JP2024153398A - Battery System - Google Patents

Abstract

To accurately estimate whether a secondary battery including a nonaqueous electrolyte solution deteriorates.SOLUTION: A battery system is to estimate whether a secondary battery including a nonaqueous electrolyte solution deteriorates. The battery system includes a voltage sensor 21 and an ECU 40. The voltage sensor 21 detects a voltage value VV of a battery 20. The ECU 40 is configured to perform a stopping process, a calculating process, and an estimating process. The stopping process includes a process of stopping charging of the battery 20 when the change rate of dQ/dV of the battery 20 to SOC of the battery 20 is less than a threshold. The term dQ/dV is the ratio of a power storage quantity change quantity dQ of the battery 20 to a voltage change quantity dV of the battery 20. The calculating process includes a process of calculating an evaluation value for evaluating the degree of polarization relaxation after the battery 20 is charged, in accordance with the voltage value after the stopping process. The estimating process includes a process of estimating whether the deterioration occurs in accordance with the evaluation value.SELECTED DRAWING: Figure 2

Description

This disclosure relates to a battery system, and in particular to a battery system for estimating the presence or absence of degradation of a secondary battery containing a non-aqueous electrolyte.

Secondary batteries with non-aqueous electrolytes, such as lithium-ion batteries, have been attracting attention. When such secondary batteries are repeatedly charged or discharged at high rates (high currents), the ion concentration in the non-aqueous electrolyte becomes biased. As a result, the internal resistance of the secondary battery increases, causing the secondary battery to deteriorate. Such deterioration of secondary batteries is also called "high-rate deterioration."

JP 2017-103080 A (Patent Document 1) discloses a battery system. The battery system includes a secondary battery, a current sensor, and a control device. The current sensor detects the charging current or discharging current of the secondary battery. The control device calculates an evaluation value for evaluating high-rate degradation of the secondary battery based on the detection value of the current sensor. The control device determines whether an integrated value of the evaluation value is higher than a threshold value. If the integrated value is higher than the threshold value, the control device limits the charging power or discharging power of the battery to prevent excessive high-rate degradation.

JP 2017-103080 A

According to the above battery system, when the detection value of the current sensor includes a detection error, the error caused by the detection error may accumulate in the integrated value. As a result, the error accumulated in the integrated value may become too large to be ignored. In this case, it may not be possible to accurately estimate the presence or absence of high-rate degradation based on the integrated value (it may not be possible to limit the charging power or discharging power at an appropriate time).

The present disclosure has been made to solve the above problems, and its purpose is to provide a battery system that can accurately estimate the presence or absence of degradation of a secondary battery containing a nonaqueous electrolyte.

The battery system of the present disclosure is a battery system for estimating the presence or absence of deterioration of a secondary battery containing a non-aqueous electrolyte. This deterioration is a phenomenon in which the internal resistance of the secondary battery increases due to a bias in the ion concentration in the non-aqueous electrolyte. The battery system includes a voltage sensor and a processing device. The voltage sensor detects the voltage value of the secondary battery. The processing device is configured to execute a stop process, a calculation process, and an estimation process. The stop process includes a process of stopping charging of the secondary battery when the rate of change of dQ/dV of the secondary battery relative to the SOC of the secondary battery is smaller than a threshold value. dQ/dV is the ratio of the amount of change in the amount of stored electricity dQ of the secondary battery to the amount of change in voltage dV of the secondary battery. The calculation process includes a process of calculating an evaluation value for evaluating the degree of polarization relaxation after charging of the secondary battery according to the voltage value after the stop process. The estimation process includes a process of estimating the presence or absence of deterioration according to the evaluation value.

The presence or absence of deterioration of the secondary battery is related to the degree of polarization relaxation of the secondary battery. After the stop process, the detection value of the voltage sensor may change due to both the polarization relaxation of the secondary battery and the fluctuation of the OCV of the secondary battery. When the above-mentioned rate of change is smaller than the threshold value, the fluctuation of the OCV is smaller than in other cases. As a result, the detection value is less affected by the fluctuation of the OCV (more specifically, the apparent resistance of the secondary battery changes due to this fluctuation, and the voltage drop of the secondary battery caused by this resistance change). Therefore, the evaluation value can accurately reflect the degree of polarization relaxation. By adopting the above configuration, a situation in which the evaluation value is less affected by the fluctuation of the OCV due to the stop process is forcibly created. As a result, the evaluation value accurately reflects the degree of polarization relaxation. As a result, the presence or absence of deterioration can be accurately estimated according to the evaluation value.

