Method for determining the aging state of at least one electrochemical energy store

Abstract

The invention relates to a method for determining the aging state of at least one electrochemical energy store.

Description

Technical Field

[0001] The invention proceeds from a method for determining the aging state of at least one electrochemical energy store, a diagnostic device, a computer program, and a use of a diagnostic device according to the preambles of the independent claims. Background Art

[0002] The battery's state of health (SOH), the value of which is calculated and stored in the battery control unit (BCU), can be read out, for example, in a vehicle workshop during an inspection of an electrically driven vehicle including a battery via a diagnostic interface (on-board diagnostic interface, OBD interface) using a diagnostic device.

[0003] These values ​​are determined during or after a driving cycle, during or after a charging process, in a dynamic or static state under different conditions depending on the SOH algorithm.

[0004] Each manufacturer uses a different method, sometimes even different between the same vehicle model or battery model, and the workshop relies on the value of the aging state, which has a correspondingly large inaccuracy / accuracy.

[0005] Document US 2010 / 090650 discloses a system and method for accurately characterizing the thermodynamic and material properties of electrodes and electrochemical energy storage systems and energy conversion systems.

[0006] Document CN 106526486 discloses a method for identifying the degree of aging of a lithium battery.

[0007] The object of the present invention is to further improve the prior art. This object is achieved by the features of the independent claims. Summary of the Invention

[0008] Advantages of the present invention

[0009] The procedure according to the invention having the characterizing features of the independent claims has the following advantages over this: The method for determining the aging state of at least one electrochemical energy store comprises the following steps according to the invention:

[0010] a) obtaining a voltage magnitude, where the voltage magnitude represents a voltage of the electrochemical energy storage device;

[0011] b) comparing the acquired voltage with a predetermined rated voltage;

[0012] c) generating a signal for charging and / or discharging the electrochemical energy store based on the result of the comparison;

[0013] d) discharging the electrochemical energy store with a low current for a predetermined period of time;

[0014] e) detecting a voltage magnitude during the discharge and determining a voltage gradient of the detected voltage magnitude for a predetermined time period;

[0015] f) comparing the voltage gradient with a predetermined rated voltage gradient;

[0016] g) determining an aging state of the electrochemical energy storage device based on a result of the comparison;

[0017] The aging state of the electrochemical energy store is thus determined with high precision in a defined state of charge, thereby allowing reliable lifespan predictions and economical statements for the electrochemical energy store, for example during repair or replacement of the electrochemical energy store.

[0018] Furthermore, it is advantageous that the method according to the invention can be used as a standard test method for electrochemical energy stores having a characteristic voltage profile, thereby also enabling comparability of different electrochemical energy stores, which is particularly relevant for possible second-life applications of energy stores.

[0019] Further advantageous embodiments are described in the dependent claims.

[0020] The method furthermore comprises the following advantageous steps:

[0021] a.1) obtaining a temperature value, which represents the temperature of the electrochemical energy storage device;

[0022] a.2) comparing the acquired temperature with a predetermined setpoint temperature;

[0023] a.3) generating a signal for heating and / or cooling the electrochemical energy storage device based on the result of the comparison;

[0024] As a result, the method according to the invention can be carried out at a fixed, defined temperature, so that no temperature control by the electrochemical energy store is necessary.

[0025] The method further comprises the following advantageous steps:

[0026] c.1) waiting for a predetermined period of time for the electrochemical energy storage device to relax;

[0027] As a result, the method according to the invention can be carried out under defined and virtually identical conditions, thereby achieving a higher accuracy and comparability compared to the prior art.

[0028] The method further comprises the following advantageous steps:

[0029] e.1) discharging the electrochemical energy store with a low current for a further predetermined period of time;

[0030] e.2) Repeat steps d) and e) at least once);

[0031] e.3) determining a voltage gradient from an average value of the determined voltage gradients;

[0032] The method according to the invention can thus be carried out fully automatically, thereby eliminating systematic or accidental measurement deviations.

[0033] The method further comprises the following advantageous steps:

[0034] h) verifying the aging state by evaluating the voltage level during the discharge and / or relaxation of the electrochemical energy store and / or by evaluating the voltage profile after a current jump;

[0035] The determined aging state can thus be verified by other methods and determined with high accuracy. A highly accurate aging state offers significant advantages, in particular to vehicle owners and / or fleet operators, with respect to the service life of an electrochemical energy store or an electrically driven vehicle comprising an electrochemical energy store.

