Methods for forming battery cells

Abstract

Method for forming battery cells (18), comprising a device for forming battery cells (18) with the following process steps: a) a forming stage or forming electronics unit (10) provides a regulated output voltage for several battery cells (18) with integrated power electronics (30, 48) to be formed in parallel (19), b) an output voltage U of the forming stage or forming electronics unit (10) has a higher value than a quiescent voltage of all battery cells (18) to be formed in parallel that currently have the highest state of charge or the highest quiescent voltage when positive forming currents are applied, or c) the output voltage of a forming stage of the forming electronics unit (10) has a lower value than a quiescent voltage of all battery cells (18) to be formed in parallel with integrated power electronics (30, 48) when negative forming currents are applied.which currently has the lowest state of charge or the lowest resting voltage, d) wherein the battery cell (18) to be formed with integrated power electronics (30, 48) individually regulates its forming current.

Description

State of the art The invention relates to a method for forming battery cells with a forming stage or forming electronics unit with power electronics that provides a regulated output voltage or a regulated output current. US 6,291,972 B1 discloses an electrical circuit for forming lithium-ion battery cells. Parallel-connected battery cells are disclosed, which are controlled with a uniform voltage profile. The individual battery cells draw a current according to their individual state of health (SOH). Circuit elements are located outside the battery cells. DE 10 2009 035 466 A1 concerns the formation of individual cells. A method for forming individual cells of a battery, in particular lithium-ion individual cells, is proposed. The method comprises at least one predefined charging process and one predefined discharging process for activating electrochemical processes within the individual cells. The individual cells are electrically connected in a cell assembly, either in series or in parallel, and formed together. EP 2 424 069 A2 relates to a system for forming lithium-ion cells. According to this solution, a forming system is proposed that includes a battery management system located externally to the battery. The individual lithium-ion cells can be connected to this system. DE 10 2004 060 359 A1 relates to a charge controller arrangement and a method for charging a battery. Partial currents are provided by a DC / DC converter and a linear regulator. A control unit regulates the DC / DC converter and the linear regulator depending on the actual charging current of the battery. The proposed method reduces power loss with a smaller chip area, thus extending the service life of the battery being charged. The charge controller arrangement can be enclosed within the device housing or implemented as an external device. DE 10 2012 214 097 A1 discloses a forming device and a method for forming battery cells. During the charging and discharging process, block-shaped forming currents are impressed into the battery cell. DE 44 39 785 C2 discloses a method for charging a loadable battery, wherein the charging current or voltage is regulated such that the battery temperature remains constant. From DE 10 2004 060 359 A1, a charge controller arrangement and a method for charging a battery are known. A control unit controls a DC / DC converter and the linear regulator depending on the actual charging current of the battery. The formation process is particularly important in the manufacturing of lithium-ion battery cells. This process activates each individual battery cell and, through a pre-aging process, aims to achieve a defined formation and stabilization of the SEI layer (SEI = Solid Electrolyte Interface). The SEI layer is a corrosion layer that forms on the anode of lithium-ion battery cells. This corrosion layer significantly determines the aging behavior of the battery cells. With current manufacturing methods for large battery cells (for example, with a capacity of 60 Ah), the formation and pre-aging process takes between 10 and 14 days. Current methods for formation utilize power output stages that operate either as linear regulators or as current-controlled switched-mode output stages in a half-bridge configuration.Until now, the formation of lithium-ion battery cells has been carried out using a single power electronics unit dedicated to exactly one cell. This means that no parallel or series connection of battery cells is used during the formation process. Consequently, this requires a large number of individual, expensive power electronics units. For this reason, formation currently represents one of the most complex and costly steps in the production of lithium-ion battery cells. Description of the invention The invention relates to methods for forming battery cells with integrated power electronics with the device for forming battery cells, wherein in one method variant parallel formation is proposed and in an alternative method variant forming in series connection of the battery cells is proposed. According to the method for forming battery cells with a battery cell forming device with integrated power electronics, the following process steps are carried out: a) The forming stage or forming electronics provide a regulated output voltage U for several battery cells to be formed in parallel, b) the