WO2025041403A1 - Charger and method for acquiring ocv data - Google Patents

Abstract

A charger (20) is provided with a control unit (21), a voltage measurement unit (22), and an OCV data extraction unit (25). The control unit (21) controls charging of a secondary battery (90) when the secondary battery (90) is attached to the charger (20). The voltage measurement unit measures the terminal voltage of the secondary battery (90) during charging. The OCV data extraction unit (25) extracts OCV data that can be used for analyzing the degree of deterioration of the secondary battery (90). The charger (20) has a first mode and a second mode as one cycle of charging of the secondary battery (90). In the first mode, the control unit (21) charges the secondary battery (90) with a predetermined current value. The voltage measurement unit (22) measures a terminal voltage value (α) of the secondary battery (90). The control unit (21) and the voltage measurement unit (22) transition to the second mode after the end of the first mode. In the second mode, the control unit 21 stops charging for a predetermined pause time. The voltage measurement unit (22) measures an OCV value (β) of the secondary battery (90) immediately after the lapse of the pause time. The control unit (21) and the voltage measurement unit (22) return to the first mode after the end of the second mode. The control unit (21) compares a terminal voltage value (αA) acquired by the first mode with a terminal voltage value (αB) acquired by the first mode in the previous cycle. The control unit (21) controls a first time so that the difference value between the terminal voltage value (αA) and the terminal voltage value (αB) becomes a constant value. The OCV data extraction unit (25) acquires OCV data using the OCV value (β) measured in each of a plurality of cycles.

Description

Charger and method for acquiring OCV data

The present invention relates to a technology for acquiring OCV data for OCV degradation analysis, which is used as one of the methods for analyzing the degradation of secondary batteries.

Patent Document 1 describes a method for estimating the battery state. In the method of Patent Document 1, the battery is discharged from a fully charged state until it reaches a lower limit of charge, and the battery capacity is calculated by integrating the discharge current during that time.

In the method of Patent Document 1, charging is performed each time the battery reaches multiple defined measurement points between the lower limit charge state and the fully charged state, then a charging wait is performed, and the open circuit voltage of the battery after the charging wait is measured. In the method of Patent Document 1, the correlation characteristics of the battery are obtained based on the charging rate at each measurement point and the open circuit voltage measured at each measurement point.

JP 2019-074501 A

The method in Patent Document 1 merely attempts to estimate the degradation state from the difference in open circuit voltage at defined measurement points. In addition, as the battery degradation progresses, measurements cannot be taken when the initial SOC is near 0% and 100%, and the number of measurement points decreases, resulting in the problem that there may be no defined measurement points to compare with.

The object of the present invention is therefore to perform measurements that suppress a reduction in the number of OCV measurement points, which can cause a decrease in the accuracy of degradation analysis, even for degraded batteries.

The charger of this invention includes a control unit, a voltage measurement unit, and an OCV data extraction unit. The control unit controls charging of the lithium-ion secondary battery when the lithium-ion secondary battery is attached to the charger. The voltage measurement unit measures the terminal voltage of the lithium-ion secondary battery during charging. The OCV data extraction unit extracts OCV data that can be used to analyze the degree of deterioration of the lithium-ion secondary battery.

The charger has a first mode and a second mode for one charging cycle of the lithium ion secondary battery.

In the first mode, the control unit charges the lithium ion secondary battery at a predetermined current value. The voltage measurement unit measures the terminal voltage value α of the lithium ion secondary battery. The control unit and the voltage measurement unit transition to the second mode after the first mode ends.

In the second mode, the control unit pauses charging for a predetermined pause time. The voltage measurement unit measures the OCV value β of the lithium-ion secondary battery immediately after the pause time has elapsed. The control unit and the voltage measurement unit return to the first mode after the second mode ends.

The control unit compares the terminal voltage value αA obtained in the first mode with the terminal voltage value αB obtained in the first mode one cycle before. The control unit controls charging in the first mode so that the difference between the terminal voltage value αA and the terminal voltage value αB becomes a constant value.

The OCV data extraction unit extracts OCV data using the OCV value β measured in each of the multiple cycles.

In this configuration, the terminal voltage value at a 100% charged state and the terminal voltage value at a 0% charged state are approximately constant in a lithium-ion secondary battery regardless of the degree of deterioration, and multiple OCV values are obtained using the terminal voltage values. This allows the number of OCV value measurement points to be kept constant during charging to obtain the SOC-OCV characteristics without being affected by the degree of deterioration of the lithium-ion secondary battery.

　This invention makes it possible to measure the OCV value to obtain the SOC-OCV characteristic without reducing the number of measurement points.

