BATTERY DIAGNOSTIC DEVICE AND BATTERY DIAGNOSTIC PROCEDURES

Abstract

The present invention is intended to provide a technique capable of accurately and rapidly diagnosing a battery's condition without pre-accumulating measurement data. A battery diagnostic device according to the present invention specifies a first frequency at which a component caused by a diffusion resistance of an equivalent circuit of a battery begins to appear in a Nyquist diagram of the battery; specifies a second frequency at which a phase of the voltage and a phase of the current coincide in phase-frequency characteristics of the voltage and current; and diagnoses a battery's condition using the respective real parts of a first impedance of the battery at the first frequency and a second impedance of the battery at the second frequency.

Description

Technical field

[0001] The present invention relates to a technique for diagnosing the condition of a battery. State of the art

[0002] To use secondary batteries safely, a technique for accurately diagnosing the battery's condition is essential. For example, it is necessary to diagnose a battery's condition, such as (a) whether an aged battery meets requirements, such as capacity and performance, needed for a desired application, and (b) when the battery's lifespan will end.

[0003] Battery diagnostics are performed using measurement data such as battery voltage, current, and temperature. However, there are instances where an outlier may occur in the measurement data. This outlier could, for example, indicate a battery failure or a sign of one. Therefore, it is essential to identify such an outlier early and take appropriate action.

[0004] The following WO 2020 / 129477 A describes a technology in which "a voltage of a battery cell and a current flowing through the battery cell are measured. An open-circuit voltage (OCV) of the battery cell is estimated based on the measured voltage, the measured current, and an equivalent circuit based on the electrochemistry of the battery cell. In particular, the positive electrode and / or the negative electrode of the battery cell is a mixed electrode containing a variety of materials. The equivalent circuit also represents a model that includes a diffusion resistance component for each of the many materials used for the positive and negative electrodes." (see summary) List of literature on patent literature

[0005] Patent literature 1: WO2020 / 129477 Summary of the invention: Technical problem

[0006] Outliers are typically identified by comparing a threshold value with a measured value. However, it is difficult to assume an error mode for an outlier that was caused by a random error beforehand. Therefore, it is equally difficult to properly adjust the threshold value used to find the outlier.

[0007] It is assumed that the conventional diagnostic procedure, as in WO 2020 / 129477 A, can diagnose the battery by estimating the OCV (overall calorific value). However, to adequately remove outliers in the OCV estimation, it is assumed that data accumulation of both outlier and normal values ​​is necessary. This is because it is generally difficult to anticipate an outlier. Since the conventional diagnostic procedure relies on the accumulation of such data, the applicable scenarios may be correspondingly limited.

[0008] The present invention was developed with regard to the above problems, and one of its objectives is to provide a technique that is able to diagnose a battery condition accurately and quickly without accumulating measurement data in advance. Solution to the problem

[0009] A battery diagnostic device according to the present invention specifies a first frequency at which a component caused by a diffusion resistance of an equivalent circuit of a battery begins to appear in a Nyquist diagram of the battery, specifies a second frequency at which a phase of the voltage and a phase of the current coincide in phase frequency characteristics of the voltage and current, and diagnoses a state of the battery using respective real parts of a first impedance of the battery at the first frequency and a second impedance of the battery at the second frequency. Advantageous effects of the invention

