Cell cluster

Abstract

A cell assembly (10) of a high-voltage storage device is presented. The cell assembly (10) has several cells (12), each cell (12) having a cell terminal (30) formed by a cell extension (28) of a first pole (24) and a second pole (26) forming a cell housing (34). The cell assembly (10) also includes connecting conductors (14) that electrically connect the cell terminals (30) and / or the second poles (26) to each other. Additionally, a short-circuit connection (42) is provided outside the cells (12) through which the cell terminal (30) and the second pole (26) are directly electrically connected when a predefined first reference temperature is exceeded.

Description

[0001] The invention relates to a cell assembly of a high-voltage storage device with multiple cells. In particular, the invention relates to a cell assembly for a vehicle high-voltage storage device.

[0002] High-voltage storage systems comprise a large number of battery cells grouped together in a cell array. Such high-voltage storage systems are used, for example, in motor vehicles, where typically four to six cells are combined in a parallel array. This parallel array is also known as a logic cell. The cells are preferably vertical cylindrical cells, with the individual cylindrical cells connected to each other via their terminals. The connection of the individual terminals is usually made via an electrical conductor.

[0003] To ensure thermal safety, various measures can be incorporated into the cell array to minimize the impact of a thermal event. These measures are specifically designed to prevent propagation following a thermal event within a single cell.

[0004] For this purpose, the cell assembly can be designed to contain cooling units, with the individual cells arranged between these units. Furthermore, a valve is typically provided at the bottom of the cell to allow pressure, material, and heat to escape in the event of a thermal event inside the cell. Additionally, the electrical connecting conductors are usually equipped with a fuse, particularly an overcurrent fuse, which isolates the defective cell from the other cells in the assembly. Such overcurrent protection can be provided, for example, by a P-fuse, an S-fuse, or wire bonds. For thermal isolation, it is also known to provide a spacer or a foam pad in the terminal area, so that a cavity is created when the temperature rises in the cell assembly, allowing the released thermal energy to be directed into the connecting conductor.This allows for thermal separation of a fuse provided in the connecting conductor and a resulting interruption of the current flow.

[0005] In the event of a thermal incident, such as a short circuit, the battery cell heats up due to the resulting temperatures, leading to overpressure within the cell. Additionally, the high temperatures in the defective cell can damage the electrically insulating cell seal, typically a plastic sealing ring, located between the two poles of the cell at the cell terminal (the protruding pole, usually the anode). This electrically insulating cell seal is typically made of polymers such as epoxy mold compounds (EMC), polyphenylene sulfite (PPS), or perfluoroalkoxy (PFA).

[0006] Damage to the electrically insulating cell seal, particularly due to additional external forces, causes the cell terminal to collapse, resulting in a secondary short circuit, commonly referred to as a secondary short circuit. Such secondary short circuits are classified as high-resistance, medium-resistance, or low-resistance. In a high-resistance secondary short circuit, the defective cell discharges through the other cells in the battery pack. In a low-resistance secondary short circuit, however, a current spike occurs, which can rupture the connecting conductor at the fuse, especially the overcurrent fuse.In a medium-resistance secondary short circuit, the short-circuit current is not high enough to trip the aforementioned overcurrent protection, and likewise, the temperature is not high enough to guarantee tripping at a fuse. Instead, the defective cell heats up continuously, potentially reaching very high temperatures. These high temperatures can cause thermal runaway, which must be prevented. Thermal runaway refers to the thermal damage of adjacent cells.

[0007] It is therefore an object of the invention to provide a cell assembly that ensures a low-resistance secondary short circuit in the event of a thermal event.

[0008] The problem is solved according to the invention by a cell array of a high-voltage storage device. The cell array has several cells, each cell having a cell terminal formed by a cell extension representing a first pole and a second pole forming a cell housing. The cell array also includes connecting conductors that electrically connect the cell terminals and / or second poles to each other. In addition, a short-circuit connection is provided outside the cells, through which the cell terminal and the second pole are directly electrically connected when a predefined first reference temperature is exceeded.

