JP2022108675A - Battery deterioration determination device, and battery deterioration determination method - Google Patents

Abstract

To provide a battery deterioration determination device and battery deterioration determination method that can determine a state of health in progress of a battery.SOLUTION: A battery deterioration determination device 100 comprises: a cooling control unit 22 that controls an environment temperature of a battery to a measurement temperature equal to or lower than 15°C within any temperature range centering around a point where an allocation rate between solution resistance or ion movement resistance of preliminarily set AC impedance and charge movement resistance thereof is comparable; a battery AC impedance measurement device 120 that measures AC impedance data on the battery at the measurement temperature; and a battery deterioration determination unit 160 that determines a deterioration degree of the battery in comparison of measurement data which the battery AC impedance measurement device 120 measures with reference AC impedance data preliminarily measured under the same conditions as those of a reference battery.SELECTED DRAWING: Figure 8

Description

There is an application for the application of Article 30, Paragraph 2 of the Patent Act. IVCST website address https://ivcst. sut. ac. th/2020/conference-programs Website publication date August 20, 2020 2. IVCST online oral presentation website address https://ivcst. sut. ac. th/2020/conference-programs Announcement date August 25, 2020 3. JIME website address https://ivcst. sut. ac. th/2020/conference-programs Website publication date October 22, 2020 4. JIME 90th (2020) Marine Engineering Scientific Lecture Proceedings Distribution date October 22, 2020 5. JIME 90th (2nd year of Reiwa) Marine Engineering Academic Lecture Online Lecture Distribution date October 22nd, 2020 5. Suzuki Foundation 2020 Annual Report Publication date December 22, 2020 6. Suzuki Foundation website address http://www. suzuki found. jp/03public/annualreport/2020/top. html Website publication date December 25, 2020

TECHNICAL FIELD The present invention relates to a battery deterioration determination device and a battery deterioration determination method for determining the deterioration state of a lithium-ion battery including an all-solid state.

Nickel is used in various fields such as drive systems for land, sea and air vehicles (ships, railways, automobiles, aircraft, etc.), backup UPS (Uninterruptible Power Supply), large-scale power storage equipment for power system stabilization, etc. Secondary batteries such as hydrogen batteries and lithium ion batteries are used.
In designing a storage battery system, it is important to estimate the capacity of the storage battery to be installed in order to optimize the total cost of the system. In this case, it is required to accurately estimate how much capacity the battery maintains even with aging deterioration.
In addition, the hybridization and electrification of vehicles such as automobiles and railways and construction machinery are progressing, and applications using storage batteries are increasing more and more. In particular, in the case of a mobile object, deterioration information as well as the remaining amount of the secondary battery is information necessary for battery replacement timing and maintenance.

The battery state is grasped by SOC (State of Charge: charging rate) or SOH (State of Health: deterioration state). In hybrid cars, being able to monitor the SOC and SOH in the vehicle when necessary contributes to optimal battery management and extension of battery life. Methods for monitoring the SOC and SOH while mounted on a vehicle include determination of a voltage drop at engine start and current integration and voltage drop determination during normal running.

In the AC impedance measurement method, a minute sinusoidal AC signal is applied, and the physical properties and reaction of the interface are measured from the phase difference between the input signal and the output signal. Impedance is measured at a plurality of frequencies for the equivalent circuit, and phenomena occurring inside the battery such as the charge transfer resistance _Rct at the electrode/electrolyte interface and the mass transfer process in the electrolyte are analyzed from the measurement results.
A plot of measured values measured by an AC impedance measurement method on a complex plane is generally called a Cole-Cole plot or a Nyquist plot.

In the determination of battery deterioration, the secondary battery is regarded as an equivalent circuit, the measured AC impedance is compared with the Nyquist plot of this equivalent circuit, and each parameter (solution resistance _Rsol , charge transfer resistance _Rct , etc.) is minimized. It is obtained by fitting using the squared error method. Degradation determination is performed based on the measurement results (R _sol , R _ct ).

