DE102022128236A1 - Method for the electrically conductive connection of a pole of a battery cell to a contact element, battery cell and battery module - Google Patents

Abstract

Method for the electrically conductive connection of a pole (1, 2) of a battery cell (3, 14) to a contact element (4), wherein the pole (1, 2) and the contact element (4) each comprise at least 90% by weight of aluminum at least in the region of the contact surfaces (5, 6) that come into contact with one another; wherein the electrically conductive connection is made by resistance projection welding. In addition, a battery cell and a battery module are specified.

Description

The invention relates to a method for the electrically conductive connection of a pole of a battery cell to a contact element, a battery cell and a battery module.

Electrically driven or powered motor vehicles, such as electric or hybrid vehicles, typically have an electric motor as a drive machine, which is coupled to an internal (high-voltage) electrical energy storage device in the vehicle to supply electrical energy. Such energy storage devices are designed, for example, in the form of (vehicle) batteries.

An (electrochemical) battery is understood here to mean in particular a so-called secondary battery (secondary battery) of the motor vehicle, in which a used chemical energy can be restored by means of an electrical charging process. Such batteries are designed in particular as electrochemical accumulators, for example as lithium-ion accumulators. In order to generate or provide a sufficiently high operating voltage, such batteries typically have several individual battery cells that are interconnected to form a battery module.

Batteries of the type mentioned have at least one cathode and one anode as well as a separator and an electrolyte on a battery cell level. The electrodes, i.e. the anode and the cathode, are made of at least one respective (electrode) active material. In particular, the active material is applied as a coating to a carrier material, e.g. a metallic foil, in particular on both sides. Materials containing copper or aluminum are used as metallic foils in particular.

The electrodes and possibly separator material (hereinafter referred to as electrode sheets) are arranged on top of one another and form a stack that is arranged in a housing. An electrolyte can be arranged as a liquid in the housing or as a solid within the stack (in a so-called all-solid-state battery cell). The housing can be made of an elastically deformable composite film (pouch cell) or a material that can only be plastically deformed (prismatic cell).

The anodes and cathodes arranged inside the housing are connected to an electrical circuit outside the housing via so-called conductors. The conductors extend outwards through the gas-tight housing either to at least one positive pole arranged on the housing or to a negative pole arranged on the housing. Inside the housing, the conductors are electrically connected to the large number of electrodes of the same type, i.e. anodes or cathodes. The conductors and the poles in particular have a material corresponding to the carrier materials, i.e. a copper-containing material or an aluminum-containing material.

Each battery cell therefore has at least one positive pole and at least one negative pole (each also referred to as a terminal). Within a battery module, several battery cells are connected to one another in an electrically conductive manner via their poles. A contact element, e.g. a busbar, is used for the connection, which is firmly connected to the poles via welded connections. The battery cells can be connected to one another in series or in parallel via the contact elements.

This welded connection is generally made by laser welding. Each connection between the contact element and a pole is contacted individually by the laser beam, so that a plurality of such connections can only be created one after the other with a laser beam. This means that long cycle times are required for the production of battery modules. At the same time, the provision of laser welding equipment requires a high level of investment in the system. Laser welding also requires complex clamping technology so that the components to be welded can be arranged as precisely as possible in relation to the laser beam, e.g. to create a joint gap of less than 0.2 millimeters and to ensure reliable welding. There is a risk of hot cracks forming, particularly with aluminum connections.

From the EN 10 2015 210 035 A1 A device and a method for connecting battery cells are known. Cell connectors are arranged on a carrier material and connected to one another via this.

From the EN 10 2017 004 939 A1 A method for connecting the electrical poles of two battery cells is known. The poles are connected to a cell connector plate using ultrasonic bonding or welding.

From the WO 2018/071765 A1 A multilayer connecting element for connecting battery cells is known.

The object of the present invention is to at least partially solve the problems mentioned with reference to the prior art and in particular to provide a particularly suitable method for producing an electrically conductive connection of a pole of a battery cell with a contact element. In particular, the method should be process-safe and thus reproducible, have or enable the shortest possible cycle time and have a large tolerance with regard to component or assembly inaccuracies.

A method with the features according to claim 1 contributes to the solution of these tasks. Advantageous further developments are the subject of the dependent claims. The features listed individually in the claims can be combined with one another in a technologically meaningful way and can be supplemented by explanatory facts from the description and/or details from the figures, whereby further embodiments of the invention are shown.