According to the present disclosure, it is possible to accurately estimate the presence or absence of degradation of a secondary battery containing a non-aqueous electrolyte.

1 is a diagram showing roughly the overall configuration of a charging system including a vehicle on which a battery system according to a first embodiment is mounted; FIG. 2 is a diagram showing in detail the hardware configuration of a vehicle and a charging facility. FIG. 2 is a diagram for explaining a dQ/dV characteristic line of a battery. 11 is a diagram for explaining that the amount of change in voltage value VV during polarization relaxation differs depending on whether or not high-rate degradation occurs. FIG. 3 is a flowchart illustrating a process executed by an ECU (Electronic Control Unit) in the embodiment. 10 is a flowchart illustrating a process executed by an ECU in a second embodiment.

[First embodiment]
Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The same or corresponding parts in the drawings are denoted by the same reference numerals, and the description thereof will not be repeated. Each of the embodiments and their modified examples may be appropriately combined with each other.

Figure 1 is a diagram that shows a schematic diagram of the overall configuration of a charging system including a vehicle equipped with a battery system according to the first embodiment. With reference to Figure 1, the charging system 100 includes a vehicle 1 and a charging facility 5.

Vehicle 1 is an electric vehicle equipped with a battery 20, for example, an electric vehicle (BEV: Battery Electric Vehicle). Vehicle 1 may be another type of electric vehicle, such as a plug-in hybrid electric vehicle (PHEV: Plug-in Hybrid Electric Vehicle). Vehicle 1 is electrically connected to charging equipment 5 via a charging cable 6, and is configured to be capable of performing external charging, in which the battery 20 is charged by a charging current supplied from the charging equipment 5.

The charging equipment 5 is provided outside the vehicle 1. The charging equipment 5 is configured to be able to supply high-current power (DC power) to the battery 20 via the charging cable 6 during external charging.

Figure 2 is a diagram showing in detail the hardware configuration of the vehicle 1 and the charging equipment 5. Referring to Figure 2, the charging equipment 5 includes an AC/DC converter 51, an HMI (Human Machine Interface) device 53, and a control circuit 55.

The AC/DC converter 51 converts AC power from the power grid (AC power source) 7 into DC power (charging power for the battery 20). The HMI device 53 receives a user operation to instruct the start of external charging of the vehicle 1. The control circuit 55 controls the AC/DC converter 51 and exchanges various information with the vehicle 1, for example, via CAN (Controller Area Network) communication.

The vehicle 1 includes an inlet 11, charging relays 131, 132, a PCU (Power Control Unit) 16, a motor generator 17, and drive wheels 19. The vehicle 1 further includes a battery 20, system main relays (SMRs) 141, 142, a voltage sensor 21, a current sensor 22, a temperature sensor 23, a start switch (ST-SW) 35, and an ECU 40.

The inlet 11 is configured to be connectable to the charging connector 61 of the charging cable 6. The charging relays 131, 132 are connected to the charging lines PL1, NL1, respectively. The PCU 16 is electrically connected between the power lines PL2, NL2 and the motor generator 17. The PCU 16 is configured to drive the motor generator 17 by converting the output power of the battery 20 into AC power. When the output torque of the motor generator 17 is transmitted to the drive wheels 19, the vehicle 1 runs. The PCU 16 is configured to be able to convert the AC power generated by the motor generator 17 into DC power to charge the battery 20.

Battery 20 is a secondary battery containing a non-aqueous electrolyte, and in this example is a lithium ion battery. Battery 20 stores electric power for generating driving force for vehicle 1. The positive electrode of battery 20 is electrically connected to charging line PL1 and power line PL2 via SMR 141. The negative electrode of battery 20 is electrically connected to charging line NL1 and power line NL2 via SMR 142.

The polarization of battery 20 is known as a phenomenon in which, after a current flows through battery 20, an electromotive force is temporarily generated in the opposite direction to the current. For example, after charging battery 20, polarization is a phenomenon in which the voltage VB temporarily increases after charging battery 20. The polarization relaxes over time and is eliminated after a sufficiently long time has passed (the electromotive force becomes zero and the voltage of battery 20 stabilizes).