Patent Literature 1 describes a battery state determination device that determines the degree of battery deterioration based on AC impedance measurement data of the battery. The battery state determination device described in Patent Document 1 fits AC impedance (also referred to as AC impedance) measurement data to an equivalent circuit model having one or more circuit blocks in which a resistance R and a CPE (Constant Phase Element) are connected in parallel. and a fitting unit that obtains the circuit constants of the equivalent circuit model.

Patent Literature 2 describes a method for measuring AC impedance of a storage battery. The AC impedance measurement method described in Patent Document 2 includes the steps of flowing a current from a storage battery to a capacitor, measuring a voltage change in the output voltage of the capacitor while the current is flowing to the capacitor, and from the voltage change, and calculating an AC impedance of the storage battery.

Patent Document 3 describes a secondary battery temperature estimation method for estimating the temperature of a power storage unit, which is the internal temperature of the secondary battery. The secondary battery temperature estimation method described in Patent Document 3 is based on the internal resistance of the secondary battery obtained using the AC impedance method, the duration after the start of charging and discharging of the secondary battery, and the secondary battery An internal resistance map representing the relationship between the SOC, which is the ratio of the remaining battery capacity to the battery capacity in the fully charged state, and the temperature of the power storage unit is prepared in advance. In this temperature estimating method, the internal resistance of the power storage unit is obtained based on the internal resistance map at each predetermined time by dividing the duration time as soon as the charging and discharging of the secondary battery is started. Furthermore, in this temperature estimation method, the amount of heat generated by the power storage unit is calculated using the obtained internal resistance, and the calculated heat value is used to estimate the power storage unit at the time when the secondary battery continues to be charged and discharged. Calculates the temperature.

Patent Document 4 discloses a charge level acquisition unit that acquires the charge level of a lead-acid battery, a temperature acquisition unit that acquires the temperature of the lead-acid battery, and a control unit that controls the charge level and the temperature of the lead-acid battery within predetermined ranges. and a measuring unit for measuring the impedance of the lead-acid battery. The lead-acid battery device described in Patent Document 4 controls the charge level and measurement temperature of the lead-acid battery to a predetermined temperature (10° C. or less) and measures AC impedance. As a result, it is possible to accurately specify the degree of deterioration even for a lead-acid battery whose degree of deterioration has not progressed.

JP 2013-26114 A Japanese Patent Application Laid-Open No. 2013-54003 JP 2013-101884 A Japanese Unexamined Patent Application Publication No. 2018-181430

However, the battery deterioration determination techniques of Patent Documents 1 to 4 have the following problems.
(1) The battery state is most stable when it is in the room temperature range. For this reason, when diagnosing deterioration in the normal temperature range where the battery is stable, there is a problem that the deterioration cannot be judged until the battery reaches the end of its life (approximately 1500 times or more).

(2) The battery temperature is controlled based on the measured temperature in the room temperature environment. Since it is not possible to know the state of deterioration in the middle of a battery with a small number of charge/discharge cycles, a considerable temperature range (plus or minus 10°C) is provided for control. For this reason, inappropriate temperature and charge/discharge management must be continued, and there is a problem of shortening the life of the battery.

(3) The deterioration of the battery is surely caused by repeated charging and discharging. However, the number of times of charge/discharge varies from battery cell to battery cell, and an accurate deterioration level cannot be determined. For batteries in the middle of deterioration, when the deterioration level is moderate (about several hundred times of charge/discharge), the deterioration behavior is not remarkable, and deterioration detection is difficult, so it is not possible to manage appropriate temperature and charge/discharge control. and the battery life cannot be extended. For the same reason, it is difficult to distinguish between a new battery with an initial deterioration level and a used battery with a small number of charge/discharge cycles.

(4) Patent Literature 4 describes a lead-acid battery device. In a lead-acid battery, the internal resistance of AC impedance rises linearly with respect to the deterioration state, and the deterioration state can be easily grasped by measuring the internal resistance. However, the lithium-ion battery differs from the lead-acid battery not only in the constituent materials of the battery case but also in the electrochemical storage principle. However, the behavior is also different, such as lowering the impedance value.

