Method for forming battery cell and device for controlling a formation

Abstract

The invention relates to a method for forming a battery cell, in particular for forming a solid-electrolyte interface (SEI), in which a time-dependent current intensity (1', 2', 3') and / or voltage is used to form the battery cell, wherein the method is characterized in that a complex-valued cell internal resistance (1, 2, 3) of the battery cell is detected multiple times during the formation, and the current intensity (1', 2', 3') and / or the voltage is controlled according to the detected cell internal resistance (1, 2, 3). The invention also relates to a device for controlling a formation of a battery cell.

Description

[0001] Description

[0002] Method for forming a battery cell and device for controlling a formation

[0003] The invention relates to a method according to the preamble of claim 1 and a device according to the preamble of claim 11.

[0004] Forming a battery cell is one of the final production steps in cell manufacturing. This formation process typically takes place after the cell has been filled with electrolyte and sealed, and before the battery cell is stored and undergoes end-of-line quality control.

[0005] The formation process encompasses the initial charging and discharging cycles of the finished battery cell and aims to ensure a defined initial state that is as optimal as possible for later use. In lithium-ion cells and related technologies, the formation process aims to create a well-defined solid electrolyte interphase (SEI) on the surface of the anode. This interphase forms through reactions between the electrode and electrolyte additives within specific voltage and, if necessary, temperature ranges, which are traversed during the charging and discharging cycles of the formation process.

[0006] Within a battery cell, several complex reactions occur simultaneously, differing in their reaction kinetics. Each electrochemical reaction, especially those contributing to SEI formation, is dependent on the potential at the reaction site.

[0007] Therefore, if the specified current or applied voltage is incorrectly set over time, potentials may develop at the interfaces that are not suitable for the formation of the optimal SEI, or other reactions, such as the charging of the electrode materials, may be accelerated, which in turn negatively affect SEI formation. It is therefore essential that the formation process uses suitable current, voltage, and / or temperature profiles to generate the desired SEI. Furthermore, formation is one of the most time- and energy-intensive processes in cell production, so it must be as efficient as possible.

[0008] The aforementioned technical requirements and the complex underlying chemical reactions place high technical demands on the definition and control of the process parameters during the formation process.

[0009] Known forming processes use current and, where applicable, voltage and temperature profiles based on empirical tests on the produced cells or battery cells. The process parameters are adjusted to achieve the best possible compromise between performance and process costs. If measurements are used to control the forming process, they are limited to current and voltage measurements. For example, the cycle is performed until the measured differential capacitance falls below a certain threshold. This method requires a very precise understanding of the available process windows and still cannot completely eliminate variations in the quality of the produced cells.

[0010] The present invention is based on the objective of improving the formation of a battery cell, particularly within the framework of its manufacturing process.

[0011] The problem is solved by a method with the features of independent claim 1 and by a device with the features of independent claim 11. Advantageous embodiments and further developments of the invention are specified in the dependent claims.

[0012] In the inventive method for forming a battery cell, in particular for forming a solid-electrolyte interface (SEI), a time-dependent current and / or voltage is used for forming the battery cell. The inventive method is characterized in that a complex-valued internal cell resistance of the battery cell is repeatedly measured during the formation process, and the current and / or voltage is controlled as a function of the measured internal cell resistance.

[0013] The term "taxing" in this context also includes rules.

[0014] The battery cell is specifically designed as a lithium-ion battery cell. The cell's internal resistance is inherently complex, meaning it has a real part and an imaginary part, or equivalently, a magnitude and a phase. The cell's internal resistance is fundamentally frequency-dependent, so it is measured at one or more frequencies or within a defined frequency range.

[0015] The method according to the invention can preferably be carried out within the framework of a manufacturing process for the battery cell.

[0016] According to the invention, the complex-valued cell internal resistance (real part and / or imaginary part or magnitude and / or phase) is used to control / regulate the formation process or to control / regulate the current and / or voltage used during formation. In other words, the current and / or voltage is controlled or regulated depending on the measured complex-valued cell internal resistance. For this purpose, according to the invention, the complex-valued cell internal resistance is measured multiple times during the formation of the battery cell.

[0017] The use of the complex-valued cell internal resistance is particularly advantageous according to the invention because it essentially allows the formation of the SEI to be tracked. In other words, the cell internal resistance changes with SEI growth. The invention utilizes this change for controlling / regulating the formation process.

[0018] The invention has one or more of the following advantages:

[0019] - The formation process is optimized for each individual battery cell, meaning it is adapted to each individual battery cell.

[0020] - Electrical parameters from a measurement of the cell's internal resistance are used to control or regulate the formation process.

