METHOD FOR ELECTRICALLY CONTACTING A BATTERY BLOCK

Description

[0001] The invention relates to a method for electrically contacting a plurality of battery cells of a battery block.

[0002] In practice, battery blocks are now electrically connected using laser welding. This means that the material is locally heated and / or melted by a laser beam and / or that the heating results in metal splashes and / or contamination, which can impair battery function. However, it is generally not possible or only possible to a very limited extent to electrically connect battery cells in a battery block using ultrasonic bonding. One reason for this is that the substrate is compliant, soft or elastic and tends to resonate. This therefore does not offer ideal conditions for ultrasonic bonding. Secondly, the electrical connection contact surfaces of the battery cells cannot be bonded, or can only be bonded inadequately, using conventional means due to their hardness, grain size and grid structure.In this respect, the materials used for the battery blocks and ultrasonic bonding as a manufacturing process are largely incompatible. Relevant prior art is known, for example, from documents EP 3 109 925 A1 and JP H04 74445.

[0003] The object of the present invention is to provide a modified ultrasonic bonding method which allows battery cells of a battery block to be electrically contacted.

[0004] To achieve this object, the invention has the features of patent claim 1.

[0005] It is therefore provided according to the invention that the ultrasonic bonding method for electrically contacting a plurality of battery cells of a battery block comprises the following steps: A first connection point is produced by heating a bonding tool directly and a first connection contact surface of a first battery cell and / or the connection conductor at least locally indirectly by a laser beam directed at the bonding tool and provided by a laser, by pressing the connection conductor against the first connection contact surface of the first battery cell by means of the bonding tool and by exciting the bonding tool to ultrasonic vibrations, wherein the ultrasonic vibrations are transmitted from the bonding tool to the connection conductor; A second connection point is produced by pressing the connection conductor by the bonding tool against a second connection contact surface of a second battery cell of the battery block or a collective connection contact of the battery block and exciting it to ultrasonic vibrations.

[0006] The particular advantage of the invention is that, as a result of the invention, battery cells can be contacted using ultrasonic bonding, since the laser influences the hardness, grain size, or material properties of the connection points. Furthermore, the electrical contacting of battery blocks using ultrasonic bonding is particularly economical, i.e., quick and cost-effective. The method according to the invention is particularly suitable for series production, since the established test routines for ultrasonic bonding can be used to continuously monitor the bonding process or to perform downstream quality testing. Thus, a large number of battery cells that are connected to form battery blocks can be reliably processed.

[0007] Furthermore, the ultrasonic bonding process according to the invention can be easily automated, making it particularly suitable for the production of battery blocks for the automotive industry. For example, commercially available battery cells can be assembled and electrically contacted as needed.

[0008] With regard to the sequence of procedural steps, it is irrelevant whether the first connection point is created first and then the second connection point, or whether the second connection point is created first and then the first connection point. The skilled person will determine the sequence based on knowledge of the specific procedural details.

[0009] According to a preferred embodiment of the invention, during the production of the second connection point, the second connection contact surface or the common connection contact of the battery block is heated indirectly using the heated bonding tool, and in any case locally. Advantageously, the ultrasonic bonding process can be further optimized and, in particular, accelerated by heating the second connection contact surface. Furthermore, the ultrasonic bonding method according to the invention can be used when the contact partner for the connection conductor at the second connection point, like the first connection contact surface of the first battery cell, is difficult to bond due to its hardness, grain size, grid structure, or other material or structural properties.

[0010] In particular, according to the invention, it can be provided that the first terminal contact surface and / or the second terminal contact surface is provided as a terminal contact surface made of nickel-coated steel, CuSn6, CuFe2, or by an Sn-coated surface. The common terminal contact can be made of copper or aluminum, for example. The first terminal contact surface and / or the second terminal contact surface can be provided, for example, by a material that does not have a face-centered cubic lattice structure.

[0011] For example, a ribbon with a substantially rectangular cross-section can be used as the connecting conductor in ultrasonic ribbon bonding, or a wire with a round cross-section in ultrasonic wire bonding. The connecting conductor can be made of aluminum or copper, for example.

