Method for operating a battery system in voltage-controlled mode during loading

Abstract

The invention relates to a method for voltage-controlled operation of a battery system (4) during a load process, having at least one electrochemical battery cell (6), wherein a process damaging the battery cell (6) is characterized by at least one stored reference curve (14), wherein the reference curve (14) is a state of charge-cell voltage characteristic curve, wherein a cell voltage (UZ) of the battery cell (6) is detected, wherein a state of charge (SOC) of the battery cell (6) is determined, wherein an aging state of the battery cell (6) is determined, wherein the cell voltage (UZ) and the state of charge (SOC) are compared with the stored reference curve (14), wherein a maximum load current (IL) for the aging state of the battery cell (6) is determined from the comparison, and wherein the maximum load current (IL) is set by controlling and / or regulating the cell voltage (UZ).

Description

Technical Field

[0001] The present invention relates to a method for voltage control of a battery system under load, the battery system having at least one electrochemical cell. Background Technology

[0002] The load process here should be understood, especially in the following sense, as the charging or discharging of the battery system or the charging or discharging of individual battery cells using electrical load currents (charging current, discharging current). During charging, electrical energy is supplied to the individual battery cells through the (charging) current, and during discharging, electrical energy is output from the individual battery cells through the (discharging) current.

[0003] Electric or electrically driven vehicles, such as electric or hybrid vehicles, typically include an electric motor that can drive one or two axles. To provide electrical power, the electric motor is usually connected to an onboard (high-voltage) battery, which serves as an energy storage device.

[0004] In particular, electrochemical batteries are here and below specifically understood as the so-called secondary batteries in automobiles. Using this type of (secondary) vehicle battery, the consumed chemical energy can be recovered through an electrical (charging) process. For example, this type of vehicle battery is designed as an electrochemical battery, particularly a lithium-ion battery.

[0005] To generate or provide a sufficiently high operating voltage, such vehicle batteries typically have at least one battery module (cell module) in which several individual electrochemical cell units are modularly connected. Alternatively, a so-called Cell2Pack design can be used, in which cell units are directly combined into the vehicle battery, specifically connected in parallel, without being pre-assembled into modules.

[0006] A single battery cell, especially a lithium-ion battery, can only absorb a certain amount of load current without being damaged, depending on its temperature, current duration, and load conditions. This marginal current varies with the aging state of the battery cell. Furthermore, a challenge arises because several battery cells with different temperatures and / or aging states can be connected in parallel or series within a battery system.

[0007] Therefore, it is necessary to know the state of load and aging of all individual cells in the battery system at all times, as well as the coldest and hottest locations. Consequently, the temperature gradient within each individual cell must also be known to pinpoint the exact coldest and hottest points in the entire battery system. These two points, along with the state of charge and aging of each individual cell, determine the maximum possible load current at any given time. Since a fully relaxed individual cell can absorb currents exceeding the maximum possible continuous current in the short term, it is also necessary to know the temporal response of each individual cell to the load current. "Relaxation" or "fully relaxed" is here specifically understood as the steady state achieved by an individual cell after the termination of charging or discharging current.

[0008] For example, in a lithium-ion battery cell with a liquid electrolyte, the aging or damage process is known as lithium-plating, where metallic lithium deposits on the anode surface and undergoes an irreversible reaction with the electrolyte components. As a result, the battery cell experiences capacity loss, for example, due to a reduction in free lithium ions. Furthermore, an electrical short circuit may occur within the battery cell, potentially leading to a fire during charging. Lithium-plating occurs when the potential of the anode material and electrolyte falls below the potential of lithium. Overvoltage occurs during charging, which lowers the anode potential. Overvoltage is comprised of the separator / electrolyte share, the cathode share, and the anode share, with the anode share being the most critical component in lithium-plating. Under high load currents, the anode potential drops below the lithium potential (0 volts vs. Li / Li+), causing lithium ions to deposit on the anode surface.

