Method of determining secondary battery state and device for determining secondary battery state

Abstract

To determine states of a positive pole and a negative pole of a secondary battery in a well-balanced manner.SOLUTION: A method of determining secondary battery state comprises: a step (S2) of measuring impedance for acquiring Nyquist plot; a step (S5) of calculating minimum inclination θmin [deg] of the Nyquist plot; a step (S5) of acquiring minimum inclination imaginary number value Zimin[mΩ] from the minimum inclination θmin [deg]; a step (S6) of acquiring anode discharge reserving dispersion Rs[Ah] from the minimum inclination imaginary number value Zimin[mΩ]; a step (S7) of acquiring anode capacitance dispersion Cs[Ah] from the anode discharge reserving dispersion Rs[Ah]; a step (S8) of acquiring anode capacitance minimal value Cmin[Ah] from the anode capacitance dispersion Cs[Ah]; and a step (S9) of determining state of a nickel hydrogen storage battery based on the anode capacitance minimal value Cmin[Ah].SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The present invention relates to a method and device for determining the state of a secondary battery, and more particularly to a method and device for determining the state of a secondary battery that determine the states of the positive and negative electrodes of a secondary battery in a well-balanced manner. [Background technology]

[0002] Electric vehicles (including hybrid vehicles) equipped with electric motors run the motors using electricity stored in secondary batteries through charging. A unique feature of such electric vehicles is regenerative braking. Among secondary batteries that are repeatedly charged and discharged, alkaline secondary batteries such as nickel-metal hydride batteries are widely used for vehicles because they are capable of charging and discharging large currents.

[0003] Although such secondary batteries have different usage histories and various degrees of deterioration, they can be collected after use and inspected to see if they can be reused, and if the inspection results show that the battery's performance can be reused, they can be reused, thereby saving resources. As a method for such inspection, it is desirable to perform detailed inspections over a long period of time, such as charging and discharging from full charge to full discharge. However, it is efficient to perform a preliminary judgment of the condition of the secondary battery by a simple inspection in a short period of time before such a long inspection.

[0004] In order to accurately determine the state of such a secondary battery in a short time, the following inventions have been disclosed. In Patent Document 1, a positive electrode capacity deviation judgment unit judges the presence or absence of a positive electrode capacity deviation for a battery module that has been judged not to have a negative electrode capacity deviation based on a comparison between the slope of the complex impedance with respect to the real axis in the diffusion resistance region and a judgment value for a positive electrode capacity deviation.

[0005] The battery state determination method of Patent Document 2 obtains a feature value corresponding to the maximum absolute value of the imaginary component of the AC impedance of the battery caused by the reaction resistance included in the frequency change of the AC impedance of the battery, and calculates the remaining capacity of the battery by comparing the feature value with correlation data that indicates the correlation between a predetermined feature value and the remaining capacity of the battery.

[0006] In Patent Document 3, a parameter is calculated that is the ratio between the difference in measured angular velocities of two complex impedances with different measured angular velocities and the difference in components of the two complex impedances.Then, the charged amount of electricity in the battery is estimated based on the parameter and information indicating the relationship between the charged amount of electricity in the battery and the parameter.

[0007] In Patent Document 4, the inclination angle of a linear approximation of the complex impedance at different frequencies in the diffusion region of a secondary battery is calculated, and if the inclination angle is equal to or greater than a threshold, the capacity balance is determined to be normal. Also, if the magnitude of the imaginary axis component of the complex impedance in the diffusion region of the secondary battery is greater than a threshold, the battery is determined to have an abnormal capacity balance.

[0008] In this way, the state of the secondary battery could be determined by measuring the complex impedance. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2019-049479 A [Patent Document 2] JP 2016-065832 A [Patent Document 3] JP 2019-117180 A [Patent Document 4] International Publication No. 2013 / 115038 Summary of the Invention [Problem to be solved by the invention]

[0010] In the conventional battery evaluation using complex impedance as described above, when the evaluation is based on the arc-shaped reaction resistance in the Nyquist plot, it is mainly influenced by the state of the negative electrode. When the evaluation is based on the diffusion resistance that extends linearly from the arc-shaped part to the upper right, it is mainly influenced by the state of the positive electrode. Therefore, there is a problem that the state of the positive electrode and the negative electrode cannot be evaluated in a balanced manner when the evaluation is based on only one of them.

[0011] The problem to be solved by the secondary battery state determining method and secondary battery state determining device of the present invention is to determine the states of the positive and negative electrodes of a secondary battery in a balanced manner. [Means for solving the problem]

[0012] In order to solve the above problems, the method for determining the state of a secondary battery of the present invention includes an impedance measurement step of measuring the impedance of a secondary battery having a plurality of single cells, the state of which is to be determined, by changing the frequency at a frequency interval of a fixed magnification; a slope θ [deg] calculation step of calculating a slope θ [deg] between two plotted points in a Nyquist plot created based on data acquired in the impedance measurement step; and a slope θ [deg] calculation step of calculating the minimum slope θ [deg] among the slopes θ [deg] calculated in the slope θ [deg] calculation step. min [deg] at two points, the imaginary value Zi [mΩ] is the minimum slope imaginary value Zi min The minimum imaginary slope Zi to be obtained in [mΩ] min [mΩ] Step of acquisition and the minimum slope imaginary value Zi min [mΩ] The minimum imaginary slope value Zi obtained in the acquisition step min [mΩ] based on negative electrode capacity minimum value C min [Ah] Minimum negative electrode capacity C min and obtaining the step of [Ah].

[0013] In this case, the minimum slope imaginary value Zi min[mΩ] and the imaginary value of the minimum slope Zi, which is the relationship between the variation in negative electrode discharge reserve Rs [Ah] min [mΩ] / negative electrode discharge reserve variation Rs [Ah] Minimum slope imaginary value Zi to obtain the relationship min [mΩ] / negative electrode discharge reserve variation Rs [Ah] relationship acquisition step, and the minimum slope imaginary value Zi min [mΩ] / negative electrode discharge reserve variation Rs [Ah] Minimum slope imaginary value Zi obtained in the relationship acquisition step min Based on the relationship [mΩ] / negative electrode discharge reserve variation Rs [Ah], the minimum slope imaginary value Zi min [mΩ] Minimum slope imaginary value Zi obtained in the acquisition step min [mΩ] to obtain the negative electrode discharge reserve variation Rs [Ah]; and a negative electrode discharge reserve variation Rs [Ah] / negative electrode capacity variation Cs [Ah] relationship is obtained, which is the relationship between the negative electrode discharge reserve variation Rs [Ah] and the negative electrode capacity variation Cs [Ah] in a battery of the same type as the secondary battery whose state is to be determined in advance; and ] / negative electrode capacity variation Cs [Ah] relationship based on the negative electrode discharge reserve variation Rs [Ah] / negative electrode capacity variation Cs [Ah] relationship acquisition step, the negative electrode capacity variation Cs [Ah] is acquired from the negative electrode discharge reserve variation Rs [Ah] acquired in the negative electrode discharge reserve variation Rs [Ah] acquisition step, and the negative electrode capacity variation Cs [Ah] and the negative electrode capacity minimum value C in a battery of the same type as the secondary battery whose state is to be determined in advance are min [Ah] to obtain the relationship between the negative electrode capacity variation Cs [Ah] / negative electrode capacity minimum value C min Based on the negative electrode capacity variation Cs [Ah] / negative electrode capacity minimum value Cmin [Ah] relationship acquired in the step of acquiring the negative electrode capacity variation Cs [Ah], the negative electrode capacity minimum value Cmin [Ah] corresponding to the negative electrode capacity variation Cs [Ah] is obtained. min [Ah] Minimum negative electrode capacity C minIt is preferable to have a step of obtaining [Ah].

