Method for monitoring a forming process of a battery cell by means of a forming apparatus, computer program product, computer-readable storage medium, and forming apparatus

Abstract

The invention relates to a method for monitoring a forming process (14) of a battery cell (12) by means of a forming apparatus (10), comprising the steps of: charging the battery cell (12) with at least one first forming current (22) by means of a charging device (16) of the forming apparatus (10); detecting an actual acoustic signal (30) of the battery cell (12) during the forming process (14) by means of an acoustic detection device (18) of the forming apparatus (10); and monitoring the forming process (14) by comparing the actual acoustic signal (30) with a predefined target acoustic signal (32) by means of an electronic computing device (20) of the forming apparatus (10). Furthermore, the invention relates to a computer program product, to a computer-readable storage medium, and to a forming apparatus (10).

Description

[0001] Description

[0002] Method for monitoring a battery cell formation process using a formation device, computer program product, computer-readable storage medium and formation device

[0003] The following invention relates to a method for monitoring a formation process of a battery cell by means of a formation device according to claim 1. The invention further relates to a corresponding computer program product, a corresponding computer-readable storage medium and a formation device.

[0004] The formation of a battery cell is one of the final production steps in cell manufacturing and takes place after electrolyte filling and sealing. The formation process includes the first charging and discharging cycles of the assembled battery cell and is designed to ensure a defined initial state optimized for subsequent use. In lithium-ion batteries and related technologies, the formation of a well-defined solid electrolyte interface (SEI) on the surface of the negative electrode is crucial. This SEI grows through reactions of electrolytic components at the electrode within specific voltage ranges during controlled charge / discharge cycles of the battery cell.

[0005] Two technical limitations must be considered. Several complex reactions occur simultaneously within a battery cell, each with its own distinct kinetics. An electrochemical reaction, including SEI formation, takes place locally depending on the interfacial potential. If the time profile of the applied current or voltage is not carefully chosen, potentials may develop at the interface that are unsuitable for optimal SEI formation. Furthermore, SEI formation is one of the most time- and energy-intensive processes in cell production, necessitating efficient process management to save time and costs. These two requirements place high demands on the precise definition and control of process parameters during SEI formation.

[0006] It is already known from the prior art that most forming processes select current and, if applicable, voltage and temperature profiles based on empirical tests. The process parameters are chosen to represent the best possible compromise between performance and process costs. If measurements are used to control the forming process, these are usually limited to current and voltage measurements. For example, the process can be cycled until the measured differential capacitance falls below a certain threshold. This approach requires, on the one hand, a very precise understanding of the available process windows and, on the other hand, cannot fully account for variations in the quality of the produced battery cells.

[0007] The object of the present invention is to provide a method, a computer program product, a computer-readable storage medium and a forming device by means of which an improved monitoring of the forming process of a battery cell can be achieved.

[0008] This problem is solved by a method, a computer program product, a computer-readable storage medium, and a forming device according to the independent claims. Advantageous embodiments are specified in the dependent claims.

[0009] One aspect of the invention relates to a method for monitoring the formation process of a battery cell using a formation device. The battery cell is charged with at least a first formation current by means of a charging device of the formation device. An acoustic signal from the battery cell during the formation process is detected by means of an acoustic detection device of the formation device. The formation process is monitored by comparing the acoustic signal with a predetermined target signal by means of an electronic processing unit of the formation device.

[0010] This allows for monitoring of the formation process at predetermined intervals. Specifically, based on an acoustic signal emanating from the battery cell during the formation process, it is possible to compare whether the formation process meets the desired parameters. This allows for monitoring of the formation process and, if necessary, the implementation of countermeasures should it deviate from the desired parameters. The invention thus takes advantage of the fact that changes within the materials, such as deformation, cracking, or shearing, cause mechanical waves.The resulting acoustic signals can be converted into electrical signals by the acoustic detection device, captured by a detection unit, and analyzed by the electronic computing unit. Acoustic signals are also generated by film growth, as occurs during SEI formation (SEI - solid electrolyte interphase). Acoustic signals resulting from SEI formation are caused, for example, by gas formation or lithium intercalation.

[0011] Analyzing the actual signal can provide valuable information about the processes within the battery cell. A key component of the monitoring is a database containing the results of previous measurements, which can be accessed during the ongoing process. For example, a characteristic curve of a so-called "golden sample" can be used – that is, a battery cell that precisely meets the quality requirements of the manufacturer or a customer of the manufacturer.

