Deterioration determination device for lithium ion capacitor

Abstract

To provide a deterioration determination device for a lithium ion capacitor that can reduce the time and improve the accuracy of determining deterioration of a lithium ion capacitor.SOLUTION: A deterioration determination device for a lithium ion capacitor comprises: a storage unit that stores the SOC-OCV characteristics of a lithium ion capacitor; an acquisition unit that acquires the voltage of the lithium ion capacitor; a charge-discharge control unit that causes the lithium ion capacitor to execute predetermined charge-discharge processing; a calculation unit that calculates the resistance value of the lithium ion capacitor from the difference between a first voltage after the charge-discharge processing acquired by the acquisition unit and a second voltage after the charge-discharge processing estimated from the SOC-OCV characteristics; and a determination unit that determines the deterioration state of the lithium ion capacitor on the basis of the resistance value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an apparatus for diagnosing a lithium ion capacitor to determine whether it is in a degraded state. [Background technology]

[0002] Patent Document 1 discloses a charge / discharge control device for a lithium ion capacitor that aims to eliminate deterioration of the lithium ion capacitor and suppress performance degradation. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-186988 Summary of the Invention [Problem to be solved by the invention]

[0004] A common method for determining the degradation of a lithium-ion capacitor is to measure the capacitance and resistance separately and determine the degradation based on the measurement results. However, this conventional method not only takes time for each measurement, but also requires time for the lithium-ion capacitor to stabilize between the first and second measurements in order to improve the accuracy of the determination. Therefore, there is room for further study on methods for determining the degradation of lithium-ion capacitors to shorten the time and improve the accuracy.

[0005] The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide a lithium ion capacitor deterioration determination device that can achieve both time reduction and improved accuracy in determining the deterioration of a lithium ion capacitor. [Means for solving the problem]

[0006] In order to solve the above problems, one aspect of the disclosed technology is a lithium ion capacitor degradation determination device including: a memory unit that stores the SOC-OCV characteristic of the lithium ion capacitor; an acquisition unit that acquires the voltage of the lithium ion capacitor; a charge / discharge control unit that causes the lithium ion capacitor to perform a predetermined charge / discharge process; a calculation unit that calculates a resistance value of the lithium ion capacitor from the difference between a first voltage after the charge / discharge process acquired by the acquisition unit and a second voltage after the charge / discharge process estimated from the SOC-OCV characteristic; and a determination unit that determines the degradation state of the lithium ion capacitor based on the resistance value. [Effects of the Invention]

[0007] According to the deterioration determination device for a lithium ion capacitor disclosed above, the resistance value can be measured simultaneously with the charge / discharge process (capacity measurement) of the lithium ion capacitor, thereby achieving both time reduction and improved accuracy in deterioration determination. [Brief explanation of the drawings]

[0008] [Figure 1] A functional block diagram of a deterioration determination device for a lithium ion capacitor according to an embodiment of the present disclosure and its peripheral components. [Figure 2] Flowchart of LIC deterioration determination process executed by the lithium ion capacitor deterioration determination device [Figure 3] An example of the SOC-OCV characteristics of a lithium ion capacitor [Figure 4] FIG. 10 is a diagram showing an example of a voltage change of a lithium ion capacitor during charging processing. DETAILED DESCRIPTION OF THE INVENTION

[0009] The degradation determination device for a lithium ion capacitor according to the present disclosure calculates the resistance value of the lithium ion capacitor by excluding the resistance component due to capacitance fluctuation from the resistance component obtained by charge / discharge processing (capacity measurement), and then uses this calculated resistance value to determine degradation of the lithium ion capacitor. Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings.

[0010] <Embodiment> [composition] Fig. 1 is a functional block diagram of a lithium ion capacitor degradation determination device and its peripheral components according to an embodiment of the present disclosure. The functional block illustrated in Fig. 1 includes a lithium ion capacitor (LIC) 10, a LIC degradation determination device 20, and a sensor unit 30. The lithium ion capacitor 10, the LIC degradation determination device 20, and the sensor unit 30 may be mounted on, for example, a vehicle.

[0011] The lithium ion capacitor 10 is an electricity storage device with intermediate characteristics between a lithium ion battery (LIB), which has a high energy density, and an electric double layer capacitor (EDLC), which can be charged and discharged in a short time and has a high output density. This lithium ion capacitor 10 is typically configured as a stack in which multiple lithium ion capacitor cells are connected in series and / or parallel. When mounted on a vehicle, the lithium ion capacitor 10 is used, for example, as a redundant sub-battery for backing up a main battery that supplies power to on-board loads.