[0014] In addition, the negative electrode capacity minimum value C min [Ah] The minimum negative electrode capacity obtained in the step of obtaining min The charge-discharge charge capacity may further include a step of judging the state of a secondary battery by comparing [Ah] with a preset threshold value to judge whether the state of the secondary battery to be judged is good or bad.

[0015] It is preferable that the impedance measurement step is performed by sequentially changing the measurement frequency at a uniform rate within a frequency range of 100 [Hz] to 0.01 [Hz]. In the step of acquiring the imaginary value Zi [mΩ], the smallest gradient θ among the gradients θ [deg] calculated in the step of calculating the gradient θ [deg] min [deg] Minimum imaginary slope Zi at two points min [mΩ] is the minimum slope θ min [deg], the lower imaginary value Zi [mΩ] is the minimum slope imaginary value Zi min Alternatively, the measured value may be acquired as [mΩ].

[0016] The secondary battery can be particularly suitably applied when it is a nickel-metal hydride storage battery. In addition, the secondary battery state determination device of the present invention is a secondary battery state determination device equipped with a computer, and the secondary battery state determination device previously determines the minimum slope imaginary value Zi at two points of the minimum slope θ [deg] in a battery of the same type as the secondary battery to be determined. min [mΩ] and the imaginary value of the minimum slope Zi, which is the relationship between the variation in negative electrode discharge reserve Rs [Ah] min [mΩ] / negative electrode discharge reserve variation Rs [Ah] relationship, and in a battery of the same type as the secondary battery whose state is to be determined in advance, the relationship between the negative electrode discharge reserve variation Rs [Ah] and the negative electrode capacity variation Cs [Ah], and in a battery of the same type as the secondary battery whose state is to be determined in advance, the relationship between the negative electrode capacity variation Cs [Ah] and the negative electrode capacity minimum value C mina storage means for storing a relationship between the frequency of the battery and the battery state, and a frequency of the battery having a plurality of cells to be determined; an impedance measuring device for measuring the impedance of a secondary battery having a plurality of cells to be determined by changing the frequency at a frequency interval of a fixed magnification; a slope θ[deg] calculation device for calculating a slope θ[deg] between two plotted points in a Nyquist plot created based on data acquired by the impedance measuring device; and a slope θ[deg] calculation device for calculating a minimum slope θ[deg] among the slopes θ[deg] calculated by the slope θ[deg] calculation device. min [deg] Minimum imaginary slope Zi at two points min An imaginary value Zi [mΩ] acquisition device for acquiring the minimum slope imaginary value Zi min Based on the relationship between the negative electrode discharge reserve variation Rs [Ah] and the imaginary value Zi [mΩ] acquisition device, the minimum slope imaginary value Zi min a negative electrode discharge reserve variation Rs[Ah] acquisition device that acquires a negative electrode discharge reserve variation Rs[Ah] from the negative electrode discharge reserve variation Rs[Ah] acquired in the step of acquiring the negative electrode discharge reserve variation Rs[Ah] based on the negative electrode discharge reserve variation Rs[Ah] / negative electrode capacity variation Cs[Ah] relationship; and a negative electrode capacity minimum value Cs[Ah] acquisition device that acquires the negative electrode capacity variation Cs[Ah] from the negative electrode discharge reserve variation Rs[Ah] acquired in the step of acquiring the negative electrode discharge reserve variation Rs[Ah] based on the negative electrode capacity variation Cs[Ah] acquired by the negative electrode capacity variation Cs[Ah] acquisition device. min [Ah] Minimum negative electrode capacity C min [Ah] The present invention is characterized by comprising a control device that functions as an acquisition device. Effect of the Invention

[0017] According to the method and device for determining the state of a secondary battery of the present invention, the states of the positive and negative electrodes of the secondary battery can be determined in a well-balanced manner. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a diagram showing an example of a Nyquist plot in impedance measurement. [Diagram 2]FIG. 2 is a diagram showing each region of a Nyquist plot and an equivalent circuit of a secondary battery corresponding to these regions. [Diagram 3] 1 is a diagram showing a nickel-metal hydride storage battery according to an embodiment of the present invention and six cell batteries that constitute the battery. [Figure 4] FIG. 2 is a schematic diagram showing the positive electrode capacity and the negative electrode capacity at the start of use. [Diagram 5] FIG. 2 is a schematic diagram showing a positive electrode capacity and a negative electrode capacity when deteriorated with use. [Figure 6] This figure shows a state in which the discharge reserve amount [Ah] of only one cell battery has become negative. [Figure 7] 1 is a block diagram showing the configuration of a nickel-metal hydride battery state determination system including a measurement charge / discharge device that measures the impedance of a nickel-metal hydride battery, and a state determination device that determines the state of the nickel-metal hydride battery. [Figure 8] 4 is a flowchart showing a procedure for determining the state of a nickel-metal hydride storage battery according to the present embodiment. [Figure 9] 1 is a graph showing an example of a Nyquist plot created based on the results of impedance measurement of the nickel-metal hydride storage battery of the present embodiment. [Figure 10] 1 is a graph showing the relationship between the real value Zr [mΩ] and the inclination θ [deg]. [Figure 11] 1 is a graph showing the relationship between the measurement frequency [Hz] and the slope θ [deg] between two points in a Nyquist plot. [Figure 12] 13 is a graph showing the relationship between the minimum slope imaginary value Zimin [mΩ] of the minimum slope θmin [deg] and the negative electrode discharge reserve variation Rs [Ah]. [Figure 13] 1 is a graph showing the relationship between the negative electrode discharge reserve minimum value Rmin [Ah] and the negative electrode capacity variation Cs [Ah]. [Figure 14] 1 is a graph showing the relationship between the negative electrode SOC and the imaginary value Zi [mΩ] in a transition region where the measurement frequency of impedance measurement is 1 [Hz]. [Figure 15]1 is a graph showing the relationship between the positive electrode SOC and the imaginary value Zi in a transition region where the measurement frequency of impedance measurement is 1 [Hz]. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, a secondary battery state determining method and device of the present invention will be described using one embodiment of a state determining method using a state determining system 10 for a nickel-metal hydride storage battery 1 with reference to FIGS.

[0020] (Outline of this embodiment) First, the principle of the state determination method (FIG. 8) using the state determination system 10 (FIG. 7) for the nickel-metal hydride storage battery 1 of this embodiment will be described.

[0021] As explained in the background art, testing the battery capacity by fully charging and then completely discharging takes time. Moreover, in the nickel-metal hydride storage battery 1 of this embodiment (FIG. 3), which is a battery module made up of, for example, six cell batteries 1a-1f, it is not possible to determine the individual states of the cell batteries 1a-1f.

[0022] Therefore, as shown in Patent Documents 1 to 4, a method has been proposed in which the state of a secondary battery is determined by measuring the AC impedance of the battery, which can be completed in a short time. <Impedance measurement> Here, we will briefly explain impedance measurement. Figure 1 shows an example of a Nyquist plot in impedance measurement. Figure 2 shows each region of the Nyquist plot and the equivalent circuit of the secondary battery corresponding to these regions. In both cases, the horizontal axis indicates the real value Zr [mΩ] and the vertical axis indicates the imaginary value Zi [mΩ].

[0023] As shown in Fig. 1, impedance curve L1 is an example of a Nyquist plot corresponding to a nickel-metal hydride storage battery 1 having a predetermined SOC (e.g., 40[%]). The impedance curve L1 is generated from a Nyquist plot in which the magnitudes of real component Zr and imaginary component Zi of complex impedance Z at a predetermined measurement frequency are plotted on a complex plane. The Nyquist plot is based on the complex impedance Z measured by changing the measurement frequency of the AC current supplied from the measurement charge / discharge device 20 to the nickel-metal hydride storage battery 1.