[0012] In particular, this allows the formation process to be optimized for each individual battery cell. Since formation occurs via current pulses and not through a continuous profile, it can be performed intelligently and individually for each cell. This also makes electrical parameters such as open-circuit and overvoltages of the battery cell accessible. The SEI growth can thus be controlled. Furthermore, formation is controlled by direct material signals within the battery cell, not just by a complex analysis of electrical parameters. The process can also be accelerated by higher currents and longer pulses if this allows the battery cell to achieve the desired "golden sample" profile. Conversely, formation can be slowed down if the process would jeopardize the formation of the desired SEI. This results in a lower rejection rate for the battery manufacturer due to insufficient formation.

[0013] Known methods for measuring overvoltages or cell resistances during formation can also be combined with the formation process control presented here. This results in further improvements to the SEI method control. According to an advantageous embodiment, an evaluation of the formation process is performed depending on the monitoring. In particular, the actual signal can be evaluated by comparing it with the target signal. If, for example, the actual signal is essentially the same as the target signal depending on corresponding threshold values, the evaluation can be performed in such a way that the formation process is considered to be functioning correctly.Should corresponding deviations occur during the comparison, it can be determined that the quality of the formation process is insufficient at this point, and appropriate countermeasures must be initiated.

[0014] In a further advantageous embodiment, the acoustic target signal is provided for by an acoustic signal from a reference battery cell during the formation process. For example, the acoustic signal of the reference battery cell can be referred to as a "golden sample." In other words, this signal is recorded during the formation process of a reference battery cell that meets the relevant quality criteria. It is then specified accordingly, and the actual signal is referenced to the target signal of the battery cell. This ensures that the target signal can be reliably specified.

[0015] It is also advantageous to perform monitoring by evaluating the amplitude of the actual acoustic signal. In particular, the amplitude of the actual acoustic signal can then be assessed accordingly. For example, the amplitude level or the frequency of occurrence of a given amplitude can be used. This allows for a simple comparison.

[0016] It is also advantageous to evaluate the amplitude of the actual acoustic signal. For example, a threshold value can be defined below which an evaluation is permitted. If an acoustic signal lies above this threshold, it is considered for evaluation. This is particularly important because background noise in the actual signal is disregarded, and only acoustic signals attributable to the formation process are evaluated.

[0017] It has also proven advantageous to evaluate the frequency of amplitude occurrences in the actual acoustic signal. In particular, the frequency of occurring amplitudes can be determined more precisely. In other words, it can be stipulated, for example, that a number of occurring amplitudes be counted within a given time window. This can also be referred to as "counts." This can then be compared with the reference spectrum, especially the target spectrum, allowing conclusions to be drawn about the formation process.

[0018] It has also proven advantageous to evaluate the frequency of the occurring amplitude within a predefined time window. For example, the time window can be defined every 5 minutes or by evaluating the amplitudes occurring in the target signal. If, for instance, a cluster of acoustic signals occurs at certain times in the target signal, this can be used as a time window to search for the corresponding amplitudes occurring in the relevant specific battery cell within that time window. This enables reliable monitoring.

[0019] Another advantageous design provides that the current charging potential of the battery cell is taken into account to compare the actual signal with the target signal.

[0020] Particularly during the specific formation process, the corresponding charging potentials can vary between individual battery cells. A comparison can therefore be performed especially when the specific battery cell has, for example, the same state of charge and charging potential as the reference battery cell. This allows for an improved, time-independent comparison, enabling appropriate monitoring.

[0021] In a further advantageous embodiment, charging is carried out based on current pulses and charging pauses, and the formation process is monitored during the current pulses and / or during the charging pauses. The formation process can thus be provided with both corresponding current pulses and charging pauses or rest periods for the relaxation of the battery cell. It can be provided that monitoring can be carried out during appropriately set current pulses and also during the charging pauses. This allows different reference points to be used to achieve reliable monitoring.

[0022] It is also advantageous if, depending on the monitoring, at least a second formation current is adapted for the charging process. This allows monitoring during the formation process to initiate countermeasures should the comparison reveal that the actual signal does not substantially correspond to the target signal. The formation process can thus be regulated or controlled accordingly, enabling the specific battery cell to be aligned with the reference battery cell by adapting relevant parameters during the formation process.

[0023] It has also proven advantageous to adapt the duration and / or magnitude of the second forming current. In particular, for example, the magnitude of the current can be adapted to a corresponding current pulse, as can the duration and / or time of its application. This allows for a specific response to the cell-specific forming process, thereby improving the quality of the battery cell. Naturally, additional forming currents can be applied depending on the monitoring and duration of the respective forming process. For example, monitoring can be performed every minute, hourly, or at other intervals, and the forming current can be adjusted accordingly.