[0036] The method further comprises the following advantageous steps:

[0037] i) acquiring a further voltage magnitude, which represents the voltage of the electrochemical energy store;

[0038] j) comparing the other voltages obtained with the voltage obtained in step a);

[0039] k) generating a signal for charging and / or discharging the electrochemical energy store based on the result of the comparison;

[0040] When carrying out the method according to the invention, virtually no losses occur due to buffering or feeding back energy from the grid.

[0041] Advantageously, the diagnostic device comprises at least one device, in particular an electronic control unit, which is configured to carry out the steps of the method according to the invention.

[0042] This eliminates the need for intervention in a control unit, such as a control unit for an electrochemical energy storage device (Battery Control Unit, BCU) or a control unit for an electrically drivable vehicle (Vehicle Control Unit, VCU). In a further advantageous embodiment, the calibration of the determined aging state can be performed in a wired and / or wireless manner with the control unit and / or the infrastructure.

[0043] Furthermore, it is possible, for example, to enable workshops to reliably and highly accurately determine the aging state of almost any electrochemical energy storage device in an electrically driven vehicle under defined conditions. This standardized method enables comparability between different electrochemical energy storage devices, which is particularly valuable for potential secondary life applications of the energy storage devices.

[0044] Advantageously, the computer program according to the invention comprises commands which cause the diagnostic unit to carry out the method steps according to the invention for detecting an internal short circuit.

[0045] Advantageously, a machine-readable storage medium is provided, on which the computer program is stored.

[0046] Advantageously, the diagnostic device is used in electric vehicles, hybrid vehicles, plug-in hybrid vehicles, aircraft, electric bicycles (pedelecs) or electric bikes (e-bikes), electric hand tools, and in static storage devices used to store electrical energy, in particular regeneratively obtained energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Exemplary embodiments of the invention are shown in the drawings and are described in detail in the following description.

[0048] in:

[0049] Figure 1 a first schematic diagram showing the voltage profile of electrochemical energy stores of different ages; and

[0050] Figure 2 a flow chart illustrating an embodiment of the method according to the present invention; and

[0051] Figure 3 a schematic diagram showing a voltage profile after a discharge process of an electrochemical energy store; and

[0052] Figure 4 A second schematic diagram shows the voltage profile of electrochemical energy stores of different ages. DETAILED DESCRIPTION

[0053] The same reference numerals denote the same device components throughout the figures.

[0054] Figure 1 A first schematic diagram shows the voltage profile 100 of electrochemical energy stores of different ages, corresponding to the respective aging states, which correspond to the ratio of the currently maximum usable capacity to the nominal capacity of the electrochemical energy store. Voltage profile 101 characterizes the behavior of an electrochemical energy store with an aging state of 60%, voltage profile 102 characterizes the behavior of an electrochemical energy store with an aging state of 80%, voltage profile 103 characterizes the behavior of an electrochemical energy store with an aging state of 90%, and voltage profile 104 characterizes the behavior of an electrochemical energy store with an aging state of 100%.

[0055] Depending on the aging state at a specific temperature, the predetermined voltage 105 intersects the voltage curves 101 , 102 , 103 , 104 at a voltage-sensitive point 106 .

[0056] Figure 2 A flow chart of an embodiment of the method according to the invention is shown. In step 201 , the method is started, for example, when a diagnostic device is connected to a diagnostic interface of an electrically driven vehicle having an electrochemical energy store in a workshop.

[0057] Furthermore, in step 201 , a voltage magnitude is determined, which represents the voltage of the electrochemical energy store, and the determined voltage magnitude is compared with a predefined setpoint voltage magnitude.

[0058] The temperature and aging state of the electrochemical energy storage device are also determined from a control unit, such as the electrochemical energy storage device's control unit (Battery Control Unit, BCU) or the electrically driven vehicle's control unit (Vehicle Control Unit, VCU). The aging state is preferably determined at a defined constant temperature, such as 20°C. To this end, the electrochemical energy storage device or the electrically driven vehicle having the electrochemical energy storage device can be parked in a climate chamber or exposed to air using a blower.

[0059] In step 202 , a signal for charging and / or discharging the electrochemical energy store is generated based on the result of the comparison of the determined voltage magnitude with a predefined setpoint voltage magnitude.