[0010] According to the battery diagnostic device of the present invention, it is possible to diagnose a battery's condition accurately and quickly without accumulating measurement data in advance. Problems, configurations, effects, and the like that differ from those mentioned above will become clear from the following description of embodiments. Brief description of the drawings Fig. 1 is an equivalent circuit diagram of a secondary battery cell 1; Fig. 2 is an equivalent circuit diagram for impedance diagnostics; Fig. 3A is an example of a Nyquist diagram of a secondary battery; Fig. Figure 3B is an example where measured values ​​from a Nyquist diagram are plotted; Fig. Figure 4 shows an example of measuring battery characteristics using a rising wave or a falling wave; Fig. Figure 5 shows a charging process of the secondary battery and a current waveform or voltage waveform in a subsequent pause period; Fig. Figure 6 shows a discharge process of the secondary battery and a current waveform or voltage waveform in a subsequent pause period; Fig. Figure 7 is a graph that plots phase frequency characteristics of a battery voltage and battery current; Fig. Figure 8 is a diagram representing impedances corresponding to ω1 and ωb, respectively; Fig. Figure 9 is a diagram representing impedances corresponding to ω1 and ωb, respectively; Fig. Figure 10 is a diagram showing a decrease in battery capacity with the number of days the secondary battery is used; Fig. Figure 11 is a diagram illustrating a procedure for diagnosing accelerated secondary battery degradation; Fig. 12 is a diagram showing Nyquist plots of a normal battery cell and an abnormal battery cell; Fig. Figure 13 is a diagram illustrating a procedure for diagnosing whether a battery cell is an abnormal battery cell; Fig. Figure 14 is a flowchart to explain a procedure for diagnosing the secondary battery; Fig. Figure 15 is a flowchart to explain another procedure for diagnosing the secondary battery; Fig. Figure 16 is a block diagram of a battery diagnostic device 100 according to a second embodiment; and Fig. 17 is an example of a user interface provided by an arithmetic unit 120. Description of the embodiments<Erste Ausführungsform>

[0011] Fig. Figure 1 is an equivalent circuit diagram of a secondary battery cell 1. The equivalent circuit is, in particular, a circuit in which a solution resistor, an RC circuit of the negative electrode, an RC circuit of the positive electrode and a diffusion resistor are connected in series in that order.

[0012] Fig. Figure 2 is an equivalent circuit for impedance analysis. Secondary battery cell 1 has an impedance Zc. An AC voltage Vin is applied to secondary battery cell 1 to obtain a voltage Vo, which is amplified according to a reference resistor r0. Zc is represented by the following expression: Zc = -r0·(Vin / Vo). The impedance characteristics, as described later, Fig. 3A and Fig. The values ​​shown in 3B are further measured by applying such an alternating voltage signal to the battery.

[0013] Fig. Figure 3A is an example of a Nyquist diagram of the secondary battery. Here, the theoretical form is shown instead of the actual waveform. The arc on the left side in Fig. 3A corresponds to the negative electrode, the arc on the right corresponds to the positive electrode, and the straight section corresponds to the diffusion resistance. If the frequency of the current input to the battery is changed, the waveform can be adjusted accordingly in each area. Fig. 3A will be detected according to the change. The vertex of the arc segment in Fig. 3A corresponds here to a time constant T anode the negative electrode or the time constant T kathode the positive electrode.

[0014] Among the frequencies of the alternating voltage signal that is input into the battery when the impedance is measured, the frequency corresponding to the time constant T is kathodethe positive electrode corresponds, where ω0 = 1 / T kathode Furthermore, a frequency at which a component corresponding to the diffusion resistance begins to appear on the horizontal axis of the Nyquist diagram is defined as ω1.

[0015] Fig. Figure 3B is an example where measured values ​​from the Nyquist plot are plotted. A section corresponding to frequency ω1 appears as an inflection point. A section corresponding to frequency ω0 represents a region where the gradient of the plot is essentially linear.

[0016] Fig. Figure 4 shows an example of measuring battery characteristics using a rising or falling waveform. The rising wave, for example, is a current signal that exhibits a specific time interval between the start and end of the discharge current interruption, as described in Fig. Figure 6, which will be described later, illustrates this. The falling wave also represents, for example, a current signal that has a specific duration between the start and end of the charging current interruption, as shown in Figure 6. Fig. Figure 5 is shown, which will be described later.

[0017] If phase frequency characteristics and ωb, which are in Fig. Figure 7, which are described later, are shown, and such a rising wave or such a falling wave is applied to the battery, and a Fourier transformation is performed using a response signal at that time.