As described above, it is difficult to diagnose the deterioration of the lithium ion battery in the middle, and it is difficult to judge the deterioration unless the battery has reached the end of its life.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a battery deterioration determination device and a battery deterioration determination method capable of accurately determining an intermediate deterioration state of a battery.

In order to solve the above-mentioned problems, the battery deterioration determination device according to the present invention sets the environmental temperature of the battery centering on the point where the distribution ratio of the solution resistance or ion transfer resistance and the charge transfer resistance of the preset AC impedance is competitive. A battery temperature control unit that controls the measurement temperature to be 15 ° C or less before and after the region, an impedance measurement unit that measures the AC impedance data of the battery at the measurement temperature, and the measurement data and the reference measured by the impedance measurement unit. a battery deterioration determination unit that determines the degree of deterioration of the battery by comparing the battery measurement conditions with standard AC impedance data previously measured under the same conditions.

Advantageous Effects of Invention According to the present invention, it is possible to provide a battery deterioration determination device and a battery deterioration determination method capable of accurately determining the intermediate deterioration state of a battery.

FIG. 3 is a diagram showing the number of charge/discharge cycles and AC impedance characteristics of a battery when the measurement temperature is 25° C. for explaining the principle of the present invention; It is a figure which shows the charge-discharge frequency|count and AC impedance characteristic of a battery in the case of the measurement temperature of 10 degreeC of principle explanation of this invention. It is a figure which shows the impedance ratio regarding the measured temperature of the battery of principle explanation of this invention. FIG. 4 is a diagram showing measured frequency impedances of two types of new batteries at a measurement temperature of 25° C. in the principle explanation of the present invention, as viewed from the Mahalanobis distance. FIG. 2 is a diagram showing the measurement frequency impedance of two types of batteries with 800 charge/discharge cycles at a measurement temperature of 25° C. in the principle explanation of the present invention, viewed from the Mahalanobis distance. FIG. 4 is a diagram showing the measured frequency impedance of two types of new batteries at a measurement temperature of 10° C. in the principle explanation of the present invention, viewed from the Mahalanobis distance. FIG. 2 is a diagram showing the measurement frequency impedance of two types of batteries with 800 charge/discharge cycles at a measurement temperature of 10° C. in the principle explanation of the present invention, viewed from the Mahalanobis distance. FIG. 4 is a diagram showing the number of charge/discharge cycles and AC impedance characteristics of a battery in the case of a measurement temperature of −10° C. for explaining the principle of the present invention; FIG. 4 is a diagram showing the number of charge/discharge cycles and AC impedance characteristics of a battery when the measurement temperature is −5° C. for explaining the principle of the present invention; FIG. 4 is a diagram showing the number of charging/discharging times of a battery and AC impedance characteristics when the measurement temperature is 0° C. for explaining the principle of the present invention; FIG. 5 is a diagram showing the number of charging/discharging times of a battery and AC impedance characteristics when the measurement temperature is 5° C. for explaining the principle of the present invention; FIG. 4 is a diagram showing the number of charge/discharge cycles and AC impedance characteristics of a battery at a measurement temperature of 10° C. for explaining the principle of the present invention; FIG. 5 is a diagram showing the number of charge/discharge cycles and AC impedance characteristics of a battery at a measurement temperature of 15° C. for explaining the principle of the present invention; It is a figure which shows the impedance ratio regarding the measured temperature of the battery of principle explanation of this invention. FIG. 2 is a diagram showing AC impedance characteristics with 0° C. in between for the number of charge/discharge cycles of a new battery and a halfway deteriorated battery when the measurement temperature is -5° C. for explaining the principle of the present invention. FIG. 5 is a diagram showing AC impedance characteristics with 0° C. in between for the number of charge/discharge times of a new battery and a halfway deteriorated battery when the measurement temperature is 5° C. for explaining the principle of the present invention. FIG. 2 is a diagram showing AC impedance characteristics with 0° C. in between, with respect to the number of charge/discharge cycles of a new battery and a halfway deteriorated battery when the measurement temperature is 0° C. for explaining the principle of the present invention. FIG. 10 is a diagram showing AC impedance characteristics with 0° C. in between with respect to the number of charge/discharge cycles of a new battery and a halfway deteriorated battery when the measurement temperature is 25° C. for explaining the principle of the present invention; 1 is a block diagram showing the configuration of a battery deterioration determination device according to an embodiment of the present invention; FIG. FIG. 3 is a diagram showing an example of an AC impedance table for each reference battery deterioration degree of the battery deterioration determination device according to the embodiment of the present invention; It is a figure which shows an example of the reference new battery AC impedance table of the battery deterioration determination apparatus which concerns on embodiment of this invention. It is a flow chart which shows the whole operation of the battery degradation judging device concerning the embodiment of the present invention. It is a block diagram showing a configuration. 4 is a flowchart showing new/used battery determination processing of the battery deterioration determination device according to the embodiment of the present invention. FIG. 5 is a diagram showing the number of charge/discharge cycles and AC impedance characteristics of a new battery and a halfway deteriorated battery when the environmental temperature measured by the battery deterioration determination device according to the embodiment of the present invention is −5° C.; 4 is a flowchart showing deterioration determination processing of the battery deterioration determination device according to the embodiment of the present invention; 4 is a flowchart showing deterioration determination processing of the battery deterioration determination device according to the embodiment of the present invention; 4 is a flowchart showing deterioration determination processing of the battery deterioration determination device according to the embodiment of the present invention;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(Explanation of principle)
First, the basic concept underlying the present invention will be described.
As described in the problem to be solved, it is difficult to determine battery deterioration at room temperature. The difficulty in determining deterioration during deterioration will be described.
Lithium-ion batteries deteriorate mainly due to the phenomenon that the electrolyte deposits on the reaction surface of the electrode and covers the electrode plate. In a lithium ion battery, the thickness of the SEI (Solid Electrolyte Interphase) layer covering the reaction surface of the electrode increases due to deterioration, increasing the charge transfer resistance. Moreover, the increase in thickness accompanying deterioration is not uniform. Observation by applying high energy to the electrode surface has revealed that the SEI layer repeats adhesion and elution due to charging and discharging. Since it is difficult to quantitatively measure such a phenomenon, it is difficult to judge deterioration of the battery.