[0009] The basic idea of ​​the invention is to establish a direct electrical connection between the cell terminal and the second pole before the connecting conductor reaches its melting point. This short-circuit connection ensures that the electrical contact between the cell terminal and the second pole is sufficiently large to guarantee a low-resistance short circuit. The short-circuit connection provides an additional contact surface on the outside of the defective cell between the cell terminal and the second pole. A fuse, in particular an overcurrent fuse, preferably a fusible link, is severed by the resulting low-resistance short circuit and the associated current spike of the short-circuit current. This interrupts the connection between the defective cell and the remaining cells in the cell assembly and prevents the propagation of the thermal event.

[0010] Preferably, the overload protection is designed as a constriction, i.e., a reduction in cross-section, on the connecting conductor. In particular, the overload protection can be a so-called S-fuse, a so-called P-fuse, or a wire bond integrated into the connecting conductor.

[0011] The first reference temperature is preferably between 200°C and 400°C. High-voltage storage systems in motor vehicles typically have a maximum operating temperature of 150°C or 160°C. Therefore, the reference temperature is significantly higher than the maximum operating temperature, preventing the short circuit from being triggered unintentionally. Furthermore, a reference temperature below 400°C is well below the melting point of the connecting conductors, which are usually made of aluminum. The melting point of aluminum is 660°C. Accordingly, the reference temperature ensures that the short circuit is triggered well before the connecting conductors melt, which could cause a further short circuit, a so-called tertiary short circuit, in an adjacent cell.

[0012] According to a preferred embodiment, the short-circuit connection is achieved by a conductive melt material. The conductive melt material is located outside the cell, either on the cell itself or on a part connected to the cell, and is particularly positioned in the region of the cell extension. Its proximity to the cell extension ensures that, upon reaching the reference temperature, a direct electrical connection between the two poles is established by the molten conductive melt material.

[0013] The conductive melting material can be, for example, tin or zinc or their alloys, with tin having a melting temperature of 230°C and zinc, which is preferably used in a zinc alloy, having a melting temperature of 330°C.

[0014] Preferably, the conductive melt material is a bimetal or an alloy.

[0015] According to one embodiment, the conductive melt material is applied to the cell terminal, i.e., the cell extension. In particular, the conductive melt material can be provided as a circumferential coating on the cell terminal. Since the cell terminal is coated before the cell is integrated into the cell assembly, manufacturing is simple and production costs can be kept low.

[0016] Preferably, the coating is provided on the circumference of the cell terminal, while a coating between the cell terminal and the connecting conductor is not necessary.

[0017] According to an alternative embodiment, the conductive melt material is attached to the connecting conductor. In this case, the conductive melt material is specifically located on the underside of the connecting conductor facing the cells. Attaching the conductive melt material to the connecting conductor ensures the greatest possible distance between the conductive melt material and the second pole, as the molten, conductive material flows down the cell extension to the second pole, bridging the gap between them.

[0018] Preferably, the conductive melt material is only attached around the cell terminal on the connecting conductor, so that no additional connection is created between adjacent cells in the event that the first reference temperature is exceeded.

[0019] According to another embodiment, the connecting conductor consists at least partially of the conductive melt material, particularly in the area of ​​the cell terminal. Thus, no additional material and / or component is required, since the conductive melt material is integrated into the connecting conductor. For this purpose, the connecting conductor can, for example, be designed as a bimetal, so that the conductive melt metal forms a layer of the bimetal.

[0020] According to a further embodiment, the conductive melt material is housed in a spacer whose melting temperature is lower than that of the conductive melt material. The spacer is arranged above the cell terminal. Preferably, the spacer is a foam pad located on the connecting conductor above the cell extension. By arranging the conductive melt material in the spacer, it is thermally well insulated during normal operation of the high-voltage storage system, thus preventing premature melting of the conductive melt material even more effectively. Furthermore, the placement and application of the melt material are simple.

[0021] To store the conductive melt material in a foam pad, the conductive melt material can, for example, be in pill form. This is then either overmolded by the foam forming the foam pad or embedded within the foam pad itself.

[0022] According to another embodiment, the connecting conductor has a tongue in the region of the end face of the cell housing, which in its initial position is spaced apart from the cell terminal and the second pole. When the reference temperature is exceeded, the tongue creates a connection to the second pole. The tongue can be attached to the connecting conductor or formed integrally with it. For example, the tongue can be punched out of the connecting conductor. Thus, no additional component is required to provide the short-circuit connection.

[0023] Preferably, the tongue projects towards the cell casing, with a distance between the cell casing and the tongue in a starting position.