[0012] According to a further development of the invention, a plurality of first connection contact surfaces of different first battery cells are connected to a common collective connection contact by a number of connection conductors corresponding to the number of different first battery cells. Advantageously, the connection of the battery block produced by the ultrasonic bonding method according to the invention can be simplified by providing the common collective connection contact for a plurality of similar battery cells. The battery block or the jointly connected battery cells can be electrically contacted in particular via the common collective connection contact. For example, a plurality of collective connection contacts can be provided on a battery block, each of which provides the electrically conductive connection to a plurality of first battery cells and / or second battery cells.

[0013] According to an alternative embodiment of the invention, the first connection point of the first battery cell is formed and connected to the second connection point provided on an adjacent second battery cell. The ultrasonic bonding method according to the invention thus makes it possible to create a series circuit of various battery cells and thereby influence the voltage provided by the battery cell via the manufacturing or contacting process.

[0014] According to a further development of the invention, the first connection contact surface and / or the second connection contact surface and / or the collective connection contact are heated while the connection conductor is pressed against the first connection contact surface and / or the second connection contact surface and / or the collective connection contact by the heated bonding tool and / or while the connection conductor is excited to ultrasonic vibrations. This advantageously supports ultrasonic bonding through the additional provision of thermal energy. The stiffness or hardness of the connection contact surfaces or the collective connection contacts can thereby be reduced or dislocation movements in the metal lattice can be promoted, with the result that materials can be bonded that are commonly used in battery construction but can otherwise not be bonded or can only be bonded to a limited extent.

[0015] According to a further development of the invention, during the production of the first connection point and / or the second connection point, the laser can be deactivated or the laser power can be reduced and optimally lowered to zero. This applies in particular if, based on the process parameters determined during ultrasonic bonding, it is determined that the bonded connection of the connecting conductor to the connection contact surface or the collective connection contact can be reliably established and / or if an unacceptably high heating of the connection contact surface is detected.

[0016] According to a further development of the invention, the bonding tool can be heated before the connecting conductor is pressed against the connection contact surface or the common connection contact with the bonding tool, or before it is excited to ultrasonic vibrations. By preheating the bonding tool, individual steps of the ultrasonic bonding method according to the invention can be performed in parallel, thus accelerating the overall manufacturing process and making it more economical. In particular, the bonding tool can be heated while it is being repositioned for the next bond.

[0017] According to a further development of the invention, the laser can be operated in a pulsed mode. Due to the inertia of the heat flow, this results in sufficient and uniform heating of the bonding tool, the connection contact surface, or the common connection contact. Pulsed operation of the laser is useful, for example, when it is not possible to variably adjust the laser power. The thermal energy supplied to the bonding process is then influenced by the timing of the laser beam.

[0018] According to a further development of the invention, sensors can be provided on the device side to detect a temperature or a mechanical condition of the connection contact surface or the collective connection contact. In this respect, the process parameters for the laser, in particular a laser power or a laser activation duration, can be determined and, if necessary, controlled by means of the sensor system, so that a desired temporal progression can be mapped.

[0019] Further advantages, features, and details of the invention can be gathered from the further subclaims and the following description. Features mentioned therein may be essential to the invention individually or in any combination. Thus, the disclosure of the individual aspects of the invention can always be referenced interchangeably. The drawings serve merely as examples to clarify the invention and are not limiting in nature.