[0060] The voltage of the electrochemical energy store is thus set to a voltage level at which the sensitivity of the voltage of the electrochemical energy store is maximum. The sensitivity varies depending on the cell chemistry of the electrochemical energy store, and the voltage is not necessarily at the same voltage level for all aging states, but may vary depending on the aging state.

[0061] The aging state detected by the control unit is used as a reference value with which the method according to the present invention is initiated. A target voltage value is determined based on the detected aging state, for example, using the technical data of the electrochemical energy store stored in the diagnostic unit. Depending on the comparison of the detected voltage value with a predetermined target voltage value, the electrochemical energy store is charged or discharged.

[0062] In the simplest case, the electrochemical energy store is discharged by switching on an electrical appliance, such as an air conditioner or heater, when the deviation of the current voltage level from the nominal voltage level is very small.

[0063] In other cases, the electrochemical energy store is connected to a buffer battery and discharged until the rated voltage level is reached.

[0064] Furthermore, a connection to a charging station is possible, wherein excess energy from the electrochemical energy store is fed into the power grid. At the end of the method, the buffered or fed-back energy is fed back to the electrochemical energy store, so that virtually no energy is lost and the electrochemical energy store has the same state of charge (SOC) after the aging state has been determined.

[0065] If the predetermined setpoint voltage level is reached, the discharge process is terminated and a predetermined time period is waited for in step 203, during which the electrochemical energy store relaxes. The voltage of the electrochemical energy store thus rises, but remains in a range close to the setpoint voltage level.

[0066] In step 204, the electrochemical energy store is discharged for a predetermined duration with a low current, for example, 0.1 C to 0.5 C. If the charging station does not allow such a low adjustable current, a small load, such as an electrical consumer or a resistor, can be connected directly to the electrochemical energy store. During the discharge, the voltage level is detected, and in step 205, the voltage gradient is determined based on the curve of the voltage level detected for the predetermined duration.

[0067] In step 207, the electrochemical energy store is discharged with a low current for a further predetermined duration. After a brief measurement pause during this further discharge, steps 204 and 205 are repeated as long as the voltage level remains within a predetermined voltage range, for example, between 3.4 V and 3.2 V. For tolerance reasons, a specific number of repetitions should be performed, for which purpose the number of repetitions is compared with a predetermined number of continuous operations in step 206.

[0068] When a predetermined number of consecutive operations is reached, the voltage gradient is determined in step 208 from the average value of the determined voltage gradients.

[0069] In step 209 , the voltage gradient is compared with a predefined setpoint voltage gradient, and the aging state of the electrochemical energy store is determined based on the result of the comparison.

[0070] The method is terminated in step 210. In a further advantageous embodiment, the aging state is verified in step 210 by evaluating the voltage level during the discharge and / or relaxation of the electrochemical energy store and / or by evaluating the voltage profile after a current jump.

[0071] In a further advantageous embodiment, a further voltage magnitude is detected in step 210, the detected further voltage magnitude is compared with the voltage magnitude detected in step 201, and based on the result of the comparison, a signal for charging and / or discharging the electrochemical energy store is generated. As a result, after the aging state is determined in step 210 and the method is terminated, the electrochemical energy store has the same state of charge (SOC) as at the start of the method in step 201.

[0072] Figure 3 A schematic diagram shows a voltage profile 300 after the discharge process of an electrochemical energy store according to step 202. If a predetermined setpoint voltage level is reached, the discharge process of the electrochemical energy store is terminated. Within a predetermined time period 301, the electrochemical energy store relaxes. In step 203, the voltage rises again slightly during the predetermined time period. At time 302, the voltage can be measured according to step 204.

[0073] Figure 4 A second schematic diagram shows the voltage profile 400 of electrochemical energy stores of varying age, corresponding to the respective aging states, which correspond to the ratio of the currently maximum usable capacity to the nominal capacity of the electrochemical energy store. Voltage profile 410 characterizes the behavior of an electrochemical energy store with an aging state of 80%, voltage profile 420 characterizes the behavior of an electrochemical energy store with an aging state of 90%, and voltage profile 430 characterizes the behavior of an electrochemical energy store with an aging state of 100%.

