JP6215752B2 - Battery state determination method and battery state determination device - Google Patents

Description

  The present invention relates to a battery state determination method and a battery state determination device that determine the presence or absence of a memory effect in a secondary battery.

  2. Description of the Related Art Conventionally, there has been proposed a technique for evaluating a deterioration state and remaining life of a secondary battery by performing complex impedance analysis on the secondary battery. According to this method, since the battery state can be evaluated without destroying the secondary battery, the secondary battery determined to be normal can be reused.

  As an example of the complex impedance analysis method, a method of determining whether or not the capacity ratio between the positive electrode and the negative electrode in the secondary battery is deviated from a desired value is known (for example, see Patent Document 1). In this method, complex impedance is measured by applying an alternating voltage to a secondary battery while changing the frequency stepwise. And after calculating | requiring the real-axis component and imaginary-axis component of impedance from a measured value, a Nyquist plot is obtained by plotting those values on a two-dimensional plane. Further, two points corresponding to different frequencies included in a portion corresponding to a so-called resistance diffusion region in the Nyquist plot are connected by a line segment. And when the inclination of this line segment is smaller than a threshold value, it determines that the capacity ratio of the positive electrode in a secondary battery and the negative electrode has shifted | deviated from the desired value.

International Publication WO2013 / 115038

  By the way, when the secondary battery is used for a long period of time, a memory effect is generated, which is a phenomenon in which the electromotive force changes in the vicinity of the SOC (State of Charge), which has been frequently used. Since this memory effect causes deterioration of the secondary battery, it is desirable to determine whether or not the memory effect is present when the secondary battery is reused.

  This invention is made | formed in view of such a situation, The objective is to provide the battery state determination method and battery state determination apparatus which can determine the presence or absence of the memory effect in a secondary battery. .

In order to solve the above problems, a battery state determination method of the present invention is a battery state determination method for determining presence or absence of a memory effect in a secondary battery using a battery state determination device, wherein the battery state determination device includes: an impedance acquisition step of acquiring complex impedance of said secondary batteries, a phase calculating step of calculating a phase of each frequency of the complex impedance obtained in the impedance acquisition step, the complex impedance calculated in the phase calculating step Based on the phase, when the phase at the frequency corresponding to the resistance diffusion region of the secondary battery is equal to or less than a predetermined threshold value, a determination step of determining that the memory effect has occurred in the secondary battery is executed.

The battery state determining apparatus of the present invention is a determining battery state determining apparatus whether a memory effect in the secondary battery, and the impedance acquisition unit that acquires complex impedance of the secondary batteries, the impedance acquisition unit A phase calculation unit that calculates a phase for each frequency of the complex impedance acquired by the phase, and a phase at a frequency corresponding to the resistance diffusion region of the secondary battery based on the phase of the complex impedance calculated by the phase calculation unit is a predetermined threshold value A determination unit that determines that a memory effect is generated in the secondary battery when

  The resistance diffusion region of the complex impedance in the secondary battery is a portion that appears on the low frequency side of the frequency response of the complex impedance, and the secondary battery that has produced the memory effect is the phase of the complex impedance of the frequency corresponding to the resistance diffusion region. Is smaller than a secondary battery that does not produce a memory effect. Therefore, in the above configuration or method, the phase of the complex impedance of the frequency corresponding to the resistance diffusion region in the secondary battery to be determined is acquired, and the presence or absence of the memory effect in the secondary battery is determined based on the acquired phase of the complex impedance. I tried to do it. Thereby, the presence or absence of the memory effect can be easily determined.

  Preferably, as the battery state determination method, in the determination step, the phase of the complex impedance calculated in the phase calculation step is equal to or less than the threshold value within a frequency range corresponding to the resistance diffusion region of the secondary battery. When the phase is included, it is determined that the memory effect is generated in the secondary battery.