[0020] They show: Fig. 1 shows a first configuration of a battery block produced by means of the ultrasonic bonding method according to the invention. Fig. 2 shows a second configuration of the battery block produced by means of the ultrasonic bonding method according to the invention. Fig. 3 shows a first example of a temporal progression of a normal force, an ultrasonic power, and a laser power when using the ultrasonic bonding method according to the invention. Fig. 4 shows a second example of the temporal progression of the normal force, the ultrasonic power, and the laser power when using the ultrasonic bonding method according to the invention. Fig. 5 shows a third example of the temporal progression of the normal force, the ultrasonic power, and the laser power when using the ultrasonic bonding method according to the invention. Fig. 6 shows a fourth example of the temporal progression of the normal force, the ultrasonic power, and the laser power when using the ultrasonic bonding method according to the invention.7 shows a fifth example of the temporal progression of the normal force, the ultrasonic power, and the laser power when using the ultrasonic bonding method according to the invention. Fig. 8 shows a sixth example of the temporal progression of the normal force, the ultrasonic power, and the laser power when using the ultrasonic bonding method according to the invention. Fig. 9 shows a seventh example of the temporal progression of the normal force, the ultrasonic power, and the laser power when using the ultrasonic bonding method according to the invention. Fig. 10 shows an eighth example of the temporal progression of the normal force, the ultrasonic power, and the laser power when using the ultrasonic bonding method according to the invention. Fig. 11 shows a ninth example of the temporal progression of the normal force, the ultrasonic power, and the laser power when using the ultrasonic bonding method according to the invention.12 shows a tenth example of the temporal progression of the normal force, the ultrasonic power, and the laser power when using the ultrasonic bonding method according to the invention. Fig. 13 shows an eleventh example of the temporal progression of the normal force, the ultrasonic power, and the laser power when using the ultrasonic bonding method according to the invention. Fig. 14 shows a twelfth example of the temporal progression of the normal force, the ultrasonic power, and the laser power when using the ultrasonic bonding method according to the invention. Fig. 15 shows a thirteenth example of the temporal progression of the normal force, the ultrasonic power, and the laser power when using the ultrasonic bonding method according to the invention. Fig. 16 shows a fourteenth example of the temporal progression of the normal force, the ultrasonic power, and the laser power when using the ultrasonic bonding method according to the invention.Fig. 17 shows a fifteenth example of the temporal progression of the normal force, the ultrasonic power, and the laser power when applying the ultrasonic bonding method according to the invention. Fig. 18 shows a sixteenth example of the temporal progression of the normal force, the ultrasonic power, and the laser power when applying the ultrasonic bonding method according to the invention. Fig. 19 shows a seventeenth example of the temporal progression of the normal force, the ultrasonic power, and the laser power when applying the ultrasonic bonding method according to the invention.

[0021] Fig. 1 shows a first configuration of a battery block formed from twelve battery cells 2, 3 arranged regularly in a 3x4 matrix. The battery block provides a first row of three adjacent first battery cells 2, a second row of three second battery cells 3, a third row of three first battery cells 2, and a fourth row of three second battery cells 3. The battery cells 2, 3 are held by a housing 1 of the battery block.

[0022] Adjacent first battery cells 2 of the first row and second battery cells 3 of the second row, as well as adjacent first battery cells 2 of the third row and second battery cells 3 of the fourth row, are electrically contacted in pairs via connecting conductors 4. In each case, a first connecting contact surface 6 of the first battery cells 2 is connected to a second connecting contact surface 7 of the second battery cells 3 by establishing connection points between the connecting contact surfaces 6, 7 on the one hand and the connecting conductors 4 on the other.

[0023] The connection points, which are created between the connection conductor 4 on the one hand and the first connection contact 6 or the second connection point 7 on the other hand, are formed by ultrasonic bonding. The connection conductor 4 is pressed against the connection contact surfaces 6, 7 by means of a bonding tool (not shown) and excited to ultrasonic vibrations by the bonding tool. In addition, the connection conductor 4 and the connection contact surfaces 6, 7 are heated by means of a laser. The connection contact surfaces 6, 7 are formed, for example, from nickel-coated steel, CnSn6, CuFe2 or by Sn-coated surfaces. The connection contact surfaces 6, 7 are therefore, for example, particularly hard, fine-grained or provided by a material that has a non-face-centered cubic lattice structure.

[0024] The Fig. 1 The battery block shown can, for example, always provide identical battery cells 2, 3 in the standard 18650 format, wherein the battery cells 2, 3 have a diameter of 18 mm and a height of 65 mm. When configuring the battery block, the orientation of adjacent, different rows of assigned battery cells 2, 3 is selected such that a series connection or contacting of the adjacent battery cells 2, 3 is possible. The first connection contact surface 6 thus defines a positive pole of the first battery cell 2 and the second connection contact surface 7 a negative pole of the second battery cell 3. Contact is made via a ribbon as a connection conductor 4, which has a substantially rectangular cross-section.