output voltage U of the forming stage or forming electronics has a higher value than the open-circuit voltage (OCV) of all battery cells to be formed in parallel that currently have the highest state of charge or the highest open-circuit voltage (OCV) when positive forming currents are applied, or c) the output voltage U of the forming stage or the forming electronics unit has a lower value than the open-circuit voltage (OCV) of all battery cells to be formed in parallel when negative forming currents are applied.which currently has the lowest state of charge or the lowest open-circuit voltage (OCV), d) wherein the battery cells to be formed have integrated power electronics that individually regulate their forming current. In a further embodiment of the method proposed according to the invention for the parallel formation of battery cells, setpoint values ​​for the formation currents are specified by the externally arranged forming stage or formation electronics with respect to the battery cell via at least one communication interface of the battery cell. During the parallel formation of battery cells, the at least one integrated power semiconductor of the power electronics integrated into the battery cell is preferably operated as a longitudinal or linear regulator in active operation, wherein the formation current of the respective battery cell has no AC components.According to an advantageous further development of the method for parallel forming of battery cells, the battery cells with integrated power electronics either measure the battery cell current themselves or corresponding information about the battery cell current is transmitted from the forming stage to the battery cell to be formed, which contains the integrated power electronics, via at least one communication interface. According to the other embodiment of the method proposed according to the invention for forming battery cells with a device for forming battery cells, the following process steps are carried out: a) The forming stage or forming electronics provide a regulated output current for several battery cells to be formed that are connected in series, b) the forming current is individually influenced by the power electronics integrated in the respective ion battery cells with respect to the output current of the forming stage or forming electronics unit, in particular reduced, c) in the case of positive forming currents (charging currents), the output current of the forming stage or forming electronics unit has a maximum value of the current desired for forming the battery cells connected in series.or d) in the case of negative forming currents, the output current of the forming stage or the forming electronics unit has a minimum value of the current value required for forming the battery cell. According to the serial forming process for battery cells, the forming currents are regulated using the power electronics integrated in or on the battery cell casings such that each battery cell individually regulates its own forming current. The forming current flowing through the battery cell can be reduced compared to the current provided by the forming stage or the forming electronics unit. This is achieved by operating at least one of the semiconductor switches of the integrated power electronics as a linear or series regulator in the active region, generating a current in parallel with the current flowing through the electrochemical part of the battery cell being formed. The setpoint values ​​for the forming currents used to form the battery cells can be communicated by the external forming stage or forming electronics unit via the battery cell's at least one communication interface. The solution proposed according to the invention drastically reduces the complexity of the power electronics in the forming stage or forming electronics unit. Furthermore, it allows the forming currents required for formation to be controlled with very high precision, i.e., with a very small deviation from their setpoint, particularly with regard to the occurrence of alternating current components, which would inherently occur when using a switched-mode power stage. Advantages of the invention The device for forming battery cells, comprising a forming stage or forming electronics unit containing power electronics and at least one battery cell to be formed, drastically reduces the complexity of the power electronics in the forming devices. Forming currents, which are applied to either series or parallel forming of the battery cell to be formed, can be controlled with very high precision and very small deviations from their setpoint, especially with regard to the occurrence of alternating current components. These alternating current components would occur inherently in a forming process with switched-mode power stages, but are avoided by the solution proposed according to the invention. With the presented solution, the forming process can be carried out on several battery cells simultaneously in series and in parallel. Since the forming stage provides a regulated output voltage, the effort required for its provision is lower, resulting in cost reductions compared to prior art solutions. If battery cells are formed in parallel, the forming stage, or the forming electronics unit, provides the output voltage for several battery cells being formed in parallel. This reduces the number of forming stages or units required for the forming process. The number of forming