[0009] The starting point of lithium plating can be determined by measuring the thickness of a single battery cell or the force on the clamping device of several single battery cells. Alternatively, the starting point of lithium plating can be determined, for example, by measurement using a high-precision coulometric method.

[0010] In lithium-ion batteries, the maximum possible load current can be determined by adjusting the anode potential under load, for example, using a three-electrode single cell. This can only be achieved in a three-electrode single cell with a reference electrode. In a battery system, the decrease in load current occurs proportionally to the decrease in capacity or the increase in internal resistance during battery aging. This is described, for example, in the article by Sieg et al. (Journal of Power Sources 427(2019)260-270) DE 10 2016 007 479 A1. However, this method has the following limitations: the minimum and maximum temperatures in each single cell of the system must be known in order to select the maximum permissible load current from the characteristic curve. Furthermore, the aging state of each single cell in the battery system must be known, especially the current internal resistance, because in the process described there, the single cell with the most severe aging determines the current. In addition, for battery systems used as vehicle batteries, it is necessary to construct experimental laboratory batteries with a reference electrode from the electrodes of industrially manufactured single cells.

[0011] Furthermore, as is known, for example, from DE 10 2019 003 465A1, the maximum pulse current for each state of charge of a fully relaxed battery can be determined using a three-electrode cell. However, this method presents similar challenges to the methods described above. Additionally, a large number of characteristic curves must be determined and stored in the system.

[0012] Generally, if a well-defined load current characteristic curve is stored in the system, then the highest and lowest temperatures in the system need to be accurately determined, and the stored characteristic curve must be applied correctly. Stable and safe operation must be ensured through complex programming and comprehensive testing.

[0013] In addition, for example, the charging characteristic curve is tested for its hazard by repeated application to the battery based on temperature, state of charge and pulse duration, and then preset according to the system. Summary of the Invention

[0014] The technical problem to be solved by the present invention is to provide a method particularly suitable for operating a battery system. A further technical problem to be solved by the present invention is to provide a battery system particularly suitable for performing this method.

[0015] The technical problem is solved by the method of operating the battery system and the battery system itself.

[0016] If the following method steps are described, then an advantageous technical solution for the battery system is obtained in particular, namely, the battery system is constructed to implement one or more of these method steps.

[0017] The method according to the invention is configured, applicable, and designed for operating battery systems, particularly vehicle batteries or high-voltage batteries (traction batteries) in electric or electric-capable vehicles, such as electric or hybrid electric vehicles. Battery operation includes both resting phases where no current flows from the outside and complex operating scenarios, such as fast charging and recycling in electric or electric-capable vehicles. Battery loads can be combined as needed and can have any temporal sequence and any form, such as pulsed, graded, or continuous processes. The method is designed for voltage control of the battery system during operation under load (i.e., during the loading process of the battery system). This means that the battery system undergoes voltage control and / or voltage regulation during operation under load.

[0018] The conjunction “and / or” should be understood here and in the following text as a feature that connects two things together or substitutes for each other.

[0019] The battery system has at least one electrochemical cell. The battery system may also have multiple cells, thereby electrically connecting the cells to each other (e.g., in series and in parallel). The following embodiments particularly relate to lithium-ion batteries having a liquid electrolyte as the cell. However, embodiments can also be reasonably adapted to solid-state cells or cells with other cell chemistry compositions.

[0020] The process of damaging a single battery cell (the damage process) is characterized here using at least one stored reference curve (characteristic curve, trajectory). The reference curve is the state-of-charge-cell voltage-characteristic curve.

[0021] Damage processes are understood here specifically as processes within the battery that affect the chemistry of the battery or electrolyte and lead to reduced battery performance, such as reduced battery capacity. In particular, damaging processes are a factor limiting the charging process. For example, a damaging process is the aging process of a single battery cell. Specifically, a damaging process should be understood as one that leads to a critical state for the safety of a single battery cell, such as lithium plating, overheating of the single battery cell, damage to the active material due to excessively high loading gradients, or electrolyte decomposition. In lithium-ion batteries with liquid electrolytes, the damaging processes characterized by the method are particularly important for lithium plating.