[0012] The sensor unit 30 is configured to detect the state of the lithium ion capacitor 10. The sensor unit 30 includes detection devices such as a voltage sensor that monitors the voltage of the lithium ion capacitor 10, a current sensor that monitors the current flowing through the lithium ion capacitor 10, and a temperature sensor that monitors the temperature of the lithium ion capacitor 10. Information regarding the state of the lithium ion capacitor 10 detected by the sensor unit 30 is output to the LIC degradation determination device 20. The sensor unit 30 may be built into the lithium ion capacitor 10, or may be included in the configuration of the LIC degradation determination device 20.

[0013] The LIC degradation determination device 20 is a device for performing a predetermined diagnosis on the lithium ion capacitor 10 to determine whether the lithium ion capacitor 10 is in a degraded state. The LIC degradation determination device 20 includes a storage unit 21, an acquisition unit 22, a charge / discharge control unit 23, a calculation unit 24, and a determination unit 25.

[0014] The memory unit 21 is a storage device that stores information on the SOC-OCV characteristics of the lithium ion capacitor 10. The SOC-OCV characteristics are characteristics that indicate the correlation between the charge rate (SOC: State Of Charge) and the open circuit voltage (OCV: Open Circuit Voltage) of the lithium ion capacitor 10. FIG. 3 shows an example of the SOC-OCV characteristics of the lithium ion capacitor 10. As can be seen from FIG. 3, the charge rate and open circuit voltage of the lithium ion capacitor 10 have a positive correlation that is approximately linear.

[0015] The storage unit 21 may store a plurality of SOC-OCV characteristics for the lithium ion capacitor 10, each corresponding to a plurality of temperatures (e.g., −10° C., 25° C., etc.), or may store a plurality of SOC-OCV characteristics for a plurality of capacities (e.g., 1000 F, 1100 F, etc.). The storage unit 21 may also store the SOC-OCV characteristics during discharge and the SOC-OCV characteristics during charge at the same temperature and capacity. These SOC-OCV characteristics are determined in advance by actual measurement or simulation of the lithium ion capacitor 10.

[0016] The acquisition unit 22 acquires at least the voltage, current, and temperature as the state of the lithium ion capacitor 10 from the sensor unit 30. This information on the voltage, current, and temperature of the lithium ion capacitor 10 is acquired in a timely manner to implement the charge / discharge control unit 23, which will be described later. The voltage and temperature of the lithium ion capacitor 10 acquired by the acquisition unit 22 are used by the calculation unit 24.

[0017] The charge / discharge control unit 23 controls the charging or discharging of the lithium ion capacitor 10. The charge / discharge control unit 23 controls a charge / discharge device (not shown) such as a DC / DC converter connected to the lithium ion capacitor 10, thereby carrying out the charge / discharge process of the lithium ion capacitor 10. The charge / discharge process carried out by the charge / discharge control unit 23 will be described later.

[0018] The calculation unit 24 estimates the voltage of the lithium ion capacitor 10 after the charge / discharge process is performed by the charge / discharge control unit 23 from the SOC-OCV characteristics stored in the storage unit 21. The calculation unit 24 also calculates the resistance value of the lithium ion capacitor 10 based on the voltage difference of the lithium ion capacitor 10 before and after the charge / discharge process. The estimation and calculation performed by the calculation unit 24 will be described later.

[0019] The determination unit 25 determines the deterioration of the lithium ion capacitor 10 based on the resistance value of the lithium ion capacitor 10 calculated by the calculation unit 24. The deterioration determination performed by the determination unit 25 will be described later.

[0020] Note that part or all of the above-described LIC deterioration determination device 20 may be configured as an electronic control unit (ECU) that typically includes a processor such as a microcomputer, a memory, an input / output interface, etc. This electronic control unit can realize part or all of the functions of the above-described acquisition unit 22, charge / discharge control unit 23, calculation unit 24, and determination unit 25 by having the processor read and execute a program stored in the memory.

[0021] [control] Next, the control executed by the LIC degradation determination device 20 according to this embodiment will be described with further reference to Figures 2 and 4. Figure 2 is a flowchart illustrating the procedure for the LIC degradation determination process executed by each component of the LIC degradation determination device 20. Figure 4 is a diagram showing an example of voltage changes in the lithium ion capacitor 10 during the charging process.