  According to the above method, the presence or absence of the memory effect in the secondary battery is more easily determined based on whether or not a phase that is equal to or less than the threshold is included in the frequency range corresponding to the resistance diffusion region of the secondary battery. be able to.

Preferably, as the battery state determination method, the threshold value is set based on a complex impedance phase of a frequency corresponding to a resistance diffusion region of a secondary battery that does not produce a memory effect.
According to the above method, the phase of the complex impedance of the frequency corresponding to the resistance diffusion region of the secondary battery to be determined is set based on the phase of the complex impedance of the same frequency in the secondary battery not producing the memory effect. The presence or absence of the memory effect in the secondary battery is determined by comparing with the phase threshold value. Thereby, the structure which determines easily the presence or absence of a memory effect is realizable.

Preferably, as the battery state determination method, the frequency range of the complex impedance corresponding to the resistance diffusion region of the secondary battery is 0.01 Hz to 0.1 Hz.
In the secondary battery that has produced the memory effect, the change in complex impedance in the frequency band of 0.01 Hz to 0.1 Hz becomes significant. Therefore, in the above method, the complex impedance of 0.01 Hz to 0.1 Hz in the secondary battery to be determined is acquired, and the presence or absence of the memory effect in the secondary battery is determined based on the acquired complex impedance. Thereby, the presence or absence of the memory effect can be determined with higher accuracy.

Preferably, as the battery state determination method, the secondary battery is a nickel metal hydride storage battery.
According to the above method, the used nickel-metal hydride storage battery is appropriately determined by determining the presence or absence of the memory effect for the nickel-metal hydride storage battery, which is a secondary battery that is relatively likely to have a memory effect when used over a long period of time. Can be reused.

  According to the present invention, the presence or absence of the memory effect in the secondary battery can be determined.

The schematic diagram which shows schematic structure of one Embodiment of a battery state determination apparatus. The graph which shows transition of the change of the electromotive voltage at the time of charge in a secondary battery, and discharge. (A) is a graph which shows the frequency response of the gain of the complex impedance in a secondary battery, (b) is a graph which shows the frequency response of the phase of the complex impedance in a secondary battery. The flowchart which shows the outline | summary of the process routine performed when the battery state determination apparatus of the embodiment determines the presence or absence of the memory effect in a secondary battery.

Hereinafter, an embodiment of the battery state determination device of the present invention will be described.
As shown in FIG. 1, a battery state determination system 10 is a system for determining the presence or absence of a memory effect in a secondary battery M such as a vehicle-mounted lithium ion battery or a nickel hydride storage battery. And a determination device 12. In the present embodiment, a nickel-metal hydride storage battery that is relatively likely to generate a memory effect will be described below as a secondary battery M.

  The measuring device 11 includes an SOC adjusting unit 11a and an impedance measuring unit 11b. In the measuring device 11, the SOC adjustment unit 11a adjusts the SOC of the secondary battery M to be measured, and then the impedance measurement unit 11b applies an AC voltage or an AC current to the secondary battery M, whereby the secondary battery. Measure the complex impedance Z of M. In this case, the complex impedance Z of the secondary battery M is expressed by the following formula (1) using the real axis component Zreal and the imaginary axis component Zimg which are vector components. “J” means an imaginary axis unit.

Z = Zreal + jZimg (1)

The battery state determination device 12 includes a CPU (Central Processing Unit) 12a, a ROM (Read Only Memory) 12b, and a RAM (Random Access Memory) 12c.

  The CPU 12 a functions as an impedance acquisition unit that acquires measurement data of the complex impedance Z of the secondary battery M from the measurement device 11. Further, the CPU 12 a also functions as a phase calculation unit that calculates the phase θ for each frequency of the complex impedance Z based on the measurement data of the complex impedance Z acquired from the measurement device 11. The CPU 12a also functions as a determination unit that determines the presence or absence of the memory effect in the secondary battery M based on the calculated phase θ. In this case, the phase θ of the complex impedance Z is expressed by the following equation (2).