electronics units can be drastically reduced. The power electronics integrated on or in the battery cells being formed are used to regulate the forming current. Problems occurring during parallel forming of battery cells with one or more cells being formed, e.g., a cell that cannot be charged and / or discharged, can be electronically decoupled from the forming process, so that the forming process for the "good cells" can continue without significant interruption. The parallel forming process allows each battery cell to regulate its own forming current. This prevents variations in the internal resistance of the battery cells, which can be caused by manufacturing fluctuations and / or tolerances, from leading to different forming currents. Such variations in forming currents would otherwise occur if the battery cells to be formed were connected in parallel and operated directly on a DC link without using their internal electronics. By specifying the target values ​​for the formation currents in the parallel formation process and transferring the target values ​​for the formation currents to the respective battery cells to be formed, it can be ensured that the battery cells all perform the same formation process synchronously, e.g., all set the same charging current at the same time. If the forming alternative, i.e., forming battery cells according to the serial or series forming method, is used, the number of forming stages or forming electronics units can also be significantly reduced compared to prior art solutions. When forming battery cells in series, the forming stage provides a forming current regulated by a current control loop. The power electronics are designed for higher voltages and thus higher power outputs, since the power electronics of the forming stage or forming electronics unit drive the forming current against the sum of the series-connected battery cell voltages.The regulation of the respective forming currents is achieved using the power electronics integrated in and / or on the battery cell housings, such that each cell regulates its own individual forming current. The current through the battery cell can be reduced compared to the current provided by the forming stage or the forming electronics unit by operating at least one of the power semiconductors as a linear regulator in the active region, generating a current in parallel with every current flowing through the electrochemical part of the battery cell. This advantageously prevents deviations in the battery cell capacity values, which can be caused by manufacturing variations and tolerances, from leading to different cell voltage profiles over time.Such deviations in the battery cell voltages would occur if the battery cells to be formed were connected in series and charged or discharged directly with the same current without using the internal electronics. In the alternative method of series-connected battery cell formation, the setpoints for the formation currents for the battery cells to be formed are also specified by the external formation electronics, formation stage, or formation electronics unit via at least one communication interface to the battery cells. This ensures that all battery cells undergo the same formation process synchronously, for example, that they all exhibit the same voltage profile over time. In the series-connected battery cell formation method, if a problem occurs during the formation of the series-connected battery cells, the affected battery cell can be electronically isolated from the formation process by switching a bypass to the affected battery cell(s) via the power semiconductors of the battery cell's integrated electronics.This allows the "good cells" to continue forming without interrupting the formation process. Brief description of the drawings The invention is described in more detail below with reference to the drawings. Figure 1 shows a single forming of a battery cell with power electronics by a forming stage or forming electronics unit; Figure 2 shows a parallel forming of battery cells with integrated power electronics by a forming stage or forming electronics unit; Figure 3 shows a forming current path and active power semiconductors during the forming process of a battery cell with integrated power electronics, implemented as a half-bridge circuit; Figure 4 shows a forming current path and activated power semiconductors during the forming of a battery cell with integrated electronics, comprising a full-bridge circuit consisting of two half-bridges; Figure 5 shows a series connection of battery cells with integrated power electronics, which are formed via a forming stage or forming electronics unit.Figure 6 shows the current paths that develop when the formation current of the battery cell is reduced, with power electronics in a half-bridge configuration, and Figure 7 shows the current paths that develop when the formation current of the battery cell is reduced, with integrated power electronics, which in this case comprises a bridge circuit consisting of two half-bridges with power semiconductors and blocking diodes. Embodiments of the invention Fig. 1 shows the individual forming of a battery cell with integrated power electronics via a forming stage or forming electronics unit. Figure 1 shows that a forming stage or forming electronics unit 10 with power electronics 11 and a smoothing capacitor 12 forms a DC link 16. The DC link 16 is supplied via terminals 14. The output voltage U provided by