[0018] Fig. Figure 5 further illustrates the charging process of the secondary battery and a current waveform or voltage waveform during a subsequent pause period. When the charging process is stopped (the charging current is cut off), the absolute value of the battery current and the battery voltage also decrease. When the current interruption is complete (that is, when the charging current becomes 0), the process also enters a pause period, and the battery voltage gradually decreases over time.

[0019] The time duration from the start to the end of the interruption of the charging current until the interruption is completed is described here by τa = 1 / (2 × ωa). If ωb, which is in Fig. As shown in Figure 7, which will be described later, when the charging current is recorded, a current waveform satisfying 1 / (2 × ω0) < τa < 1 / (2 × ω1) is applied to the battery. If, however, the charging current is instantaneously cut off (that is, within a time period shorter than τa), a component corresponding to the negative battery electrode appears in the Nyquist diagram. As will be explained later with reference to Fig. As described in Section 7 and the like, in the present invention the battery is diagnosed using a component corresponding to the positive battery electrode, making it undesirable to detect characteristics corresponding to the negative battery electrode. If phase frequency characteristics, which are described in Section 7 and the like, are detected, the battery is not detected. Fig. 7 are shown, which will be described later, and are therefore captured; a battery current that is to be cut off is thus captured, while τa, which is in Fig. As shown in section 5, it is used. Since it is sufficient to perform an interruption during τa, it is not always necessary to apply an AC voltage current to the battery.

[0020] Fig. Figure 6 shows a discharge process of the secondary battery and a current waveform or voltage waveform during a subsequent pause period. When the discharge process is stopped (the discharge current is cut off), the absolute value of the battery current and the battery voltage also increase. The time duration τa from the start to the end of the interruption of the discharge current is also similar to that in Fig. 5.

[0021] Fig. Figure 7 is a graph plotting the phase frequency characteristics of a battery voltage and a battery current. A frequency at which the phase of the battery voltage and the phase of the battery current coincide in the phase frequency characteristics is defined here as ωb. Here, ωb is smaller than ωnyq (> ω0) corresponding to the Nyquist frequency and larger than ω1.

[0022] If the output current phase and the output voltage phase of the equivalent RC circuit coincide, the current component flowing through the capacitor section of the same circuit can be ignored. That is, the resistance (R) component of the equivalent RC circuit can be calculated from the output voltage / current of the equivalent RC circuit. In other words, at this frequency, the resistance (R) component (i.e., the positive electrode resistance) of the equivalent RC circuit can be calculated from the output voltage / current of the equivalent RC circuit. Therefore, in the present embodiment, the positive electrode resistance is measured using ωb, and the battery state is diagnosed based on this resistance.A real part of the impedance rb, corresponding to ωb, can also be calculated, for example, by dividing the amplitude of the battery voltage at ωb by the amplitude of the battery current at ωb based on the phase frequency characteristics.

[0023] Fig. Figure 8 is a diagram representing impedances corresponding to ω1 and ωb, respectively. ◯ represents a Nyquist plot and + an impedance plot, if the value in the diagram is 0. Fig. 5 and Fig. The current described in point 6 is applied. In the plot of Fig. In equation 8, a real part of the impedance corresponding to ω1 (first frequency) is defined as r1, and a real part of the impedance corresponding to ωb (second frequency) is defined as rb. If |r1 - rb| is equal to or less than the threshold value, the battery can be diagnosed as normal. Alternatively, if |rb / r1| is equal to or less than a threshold value, the battery can be diagnosed as normal. Since these diagnostic criteria are essentially equivalent, either one can be used.

[0024] In the case of a normal battery, it is also known that ω0 and ω1 lie in a range that is close to each other to a certain degree. Therefore, a ωb existing between ω0 and ω1 is also close to ω1 to a certain degree. In other words, r1 and rb are also considered to be close to each other. Therefore, in the present invention, the battery is diagnosed based on whether the difference between r1 and rb is sufficiently small. The diagnostic criteria in Fig. 8 are based on such a concept.