[0024] In FIG. 1, each point on the impedance curve L1 indicates one measurement frequency. In FIG. 1, the lower end side is the high frequency side, and the upper end side is the low frequency side. In this embodiment, the measurement frequency is changed sequentially at a uniform magnification between 100k [Hz] and 0.01 [Hz] to perform measurement. Specifically, the measurement frequency is changed uniformly between 100k [Hz] and 0.01 [Hz] to perform measurement at 39 points. The slope between two measured points is calculated and compared to obtain data for determining the state of the nickel-metal hydride storage battery 1. This is a feature of the present invention, which will be described in detail later.

[0025] The impedance curve L1 varies depending on the SOC and battery temperature of the nickel-metal hydride battery 1. Although the present embodiment illustrates a nickel-metal hydride battery 1, the present invention is not limited to this and can also be applied to secondary batteries such as lithium-ion secondary batteries, but the impedance curve L1 varies depending on the battery type. Furthermore, even for the same battery type, the impedance curve L1 varies when the number of cells, capacity, etc. are different.

[0026] Here, the impedance curve L1 of the nickel-metal hydride storage battery 1 will be described in detail with reference to Figs. 1 and 2. As shown in Fig. 1, the impedance curve L1 of the nickel-metal hydride storage battery 1 is divided into a plurality of regions corresponding to the characteristics of the nickel-metal hydride storage battery 1. The plurality of regions are divided into "region a", "region b", "region c", and "diffusion region d" from the high frequency side to the low frequency side of the measurement frequency. As shown in Fig. 2, "region a" is a circuit resistance region corresponding to the circuit resistance. "region b" is a solution resistance region corresponding to the solution resistance. "region c" is a reaction resistance region caused by reaction resistance. "region d" is a diffusion resistance region corresponding to a substantially linear diffusion resistance.

[0027] The circuit resistance in region a is the impedance of wiring, etc., consisting of the contact resistance in the active material and the current collector. The solution resistance in region b is the resistance to the movement of electrons, such as the resistance when ions move in the electrolyte in the separator. The reaction resistance in region c is the resistance to charge transfer in the electrode reaction. The diffusion resistance in region d is the impedance involved in material diffusion. Since each resistance influences each other, it is difficult to divide each of regions a, b, c, and d into only the parts affected by each resistance. However, at least the behavior of each of regions a, b, c, and d of the impedance curve L1 is roughly determined by the resistance component that is most affected by each of them. For example, "region c" is greatly influenced by the state of the negative electrode, and "region d" is greatly influenced by the state of the positive electrode.

[0028] Roughly speaking, the impedance curve L1 of the nickel-metal hydride storage battery 1 is a curve obtained by combining the impedance of the positive electrode and the impedance of the negative electrode. For example, in the frequency range corresponding to "region d", the impedance of the positive electrode changes significantly, while the change in the impedance of the negative electrode is small. In other words, "region d" of the impedance curve L1 is a region where the impedance of the positive electrode has a large influence, and it can be said that the state of the positive electrode is reflected. In contrast, in the frequency range corresponding to "region c", the impedance of the negative electrode changes significantly, while the change in the impedance of the positive electrode is small. In other words, "region c" of the impedance curve L1 is a region where the impedance of the negative electrode has a large influence, and it can be said that the state of the negative electrode is reflected.

[0029] For example, according to the impedance curve L1 in Figure 1, the frequency range corresponding to region d is 1 [Hz] or less, and the measurement results are shown up to 0.01 [Hz]. The frequency range corresponding to region c is greater than 1 [Hz] and less than 100 [Hz]. Incidentally, the frequency range corresponding to region b is 100 [Hz] or its vicinity, and the frequency range corresponding to region a is higher than 100 [Hz].

[0030] Therefore, in Patent Documents 1 to 4, the state of only the negative electrode or the state of the positive electrode is judged from the impedance curve in region c where the influence of the negative electrode is large or region d where the influence of the positive electrode is large. However, it is difficult to judge the state of the positive electrode and the state of the negative electrode simultaneously.

[0031] <Principle of the state determination method using the state determination system 10 for the nickel-metal hydride storage battery 1 according to the present embodiment> The inventors therefore made the following hypothesis and verified it to arrive at the method for determining the state of the nickel-metal hydride storage battery 1 of this embodiment.

[0032] FIG. 8 is a flowchart showing the procedure for determining the state of the nickel-metal hydride storage battery 1 of this embodiment. <Determining Secondary Battery State (S9)> Figure 13 shows the minimum negative electrode discharge reserve Rmin 1 is a graph showing the relationship between the negative electrode capacity variation Cs[Ah] and the negative electrode capacity variation Cs[Ah].

[0033] The inventors have determined that the deterioration of the negative electrode capacity [Ah] of the nickel-metal hydride storage battery 1 is mainly caused by a decrease in the amount of the negative electrode discharge reserve R. min The deterioration of the nickel-metal hydride storage battery 1 can be estimated by estimating the capacity [Ah].

[0034] However, the negative electrode discharge reserve minimum value R min The value of [Ah] cannot be measured immediately. Here, the negative electrode discharge reserve minimum value R min [Ah] has a strong correlation with the negative electrode capacity variation Cs [Ah] as shown in FIG. 13. Therefore, the negative electrode discharge reserve minimum value R min [Ah] was estimated from the negative electrode capacity variation Cs[Ah].

[0035] <About the negative electrode discharge reserve R> FIG. 3 shows the nickel-metal hydride storage battery 1 of this embodiment and six cell batteries 1a-1f constituting the battery. The nickel-metal hydride storage battery 1 of this embodiment is configured as a battery module in which six cell batteries 1a-1f are connected in series. Charging is performed by storing hydrogen ions in the hydrogen storage alloy MH of the negative electrode. FIG. 4 is a schematic diagram showing the positive electrode capacity and the negative electrode capacity at the start of use. The dashed line indicates that the positive electrode SOC is 0[%]. At the beginning of use, the battery capacity of the negative electrode is set to be larger than the battery capacity of the positive electrode so as to be so-called positive electrode regulation. This excess capacity of the negative electrode, which is larger than the positive electrode, is called the negative electrode discharge reserve R[Ah]. Therefore, it is possible to use 100[%] of the capacity of the positive electrode.

[0036] FIG. 5 is a schematic diagram showing the positive electrode capacity and the negative electrode capacity when it deteriorates with use. The dashed line indicates a positive electrode SOC of 0%. When the hydrogen storage alloy MH is used, it gradually collapses due to expansion and contraction caused by charging and discharging, and the amount of hydrogen ions that can be absorbed decreases. In addition, the battery capacity of the positive electrode may decrease for other reasons. If the capacity of the negative electrode is not deteriorated, hydrogen ions can be released at the limit of the capacity of the positive electrode during discharge. However, as shown in FIG. 5, the capacity of the negative electrode may decrease. In this case, even if the capacity of the positive electrode remains, the hydrogen ions that move from the negative electrode to the positive electrode during discharge are depleted, and discharging does not occur. In other words, the initial setting was a state of positive electrode regulation, but it becomes a state of negative electrode regulation, and as a result, the capacity of the entire battery module of the nickel-metal hydride storage battery 1 decreases. In addition, in such a state, the internal resistance of the battery becomes extremely large.

