Balancing device and method for controlling the state of charge of a reference electrode in a battery

Abstract

A vehicle and a balancing device and method of controlling a state of charge of a reference electrode in a battery. The balancing device includes a measurement circuit and a charging circuit. The measurement circuit is configured to obtain a measurement of a reference voltage of the reference electrode. The charging circuit is configured to adjust the reference voltage based on the measurement. The state of charge of the reference electrode is controlled based on the reference voltage.

Description

Technical Field

[0001] This invention relates to battery testing and charging maintenance, and more particularly to systems and methods for determining and controlling the state of charge on a reference electrode of a battery. Background Technology

[0002] The state of charge (SOC) of a lithium-ion battery can be estimated by measuring the voltage difference between the cathode and anode. However, this voltage can change due to charging or discharging events. To obtain improved voltage measurements, the cathode and anode voltages are typically determined by measuring their voltages relative to a reference electrode that is not involved in the energy storage process. The usefulness of a reference electrode depends on its ability to maintain a stable electrochemical potential over time. However, for reference electrodes made of lithium compounds, the potential of the reference electrode depends on its lithium concentration over time. Therefore, it is desirable to maintain control over the lithium concentration in the reference electrode. Summary of the Invention

[0003] In one exemplary embodiment, a method for controlling the state of charge of a reference electrode in a battery is disclosed. The method involves obtaining a measurement of a reference voltage of the reference electrode, adjusting the reference voltage based on the measurement, and controlling the state of charge of the reference electrode based on the reference voltage.

[0004] In addition to one or more features described herein, the reference electrode is made of lithium iron phosphate (LiFePO4). The method also includes adjusting the reference voltage when the measurement is outside a range defined with respect to a nominal voltage. This range is defined by a maximum voltage threshold and a minimum voltage threshold. Adjusting the reference voltage also includes at least one of adding lithium ions to the reference electrode and removing lithium ions from the reference electrode. Adjusting the reference voltage also includes at least one of charging the reference electrode from the anode of the battery, discharging the reference electrode to the cathode of the battery, charging the reference electrode from the cathode of the battery, and discharging the reference electrode to the anode of the battery. The method also includes using the reference voltage to determine at least one of a cathode voltage and an anode voltage.

[0005] In another exemplary embodiment, a balancing device for controlling the state of charge of a reference electrode in a battery is disclosed. The balancing device includes a measurement circuit and a charging circuit. The measurement circuit is configured to obtain a measurement of a reference voltage of the reference electrode. The charging circuit is configured to adjust the reference voltage based on the measurement, wherein the state of charge of the reference electrode is controlled based on the reference voltage.

[0006] In addition to one or more features described herein, the reference electrode is made of lithium iron phosphate (LiFePO4). The charging circuit is configured to adjust the reference voltage when the measurement is outside a range defined with respect to a nominal voltage. This range is defined by a maximum voltage threshold and a minimum voltage threshold. The charging circuit is configured to adjust the reference voltage by performing at least one of adding lithium ions to the reference electrode and removing lithium ions from the reference electrode. The charging circuit is also configured to adjust the reference voltage by performing at least one of charging the reference electrode from the anode of the battery, discharging the reference electrode to the cathode of the battery, charging the reference electrode from the cathode of the battery, and discharging the reference electrode to the anode of the battery. The measurement circuit is configured to use the reference voltage to determine at least one of the cathode voltage and the anode voltage.

[0007] In yet another exemplary embodiment, a vehicle is disclosed. The vehicle includes a battery and a balancing device. The battery has a state of charge and a reference electrode. The balancing device controls the state of charge of the reference electrode. The balancing device includes a measuring circuit and a charging circuit. The measuring circuit is configured to obtain a measurement of a reference voltage of the reference electrode. The charging circuit is configured to adjust the reference voltage based on the measurement, wherein the state of charge of the reference electrode is controlled based on the reference voltage.

[0008] In addition to one or more features described herein, the reference electrode is made of lithium iron phosphate (LiFePO4). The charging circuit is configured to adjust the reference voltage when the measurement is outside a range defined by a maximum voltage threshold and a minimum voltage threshold with respect to the nominal voltage. The charging circuit is configured to adjust the reference voltage by performing at least one of adding lithium ions to the reference electrode and removing lithium ions from the reference electrode. The charging circuit is configured to adjust the reference voltage by performing at least one of charging the reference electrode from the anode of the battery, discharging the reference electrode to the cathode of the battery, charging the reference electrode from the cathode of the battery, and discharging the reference electrode to the anode of the battery. The measurement circuit is configured to use the reference voltage to determine at least one of the cathode voltage and the anode voltage.