the forming stage or forming electronics unit 10 is transmitted to the battery cell 18 with integrated power electronics to be formed. In the case shown in Figure 1, a battery cell 18 with integrated power electronics is formed via the forming stage or forming electronics unit 10 as part of a single forming process 17. The formation currents are controlled using the power electronics integrated in or on the battery cell 18, see also the illustration in Fig. 3 and Fig. 4. Fig. 2 shows the device proposed according to the invention for forming battery cells, here as parallel formation of battery cells with integrated power electronics. Fig. 2 shows the device proposed according to the invention for forming battery cells 18 with integrated power electronics, wherein a number of battery cells 18 with integrated power electronics are shown in a parallel circuit 19. Analogous to the single forming of a battery cell 18 with integrated power electronics shown in Fig. 1, the forming stage or forming electronics unit 10 with the power electronics 11 is supplied with an input voltage at the terminals 14. The forming stage or forming electronics unit 10 includes the smoothing capacitor 12 already shown in Fig. 1 and provides the regulated output voltage in the DC link 16, with which the battery cells 18 with integrated power electronics arranged in parallel 19 are formed. The output voltage provided by the DC link 16 or the DC link 16 is...The output voltage provided by the forming stage or forming electronics unit 10 exhibits slightly higher values ​​for positive forming currents (charging currents) than the open-circuit voltage (OCV) of all battery cells 18 being formed in parallel that currently have the highest state of charge or open-circuit voltage (OCV). For negative forming currents (discharging currents), the output voltage provided by the DC link 16 exhibits slightly lower values ​​compared to the open-circuit voltage of those battery cells 18 being formed in parallel that currently have the lowest state of charge or open-circuit voltage (OCV). In parallel forming as shown in Fig. 2, the forming currents are regulated using the power electronics integrated in and / or on the housings of the battery cells 18 to be formed, such that each battery cell 18 regulates its own forming current. This advantageously prevents deviations in the internal resistances of the battery cells 18, which may be caused by manufacturing variations and tolerances, from leading to different forming currents. Such deviations in the forming currents would occur if the battery cells 18 to be formed were connected in parallel without using the internal power electronics and operated directly on the DC link 16 of the forming stage or forming electronics unit 10. Each of the battery cells 18 with integrated power electronics is provided with at least one communication interface 82, via which the setpoint values ​​for the forming currents are transmitted from the externally arranged forming stage or forming electronics unit 10 to the battery cells 18. This ensures that all battery cells 18 perform the same forming process synchronously, e.g., all set the same charging current simultaneously. If a problem occurs with one or more of the two battery cells 18 during parallel forming 19, as schematically depicted in Fig. 2, these battery cells 18 can disconnect themselves from the forming process by switching off the corresponding power semiconductors. Within the framework of the continuing parallel forming 19, "good cells" can continue forming without interrupting the formation process. Fig. 3 shows a battery cell with integrated power electronics, which in the embodiment shown in Fig. 3 is designed as a half-bridge circuit. Fig. 3 shows that the battery cell 18 with integrated power electronics includes a controller 20. The controller 20 is part of cell monitoring electronics 22 with components for controlling power semiconductors. Furthermore, the embodiment of the battery cell 18 shown in Fig. 3, which can be bypassed, includes an ultra-fast discharge device (UFDD) 24. The ultra-fast discharge device 24, as shown in Fig. 3, includes a resistor 26 connected in series with a power switch 28. Fig. 3 shows a battery cell 18 with a first integrated power electronics 30, which in this case is implemented as a half-bridge circuit. This includes a first power semiconductor 32, which can be switched on and off, and a second power semiconductor 34, which can also be switched on and off. The two power semiconductors 32 and 34 are connected in series.The 34 components can be implemented as transistors or field-effect transistors (MOSFETs). Parallel to these, in the first integrated power electronics 30, as shown in Fig. 3, are a first diode 36 and a second diode 38, both configured as blocking diodes. Furthermore, according to the embodiment shown in Fig. 3, the battery cell 18 includes a receiving device 40 for the battery cell. The battery cell 18 shown in Fig. 3 can output the voltage +Ucell or 0 V at its cell terminals 42 and 44, provided that the power semiconductors 32 and 34 operate only in fully switched-on or switched-off mode. If, as shown in Fig. 3, for example, the first power semiconductor 32 is operated in linear regulator mode 47, the forming current can be regulated.Current control is achieved via the first power semiconductor 32, which can be operated in the active region and can be operated here as a linear or series controller, with high-precision