[0025] An alternative battery block according to Fig. 2 provides the first battery cells 2 in a consistently consistent orientation in a 3x4 matrix arrangement. Contacting of the first battery cells 2 is achieved here via connecting conductors 4, which are integrally connected to the first connection contact surfaces 6 of the first battery cells 2 on the one hand and to collective connection contacts 5 on the other. The collective connection contacts 5 are designed such that adjacent rows, each containing three first battery cells 2, are always jointly contacted at a collective connection contact 5.

[0026] For the material-to-material contacting of the battery cells 2, 3, the process will depend on a normal force with which the bonding tool is pressed against the connection contact surface 6, 7 or the collective connection contact 5. Furthermore, ultrasonic power and laser power will have a significant influence on the formation of the contact. Alternative configurations for the process parameters normal force, ultrasonic power, and laser power are described below in the Fig. 3 bis 20 shown.

[0027] The process parameters presented are standardized and simplified. In reality, for example, the normal force may be increased in the second half of the bonding process, or the ultrasonic power may be reduced toward the end of the bonding process. For example, the laser power may also be reduced toward the end of the bonding process.

[0028] A first, procedurally simple case according to Fig. 3 This involves simultaneously pressing the bonding tool and exciting it to ultrasonic vibrations, and activating the laser. Since the normal force can only be changed slowly compared to the other two process variables, ultrasonic support and laser power, the graphs show a ramp-like increase or decrease in the normal force, whereas a sudden activation or switching on is provided for the ultrasonic power and laser power.

[0029] Fig. 4 shows a modified process in which the ultrasonic power is changed or adjusted during the process and, in particular, reduced abruptly.

[0030] Alternatively, as described in the Fig. 5 und 6 shown, the ultrasound power can be continuously increased or reduced.

[0031] Fig. 7 shows that according to an alternative embodiment of the method according to the invention, the ultrasound can be switched on after the bonding tool is pressed against the connection contact surfaces 6, 7 or the collective connection contact 5 and the laser is activated.

[0032] Likewise, as in Fig. 8 As shown, the laser is first activated and then the bonding tool is pressed against the connection contact surfaces 6, 7 or the collective connection contact 5. The bonding tool is therefore preheated by the laser beam before it is placed on the workpiece. After it has been placed on the workpiece, it is heated further, with the connection conductor 4 and the connection contact surfaces 6, 7 or the collective connection contact 5 being indirectly heated by the bonding tool. The ultrasound is only switched on when the parts to be joined have reached an elevated temperature. The temperature can optionally be monitored by sensors. This has the advantage of a short process time, as the connection conductor and the parts to be joined can be heated quickly, since the bonding tool is already heated when it is placed on the workpiece.In addition, the wear of the bonding tool can be reduced because the ultrasound is only activated when the joining partners have a lower strength as a result of the heating.

[0033] Another alternative embodiment of the ultrasonic bonding method according to the invention is described in Fig. 9 shown. Here, the bonding tool is first preheated using the laser beam, and then, in a subsequent step, the heated bonding tool is simultaneously pressed against the connection contact surfaces 6, 7 or the common connection contact 5, and the ultrasound is switched on.

[0034] Fig. 10 illustrates that, in particular, to prevent excessive heating of the connection contact surface 6, 7 or the common connection contact 5, the laser can be deactivated before the ultrasonic bonding process is completed. In this case, the normal force and the ultrasonic power are maintained for longer than the laser is activated.

[0035] Fig. 11 shows a modified version of the process variant described above. Here, the laser power is not switched off suddenly, but rather reduced over time. As an example, a ramp-like reduction in laser power is shown. This takes into account that toward the end of the bonding process, the joining partners are heated and the bond formation is largely complete. This reduces heat input, thus promoting microstructure formation.