The voltage sensor 21, current sensor 22, and temperature sensor 23 respectively detect the voltage value VV, current value CV, and temperature value TV of the battery 20. The voltage value VV, current value CV, and temperature value TV are the detected values of the voltage VB, current IB, and temperature TB of the battery 20, respectively. When the battery 20 is being charged, the current value CV (current IB) is positive, and when the battery 20 is being discharged, the current value CV (current IB) is negative.

The start switch 35 receives a user operation to instruct starting or stopping the traveling system of the vehicle 1. Starting the traveling system corresponds to turning on the SMRs 141 and 142 (more specifically, establishing an electrical connection between the battery 20, the PCU 16, and the MG 17). Stopping the traveling system corresponds to turning off the SMRs 141 and 142. After the traveling system is stopped (SMRs 141 and 142 are turned off), the battery 20 is electrically disconnected from the PCU 16, and charging or discharging of the battery 20 stops.

The ECU 40 includes a CPU 41 and a memory 42. The CPU 41 executes various types of calculation processing. The memory 42 includes a ROM 42A and a RAM 42B. The ROM 42A stores the programs executed by the CPU 41 and various types of data. The data includes the dQ/dV characteristic line (described later) of the battery 20.

The ECU 40 controls various devices of the vehicle 1, such as the charging relays 131 and 132, the SMRs 141 and 142, the PCU 16, and the motor generator 17. The ECU 40 controls the charging power and discharging power of the battery 20 while the vehicle 1 is running by controlling the PCU 16. The ECU 40 can also limit the charging power and discharging power while the vehicle 1 is running (set the upper limit value Win of the charging power and the upper limit value Wout of the discharging power to a small value). The ECU 40 is configured to control the on/off of the charging relays 131 and 132 and the on/off of the SMRs 141 and 142. The ECU 40 sequentially calculates the SOC (State Of Charge) of the battery 20 based on the voltage value VV, the current value CV, and the temperature value TV. The ECU 40 sequentially stores the history of the voltage value VV and the current value CV in the memory 42.

The ECU 40 can execute an external charging control process that controls external charging. During this process, the ECU 40 turns on the charging relays 131, 132 and the SMRs 141, 142, and exchanges various information with the control circuit 55 via CAN communication. For example, the ECU 40 transmits a control command to the control circuit 55 to command power supply from the charging equipment 5 to the inlet 11 (battery 20), thereby executing the external charging control process. The external charging control process includes an external charging stop process that stops external charging.

The battery 20, the voltage sensor 21, the charging relays 131, 132, the SMRs 141, 142, the PCU 16, and the ECU 40 form an example of a "battery system" of the present disclosure.

Figure 3 is a diagram for explaining the dQ/dV characteristic line of battery 20. The dQ/dV characteristic line is a line that represents the relationship between the dQ/dV of battery 20 and the SOC of battery 20. dQ/dV is the ratio of the change dQ in the amount of stored charge Q of battery 20 to the change dV in the voltage of battery 20.

Referring to FIG. 3, line 200 corresponds to the dQ/dV characteristic line. The dQ/dV characteristic line is pre-stored in memory 42 as a map, and is determined depending on, for example, temperature TB (as an example, temperature TB immediately after external charging is stopped). In this example, one dQ/dV characteristic line is shown, but memory 42 stores multiple dQ/dV characteristic lines (not shown). One of the multiple dQ/dV characteristic lines is selected by ECU 40 based on temperature TB (temperature value TV). In this example, the one dQ/dV characteristic line is line 200.

The points on line 200 when SOC is X1 and X2 are also represented as points p1 and p2, respectively. Lines 250 and 260 are tangents to line 200 at points p1 and p2, respectively. Lines 250 and 260 represent the rate of change gr when SOC is X1 and X2, respectively. The rate of change gr is the rate of change of dQ/dV with respect to SOC (more specifically, its magnitude). The rate of change gr when SOC is X1 and X2 is gr1 and gr2, respectively.

