor technology is also known from DE 10 2022 003 773 A1. In this case, the measurement is implemented within the end plate. While this is significantly better than using a pin switch in terms of the additional installation space required, it necessitates a relatively complex measuring sensor within the end plate to reliably measure, for example, force and mechanical stress. Furthermore, corresponding software and electronic enhancements are required to evaluate the generated measurements and determine the necessary actions, such as switching off the battery module. This also applies, in principle, to the use of a pin switch.

[0007] The object of the present invention is therefore to provide an improved battery module and a simple method for its assembly, which enables reliable monitoring of critical cell thickness growth with minimal effort.

[0008] According to the invention, this problem is solved by the battery module with the features of claim 1, and in particular in the characterizing part of claim 1. Advantageous embodiments and further developments of the battery module are described in the dependent claims. Furthermore, a method for assembling such a battery module, and in particular a method for monitoring cell thickness growth in such a battery module, also solves the problem. Advantageous embodiments and further developments of these are also described in the respective dependent claims.

[0009] The battery module according to the invention comprises a stack of clamped individual battery cells between two end plates. It is provided with a flexible conductor film for tapping off individual cell voltages. This flexible conductor film runs in the stacking direction between the two end plates. Typically, it is connected to a so-called battery management system, which evaluates the individual cell voltages of all or some of the battery cells in the battery module, as tapped off via the flexible conductor film or its conductor tracks, in order to, for example, balance the charge between individual cells and / or to draw conclusions about the health of the individual cells and the battery module. This design is known from the prior art.

[0010] In the battery module according to the invention, either the entire flexible conductor film or at least a parallel section of the flexible conductor film, which is designed to tap the individual cell voltage of at least one battery cell, is used to monitor cell thickness growth. For this purpose, the invention provides that the flexible conductor film or the parallel section of the flexible conductor film is mechanically fixed to the two end plates and has a predetermined breaking point. This predetermined breaking point is designed such that it fails when a predetermined distance between the two end plates is exceeded, thereby disconnecting the electrical connection of the at least one battery cell for its cell voltage monitoring.

[0011] This exceptionally simple and efficient design allows the system to detect when cell thickness growth has increased to the point where the specified distance between the end plates of the battery module is exceeded. If the flexible conductor film or its parallel section tears, at least one of the individual battery cells will no longer receive a voltage reading for individual cell voltage monitoring, allowing the battery management system to shut down the battery without significant additional effort.

[0012] The entire setup is largely cost-neutral, requiring only a minor adjustment to the flexible conductive film. The setup requires no additional installation space and virtually no additional assembly steps, as the flexible conductive film is already integrated. Therefore, there is no increase in the battery's overall weight, and no additional logistics are needed for further components to be installed within the battery module. Overall, the detection of critical cell thickness growth via a predetermined breaking point in the flexible conductive film, which reacts to changes in length, allows for longer battery operation compared to the typically very conservative shutdown via software alone. Furthermore, the shutdown can be performed directly via the battery management system, eliminating the need for any, or at least minimal, modifications to the software.

[0013] The design also allows the failure of the flexible conductor film to be tested and documented by mechanically spreading the module, which can save time-consuming and costly testing over the lifetime of a battery module during development work.

[0014] According to a highly advantageous further development, the mechanical fixation is achieved via pins on the respective end plate and corresponding holes in the flexible conductive film or its parallel section. This makes it exceptionally easy to position the holes over the pins and press them down when placing the flexible conductive film, thus mechanically fixing the flexible conductive film or its parallel section. Subsequently, for example, riveting the pin or a similar method can ensure that the flexible conductive film does not detach from its fixation to the end plates during operation.As an alternative to such riveting, gluing would also be conceivable, or a corresponding design of the pins with, for example, a mushroom-like or fir tree-like cross-sectional structure, so that the flexible conductor foil or its parallel section can be pressed onto the pins, but cannot be pulled off them again.

[0015] A particularly advantageous embodiment of the battery module according to the invention provides that only at least one parallel section is mechanically fixed to the two end plates and has the predetermined breaking point. In this design, the use of one or, optionally, several parallel sections allows the effectiveness of the predetermined breaking point to be optimized such that the parallel section(s) typically have a smaller cross-sectional area than the remaining main section of the flexible conductor film. Therefore, the desired failure upon exceeding a predetermined distance between the two end plates can be achieved even more reliably and within a tighter tolerance range.

[0016] This applies particularly when, as provided for in an advantageous further development, at least one parallel section serves to detect the individual cell voltage of exactly one battery cell. In the area of ​​the predetermined breaking point, only a single conductor element then runs within the flexible conductor film to transmit the corresponding voltage value of the affected battery cell. A comparatively small parallel section with exactly one electrical conductor element can then be very easily designed to fail quickly and reliably in the event of the critical change in the distance between the two end plates.