The present inventor expanded the environmental temperature of the battery to the use limit and measured the AC impedance, which is a deterioration index of the battery. Then, it became clear that the measured value of the battery, which showed no signs of deterioration at room temperature, changed greatly when the environmental temperature was increased to the temperature limit.
On the high temperature side, the chemical reaction of the battery reduces the impedance of the battery. Since the impedance itself becomes smaller, deterioration determination becomes difficult. On the other hand, on the low temperature side, the impedance itself becomes large, so although it becomes easy to judge the deterioration, it shows a large change that makes it difficult to make a quantitative judgment.

The present inventor conceived of determining battery deterioration in a predetermined temperature range, not in a normal temperature range where the battery state is stable, and quantified the temperature range based on research results. The present inventor found that when measured at a measurement environmental temperature of nearly 10°C lower than normal temperature (hereinafter referred to as environmental temperature), the state of the battery is more stable than normal temperature, and the impedance behavior does not show at normal temperature. It was found that a clear deterioration change was shown.

The environmental temperature (temperature range) found by the present inventor is a range (40% to 60% region).

Deterioration of the battery is determined by controlling the battery temperature to a measured temperature corresponding to the above temperature range (for example, 10° C. or less) and comparing the measured AC impedance value with standard data under the same conditions by statistical processing. This makes it possible to determine the state of deterioration in the medium usage state.

Furthermore, in this temperature range, the measured AC impedance value at the applied frequency (around 5 Hz, not much dependent on the number of charge/discharge cycles) when the delay in impedance due to the capacitance component of the load transfer resistance is maximized is compared with the standard data under the same conditions. compare. This makes it possible to determine the degree of deterioration (deterioration level).