[0074] To determine the aging state of an electrochemical energy store according to the invention, a voltage 440 is predefined which, depending on the aging state at a specific temperature, intersects the voltage profiles 410, 420, 430 at voltage-sensitive points 413, 423, 433. Depending on the aging state, the voltage-sensitive points 411, 413, 415, 421, 423, 425, 431, 433, 435 may shift between predefined voltage limits 441, 442.

[0075] In step 202, the electrochemical energy store is discharged to a nominal voltage level 440, for example, approximately 3.3 V. Due to the relaxation of the electrochemical energy store, the voltage rises slightly. In step 204, the electrochemical energy store is discharged for a predetermined duration. In step 205, first voltage gradients 412, 422, 432 are determined. In step 207, the electrochemical energy store is discharged with a low current for another predetermined duration, resulting in a voltage drop. Steps 204 and 205 are then repeated, and second voltage gradients 414, 424, 434 are determined. In a third continuous operation, third voltage gradients 416, 426, 436 are determined. In step 208, a voltage gradient is determined from the average value of the determined voltage gradients 412, 422, 432, 414, 424, 434, 416, 426, 436. In step 209, the voltage gradient is compared with a predetermined nominal voltage gradient, and the aging state of the electrochemical energy store is determined based on the result of the comparison.

Claims

1. A method for determining the aging state of at least one electrochemical energy store, comprising the following steps: a) (201) obtaining a voltage magnitude, wherein the voltage magnitude represents a voltage of the electrochemical energy storage device; b) comparing the acquired voltage with a predetermined rated voltage; c) (202) generating a signal for charging and / or discharging the electrochemical energy store based on the result of the comparison, whereby the voltage of the electrochemical energy store is set to a voltage level at which the sensitivity of the voltage of the electrochemical energy store is maximum; d) (204) discharging the electrochemical energy storage device with a low current of 0.1 C to 0.5 C for a predetermined time period; e) (205) acquiring a voltage magnitude during the discharge period and determining a voltage gradient of the voltage magnitude acquired for a predetermined duration; f) comparing the voltage gradient with a predetermined setpoint voltage gradient; g) (209) determining the aging state of the electrochemical energy storage device based on the result of the comparison.

2. The method for determining the aging state of at least one electrochemical energy store according to claim 1 , further comprising the following steps: a.1) (201) obtaining a temperature, wherein the temperature represents the temperature of the electrochemical energy storage device; a.2) (201) comparing the acquired temperature with a predetermined setpoint temperature; a.3) (201) Generating a signal for heating and / or cooling the electrochemical energy storage device based on the result of the comparison.

3. The method for determining the aging state of at least one electrochemical energy store according to claim 1 , further comprising the following steps: c.1) (203) Waiting for a predetermined period of time for the electrochemical energy store to relax.

4. The method for determining the aging state of at least one electrochemical energy store according to claim 1 , further comprising the following steps: e.1) (207) discharging the electrochemical energy store with a low current for a further predetermined time period; e.2) Repeat steps d) and e) at least once; e.3) (208) Determine a voltage gradient from an average value of the determined voltage gradients.

5. The method for determining the aging state of at least one electrochemical energy store according to claim 1 , further comprising the following steps: h) (210) Verifying the aging state by evaluating the voltage level during the discharge and / or relaxation of the electrochemical energy store and / or by evaluating the voltage profile after a current jump.

6. The method for determining the aging state of at least one electrochemical energy store according to claim 1 , further comprising the following steps: i) (210) obtaining another voltage magnitude, said other voltage magnitude representing the voltage of the electrochemical energy storage device; j) (210) comparing the other voltage magnitudes obtained with the voltage magnitude obtained in step a); k) (210) generating a signal for charging and / or discharging the electrochemical energy storage device based on the result of the comparison. 7 . A diagnostic device comprising at least one device configured to carry out the steps of the method according to claim 1 . 8 . A computer program product comprising commands for causing a diagnostic device according to claim 7 to carry out the method steps according to claim 1 . 9 . A machine-readable storage medium on which a computer program is stored, the computer program comprising commands which cause the diagnosis device according to claim 7 to carry out the method steps according to claim 1 . 10 . Use of the diagnostic device according to claim 7 in electric vehicles, hybrid vehicles, plug-in hybrid vehicles, aircraft, electric bicycles or electric bikes, electric hand tools, and in static memories used for storing electrical energy.

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