[0017] In principle, such a parallel section could be used independently of the rest of the flexible conductor film. However, this would make assembly more complex. According to a highly advantageous further development, it can therefore be provided that the at least one parallel section is connected to the main section of the flexible conductor film via at least two meandering structures. The flexible conductor film for recording the individual cell voltages of all battery cells arranged side by side in the stacking direction of the battery module can thus continue to be provided as a single-piece flexible conductor film.The meandering sections, by means of which the parallel section used as a sensor for cell thickness growth is connected, create the necessary flexibility so that the parallel section tears at its predetermined breaking point when the battery module reaches a critical length expansion, while the remaining main section of the flexible conductor film is not affected and, due to the meandering connections, which can be arranged at both ends in the stacking direction, for example, has no significant influence on the measurement.

[0018] It can be particularly advantageous if both the parallel section and the flexible conductor film itself, or the remaining main section of the flexible conductor film, have a wave-like or wave-ridge-like section to compensate for acceptable changes in the distance between the end plates. In practice, as mentioned above, a certain degree of change occurs even during operation, and a certain amount of irreversible change in the length of the battery module in the stacking direction due to cell thickness growth is acceptable. Therefore, in this highly advantageous embodiment of the inventive structure, the wave-like or wave-ridge-like section allows the flexible conductor film to grow in length in the stacking direction without being mechanically impaired and, in particular, without destroying the predetermined breaking point.

[0019] In a highly advantageous embodiment of the assembly consisting of the parallel section and the remaining flexible conductor film, the wave-like or wave-ridge-like section of the remaining main section of the flexible conductor film can be larger than that of the parallel section. "Larger" in the context of this embodiment means that the remaining main section of the flexible conductor film can withstand a greater change in length without damage or mechanical impairment than the parallel section. This ensures that the parallel section responds reliably to a critical change in the distance between the end plates, while the remaining main section of the flexible conductor film allows for continued monitoring of the individual voltages of all other battery cells not connected via the parallel section.

[0020] The inventive method for assembling such a battery module provides that the individual battery cells are stacked between the end plates and pressed together with the end plates in the stacking direction until the end plates have a predetermined initial distance from each other. This initial pressing of the individual battery cells with the predetermined initial distance, which must be maintained relatively precisely, can be achieved according to a particularly advantageous embodiment by optically detecting the pins, provided these are present on the end plates, in order to correlate directly with the distance subsequently monitored via the flexible conductor film or, in particular, the parallel section of this flexible conductor film.

[0021] Once this predetermined starting distance has been established during the initial pressing process, the end plates are connected to each other in this position via side plates and / or tie rods to complete the battery module as desired and to hold the end plates at their predetermined starting distance from each other. Subsequently, the flexible conductor film is applied, and the flexible conductor film itself, or in the advantageous embodiment described above, at least its parallel section, is mechanically fixed to the end plates.

[0022] Various techniques are conceivable for attaching the side plates and / or tie rods, such as welding, gluing, screwing, or similar methods. This also applies in particular to the mechanical fixing of the flexible conductor film, or at least its parallel section, to the end plates. However, as mentioned above, this can preferably be done via the pins, which, according to the advantageous embodiment of the method already discussed, can then also be used as markers for measuring the initial distance between the end plates, especially using optical methods.

[0023] As previously mentioned, a method for shutting down a battery module in such a configuration when a critical cell thickness growth is exceeded can now be implemented very simply within a battery management system that monitors at least the cell voltages of the individual battery cells. Depending on the design of the flexible conductor film, with or without the parallel section, if a critical cell thickness growth is exceeded, at least one of the individual battery cells will suddenly no longer be able to register its individual cell voltage. This can then be used as a signal to shut down the battery module and, in particular, to trigger a suitable warning signal, for example, in the form of a visual, acoustic, and / or haptic signal, especially as a display on a screen in a vehicle equipped with the battery module.

[0024] Advantageous further developments of the battery module according to the invention and of the method for its assembly also result from the exemplary embodiment, which is described in more detail below with reference to the figures.

[0025] This shows: Fig. 1 A schematic three-dimensional view of a battery module with two cell stacks between two end plates; Fig. 2 an enlargement of section IIa or IIb in Fig. 1; Fig. 3. A view of the battery module during assembly; Fig. 4 a top view of a flexible conductive film for implementing the method according to the invention; Fig. 5 an enlargement of section V in Fig. 4; Fig. 6 each an enlargement of section VIa and VIb in Fig. 4; Fig. 7. the battery module after attaching the flexible conductive film; and Fig. 8 an enlargement of section VIII in Fig. 7.