[0025] Fig. Figure 9 is a diagram representing impedances corresponding to ω1 and ωb, respectively. As a diagnostic procedure, it differs from the one in Fig. If the Nyquist plot differs in its method of differentiation, the following can also be used. The frequency at the point where the Nyquist plot intersects the real axis (the point corresponding to the solution resistance) is defined as ω3, and the real part of the impedance at that time as r3. If |(r1 - r3) - (rb - r3)| is equal to or less than the threshold, the battery can be diagnosed as normal. Alternatively, if |(rb / r3) / (r1 / r3)| is equal to or less than the threshold, the battery can be diagnosed as normal. Since these diagnostic criteria are essentially equivalent, either can be used.

[0026] If the battery is in good condition, its state of health (SOH) can also be determined. Since the SOH (or maximum charge capacity) and (rb - r3) are inversely proportional, the SOH can be derived from (rb - r3) by referring to data that establishes a correspondence between the SOH and (rb - r3).

[0027] Fig. Figure 10 is a diagram illustrating the decrease in battery capacity with the number of days the secondary battery is used. Generally, the secondary battery's charge capacity gradually decreases as the number of days of use increases, but the rate of decrease (i.e., the degradation acceleration) gradually increases with the number of days of use. Therefore, when the battery's condition is diagnosed, there is a case where the degradation acceleration is diagnosed along with the battery's condition. A specific procedure for this is described below.

[0028] Fig. Figure 11 is a diagram illustrating a procedure for diagnosing the degradation acceleration of the secondary battery. r1 and rb on the Nyquist plot are calculated in the same way as in [reference]. Fig. 8 and Fig. 9. In the battery where degradation is advanced, r1 and rb are largely separated. Therefore, if (r1 - rb) > threshold, it can be diagnosed that the degradation acceleration is large. Alternatively, if (r1 / rb) > threshold, it can be diagnosed that the degradation acceleration is large. Since these diagnostic criteria are essentially equivalent, either can be used.

[0029] Fig. Figure 12 is a diagram showing Nyquist plots of a normal battery cell and an abnormal battery cell. The Nyquist plot in an abnormal battery cell may have different characteristics than a normal battery cell, which can determine whether the battery is abnormal, as described below.

[0030] Fig. Figure 13 is a diagram illustrating a procedure for diagnosing whether a battery cell is abnormal. Unlike a normal battery cell, an abnormal battery cell satisfies r1 < rb. Therefore, if r1 is less than rb, it can be considered abnormal.

[0031] Fig. Figure 14 is a flowchart illustrating a procedure for diagnosing the secondary battery. This flowchart describes the diagnostic procedure described above in a flowchart format. Each step can be performed using an arithmetic unit 120, which will be described later. Furthermore, each step of the Fig. 14 described below. (Fig. 14: Step S1401: Part 1)

[0032] The arithmetic unit 120 captures the following parameters. These parameters can be captured by actual measurement or as known values ​​based on the battery's performance specifications. (a) Frequency ω0, corresponding to the time constant of the RC electrode of the battery's equivalent circuit; (b) Frequency ω1, at which a component corresponding to the diffusion resistance begins to appear in the Nyquist diagram; (c) Frequency ωa (ω1 < ωa < ω0), corresponding to the time duration τa from the start to the end of the discharge / charge current interruption. (Fig. 14: Step S1401: Part 2)

[0033] The arithmetic unit 120 captures a battery voltage waveform when a battery current of τa = 1 / (2 × ωa) is applied. (Fig. 14: Step S1402)

[0034] The arithmetic unit 120 performs a Fourier transform (FFT) on each of the battery voltage and battery current values ​​before and after the discharge or charge current is cut off. The sampling frequency is 1 / (2ωa). (Fig. 14: Steps S1403 to S1404)

[0035] The arithmetic unit 120 specifies the frequency ωb at which the phases of the battery voltage and battery current coincide on the phase frequency characteristics of the battery voltage and battery current (S1403). Furthermore, the arithmetic unit 120 calculates a real part rb of the battery impedance at ωb (S1404). (Fig. 14: Step S1405)