[0024] A cell seal can be provided between the cell extension and the cell housing, which is destroyed upon reaching a second reference temperature, whereby the cell extension is at least partially immersed in the cell housing. The second reference temperature is preferably lower than the first reference temperature.

[0025] Preferably, the tongue is positioned far enough away from the end face of the cell housing in its initial position that it abuts the end face when the cell extension is immersed. This ensures a short-circuit connection not only upon a temperature increase or the input of thermal energy into the connecting conductor, but directly during the thermal event.

[0026] Further advantages and features of the invention will become apparent from the following description and from the referenced drawings. The drawings show: - Fig. 1 a schematic representation of a cell assembly according to the invention in top view; - Fig. 2 a schematic representation of a cell of the in Fig. 1 cell assembly shown according to a first embodiment; - Fig. 3 a schematic cross-section of the in Fig. 2 shown cell in the area of ​​the cell terminal; - Fig. 4 a schematic representation of a cell of the in Fig. 1 cell assembly shown according to a second embodiment; - Fig. 5 a schematic representation of a cell of the in Fig. 1 cell assembly shown according to a third embodiment; - Fig. 6 a schematic representation of a cell of the in Fig. 1 cell assembly shown according to a fourth embodiment; and - Fig. 7A and Fig. 7B Schematic representations of a connecting conductor, wherein Fig. 7A a top view of the in Fig. 6 shown embodiment of the connecting conductor and Fig. Figure 7B is a top view of an alternative embodiment of the connecting conductor.

[0027] In Fig. Figure 1 shows a cell assembly 10 of a high-voltage storage device. The cell assembly 10 comprises several cells 12 and connecting conductors 14 (here, 4 connecting conductors 14 in this example), which are part of a cell contacting system 16 (see Figure 1). Fig. 2).

[0028] A in Fig. 1 upper connecting conductor 14 connects eight cells 12 to each other to form a parallel assembly 18, the second and third from the top each connect ten cells 12 and the bottom one connects five cells 12, the parallel assembly 18 also being connected in series with each other.

[0029] Of course, other configurations of the cells 12 with the connecting conductors 14 are also possible to form the parallel connections 18. The invention is not limited to these.

[0030] The parallel arrays 18 are also referred to as a logical cell.

[0031] The cells 12 are preferably cylindrical cells, in particular cylindrical cells corresponding to 4.2 volt batteries each. Thus, conventional cells 12 can be used in the high-voltage storage system, thereby reducing costs.

[0032] The cells 12 are arranged in rows, with cells 12 from adjacent rows being offset from each other. Furthermore, the cells 12 project into the spaces between adjacent round cells of neighboring rows, in order to, with respect to Fig. 1. To be built compactly in the vertical direction. Nevertheless, electrically insulating seals 20 and / or cooling elements (not shown) can be positioned between the respective rows of cells 12.

[0033] The connecting conductor 14 has freely projecting contact arms 22 that extend in opposite directions. The contact arms 22 are part of the cell contacting system 16 and serve to establish an electrical connection between individual cells 12.

[0034] The contact arms 22 are divided into contacts for first poles 24 and second poles 26, whereby the first pole 24 is usually the positive pole, i.e. the anode, and the second pole 26 is usually the negative pole, i.e. the cathode.

[0035] The connecting conductor 14 is usually made of aluminium and therefore has a melting point of 660°C.

[0036] Fig. 2 and Fig. Figure 3 shows a cell 12 and the cell contacting system 16 of the cell assembly 10 according to a first embodiment. The cell 12 comprises a cell terminal 30 formed by a cell extension 28, which forms the first pole 24.

[0037] As particularly in Fig. As can be clearly seen in Figure 3, the cell terminal 30 extends through an opening 32 in a cell housing 34, which forms the second pole 26. An electrically insulating, annular cell seal 36 is arranged between the cell terminal 30 and the edge of the opening 32 of the cell housing 34.

[0038] As previously mentioned, the cell contacting system 16 comprises a connecting conductor 14, in particular a contact arm 22 of the connecting conductor 14, which is located in Fig. 2 and Fig. 3 is located at the top of the cell terminal 30. Following the contact point between the connecting conductor 14 and the cell terminal 30, an overload protection device 38, in particular a fuse, is installed.