[0037] FIG. 6 shows a state where only the cell battery 1a has a negative discharge reserve [Ah]. The horizontal line indicates a state where the negative electrode discharge reserve R is zero, and above this horizontal line the negative electrode discharge reserve R is positive, and below this horizontal line the negative electrode discharge reserve R is negative, i.e. insufficient. For the reasons mentioned above, if the discharge reserve [Ah] of even one of the cell batteries 1a to 1f decreases, the entire nickel-metal hydride storage battery 1 will deteriorate. For the reasons mentioned above, the negative electrode capacity minimum value C min By estimating [Ah], the state of the nickel-metal hydride storage battery 1 can be determined.

[0038] <Negative electrode capacity minimum value C min [Ah]> However, it is difficult to measure the negative electrode capacity [Ah] of each of the cell batteries 1a to 1f in a short time. min In order to estimate the negative electrode capacity minimum value Cs[Ah] in a short time, min Here, according to the experiments of the present inventors, the value of the negative electrode capacity variation Cs [Ah] and the negative electrode capacity minimum value C minIt is known that there is a correlation between the negative electrode capacity variation Cs [Ah] and the negative electrode capacity minimum value C min [Ah] can be estimated and obtained.

[0039] <Negative electrode capacity minimum value C min [Ah] Acquisition step (S8)> In this embodiment, the negative electrode capacity variation Cs [Ah] and the negative electrode capacity minimum value C min The relationship with [Ah] is obtained in advance and stored in the storage means (S12).

[0040] The negative electrode capacity variation Cs [Ah] obtained in the step of obtaining the negative electrode capacity variation Cs [Ah] (Figure 8: S7) / the negative electrode capacity minimum value C min Based on the relationship, the negative electrode capacity minimum value C according to the negative electrode capacity variation Cs [Ah] min Get [Ah].

[0041] <Step of obtaining negative electrode capacity variation Cs [Ah] (S7)> So, how can the negative electrode capacity variation Cs [Ah] be obtained? In this embodiment, the negative electrode capacity variation Cs [Ah] is obtained by the following method.

[0042] In advance, for a battery of the same type as the nickel-metal hydride storage battery 1, the relationship between the negative electrode reserve variation Rs [Ah] and the negative electrode capacity variation Cs [Ah], that is, the negative electrode discharge reserve variation Rs [Ah] / negative electrode capacity variation Cs [Ah] is obtained (S11). Basically, the negative electrode capacity variation Cs [Ah] has a strong correlation with the negative electrode discharge reserve variation Rs [Ah]. Therefore, the negative electrode capacity variation Cs [Ah] can be estimated and obtained from the negative electrode discharge reserve variation Rs [Ah].

[0043] <Step (S6) of acquiring negative electrode discharge reserve variation Rs [Ah]> Figure 12 shows the minimum slope θ minMinimum slope imaginary value Zi in [deg] min 1 is a graph showing the relationship between the capacitance [mΩ] and the negative electrode discharge reserve variation Rs [Ah].

[0044] Here, the negative electrode discharge reserve variation Rs [Ah] can be obtained by the following method. According to the present inventors, as shown in FIG. 12, in a battery of the same type as the nickel-metal hydride storage battery 1 of the present embodiment, the minimum slope imaginary value Zi min It was found that there is a strong correlation between the negative electrode discharge reserve variation Rs [Ah] and the minimum slope imaginary value Zi min Based on the relationship [mΩ] / negative electrode discharge reserve variation Rs [Ah], the minimum slope imaginary value Zi min The negative electrode discharge reserve variation Rs [Ah] can be estimated from [mΩ].

[0045] <Minimum slope imaginary value Zi min [mΩ] Acquisition Step (S5)> Here, the minimum slope imaginary value Zi min [mΩ]" is the value calculated as follows. This "minimum slope imaginary value Zi min In order to obtain "Voltage [mΩ]", the impedance of the nickel-metal hydride storage battery 1 is measured (S2), and a Nyquist plot is created based on the values ​​measured in the impedance measurement (S3).

[0046] <Step (S4) of calculating the inclination θ [deg]> Fig. 9 shows an example of a Nyquist plot created based on the results of impedance measurement of the nickel-metal hydride storage battery 1 of this embodiment. As shown in Fig. 1, the Nyquist plot can be divided into regions a to d. In the Nyquist plot, the angle between the horizontal axis and a straight line connecting two consecutive plot points with different frequencies is defined as the "slope θ [deg]."

[0047] FIG. 10 is a graph showing the relationship between the real value Zr [mΩ] and the slope θ [deg]. As shown in FIG. 9 and FIG. 10, in the Nyquist plot, when the imaginary value Zi=0, the slope θ is 90 [deg], and in the region a on the lower high frequency side in FIG. 9 where the imaginary value Zi<0, the slope θ [deg] slopes downward to the right and becomes a negative value. In the region c where the imaginary value Zi>0, the slope becomes arc-shaped, and the slope θ [deg] slopes upward from 90 [deg] to the right and gradually changes to approach the horizontal of 0 [deg]. Furthermore, in the region d on the low frequency side, the slope becomes a straight line extending from the arc in the region c to the upper right.

[0048] <About the transition region> In this embodiment, the portion that transitions from region c to region d is called the "transition region cd." As described above, region c is heavily influenced by the negative electrode, and region d is heavily influenced by the negative electrode. This transition region cd is simultaneously influenced by the positive electrode and the negative electrode. Therefore, by analyzing the nickel-metal hydride storage battery 1 based on the impedance in this transition region cd, an analysis that simultaneously reflects the influences of the positive electrode and the negative electrode can be performed.

[0049] The horizontal axis indicates the real value Zr [mΩ] in Figure 9, and the vertical axis indicates the gradient θ [deg] between the two points at that time. The transition region cd is the position where the gradient θ [deg] changes, in other words, the downward apex of the gradient θ [deg]. Therefore, the part with the minimum gradient θ [deg] between region c and region d in Figure 10 can be determined to be the transition region cd.

[0050] In FIG. 9, the slope θ [deg] of the line connecting plot point P1 and plot point P2 is the minimum slope θ min [deg], it is determined that the transition region cd is between plot point P1 and plot point P2.

[0051] <Dependence of SOC[%] in the transition region cd> Fig. 11 is a graph showing the relationship between the measurement frequency [Hz] and the slope θ [deg] between two points in the Nyquist plot. The horizontal axis shows the measurement frequency [Hz] applied in impedance determination, and the vertical axis shows the angle θ [deg] with respect to the horizontal axis of the line connecting two consecutive plot points at that time, as shown in Fig. 9.

[0052] As shown in Figure 11, the transition region cd appears at a measurement frequency of approximately 1 [Hz]. Therefore, the imaginary value Zi [mΩ] at this 1 [Hz] was measured for each SOC [%] for the negative and positive electrodes.

[0053] FIG. 14 is a graph showing the relationship between the negative electrode SOC and the imaginary value Zi [mΩ] in the transition region where the measurement frequency of the impedance measurement is 1 [Hz]. As shown in FIG. 14, when the frequency is 1 [Hz], the resistance increases in the low SOC region near SOC 0 [%]. Also, at SOC 10 [%], the resistance is the smallest. Also, when the SOC is 10 [%] or more, the resistance increases almost linearly up to about SOC 60 [%] as the SOC increases. In other words, if there is a large variation in the negative electrode capacity of the cell batteries 1a to 1f, the SOC [%] will differ greatly between the cell batteries 1a to 1f when measured at a frequency of about 1 [Hz]. Then, the cell batteries 1a to 1f in the same module will have high SOC and low SOC. If there is a large variation in SOC [%], the resistance value will differ greatly between the cell batteries 1a to 1f. As a result, the internal resistance of the entire module of the nickel-metal hydride storage battery 1 will increase.