[0009] The above-described features and advantages, as well as other features and advantages, of this disclosure will become apparent from the following detailed description when taken in conjunction with the accompanying drawings. Attached Figure Description

[0010] Other features, advantages, and details appear only by way of example in the following detailed description, which refers to the accompanying drawings, wherein:

[0011] Figure 1 The vehicle is shown in an illustrative embodiment;

[0012] Figure 2 A schematic diagram of the battery cells in the battery pack is shown;

[0013] Figure 3 An illustrative embodiment is shown. Figure 2 Detailed view of the reference electrode;

[0014] Figure 4 A graph illustrating the relationship between the reference voltage of the reference electrode and the depth of discharge of the reference electrode is shown.

[0015] Figure 5 A schematic diagram of the balancing device in an illustrative embodiment is shown;

[0016] Figure 6 A graph illustrating the discharge steps that can be used to control or adjust the reference voltage is shown;

[0017] Figure 7 A graph illustrating the charging steps that can be used to control or adjust the reference voltage is shown;

[0018] Figure 8 A flowchart is shown for a method of maintaining a reference voltage at its nominal value; and

[0019] Figure 9 A graph showing the change of the anode reference voltage over time during the balancing step in an illustrative embodiment is shown. Detailed Implementation

[0020] The following description is exemplary in nature only and is not intended to limit this disclosure, its application, or use. It should be understood that in all the drawings, corresponding reference numerals denote the same or corresponding parts and features.

[0021] According to an exemplary embodiment, Figure 1 A vehicle 100 is shown. The vehicle 100 includes a battery pack 102, an electrical load 104, and a balancing device 106. In various embodiments, the battery pack 102 is a lithium battery. The battery pack 102 provides power to the electrical load 104. The electrical load 104 may include a motor and / or electrical equipment, such as a radio, communication system, lights, a computer processor, etc. In embodiments where the vehicle 100 includes an electric motor for propulsion, the battery pack 102 can provide power for propulsion, etc. The balancing device 106 performs various measurements to determine the state of charge of the battery pack 102. In one embodiment, the balancing device 106 obtains a measurement of a reference voltage disposed on a reference electrode in the battery pack 102. The balancing device 106 may also charge or discharge the reference electrode to adjust the reference voltage to within a standard nominal voltage range and monitor the state of charge of the battery pack 102 based on the adjusted reference voltage. Although the balancing device 106... Figure 1 The component shown is part of vehicle 100, but in various embodiments, the balancing device 106 may be part of a station independent of the vehicle, such as a repair station or charging station.

[0022] Figure 2A schematic diagram of a battery cell 200 of a battery pack 102 is shown. The battery cell 200 includes a cathode 202, an anode 204, and a reference electrode 206 typically disposed between the cathode 202 and the anode 204. The state of charge of the battery cell 200 is determined by measuring the cathode voltage and the anode voltage. The cathode voltage is measured between the cathode 202 and the reference electrode 206, and the anode voltage is measured between the anode 204 and the reference electrode 206.

[0023] Figure 3 An illustrative embodiment is shown. Figure 2 A detailed view 300 of the reference electrode 206. The reference electrode 206 includes a separator 302 that holds a reference strip 304 in place. The reference strip 304 includes a conductive strip 306 connected to a reference material 308. In various embodiments, the conductive strip 306 is made of gold (Au), and the reference material 308 is made of lithium iron phosphate (LiFePO4).

[0024] Figure 4 A graph 400 shows the relationship between the reference voltage (i.e., the potential of reference electrode 206) and the depth of discharge of the reference electrode. The depth of discharge is the amount of charge removed from a fully charged battery. The depth of discharge is expressed as a percentage (%) on the horizontal axis and the voltage is expressed as volts (V) on the vertical axis.

[0025] Curve 402 represents the reference voltage of reference electrode 206 as a function of depth of discharge. As can be seen from curve 402, the reference voltage is stable over a wide range of depth of discharge (e.g., between approximately 5% and approximately 95%), and remains within a tight voltage range of the nominal voltage (e.g., approximately 3.35V) within this range. When the depth of discharge decreases below approximately 5%, the reference voltage rapidly increases outside this range. When the depth of discharge increases above approximately 95%, the reference voltage rapidly decreases outside this range.

[0026] Curve 400 includes the maximum voltage threshold 404 (VT) max ) and minimum voltage threshold 406 (VT) min In various embodiments, the maximum voltage threshold 404 is approximately 3.434V, and the minimum voltage threshold 406 is approximately 3.410V. The maximum voltage threshold 404 and the minimum voltage threshold 406 can be used to activate charging and / or discharging events. When the reference voltage of curve 402 rises above the maximum voltage threshold 404, the balancing device 106 can take action to lower the reference voltage, thereby restoring the reference voltage to its nominal value. When the reference voltage falls below the minimum voltage threshold 406, the balancing device 106 can take action to raise the reference voltage, thereby restoring the reference voltage to its nominal value. Therefore, action is taken when the reference voltage is outside the voltage range defined with respect to the nominal value.