[0021] - The formation process can be accelerated by lower currents if higher currents are required to maintain or tolerate the anode potential due to increased internal cell resistance.

[0022] - The formation process can be slowed down if it would jeopardize the formation of the desired SEI. This can result in a lower reject rate during battery cell manufacturing.

[0023] - The formation time can be adjusted via the SEI signals from the cell internal resistance measurement. If a particular cell develops a high-quality SEI earlier than the median time, the formation process can be terminated prematurely to save time and energy.

[0024] The device according to the invention for controlling the formation of a battery cell, in particular for the formation of a solid-electrolyte interface (SEI), comprises a control unit and a measuring unit, wherein the control unit is configured to control a time-dependent current and / or voltage for the formation of the battery cell. The device according to the invention is characterized in that the measuring unit is configured to repeatedly detect a complex-valued internal cell resistance of the battery cell during the formation, and the control unit is configured to control the current and / or voltage as a function of the detected internal cell resistance.

[0025] Similar advantages and / or embodiments of the device according to the invention result from the method according to the invention, which are equivalent and have the same effect.

[0026] According to an advantageous embodiment of the invention, the cell internal resistance is determined by means of electrochemical impedance spectroscopy.

[0027] In other words, the individual cell internal resistance, or rather the complex-valued value of the cell internal resistance, is repeatedly measured during the battery cell formation process using electrochemical impedance spectroscopy (EIS). This results in multiple EIS spectrum measurements. Electrochemical impedance spectroscopy is thus used for cell-specific control of the formation process. Advantageously, the individual production history can be taken into account within the manufacturing process. Furthermore, the SEI growth can be monitored using the EIS measurements.

[0028] In an advantageous embodiment of the invention, the cell internal resistance is measured at a frequency in the range of 1 kilohertz to 10 kilohertz.

[0029] This results in improved control of the formation process. This is because SEI training is typically associated with processes / frequencies in the range of 1 kilohertz to 10 kilohertz.

[0030] According to an advantageous embodiment of the invention, the cell's internal resistance is measured at regular intervals during the formation process. This ensures advantageous, regular monitoring of the SEI formation and correspondingly advantageous control of the process. For measuring the cell's internal resistance, the current and / or voltage can preferably be switched off. In other words, the cell's internal resistance is preferably measured during periods without current and / or voltage during the formation process. Alternatively or additionally, the cell's internal resistance can be measured during periods of continuous current and / or voltage during the formation process.

[0031] In an advantageous further development of the invention, the time remaining for formation is controlled depending on the detected internal cell resistance.

[0032] In other words, the formation time is determined by the cell's internal resistance. A remaining time can be calculated and / or a termination criterion can be defined based on the cell's internal resistance. This advantageously ensures that the formation time used is precisely that required to develop the desired and intended SEI. Depending on the specific cell, this can lead to a shorter formation time, thus saving both time and energy.

[0033] According to an advantageous embodiment of the invention, the cell internal resistance is detected at a frequency in the range of 1 to 100 Hz, in particular in the range of 1 to 10 Hz, to control the duration of the process.

[0034] In other words, lower frequencies are advantageous for controlling the duration. However, higher frequencies in the range of 1 kHz to 10 kHz are advantageous for the fundamental control / regulation of the formation process. Here, the complex internal cell resistance is preferably measured at frequencies in the range of 1 kHz to 10 kHz at the beginning of the formation process. Later in the formation process, the internal cell resistance is then measured alternatively or additionally at lower frequencies in the range of 1 to 100 Hz to determine the duration.

[0035] In other words, the formation process has at least two time periods, whereby the cell's internal resistance is measured at a frequency in the range of 1 kHz to 10 kHz within the first time period, and the cell's internal resistance is measured at a frequency in the range of 1 Hz to 100 Hz within the second time period. Additionally, measurement within the frequency range of 1 kHz to 10 kHz may be provided within the second time period.

[0036] In an advantageous embodiment of the invention, the duration of the formation is determined by a termination criterion, wherein the formation is terminated when the real part and / or imaginary part of the detected cell internal resistance at a frequency and / or within a defined frequency range is essentially equal to a defined target real part or target imaginary part.

[0037] In other words, the real and / or imaginary part of the cell's internal resistance is advantageously used to control the time duration. Here, the measured real part and the target real part are essentially equal if their squared deviation is less than or equal to a defined threshold. The threshold thus determines the accuracy of the match. The same applies analogously to the imaginary part.

[0038] According to an advantageous embodiment of the invention, the real part and / or imaginary part of the complex-valued cell internal resistance is detected.