current control. Due to the underlying principles, no alternating current components occur, as the first power semiconductor 32 operates in linear mode and not in switching mode. Fig. 4 shows a battery cell whose integrated power electronics comprise a bridge circuit consisting of a first half-bridge and a second half-bridge. The battery cell 18, analogous to the battery cell 18 shown in Fig. 3, includes the controller 20, which is part of cell monitoring electronics 22 with components for controlling power semiconductors. Furthermore, as shown in Fig. 4, the battery cell 18 includes the rapid discharge device 24 (UFDD), which comprises the resistor 26 connected in series with the power switch 28. In contrast to the representation in Fig. 3, Fig. 4 shows a full-bridge circuit as the second integrated power electronics 48 within the battery cell 18, comprising a first half-bridge 50 and a second half-bridge 52. The first half-bridge 50 holds the first power semiconductor 32 (switchable on and off) and the second power semiconductor 34, which is also switchable on or off. Furthermore, the first half-bridge 50 includes the first diode 36 and the second diode 38, both of which are configured as blocking diodes. The second half-bridge 52 is configured analogously to the first half-bridge 50 of the full-bridge circuit. The second half-bridge 52 comprises a third power semiconductor 54, which is also configured to be switched on and off, and a fourth power semiconductor 56, which is also configured to be switched on and off. Furthermore, the second half-bridge 52 of the full-bridge circuit comprises a third diode 58 and a fourth diode 60. As can be seen in Fig. 4, the second integrated power electronics 48, in the form of the full-bridge circuit, can be used to influence the formation current of the battery cell 18 according to the embodiment shown in Fig. 4. For this purpose, to give an example, the second power semiconductor 34 is operated in a first linear regulator mode 62, and the third power semiconductor 54 of the second half-bridge 52 of the full-bridge circuit is operated in a second linear regulator mode 64.The two power semiconductors, identified by reference numerals 62 and 64 and circled with dashed lines, allow for the regulation of the forming current of battery cell 18, which in this case is equipped with a second integrated power electronics unit 48 configured as a full bridge circuit. Depending on the configuration of the two half-bridges 50 and 52, battery cell 18 is capable of setting a voltage of +Ucell or -Ucell between the first cell terminal 42 and the second cell terminal 44. It is also possible to connect the two half-bridges 50 and 52 such that a voltage U of 0 V is established between the two terminals 42 and 44. In the first case, the first terminal 42 is connected to the positive terminal of battery cell 18 and the second terminal 44 to the negative terminal of battery cell 18. In the second case, the connection is reversed. The illustration in Fig. 5 shows a serial formation of battery cells with integrated power electronics. The basic circuit diagram according to Fig. 5 shows that, in the case of series-connected formation 70 of battery cells 18, a number of battery cells 18 are arranged one behind the other in series 70. Fig. 5 shows that the formation stage or formation electronics unit 10 contains, in addition to the power electronics 11 and the connection terminals 14, a smoothing choke 72 and an ammeter 74. The formation stage or formation electronics unit 10, shown schematically in Fig. 5, provides a formation current that can be adjusted by means of a current control loop. The power electronics 11 of the formation stage 10 or the formation electronics unit 10 is designed for higher voltage and thus for higher power, since it drives the formation current of the battery cells 18 to be formed in series 70 against the sum of the series-connected battery cell voltages.The output current of the forming stage or forming electronics unit 10, as shown in Fig. 5, has the maximum value of the current required for forming the battery cells 18 connected in series 70 when operating with positive forming currents, i.e., charging currents. (In the case of a charging current of 1 C, this corresponds to the charging current required by the battery cell with the largest capacity). Conversely, in the case of negative forming currents, i.e., discharging currents, the output current of the forming stage or forming electronics unit 10 has the minimum value of the current required for forming the battery cells 18 arranged in series 70. In the case of a discharge current of 1 C, this corresponds to the discharge current required by the battery cell with the largest capacity. The respective forming currents are regulated by means of the power electronics integrated in and / or on the housings of the battery cells 18 to be formed, such that each battery cell 18 regulates its own forming current individually. A forming current flowing through the battery cell 18 can be reduced compared to the output current provided by the forming stage or forming electronics unit 10 by operating at least one of the power semiconductors 32, 34 or 54, 56 (see illustrations in Fig. 6 and Fig. 7) as a linear or series regulator in the active region and generating a current in parallel with the current flowing through the electrochemical part of the respective battery cell 18 to be formed.This advantageously prevents deviations in