[0027] Figure 5 A schematic diagram of a balancing device 106 in an illustrative embodiment is shown. This balancing device 106 periodically measures a reference voltage under known conditions and, when the reference voltage is outside a selected range of nominal potentials, adds or removes lithium to a reference electrode to restore the nominal potential. This range is represented by a maximum voltage threshold 404 and a minimum voltage threshold 406. The balancing device 106 restores the reference voltage by adding or removing lithium to a reference electrode 206. Once the reference voltage is restored, it can be used to determine the anode voltage and / or cathode voltage, and thus the state of charge of the battery cell 200.

[0028] The balancing device 106 includes a measurement circuit 502, a charging circuit 504, and a processor 506. The measurement circuit 502 is electrically coupled to a reference electrode 206 and measures the reference voltage. The charging circuit 504 controls the inflow and outflow of lithium ions from the reference electrode 206. For example, the charging circuit 504 can discharge the reference electrode 206 to the cathode 202 to transfer lithium ions out of the reference electrode. The measurement circuit 502 periodically checks the reference voltage. When the reference voltage differs from the nominal voltage by a selected amount, charging / discharging occurs.

[0029] In various embodiments, the measurement circuit 502 can also be used to measure the voltage difference (i.e., anode voltage) between the reference electrode 206 and the anode 204, and the voltage difference (i.e., cathode voltage) between the reference electrode 206 and the cathode 202. The charging circuit 504 can also be used to control the charging state of the reference electrode 206.

[0030] The processor 506 obtains a measurement of the reference voltage from the measurement circuit 502 and controls the operation of the charging circuit 504 based on this measurement. For example, when the reference voltage is greater than a maximum voltage threshold (e.g., about 3.434V), the charging circuit 504 can discharge the reference electrode 206 to the anode 204 to add lithium ions to the reference electrode 206, thereby lowering the reference voltage. When the reference voltage is less than a minimum voltage threshold (e.g., about 3.410V), lithium ions can be removed from the reference electrode 206 to increase the reference voltage. The charging circuit 504 can charge or discharge the reference electrode 206 using either the cathode 202 or the anode 204.

[0031] Figure 6A graph 600 illustrating the discharge steps that can be used to control or adjust the reference voltage is shown. Potential (V) is shown along the y-axis, and for ease of illustration, representative battery elements are distributed along the x-axis. Cathode voltage 602 represents the voltage range of cathode 202. Anode voltage 604 represents the voltage range of anode. Reference voltage 606 represents the voltage range of reference electrode 206. In various embodiments, the discharge steps can be performed without the use of an additional power source. Cathode discharge step 608 includes discharging reference electrode 206 to cathode 202 and removing one or more lithium ions from the reference electrode. Anode discharge step 610 includes discharging reference electrode 206 to anode 204 and adding one or more lithium ions to the reference electrode.

[0032] Figure 7 A graph 700 illustrating the charging steps that can be used to control or adjust the reference voltage is shown. The potential (V) is shown along the y-axis, and for ease of illustration, representative battery elements are distributed along the x-axis. The charging steps are performed using a current source and a controller. Cathode charging step 702 includes charging the reference electrode 206 through the cathode 202 and adding one or more lithium ions to the reference electrode. Anode charging step 704 includes charging the reference electrode 206 using the anode 204 and removing one or more lithium ions from the reference electrode.

[0033] Figure 8 A flowchart 800 is shown for a method of maintaining a reference voltage at its nominal value. In block 802, the battery is charged. In block 804, a measurement is taken to determine if the reference voltage falls within an acceptable range. This includes checking the reference voltage against a known potential of the other electrode (i.e., cathode 202 or anode 204). In one embodiment, the anode potential is used at the end of a charging event (i.e., when the anode electrode is fully lithiated). The charge is then maintained at the maximum voltage until the current drops below a certain threshold. At this point, the anode is fully lithiated and exhibits a constant, reproducible electrochemical potential. Throughout the battery's lifespan, the anode voltage should always be charged to the same end-of-charge state, thus serving as an anchor point for checking the reference potential.

[0034] If the voltage difference is within an acceptable range, the method proceeds to block 806, where it terminates. If the voltage difference is outside the acceptable range, the method proceeds to block 808.