[0036] Another alternative to the above ultrasonic bonding process according to Fig. 12 provides for reducing the laser power in two stages. In particular, the laser power can be reduced and / or completely switched off to prevent excessive heating of the connection contact surface 6, 7 or the collective connection contact 5.

[0037] Fig. 13 shows a process variant in which the laser power is increased to preheat the bonding tool before activating the ultrasound or before pressing the bonding tool. Overall, preheating the bonding tool during its repositioning can reduce the process time.

[0038] According to an alternative embodiment of the invention, it can be provided that the laser is operated continuously to heat the bonding tool (see Fig. 14 ).

[0039] Alternatively, Fig. 15 It can be provided that a continuously operated laser is provided and the laser power is temporarily increased while the bonding tool is pressed against the connection contact surface 6, 7 or the common connection contact 5 and / or the ultrasound is switched on. The bonding tool is therefore continuously heated by means of the laser beam at low power. When the bonding tool presses the connection conductor 4 against the connection contact surfaces 6, 7 or the common connection contact 5, the laser power is increased so that more heat flows away towards the joining partners. In particular, due to the continuous heating of the bonding tool, the bonding time can be reduced or kept short. The connection conductor 4 and the joining partners therefore heat up comparatively quickly. According to an alternative embodiment of the invention, the laser can be operated in pulsed mode.Corresponding variants of the ultrasonic bonding process are described in the . Fig. 16 and 17 In pulsed operation, the laser power and pulse frequency can be selected so that, compared to non-pulsed operation, the same thermal effect can be achieved with respect to the bonding tool on the one hand and the joining partners on the other. For example, the Fig. 16 Laser power shown according to Fig. 3 Pulsed operation is suitable, for example, when the laser's design means it can only be operated in pulsed mode and / or the laser power cannot be set as low as required for optimal heating of the bonding tool or the joining partners.

[0040] Fig. 18 This clearly shows that the laser power can be individually selected or controlled as needed. For example, a sensor component can be used to determine the temperature of the connection contact surface 6, 7 or the common connection contact 5, and the laser power can be adjusted depending on the temperature so that a secure and reliable bond between the battery cells 2, 3 and the connection conductor 4 or the common connection contact 5 is always established.

[0041] The bonding tool is continuously heated or heated with a low laser power and maintained at an elevated operating temperature. This applies both during the production of the individual connection points and in the interim, for example, when moving and / or repositioning the bonding tool, as this can reduce the warm-up time for the bonding tool and / or improve process stability and bond quality.

[0042] As soon as the bonding tool is placed and the connecting conductor 4 is pressed against the connection contact surface 6, 7 or the collective connection contact 5, the laser power is increased in order to heat the joining partners. During the bonding process, the laser power is then regulated or continuously reduced in order to keep the temperature of the bonding tool constant despite the increasing temperature of the joining partners and the resulting low heat dissipation. The advantage is an increased process speed through preheating the bonding tool and uniform heating of the bonding tool and the joining partners through temperature control. For example, the bonding tool can be heated to very high temperatures for a short time if the temperature of the joining partners is monitored and it can be ensured that an unacceptably high temperature of the joining partners can be avoided through process control.

[0043] In the diagrams according to the Fig. 14 , 15 and 18 It is shown that the laser is not deactivated after the first connection point and / or the second connection point has been created and continues to operate at full or reduced laser power. This applies if at least one further connection point is created after the currently created connection point. Of course, the laser can be turned off, or the laser will be turned off, once all connection points have been created on the battery block currently being processed, or the ultrasonic laser bonding device provided for carrying out the process is turned off.

[0044] Two further variants of the ultrasonic bonding process according to the invention are described in the Fig. 19 und 20Here, the ultrasonic power is only provided temporarily, and after the ultrasound is deactivated, heat can still be introduced into the joint with the laser.

[0045] With regard to the implementation of the method according to the invention, it is pointed out that, depending on the material properties of the various connection contact surfaces 6, 7 or collective connection contacts 5, the process duration can be adapted and, in particular, the second connection point on the collective connection contact 5 can also be produced conventionally and, in this respect, heating by means of a laser can be dispensed with for the second connection point.