[0024] It has also proven advantageous to use an acoustic detection device designed as a piezoelectric element to capture the actual acoustic signal. In particular, the piezoelectric element can convert the acoustic signal into an electrical signal, which can then be fed to the electronic processing unit for evaluation. This allows for simple monitoring.

[0025] The presented method is essentially a computer-implemented method. Therefore, a further aspect of the invention relates to a computer program product with program code means which, when the program code means are executed by the electronic computing device, cause it to carry out a method according to the preceding aspect.

[0026] Furthermore, the invention also relates to a computer-readable storage medium with at least one computer program product according to the preceding aspect. A further aspect of the invention relates to a forming device for monitoring a battery cell forming process, comprising at least one charging device, an acoustic detection device, and an electronic computing device, wherein the forming device is configured to carry out a method according to the preceding aspect. In particular, the method is carried out by means of the forming device.

[0027] Advantageous embodiments of the process are to be regarded as advantageous embodiments of the computer program product, the computer-readable storage medium, and the forming device. The forming device possesses tangible features to enable the corresponding process steps to be carried out.

[0028] A computing unit / electronic computing device can be understood, in particular, as a data processing device containing a processing circuit. The computing unit can therefore process data to perform arithmetic operations. This may also include operations to perform indexed access to a data structure, such as a lookup table (LUT).

[0029] The computing unit may, in particular, contain one or more computers, one or more microcontrollers, and / or one or more integrated circuits, for example, one or more application-specific integrated circuits (ASICs), one or more field-programmable gate arrays (FPGAs), and / or one or more systems on a chip (SoCs). The computing unit may also contain one or more processors, for example, one or more microprocessors, one or more central processing units (CPUs), one or more graphics processing units (GPUs), and / or one or more signal processors, in particular one or more digital signal processors (DSPs). The computing unit may also include a physical or virtual array of computers or other units of the aforementioned type.

[0030] In various embodiments, the processing unit includes one or more hardware and / or software interfaces and / or one or more memory units. A memory unit can be volatile data storage, for example, dynamic random access memory (DRAM) or static random access memory (SRAM), or non-volatile data storage, for example, read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), flash memory or flash EEPROM, or ferroelectric random access memory.FRAM (ferroelectric random access memory), MRAM (magnetoresistive random access memory), or PCRAM (phase-change random access memory) can be designed as random access memory.

[0031] Here and in the following, an artificial neural network can be understood as software code stored on a computer-readable storage medium that represents one or more interconnected artificial neurons or can replicate their function. The software code can also contain multiple software code components, which may, for example, have different functions. In particular, an artificial neural network can implement a nonlinear model or a nonlinear algorithm that maps an input to an output, where the input is given by an input feature vector or an input sequence, and the output may, for example, include a category for a classification task, one or more predicted values, or a predicted sequence.

[0032] For use cases or application situations that may arise in a method according to the invention and that are not explicitly described herein, it may be provided that, according to the method, an error message and / or a request for user feedback is issued and / or a default setting and / or a predetermined initial state is set.

[0033] Regardless of the grammatical gender of a given term, persons of male, female, or other gender identities are included. Further features and combinations of features of the invention are apparent from the figures and their descriptions, as well as from the claims. In particular, further embodiments of the invention need not necessarily include all features of any one of the claims. Further embodiments of the invention may have features or combinations of features not mentioned in the claims.

[0034] This shows:

[0035] Fig. 1 shows a schematic block diagram according to one embodiment of a forming device;

[0036] Fig. 2 shows a schematic flowchart according to one embodiment of the method; and

[0037] Fig. 3 is a schematic time-amplitude diagram.

[0038] In the figures, identical or functionally equivalent elements are provided with the same reference symbols.

[0039] Fig. 1 shows a schematic block diagram according to an embodiment of a forming device 10 for a battery cell 12. The forming device 10 is designed in particular for monitoring a forming process 14. Furthermore, the forming device 10 is also designed for carrying out the forming process 14.

[0040] The forming device 10 has in particular a loading device 16, an acoustic detection device 18 and an electronic computing device 20.