In this example, when the SOC is within the range RNG of 60% or more and less than 80%, the rate of change gr is generally smaller than when it is not within the range RNG (the dQ/dV characteristic line is flat). As a result, when the SOC is within the range RNG, the fluctuation in the OCV (Open Circuit Voltage) of the battery 20 is smaller than when it is not within the range RNG. In this example, it is assumed that when the SOC reaches X2, the rate of change gr becomes smaller than a predetermined threshold value TH (described below).

When the battery 20 is frequently charged and discharged at a high rate, for example, when external charging using the charging equipment 5 is frequently repeated, the ion concentration in the non-aqueous electrolyte of the battery 20 becomes biased. As a result, the internal resistance of the battery 20 increases, causing deterioration of the battery 20. Such deterioration, that is, the phenomenon in which the internal resistance of the battery 20 increases due to the bias in the ion concentration in the non-aqueous electrolyte of the battery 20, is also called "high-rate deterioration" of the battery 20. When high-rate deterioration of the battery 20 exists, it is preferable that the ECU 40 limits the charging power and discharging power during driving to prevent further progression of high-rate deterioration. In order to limit the charging power and discharging power in this way at the appropriate time, it is necessary to appropriately estimate the presence or absence of high-rate deterioration.

One method for estimating the presence or absence of high-rate degradation is to calculate an integrated value of the detection value (current value CV) of the current sensor 22, and estimate the presence or absence of high-rate degradation based on this integrated value. However, in this method, due to detection errors contained in each current value CV, detection errors of the current value CV may accumulate in the integrated value. This may lead to a decrease in the accuracy of the estimation result of the presence or absence of high-rate degradation.

The inventors have noted that the presence or absence of high-rate degradation is reflected in the degree of polarization relaxation of the battery 20; specifically, when high-rate degradation is present, the amount of change in the voltage value VV (voltage VB) during polarization relaxation changes. This point will be explained below.

Figure 4 is a diagram for explaining that the amount of change in the voltage value VV during polarization relaxation differs depending on whether or not high-rate degradation occurs. Referring to Figure 4, the amount of change ΔVV is the amount of change in the voltage value VV during polarization relaxation after external charging of the battery 20 is stopped, and corresponds to VV(t0)-VV(t). Time t0 is the time when external charging is stopped.

Lines 300 and 320 represent the progression of the change amount ΔVV in cases A and B, respectively. In this example, it is assumed that there is high-rate degradation in case A and there is no high-rate degradation in case B. In both cases A and B, polarization relaxation begins after time t0 and the change amount ΔVV increases, while at time t1 the polarization is already eliminated (the change amount ΔVV becomes constant because the voltage VB becomes stable and constant). Time t01 is a predetermined time that is a predetermined time PT after time t0 and before time t1.

The amount of change ΔVV after time t1 (i.e., when polarization is eliminated) is also referred to as the amount of change ΔV01. When polarization is eliminated, it refers to the time when the polarization of the battery 20 is eliminated. The amount of change ΔV01 corresponds to the amount of polarization relaxation of the battery 20. The amount of polarization relaxation is the amount of change ΔVV from when polarization begins to when it is eliminated. ΔV01a and ΔV01b correspond to the amount of change ΔV01 (amount of polarization relaxation) in cases A and B, respectively. ΔV01a is greater than ΔV01b. In this way, the presence or absence of high-rate degradation is reflected in the amount of change ΔV01. The magnitude of the difference between ΔV01a and ΔV01b is also referred to as the difference Diff.

In the embodiment, the ECU 40 has a configuration for appropriately estimating the presence or absence of high-rate degradation of the battery 20. Specifically, the ECU 40 is configured to execute an external charging stop process, a calculation process, and an estimation process. The calculation process corresponds to a process of calculating an evaluation value for evaluating the degree of polarization mitigation after external charging according to the voltage value VV after external charging is stopped (more specifically, after the external charging stop process). The estimation process corresponds to a process of estimating the presence or absence of high-rate degradation according to the evaluation value thus calculated.

The evaluation value is, for example, a change amount ΔV01, which is the difference value (more specifically, its magnitude) between the voltage value VV at time t0 and the voltage value VV at time t1. In this case, the estimation process includes a process of estimating that there is no high-rate degradation when the change amount ΔV01 is smaller than a predetermined reference value RV, and a process of estimating that there is high-rate degradation when the change amount ΔV01 is equal to or greater than the reference value RV. The reference value RV is stored, for example, in memory 42.