[0026] In the presentation of the Fig. Figure 1 shows a battery module, designated as 1 in its entirety. It consists of two stacks of individual battery cells 2 arranged in the stacking direction S, only some of which are marked with a reference symbol. The two battery terminals 3 and a rupture vent, designated 4, are visible on the surface of these individual battery cells 2. This vent ruptures in the event of thermal runaway of the individual battery cell to release pressure and hot gases into the environment. This design is well-known and common for prismatic individual battery cells. These two stacks of individual battery cells 2 are then pressed together between two end plates designated 5 and 6. On these end plates 5 and 6, the markings IIa and IIb, respectively, are located in the areas described in Figure 1. Fig. The two enlarged areas each contain pins labeled with 7, which will be discussed in more detail later.

[0027] In the presentation of the Fig. Figure 3 shows a state of battery module 1 during assembly. Starting from the one in Fig. In the setup shown in Figure 1, the two end plates 5 and 6 are mechanically pressed against each other, so that the two stacks of individual battery cells 2 are also pressed together in the stacking direction S. This pressing continues until the two end plates 5 and 6 have a fixed starting distance from each other. This starting distance is shown in the illustration of the Fig. The starting distance, designated x, must be maintained very precisely, for example with a tolerance of ±0.1 mm. Preferably, this starting distance can be determined using a CCD camera via the position of the protruding pins 7. In the mechanical state thus maintained by the pressing device during assembly, side plates 8 are now formed, of which the illustration shows the Fig. Only one end plate is visible, connected to end plates 5 and 6, for example by gluing and / or welding. This means that the starting distance x between end plates 5 and 6, and therefore also the starting distance of pins 7 of the respective end plates 5 and 6, is fixed relative to each other with the tolerance mentioned above.

[0028] In the presentation of the Fig. Figure 4 shows a flexible conductive film 9, which has corresponding conductor tracks for contacting the individual battery cells 2 in order to tap the individual cell voltages and make them available to a battery management system (not shown here). The special feature of the flexible conductive film 9 compared to conventional flexible conductive films is that it is divided into a parallel section 10 and the remaining portion, which is subsequently referred to as the main section 11. In the area of ​​the parallel section 10, as shown in the enlarged section, there is a Fig. Section 5, which is recognizable, contains a predetermined breaking point. Furthermore, as can be seen from the enlarged illustrations in Fig. 6a and Fig. As can be seen in Figure 6b, each parallel section 10 is connected to the main section 11 of the flexible conductive foil 9 via a meandering structure 12. It is thus correspondingly flexible relative to the main section, meaning it can move independently of it to a certain degree and, in particular, expand in the stacking direction S. The parallel section 10 has two holes, each labeled 13. These holes 13 correspond to the pins 7. This allows the parallel section 10 to be plugged onto these pins 7 during assembly. It is then firmly connected to these pins 7 to prevent it from coming loose during operation. This can be achieved, for example, by riveting the pins 7. However, it would also be conceivable to design the pins with a mushroom-like or Christmas tree-like structure, so that the holes 13 of the parallel section 10 can be slid over the pins 7 but cannot be pulled off them again.

[0029] The distance between the two end plates 5, 6, and thus the distance between the two pins 7, is crucial for the critical cell thickness growth. During assembly, this corresponds to the distance between the holes 13 on the parallel section 10 of the flexible conductor film 9. Since a certain amount of cell thickness growth is not critical over the lifetime of the battery module 1, and no action should be taken in response to such growth, the parallel section 10 has a profile shown in the diagram. Fig. 6a shows a recognizable wave-like section 14. This wave-like section 14, formed here as a wave crest, allows for a certain degree of expansion. For example, during assembly, the battery module 1 can have an initial distance x between the two pins 7 in the stacking direction of 795 mm. It can be considered critical if this distance increases to more than 800 mm. The wave-like section 14 in the parallel section 10 thus allows for such a length increase of 5 mm. The wave-like section 14, originally formed upwards as a wave or wave crest, would be smoothed out in such a state of the battery module 1 with a distance between the two pins 7 or holes 13 of 800 mm, so that the parallel section 10 is completely flat. If the distance between the two pins 7 or holes 13 increases further, the parallel section 10 would be damaged in the area of ​​the predetermined breaking point 15, as shown in Fig. As indicated in point 5, the parallel section 10 would be mechanically destroyed and electrically isolated, so that the connected battery management system would no longer receive a measurement for at least the single-cell voltage tapped via parallel section 10. In this case, the battery management system can initiate the shutdown of battery module 1 and issue a corresponding warning message.