[0022] The LIC deterioration determination process illustrated in FIG. 2 is started, for example, at a predetermined timing when it is desired to check the state of the lithium ion capacitor 10 (such as a timing to update the deterioration determination).

[0023] (Step S201) The acquisition unit 22 acquires the voltage V0 [V] and temperature T [°C] of the lithium ion capacitor (LIC) 10 from the sensor unit 30. Here, the voltage V0 acquired by the acquisition unit 22 is the voltage of the lithium ion capacitor 10 before the charge / discharge process is performed by the charge / discharge control unit 23.

[0024] When the voltage V0 and temperature T of the lithium ion capacitor 10 are acquired by the acquisition unit 22, the process proceeds to step S202.

[0025] (Step S202) The charge / discharge control unit 23 performs a charge / discharge process on the lithium ion capacitor (LIC) 10. More specifically, the charge / discharge control unit 23 causes a constant current I [A] to flow into the lithium ion capacitor 10 for a predetermined time t [h], i.e., charges the lithium ion capacitor 10 to a capacity X (= I × t) [Ah]. Alternatively, the charge / discharge control unit 23 causes a constant current I to flow out of the lithium ion capacitor 10 for a predetermined time t, i.e., discharges the lithium ion capacitor 10 to a capacity X. The solid line in FIG. 4 shows the voltage change of the lithium ion capacitor 10 when charging is performed for a time t at a constant current I. The current I and the time t can be appropriately set based on the storage capacity and performance of the lithium ion capacitor 10.

[0026] When the charge / discharge control unit 23 performs the charge / discharge process of the lithium ion capacitor 10 with the capacity X, the process proceeds to step S203.

[0027] (Step S203) The acquisition unit 22 acquires the voltage V1 (first voltage) [V] of the lithium ion capacitor (LIC) 10 from the sensor unit 30. The voltage V1 acquired by the acquisition unit 22 here is the voltage of the lithium ion capacitor 10 after the charge / discharge process is performed by the charge / discharge control unit 23 (see FIG. 4). This voltage V1 includes both a voltage fluctuation component caused by an increase or decrease in the capacitance X due to charging / discharging, and a voltage fluctuation component caused by a change in resistance value due to the charging / discharging action.

[0028] Once the voltage V1 of the lithium ion capacitor 10 is acquired by the acquisition unit 22, the process proceeds to step S204.

[0029] (Step S204) The calculation unit 24 derives the voltage fluctuation caused by an increase or decrease in the capacity X due to charging and discharging, based on the SOC-OCV characteristics of the lithium ion capacitor 10 stored in the storage unit 21. More specifically, the calculation unit 24 identifies the SOC-OCV characteristic corresponding to the temperature T (and further the capacity of the lithium ion capacitor 10) from the multiple SOC-OCV characteristics stored in the storage unit 21. Then, when the charging process is performed in the above step S202, the calculation unit 24 derives a voltage V2 (second voltage) [V] corresponding to the charge rate SOC2 (=SOC0+X / full charge capacity×100) obtained by increasing the capacity X from the charge rate SOC0 corresponding to the open circuit voltage=voltage V0 in the identified SOC-OCV characteristics. Alternatively, when the discharging process is performed in step S202, the calculation unit 24 derives the voltage V2 corresponding to the charge rate SOC2 (=SOC0-X / full charge capacity×100), which is the charge rate SOC0 minus the capacity X. Therefore, this voltage V2 contains only the voltage fluctuation component resulting from the increase or decrease in capacity X due to charging and discharging. Note that the SOC-OCV characteristic corresponding to temperature T can be, for example, the SOC-OCV characteristic having the temperature closest to temperature T. The dashed line in FIG. 4 shows an image of the voltage (LIC voltage) of the lithium ion capacitor 10 changing from voltage V0 to voltage V2 on the SOC-OCV characteristic due to an increase in capacity X.

[0030] When the calculation unit 24 derives the voltage V2 of the lithium ion capacitor 10 based on the increase or decrease in the capacity X due to charging or discharging from the SOC-OCV characteristics at the temperature T, the process proceeds to step S205.

[0031] (Step S205) The calculation unit 24 calculates the resistance value R [Ω] of the lithium ion capacitor (LIC) 10. This resistance value R is calculated according to the following (Equation 1) using the absolute value of the difference (ΔV) between the voltage V1 and the voltage V2 so that it is based only on the component of the voltage fluctuation caused by the change in resistance value due to charging and discharging. R=|V1-V2| / I … (Equation 1)

[0032] Once the calculation unit 24 has calculated the resistance value R of the lithium ion capacitor 10, the process proceeds to step S206.