[0039] The real part of the complex-valued cell internal resistance forms the ohmic resistance. Equivalent to the real and imaginary parts, the magnitude and / or phase of the complex-valued cell internal resistance can be determined.

[0040] In an advantageous embodiment of the invention, the current is increased when the real part of the detected cell internal resistance is below a first defined threshold value.

[0041] This advantageously improves SEI formation. This is because the electrode potential profile during the formation process should be as similar as possible for each battery cell, as this leads to the most uniform SEIs of the battery cells. The electrode potential of a graphitic electrode, for example, is given by the equation: [Graphite = Graphite, OCP + T] = Graphite, OCP + I'Re{Z}, where I'Graphite.OCP d as Resting potential (OCP) and ?7 denote the overvoltage. The overvoltage r] depends on the current and the real part of the cell's internal resistance (impedance).

[0042] According to an advantageous embodiment of the invention, the current is reduced when the real part of the detected cell internal resistance is above a second defined threshold value. This advantageously further improves the SEI formation.

[0043] Further advantages, features, and details of the invention will become apparent from the exemplary embodiments described below and from the drawings. These show, schematically:

[0044] Figure 1 shows a sequence of a process according to one embodiment of the invention; and

[0045] Figure 2 shows a determination of the duration of a formation according to an embodiment of the invention;

[0046] Similar, equivalent or equivalent elements may be provided with the same reference symbols in one or more of the figures.

[0047] Figure 1 shows a schematic sequence of a process or a time period of the process according to an embodiment of the invention.

[0048] The left diagram shows the curve of an initial current of 1' with which the formation process begins. Time, in arbitrary units, is plotted on the abscissa (100) of the diagram. Current, in arbitrary units, is plotted on the ordinate (102).

[0049] After the formation process begins, electrochemical impedance spectroscopy (EIS measurement) is performed to determine the complex-valued internal cell resistance. Figure 1 illustrates this in the middle diagram for three different battery cells. The real part of the internal cell resistance is plotted on the abscissa 101 and the imaginary part on the ordinate 103, each in arbitrary units.

[0050] The middle diagram shows three different frequency-dependent curves of the cell internal resistance 1, 2, 3. Each point shown corresponds to the measured cell internal resistance at a specific frequency. The cell internal resistance is thus determined for each of the three battery cells between a minimum and maximum frequency, in particular between 1 kHz and 10 kHz. In the middle diagram, the real parts of the cell internal resistances are specifically labeled with the reference numerals 1, 2, 3. The right-hand diagram in Figure 1 shows the current control provided according to the embodiment of the invention as a function of the measured cell internal resistances 1, 2, 3. In this embodiment, the real part of the cell internal resistance 1, 2, 3 is used for control, with the cell internal resistance 1 corresponding to a reference cell (golden sample), meaning that at least one target real part is defined.

[0051] For battery cell 2, the real part of its internal resistance 2 is smaller than the target real part 1. For battery cell 3, the real part of its internal resistance 3 is larger than the target real part 1. According to the present configuration, the current 2' is thus increased compared to the initial or target current T. Conversely, the current 3' is thus decreased compared to the initial or target current T. This change / control of the respective current is illustrated by the right-hand diagram in Figure 1.

[0052] In other words, the battery cell is initially formed using a standard charging current of 1'.

[0053] Subsequently, the cell's internal resistance, particularly its ohmic resistance, is checked or recorded at regular intervals using an EIS measurement. For this purpose, the real and imaginary parts of the measured impedance (Z) at a defined frequency, for example in the range of 1 to 10 kHz, are used.

[0054] Based on the measured impedance Z (cell internal resistance), the charging current is controlled as follows:

[0055] - If the cell has a smaller real part 2 than the target real part 1, the current is increased from 1' to 2'.

[0056] - If the cell has a larger real part 3 than the target real part 1, the current is reduced from 1' to 3'.

[0057] Figure 2 shows a determination of the duration of a formation according to an embodiment of the invention, particularly in a later stage of the formation.

[0058] In other words, later in the formation process, the acquisition of the ELS spectrum is adjusted so that lower frequencies, particularly in the range of 1 Hz to 100 Hz, are also captured and used. This controls or regulates at least the formation time, since the time required to generate a high-quality SEI can vary from cell to cell. This control / regulation of the formation time is illustrated in Figure 2.

[0059] Figure 2 includes a left, middle, and right diagram.

[0060] The abscissa 100 of the left and right diagrams shows time in arbitrary units.

[0061] The current intensity is plotted in arbitrary units on the ordinate 102 of the left and right diagrams.

[0062] The abscissa 101 of the middle diagram shows the real part of the complex-valued cell internal resistance in arbitrary units.