1. a) Bereitstellen der Batteriezelle mit dem Pol, wobei der Pol eine erste Kontaktfläche aufweist;
2. b) Bereitstellen des Kontaktelements, wobei das Kontaktelement eine zweite Kontaktfläche aufweist;
3. c) Anordnen des Kontaktelements an dem Pol, so dass die Kontaktflächen einander über mindestens zwei Buckel, die an zumindest einer der Kontaktfläche ausgeformt sind, kontaktieren;
4. d) Anordnen einer ersten Elektrode einer Widerstandsbuckelschweißmaschine an dem Kontaktelement in einem Bereich eines ersten Buckels und Anordnen einer zweiten Elektrode der Widerstandsbuckelschweißmaschine an dem Kontaktelement in einem Bereich eines zweiten Buckels;
5. e) Durchführen einer Widerstandsbuckelschweißung und Verbinden der Kontaktflächen über die Buckel.

A method for electrically conductively connecting a pole of a battery cell to a contact element is proposed. In particular, the pole and the contact element each comprise at least 90% by weight of aluminum, preferably at least 95% by weight, particularly preferably at least 99% by weight, at least in the region of the contact surfaces that come into contact with one another. The method comprises at least the following steps:

1. a) providing the battery cell with the pole, wherein the pole has a first contact surface;
2. b) providing the contact element, wherein the contact element has a second contact surface;
3. c) arranging the contact element on the pole so that the contact surfaces contact each other via at least two projections formed on at least one of the contact surfaces;
4. d) arranging a first electrode of a resistance projection welding machine on the contact element in a region of a first projection and arranging a second electrode of the resistance projection welding machine on the contact element in a region of a second projection;
5. e) Perform resistance projection welding and connect the contact surfaces via the projections.

The above (non-exhaustive) classification of the process steps into a) to e) is primarily intended to serve only as a means of differentiation and does not enforce any order and/or dependency. The frequency of the process steps can also vary. It is also possible for process steps to overlap one another at least partially in time. Most preferably, process steps a) and b) take place before steps c) to e). In particular, steps c) to e) take place one after the other in the order given and at least partially simultaneously or overlapping one another. In particular, step e) is carried out after steps a) to d). In particular, steps a) to e) are carried out in the order given.

In particular, the use of the resistance projection welding process in battery cell production is proposed for the first time, in particular for connecting a battery cell to a contact element which is used for the electrically conductive connection of the battery cells to one another.

Resistance projection welding is a variant of resistance pressure welding. The welding point is heated in particular as a result of Joule resistance heating when a current flows through an electrical conductor. The resistance that occurs during resistance heating is made up in particular of the contact resistances of the two contact surfaces and the material resistance of the materials of the contact surfaces.

The current concentration at the welding point is achieved in particular by embossed projections in at least one of the components to be connected (i.e. the pole and/or the contact element) or by the shape of these components. During the resistance projection welding, the projections are at least partially reshaped by the electrode force and by the heating as a result of the current flow. This reshaping is usually not complete, whereby the remaining surface shape or deformation on the component with the projection is retained. The reshaped projection during welding forms a material-locking connection in the form of a weld nugget.

The joining partner also heats up (partly to the melting point), so that the pressure applied creates a material bond with the material of the projection. In particular, the electric current is applied first and then the pressure is increased, in particular continuously. When the current is off, pressure is continued until the weld nugget has cooled down.

The heat generation depends on the resistance conditions at the joint (i.e. the contact surfaces that come into contact with each other) and the square of the flowing current. The contact resistance and the material resistance of the joining partners or components involved contribute significantly to the weld nugget. The contact resistance between the joining partners is influenced by the projection geometry, the contact pressure and the surface condition of the components.

In step a), the battery cell is provided with the pole, wherein the pole has a first contact surface.

In step b), the contact element is provided, wherein the contact element has a second contact surface.

In step c), the contact element is arranged on the pole of the battery cell so that the contact surfaces contact each other via at least two bumps that are formed on at least one of the contact surfaces. In this case, one bump can also be formed on each contact surface. The respective bump can be created by forming, e.g. by embossing, or can already be present on the component, e.g. as a result of shaping. The bumps are preferably provided on the contact element.

In step d), a first electrode of a resistance projection welding machine is arranged on the contact element in an area of a first projection and a second electrode of the resistance projection welding machine is arranged on the contact element in an area of a second projection. The electrodes contact the contact element in particular on a surface of the contact element opposite the projection. In particular, the electrodes have a different polarization, so that in step e) a current is transmitted between the two electrodes via the at least two projections.