When the deterioration level of the battery in the middle of deterioration is obtained, the temperature range of the battery is reviewed from the initial value, and the SOC, temperature, or load current, which are deterioration factors of the battery, are lowered. By appropriately controlling the battery in this way, it is possible to extend the life of the battery.

The AC impedance measurement temperature should be less than 0°C. This makes it possible to determine whether the battery is new or has been used.

(embodiment)
This embodiment determines deterioration of a lithium-ion battery (simply referred to as a battery in the following description) including all solids. Battery deterioration can be measured by AC impedance.
The procedure of experiment and measurement is obtained by repeating the charge/measurement/discharge/measurement cycle. After waiting for the state of the battery to stabilize, the measurement obtains the AC impedance characteristics. In addition, the impedance of the battery is very small, ranging from several mΩ to ten and several mΩ, and in order to eliminate the influence of the current resistance of the lead wire and the like as much as possible, the measurement wire was soldered to the battery and measured immediately. Alternating current impedance was measured by ^varying the frequency from 4 Hz to 20 Hz in steps of 1 Hz, then in steps of 10 Hz and then in steps of 100 Hz ^. It was measured.

[Measurement environment temperature (measurement temperature) consideration]
<AC impedance measurement>
1A and 1B are diagrams showing the number of charge/discharge cycles and AC impedance characteristics of a battery (reference battery). indicates the number of charge/discharge cycles and AC impedance characteristics of the battery when the measurement temperature is 10°C. In FIGS. 1A and 1B, the horizontal axis is the impedance real component Z ^′ [mΩ], and the vertical axis is the impedance imaginary component Z ^″ [mΩ ^] . The arc (semicircle) drawn by the Nyquist plot (Nyquist curve) _{indicates the impedance of the charge transfer resistance Rct .} When the battery deteriorates, the charge transfer resistance _Rct including the interfacial impedance between the electrolyte and the electrode increases (the arc becomes larger and shifts to the right).

When the AC impedance of the battery is plotted on the complex plane, the impedance without lead/lag is plotted on the real axis, and the impedance (capacitance) with lag is plotted on the imaginary axis, the semicircular trajectory shown in FIGS. 1A and 1B can be drawn. Become. The AC impedance of the battery is measured by changing the frequency applied to the battery, but it is a crushed semicircle, indicating that the battery does not respond well to the applied frequency like an electric circuit element. Looking at the AC impedance curve, it can be confirmed that a large arc is drawn as the cycle progresses, indicating that the battery is deteriorating.

<Relationship between measured temperature and room temperature>
For batteries at the same deterioration position, the AC impedance increases when the measurement temperature (measuring environment temperature) is lowered from room temperature, and decreases when the measurement temperature is raised from room temperature. It can be confirmed that the change in AC impedance due to the change in the measurement environment temperature behaves very similarly even when the batteries that have passed the same cycle are compared. When confirming the deterioration state of the battery from the locus of the semicircle drawn by the AC impedance, it is easier to determine if the measurement environment temperature is lowered from room temperature. When the measurement environment temperature is raised from room temperature, the semicircle drawn by the AC impedance becomes so small that it becomes difficult to confirm.

In the explanation of each figure below, "Active" in the figure represents a new battery, and the numerical value in the figure represents a battery that has been repeatedly charged and discharged the number of times (for example, "80" in the figure represents a battery that has been charged and discharged 80 times. "800" represents a battery with 800 charge-discharge cycles).

As shown in FIG. 1A, when the measurement temperature is 25° C., there is a difference in the real component Z ^′ [mΩ] between the new battery and the battery in each charge/discharge cycle, but there is a significant difference in the imaginary component Z ^″ [mΩ]. In other words, when comparing the apex (where the slope becomes 0) of the arcs drawn by the Nyquist plots of the new battery and the battery of each charge/discharge cycle, the difference in the imaginary component Z ^″ is small.