[0063] The imaginary part of the complex-valued cell internal resistance is plotted in arbitrary units on the ordinate 103 of the middle diagram.

[0064] The middle diagram thus shows the frequency-dependent course of the cell's internal resistance in a low frequency range, especially in the range of 1 Hz to 100 Hz.

[0065] An initial time period corresponding to an initial current T can be seen from the left diagram and is also associated with the reference symbol T.

[0066] Depending on the measured cell internal resistances 2, 3, the formation time is controlled or adjusted. This results in the shorter duration 3' and the longer duration 2' shown in the right-hand diagram. The durations 2' and 3' are longer and shorter, respectively, compared to the initial duration 1'.

[0067] In other words, an initial forming time T is first defined or assumed, which results from a defined current T up to a specific voltage value, and is initially used for all cells. This procedure can be carried out (possibly multiple times) for control / regulation for each voltage limit to be reached.

[0068] According to the present control system, ELS spectra of the cells are recorded to track the formation of the SEI. For this purpose, the Z-values ​​2 and 3 of the respective cell internal resistances are used at the characteristic excitation frequency of the SEI, particularly in the range of 1 to 100 Hz.

[0069] The formation duration is adjusted based on the determined Z-value (2, 3) depending on the stage of SEI development. This value (2, 3) is compared to a reference value (1) to determine the remaining process duration. In combination with the cell's internal resistance, this allows not only for cell-specific adjustment of the current during the formation process, but also, advantageously, for determining the duration of the formation process.

[0070] Although the invention has been illustrated and described in detail by the preferred embodiments, the invention is not limited by the disclosed examples, nor can other variations be derived from them by a person skilled in the art without leaving the scope of protection of the invention.

[0071] Reference symbol list

[0072] 1, 2, 3 Cell internal resistance

[0073] T, 2', 3' Current / Duration

[0074] 100 Abscissa (time)

[0075] 101 Abscissa (real part)

[0076] 102 Ordinate (current intensity)

[0077] 103 Ordinate (Imaginary Part)

Claims

Patent claims 1. Method for forming a battery cell, in particular for forming a solid electrolyte interface (SEI), in which a time-dependent current (T, 2', 3') and / or voltage is used for forming the battery cell, characterized in that a complex-valued cell internal resistance (1 , 2, 3) of the battery cell is detected multiple times during the formation, and the control of the current (1', 2', 3') and / or the voltage is carried out as a function of the detected cell internal resistance (1 , 2, 3).

2. Method according to claim 1 , characterized in that the cell internal resistance (1 , 2, 3) is detected by means of electrochemical impedance spectroscopy.

3. Method according to claim 2, characterized in that the cell internal resistance (1 , 2, 3) is detected at a frequency in the range of 1 kilohertz to 10 kilohertz.

4. Method according to one of the preceding claims, characterized in that the cell internal resistance (1, 2, 3) is recorded at regular intervals during formation.

5. Method according to one of the preceding claims, characterized in that the time remaining for formation is controlled depending on the detected internal cell resistance (1, 2, 3).

6. Method according to claim 5, characterized in that the cell internal resistance (1 , 2, 3) is detected at a frequency in the range of 1 to 100 Hz, in particular in the range of 1 to 10 Hz, in order to control the duration.

7. Method according to claim 5 or 6, characterized in that the duration of the formation is determined by a termination criterion, wherein the formation is terminated when the real part and / or imaginary part of the detected cell internal resistance (1, 2, 3) at a frequency and / or within a defined frequency range is substantially equal to a defined target real part.

8. Method according to one of the preceding claims, characterized in that the real part and / or imaginary part of the complex-valued cell internal resistance (1 , 2, 3) is detected.

9. Method according to one of the preceding claims, characterized in that the current (T, 2', 3') is increased when the real part of the detected cell internal resistance (1 , 2, 3) is below a first defined threshold value.

10. A method according to any one of the preceding claims, characterized in that the current (T, 2', 3') is reduced when the real part of the detected cell internal resistance (1, 2, 3) is above a second defined threshold value.

11. A device for controlling the formation of a battery cell, in particular for Formation of a solid-electrolyte interface (SEI) comprising a control unit and a measuring unit, wherein the control unit is configured to control a time-dependent current (1', 2', 3') and / or voltage for the formation of the battery cell, characterized in that the measuring unit is configured to repeatedly detect a complex-valued cell internal resistance (1, 2, 3) of the battery cell during the formation, and the control unit is configured to control the current (T, 2', 3') and / or the voltage as a function of the detected cell internal resistance (1, 2, 3).

Images