The error contained in the change amount ΔV01 is basically just the detection error of the voltage sensor 21 (specifically, the detection error of the voltage value VV at times t0 and t1) and is not easily affected by other detection errors. Because the evaluation value is calculated as the change amount ΔV01, it is not easily affected by detection errors other than the detection error of the voltage sensor 21. As a result, the presence or absence of high-rate degradation can be accurately estimated according to the evaluation value.

After external charging is stopped, the change amount ΔV01 may change due to both polarization relaxation of the battery 20 and fluctuations in the OCV of the battery 20. In order to accurately estimate the presence or absence of high-rate degradation according to the change amount ΔV01, it is desirable to reduce the fluctuations in the OCV as much as possible. Therefore, it is preferable for the ECU 40 to execute the calculation process and the estimation process in a situation where the fluctuations in the OCV are reduced as much as possible.

The ECU 40 is configured to execute an external charging stop process so as to forcibly create such a situation. Specifically, this process corresponds to a process of stopping external charging when the rate of change gr (FIG. 3) during external charging is smaller than a threshold value TH (for example, when the SOC reaches X2). The threshold value TH is stored in the memory 42.

When the rate of change gr is smaller than the threshold value TH, the OCV fluctuates less than when it is not. As a result, the evaluation value (amount of change ΔV01) is less affected by the OCV fluctuation (more specifically, the fluctuation causes a change in the apparent resistance of the battery 20, and the voltage VB decreases due to this resistance change). In this case, the evaluation value is less affected by the OCV fluctuation, and therefore can accurately reflect the degree of polarization relaxation.

The above external charging stop process forces the creation of a situation in which the evaluation value is less affected by fluctuations in OCV. This allows the evaluation value to accurately reflect the degree of polarization relaxation. As a result, the presence or absence of high-rate degradation can be accurately estimated according to the evaluation value. For example, when the amount of change ΔV01 is smaller than the reference value RV, the ECU 40 estimates that there is no high-rate degradation (line 320). On the other hand, when the amount of change ΔV01 is equal to or greater than the reference value RV, the ECU 40 estimates that there is high-rate degradation (line 300).

When ECU 40 estimates that there is no high-rate degradation, it sets upper limit value Win to its default value and sets upper limit value Wout to its default value. On the other hand, when ECU 40 estimates that there is high-rate degradation, it sets upper limit value Win to a value smaller than its default value and sets upper limit value Wout to a value smaller than its default value. This limits the charging power or discharging power of battery 20. The default values of upper limit value Win and upper limit value Wout are pre-stored in memory 42.

The ECU 40 may execute an estimation process if the charging current of the battery 20 during a predetermined period before external charging is stopped is equal to or greater than a threshold current (more specifically, if the positive current value CV is equal to or greater than a predetermined value). Information representing the length of the predetermined period is stored in the memory 42. The predetermined value is a value representing the threshold current, and is stored in the memory 42.

The larger the charging current, the greater the degree of polarization (the temporary increase in voltage VB) after charging of battery 20 during high-rate degradation. As a result, the degree of polarization relaxation of this battery (ΔV01a) also becomes greater, and the difference Diff becomes larger. Therefore, by the ECU 40 appropriately setting the reference value RV (for example, to the average value of ΔV01a and ΔV01b), it becomes easier to distinguish whether high-rate degradation has occurred according to the amount of change ΔV01 (ΔV01a, ΔV01b). With the above configuration, when the charging current is large enough to be equal to or greater than the threshold current, that is, when the presence or absence of high-rate degradation is easily distinguished according to the amount of change ΔV01, the estimation process is executed. This makes it easier to estimate the presence or absence of high-rate degradation.

Figure 5 is a flowchart illustrating the process executed by ECU 40 in the embodiment. This flowchart starts when ECU 40 receives information from control circuit 55 indicating that external charging has been instructed to start and starts external charging. In the following, steps are abbreviated as "S" and Figures 3 and 4 will be referenced as appropriate. In this example, the charging start SOC is assumed to be X1.

Referring to FIG. 5, the ECU 40 acquires the voltage value VV, the current value CV, and the temperature value TV from the voltage sensor 21, the current sensor 22, and the temperature sensor 23, respectively (S15). The ECU 40 calculates the SOC according to the voltage value VV, the current value CV, and the temperature value TV (S20).