[0036] An alternating current with frequency ω1 is applied to the battery. The arithmetic unit 120 calculates a real part r1 of the battery impedance at ω1. (Fig. 14: Steps S1406 to S1408)

[0037] The arithmetic unit 120 determines whether |r1 - rb| is equal to or less than the threshold (S1406). If it is equal to or less than the threshold (S1406: Yes), the battery is diagnosed as normal. Additionally, an AC current with a frequency ω3 is applied to the battery. The arithmetic unit 120 calculates rb - r3 for this purpose (S1407) and estimates the state of health (SOH) of the battery by referring to the data describing the correspondence between rb - r3 and the SOH (or the maximum charge capacity) (S1408). (Fig. 14: Step S1409)

[0038] If |r1 - rb| exceeds the threshold, the battery is assumed to be in an abnormal state (a state like in the Fig. 12 and Fig. 13) or a state in which degradation is advanced (a state such as in the Fig. 10 and Fig. (shown in Figure 11). The arithmetic unit 120 also compares r1 - rb with the threshold value. If (r1 - rb) > threshold value, it is diagnosed that the degradation rate is high. If rb is greater than r1, it is also diagnosed that the battery is abnormal (that is, in a condition as shown in Figure 11). Fig. 13 shown). (Fig. 14: Steps S1406 and S1409: Supplement)

[0039] As in Fig. As described in section 8, in S1406 |rb / r1| can also be used instead of |r1 - rb|. As in Fig. As described in section 11, (r1 / rb) can also be used instead of (r1 - rb) in S1409. Furthermore, the threshold can be changed depending on the expression used. In S1409, the degradation acceleration (first degradation acceleration) when (r1 - rb) > threshold and the degradation acceleration (second degradation acceleration) when (r1 / rb) > threshold can also be the same or different.

[0040] Fig. Figure 15 is a flowchart to explain an alternative procedure for diagnosing the secondary battery. This flowchart uses the one described in Figure 15. Fig. 9 described procedures instead of the one in Fig. The procedure described in section 8. Each step can be performed using an arithmetic unit 120, which will be described later. In particular, steps S1501 and S1502 are performed instead of S1405 and S1406, respectively. The other steps are the same as those in [section / document name]. Fig. 14 similar. (Fig. 15: Step S1501)

[0041] The alternating current at each of the frequencies ω1 and ω3 is applied to the battery. The arithmetic unit 120 then calculates the real parts r1 and r3 of the battery impedances at ω1 and ω3, respectively. (Fig. 15: Step S1502)

[0042] The arithmetic unit 120 determines whether |(r1 - r3) - (rb - r3)| is equal to or less than a threshold value. If this is equal to or less than the threshold value (S1502: Yes), the battery is diagnosed as normal. Since the real part of the impedance r3 at frequency ω3 was measured in S1501, it is therefore not necessary to measure the real part of the impedance r3 again in S1407. <Zweite Ausführungsform>

[0043] Fig. Figure 16 is a block diagram of a battery diagnostic device 100 according to a second embodiment of the present invention. The battery diagnostic device 100 is a device that diagnoses a battery's condition using the method described in the first embodiment. The battery diagnostic device 100 comprises a detection unit 110, a processing unit 120, and a storage unit 130. The detection unit 110 acquires measurement results of the battery voltage and battery current. The processing unit 120 also performs the diagnostic procedure described in the first embodiment. The storage unit 130 further stores data (for example, a parameter obtained in S1401 is pre-stored, and data that stores the relationship between rb - r3 and the charge capacity) that is used by the processing unit 120.