[0022] According to this method, the voltage of a single battery cell is detected during load operation, and the state of charge and aging status of the single battery cell are determined. The state of health (SOH) of a single battery cell is a measure of the aging process that occurs within the single battery cell, i.e., the damaging processes that lead to changes in battery characteristics, such as maximum energy storage capacity, cell internal resistance, cell voltage, or cell geometry.

[0023] The current cell voltage and current state of charge (SOC) are compared with a stored reference curve. This comparison determines the maximum possible load current for the corresponding aging state of the cell, at which a damage process will not occur. Subsequently, the current load current of the cell is controlled and / or adjusted to the maximum current value by setting the cell voltage according to the cell temperature. In other words, according to this method, by controlling and / or adjusting the load current for various aging states of the cell using a comparison of the cell voltage and SOC with a stored reference curve, a favorable and / or non-destructive maximum load current can be set. This maximizes the load current while avoiding damage processes.

[0024] This invention is based on the knowledge that the determination of the maximum load current (provided the failure process is the limiting factor) results in a voltage trajectory that is almost independent of temperature. Specifically, compared to the state of charge (SOC) of a single battery cell, the single-cell voltage has little or no temperature dependence. This means that the single-cell voltage exhibits a nearly constant process for different single-cell temperatures, compared to the SOC of a single battery cell. Thus, the load process can be controlled and / or regulated based solely on a single reference curve. In particular, temperature monitoring of each individual cell in the battery system is unnecessary. Therefore, the complex temperature monitoring achieved through direct measurement or modeling of each individual battery cell can be eliminated. Consequently, a method particularly suitable for voltage-controlled operation of a battery system under load is realized.

[0025] If the state of charge (SOC) of each individual cell in the battery system is known during charging, measuring the individual cell voltage is sufficient to determine the current maximum load current. For this process, it is advantageous to monitor the voltage individually for each individual cell or each parallel connection of individual cells within the battery system. Using this method, it is no longer necessary to know precisely the coldest and hottest points in the battery system.

[0026] The voltage trajectory of the reference curve provides the maximum voltage under continuous energization for each state of charge. If current is applied to a fully relaxed single cell, it continues until all overvoltages build up in that single cell, and the single-cell voltage reaches the voltage limit for continuous energization. Since the anode overvoltage accounts for only a certain share of the total overvoltage and is crucial here, the estimate of the maximum load current is always conservative. Therefore, if the current is to be charged with the maximum current, it is only necessary to adjust the current in such a way that the single-cell voltage lies exactly on the voltage trajectory for continuous current.

[0027] The method according to the invention ensures particularly advantageous operation of the battery system, wherein damage mechanisms and processes are avoided through voltage regulation or control of individual cell-by-cell, partial, or overall cell-by-cell operation. This method ensures optimal distribution of load current across interconnected individual cells in all operating conditions without achieving unfavorable operating conditions (such as lithium plating).

[0028] The method is explained in more detail below through its application in the fast charging process of vehicle batteries. When a vehicle battery or battery system is fast charged, a high current flows into each individual cell. Adverse conditions within the vehicle battery can occur in various ways. In particular, to prevent lithium plating, the anode potential must be set to a value greater than 0 volts, which can be determined in advance. However, heat is generated during charging, which can cause the battery temperature to rise above the adverse value. Furthermore, the power dissipation that occurs is a function of the cell overvoltage. For example, the cell overvoltage is a function of the cell temperature, state of charge, history, and aging state. To reduce the battery temperature, corresponding further control loops are needed, such as load current or battery cooling. Moreover, any external influence can alter the battery temperature and heating behavior. Therefore, the load current cannot be adjusted back to the previously determined anode potential. The stored reference curve represents the maximum voltage at continuous current under each state of charge without lithium plating. Since the reference curve corresponds to a substantially temperature-independent process of cell voltage, the stored reference curve takes into account all battery dynamics and cooling, as well as any external influences, thus allowing reliable control of fast charging operation based on this reference curve.