1A and 1B are conceptual diagrams showing the capacities before and after degradation of the positive and negative electrodes of a lithium-ion secondary battery, and FIG. 1C is a diagram showing an example of the relationship between SOC and OCV (before and after degradation). FIG. 2 is a configuration diagram of a charging system including a charger and a secondary battery according to an embodiment of the present invention, and capable of acquiring OCV data. FIG. 3 is a graph showing an example of the distribution of measurement points in the present invention and the prior art. FIG. 4 is a table showing the relationship between the combination of current and charging time and the number of measurement points in the present invention, and the relationship between the combination of current and charging time and the number of measurement points in the conventional example. FIG. 5 is a flowchart showing an example of a method for acquiring OCV data according to an embodiment of the present invention. FIG. 6 is a configuration diagram of a charging system capable of acquiring OCV data, including a secondary battery equipped with a voltage value output terminal.

[First embodiment]
A charger and a method for acquiring OCV data according to a first embodiment of the present invention will be described with reference to the drawings.

(Concept of OCV value measurement)
1(A) and 1(B) are conceptual diagrams showing the capacities of the positive and negative electrodes of a lithium ion secondary battery before and after degradation, and FIG. 1(C) is a diagram showing an example of the relationship between SOC and OCV (before and after degradation). FIG. 1(A) shows the possible ranges of the positive electrode capacity and the negative electrode capacity before degradation, and FIG. 1(B) shows an example of the possible ranges of the positive electrode capacity and the negative electrode capacity after degradation. In FIG. 1(C), the horizontal axis shows the SOC of the lithium ion secondary battery, and the vertical axis shows the OCV. In FIG. 1(C), the solid line shows a state of 0% degradation, and the dashed line shows a state where the degree of degradation has progressed to a certain extent.

. The capacity of a lithium-ion secondary battery is determined by the amount of lithium ions that move between the positive electrode active material and the negative electrode active material. As shown in the models in Figures 1(A) and 1(B), the capacity of a lithium-ion secondary battery is determined by the overlapping range of the possible positive electrode capacity and the possible negative electrode capacity.

As shown in Figure 1 (A), before degradation, the entire area where the positive electrode capacity and negative electrode capacity overlap represents the capacity of the lithium-ion battery, with the left end representing 0% SOC before degradation and the right end representing 100% SOC before degradation.

When charging and discharging are repeated, degradation occurs in both the positive and negative electrode active materials, and as shown in Figure 1 (B), the range of possible capacity for each decreases, and the overlap between the possible range of positive electrode capacity and the possible range of negative electrode capacity becomes smaller. In other words, the left end of the degraded negative electrode shown in Figure 1 (B) is a degraded SOC of 0%, and the right end of the degraded positive electrode is a degraded SOC of 100%. As a result, the capacity of the degraded lithium-ion secondary battery decreases to the range where the degraded positive electrode capacity and the degraded negative electrode capacity overlap.

For this reason, as shown by the solid line in Figure 1(C), in the pre-degradation state (undegraded state), the OCV value is minimum (e.g., 3.2 V) when the SOC is 0%, and maximum (e.g., 4.2 V) when the SOC is 100%, and the OCV value can be measured between 0% and 100% SOC.

However, as the degree of degradation progresses, the range narrower than the range of SOC 0% to SOC 100% before degradation changes to the range of SOC 0% to SOC 100% after degradation, as shown by the dashed line in Figure 1 (B).

As a result, if you try to measure the OCV value by intermittent charging at a constant current and time, using the SOC range before deterioration as the standard, the number of measurement points will be reduced.

On the other hand, as shown in Figure 1 (C), the maximum and minimum OCV values do not change before and after degradation. Therefore, by keeping the difference in terminal voltage values between multiple measurement points constant, the number of measurement points does not change, and the reduction in the number of measurement points is suppressed.

(Configuration of power storage system and storage battery)
FIG. 2 is a configuration diagram of a charging system including a charger and a secondary battery according to an embodiment of the present invention, and capable of acquiring OCV data.

As shown in FIG. 2, the charger 20 includes a control unit 21, a voltage measurement unit 22, a memory unit 23, an OCV data extraction unit 25, and a charging terminal 290. The control unit 21 includes a charging control unit 211 and a comparison unit 212.

The control unit 21 is realized by, for example, an electric/electronic circuit that combines an arithmetic processing unit such as an MPU with a power supply circuit. The voltage measurement unit 22 is realized by a DC voltmeter. The storage unit 23 is realized by various types of memory. The OCV data extraction unit 25, like the control unit 21, is realized by an arithmetic processing unit. Although not shown in the figure, each functional unit of the charger 20 is supplied with power from a commercial power source or the like.