[0054] Figure 15 is a graph showing the relationship between the positive electrode SOC and the imaginary value Zi in the transition region where the measurement frequency of the impedance measurement is 1 [Hz]. As shown in Figure 15, the influence of the positive electrode, when the frequency is 1 [Hz], the resistance rises in the low SOC region near SOC 0 [%]. As the positive electrode SOC [%] increases, the resistance gradually decreases, and the change becomes small from about 60 [%]. In a cell battery with a large negative electrode discharge reserve R [Ah], the capacity of the opposing positive electrode is relatively low, and the positive electrode SOC [%] tends to be large.

[0055] As a result, in impedance measurement, by measuring the imaginary value Zi [mΩ] per 1 [Hz], which is the transition region cd, it is possible to measure the value influenced by both positive and negative poles.

[0056] In this manner, the imaginary value Zi [mΩ] in the transition region cd where the frequency is near 1 [Hz] in this embodiment is particularly affected by both the positive electrode SOC [%] and the negative electrode SOC [%]. For this reason, the minimum slope imaginary value Zi min By calculating and analyzing [deg], it becomes possible to determine the state of the positive and negative electrodes of the nickel-metal hydride storage battery 1 in a well-balanced manner.

[0057] <Minimum slope imaginary value Zi min Determination of [mΩ]> In this embodiment, the minimum inclination θ [deg] among the inclinations θ [deg] calculated in the step of calculating the inclination θ [deg] is min [deg] at two points, the imaginary value Zi [mΩ] is the minimum slope imaginary value Zi min Obtained as [mΩ].

[0058] Here, the minimum slope θ min [deg] is specified by plot points P1 and P2 in FIG. 9. Here, the minimum slope imaginary value Zi min The following method can be considered. First, the smaller (or larger) value of the imaginary value Zi of the plot points P1 and P2 is taken as the minimum slope imaginary value Zi min [mΩ]. The imaginary values ​​Zi of the plot points P1 and P2 are averaged to obtain the minimum slope imaginary value Zi min The value is expressed as [mΩ].

[0059] <Characteristics of state determination of nickel-metal hydride storage battery 1 according to this embodiment> As described above, according to the research of the present inventors, the state of the nickel-metal hydride storage battery 1 is the negative electrode capacity minimum value C min It was found through experiments that the capacity can be determined by the negative electrode capacity minimum value C [Ah], which cannot be measured directly. min[Ah] is the minimum slope imaginary value Zi min It was also analyzed that there is a certain relationship with the minimum slope imaginary value Zi min If [mΩ] can be obtained, the minimum negative electrode capacity C can be obtained by following certain steps. min It was also found that the impedance [Ah] can be obtained. Based on such findings by the inventors, the method for determining the state of the nickel-metal hydride storage battery 1 according to the present embodiment is characterized in that the state of the nickel-metal hydride storage battery 1 can be easily determined simply by measuring the impedance.

[0060] (Configuration of this embodiment) <Nickel-metal hydride battery 1 state determination system 10> FIG. 7 is a block diagram showing the configuration of a system 10 for determining a state of a nickel-metal hydride storage battery 1 that includes a measurement circuit for measuring the impedance of the nickel-metal hydride storage battery 1 and a state determination device 30 for determining the state of the nickel-metal hydride storage battery 1.

[0061] <Measurement circuit> 7, the measurement circuit for measuring the impedance of the nickel-metal hydride battery 1 includes the nickel-metal hydride battery 1 and a measurement charge / discharge device 20 that supplies a direct current and an alternating current between the terminals of the nickel-metal hydride battery 1. The measurement circuit also includes a voltage meter 21 that measures the voltage between the terminals of the nickel-metal hydride battery 1, and a current meter 22 that measures the current flowing between the measurement charge / discharge device 20 and the nickel-metal hydride battery 1.

[0062] <Measurement charging / discharging device 20> The measurement charging / discharging device 20 can charge a predetermined amount of direct current to the nickel-metal hydride storage battery 1, and can discharge a predetermined amount of direct current from the nickel-metal hydride storage battery 1. In other words, the measurement charging / discharging device 20 can adjust the SOC (charged electricity amount) of the nickel-metal hydride storage battery 1.

[0063] The measurement charging / discharging device 20 can also supply an AC current for impedance measurement to the nickel-metal hydride storage battery 1. The measurement charging / discharging device 20 generates an AC current of a predetermined measurement frequency and outputs the generated AC current between the terminals of the nickel-metal hydride storage battery 1. The waveform of the AC current is not limited to a sine wave, and other waveforms such as a rectangular wave can also be used. The measurement charging / discharging device 20 can also change the measurement frequency of the AC current. The measurement charging / discharging device 20 is set with a frequency range of an output current and a measurement frequency, and outputs the AC current of the set output current as a measurement frequency that changes within the same set frequency range. The set frequency range is, for example, from 100 kHz on the high frequency side to 0.01 Hz on the low frequency side. However, it is not limited to this, and the high frequency side may be higher than 100 kHz, and the low frequency side may be lower than 0.01 Hz. However, it is necessary to output in detail the target frequency range, that is, the range around 1 [Hz] in this embodiment, for the "transition region cd" near plot points P1 and P2 shown in Fig. 9. In addition, in order to determine the transition region cd, the frequency must cover the region d, which is the diffusion resistance region, and the region c, which is the reaction resistance region.

[0064] Measurement charging / discharging device 20 outputs signals relating to the set value of the AC current being output and the set value of the measurement frequency to state determination device 30. Furthermore, measurement charging / discharging device 20 switches between outputting and stopping the AC current in response to an output start signal and an output stop signal input from state determination device 30.

[0065] The voltage measuring device 21 outputs to the state determining device 30 a voltage signal corresponding to the AC voltage and DC voltage measured between the electrodes of the nickel-metal hydride storage battery 1 . The current measuring device 22 outputs to the state determining device 30 a current signal corresponding to the AC current and DC current measured between the measuring charge / discharge device 20 and the nickel-metal hydride storage battery 1 .

[0066] The nickel-hydrogen storage battery 1 is equipped with a temperature measuring device 23 that measures the temperature of the battery. The temperature measuring device 23 outputs a temperature signal corresponding to the measured temperature of the nickel-hydrogen storage battery 1 to the state determination device 30.

[0067] <State determination device 30> The state determination device 30 determines the state of the nickel-hydrogen storage battery 1. Specifically, it estimates the amount of negative electrode discharge reserve R [Ah], and preliminarily excludes the nickel-hydrogen storage battery 1 with insufficient amount of negative electrode discharge reserve R [Ah] from the product, thereby reducing the burden of time-consuming charge and discharge inspections.

[0068] The state determination device 30 acquires the terminal voltage of the nickel-hydrogen storage battery 1 based on the voltage signal input from the voltage measuring device 21, and acquires the current flowing between the measurement charge and discharge device 20 and the nickel-hydrogen storage battery 1 based on the current signal input from the current measuring device 22. The state determination device 30 acquires setting information of the alternating current, etc. from the signal input from the measurement charge and discharge device 20. The state determination device 30 acquires the temperature of the nickel-hydrogen storage battery 1 based on the temperature signal input from the temperature measuring device 23.

[0069] The state determination device 30 includes a processing unit 40 and a storage unit 50. <Processing unit 40> The processing unit 40 is configured to include a computer equipped with a CPU, a ROM, and a RAM. And the processing unit 40 exhibits the following functions according to the stored program. That is, the SOC adjustment unit 41, the temperature measurement unit 42, the impedance measurement unit 43, the Nyquist diagram creation unit 44, Zi min The acquisition unit 45, the Rs acquisition unit 46, the Cs acquisition unit 47, C min The acquisition unit 48, the state determination unit 49 function as such. These correspond to the impedance measurement device, the inclination θ [deg] calculation device, the imaginary value Zi [mΩ] acquisition device, the negative electrode discharge reserve variation Rs [Ah] acquisition device, the negative electrode capacity variation Cs [Ah] acquisition device, and the negative electrode capacity minimum value C min [Ah] acquisition device of the present invention.