On the other hand, as shown in FIG. 1B, when the measurement temperature is 10° C., in addition to the difference between the real number component Z ^′ [mΩ] of the new battery and the battery of each charge/discharge cycle, the imaginary number component Z ^″ [mΩ] It can be seen that there is a notable difference: when comparing the peaks of the arcs of the Nyquist plots of the new battery and the battery of each charge/discharge cycle, the difference in the imaginary component Z ^'' is very large.

When measured at a measurement environment temperature (measurement temperature) of nearly 10°C, which is lower than normal temperature (measurement temperature of 25°C), it became clear that a clear deterioration change that is not shown at normal temperature is shown. However, the difference is such that it can be overlooked by visual inspection. Therefore, in the present embodiment, the shape of the arc is determined using Mahalanobis distance analysis (described later), which is one of statistical methods.
It was also found that in the temperature range near 10°C shown in Fig. 1B, the ratio (impedance ratio) between the charge transfer resistance _Rct and the solution resistance _Rsol , which constitute the impedance of the battery, is about half. did.
At room temperature, it cannot be detected unless the deterioration has progressed. However, when the measurement temperature is set to 15° C. or lower (for example, 10° C.), the imaginary component difference becomes clear even with a small number of charge/discharge cycles.

<Measurement temperature range for determining battery deterioration>
FIG. 2 is a diagram showing the impedance ratio with respect to the measured temperature of the battery. In FIG. 2, the horizontal axis is the measured temperature [° C.], and the vertical axis is the impedance ratio ^Z′_Rct _[ %] of the charge transfer resistance _Rct . The impedance ratio ^Z'_Rct [%] is charge transfer resistance _Rct /(solution resistance _Rsol + charge transfer _{resistance Rct )} .

As shown in the dashed box a in FIG. 2, it can be seen that determination is possible in the range of 12 to 13° C. or less and excluding the vicinity of 0° C.

<Relationship between measured temperature and charge/discharge cycle>
3A and 3B are diagrams showing the measurement frequency impedance of the battery (reference battery) when the measurement temperature is 25 ° C. as viewed by the Mahalanobis distance. Li100) shows the measured frequency impedance of the battery (Active), and FIG. 3B shows the measured frequency impedance of the two types of batteries (Li56, Li57) with 800 charge-discharge cycles (800) at a measurement temperature of 25 ° C. . 3A and 3B, the horizontal axis is the measured frequency impedance [Hz], and the vertical axis is the Mahalanobis distance.
As shown in FIGS. 3A and 3B, comparing the battery (Active) at the measurement temperature of 25° C. and the battery (800) with 800 charge/discharge cycles, there is little difference in the measured frequency impedance of the battery at the measurement temperature of 25° C. It turns out that there is no

<Mahalanobis distance analysis>
The semicircle drawn by the AC impedance measured at the measurement temperature of 25° C. is small, and it is difficult to confirm the deterioration state of the battery by the AC impedance. Therefore, in the present embodiment, deterioration of the battery is determined in detail using Mahalanobis distance analysis, which is a statistical analysis method.
The method of Mahalanobis distance analysis of the measured frequency impedance is disclosed by the present inventor for the first time.

However, at the measurement temperature of 25° C., it is difficult to confirm the correlation between battery deterioration and AC impedance even when the statistical method using the Mahalanobis distance is used for analysis. The inventors have found that when the measurement temperature is low (for example, 10° C.), it is easier to check the degree of deterioration of the battery than when the temperature is normal or high. It should be noted that the degradation of a battery reaching deterioration can be accurately diagnosed regardless of the measured temperature.

Further, by setting the measurement temperature to less than 0° C., it becomes possible to determine whether the battery is new or used from the shape of the impedance curve without performing Mahalanobis distance analysis (see FIG. 13 below).

4A and 4B are diagrams showing the measurement frequency impedance of the battery (reference battery) when the measurement temperature is 10 ° C. as viewed by the Mahalanobis distance. Li100) shows the measured frequency impedance of the battery (Active), and FIG. 4B shows the measured frequency impedance of one type (Li57) of the battery (800) with 800 charge-discharge cycles at a measurement temperature of 10°C. 4A and 4B, the horizontal axis is the measured frequency impedance [Hz], and the vertical axis is the Mahalanobis distance.