The secondary battery 90 is, for example, a lithium ion secondary battery. The secondary battery 90 can be charged by connecting it to the charging terminal 290.

The charger 20 sets one cycle in which the first mode and the second mode are paired to obtain the SOC-OCV characteristics of the secondary battery 90. The charger 20 charges the secondary battery 90 connected to the charging terminal 290 by repeating the above one cycle of processing from a completely uncharged state to a fully charged state.

In this case, the charger 20 measures the OCV value for each cycle of the secondary battery 90. Then, the charger 20 uses the measured OCV value (multiple OCV values) for each cycle to extract OCV data for obtaining the SOC-OCV characteristics.

More specifically, the charger 20 executes the following process:

(First mode)
The charging control unit 211 charges the secondary battery 90 at a predetermined constant current value.

The voltage measurement unit 22 constantly measures the terminal voltage value of the secondary battery 90. The control unit 21 charges in the first mode until a predetermined voltage change is measured, and then switches to the second mode.

The voltage measurement unit 22 also outputs the terminal voltage value α measured at the timing closest in time to the timing of switching from the first mode to the second mode to the measurement voltage value storage unit 231 of the storage unit 23. The measurement voltage value storage unit 231 stores the input terminal voltage value α as the terminal voltage value αB measured in the first mode one cycle before.

The comparison unit 212 compares the difference (αA-αB) between the terminal voltage value α of the current cycle measured by the voltage measurement unit 22 and the terminal voltage value αB measured in the first mode one cycle before with the switching reference value TH.

The comparison unit 212 determines the switching reference value TH, which determines the timing of switching from the first mode to the second mode, as a voltage value, and is the difference between the maximum and minimum values of the OCV divided by an integer n determined based on the number of SOC data acquisitions.

When the difference value (αA-αB) reaches the switching reference value TH, the comparison unit 212 outputs an instruction to stop the first mode to the charging control unit 211. This instruction triggers the charging control unit 211 to stop charging. This ends the first mode for one cycle, and switches to the second mode.

(Second Mode)
During the second mode period (pause time), the charging control unit 211 pauses charging of the secondary battery 90. The length of the pause time is set to the time required for the overvoltage caused by the internal resistance of the secondary battery 90 to be alleviated.

The voltage measurement unit 22 measures the terminal voltage value after the pause time has elapsed and outputs it as the OCV value β. The voltage measurement unit 22 stores the OCV value β in the OCV value storage unit 232 of the storage unit 23.

The OCV value storage unit 232 of the storage unit 23 stores the OCV value β measured in the second mode in each cycle in association with the capacity value charged in the first mode. The capacity value is calculated from the product of the charging current and time.

(Extraction of OCV data)
When the control unit 21 detects that the pause time has elapsed, the control unit 21 ends the second mode and returns to the first mode. The control unit 21 repeats this cycle consisting of a pair of the first mode and the second mode until the control unit 21 detects a fully charged state based on the terminal voltage value αA.

As a result, the OCV value storage unit 232 of the storage unit 23 stores OCV values at multiple measurement points that divide the voltage between when the secondary battery 90 is empty and when it is fully charged at equal intervals. As described above, the empty voltage and the fully charged voltage are not affected by the degree of deterioration, so the number of measurement points for the OCV value does not change without being affected by the degree of deterioration of the secondary battery 90.

The OCV data extraction unit 25 collectively extracts the OCV values at multiple measurement points stored in the OCV value storage unit 232 as OCV data.

(Comparison of the charger of the present invention with the prior art)
Conventional constant-current, constant-time intermittent charging is equivalent to setting measurement points based on the horizontal axis of FIG. 1C, with the number of measurement points varying depending on the degree of deterioration, and the number of measurement points decreasing as the degree of deterioration increases.

On the other hand, the charger 20 uses the difference in terminal voltage values as the criterion for switching between the first and second modes, which is equivalent to setting the measurement points based on the vertical axis in FIG. 1(C). Although the time required for the first mode changes for each cycle, the number of measurement points does not change according to the degree of deterioration, and a reduction in the number of measurement points is suppressed.

This allows the charger 20 to measure the OCV value regardless of the degree of deterioration and without reducing the number of measurement points for the OCV value to obtain the SOC-OCV characteristics.