[0070] <SOC adjustment unit 41> The SOC adjustment unit 41 adjusts the nickel-metal hydride battery 1 to a predetermined SOC by instructing the charge and discharge of current to the measurement charge and discharge device 20.

[0071] <Temperature measurement unit 42> The temperature measurement unit 42 measures the temperature of the nickel-metal hydride battery 1 with the temperature measuring device 23. <Impedance measurement unit 43> The impedance measurement unit 43 measures the impedance by applying an alternating current while changing the frequency at a constant magnification frequency interval to the nickel-metal hydride battery 1.

[0072] <Nyquist plot creation unit 44> The Nyquist plot creation unit 44 creates a Nyquist plot as shown in FIG. 9 based on the data acquired by the impedance measurement unit 43.

[0073] <Zi min Acquisition unit 45> In the Nyquist plot created by the Nyquist plot creation unit 44, the slope θ [deg] between the two plotted points is calculated. Among the calculated slopes θ [deg], the minimum slope θ min [deg] at the two points of the minimum slope imaginary value Zi min [mΩ] is acquired.

[0074] <Rs acquisition unit 46> In the Rs acquisition unit 46, the Zi in the storage unit 50 min / Rs relationship 51 stores the minimum slope imaginary value Zi min [mΩ] / negative electrode discharge reserve variation Rs [Ah] relationship is referred to. Then, the negative electrode discharge reserve variation Rs [Ah] is acquired from the minimum slope imaginary value Zi min [mΩ] acquired by the imaginary value acquisition device.

[0075] <Cs acquisition unit 47> The Cs acquisition unit 47 refers to the relationship of the negative electrode discharge reserve variation Rs [Ah] / negative electrode capacity variation Cs [Ah] stored in the Rs / Cs relationship 52 in the memory unit 50. Based on this, the negative electrode capacity variation Cs [Ah] is acquired from the negative electrode discharge reserve variation Rs [Ah] acquired in the step of acquiring the negative electrode discharge reserve variation Rs [Ah].

[0076] <C min Acquisition section 48> C min [Ah] The acquisition unit 48 acquires the Cs / C min Refer to the relationship 53. Based on this, the negative electrode capacity minimum value C min Get [Ah].

[0077] <State determination unit 49> The state determination unit 49 refers to the determination threshold value 54 in the memory unit 50. Based on these, the negative electrode capacity minimum value C min [Ah] The minimum negative electrode capacity obtained in the step of obtaining min [Ah] is compared with a preset threshold value to determine whether the secondary battery being judged is in good condition.

[0078] <Storage section 50> The storage unit 50 stores, in a storage medium such as a hard disk or SSD, Zi min / Rs relationship 51, Rs / Cs relationship 52, Cs / C min The data on the relationship 53 and the decision threshold 54, as well as other programs and data, are stored.

[0079] <Zi min / Rs51> Zi min The / Rs relationship 51 is a relationship that is determined in advance based on the minimum slope imaginary value Zi min The relationship between the resistance [mΩ] and the variation Rs [Ah] in the negative electrode discharge reserve is stored, for example, in the form of a storage table.

[0080] <Rs / Cs Relationship 52> In a battery of the same type as the nickel-metal hydride battery 1 that is the object of state determination in advance, the relationship between the negative electrode discharge reserve variation Rs [Ah] / the negative electrode capacity variation Cs [Ah] is stored, for example, in the form of a memory table. The relationship between the negative electrode discharge reserve variation Rs [Ah] / the negative electrode capacity variation Cs [Ah] is the relationship between the negative electrode discharge reserve variation Rs [Ah] and the negative electrode capacity variation Cs [Ah].

[0081] <Cs / C min Relationship 53> In a battery of the same type as the nickel-metal hydride battery 1 that is the object of state determination in advance, the relationship between the negative electrode capacity variation Cs [Ah] and the minimum negative electrode capacity C min [Ah] is stored, for example, in the form of a memory table.

[0082] <Determination Threshold 54> In a battery of the same type as the nickel-metal hydride battery 1 that is the object of state determination in advance, a preset threshold value for determining pass / fail by comparing with the negative electrode capacity variation Cs [Ah] obtained in the step of obtaining the negative electrode capacity variation Cs [Ah] is stored.

[0083] <Procedure for Determining the State of the Nickel-Metal Hydride Battery 1 of the Present Embodiment> With the state determination system 10 of the nickel-metal hydride battery 1 having the configuration as described above, as shown in FIG. 8, the state of the nickel-metal hydride battery 1 is determined by the following procedure.

[0084] In determining the state of the nickel-metal hydride battery 1 of the present embodiment, first, necessary data for the secondary battery to be inspected is collected and stored. Specifically, it is each procedure of "acquiring the relationship between the minimum slope imaginary value Z min [mΩ] / the negative electrode discharge reserve variation Rs [Ah] (S10)", "acquiring the relationship between the negative electrode discharge reserve variation Rs [Ah] / the negative electrode capacity variation Cs [Ah] (S11)", "acquiring the relationship between the negative electrode capacity variation Cs [Ah] / the minimum negative electrode capacity C min [Ah] (S12)", and "setting the secondary battery determination threshold (S13)".

[0085] After the above steps S10 to S13 are completed, the actual state of the nickel-metal hydride storage battery 1 is determined. <Battery Acceptance Classification (S1)> If necessary, data to be called up from the storage unit 50 is selected for the secondary battery to be inspected.

[0086] <Impedance measurement (S2)> The impedance of the secondary battery to be inspected is measured. <Nyquist plot creation (S3)> A Nyquist plot is created based on the data acquired in the impedance measurement (S2) procedure.

[0087] <Calculation of tilt θ [deg] (S4)> The gradient θ [deg] between the two points of the Nyquist plot created in the Nyquist plot creation procedure (S3) is calculated.

[0088] <Minimum slope θ min Minimum slope imaginary value Zi in [deg] min [mΩ] acquisition (S5)> Among the inclinations θ [deg] calculated in the inclination θ [deg] calculation (S4) step, the minimum inclination θ min Get [deg].

[0089] In addition, the obtained tilt θ min The minimum slope imaginary value Zi [mΩ] based on plot points P1 and P2 in the Nyquist plot of [deg] min Get [deg].

[0090] <Obtain negative electrode discharge reserve variation Rs [Ah] (S6)> Minimum slope θ min Minimum slope imaginary value Zi in [deg] min [mΩ] The imaginary value Zi obtained in the procedure (S5) min [deg] to Zi minThe negative electrode discharge reserve variation Rs [Ah] is obtained based on the / Rs relationship 51.

[0091] <Obtain negative electrode capacity variation Cs [Ah] (S7)> The negative electrode capacity variation Cs [Ah] is obtained based on the Rs / Cs relationship 52 from the negative electrode capacity variation Rs [Ah] obtained in the procedure of obtaining the negative electrode discharge reserve variation Rs [Ah] (S6).

[0092] <Negative electrode capacity minimum value C min [Ah] Acquisition (S8)> From the negative electrode capacity variation Cs [Ah] obtained in the procedure of obtaining the negative electrode capacity variation Cs [Ah] (S7), Cs / C min Based on the relationship 53, the negative electrode capacity minimum value C min Get [Ah].