θ = tan ⁻¹ (Zimg / Zreal) (2)

The ROM 12b stores a program used for determining whether or not there is a memory effect in the secondary battery M. The ROM 12b stores the measurement frequency F and the phase threshold value θx set for the secondary battery M to be determined through experiments and the like. In this case, different values are set for the measurement frequency F and the phase threshold θx for each type of secondary battery such as a lithium ion battery or a nickel metal hydride storage battery (in this embodiment, a nickel metal hydride storage battery). Then, when determining the presence or absence of the memory effect in the secondary battery M, the CPU 12a appropriately reads and sets the measurement frequency F and the phase threshold value θx corresponding to the type of the secondary battery M to be determined from the ROM 12b.

  For example, an output device 13 including a display device or a printing device is connected to the battery state determination device 12. Then, the determination result of the presence or absence of the memory effect in the secondary battery M is output from the battery state determination device 12 to the output device 13.

  FIG. 2 shows the transition of the change in electromotive voltage during charging and discharging in the secondary battery M to be determined in the present embodiment. As shown by the solid line L1 in FIG. 2, the secondary battery M in the initial state where the memory effect is not generated generates hysteresis, which is a phenomenon in which the transition of the change in electromotive voltage during charging and discharging is different from each other. In addition, as shown by a broken line L2 in FIG. 2, the used secondary battery M that produces the memory effect similarly causes hysteresis during charging and discharging. However, in the used secondary battery M in which the memory effect is generated, the magnitude of the hysteresis in the SOC range in which the frequency of use is high, compared with the secondary battery M in the initial state in which the memory effect is not generated. It becomes relatively large. In addition, in the in-vehicle secondary battery M that is a determination target in the present embodiment, control is performed such that the use frequency is increased within the range of SOC 20% to 80%. Therefore, as shown in FIG. 2, in the present embodiment, the used secondary battery M that produces a memory effect has a hysteresis size within the range of SOC 20% to 80% that does not produce a memory effect. It becomes larger than the secondary battery M in the initial state.

  FIGS. 3A and 3B show changes in the frequency response of the gain G of the complex impedance Z and the phase θ in the secondary battery M to be determined in the present embodiment. In FIGS. 3A and 3B, changes in the frequency response of the gain G of the complex impedance Z and the phase θ in the secondary battery M in the initial state where no memory effect is generated are indicated by solid lines L3 and L4. ing. 3A and 3B show changes in the frequency response of the gain G of the complex impedance Z and the phase θ in the used secondary battery M that has caused the memory effect by broken lines L5 and L6. It is shown. In this case, the change in the frequency response of the gain G and the phase θ of the complex impedance Z in the secondary battery M causing the memory effect and the secondary battery M not producing the memory effect affects the measured value of the complex impedance Z. It is measured under the same measurement conditions including the battery temperature that can be exerted.

The gain G of the complex impedance Z is expressed by the following equation (3).

G = | Z | = √ (Zimg ² + Zreal ² ) (3)

In addition, the resistance diffusion region, which is a low frequency region in the frequency band of the complex impedance Z in the secondary battery M, is a region where an impedance related to material diffusion appears and is included in a range of 0.01 Hz to 0.1 Hz. It is.

  Here, as shown in FIG. 3A, the gain G of the complex impedance Z is such that both the secondary battery M in which the memory effect is generated and the secondary battery M in which the memory effect is not generated have a high frequency from a low frequency region. The tendency is almost common in all frequency bands over the region. That is, in the secondary battery M that has produced the memory effect, although the magnitude of the electromotive voltage in the SOC range that is frequently used compared to the secondary battery M that has not produced the memory effect changes, The amount of change in the gain G of the complex impedance Z accompanying the change in is so small that it cannot be used to determine the presence or absence of the memory effect in the secondary battery M.