The ECU 40 determines whether the rate of change gr of dQ/dV is smaller than a threshold value TH (S26). The rate of change gr is calculated sequentially based on a dQ/dV characteristic line (e.g., line 200) selected based on the temperature value TV (temperature TB) and the SOC calculated in S20. If the rate of change gr is equal to or greater than the threshold value TH, for example, if the SOC has not yet reached X2 (NO in S26), the process returns to S15. If the rate of change gr is smaller than the threshold value TH, for example, if the SOC has reached X2 (YES in S26), the process proceeds to S30.

The ECU 40 executes an external charging stop process to stop external charging (S30), and stores in the memory 42 the voltage value VV at the time when external charging was stopped. After external charging is stopped, the ECU 40 determines whether the charging current during a predetermined period before external charging was stopped is equal to or greater than a threshold current (S35). If such a charging current is equal to or greater than the threshold current (YES in S35), the process proceeds to S45. If not (NO in S35), the process ends.

The ECU 40 determines whether the polarization has been eliminated according to the voltage value VV (S45). Specifically, the ECU 40 executes this determination process based on whether the voltage value VV is constant (whether the amount of change ΔVV is constant). If the polarization has not yet been eliminated (NO in S45), the ECU 40 repeats S45 until the polarization is eliminated. If the polarization has been eliminated (YES in S45), the process proceeds to S50.

The ECU 40 calculates the amount of change ΔV01 as an evaluation value (S50) and performs estimation processing (S70) based on this evaluation value. S70 includes S72, S74, and S76.

The ECU 40 determines whether the evaluation value (change amount ΔV01) is equal to or greater than the reference value RV (S72). If the evaluation value is equal to or greater than the reference value RV (YES in S72), the ECU 40 estimates that high-rate degradation is present (S74). If the evaluation value is smaller than the reference value RV (NO in S72), the ECU 40 estimates that high-rate degradation is not present (S76).

In the above, S35 is not necessarily required. In this case, if the rate of change gr is smaller than the threshold value TH (YES in S26), the process proceeds from S30 to S45.

As described above, the ECU 40 executes an external charging stop process that stops external charging when the change rate gr of dQ/dV is smaller than the threshold value TH. After external charging is stopped, the ECU 40 calculates an evaluation value (amount of change ΔV01) according to the voltage value VV, and estimates the presence or absence of high-rate degradation according to this evaluation value. With this configuration, the evaluation value is calculated in a situation where the fluctuation of the OCV of the battery 20 is reduced as much as possible. As a result, the evaluation value accurately reflects the degree of polarization relaxation. As a result, the ECU 40 can accurately estimate the presence or absence of high-rate degradation according to the evaluation value. Therefore, the ECU 40 can limit the charging power and discharging power during driving at an appropriate timing, thereby appropriately protecting the battery 20.

[Modification of the first embodiment]
4 again, the evaluation value may be the ratio of the amount of change ΔVV at time t01 to the amount of change ΔV01 (amount of polarization relaxation). This ratio is also referred to as the "polarization relaxation rate." In this example, the amount of change ΔV01 is a value that is determined in advance depending on the temperature value TV immediately after external charging and the SOC at the end of external charging (end-of-charging SOC), and is stored in advance in the memory 42 in both cases A and B.

In this modified example, the ECU 40 calculates the polarization relaxation rate at time t01 according to the amount of change ΔVV at time t01 and the amount of change ΔV01 stored in the memory 42. The ECU 40 determines whether this polarization relaxation rate is equal to or greater than a predetermined threshold rate, and executes an estimation process according to the result of the determination. Specifically, this estimation process includes a process of estimating that there is no high-rate degradation when the polarization relaxation rate is equal to or greater than the threshold rate, and a process of estimating that there is high-rate degradation when the polarization relaxation rate is less than the threshold rate. The threshold rate is stored in the memory 42.

The presence or absence of high-rate degradation also relates to whether the polarization relaxes relatively quickly or slowly. Whether the polarization relaxation is fast or slow is reflected in the polarization relaxation rate at time t01. For example, as shown by line 320, when there is no high-rate degradation, the polarization is almost eliminated at time t01, so the polarization relaxation rate is relatively high (polarization relaxation is fast). On the other hand, as shown by line 300, when there is high-rate degradation, the polarization has not yet been sufficiently eliminated at time t01, so the polarization relaxation rate is relatively low (polarization relaxation is slow).