[0039] The overload protection device 38 serves to disconnect the connection between the cell terminal 30 and the connecting conductor 14, which is in contact with the other cells 12, in the event of a thermal event. The overload protection device 38 thus serves to prevent the propagation of a thermal event, a so-called thermal runaway, by interrupting the short-circuit current.

[0040] The overload protection 38 can be formed by a constriction on the connecting conductor 14. Alternatively, the overload protection 38 can also have two webs.

[0041] A placeholder 40 is positioned above the cell terminal 30 and on the connecting conductor 14. The placeholder 40 is preferably a foam pad that supports thermal isolation of the connecting conductor 14 in the event of a thermal event and bridges the space between the cell contacting system 16 and a housing during operation.

[0042] The foam pad is located on the connecting conductor 14 above the cell terminal 30 and melts upon thermal input, creating a cavity that allows a high temperature input into the connecting conductor 14.

[0043] Also in Fig. 2 and Fig. Figure 3 shows a short-circuit connection 42 provided outside the cell 12, which serves to directly electrically connect the cell terminal 30 and the second pole 26, i.e. the cell housing 34, when a previously defined first reference temperature is exceeded.

[0044] The first reference temperature is between 200°C and 400°C, so that the short-circuit connection 42 is established well before the melting point of the connecting conductor 14 is reached, especially if it is made of aluminum, as is usually the case. Furthermore, the first reference temperature is high enough to prevent unintentional activation of the short-circuit connection 42 during operation, since the maximum operating temperature is 60°C and the critical limit temperature is 150°C or 160°C.

[0045] At the in Fig. 2 and Fig. In the embodiment shown in Figure 3, the short-circuit connection 42 is provided by an electrically conductive melt material 44, which is provided outside the cell 12 in the area of ​​the cell terminal 30.

[0046] Here, the conductive melt material 44 is provided in particular on the connecting conductor 14, that is, a part connected to the cell 12.

[0047] The conductive melt material 44 can be a bimetal or an alloy, preferably containing tin or zinc. Both tin and zinc alloys have melting points below the maximum reference temperature, so the short-circuit connection 42 can be activated well before the melting point of the connecting conductor 14. As already mentioned, the connecting conductor 14 is usually made of aluminum and therefore has a melting point of 660°C. The melting point of tin, on the other hand, is 230°C, while the melting point of a zinc alloy is approximately 330°C.

[0048] In the Fig. In the embodiment shown in Figure 2, the conductive melt material 44 is attached to the underside 45 of the connecting conductor 14 in the region of the cell terminal 30, i.e., the side facing the cell 12. It can be seen that the conductive melt material 44 is not located in the contact area between the connecting conductor 14 and the cell terminal 30, but rather in the area of ​​the connecting conductor 14 that directly surrounds the cell terminal 30.

[0049] In this embodiment of the short-circuit connection 42, an alloy is preferably used.

[0050] The following explains the function of the short-circuit connection 42 in the event of a thermal event.

[0051] In the event of a thermal event within cell 12, the temperature rises and the cell seal 36 is damaged. Due to the destruction of the cell seal 36, the cell terminal 30 sags and at least partially enters the cell housing 34. This results in an unpredictable contact between the cell terminal 30 and the cell housing 34, causing a secondary short circuit.

[0052] A distinction is made between low-resistance, medium-resistance, and high-resistance secondary short circuits. In a low-resistance secondary short circuit, short-circuit currents of at least 1000 A occur, so that the current peak is high enough to trip the overload fuse 38. Thus, the defective cell 12 is no longer connected to the other cells 12 in the cell assembly 10 via the connecting conductor 14, and thermal runaway can be prevented.

[0053] In the case of a high-resistance secondary short circuit, however, the defective cell 12 discharges via the other cells 12 in the cell cluster 10.

[0054] Medium-resistance secondary short circuits, on the other hand, are difficult to control because their voltage is not high enough to trip the overload protection 38. Instead, they continuously release heat, so that very high temperatures, well over 1000°C, can be reached within the cell assembly 10. Since the connecting conductor 14, which is usually made of aluminum, has a melting point of 660°C, it melts at such temperatures. The melting of the connecting conductor 14 can lead to a tertiary short circuit if the melt creates an electrical connection between the cell terminal 30 and the cell housing 34 of an adjacent cell 12.