[0030] To ensure continued monitoring of a large proportion of the individual battery cells 2 and to avoid impairing the response of the predetermined breaking point 15 of the parallel section 10 due to the mechanically more stable structure of the main section 10, meandering structures 12 are provided. Furthermore, the main section 11 also features a wave-like section 16 to compensate for the permissible change in length. In contrast to the wave-like section 14 of the parallel section 10, the wave-like section 16 of the main section 11 is designed to be larger, allowing the main section 11 to be stretched to a length of up to 805 mm in the numerical example described above.

[0031] As soon as the battery module 1 reaches a distance of 800 mm between the pins 7 or holes 13 and continues to grow, the predetermined breaking point 15 in the parallel section 10 tears open. The parallel section 10 is decoupled from the main section 11 via the meandering structures 12, so that the latter is not damaged and could continue to be used up to a length of 805 mm, which would then typically no longer be achievable, due to its wave structure 16.

[0032] In the presentation of the Fig. Figure 7 shows the fully assembled battery module 1 with the flexible conductor film 9, with the enlarged section of the Fig. 8 Here, purely as an example, the left side of the assembly with the hole 13 of the parallel section 10 of the flexible conductor film 9 pushed onto the pin 7 is shown again in detail.

Claims

[1] Battery module (1) comprising at least one stack of battery cells (2) clamped between two end plates (5, 6), and a flexible conductor film (9) for tapping individual cell voltages, which runs in the stack direction (S) between the two end plates (5, 6), characterized by , that the flexible conductor foil (9) or at least a parallel section (10) of the flexible conductor foil (9), which is designed for tapping the individual cell voltage of at least one of the battery individual cells (2), is mechanically fixed to the two end plates (5, 6) and has a predetermined breaking point (15) which fails when a predetermined distance between the end plates (5, 6) is exceeded and disconnects the electrical connection of the at least one battery individual cell (2) to the tapping of the individual cell voltages. [2] Battery module (1) according to claim 1, characterized by, that the mechanical fixing is carried out via pins (7) on the respective end plate (5, 6) and corresponding holes (13) on the flexible conductor foil (9) or the parallel section (10). [3] Battery module (1) according to claim 1 or 2, characterized by , that the mechanical fixing on the two end plates (5, 6) and the predetermined breaking point (15) is provided only in the area of ​​at least one parallel section (10). [4] Battery module (1) according to claim 3, characterized by , that at least one parallel section (10) is provided for tapping the single cell voltage of exactly one battery cell (2). [5] Battery module (1) according to claim 3 or 4, characterized by , that the at least one parallel section (10) is connected via at least two meander structures (12) to a main section (11) of the flexible conductor foil (9). [6] Battery module (1) according to claim 3, 4 or 5, characterized by, that the parallel section (10) of the flexible conductor foil (9) and the main section (11) of the flexible conductor foil (9) has a wave-like or wave-ridge-like section (14, 16) to compensate for an accepted change in the distance between the end plates (5, 6). [7] Battery module (1) according to claim 6, characterized by , that the wave- or wave-ridge-like section (16) in the main section (11) of the flexible conductor foil (9) is larger than the wave- or wave-ridge-like section (14) in the parallel section (10) of the flexible conductor foil (9). [8] Method for assembling a battery module according to any one of claims 1 to 7, characterized by, that the battery individual cells (2) are stacked between the end plates (5, 6) and pressed together with the end plates (5, 6) in the stacking direction (S) until the end plates (5, 6) have a predetermined starting distance (x) to each other, after which the end plates (5, 6) are connected to each other in this position via side plates (8) and / or tie rods, and after which the flexible electrical conductor film (9) is applied and the flexible electrical conductor film (9) or its parallel section (10) is mechanically fixed to the end plates (5, 6). [9] Method according to claim 8, in the assembly of a battery module according to any one of claims 2 to 7, characterized by , that the measurement of the specified starting distance (x) of the end plates (5, 6) to each other is carried out by means of an optical detection of the pins (7) on the end plates (5, 6). [10] Method for switching off a battery module according to any one of claims 1 to 7 when a critical cell thickness growth is exceeded, characterized by , that a battery management system monitors the individual cell voltages of the battery individual cells (2), for which purpose it is connected to the battery individual cells (2) via the flexible electrical conductor element (9), wherein in the event of an individual cell voltage of at least one of the battery individual cells (2) not being detectable an electrical shutdown of the battery module (1) takes place. [11] Method according to claim 10, characterized by , that a warning message is generated in parallel with the shutdown of the battery module (1).

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