According to the above estimation process, the presence or absence of high-rate degradation is estimated according to whether the polarization relaxation rate at time t01 is relatively high or low (in other words, whether the polarization relaxation is fast or slow). The error contained in the polarization relaxation rate is basically only the detection error of the voltage sensor 21 (specifically, the detection error of the voltage value VV at times t0 and t01), and is not easily affected by other detection errors. Therefore, even in this modified example, the presence or absence of high-rate degradation can be accurately estimated according to the evaluation value. Furthermore, since the voltage value VV at the time of polarization elimination is a value stored in the memory 42, the ECU 40 can calculate the polarization relaxation rate before the polarization elimination (for example, time t1). Therefore, even if the user of the vehicle 1 starts driving the vehicle 1 after the end of external charging without waiting for the polarization elimination, the ECU 40 can estimate the presence or absence of high-rate degradation early and accurately.

[Embodiment 2]
Polarization may also occur after discharging the battery 20. The polarization after discharging differs from the polarization after charging in that it is a phenomenon in which the voltage VB temporarily drops, but is similar to the polarization after charging in that it disappears after a sufficiently long time has passed. In the second embodiment, the ECU 40 is configured to estimate the presence or absence of high-rate degradation according to the degree of polarization relaxation after discharging the battery 20.

Specifically, the ECU 40 is configured to be capable of executing a calculation process after the driving system is stopped, which calculates an evaluation value for evaluating the degree of polarization relaxation of the secondary battery after discharge according to the voltage value VV after the driving system is stopped. In this example, it is assumed that discharging is stopped due to the driving system of the vehicle 1 being stopped (SMRs 141, 142 being turned off). The calculation process after the driving system is stopped is included in the calculation process described above.

When the traveling system is stopped (when discharging of the battery 20 is stopped), the ECU 40 calculates the SOC and calculates the rate of change gr based on the SOC and the dQ/dV characteristic line (line 200 in this example). The ECU 40 determines whether the rate of change gr calculated in this manner is smaller than the threshold value TH. If the rate of change gr is smaller than the threshold value TH (for example, if the SOC when the traveling system is stopped is X2), the ECU 40 executes the calculation process after the traveling system is stopped. If not, the ECU 40 does not execute the calculation process after the traveling system is stopped. The estimation process in the second embodiment corresponds to a process of estimating the presence or absence of high-rate degradation according to the evaluation value calculated by the calculation process after the traveling system is stopped.

By configuring in this way, the evaluation value calculated by the calculation process after the driving system is stopped is less affected by fluctuations in OCV and can accurately reflect the degree of polarization mitigation. This allows the ECU 40 to accurately estimate the presence or absence of high-rate degradation according to the evaluation value even after the driving system is stopped (discharge is stopped).

The evaluation value is, for example, the amount of change in voltage VB after the driving system is stopped. This amount of change corresponds to the difference (more specifically, the magnitude) between the voltage value VV when the driving system is stopped and the voltage value VV when the polarization of battery 20 is eliminated after the driving system is stopped, and corresponds to the amount of change ΔV01 (Figure 4).

Figure 6 is a flowchart illustrating the processing executed by the ECU 40 in the second embodiment. With reference to Figure 6, this flowchart differs from the flowchart of the embodiment (Figure 5) in that it is started when the driving system is stopped, S30 and S35 are omitted, and S15A and S70A are executed instead of S15 and S70, but is otherwise similar to the flowchart of Figure 5.

The ECU 40 acquires the voltage value VV, the current value CV, and the temperature value TV when the driving system is stopped (S15A), and calculates the SOC based on the acquired values (S20).