In step e), resistance projection welding is carried out and the contact surfaces are connected via the projections. In particular, the electrical current (with two electrodes and two projections) is transferred from one electrode via one projection to the pole and via the other projection and the contact element to the other electrode. As a result of the at least two electrodes, the current used for welding is only conducted via the components to be connected and not via the battery cell itself (e.g. via the conductors or electrodes in the stack).

In particular, in step e), a first weld nugget is produced in the area of contact between the first projection and the other contact surface, and a second weld nugget is produced in the area of contact between the second projection and the other contact surface. The weld nugget is formed in particular by the materials of both components (i.e. the contact element and the pole), so that a material connection is formed between the contact surfaces.

In particular, in step a), a plurality of battery cells are provided. In particular, in step c), at least one contact element is arranged on each pole of the plurality of battery cells. In particular, in step d), at least one pair of a first electrode and a second electrode is provided for each battery cell. In particular, in step e), the plurality of poles are connected to the at least one contact element by welding.

In particular, in step e), at least two battery cells are simultaneously connected via the respective pole to the at least one (i.e. to exactly one) contact element via the resistance projection welding.

In particular, in step e), at least two battery cells are connected via the respective pole with a time offset to the at least one contact element via the resistance projection welding.

In particular, a plurality of battery cells can be connected to one another via a contact element. Alternatively, a plurality of battery cells can be connected to one another via a plurality of contact elements, in particular two battery cells each via one contact element.

In particular, within the scope of step e), more than 50, preferably more than 100 or even more than 150, resistance projection welds (i.e. material-locking connections between a projection and a component of the contact element and pole) can be produced simultaneously.

In particular, the battery cells are connected in series with one another via the contact element (i.e. different poles of two battery cells are connected to one another via the contact element) or in parallel with one another (i.e. the same poles of two battery cells are connected to one another via the contact element). A large number of battery cells can also be connected in parallel with one another via the contact element and this large number of battery cells can be connected in series with another large number of battery cells (which are also connected in parallel with one another via the one contact element) via the same contact element.

In particular, in at least one of steps c), d) and e), at least one projection is deformed so that a height adjustment occurs between a first layer of the contact surfaces on a first pole and a second layer of the contact surfaces on a second pole. In particular, this deformation takes place in one of steps c) and d), i.e. before carrying out the resistance projection welding according to step e).

Preferably, the bumps are arranged on the contact element.

In particular, the at least one resistance projection weld is produced by a capacitor discharge of the resistance projection welding machine.

A battery cell is also proposed, comprising at least one housing and a stack of electrode sheets or electrodes arranged therein. A first pole and a second pole for electrically contacting the electrode sheets or electrodes are arranged on the housing. In particular, the battery cell additionally has a contact element which is integrally connected to one of the poles via a resistance projection weld. In particular, this pole and the contact element each have at least 90% by weight of aluminum, at least in the region of the contact surfaces that come into contact with one another.

A battery module is further proposed, at least comprising a plurality of the described battery cells, wherein at least the respective identical poles or at least the mutually different poles of the battery cells are electrically conductively connected to one another via the contact element.

The battery module is used in particular in a motor vehicle as an energy storage device. The energy storage device supplies a traction drive with energy.

In particular, at least one data processing system is provided which has means which are suitably equipped, configured or programmed to carry out at least part of the method, in particular to carry out step e), or which carry out the method. The means is or are suitably designed in particular to control the resistance projection welding machine and, if necessary, to record and evaluate measured values.

The means include, for example, a processor and a memory in which instructions to be executed by the processor are stored, as well as data lines or transmission devices that enable a transmission of instructions, measured values, e.g. from sensors, data or the like between the elements mentioned.

The means may in particular comprise one or more of the following components: controller(s), microcontroller, data storage, data connection, display devices (such as a display), counter or timer, at least one further sensor, an energy source, etc.

A computer program is further proposed, comprising instructions which, when the program is executed by a computer, cause the computer to carry out the described method or the steps of the described method.

Furthermore, a computer-readable storage medium is proposed, comprising instructions which, when executed by a computer, cause the computer to carry out the described method or at least some of the steps of the described method.

The statements on the method are particularly transferable to the battery cell, the battery module, the data processing system and/or the computer-implemented method (i.e. the computer program and the computer-readable storage medium) and vice versa.

The use of indefinite articles ("a", "an", "an" and "another"), particularly in the patent claims and the description reflecting them, is to be understood as such and not as a number. Terms or components introduced accordingly are therefore to be understood as being present at least once and, in particular, can also be present multiple times.