[0044] Fig. Figure 17 is an example of a user interface provided by Computing Unit 120. Computing Unit 120 can provide a user interface, such as the one provided by Fig. 17. Generate and display on a display device, such as a screen. The user interface may, for example, display the following information: (a) ω0, ω1, ωa, ωb; (b) a Nyquist plot; (c) r1, rb, r3; and (d) a diagnostic result. <Modifikationen der vorliegenden Erfindung>

[0045] The present invention is not limited to the embodiments described above and includes various modifications. Furthermore, the above embodiments have been described in such detail only to present the invention in an easily understandable manner, and the embodiments need not necessarily be limited to those that have all the described configurations. Moreover, a part of the configuration of one embodiment can be replaced by the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. In addition, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

[0046] In the above embodiment, ω1 is also typically equal to or less than five times ω0 (ω1 ≤ 5ω0). Therefore, when phase frequency characteristics of the battery voltage and battery current are obtained to specify ωb, it should also be noted that a current waveform where τa is the one in Fig. 5 and Fig. 6 is described, according to ω1 and ω0, which must be applied to the battery and meet these conditions.

[0047] In the above embodiment, the computing unit can further be configured by hardware, such as a circuit device on which the function is implemented, or by executing software on which the function is implemented, by a computing device, such as a central processing unit (CPU).

[0048] In the above embodiment, the reason for using the characteristics corresponding to the positive electrode on the Nyquist diagram is further explained. If the characteristics on the negative electrode side were used, values ​​such as r1 and rb in the present invention and the value (r3) of the solution resistance could essentially coincide. In such a case, it would be difficult to determine the value of each measured real part of the impedance, complicating diagnosis. Therefore, in the present invention, the characteristics on the positive electrode side are used. Reference symbol list 100 Battery diagnostic device 110 detection unit 120 arithmetic units 130 storage units QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] WO 2020 / 129477 A [0004, 0007] WO 2020 / 129477

[0005]