[0055] The short-circuit connection 42 is designed to ensure a low-resistance secondary short circuit in the event of a thermal event, thus isolating the defective cell 12 from the other cells 12 in the cell assembly 10 as quickly as possible. Due to its high current peak of the short-circuit current and the resulting tripping of the overload protection 38, the low-resistance secondary short circuit is the easiest to control and typically results in the least damage to the high-voltage storage system.

[0056] Due to the temperature increase caused by the thermal event, the conductive melt material 44 melts when a first, predefined reference temperature is exceeded. This first reference temperature corresponds to the melting temperature of the conductive melt material 44.

[0057] In the Fig. 2 and Fig. In the embodiment shown in Figure 3, the conductive melt material 44, after exceeding the first reference temperature, runs from the connecting conductor 14 down the sides of the cell terminal 30 to the cell housing 34, thus providing a direct electrical connection that defines the short-circuit connection 42.

[0058] In particular, the area of ​​the direct electrical contact between the cell terminal 30 and the cell housing 34 is increased to ensure that the short-circuit current is sufficiently high to disconnect the overload protection 38 of the connecting conductor 14.

[0059] According to a second embodiment, not shown in the figures, the connecting conductor 14 consists at least partially of the conductive melt material 44. Here too, the conductive melt material 44 is preferably provided in the area of ​​the cell terminal 30.

[0060] Alternatively, the melting material 44 can be applied to the underside of the connecting conductor 14 (see Fig. 3) as well as laterally at cell terminal 30 (see Fig. 4) be appropriate, as is suggested in some detail in Fig. 2 is recognizable.

[0061] For example, the connecting conductor 14 can consist of a bimetal, wherein a bottom layer of the bimetal corresponds to the conductive melt material 44.

[0062] In the Fig. In the embodiment shown in Figure 4, the conductive melt material 44 forming the short-circuit connection 42 is present on the cell 12 itself. The conductive melt material 44 is attached laterally directly to the cell terminal 30, preferably around its entire circumference. To prevent an unintended short circuit, the conductive melt material 44 is spaced apart from the cell housing 34 in its initial position.

[0063] For example, a circumferential coating of the cell terminal 30 with the conductive melt material 44 is carried out, while a coating on the side of the cell terminal 30 facing the connecting conductor 14 is not absolutely necessary.

[0064] In this embodiment as well, a temperature increase during a thermal event within the cell 12 causes the conductive melt material 44 to melt after exceeding the first reference temperature, run down and thus directly electrically connect the cell terminal 30 with the cell housing 34.

[0065] A third embodiment is in Fig. Figure 5 shows the conductive melt material 44 being stored in the placeholder 40, where the melting temperature of the placeholder 40 is lower than the melting temperature of the conductive melt material 44.

[0066] Accordingly, during a thermal event within the cell 12, the placeholder 40 melts first, and only subsequently, after exceeding the first reference temperature, does the conductive melt material 44 melt, which, due to gravity, runs down the sides of the cell terminal 30 towards the cell housing 34 and thus establishes a direct electrical connection.

[0067] To store the conductive melt material 44 in the placeholder 40, the conductive melt material 44 can, for example, be pill-shaped so that it can be embedded in the placeholder 40. Alternatively, the conductive melt material 44 can also be overmolded / over-foamed by the placeholder 40, especially if it is the foam pad.

[0068] In Fig. 6, Fig. 7A and Fig. Figure 7B shows another embodiment of a short-circuit connection 42. In this case, the short-circuit connection 42 is not provided via a conductive melt material 44, but via a tongue 46.

[0069] The connecting conductor 14 has the tongue 46 in the region of the end face 48 of the cell housing 34. The tongue 46 can accordingly be attached to the connecting conductor 14 or be formed integrally with the connecting conductor 14.

[0070] In the Fig. 6 and Fig. In the embodiment shown in 7A, the tongue 46 is punched out of the connecting conductor 14, as in particular in Fig. 7A can be seen.

[0071] In its initial position, the tongue 46 is spaced away from both the cell terminal 30 and the cell housing 34. However, if a reference temperature is exceeded, particularly due to a thermal event within the cell 12, the tongue 46 deforms towards the cell housing 34, thus establishing a direct electrical connection to the second pole 26, i.e., the end face 48 of the cell housing 34.