[0029] The method of the present invention can also be used, for example, as an evaluation method or for characterizing a battery system or its individual cells.

[0030] In the extended design using this method, the aging state of a single battery cell is determined periodically, for example, cyclically. Adjusting at least one reference curve based on the aging state is appropriate. This ensures the battery system operates normally throughout its entire lifespan. Therefore, control of the stored reference curve allows for a conservative estimate of the maximum load current at any time.

[0031] To determine aging conditions, one can determine, for example, the current capacity of all individual cells or the parallel circuit of individual cells. This can be done, for example, based on adjustments to the open circuit voltage (OCV) curve. To determine aging conditions, it is sufficient to determine only the reduction in individual cell capacity, rather than determining internal resistance.

[0032] Changes in internal resistance are automatically included in the load voltage measurement (single-cell voltage). This eliminates the need for time-consuming methods, such as calculating PT1 behavior, to determine the maximum possible pulse current, and instead provides a conservative and intrinsically safe estimate. This means there is no need to determine the aging state by measuring the internal resistance through pulse current measurements to adjust the reference curve. Therefore, the additional implementation of pulse current can be omitted in addition to continuous load current.

[0033] In a preferred embodiment, different reference curves for the charging and discharging processes of a single battery cell are stored. Specifically, only one reference curve for the charging process and one reference curve for the discharging process are stored. For each charging process, only one voltage characteristic curve is stored in the system, thus eliminating the need for error-prone interpolation between an arbitrary number of current characteristics. To prevent these adverse conditions, an upper limit voltage for battery charging is defined based on the state of charge of each individual battery cell. For battery discharging, a lower limit voltage is defined accordingly based on the state of charge of each individual battery cell. Individual limiting voltages can be defined and implemented for each individual battery cell using the reference curves.

[0034] In an advantageous embodiment, at least one reference curve is pre-characterized using a laboratory single cell. The laboratory cell is a three-electrode single cell with an anode, a cathode, and a reference electrode operating without current. The three-electrode single cell allows for direct measurement and detection of continuous voltage trajectories or current characteristic graphs. The voltage trajectory determined in the three-electrode cell is stored as a reference curve for the battery system. For example, instead of directly using the voltage trajectory from the three-electrode laboratory single cell, a specific current characteristic graph with the original single-cell safety margin can be stored in the battery system.

[0035] In addition to measurements on a 3-electrode laboratory cell, other methods can be used to determine the charging voltage trajectory on a single cell, such as pressure measurements, thickness measurements, or high-precision coulometric measurements. Specifically, a reference curve can be determined by measuring coulometric efficiency or by measuring changes in single-cell expansion and / or single-cell geometry.

[0036] In an alternative, equally advantageous embodiment, at least one reference curve is determined by simulation. In particular, the voltage trajectory is determined by simulating a single-cell voltage, for example, based on a semi-single-cell model. This allows for the determination of the reference curve in a particularly cost-effective and labor-saving manner.

[0037] Voltage regulation or control of a battery or single-cell voltage, taking into account a reference curve, can be performed using the battery's terminal voltage. However, due to technical reasons, the single-cell voltage cannot typically be directly captured from the battery. Additional voltage may be generated at other voltage measurement points, for example, through the current rail. In conceivable extended designs, a safety factor is incorporated into the reference curve before it is stored. This safety factor allows the additional voltage to be accounted for in the reference curve. This simplifies the measurement or detection of the single-cell voltage.

[0038] An additional or further aspect of the invention specifies that the method is interrupted or suspended when a predetermined or stored state of charge (SOC) of the individual battery cell is reached. In other words, the SOC of the individual battery cell is monitored during the method and compared with a stored SOC or SOC value, thereby suspending or interrupting the method when the stored SOC is reached or exceeded. The suspension or interruption may occur in the form of a predetermined waiting time or duration, after which the process will automatically resume. During the suspension or interruption, a favorable balancing process may occur or be initiated in the battery system and / or the individual battery cell. Preferably, a predefined load current and / or reference curve is set during the suspension.