[0093] <Battery state determination (S9)> Negative electrode capacity minimum value C min [Ah] The minimum negative electrode capacity C obtained in the procedure (S8) min From [Ah], the state of the nickel-metal hydride storage battery 1, which is the secondary battery to be inspected, is judged based on the judgment threshold 54. Based on this judgment, it is decided whether or not the nickel-metal hydride storage battery 1 has standard performance as a product. If it is determined that it has the standard performance, it moves to the next step of detailed inspection as a product. If it is determined that it has the standard performance, it is excluded as a defective product and does not move to the next step of detailed inspection.

[0094] (Action of this embodiment) In the method for determining the state of the nickel-metal hydride storage battery 1 of this embodiment, the state of both the positive and negative electrodes of the nickel-metal hydride storage battery 1 can be determined simply by performing impedance measurement, without measuring the battery capacity from full charge to full discharge, which takes time.

[0095] (Effects of this embodiment) (1) The method for determining the state of the nickel-metal hydride storage battery 1 and the system 10 for determining the state of the nickel-metal hydride storage battery 1 according to the present embodiment have the advantage of being able to determine the states of the positive and negative electrodes of the secondary battery in a well-balanced manner.

[0096] (2) In particular, the minimum negative electrode capacity C can be determined by impedance measurement alone, which can be completed in a relatively short time. min It is possible to estimate the battery capacity [Ah] and determine the battery condition. Therefore, by using it for a preliminary test before the test that measures the battery capacity from full charge to full discharge, which takes time, the efficiency of the entire test can be improved.

[0097] (3) In the method for determining the state of the nickel-metal hydride storage battery 1 according to the present embodiment, the negative electrode capacity minimum value C min [Ah] The minimum negative electrode capacity obtained in the step of obtaining min [Ah] is compared with a preset threshold value to judge the quality of the secondary battery. min This has the effect of making it possible to determine the state of the nickel-metal hydride storage battery 1 based on [Ah].

[0098] (4) Minimum negative electrode capacity C min [Ah] is the negative electrode capacity variation Cs [Ah] / negative electrode capacity minimum value C min Based on the relationship, the negative electrode capacity minimum value C according to the negative electrode capacity variation Cs [Ah] min [Ah] is obtained. Therefore, the negative electrode capacity minimum value C min This has the effect of enabling the negative electrode capacity variation Cs[Ah] to be accurately estimated based on the negative electrode capacity variation Cs[Ah].

[0099] (5) The negative electrode capacity variation Cs [Ah] is determined by comparing the negative electrode capacity variation Cs [Ah] and the negative electrode capacity minimum value C min Therefore, the relationship between the negative electrode capacity variation Cs[Ah] and the negative electrode capacity minimum value C min This has the effect of enabling accurate estimation of [Ah].

[0100] (6) The negative electrode capacity variation Cs [Ah] can be easily obtained based on the relationship of the negative electrode discharge reserve variation Rs [Ah] / negative electrode capacity variation Cs [Ah]. The relationship of the negative electrode discharge reserve variation Rs [Ah] / negative electrode capacity variation Cs [Ah] is obtained in advance by experimentation on a battery of the same type as the nickel-metal hydride storage battery 1, the state of which is to be determined. This has the effect of easily and accurately estimating the negative electrode capacity variation Cs [Ah].

[0101] (7) The negative electrode discharge reserve variation Rs [Ah] is the minimum slope imaginary value Zi min [mΩ] / negative electrode discharge reserve variation Rs [Ah] relationship minimum slope imaginary value Zi min This has the effect of easily and accurately obtaining the value from [mΩ].

[0102] Also, the minimum slope imaginary value Zi min The relationship between the negative electrode discharge reserve variation Rs [Ah] and the negative electrode discharge reserve variation Rs [mΩ] is obtained in advance by experimentation on a battery of the same type as the nickel-metal hydride storage battery 1, the state of which is to be determined. This has the effect of easily and accurately estimating the negative electrode discharge reserve variation Rs [Ah].

[0103] (8) Minimum slope imaginary value Zi min [mΩ] is calculated by calculating the slope θ [deg] between two plotted points in a Nyquist plot created based on data obtained by impedance measurement. Among these slopes θ [deg], the minimum slope θ min [deg] at two points, the imaginary value Zi [mΩ] is the minimum slope imaginary value Zi min Therefore, the minimum slope imaginary value Zi min This has the effect of enabling the acquisition of [mΩ].

[0104] (9) Minimum slope imaginary value Zi min[mΩ] is data acquired in the transition region cd, and reflects both the positive and negative electrode states of each cell battery. Therefore, in a battery module equipped with multiple cell batteries, the data reflects the difference in negative electrode SOC [%] due to the difference in the negative electrode discharge reserve. As a result, it is possible to determine whether any of the cell batteries has deteriorated by simply measuring the impedance of the entire nickel-metal hydride storage battery 1, which is a battery module.

[0105] (Modification) In the present embodiment, a nickel-metal hydride battery 1 has been described as an example of a secondary battery. However, the secondary battery is not limited to the nickel-metal hydride battery 1 and can be other alkaline electrolyte secondary batteries, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries, etc.

[0106] Although the nickel-metal hydride storage battery 1 of the present embodiment has been described taking as an example a battery module including six cell batteries 1a to 1f, the configuration is not limited as long as the battery includes a plurality of unit cells.

[0107] The configuration of the impedance measurement is not particularly limited as long as the target impedance can be measured, and the applied voltage, current, application time, waveform, frequency interval, etc. can be appropriately selected by those skilled in the art.

[0108] In this embodiment, the transition region cd is in the vicinity of 1 [Hz]. However, depending on the type of secondary battery, the frequency may be, for example, 0.1 [Hz]. min [deg] is approximately 0 [deg] (approximately horizontal), but may have a positive (upward to the right) or negative (downward to the right) inclination.

[0109] The numerical values ​​and numerical ranges exemplified in the embodiments do not limit the present invention, and may be optimized as appropriate by those skilled in the art depending on the secondary battery to be tested. ○ In the step of obtaining the imaginary value Zi [mΩ], the minimum slope θ [deg] among the slopes θ [deg] calculated in the step of calculating the slope θ [deg] is min [deg] Minimum imaginary slope Zi at two points min [mΩ] is the minimum slope θ min It may be possible to obtain the value by taking the average value of two points of [deg] or the higher value.

[0110] The flowchart shown in Fig. 8 is one example of the method for determining the state of a secondary battery of the present invention, and the method for determining the state of a secondary battery of the present invention is not limited to such a procedure. Those skilled in the art can add or delete appropriate procedures, change the order of the procedures, or replace the procedures with other equivalent procedures.

[0111] The graphs shown in the drawings are shown to explain the state determination method of this embodiment, and do not need to be actually visualized, but may be processed on the data. In addition, it goes without saying that those skilled in the art can add, delete, or modify the configuration of the present invention without departing from the scope of the claims. [Explanation of symbols]

[0112] 1...Nickel metal hydride battery 1a~1f…cell battery (single cell) L1…Impedance curve 1... Nickel-metal hydride battery (battery module) 10...Nickel-metal hydride battery status determination system 20…Charging / discharging device for measurement 21...Voltage measuring instrument 22...Current measuring device 23…Temperature measuring device 30...Status determination device 40... Processing section 41...SOC adjustment section 42...Temperature measurement section 43...Impedance measurement section 44…Nyquist diagram creation section 45…Zi min Acquisition department 46…Rs acquisition department 47…Cs acquisition department 48…C min Acquisition department 49…Status determination section 50...Storage section 51…Zi min / Rs 52…Rs / Cs relationship 53…Cs / C min relationship 54…Decision threshold a~d…area cd…transition area θ[deg]...inclination θ min [deg]…Minimum inclination Zi [mΩ]…imaginary value Zi min [mΩ]…Minimum slope imaginary value R[Ah]…Negative discharge reserve Rs [Ah]…Negative electrode discharge reserve variation R min [Ah]…Negative electrode discharge reserve minimum value C min [Ah]…Negative electrode capacity minimum value Cs[Ah]…Negative electrode capacity variation