FIG. 3 is a graph showing an example of the distribution of measurement points in the present invention and in a conventional example. In FIG. 3, the horizontal axis is the capacity value of the secondary battery, and the vertical axis is the terminal voltage value. In FIG. 3, ○ indicates a measurement point where the capacity degradation of the secondary battery is 0% (before degradation), × indicates a measurement point where the capacity degradation of the secondary battery is 20%, and △ indicates a measurement point where the capacity degradation of the secondary battery is 40%. The conventional example uses the constant current, constant time control described above.

As shown in FIG. 3, in the present invention, the number of measurement points does not change regardless of the capacity degradation (degree of degradation) of the secondary battery. On the other hand, in the conventional example, the number of measurement points decreases as the capacity degradation (degree of degradation) of the secondary battery increases.

FIG. 4 is a table showing the relationship between the combination of current and charging time and the number of measurement points in the present invention, and the relationship between the combination of current and charging time and the number of measurement points in the conventional example. FIG. 4 shows two aspects of the present invention: an aspect in which the charging time is adjusted, and an aspect in which the charging current is adjusted. The aspect in which the charging time is adjusted corresponds to the aspect explained above. The conventional example in FIG. 4 is the same as the conventional example in FIG. 3.

As shown in FIG. 4, in the present invention, the number of measurement points does not change regardless of the capacity degradation (degree of degradation) of the secondary battery. On the other hand, in the conventional example, the number of measurement points decreases as the capacity degradation (degree of degradation) of the secondary battery increases.

In this way, the charger 20 of the present invention can measure the OCV value regardless of the degree of deterioration and without reducing the number of measurement points for the OCV value to obtain the SOC-OCV characteristics.

Also, as shown in FIG. 4, the charging current in the first mode may be adjusted. In this embodiment, the charger 20 can measure the OCV value without depending on the degree of deterioration and without reducing the number of measurement points for the OCV value to obtain the SOC-OCV characteristics.

(Method of acquiring OCV data)
Fig. 5 is a flowchart showing an example of a method for acquiring OCV data according to an embodiment of the present invention. Since the specific description of each process in the flowchart shown in Fig. 5 has been given in the description of the configuration described above, detailed description will be omitted here except for necessary points. In addition, the following description will be given mainly on the charger 20, but each process is performed by each functional unit constituting the charger 20 as described above.

The charger 20 measures the terminal voltage value α while charging the secondary battery 90 in the first mode (S11). The charger 20 calculates the voltage difference (αA-αB) between the current terminal voltage value αA and the terminal voltage value αB of the previous cycle (S12). If the voltage difference has not reached the switching reference value TH (S13: NO), the charger 20 continues the first mode.

When the voltage difference reaches the switching reference value TH (S13: YES), the charger 20 switches from the first mode to the second mode (S14).

When the charger 20 transitions to the second mode, it pauses charging for a pause time and measures the OCV value β immediately after the pause time has elapsed (S15).

The charger 20 completes the measurement when it has measured all OCV values β within the range of the SOC used in the OCV analysis. For example, when the upper charging voltage limit of the secondary battery 90 is reached, the charger 20 is controlled so as not to exceed the upper charging voltage limit by appropriately reducing the charging current, and completes the measurement after the current value of the stop condition is reached. If the measurement is not completed (S16: NO), the charger 20 returns to the first mode and continues charging and measurement.

When the measurement is completed (S16: YES), the charger 20 acquires (extracts) OCV data using the multiple OCV values β measured during the charging process described above (S17).

By using this method, the OCV data acquisition method is independent of the degree of deterioration and can measure the OCV value without reducing the number of measurement points for the OCV value to obtain the SOC-OCV characteristics.

(Example of derivation)
FIG. 6 is a configuration diagram of a charging system capable of acquiring OCV data, including a secondary battery equipped with a voltage value output terminal.

As shown in FIG. 6, the charging system includes a charger 20A and a secondary battery 90A. The secondary battery 90A includes a voltage value output terminal that outputs the voltage value of the battery cells (not shown) that make up the secondary battery 90A.

In this case, the voltage measurement unit 22 of the charger 20A is connected to the voltage value output terminal of the charger 20A and measures this output voltage.

Even with this configuration, the same effects can be achieved.