[0039] The battery system according to the invention is configured, applicable to, and designed as a vehicle battery or high-voltage battery for automobiles (particularly electric or electric-capable automobiles, such as electric vehicles or hybrid vehicles). The battery system is particularly a lithium-ion battery system. The battery system has at least one electrochemical cell. In particular, several cells are interconnected in series or parallel. Furthermore, each cell or each parallel circuit of cells is equipped with a voltmeter for voltage measurement. In addition, a voltage regulator and a controller, i.e., a control unit, are also provided. For example, the controller is part of the battery management system of the battery system.

[0040] The controller is typically configured using programming and / or circuitry techniques to execute the methods described above according to the invention. Therefore, the controller is specifically designed to determine the state of charge (SOC) of individual battery cells and receive measurement data from a voltmeter. For example, the controller has a memory storing reference curves. The controller evaluates the current cell voltage and SOC based on the reference curves and controls the voltage regulator accordingly. The voltage regulator consistently adjusts the charging power or load current so that the voltage of all individual cells in the system is kept below or equal to the reference curve. Appropriately, the SOC of each individual battery cell or the parallel circuit of individual battery cells is determined at any time, and these states are periodically adjusted using a balancing scheme. Furthermore, the controller periodically determines the current capacity (aging state) of all individual battery cells or the parallel circuit of individual battery cells based on the voltage data and adjusts the reference curves accordingly. A method based on OCV curve comparison can be used here.

[0041] In a preferred embodiment, the controller is formed, at least in its core, by a microcontroller having a processor and data storage, wherein the functions for performing the methods of the invention are technically implemented in the form of running software (firmware), so that the method—interacting with the device user when necessary—is executed automatically when the running software is executed in the microcontroller. However, the controller may also alternatively be constructed within the framework of the invention by non-programmable electronic components, such as application-specific integrated circuits (ASICs), wherein the functions for performing the methods of the invention are implemented using devices employing circuitry techniques.

[0042] This resulted in a particularly suitable battery system. Attached Figure Description

[0043] The embodiments of the present invention are explained in more detail below with reference to the accompanying drawings. In the drawings:

[0044] Figure 1 A schematic diagram of a car with a battery system is shown.

[0045] Figure 2 This shows the state-of-load (SOC) ratio plot for the battery at different temperatures.

[0046] Figure 3 This shows the state-of-load (SOLO) voltage plots of the battery at different temperatures with reference curves.

[0047] Figure 4 A schematic diagram of the simulation model.

[0048] Figure 5 The load-C ratio plot is shown for comparison between the simulation model and the three-electrode measurements.

[0049] Figure 6 A schematic diagram showing the composition of overvoltage in a battery, and

[0050] Figure 7 The state-of-charge-C ratio diagram is shown to compare the simulation model with the limit values.

[0051] The corresponding parts and parameters are always given the same reference numerals in all the accompanying drawings. Detailed Implementation

[0052] Figure 1 A schematic and simplified diagram illustrate an electric or electric-capable vehicle 2 having a battery system 4 for powering a traction drive (not shown). The battery system 4 is designed as a lithium-ion system having several electrochemical single cells 6. The battery system 4 also includes a voltmeter 8, a voltage regulator 10, and a controller 12.

[0053] Controller 12 is adapted and configured to perform voltage control on battery system 4 during load operation. Reference curve 14 ( Figure 3 The data, stored in the memory of controller 12, characterizes the process of damaging a single battery cell 6. Reference curve 14 is preferably a load state-single-cell voltage-characteristic curve. In this embodiment, the characterized damage process is particularly lithium-plating.

[0054] Preferably, different reference curves 14 are stored for the charging and discharging processes of a single battery cell 6. The following describes only the charging process, for example, in detail, where electrical energy is fed into the single battery cell 6 through a load current IL (or charging current). In other words, the load process should be understood, in particular, as the charging process, such as a fast charging process.