As a precaution, it should be noted that the numerals used here ("first", "second", ...) primarily serve (only) to distinguish between several similar objects, sizes or processes, and in particular do not necessarily specify a dependency and/or sequence of these objects, sizes or processes. If a dependency and/or sequence is required, this is explicitly stated here or it is obvious to the person skilled in the art when studying the specifically described design. If a component can occur multiple times ("at least one"), the description of one of these components can apply equally to all or part of the majority of these components, but this is not mandatory.

• 1: ein aus dem Stand der Technik bekanntes Verfahren;
• 2: das Verfahren mit einer Widerstandsbuckelschweißmaschine;
• 3: die Schritte d) und e) des Verfahrens;
• 4: eine Detailansicht des Schrittes e) des Verfahrens; und
• 5: ein besonderes Detail des Verfahrens.

The invention and the technical environment are described below with reference to the attached figures. ren in more detail. It should be noted that the invention is not intended to be limited by the exemplary embodiments given. In particular, it should be noted that the figures and in particular the size relationships shown are only schematic. They show:

• 1 : a method known from the state of the art;
• 2 : the process using a resistance projection welding machine;
• 3 : steps d) and e) of the procedure;
• 4 : a detailed view of step e) of the method; and
• 5 : a special detail of the procedure.

1 shows a method known from the prior art for the electrically conductive connection of poles 1, 2 of a battery cell 3, 14 with contact elements 4.

In 1 a battery module 19 is shown, consisting of a plurality of battery cells 3, 14 which are connected in series with one another. Two battery cells 3, 14 are connected in series with one another via a contact element 4 (i.e. different poles 1, 2 of two battery cells 3, 14 are connected to one another via the contact element 4).

The welded connection between contact element 4 and pole 1, 2 is realized by laser welding. Each connection between contact element 4 and a respective pole 1, 2 is created by the laser beam, so that a plurality of such connections can only be created one after the other with a laser beam. Long cycle times are therefore required for the manufacture of the battery module 19. At the same time, the provision of laser welding devices (laser 21) requires a high investment volume in equipment. Laser welding also requires complex clamping technology.

2 shows the method for the electrically conductive connection of poles 1, 2 of a battery cell 3, 14 with contact elements 4 using a resistance projection welding machine 10.

In 2 a battery module 19 is shown, consisting of a plurality of battery cells 3, 14 which are connected in series with one another. Two battery cells 3, 14 are connected in series with one another via a contact element 4 (i.e. different poles 1, 2 of two battery cells 3, 14 are connected to one another via the contact element 4).

To achieve resistance projection welding, it is necessary to conduct the current over adjacent projections, with the current flowing over the first component into one projection and to the second component and from there over the other projection back to the first component. This current flow is achieved by arranging two electrodes of the resistance projection welding machine in the area of the projections.

3 shows steps d) and e) of the procedure.

In step a), two battery cells 3, 14 are provided, each with a first pole 1 and a second pole 2. The first poles 1 have a first contact surface 5, which is made of a material with at least 90% by weight aluminum.

The battery cells 3, 14 each comprise a housing 17 and a stack of electrode sheets 18 or electrodes arranged therein. A first pole 1 and a second pole 2 for electrically contacting the electrode sheets 18 or electrodes are arranged on the housing 17.

In step b), the contact element 4 is provided, wherein the contact element 4 has a second contact surface 6 which is formed from a material with at least 90% by weight of aluminum.

In step c), the contact element 4 is arranged on the first poles 1 of the battery cells 3 so that the contact surfaces 5, 6 contact each other via two bumps 7, 8 that are formed on the first contact surface 5. The bumps 7, 8 are each produced by a deformation, e.g. by embossing.

In step d), a first electrode 9 of the resistance projection welding machine 10 is arranged on the contact element 4 in an area of the first projection 7 and a second electrode 11 of the resistance projection welding machine 10 is arranged on the contact element 4 in an area of the second projection 8. The electrodes 9, 11 contact the contact element 4 on a surface of the contact element 4 opposite the projection 7, 8. The electrodes 9, 11 have a different polarization (plus and minus, as shown) from one another, so that in step e) a current is transmitted between the two electrodes 9, 11 via the two projections 7, 8.