As shown in FIGS. 4A and 4B, when comparing the battery (Active) at a measurement temperature of 10° C. and the battery (800) with 800 charge-discharge cycles, when the measurement temperature is 10° C., the 8 Hz part (symbol b in FIG. 4B) ), it was found that the measured frequency impedance of the battery was clarified. That is, when the measured frequency impedance of the battery is analyzed by the Mahalanobis distance, the behavior of the measured frequency impedance changes at the 8 Hz portion (see symbol b in FIG. 4B) for the battery with 800 charge-discharge cycles (800). , the state of deterioration of the battery could be confirmed.

As shown in FIG. 4B, when the measurement temperature is set to 10° C., the difference in the imaginary number component becomes clear when comparing the batteries in the middle of deterioration even with a small number of charge-discharge cycles.

<Upper and lower limit of measurement temperature>
5A-5F are diagrams showing the number of charge/discharge cycles and AC impedance characteristics of the battery (reference battery), FIG. 5C is for a measurement temperature of 0°C, FIG. 5D is for a measurement temperature of 5°C, FIG. 5E is for a measurement temperature of 10°C, and FIG. 5F is for a measurement temperature of 15°C. Each case is shown. 5A-5F, the horizontal axis is the impedance real component Z ^' [mΩ], and the vertical axis is the impedance imaginary component Z ^' ' [mΩ].

In the case of the measured temperature of 15° C. shown in FIG. 5F, there is no clear deterioration change, whereas in the case of the measured temperature of 10° C. or less shown in FIGS. 5A-5E, there is a clear deterioration change. Therefore, it can be seen that the measurement temperature should be 10° C. or lower. However, when the measured temperature is 0° C. shown in FIG. 5C, the measured frequency impedance of the battery with 800 charge-discharge cycles and 80 cycles with respect to the measured frequency impedance of the new battery (Active) is shown in FIGS. are different from the measured frequency impedance of the batteries with 800 and 80 charge-discharge cycles. That is, when the measurement temperature is 0 ° C. shown in FIG. 5C, the battery with 80 charge-discharge cycles is more deteriorated than the battery with 800 charge-discharge cycles (the battery with 800 charge-discharge cycles is more deteriorated than the battery with 800 charge-discharge cycles). However, it has not deteriorated like a new battery (Active)). At the measurement temperature of 0° C., it is conceivable that the behavior of the measurement frequency impedance is affected for reasons such as coagulation of water contained in the battery (described later).
When the battery deteriorates, the charge transfer resistance _Rct including the interfacial impedance of the electrolyte increases (the arc becomes larger and shifts to the right).
From the above, the measurement temperature should be 10°C or less except 0°C.

<Excluding 0°C from the measurement temperature>
FIG. 6 is a diagram showing the impedance ratio with respect to the measured temperature of the battery. In FIG. 6, the horizontal axis is the measured temperature [°C], and the vertical axis is ^Z'_Rsol [ _mΩ ].
As shown in the dashed box c in FIG. 6, when the measured temperature is around 0° C., the charge transfer resistance _Rct of the AC impedance of the new battery (Active) changes greatly. This is thought to be due to the change in the charge transfer resistance _Rct of the AC impedance due to the slight amount of moisture contained in the constituent members in the container during manufacture, which solidified at the freezing point.

When the temperature is further lowered, the locus (Nyquist plot) drawn by the charge transfer resistance _Rct of the AC impedance of the new battery (Active) is clearly different from that of the battery (80), which has been used even slightly. It turned out (see dashed box d in FIG. 6).
As shown in the dashed box a in FIG. 2, it can be seen that determination is possible in the range of 12 to 13° C. or less and excluding the vicinity of 0° C.