[0072] The electrical connection to the second pole 26 is thus created in particular by the fact that the profiled tongue 46 deforms in the direction of the thermal mass when heat is applied. Since the heat originates from the cell 12 itself during a thermal event within the cell 12, the tongue 46 deforms in the direction of the cell housing 34.

[0073] Alternatively or additionally, the tongue 46 can create the short circuit between the poles 24, 26 by causing the cell terminal 30 to sag together with the connecting conductor 14 and tongue 46 when the cell seal 36 melts, until the tongue 46 rests against the pole 26.

[0074] In the embodiment shown here, as in particular in Fig. 6 and Fig. As can be seen in 7B, the tongue 46 already extends in the initial state towards the cell casing 34, but is not in contact with it.

[0075] The tongue 46 is positioned so far from the end face 48 of the cell housing 34 in its initial position that, when the cell terminal 30 is immersed in the cell housing 34, it abuts the end face 48 of the cell housing 34. Thus, even with insufficient heat input to deform the tongue 46 as intended, a short-circuit connection 42 between the cell terminal 30 and the cell housing 34 can be ensured.

[0076] In Fig. Figure 7B shows an alternative embodiment of the connecting conductor 14 with the tongue 46. In this embodiment, the tongue 46 is attached laterally to the connecting conductor 14, instead of as in Figure 7B. Fig. 6 and Fig. 7A is punched out in the middle of the connecting conductor 14.

[0077] As an alternative to the embodiment shown here, the tongue 46 can also initially lie in a plane with the connecting conductor 14 and only deform towards the cell housing 34 due to the input of heat.

Claims

[1] Cell assembly (10) of a high-voltage storage device, comprising several cells (12), wherein each cell (12) has a cell terminal (30) formed by a cell extension (28) of a first pole (24) and a second pole (26) forming a cell housing (34), and connecting conductors (14) that electrically connect the cell terminals (30) and / or second poles (26) to each other, wherein a short-circuit connection (42) is additionally provided outside the cells (12) by which the cell terminal (30) and the second pole (26) are directly electrically connected when a previously defined first reference temperature is exceeded. [2] Cell assembly (10) according to claim 1, characterized by , that the first reference temperature is between 200°C and 400°C. [3] Cell assembly (10) according to any of the preceding claims, characterized by, that the short-circuit connection (42) is provided by a conductive melt material (44) which is located outside the cell (12) on the cell (12) itself and / or on a part connected to the cell (12), in particular in the area of ​​the cell terminal (30). [4] Cell assembly (10) according to claim 3, characterized by , that the conductive melt material (44) is a bimetal or an alloy. [5] Cell assembly (10) according to claim 3 or 4, characterized by , that the conductive melt material (44) is attached to the cell terminal (30), in particular as a circumferential coating. [6] Cell assembly (10) according to any one of claims 3 to 5, characterized by , that the conductive melt material (44) is attached to the connecting conductor (14), in particular on a bottom side (45) of the connecting conductor (14) facing the cells (12). [7] Cell assembly (10) according to any one of claims 3 to 6, characterized by, that the connecting conductor (14) consists at least partially of the conductive melt material (44), particularly in the area of ​​the cell terminals (30). [8] Cell assembly (10) according to any one of claims 3 to 7, characterized by , that the conductive melt material (44) is stored in a placeholder (40) whose melting temperature is lower than the melting temperature of the conductive melt material (44), wherein the placeholder (40) is arranged above the cell terminal (30), in particular wherein the placeholder (40) is a foam pad which is located on the connecting conductor (14) above the cell terminal (30). [9] Cell assembly (10) according to any of the preceding claims, characterized by, that the connecting conductor (14) has a tongue (46) in the region of an end face (48) of the cell housing (34) which in an initial position is spaced apart from the cell terminal (30) and the second pole (26), wherein the tongue (46) provides a connection to the second pole (26) when the reference temperature is exceeded, so that the short-circuit connection (42) is provided by the tongue (46). [10] Cell assembly (10) according to any of the preceding claims, characterized by , that a cell seal (36) is provided between the cell terminal (30) and the cell housing (34), which is destroyed when a second reference temperature is reached, causing the cell terminal (30) to at least partially immerse itself in the cell housing (34). [11] Cell assembly (10) according to claims 9 and 10, characterized by, that the tongue (46) is so far away from the front face (48) of the cell casing (34) in the starting position that it touches the front face (48) of the cell casing (34) when the cell terminal (30) is immersed.

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