In step e), resistance projection welding is carried out and connecting the contact surfaces 5, 6 via the bumps 7, 8. The electric current flows from the first electrode 9 via the first bump 7 to the pole 1 and via the second bump 8 and the contact element 4 to the second electrode 11. As a result of the provision of two electrodes 9, 11 arranged spatially close to one another, the current used for welding is only conducted via the components to be connected (contact element 4 and pole 1) and not via the battery cell 3 itself (i.e., e.g. via the conductors or electrodes in the stack).

The resistance projection welding machine 10 comprises a system 20 for data processing, which has means that are suitably equipped, configured or programmed to carry out at least part of the method, in particular to carry out step e), or which carry out the method. The means is, for example, a control unit that controls the resistance projection welding machine 10 (capacitor charging and at least partial discharging, feeding the electrodes 9, 11, selection of the electrodes 9, 11 to be fed, selection of the electrodes 9, 11 to be supplied with current, selection and control of the contact force of the electrodes 9, 11, determination of the temporal sequence of the welding processes, analysis and evaluation of the welding carried out) and, if necessary, for recording and evaluating measured values (e.g. values and progression of current, voltage, resistance, etc.; in particular for each electrode 9, 11 or each electrode pair).

4 shows a detailed view of step e) of the process. Please refer to the explanations for 2 and 3 is referred to.

In step e), a first welding lens 12 is produced in the area of contact between the first projection 7 and the second contact surface 6 of the pole 1, and a second welding lens 13 is produced in the area of contact between the second projection 8 and the second contact surface 6. The welding lens 12 is formed by the materials of both components (i.e. the contact element 4 and the pole 1), so that a material connection is formed between the contact surfaces 5, 6.

In step e), the two battery cells 3, 14 shown can be connected simultaneously to the one contact element 4 via the respective first pole 1 using the resistance projection welding. Alternatively, in step e), the two battery cells 3, 14 shown can be connected at different times to the one contact element 4 via the respective first pole 1 using the resistance projection welding.

5 shows a special form of the procedure. The comments on 2 to 4 is referred to.

In one of steps c), d) and e), the projections 7, 8 can be deformed so that a height adjustment occurs between a first layer 15 of the contact surfaces 5, 6 on a first pole 1 of the first battery cell 3 and a second layer 16 of the contact surfaces 5, 6 on a second pole 2 of the second battery cell 14. Preferably, this deformation takes place in one of steps c) and d), i.e. before carrying out the resistance projection welding according to step e).

In 5 it is shown that this deformation can also take place as part of step e). In step d), the electrodes 9, 11 are arranged on the contact element 4 and are moved until the projections 7, 8 rest on the second contact surface 6 of the poles 1, 2. A deformation of the projections 7, 8 can then take place as part of the resistance projection welding, during which the material of the projections 7, 8 is at least partially melted and deformable as a result of the resistance heating.

The height compensation is necessary in order to compensate for any positional tolerances that may exist, especially in the poles 1, 2 of the battery cells 3, 14. This positional tolerance results in particular from the length tolerance of the battery cells 3, 14 (i.e. the distance between the second contact surfaces 6 of the two poles 1, 2 of a battery cell) and the stacking tolerance of the battery cells 3, 14 that are arranged next to one another and are to be connected by the at least one contact element 4.

With a resistance projection welding machine 10, a large number of battery cells 3, 14 can be connected simultaneously via one or more contact elements 4. The one resistance projection welding machine 10 can have a large number of electrodes 9, 11 that can be moved simultaneously or at different times to one another and can carry out welding. With the one resistance projection welding machine 10, for example, over 100 electrodes, preferably over 150 electrodes, can be operated or controlled to carry out welding processes simultaneously.

In particular, welding processes on a contact element 4 can be controlled in such a way that, for example, in the case of several adjacent battery cells 3, 14, initially only every other battery cell 3, 14 is welded at the same time. This allows the heat induced in the contact element 4 to be dissipated in the meantime, so that the welding on the other battery cells can then be carried out at different times. len 3, 14 can be carried out. This control of the resistance projection welding machine 10 is in 3 In contrast, in 5 a simultaneous welding of the battery cells 3, 14 arranged adjacent to each other is shown.

The resistance projection welding process enables better compensation of tolerances that may occur due to the electrodes 9, 11 that are moved, so that a reproducible quality of the welds can be produced. Furthermore, each weld can be analyzed based on the values for current, voltage, etc. present in the resistance projection welding machine 10, or possible deviations from the norm or suspected process errors can be displayed. Due to the large number of electrodes 9, 11, which can be controlled simultaneously or at different times by just one resistance projection welding machine 10, a very short cycle time results for the production of a battery module 19 that comprises a large number of battery cells 3, 14.