Claims

1. an impedance measurement step of measuring the impedance of a secondary battery having a plurality of cells as a state determination target, while changing the frequency at a frequency interval of a fixed magnification; a step of calculating a slope θ [deg] between two plotted points in a Nyquist plot created based on the data acquired in the impedance measurement step; Among the inclinations θ [deg] calculated in the step of calculating the inclination θ [deg], the minimum inclination θ ｍｉｎ The imaginary value Zi [mΩ] at two points of [deg] is the minimum slope imaginary value Zi ｍｉｎ The minimum slope imaginary value Zi to be obtained as [mΩ] ｍｉｎ [mΩ] acquisition step; The minimum slope imaginary value Zi ｍｉｎ [mΩ] The minimum slope imaginary value Zi obtained in the acquisition step ｍｉｎ Based on [mΩ], the negative electrode capacity minimum value C ｍｉｎ Minimum negative electrode capacity C for obtaining [Ah] ｍｉｎ [Ah] acquisition step and A method for determining a state of a secondary battery, comprising:

2. The minimum slope imaginary value Zi in a battery of the same type as the secondary battery whose state is to be judged in advance ｍｉｎ [mΩ] and the negative electrode discharge reserve variation Rs [Ah], which is the relationship between the imaginary value of the minimum slope Zi ｍｉｎ [mΩ] / negative electrode discharge reserve variation Rs [Ah] Minimum slope imaginary value Zi to obtain the relationship ｍｉｎ [mΩ] / negative electrode discharge reserve variation Rs [Ah] relationship acquisition step; The minimum slope imaginary value Zi ｍｉｎ [mΩ] / negative electrode discharge reserve variation Rs [Ah] Minimum slope imaginary value Zi acquired in the step of acquiring the relationship ｍｉｎ Based on the relationship [mΩ] / negative electrode discharge reserve variation Rs [Ah], the minimum slope imaginary value Zi ｍｉｎ [mΩ] The minimum slope imaginary value Zi obtained in the acquisition step ｍｉｎ a step of acquiring a negative electrode discharge reserve variation Rs [Ah] from the negative electrode discharge reserve variation Rs [Ah]; a step of acquiring a negative electrode discharge reserve variation Rs [Ah] / negative electrode capacity variation Cs [Ah] relationship, which is a relationship between the negative electrode discharge reserve variation Rs [Ah] and the negative electrode capacity variation Cs [Ah], in a battery of the same type as the secondary battery whose state is to be determined in advance; a step of acquiring a negative electrode capacity variation Cs [Ah] from the negative electrode discharge reserve variation Rs [Ah] acquired in the step of acquiring the negative electrode discharge reserve variation Rs [Ah] based on the negative electrode discharge reserve variation Rs [Ah] / negative electrode capacity variation Cs [Ah] relationship acquired in the step of acquiring the negative electrode discharge reserve variation Rs [Ah] relationship; In a battery of the same type as the secondary battery whose state is to be judged in advance, the negative electrode capacity variation Cs [Ah] and the negative electrode capacity minimum value C ｍｉｎ [Ah] to obtain the relationship between the negative electrode capacity variation Cs [Ah] / negative electrode capacity minimum value C ｍｉｎ [Ah] A step of acquiring a relationship; Based on the negative electrode capacity variation Cs [Ah] / negative electrode capacity minimum value Cmin [Ah] relationship acquired in the step of acquiring the negative electrode capacity variation Cs [Ah], ｍｉｎ Minimum negative electrode capacity C for obtaining [Ah] ｍｉｎ [Ah] acquisition step and The method for determining a state of a secondary battery according to claim 1, further comprising:

3. The negative electrode capacity minimum value C ｍｉｎ [Ah] The minimum negative electrode capacity C obtained in the step of obtaining ｍｉｎ The secondary battery state determination method according to claim 1 or 2, characterized in that it includes a secondary battery state determination step of comparing [Ah] with a preset threshold value to determine whether the state of the secondary battery being determined is good or bad.

4. The secondary battery state determination method according to claim 1 or 2, characterized in that the impedance measurement step measures the impedance by sequentially changing the measurement frequency at a uniform rate at least between 100 [Hz] and 0.01 [Hz].

5. In the step of acquiring the imaginary value Zi [mΩ], the minimum gradient θ among the gradients θ [deg] calculated in the step of calculating the gradient θ [deg] is ｍｉｎ Minimum slope imaginary value Zi at two points [deg] ｍｉｎ [mΩ] is the minimum slope θ ｍｉｎ The lower imaginary value Zi [mΩ] of the two points [deg] is the minimum slope imaginary value Zi ｍｉｎ 3. The method for determining the state of a secondary battery according to claim 2, wherein the measured value is obtained as [mΩ].

6. 3. The method for determining a state of a secondary battery according to claim 1, wherein the secondary battery is a nickel-metal hydride battery.

7. A secondary battery state determination device including a computer, The imaginary value Zi of the minimum slope at two points of the minimum slope θ [deg] in a battery of the same type as the secondary battery whose state is to be judged in advance ｍｉｎ [mΩ] and the negative electrode discharge reserve variation Rs [Ah], which is the relationship between the imaginary value of the minimum slope Zi ｍｉｎ [mΩ] / negative electrode discharge reserve variation Rs [Ah] relationship; A negative electrode discharge reserve variation Rs [Ah] / negative electrode capacity variation Cs [Ah] relationship, which is a relationship between the negative electrode discharge reserve variation Rs [Ah] and the negative electrode capacity variation Cs [Ah] in a battery of the same type as the secondary battery whose state is to be determined in advance; In a battery of the same type as the secondary battery whose state is to be judged in advance, the negative electrode capacity variation Cs [Ah] and the negative electrode capacity minimum value C ｍｉｎ The relationship with [Ah] A storage means for storing the an impedance measuring device for measuring the impedance of a secondary battery having a plurality of cells as a state judgment target, by changing a frequency at a frequency interval of a fixed magnification; a slope θ [deg] calculation device that calculates a slope θ [deg] between two plotted points in a Nyquist plot created based on data acquired by the impedance measuring device; The minimum inclination θ among the inclinations θ [deg] calculated by the inclination θ [deg] calculation device ｍｉｎ Minimum slope imaginary value Zi at two points [deg] ｍｉｎ An imaginary value Zi [mΩ] acquisition device for acquiring an imaginary value Zi [mΩ]; The minimum slope imaginary value Zi ｍｉｎ Based on the relationship between negative electrode discharge reserve variation Rs [Ah] and the imaginary value Zi [mΩ] acquisition device, the minimum slope imaginary value Zi [mΩ] is obtained. ｍｉｎ a negative electrode discharge reserve variation Rs [Ah] acquisition device that acquires a negative electrode discharge reserve variation Rs [Ah] from [mΩ]; a negative electrode capacity variation Cs [Ah] acquisition device that acquires the negative electrode capacity variation Cs [Ah] from the negative electrode discharge reserve variation Rs [Ah] acquired in the step of acquiring the negative electrode discharge reserve variation Rs [Ah] based on the negative electrode discharge reserve variation Rs [Ah] / negative electrode capacity variation Cs [Ah] relationship; A negative electrode capacity minimum value C according to the negative electrode capacity variation Cs [Ah] acquired by the negative electrode capacity variation Cs [Ah] acquisition device ｍｉｎ Minimum negative electrode capacity C for obtaining [Ah] ｍｉｎ [Ah] A control device that functions as an acquisition device; A secondary battery state determination device comprising:

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