  On the other hand, as shown in FIG. 3B, the phase θ of the complex impedance Z of the frequency corresponding to the resistance diffusion region in the secondary battery M is greater in the memory effect in the secondary battery M in which the memory effect occurs. It shows a tendency to be smaller than that of the secondary battery M that does not cause the problem. Therefore, in the present embodiment, the phase θ of the complex impedance Z of the frequency corresponding to the resistance diffusion region in the secondary battery M in which the memory effect is generated and the resistance diffusion region in the secondary battery M in which the memory effect is not generated. A phase between the phase θ of the complex impedance Z of the corresponding frequency is set for each frequency as the phase threshold θx. That is, the phase threshold value θx is a threshold value for determining a secondary battery M that exhibits a complex impedance equal to or smaller than the phase threshold value θx as a secondary battery M that has a memory effect. In FIG. 3B, the phase threshold θx set corresponding to the frequency fx included in the resistance diffusion region is shown as an example.

Next, an outline of a processing routine executed when the CPU 12a of the battery state determination device 12 according to the present embodiment determines the presence or absence of the memory effect in the secondary battery M will be described.
First, as shown in FIG. 4, the CPU 12a adjusts the SOC of the secondary battery M by transmitting a control signal to the SOC adjustment unit 11a of the measurement device 11 (step S10). In this case, the SOC adjustment unit 11a charges or discharges the secondary battery M until it reaches the SOC value of the secondary battery that is a reference for setting the phase threshold θx.

  Then, the CPU 12a measures the complex impedance Z of the secondary battery M by transmitting a control signal to the impedance measuring unit 11b of the measuring device 11 (step S11). In this case, the measurement of the complex impedance Z of the secondary battery M includes the measurement of the complex impedance Z of the secondary battery M, which is a reference for setting the phase threshold θx, including the battery temperature that may affect the measured value. The measurement is performed under the same measurement conditions. And CPU12a acquires the measurement data of the complex impedance Z of the secondary battery M which the impedance measurement part 11b measured as an impedance acquisition process.

  Subsequently, the CPU 12a, as the phase calculation step, from the measurement data of the complex impedance Z of the secondary battery M acquired from the measurement device 11, the phase of the complex impedance Z of the frequency corresponding to the resistance diffusion region that becomes the low frequency region. The value of θ is read and calculated (step S12). Next, as a determination step, the CPU 12a determines whether or not the read phase θ value is equal to or less than the phase threshold θx (step S13). Specifically, the CPU 12a determines whether or not the phase θ of the complex impedance Z read from the frequency range corresponding to the resistance diffusion region in the secondary battery M includes a phase that is equal to or smaller than the phase threshold θx. judge.

  When the phase θ read out within the frequency range corresponding to the resistance diffusion region includes a value equal to or smaller than the phase threshold θx (step S13 = YES), the CPU 12a stores the memory in the determination target secondary battery M. It determines with the effect having arisen (step S14). On the other hand, when all the values of the read phase θ are larger than the phase threshold θx (step S13 = NO), the CPU 12a determines that the memory effect is not generated in the determination target secondary battery M (step S15). Thereafter, the CPU 12a outputs information indicating the determination result of the presence or absence of the memory effect in the secondary battery M to the output device 13, and then ends the processing routine illustrated in FIG.

Next, the operation of the battery state determination device 12 configured as described above will be described.
The inventor of the present application has found that the phase θ of the complex impedance Z having a frequency corresponding to the resistance diffusion region in the secondary battery M changes significantly depending on the presence or absence of the memory effect in the secondary battery M. Therefore, in the present embodiment, the change in the frequency response of the phase θ of the complex impedance Z in the secondary battery M in which the memory effect is generated and the secondary battery M in which the memory effect is not generated is measured in advance, and the measurement result Based on the above, a phase threshold θx that is a reference for determining the presence or absence of the memory effect in the secondary battery M is preset. Then, by determining whether or not the value of the phase θ of the complex impedance Z of the frequency corresponding to the resistance diffusion region acquired from the secondary battery M to be determined is equal to or less than the preset phase threshold θx, the secondary The presence or absence of the memory effect in the battery M is determined. For this reason, the secondary batteries M that have a relatively low degree of deterioration without being subjected to the memory effect are selected from the used secondary batteries M, so that the used secondary batteries M can be appropriately reused. Is called.