the capacity values ​​of the battery cells 18, which may be caused by manufacturing variations and / or tolerances, from leading to different voltage profiles over time. Such deviations in battery cell voltages would, however, occur if the battery cells 18 to be formed were charged and discharged directly with the same current in a series connection 70 without the use of internal electronics. Analogous to the parallel formation 19 of battery cells 18, the setpoint values ​​for the formation currents of the battery cells 18 can be specified by the external formation stage or formation electronics unit 10 via at least one communication interface 82 of the battery cells 18. This advantageously ensures that all battery cells 18 synchronously perform the same formation process, e.g., that they all exhibit the same voltage profile over time. Should a problem occur with one or more battery cells during the formation process in series connection 70 of battery cell 18, these battery cells 18 can disconnect themselves from the formation process by connecting a bypass to the affected battery cell(s) 18 via the power semiconductors 32, 34, 54, 56. The "good cells" remaining in the series formation process, however, can continue to be formed without significant interruption of the formation process. Based on Fig. 6 and Fig. 7, various embodiments of the integrated power electronics of battery cells 18 to be formed by serial formation are described below. Fig. 6 shows a battery cell 18 whose integrated power electronics comprise a half-bridge circuit 30. The battery cell 18 comprises the cell monitoring electronics 22, which includes components for controlling the power semiconductors 32, 34 of the first integrated power electronics 30 (half-bridge circuit). Furthermore, a rapid discharge device 24 (UFDD) is provided in the battery cell 18, which includes the resistor 26 and, connected in series with it, the power switch 28 for rapid discharge of the battery cell 18. In the embodiment shown in Fig. 6, the first integrated power electronics 30 of the battery cell 18 is configured as a half-bridge circuit, comprising the first power semiconductor 32, which can be switched on and off, and the second power semiconductor 34, which can also be switched on and off. Diodes 36, 38 are connected in parallel to these; in the embodiment of the half-bridge circuit shown in Fig. 6, these diodes are each configured as blocking diodes.The actual battery cell is housed in the receiving device 40. The battery cell 18 comprises the first cell terminal 42 and the second cell terminal 44. A current path for the formation process is identified by reference numeral 46. If, for example, the second power semiconductor 34 is operated in linear regulator mode 47 in the illustration according to Fig. 6, the formation current for the battery cell 18, which flows in the first formation current path 46, is reduced by the fact that a current also flows in a first current path 76 at a reduced formation current, which further reduces the formation current for the battery cell 18. The battery cell 18 shown in Fig. 6 is able to output the voltage Ucell or U = 0 V at the first cell terminal 42 and at the second cell terminal 44, provided that the power semiconductors 32, 34 operate only in fully switched-on or switched-off mode. Fig. 7 shows a battery cell 18 whose second integrated power electronics 48 is configured as a full bridge circuit. The full bridge circuit 48 according to Fig. 7 comprises the first half-bridge 50 and the second half-bridge 52. The first half-bridge 50 comprises the first power semiconductor 32, the second power semiconductor 34, and two diodes 36 and 38, respectively, which in the embodiment according to Fig. 7 are configured as blocking diodes. The second half-bridge 52, on the other hand, contains the third power semiconductor 54 and the second power semiconductor 56. Furthermore, the second half-bridge 52 according to Fig. 7 includes a third diode 58 and a fourth diode 60, both of which are configured as blocking diodes and are connected in the opposite direction to the switchable third and fourth power semiconductors 54 and 56. In addition, the battery cell 18 according to the representation in Fig.7 the receiving device 40, in which the actual battery cell is received. The forming current path, which occurs during series formation of the battery cell 18, which in this case is included in the series assembly shown in Fig. 3, is identified by reference numeral 66. Fig. 7 further shows that in this embodiment of the battery cell 18, indicated by the circles, the first power semiconductor 32 can be operated in the first linear regulator mode 62, and the fourth power semiconductor 56 in the second linear regulator mode 64, each in the active region. If at least one of the two power semiconductors 32 or 56 is operated in the active region as a linear or series regulator, the forming current flowing in the second forming current path 66 is reduced. In this case, a current flows either in the second current path with a reduced forming current, cf. position 78, and / or in the third current path with a reduced forming current according to position 80, as schematically indicated in Fig. 7. The invention is not limited to the embodiments described here and the aspects highlighted therein. Rather, within the scope specified by the claims, a multitude of modifications are possible that fall within the bounds of what is considered skilled in the art.