[0055] During load testing, the single-cell voltage UZ of individual battery cell 6 is detected using voltmeter 8. Controller 12 determines or monitors the state of charge (SOC) of individual battery cells 6 during load testing. Furthermore, controller 12 periodically determines the capacity (aging state) of all individual battery cells 6 or the parallel connection of individual battery cells 6 based on the voltage data from voltmeter 8. This can be achieved using a method based on OCV curve comparison.

[0056] The corresponding current state of charge (SOC) and current single-cell voltage (UZ) are compared with the stored reference curve 14. The controller 16 evaluates the current unit of the single-cell voltage (UZ) and SOC based on the reference curve 14. By comparing the values ​​of the single-cell voltage (UZ) and SOC with the stored reference curve 14, the controller 12 determines the maximum possible load current (IL) of the single cell 6 of the battery without causing a damage process, based on the comparison and state of aging (SOH). Consideration of the aging state is made, for example, by adapting the reference curve 14 accordingly to a specific aging state. Subsequently, the current load current (IL) is controlled and / or regulated to the maximum current by means of the controller, through the control voltage regulator 10, independent of the battery temperature.

[0057] Therefore, voltage regulator 10 constantly adjusts the load power or load current IL so that the voltage UZ of all individual cells in the system remains below or the same as the reference curve 14. Appropriately, the state of charge (SOC) of each individual cell 6 or the parallel connection of individual cells 6 is determined by controller 12 at any time and adjusted periodically by a balancing scheme. This adjustment is, for example, performed during the pause or interruption of a method executed by controller 12. For this purpose, predetermined SOC values ​​are stored in controller 12, wherein controller 12 pauses the aforementioned method for balancing when the SOC value is reached or exceeded.

[0058] If battery system 2 needs to absorb power, battery system 2 or controller 10 compares the current state of charge (SOC) of each individual cell 6 with the current cell voltage UZ and the load voltage trajectory of the stored reference curve 14. The load current IL can be increased or maintained as long as the cell voltage UZ at the current SOC is less than or equal to the stored reference curve 14.

[0059] Below Figures 2 to 7 The method of the present invention will be described in more detail based on this.

[0060] Figure 2 A state-of-charge (SOC) ratio plot for battery 6 is shown. The C-ratio (CR) describes the charging (or discharging) current of battery 6 relative to its capacity. The SOC is plotted as a percentage (%) on the horizontal axis (X-axis), and the C-ratio (CR) is plotted as a unitless value on the vertical axis (Y-axis). The plot shows the process of the load current IL or C-rate CR of battery 6 at different temperatures. In particular, nine curves are shown for temperatures between 10°C and 50°C, with temperature steps of 5°C.

[0061] from Figure 2 The current diagram clearly shows that the load current IL has a relatively high temperature dependence. For example, the C ratio CR differs by about 2 times at 10℃ and 50℃.

[0062] Figure 3 It shows Figure 2 State of charge (SOC) - single-cell voltage plot for the load process. SOC is plotted as a percentage (%) along the horizontal axis (X-axis), and single-cell voltage (UZ) is plotted in volts (V) along the vertical axis (Y-axis).

[0063] from Figure 3 It can be seen relatively clearly that the single-cell voltage UZ has a lower temperature dependence than the load current IL. Considerations made using the single-cell model indicate that the variation in the voltage curve is attributed to the moderate quality of the three-electrode laboratory cell used, and that the voltage curve remains virtually constant above the critical temperature at which the cell behavior changes significantly. The voltage curve exhibits a relatively large deviation below 10% state of charge (SOC), because within this SOC range, the loading process begins with a finite current based on the chosen test bench until the anode potential reaches 0V vs. Li / Li+, and the test bench is able to take over control of the current.

[0064] Since the diffusion of the voltage curve is small at different temperatures, the behavior can be approximated by a single reference curve 14, which represents the barrier of the single-cell voltage UZ, at which continuous current does not cause lithium plating.