Claims

[1] A battery diagnostic device that diagnoses the condition of a battery, the battery diagnostic device comprising: a detection unit that records detection values ​​of a voltage and a current output by the battery; and an arithmetic unit that diagnoses the state of the battery, whereby The arithmetic unit specifies a first frequency at which a component caused by a diffusion resistance of an equivalent circuit of the battery begins to appear in a Nyquist diagram of the battery. The arithmetic unit specifies a second frequency at which a phase of the voltage and a phase of the current coincide in phase frequency characteristics of the voltage and current when an increasing or decreasing current is applied to the battery. The arithmetic unit captures a first impedance of the battery at the first frequency and a second impedance of the battery at the second frequency. the arithmetic unit diagnoses a state of the battery using a real part of the first impedance and a real part of the second impedance, and The arithmetic unit specifies the second frequency by a waveform if a time period from a start to an end of the rise of the increasing current or a time period from a start to an end of the fall of the falling current is a value between a value determined based on a time constant of an RC circuit of the positive electrode of the equivalent circuit and a value determined based on the first frequency. [2] The battery diagnostic device according to claim 1, wherein The arithmetic unit diagnoses that the battery is normal if an absolute difference between a real part of the first impedance and a real part of the second impedance is equal to or less than a threshold value, or The arithmetic unit diagnoses that the battery is normal if a ratio of the real part of the second impedance to the real part of the first impedance is equal to or less than a threshold value. [3] The battery diagnostic device according to claim 1, wherein The arithmetic unit specifies a third frequency at which a component caused by a solution resistance of the equivalent circuit begins to appear in the Nyquist diagram. the arithmetic unit captures a real part of a third impedance of the battery at the third frequency, the arithmetic unit captures a correspondence relationship between a difference obtained by subtracting the real part of the third impedance from the real part of the second impedance and a state of health of the battery, and The arithmetic unit estimates the battery's health status using the correspondence relationship. [4] The battery diagnostic device according to claim 1, wherein The arithmetic unit estimates that the battery is damaged with a first degradation acceleration if the real part of the first impedance is greater than the real part of the second impedance by a predetermined value or more. The arithmetic unit estimates that the battery is damaged with less than the first degradation acceleration if the real part of the first impedance is not equal to or greater than the predetermined value with respect to the real part of the second impedance. The arithmetic unit estimates that the battery is damaged with a second degradation acceleration if a ratio of the first impedance to the real part of the second impedance is a predetermined value or greater, and The arithmetic unit estimates that the battery is damaged with less than the second degradation acceleration if the ratio of the first impedance to the real part of the second impedance is smaller than the predetermined value. [5] The battery diagnostic device according to claim 1, wherein the arithmetic unit diagnoses that the battery is abnormal when the real part of the second impedance is greater than the real part of the first impedance. [6] The battery diagnostic device according to claim 1, wherein The arithmetic unit specifies a third frequency at which a component caused by the solution resistance of the equivalent circuit begins to appear in the Nyquist diagram. the arithmetic unit captures the real part of the third impedance of the battery at the third frequency, The arithmetic unit diagnoses that the battery is normal if an absolute difference between a first difference obtained by subtracting the real part of the third impedance from the real part of the first impedance and a second difference obtained by subtracting the real part of the third impedance from the real part of the second impedance is equal to or less than a threshold value. the arithmetic unit obtains a first ratio of the real part of the first impedance to the real part of the third impedance and a second ratio of the real part of the second impedance to the real part of the third impedance, and The arithmetic unit diagnoses that the battery is normal if the ratio of the second ratio to the first ratio is equal to or less than a threshold value. [7] The battery diagnostic device according to claim 6, wherein the arithmetic unit captures a correspondence relationship between a difference obtained by subtracting the real part of the third impedance from the real part of the second impedance and a state of health of the battery, and The arithmetic unit estimates the battery's health status using the correspondence relationship. [8] The battery diagnostic device according to claim 6, wherein The arithmetic unit estimates that the battery is damaged with a first degradation acceleration if the real part of the first impedance is greater than the real part of the second impedance by a predetermined value or more. The arithmetic unit estimates that the battery is damaged with less than the first degradation acceleration if the real part of the first impedance is not equal to or greater than the predetermined value with respect to the real part of the second impedance. The arithmetic unit estimates that the battery is damaged with a second degradation acceleration if a ratio of the first impedance to the real part of the second impedance is a predetermined value or greater, and The arithmetic unit estimates that the battery is damaged with less than the second degradation acceleration if the ratio of the first impedance to the real part of the second impedance is smaller than the predetermined value. [9] The battery diagnostic device according to claim 6, wherein the arithmetic unit diagnoses that the battery is abnormal when the real part of the second impedance is greater than the real part of the first impedance. [10] The battery diagnostic device according to claim 1, wherein the arithmetic unit performs a Fourier transform on each of the current and voltage with a value greater than the reciprocal of a time constant of an RC circuit of the positive electrode of the equivalent circuit, as a Nyquist frequency, and The arithmetic unit captures the real part of the second impedance based on a result of the Fourier transform. [11] The battery diagnostic device according to claim 1, wherein the arithmetic unit specifies the second frequency in a frequency range that is lower than a Nyquist frequency in phase frequency characteristics of voltage and current, and The arithmetic unit captures the real part of the second impedance by dividing the amplitude of the voltage at the second frequency by the amplitude of the current at the second frequency. [12] The battery diagnostic device according to claim 1, wherein the first frequency is five or less times the reciprocal of a time constant of an RC circuit of the positive electrode of the equivalent circuit. [13] A battery diagnostic procedure that diagnoses the condition of a battery, comprising the battery diagnostic procedure: a step of capturing detection values ​​of a voltage and current output by the battery; and a step in diagnosing a battery condition, whereby In the diagnostic step, a first frequency is specified at which a component caused by a diffusion resistance of an equivalent circuit of the battery begins to appear in a Nyquist diagram of the battery. In the diagnostic step, a second frequency is specified at which a phase of the voltage and a phase of the current coincide in phase frequency characteristics of the voltage and current when an increasing or decreasing current is applied to the battery. In the diagnostic step, a first battery impedance at the first frequency and a second battery impedance at the second frequency are recorded. In the diagnostic step, the battery's condition is diagnosed using a real part of the first impedance and a real part of the second impedance, and In the diagnostic step, the second frequency is specified by a waveform if a time period from a start to an end of the rise of the increasing current or a time period from a start to an end of the fall of the falling current is a value between a value determined based on a time constant of an RC circuit of the positive electrode of the equivalent circuit and a value determined based on the first frequency.

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