[0033] (Step S206) The determination unit 25 determines whether the lithium ion capacitor 10 has deteriorated based on the calculated resistance value R of the lithium ion capacitor (LIC) 10. An example of a method for determining deterioration is to determine that the lithium ion capacitor 10 has deteriorated if the difference between a predetermined reference resistance value of the lithium ion capacitor 10 and the resistance value R is equal to or greater than a predetermined threshold, and to determine that the lithium ion capacitor 10 has not deteriorated if the difference is less than the predetermined threshold. In this case, multiple thresholds may be set depending on the degree of deterioration, etc.

[0034] When the determination unit 25 determines whether the lithium ion capacitor 10 has deteriorated, the LIC deterioration determination process ends.

[0035] <Actions and Effects> As described above, the LIC deterioration determination device 20 for the lithium ion capacitor 10 according to an embodiment of the present disclosure calculates the resistance value R of the lithium ion capacitor 10 from the difference between the voltage V1 (first voltage) after the charge / discharge process of the lithium ion capacitor 10 and the voltage V2 (second voltage) after the charge / discharge process estimated from the SOC-OCV characteristics of the lithium ion capacitor 10. Then, the deterioration state of the lithium ion capacitor 10 is determined based on this calculated resistance value R.

[0036] This process enables the LIC deterioration determination device 20 to measure the resistance value R simultaneously with the charge / discharge process (capacity measurement) of the lithium ion capacitor 10, thereby shortening the time required to determine the deterioration of the lithium ion capacitor 10 and improving the accuracy of the deterioration determination.

[0037] The above describes one embodiment of the present disclosure, but the present disclosure can be understood as not only a deterioration determination device for a lithium ion capacitor, but also a deterioration determination method executed by a deterioration determination device equipped with a processor and memory, a control program for executing the deterioration determination method, a computer-readable non-transitory storage medium storing the control program, and a vehicle equipped with a deterioration determination device. [Industrial Applicability]

[0038] The lithium ion capacitor degradation determination device of the present disclosure can be used to diagnose a lithium ion capacitor and determine whether it is in a degraded state. [Explanation of symbols]

[0039] 10 Lithium-ion capacitor (LIC) 20 LIC deterioration determination device 21 Memory section 22 Acquisition Department 23 Charge / discharge control unit 24 Calculation section 25 Judgment section 30 Sensor Unit

Claims

1. A deterioration determination device for a lithium ion capacitor, a storage unit that stores the SOC-OCV characteristics of the lithium ion capacitor; an acquisition unit that acquires a voltage of the lithium ion capacitor; a charge / discharge control unit that causes the lithium ion capacitor to perform a predetermined charge / discharge process; a calculation unit that calculates a resistance value of the lithium ion capacitor from a difference between a first voltage after the charge / discharge process acquired by the acquisition unit and a second voltage after the charge / discharge process estimated from the SOC-OCV characteristic; a determination unit that determines a deterioration state of the lithium ion capacitor based on the resistance value. A device for determining the deterioration of lithium-ion capacitors.

2. the determination unit determines a degradation state of the lithium ion capacitor based on a change in the resistance value with respect to a reference resistance value of the lithium ion capacitor. The deterioration determination device for a lithium ion capacitor according to claim 1 .

3. the storage unit stores a plurality of the SOC-OCV characteristics of the lithium ion capacitor at different temperatures; The acquisition unit further acquires a temperature of the lithium ion capacitor, The calculation unit estimates the second voltage using the SOC-OCV characteristic according to the temperature acquired by the acquisition unit. The deterioration determination device for a lithium ion capacitor according to claim 1 or 2.

4. the storage unit stores a plurality of the SOC-OCV characteristics each having a different capacity of the lithium ion capacitor; The calculation unit estimates the second voltage using the SOC-OCV characteristic according to the capacity of the lithium ion capacitor. The deterioration determination device for a lithium ion capacitor according to claim 1 or 2.

5. the storage unit stores a plurality of the SOC-OCV characteristics of the lithium ion capacitor, each having a different temperature and capacity; The acquisition unit further acquires a temperature of the lithium ion capacitor, the calculation unit estimates the second voltage using the SOC-OCV characteristics according to the temperature and the capacity of the lithium ion capacitor acquired by the acquisition unit; The deterioration determination device for a lithium ion capacitor according to claim 1 or 2.

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