[0065] For battery 6, which is transferred from the characteristic curves of a laboratory battery to the automotive battery system 2, a safety margin M is used to account for the uniformity of temperature and state of charge in a large single battery cell 6. Therefore, Figure 3 The reference curve 14 shown is reduced by approximately 10% compared to the measured voltage trajectory. The safety margin M can be designed as a multiplication factor or voltage offset. The resulting reference curve 14 is stored in the battery system 4 or the controller 14.

[0066] Voltage regulation or control of the battery or single-cell voltage UZ, taking into account reference curve 14, can be performed using the terminal voltage of battery cell 6. The voltage measurement point of voltmeter 8 can also have an additional voltage, for example, via a current rail. In possible extended designs, a corresponding safety factor is considered in the safety margin M.

[0067] To explain the favorable operation of battery system 2 in the parallel circuit of battery cells 6, where the temperature of each cell is unknown, a simulation was performed in which the voltage of the parallel circuit of the cells was adjusted to the voltage trajectory of the reference curve.

[0068] Figure 4 A schematic diagram of the simulated scenario is shown. This scenario connects two battery cells, 6a and 6b, in parallel. The temperature of battery cell 6a is 10°C, and the temperature of battery cell 6b is 50°C. The voltage curve in this scenario is used as reference curve 14.

[0069] Figure 5 The state-of-charge (SOC) ratio plot is displayed to compare the maximum possible load current IL between simulation and measurement. The SOC is plotted as a percentage (%) along the horizontal axis (X-axis), while the C-ratio (CR) or load current IL is plotted along the vertical axis (Y-axis). Figure 5 Four curves, 16, 18, 20, and 22, are displayed. Curve 16 shows the three-electrode measurement process for battery cell 6a at 10°C, while curve 18 shows the corresponding simulation process. Correspondingly, curve 20 shows the three-electrode measurement process for battery cell 6b at 50°C, and curve 22 shows the simulation process. From... Figure 5 It can be seen relatively clearly that the simulated single-cell current for both temperatures is within the maximum possible load current range, which was determined by three-electrode measurements (3E measurements).

[0070] The following explains how to determine the load current pulse based on the charge quantity. In the article "Determining the maximum charging currents of lithium-ion cells for small charge quantities" (Power Sources, 2017) by Grismmann et al., it is explained that the maximum pulse current and the charge quantity or state of charge (SOC) have an approximately 1 / √SOC correlation (1 divided by the square root of the state of charge).

[0071] The achievable charge amount is determined based on the current intensity by simulating and measuring voltage trajectories from three electrodes.

[0072] Figure 6 It includes two vertical, stacked segments 24 and 26.

[0073] Section 24 shows a schematic state-of-charge-current diagram. The state of charge (SOC) is plotted horizontally along the x-axis (X-axis), and the current I is plotted along the vertical y-axis (Y-axis). The height of the current curve (shown as a double arrow in section 24) represents the maximum load current IL.

[0074] Section 26 shows a schematic state-of-charge-voltage diagram. The state of charge (SOC) is plotted horizontally along the x-axis (X-axis), and the voltage U is plotted along the y-axis (Y-axis). Section 26 displays two curves, 28 and 30. Curve 28 here corresponds to the voltage trajectory of reference curve 14, while curve 30 represents an overvoltage.

[0075] Section 26 of the figure shows the composition of the overvoltage, consisting of the separator / electrolyte component 30a, the cathode component 30b, and the anode component 30c, of which only the anode component 30c is important for the (fast) charging process. From the correlation, it can be concluded that a favorable load current range can always be guaranteed through voltage control of the relative voltage trajectory of the single-cell voltage.

[0076] To determine the achievable charge amount based on the current intensity, the battery cell 6 is continuously charged with current pulses (section 24) until the battery's overvoltage and voltage trajectory intersect. The change in state of charge caused by the current pulses... Figure 6 The value is marked with ΔSOC.