[0046] With regard to the ultrasonic bonding method according to the invention, it is irrelevant whether the first connection point is created first and then the second connection point, or first and then the second connection point. Likewise, three or more connection points can be created on one connecting conductor 4.

[0047] Identical components and component functions are identified by the same reference symbols.

Claims

1. A method for electrically contacting a plurality of battery cells (2, 3) of a battery block, comprising the following steps: - a first connection point is produced by a bonding tool being heated directly and a first connection contact surface (6) of a first battery cell (2) and / or a connection conductor (4) being heated in any case locally indirectly by a laser beam directed onto the bonding tool and provided by a laser, by the connection conductor (4) being pressed against the first connection contact surface (6) of the first battery cell (2) by means of the bonding tool, and by the bonding tool being excited to ultrasonic vibrations, the ultrasonic vibrations being transmitted from the bonding tool to the connection conductor; - a second connection point is produced by the connection conductor (4) being pressed by the bonding tool against a second connection contact surface (7) of a second battery cell (3) of the battery block or a collective connection contact (5) of the battery block and being excited to ultrasonic vibrations.

2. The method according to claim 1, characterized in that during the production of the second connection point the bonding tool is heated directly by means of the laser beam and, as a result of the heating of the bonding tool by the latter, the connection conductor (4) and / or the second connection contact surface (7) and / or the common connection contact (5) are heated with the aid of the bonding tool indirectly and in any case locally.

3. The method according to claim 1 or 2, characterized in that a plurality of first connection contact surfaces (6) of different first battery cells (2) are connected to a shared common connection contact (5) by a plurality of connection conductors (4) corresponding to the number of different first battery cells (2).

4. The method according to any of claims 1 to 3, characterized in that the first connection contact surface (6) of the first battery cell (2) is connected to the second connection contact surface (7) of a second battery cell (3) arranged adjacent to the first battery cell (2).

5. The method according to any of claims 1 to 4, characterized in that the bonding tool is heated directly with the aid of the laser beam and the first connection contact surface (6) and / or the second connection contact surface (7) and / or the common connection contact (5) are heated indirectly by means of the bonding tool, while the connection conductor (4) is pressed against the first connection contact surface (6) and / or the second connection contact surface (7) or the common connection contact (5) and / or is excited to ultrasonic vibrations.

6. The method according to any of claims 1 to 5, characterized in that during the production of the first connection point and / or of the second connection point an ultrasonic power is reduced and / or lowered to zero.

7. The method according to any of claims 1 to 6, characterized in that the bonding tool is heated by means of the laser beam before the connection conductor (4) is pressed by means of the bonding tool and / or excited to ultrasonic vibrations.

8. The method according to any of claims 1 to 7, characterized in that the laser is deactivated while the connection conductor (4) is pressed by the bonding tool against the first connection contact surface (6) and / or the second connection contact surface (7) and / or the common connection contact (5) and / or is excited to ultrasonic vibrations.

9. The method according to any of claims 1 to 8, characterized in that the laser is operated in a pulsed manner during the direct and / or indirect heating of the bonding tool and / or of the first connection contact surface (6) and / or of the second connection contact surface (7) and / or of the common connection contact (5).

10. The method according to any of claims 1 to 9, characterized in that the laser is continued to be operated after the ultrasound is deactivated.

11. The method according to any of claims 1 to 10, characterized in that the first connection contact surface (6) and / or the second connection contact surface (7) is provided as a CuSn2 connection contact surface (6, 7) and / or a CuFe2 connection contact surface (6, 7) and / or is provided on nickel-coated steel and / or is provided by an Sn-coated surface.

12. The method according to any of claims 1 to 11, characterized in that the laser beam is guided in a longitudinal recess which is provided in the bonding tool, and / or in that the laser beam is directed onto a tool tip of the bonding tool.

13. The method according to any of claims 1 to 12, characterized in that the laser is operated continuously in such a manner that a deactivation of the laser after the production of the first connection point and / or of the second connection point does not take place if at least one further connection point is subsequently produced.