The ECU 40 determines whether the rate of change gr of dQ/dV is smaller than the threshold value TH (S26). If the rate of change gr is equal to or greater than the threshold value TH, for example, if the SOC when the driving system is stopped is outside the range RNG (NO in S26), the process ends. If the rate of change gr is smaller than the threshold value TH, for example, if the SOC when the driving system is stopped is X2 (YES in S26), the ECU 40 determines whether the polarization is eliminated according to the voltage value VV (S45). If the polarization is not eliminated (NO in S45), the ECU 40 repeats S45 until the polarization is eliminated. If the polarization is eliminated (YES in S45), the ECU 40 calculates an evaluation value by executing a calculation process after the driving system is stopped (S50A), and executes an estimation process (S70A) according to the evaluation value. S70A includes S72A, S74, and S76.

The ECU 40 determines whether the evaluation value calculated in S50A is equal to or greater than a reference value (S72A). This reference value may be equal to or different from the reference value RV. If the evaluation value is equal to or greater than the reference value (YES in S72A), the ECU 40 estimates that high-rate degradation is present (S74). If the evaluation value is less than the reference value (NO in S72A), the ECU 40 estimates that high-rate degradation is not present (S76).

According to this second embodiment, it is possible to accurately estimate the presence or absence of high-rate degradation even after the driving system has stopped. This increases the opportunities to accurately estimate the presence or absence of high-rate degradation.

[Modification of the second embodiment]
6 again, if the rate of change gr of dQ/dV is smaller than the threshold value TH (YES in S26), the ECU 40 may determine whether the charge/discharge current (more specifically, its magnitude) of the battery 20 during the predetermined period before the driving system is stopped is equal to or greater than the threshold current. If such charge/discharge current is equal to or greater than the threshold current, the ECU 40 executes S45 to S70A. On the other hand, if the charge/discharge current is smaller than the threshold current, the ECU 40 ends the process. Information indicating the length of the predetermined period before the driving system is stopped is stored in the memory 42.

By executing S45 to S70A as described above, it becomes easier to distinguish whether high-rate degradation exists, as explained in the first embodiment. As a result, it becomes easier to estimate whether high-rate degradation exists.

The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is indicated by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

1 vehicle, 5 charging equipment, 20 battery, 21 voltage sensor, 22 current sensor, 23 temperature sensor, 35 start switch, 42 memory, 100 charging system.

Claims (5)

A battery system for estimating the presence or absence of deterioration of a secondary battery including a non-aqueous electrolyte, the deterioration being a phenomenon in which an internal resistance of the secondary battery increases due to a bias in an ion concentration in the non-aqueous electrolyte,
a voltage sensor for detecting a voltage value of the secondary battery;
a processing device configured to perform a stopping process, a calculating process, and an estimating process;
the stopping process includes a process of stopping charging of the secondary battery when a rate of change of dQ/dV of the secondary battery with respect to an SOC of the secondary battery is smaller than a threshold value;
The dQ/dV is a ratio of a change in the amount of charge stored in the secondary battery, dQ, to a change in the voltage, dV, of the secondary battery,
the calculation process includes a process of calculating an evaluation value for evaluating a degree of polarization relaxation after charging of the secondary battery in accordance with the voltage value after the stopping process,
The estimation process includes a process of estimating the presence or absence of deterioration in accordance with the evaluation value. the evaluation value is a difference value between the voltage value at the time when the charging is stopped and the voltage value at the time when the polarization of the secondary battery is eliminated after the charging is stopped,
The estimation process includes:
If the difference value is smaller than a reference value, it is determined that the deterioration does not occur.
The battery system according to claim 1 , further comprising a process of estimating that the deterioration exists when the difference value is equal to or greater than the reference value. The battery system is mounted on a vehicle,
3. The battery system according to claim 1, wherein the processing device executes the stop process when external charging is being performed to charge the secondary battery with a charging current supplied from a charging facility provided outside the vehicle. The battery system of claim 3, wherein the processing device executes the estimation process when the charging current during a predetermined period before the external charging is stopped is equal to or greater than a threshold current. The battery system is mounted on a vehicle,
The calculation process further includes a calculation process after a driving system is stopped, the calculation process calculating an evaluation value for evaluating a degree of polarization relaxation after discharging of the secondary battery according to the voltage value after a driving system of the vehicle is stopped,
The calculation process after the traveling system is stopped is executed when the rate of change is smaller than the threshold value after the traveling system is stopped,
3 . The battery system according to claim 1 , wherein the estimation process further includes a process of estimating the presence or absence of the deterioration in accordance with the evaluation value calculated by the calculation process after the traveling system is stopped.

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