  In particular, in the present embodiment, the phase θ in the frequency range corresponding to the resistance diffusion region of the complex impedance Z is read from the secondary battery M to be determined, and the phase threshold θx is equal to or less than the read phase θ. It is determined whether or not a certain phase is included. Therefore, as compared with the case based on the phase at a specific frequency included in the resistance diffusion region of the complex impedance Z, the presence or absence of the memory effect in the secondary battery M can be more easily determined.

  Further, in the present embodiment, the memory effect in the secondary battery M is based on the frequency response of the complex impedance Z of the secondary battery M when an alternating voltage or alternating current is applied to the secondary battery M to be determined. Whether or not there is. Therefore, in this embodiment, when determining the presence or absence of the memory effect in the secondary battery M to be determined, it is not necessary to measure the transition of the change in electromotive voltage during charging and discharging shown in FIG. . That is, in order to measure the transition shown in FIG. 2, it is generally necessary to repeat charging and discharging over several hours, but in this embodiment, it is not necessary to perform such charging and discharging. Therefore, the presence or absence of the memory effect in the secondary battery M can be quickly determined.

  Moreover, in this Embodiment, when an alternating voltage is applied with respect to the secondary battery M used as determination object, the electric current which flows into the secondary battery M is very small. Therefore, in this embodiment, when determining the presence or absence of the memory effect in the secondary battery M to be determined, the SOC of the secondary battery M is hardly changed. Therefore, when determining the presence or absence of the memory effect in the secondary battery M, it is possible to suppress the deterioration of the secondary battery M due to the change in the SOC of the secondary battery M.

As described above, according to the battery state determination device of the above embodiment, the following effects can be obtained.
(1) The resistance diffusion region of the complex impedance Z in the secondary battery M is a portion that appears on the low frequency side of the frequency response of the complex impedance Z, and the secondary battery M that has produced the memory effect corresponds to the resistance diffusion region The phase θ of the complex impedance Z of the frequency to be reduced is smaller than that of the secondary battery M not producing the memory effect. Therefore, the phase θ of the complex impedance Z of the frequency corresponding to the resistance diffusion region in the secondary battery M to be determined is acquired, and the presence or absence of the memory effect in the secondary battery M is determined based on the acquired phase θ of the complex impedance Z. I tried to do it. Thereby, the presence or absence of the memory effect can be easily determined.

  (2) Presence or absence of the memory effect in the secondary battery M based on whether or not the phase θ that is equal to or less than the phase threshold θx is included in the frequency range corresponding to the resistance diffusion region of the complex impedance Z of the secondary battery M Can be more easily determined.

  (3) The phase θ of the complex impedance Z of the frequency corresponding to the resistance diffusion region of the secondary battery M to be determined is changed to the phase θ of the complex impedance Z of the same frequency in the secondary battery M not producing the memory effect. Compared with the phase threshold value θx set based on this, the presence or absence of the memory effect in the secondary battery M is determined. Thereby, the structure which determines easily the presence or absence of a memory effect is realizable.

  (4) In the secondary battery M that has produced the memory effect, the change in the phase θ of the complex impedance Z in the frequency band of 0.01 Hz to 0.1 Hz becomes significant. Therefore, the phase θ of the complex impedance Z of 0.01 Hz to 0.1 Hz in the secondary battery M to be determined is acquired, and the presence or absence of the memory effect in the secondary battery M is determined based on the acquired phase θ of the complex impedance Z. I tried to do it. Thereby, the presence or absence of the memory effect can be determined with higher accuracy.