[0035] In box 808, determine whether the voltage difference is greater than the maximum voltage threshold 404 or less than the minimum voltage threshold 406. If the voltage difference is less than the minimum voltage threshold 404 (VT... minIf the voltage difference is greater than the maximum voltage threshold 406 (VT), the method proceeds to block 810. In block 810, lithium ions are removed from the reference electrode by discharging the reference electrode 206 to the cathode 202. From block 810, the method cycles back to block 804. Returning to block 808, if the voltage difference is greater than the maximum voltage threshold 406 (VT), the method proceeds to block 808. max If the anode is discharged to the reference electrode 206, the method proceeds to block 812. In block 812, lithium ions are added to the reference electrode by discharging the anode to the reference electrode 206. From block 812, the method cycles back to block 804.

[0036] Figure 9 A graph 900 illustrating the anode reference voltage (V_AR) versus time (T) during the balancing step in an illustrative embodiment is shown. Time is expressed in hours along the horizontal axis and the anode reference voltage in volts (V) along the vertical axis. When the anode reference voltage drops to 3.345V or below, the processor 506 triggers the charging circuit 504. At time t=0 hours, the anode reference voltage is approximately 3.345V, which triggers the lithium balancing step. During the balancing step, the reference electrode 206 discharges to the cathode 202, causing the anode reference voltage to increase. When the anode reference voltage reaches 3.40V at approximately t=10 hours, the charging circuit 504 stops discharging. The anode reference voltage then decreases, reaching the final balancing voltage (approximately 3.35V) at approximately t=14 hours. Therefore, the balancing device 106 is able to detect suboptimal reference voltages, initiate the balancing step, and end the balancing step at the appropriate time to achieve the desired reference voltage.

[0037] While the foregoing disclosure has been described with reference to exemplary embodiments, those skilled in the art will understand that various changes can be made and equivalents can replace its elements without departing from its scope. Furthermore, many modifications can be made to adapt particular situations or materials to the teachings of this disclosure without departing from its essential scope. Therefore, it is intended that this disclosure be limited to the specific embodiments disclosed, but will include all embodiments falling within its scope.

Claims

1. A method for controlling the state of charge of a reference electrode in a battery, comprising: The anode of the battery is charged to a fully lithium-ionized state. The battery includes an anode, a cathode, and a reference electrode between the anode and the cathode. Measurement of the anode reference voltage of a battery with the anode in a fully lithium-ionized state; When the anode reference voltage drops below the minimum voltage threshold, discharge from the reference electrode to the cathode begins to remove lithium ions from the reference electrode to the cathode. Monitor the anode reference voltage during the discharge from the reference electrode to the cathode; as well as The discharge ends when the anode reference voltage reaches the selected voltage.

2. The method of claim 1, wherein, The reference electrode is made of lithium iron phosphate (LiFePO4).

3. The method of claim 1, further comprising adjusting the anode reference voltage when the measurement is outside the range defined with respect to the nominal voltage.

4. The method of claim 1, wherein, Adjusting the anode reference voltage further includes at least one of the following: (i) adding lithium ions to the reference electrode; and (ii) removing lithium ions from the reference electrode.

5. The method of claim 1, wherein, Adjusting the anode reference voltage further includes at least one of the following: (i) charging the reference electrode from the anode of the battery; (ii) charging the reference electrode from the cathode of the battery; and (iii) discharging the reference electrode to the anode of the battery.

6. A balancing device for controlling the state of charge of a reference electrode in a battery, comprising: A measurement circuit configured to obtain a measurement of the anodic reference voltage between the anode and a reference electrode of the battery; as well as The charging circuit is configured as follows: Charge the anode of the battery to a fully lithium-ionized state; Measurement of the anode reference voltage of a battery with the anode in a fully lithium-ionized state; When the anode reference voltage drops below the minimum voltage threshold, discharge from the reference electrode to the cathode begins to remove lithium ions from the reference electrode to the cathode. Monitor the anode reference voltage during the discharge from the reference electrode to the cathode; as well as The discharge ends when the anode reference voltage reaches the selected voltage.

7. The balancing device of claim 6, wherein, The reference electrode is made of lithium iron phosphate (LiFePO4).

8. The balancing device of claim 6, wherein, The charging circuit is configured to adjust the anode reference voltage when the measurement is outside the range defined with respect to the nominal voltage.

9. The balancing device of claim 6, wherein, The charging circuit is configured to adjust the anode reference voltage by performing at least one of the following: (i) adding lithium ions to the reference electrode; and (ii) removing lithium ions from the reference electrode.

10. The balancing apparatus of claim 6, wherein, The charging circuit is configured to adjust the anode reference voltage by performing at least one of the following: (i) charging a reference electrode from the anode of the battery; (ii) charging a reference electrode from the cathode of the battery; (iii) Discharge the reference electrode to the anode of the battery.

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