<1> A control unit that controls charging of a lithium ion secondary battery when the lithium ion secondary battery is attached to a charger;
a voltage measuring unit for measuring a terminal voltage of the lithium ion secondary battery during charging;
an OCV data extraction unit that extracts OCV data that can be used to analyze a deterioration level of the lithium ion secondary battery;
Equipped with
One charging cycle of the lithium ion secondary battery includes a first mode and a second mode,
In the first mode,
The control unit charges the lithium ion secondary battery at a predetermined current value,
The voltage measurement unit measures a terminal voltage value α of the lithium ion secondary battery,
the control unit and the voltage measurement unit transition to the second mode after the first mode ends,
In the second mode,
The control unit pauses charging for a predetermined pause time,
the voltage measurement unit measures an OCV value β of the lithium ion secondary battery immediately after the rest time has elapsed;
the control unit and the voltage measurement unit return to the first mode after the second mode ends,
The control unit is
comparing a terminal voltage value αA acquired in the first mode with a terminal voltage value αB acquired in the first mode one cycle before;
controlling charging in the first mode so that a difference value between the terminal voltage value αA and the terminal voltage value αB becomes a constant value;
The OCV data extraction unit extracts the OCV data by using an OCV value β measured in each of a plurality of cycles.

<2> The charger described in <1>, in which the control unit adjusts the charging time or charging current for each cycle.

<3> The charger is
When a lithium ion secondary battery is attached, charging of the lithium ion secondary battery is controlled so that one charging cycle of the lithium ion secondary battery has a first mode and a second mode;
In the first mode,
Charging the lithium ion secondary battery at a predetermined current value;
Measure a terminal voltage value α of the lithium ion secondary battery;
After the first mode is completed, a second mode is entered;
In the second mode,
Charging is suspended at a specified interval.
Measure an OCV value β of the lithium ion secondary battery immediately after the rest time has elapsed;
returning to the first mode after the second mode is terminated;
comparing a terminal voltage value αA acquired in the first mode with a terminal voltage value αB acquired in the first mode one cycle before;
controlling charging in the first mode so that a difference value between the terminal voltage value αA and the terminal voltage value αB becomes a constant value;
A method for acquiring OCV data, comprising extracting OCV data using an OCV value β measured in each of a plurality of cycles.

<4> A method for acquiring OCV data described in <3>, in which the charger adjusts the charging time or charging current for each cycle.

20, 20A: Charger 21: Control unit 22: Voltage measurement unit 23: Storage unit 25: OCV data extraction unit 90, 90A: Secondary battery 211: Charging control unit 212: Comparison unit 231: Measurement voltage value storage unit 232: OCV value storage unit 290: Charging terminal

Claims (4)

a control unit that controls charging of the lithium ion secondary battery when the lithium ion secondary battery is attached to a charger;
a voltage measuring unit for measuring a terminal voltage of the lithium ion secondary battery during charging;
an OCV data extraction unit that extracts OCV data that can be used to analyze a deterioration level of the lithium ion secondary battery;
Equipped with
One charging cycle of the lithium ion secondary battery includes a first mode and a second mode,
In the first mode,
The control unit charges the lithium ion secondary battery at a predetermined current value,
The voltage measurement unit measures a terminal voltage value α of the lithium ion secondary battery,
the control unit and the voltage measurement unit transition to the second mode after the first mode ends,
In the second mode,
The control unit pauses charging for a predetermined pause time,
the voltage measurement unit measures an OCV value β of the lithium ion secondary battery immediately after the rest time has elapsed;
the control unit and the voltage measurement unit return to the first mode after the second mode ends,
The control unit is
comparing a terminal voltage value αA acquired in the first mode with a terminal voltage value αB acquired in the first mode one cycle before;
controlling charging in the first mode so that a difference value between the terminal voltage value αA and the terminal voltage value αB becomes a constant value;
The OCV data extraction unit extracts the OCV data using an OCV value β measured in each of a plurality of cycles.
Charger. The control unit adjusts the charging time or the charging current for each cycle.
The charger of claim 1. The charger is
When a lithium ion secondary battery is attached, charging of the lithium ion secondary battery is controlled so that one charging cycle of the lithium ion secondary battery has a first mode and a second mode;
In the first mode,
Charging the lithium ion secondary battery at a predetermined current value;
Measure a terminal voltage value α of the lithium ion secondary battery;
After the first mode is completed, a second mode is entered;
In the second mode,
Charging is suspended at a specified interval.
Measure an OCV value β of the lithium ion secondary battery immediately after the rest time has elapsed;
returning to the first mode after the second mode is terminated;
comparing a terminal voltage value αA acquired in the first mode with a terminal voltage value αB acquired in the first mode one cycle before;
controlling charging in the first mode so that a difference value between the terminal voltage value αA and the terminal voltage value αB becomes a constant value;
Extracting OCV data using the OCV value β measured in each of the multiple cycles;
How to obtain OCV data. The charger adjusts the charging time or charging current on a cycle-by-cycle basis.
The method for acquiring OCV data according to claim 3 .

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