  (5) Appropriate reuse of used nickel-metal hydride storage batteries by determining the presence or absence of the memory effect for nickel-metal hydride storage batteries, which are secondary batteries M that are relatively likely to produce a memory effect when used over a long period of time can do.

In addition, the said embodiment can also be implemented with the following forms.
In the above embodiment, the phase θ of the complex impedance Z of the frequency corresponding to the resistance diffusion region in the secondary battery M causing the memory effect and the resistance diffusion region in the secondary battery M not producing the memory effect The phase between the complex impedance Z and the phase θ of the frequency to be set was set as the phase threshold θx. However, if the phase θ of the complex impedance Z of the frequency corresponding to the resistance diffusion region in the secondary battery M not producing the memory effect is obtained in advance, a value slightly smaller than the phase θ is set as the phase threshold θx. It may be set.

  In the above embodiment, if the frequency is included in the resistance diffusion region of the complex impedance Z in the secondary battery M, the presence or absence of the memory effect in the secondary battery M is determined based only on the phase θ of the complex impedance Z at a specific frequency. You may judge.

  In the above embodiment, if the SOC usage range is determined when the secondary battery M to be determined is used, the complex impedance Z is obtained from the secondary battery M without adjusting the SOC of the secondary battery M. You may get it.

  In the above-described embodiment, the nickel-metal hydride storage battery that is relatively easy to generate a memory effect has been described as a determination target. However, as long as it is a secondary battery that produces a memory effect, another secondary battery such as a nickel hydride cadmium battery may be determined. Further, even a lithium ion battery or the like may be a determination target of the present invention because it may cause a memory effect although it is minute.

  DESCRIPTION OF SYMBOLS 10 ... Battery state determination system, 11 ... Measuring apparatus, 11a ... SOC adjustment part, 11b ... Impedance measurement part, 12 ... Battery state determination apparatus, 12a ... CPU, 12b ... ROM, 12c ... RAM, 13 ... Output device, F ... Measurement frequency, θx: phase threshold, M: secondary battery.

Claims (6)

A battery state determination method for determining presence or absence of a memory effect in a secondary battery using a battery state determination device,
The battery state determination device is
An impedance acquisition step of acquiring complex impedance of the secondary batteries,
A phase calculation step of calculating a phase for each frequency of the complex impedance acquired in the impedance acquisition step;
Based on the phase of the complex impedance calculated in the phase calculation step, a memory effect occurs in the secondary battery when the phase at a frequency corresponding to the resistance diffusion region in the secondary battery is equal to or less than a predetermined threshold value. A battery state determination method comprising: performing a determination step of determining that the battery is present.   In the determination step, when the phase of the complex impedance calculated in the phase calculation step includes a phase that is equal to or less than the threshold within a frequency range corresponding to a resistance diffusion region in the secondary battery, The battery state determination method according to claim 1, wherein the memory effect is determined to occur in the secondary battery.   3. The battery state determination method according to claim 1, wherein the threshold is set based on a complex impedance phase of a frequency corresponding to a resistance diffusion region in a secondary battery that does not produce a memory effect.   The battery state determination method according to any one of claims 1 to 3, wherein a frequency range of a complex impedance corresponding to a resistance diffusion region in the secondary battery is 0.01 Hz to 0.1 Hz.   The battery state determination method according to claim 1, wherein the secondary battery is a nickel metal hydride storage battery. A battery state determination device for determining the presence or absence of a memory effect in a secondary battery,
An impedance acquisition unit that acquires complex impedance of the secondary batteries,
A phase calculation unit that calculates a phase for each frequency of the complex impedance acquired by the impedance acquisition unit;
When the phase at the frequency corresponding to the resistance diffusion region in the secondary battery is equal to or less than a predetermined threshold based on the phase of the complex impedance calculated by the phase calculation unit, the memory effect is generated in the secondary battery. A battery state determination device comprising: a determination unit for determining.

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