[0077] A comparison of the determined maximum load current pulse with the manufacturer's specifications for a single battery cell (6 cells) and the theoretical value based on Grimsmann's data is as follows: Figure 7 As shown. Figure 7A graph is shown where the change in state of charge ΔSOC is plotted horizontally along the x-axis (X-axis) and the C ratio CR or load current IL is plotted along the y-axis (Y-axis). The graph uses curves 32 and 34 to illustrate the process of two simulated load current pulses. Curve 32 shows the process at 12% state of charge, and curve 34 shows the process at 60% state of charge. Figure 7 A line 36 is also shown, corresponding to Grimsmann's theoretical value, along with two curves 38 and 40. Curve 38 corresponds to the process according to the manufacturer's instructions for a 12% state of charge, and curve 40 corresponds to the process according to the manufacturer's instructions for a 60% state of charge. Figure 7 It is clearly shown that the simulated load current pulse is almost entirely lower than the manufacturer's specifications and Grimsmann's theoretical values.

[0078] The claimed invention is not limited to the embodiments described above. Conversely, other variations of the invention can be derived by those skilled in the art within the scope of the disclosed claims without departing from the technical solution of the claimed invention. In particular, all individual features described in combination with different embodiments can also be combined in other ways within the scope of the disclosed claims without departing from the technical solution of the claimed invention.

[0079] List of reference numerals

[0080] 2. Cars

[0081] 4. Battery System

[0082] 6 batteries

[0083] 8. Voltmeter

[0084] 10. Voltage Regulator

[0085] 12 controllers

[0086] 14 Reference Curve

[0087] Curves 16, 18, 20, and 22

[0088] Sections 24 and 26

[0089] 28, 30 curves

[0090] 30a Separator / Electrolyte Ratio

[0091] 30b cathode fraction

[0092] 30c anode fraction

[0093] Curves 32 and 34

[0094] 36 lines

[0095] 38, 40 curves

[0096] U voltage

[0097] UZ single-cell voltage

[0098] I Current

[0099] IL load current

[0100] State of charge (SOC)

[0101] C Ratio

[0102] M represents the safety margin.

Claims

1. Method for operating a battery system (4) in a voltage-controlled manner during a load process, the battery system having at least one electrochemical battery cell (6), wherein a process of damaging the battery cell (6) is characterized by at least one stored reference curve (14), wherein the reference curve (14) is a state-of-charge-cell-voltage characteristic and represents the maximum voltage at a continuous current for each state of charge, - wherein, - wherein the cell voltage (UZ) of the battery cell (6) is detected, - wherein the state of charge (SOC) of the battery cell (6) is detected, - wherein the aging state of the battery cell (6) is determined, - wherein the cell voltage (UZ) and the state of charge (SOC) are compared with the stored reference curve (14), - wherein the maximum load current (IL) is determined based on the aging state of the battery cell (6) from the comparison, and - wherein the maximum load current (IL) is set by controlling and / or regulating the cell voltage (UZ).

2. The method of claim 1, wherein, The aging state of the battery cell (6) is determined periodically.

3. The method of claim 1, wherein, Different reference curves (14) are stored for a charging process and a discharging process of the battery cell (6).

4. The method of claim 1, wherein, At least one reference curve (14) is pre-characterized with laboratory cells.

5. The method of claim 1, wherein, At least one reference curve (14) is determined by measurement of the coulomb efficiency.

6. The method of claim 1, wherein, At least one reference curve (14) is determined by measurement of the cell swelling and / or cell geometry change.

7. The method of claim 1, wherein, At least one reference curve (14) is determined by simulation.

8. The method of claim 1, wherein, At least one reference curve (14) is provided with a safety factor before storage.

9. The method of claim 1, wherein, The method is interrupted and / or paused at a predefined state of charge (SOC), during which a predefined load current (IL) and / or reference curve (14) is set.

10. Battery system (4) having at least one battery cell (6), wherein a voltage meter (8) and a voltage regulator (10) are connected to the battery cell (6), and the battery system (4) has a controller (12) for implementing the method according to any one of claims 1 to 9.

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