[0041] According to Fig. 1, a forming current 22, particularly in the form of a current pulse, can be applied to the battery cell 12, especially by the charging device 16. A current / voltage measurement 24 takes place, which is also transmitted to the electronic computing device 20. Furthermore, an amplifier element 26 and a detector element 28 can be provided, which can detect and amplify an acoustic actual signal 30 from the battery cell 12. The electronic computing device 20, in turn, has a corresponding acoustic target signal 32, which serves for comparison. Fig. 2 shows a schematic flow diagram according to one embodiment of the method. In a first step S1, the battery cell 12 is charged with at least the first forming current 22.In a second step S2, the acoustic actual signal 30 of the battery cell 12 is recorded during the formation process 14 using the acoustic detection device 18. In a third step S3, the formation process 14 is monitored by comparing the acoustic actual signal 30 with the specified acoustic target signal 32 using the electronic computing device 20. In a potential fourth step S4, an evaluation of the formation process 14 can be carried out based on the comparison, and, for example, an adjustment of the formation current 22 can be made.

[0042] In particular, it may be provided that the acoustic target signal 32 is an acoustic signal from a reference battery cell during the formation process 14. Furthermore, it may be provided that the current charging potential of the battery cell 12 is taken into account to compare the actual signal 30 with the target signal 32. Additionally, it may be provided that charging is carried out based on current pulses and charging pauses, and that the formation process 14 is monitored during the current pulses and / or during the charging pauses. Furthermore, as already mentioned, it may be provided that, depending on the monitoring, at least a second formation current is adapted for the charging process. Furthermore, the duration and / or the magnitude of the second formation current may also be adapted.

[0043] Furthermore, it may be provided in particular that the acoustic actual signal 30 is detected by means of an acoustic detection device 18 designed as a piezo element.

[0044] Fig. 3 shows a time-amplitude diagram. In particular, time t is plotted on the abscissa and amplitude A on the ordinate. Fig. 3 thus shows a recorded actual signal 30. Corresponding threshold values ​​34 are shown. Furthermore, Fig. 3 shows, in particular, a first amplitude 36 and a maximum amplitude 44, which is above the threshold value 34. A duration 38 is also shown, during which the amplitudes are correspondingly above the threshold value 34. A final amplitude 40 is also shown. Finally, a rise time 42 is shown.

[0045] In particular, Fig. 3 shows that monitoring is carried out, for example, based on an amplitude evaluation of the acoustic actual signal 30. Specifically, an evaluation of the amplitude of the acoustic actual signal 30 can be performed, and / or alternatively, an evaluation of the frequency of an occurring amplitude in the acoustic actual signal 30 can be performed. Furthermore, the frequency of the occurring amplitude within the specified time window can also be evaluated.

[0046] In particular, the presented method takes advantage of the fact that changes within materials, such as deformation, cracking, or shearing, cause mechanical waves. The resulting acoustic signals 30 can be converted into electrical signals by means of a piezoelectric sensor, captured by a corresponding detector system, and transmitted to the electronic computing unit 20 for analysis. Acoustic signals are also generated by film growth, as occurs during SEI formation (SEI - Solid Electrolyte Interphase). Acoustic signals resulting from SEI formation are caused, for example, by gas formation or lithium intercalation.

[0047] The generated signals, as shown in Fig. 3, can be analyzed in a variety of ways. A limit value, in particular the threshold value 34, is defined beforehand to separate actual signals triggered by electrochemical reactions from background noise. Particularly valuable information is then provided by values ​​such as the maximum amplitude 44, the number of strokes per unit of time, especially so-called counts, and the duration 38 of the actual acoustic signal 30. For processing the signals, they are analyzed, for example, using a computer program.

[0048] The control of the formation process is again illustrated in Fig. 1 and utilizes, in particular, the electronic computing unit 20 for control purposes, for example, to specify the current intensity and duration of a current pulse acting on the battery cell 12 to the charging unit 16, which can also be referred to as a cycler. The energy of the pulse causes SEI-forming reactions to occur on the surface of the electrode. These reactions generate a mechanical wave, which is detected by a piezoelectric sensor with amplifier 26 at the detector element 28. This signal is then read out by the electronic computing unit 20.

[0049] Analyzing the actual signal 30 can provide valuable information about the processes within battery cell 12. A key component of the control system is a database containing the results of previous simulations, which can be accessed during the ongoing process. An important part of this database is the characteristic curve of the so-called golden sample, i.e., the reference battery cell—a battery cell that meets the quality requirements of, for example, the manufacturer or customer for battery cell 12.