Claims

Method for forming battery cells (18), comprising a device for forming battery cells (18) with the following process steps: a) a forming stage or forming electronics unit (10) provides a regulated output voltage for several battery cells (18) with integrated power electronics (30, 48) to be formed in parallel (19), b) an output voltage U of the forming stage or forming electronics unit (10) has a higher value than a quiescent voltage of all battery cells (18) to be formed in parallel that currently have the highest state of charge or the highest quiescent voltage when positive forming currents are applied, or c) the output voltage of a forming stage of the forming electronics unit (10) has a lower value than a quiescent voltage of all battery cells (18) to be formed in parallel with integrated power electronics (30, 48) when negative forming currents are applied.which currently has the lowest state of charge or the lowest resting voltage, d) wherein the battery cell (18) to be formed with integrated power electronics (30, 48) individually regulates its forming current. Method according to claim 1, characterized in that the specification of setpoint values ​​for the forming currents is carried out externally, with reference to the battery cell (18), by the forming stage or forming electronics unit (10) via a communication interface (82) of the battery cell (18). Method according to claim 1, characterized in that the at least one integrated power semiconductor (32, 34; 54, 56), which is operated as a longitudinal controller or linear controller in active operation, and the forming current of the respective battery cell (18) with integrated power electronics (30, 48) have no alternating components. Method according to claim 1, characterized in that the battery cell (18) with integrated power electronics (30, 48) either measures the battery cell current itself or receives information about the battery cell current from the forming stage or forming electronics unit (10). Method for forming battery cells (18), comprising a device for forming battery cells (18) with the following process steps: a) a forming stage or forming electronics unit (10) provides a regulated output current for several battery cells (18) to be formed in series (70), b) the forming current is individually influenced, in particular reduced, by the power electronics (30, 48) integrated in the respective battery cells (18) to be formed, relative to the output current of the forming stage or forming electronics unit (10), wherein, in the case of positive forming currents, the output current of the forming stage or forming electronics unit (10) has a maximum value of the current desired for forming the battery cells (18) to be formed in series (70).ord) in the case of negative forming currents, the output current of a forming stage or forming electronics unit (10) has a minimum value of the current value required for the forming of the battery cell (18) to be formed with integrated power electronics (30, 48). Method according to the preceding claim, characterized in that the forming current through the battery cell (18) to be formed with integrated power electronics (30, 48) is reduced compared to the output current provided by the forming stage or the forming electronics unit (10) by operating at least one of the power semiconductors (32, 34; 54, 56) in the active region as a linear or series regulator and generating a current in parallel to that current which flows through the electrochemical part of the battery cell (18) to be formed with integrated power electronics (30, 48). Method according to claim 5 characterized in that the setpoint values ​​for the forming currents of the battery cells (18) to be formed with integrated power electronics (30, 48) are specified by the external forming stage or forming electronics unit (10) via at least one communication interface (82) of the battery cells (18) to be formed with integrated power electronics (30, 48).

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