With the known laser welding process, this monitoring of the welding points can only be achieved using complex sensors, e.g. optical sensors. Furthermore, the laser welding process is much more susceptible to tolerances that may exist, so that faulty welds or welded joints can occur more frequently. For this reason, laser welding requires complex clamping technology or the requirements for component tolerances must be increased. Furthermore, the individual welded joints can only be created one after the other with a laser, so that a shorter cycle time can only be achieved by providing several lasers.

List of reference symbols

1

first pole

2

second pole

3

Battery cell

4

Contact element

5

first contact surface

6

second contact surface

7

first hump

8th

second hump

9

first electrode

10

Resistance projection welding machine

11

second electrode

12

first welding lens

13

second welding lens

14

second battery cell

15

first layer

16

second layer

17

Housing

18

Electrode sheet

19

Battery module

20

system

21

Laser

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• DE 102015210035 A1 [0009]
• DE 102017004939 A1 [0010]
• WO 2018/071765 A1 [0011]

Claims (10)

Method for the electrically conductive connection of a pole (1, 2) of a battery cell (3, 14) to a contact element (4), wherein the pole (1, 2) and the contact element (4) each have at least 90% by weight of aluminum at least in the region of the contact surfaces (5, 6) that contact one another; at least comprising the following steps: a) providing the battery cell (3, 14) with the pole (1, 2), wherein the pole (1, 2) has a first contact surface (5); b) providing the contact element (4), wherein the contact element (4) has a second contact surface (6); c) arranging the contact element (4) on the pole (1, 2) so that the contact surfaces (5, 6) contact one another via at least two humps (7, 8) that are formed on at least one of the contact surfaces (5, 6); d) arranging a first electrode (9) of a resistance projection welding machine (10) on the contact element (4) in a region of a first projection (7) and arranging a second electrode (11) of the resistance projection welding machine (10) on the contact element (4) in a region of a second projection (8); e) carrying out a resistance projection weld and connecting the contact surfaces (5, 6) via the projections (7, 8). Procedure according to Patent claim 1 , wherein in step e) a first welding nugget (12) is produced in the region of the contact between the first projection (7) and the other contact surface (5, 6) and a second welding nugget (13) is produced in the region of the contact between the second projection (8) and the other contact surface (5, 6). Method according to one of the preceding claims, wherein in step a) a plurality of battery cells (3, 14) are provided; wherein in step c) at least one contact element (4) is arranged on a respective pole (1, 2) of the plurality of battery cells (3, 14); wherein in step d) at least one pair of a first electrode (9) and a second electrode (11) is provided for each battery cell (3, 14); wherein in step e) the plurality of poles (1, 2) are connected to the at least one contact element (4) by welding. Procedure according to Patent claim 3 , wherein in step e) at least two battery cells (3, 14) are simultaneously connected via the respective pole (1, 2) to the at least one contact element (4) via the resistance projection welding. Method according to one of the preceding Patent claims 3 and 4 , wherein in step e) at least two battery cells (3, 14) are connected via the respective pole (1, 2) with a temporal offset to the at least one contact element (4) via the resistance projection welding. Method according to one of the preceding Patent claims 3 until 5 , wherein in at least one of steps c), d) and e) a deformation of at least one hump (7, 8) takes place, so that a height compensation takes place between a first layer (15) of the contact surfaces (5, 6) on a first pole (1) of a first battery cell (3) and a second layer (16) of the contact surfaces (5, 6) on a first pole (1) of a second battery cell (14). Method according to one of the preceding claims, wherein the projections (7, 8) are arranged on the contact element (4). Method according to one of the preceding claims, wherein the at least one resistance projection weld is produced by a capacitor discharge of the resistance projection welding machine (10). Battery cell (3, 14) comprising at least one housing (17) and a stack of electrode sheets (18) arranged therein, wherein a first pole (1) and a second pole (2) for electrically contacting the electrode sheets (18) are arranged on the housing (17); wherein the battery cell (3, 14) additionally has a contact element (4) which is integrally connected to one of the poles (1, 2) via a resistance projection weld; wherein this pole (1, 2) and the contact element (4) each have at least 90% by weight aluminum, at least in the region of the contact surfaces (5, 6) which contact one another. Battery module (19), at least comprising a plurality of battery cells (3, 14) according to Patent claim 9 , wherein the respective identical poles (1, 2) of the battery cells (3, 14) are electrically connected to one another via the contact element (4).

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