[0050] The current intensity of the pulse is controlled primarily via the amplitude and the so-called counts of the acoustic actual signal 30. If the intensity of the actual signal 30 is significantly lower than that of the golden sample, a pulse with a higher current intensity is sent to battery cell 12 in the next step. Conversely, if the amplitude is too high, the current intensity is reduced to make the reactions more controllable.

[0051] The pulse duration correlates with the time interval and corresponding counts of the acoustic measurement. If the reactions occur too rapidly, SEI formation can proceed uncontrollably. The reaction products and thickness of the SEI will then be more difficult to influence. By comparing with the database, the current pulse duration can be adjusted to match that of the reference battery cell.

[0052] To further explain the invention, the control of the current via the amplitude is illustrated by way of example. Initially, a measurable open-circuit voltage of Vi is applied to battery cell 12. A current pulse is then set analogously to the Golden Sample. The acoustic emission is measured and compared with the acoustic signal of the Golden Sample at the same open-circuit voltage Vi. If the amplitudes of the two signals differ, the current of the following pulse is adjusted, particularly at an open-circuit voltage of V2. If the signal duration differs, the duration of the following pulse is adjusted. Through iterative corrections of the subsequent current pulses, the control system is intended to ensure acoustic emission signals similar to those of the Golden Sample, particularly at the same open-circuit voltage. This allows the SEI formation to proceed analogously to the Golden Sample.

[0053] Reference symbol list

[0054] 10 Forming device

[0055] 12 battery cells

[0056] 14 Formation process

[0057] 16 Forming device

[0058] 18 acoustic detection devices

[0059] 20 electronic computing equipment

[0060] 22 Forming current

[0061] 24 Current / Voltage Signal

[0062] 26 Amplifier element

[0063] 28 Detector element

[0064] 30 acoustic actual signal

[0065] 32 acoustic target signal

[0066] 34 Threshold

[0067] 36 first amplitude

[0068] 38 Duration

[0069] 40 last amplitude

[0070] 42 ascent time

[0071] 44 maximum amplitude

[0072] S1 to S4 steps of the procedure

Claims

Patent claims 1. Method for monitoring a formation process (14) of a battery cell (12) using a formation device (10), comprising the steps: - Charging the battery cell (12) with at least one first formation current (22) by means of a charging device (16) of the formation device (10); - Detection of an acoustic actual signal (30) of the battery cell (12) during the formation process (14) by means of an acoustic detection device (18) of the formation device (10); and - Monitoring the formation process (14) by comparing the actual acoustic signal (30) with a predetermined target acoustic signal (32) using an electronic computing device (20) of the formation device (10).

2. Method according to claim 1, characterized in that an evaluation of the formation process (14) is carried out depending on the monitoring.

3. Method according to claim 1 or 2, characterized in that the acoustic target signal (32) is an acoustic signal from a reference battery cell during the formation process (14).

4. Method according to one of the preceding claims, characterized in that monitoring is carried out by an amplitude evaluation of the acoustic actual signal (30).

5. Method according to claim 4, characterized in that an evaluation of the amplitude of the acoustic actual signal (30) is carried out.

6. Method according to claim 4 or 5, characterized in that an evaluation of the frequency of an occurring amplitude in the acoustic actual signal (30) is carried out.

7. Method according to claim 6, characterized in that the frequency of the occurring amplitude is evaluated in a predetermined time window.

8. Method according to one of the preceding claims, characterized in that To compare the actual signal (30) with the target signal (32), a current charging potential of the battery cell (12) is taken into account.

9. Method according to one of the preceding claims, characterized in that the charging is carried out on the basis of current pulses and charging pauses and the formation process (14) is monitored during the current pulses and / or during the charging pauses.

10. Method according to one of the preceding claims, characterized in that, depending on the monitoring, at least a second forming current is adapted for the charging process.

11. Method according to claim 10, characterized in that a duration of the second forming current and / or a level of the second forming current is adapted.

12. Method according to one of the preceding claims, characterized in that the acoustic actual signal (30) is detected by means of an acoustic detection device (18) designed as a piezoelectric element.

13. Computer program product comprising program code means which cause an electronic computing device (20) to perform a method according to one of claims 1 to 12 when the program code means are processed by the electronic computing device (20).

14. Computer-readable storage medium comprising at least one computer program product according to claim 13.

15. Forming device (10) for monitoring a formation process (14) of a battery cell (12), comprising at least one charging device (16), an acoustic detection device (18) and an electronic computing device (20), wherein the forming device (10) is configured to carry out a method according to one of claims 1 to 12.

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