<New battery judgment>
7A-7D are diagrams showing AC impedance characteristics with the freezing point (0 ° C.) in between for the number of charge and discharge cycles of a new battery (Active) and a partially deteriorated battery. 7B shows the case of the measured temperature of 5° C., FIG. 7C shows the case of the measured temperature of 0° C., and FIG. 7D shows the case of the measured temperature of 25° C., respectively. 7A-7D, the horizontal axis is the impedance real component Z ^' [mΩ], and the vertical axis is the impedance imaginary component Z ^' ' [mΩ].

In the case of a measurement temperature of -5°C, the impedance imaginary component Z ^″ of the new battery (Active) indicated by symbol e in FIG. 7A and the halfway deteriorated battery (80) (800) indicated by symbol f in FIG. 7A, that is, the charge of the AC impedance The Nyquist plots drawn by the transfer resistance R _ct are significantly different, so that when the measured temperature is -5° C., it is possible to distinguish between a new battery and a halfway deteriorated battery.

When the measurement temperature is 5°C, the difference in impedance imaginary component Z ^″ between the new battery (Active) and the partially deteriorated battery (80) (800) is close to each other, as indicated by symbol g in Fig. 7B. The measurement temperature is 15°C. At ~0°C, it is difficult to reliably distinguish between new batteries and halfway deteriorated batteries.
It should be noted that if identification is possible without using the Mahalanobis distance, it is possible to avoid using the Mahalanobis distance, but if identification is not possible using the Mahalanobis distance may result in an error.

When the measurement temperature is 25°C, as shown in Fig. 7D, the difference in impedance imaginary component Z ^″ between the new battery (Active) and the halfway deteriorated batteries (80, 800) is closer. When the measurement temperature is 25°C. , it is more difficult to distinguish between a new battery and a partially deteriorated battery.

In the case of the measurement _temperature of 0° C., as shown in FIG. The difference in the Nyquist plot drawn by the charge transfer resistance _Rct of the partially deteriorated battery (80) with a low degree of deterioration is increasing. That is, when the measured temperature is 0° C., the identification of a new battery and a partially deteriorated battery is unreliable (see <Exclude 0° C. from the measured temperature>).

Thus, when the measured temperatures were 25°C, 5°C, and 0°C, the difference between the Nyquist plots drawn by the charge transfer resistance _Rct of the new battery (Active) and the partially deteriorated battery (80) was not large, but the measured temperature At −5° C., the impedance imaginary component Z ^″ is significantly different, and therefore it is easy to determine whether the battery is new (Active) or whether the battery has deteriorated.

<Relationship between battery deterioration and measurement frequency>
According to the experimental results, as the deterioration progresses, a difference appears in the direction in which the measurement frequency decreases. In this embodiment, in the determination routine of FIG. 14C described later, determination is made in the direction of lowering the measurement frequency.

[Battery deterioration determination device]
FIG. 8 is a block diagram showing the configuration of a battery deterioration determination device according to one embodiment of the present invention based on the above basic idea. This embodiment is an example applied to a battery deterioration determination device that determines the deterioration state of a lithium ion battery.
As shown in FIG. 8, the battery deterioration determination device 100 includes a battery condition setting unit 110 (battery temperature control means) that sets the battery condition of the battery 10 to be measured (battery to be measured), and an AC impedance of the battery 10 to be measured. A battery AC impedance measuring device 120 (impedance measuring means) for measuring, a solution resistance calculating unit 130 (solution resistance calculating means) for calculating the solution resistance of the AC impedance of the battery 10, and the charge transfer resistance of the AC impedance of the battery 10 A charge transfer resistance calculation unit 140 (charge transfer resistance calculation means) for calculation, a Mahalanobis distance calculation unit 150 (distance calculation means) for calculating the Mahalanobis distance by a statistical method, and a battery deterioration determination unit for determining the degree of deterioration of the battery 10 160 (battery deterioration determination means).

The charge transfer resistance calculation unit 140 includes a charge transfer resistance calculation unit 140A that calculates the charge transfer resistance of the AC impedance of the battery measured this time, and a charge transfer resistance calculation unit 140B that calculates the charge transfer resistance of the AC impedance of the battery measured last time. And prepare.

The Mahalanobis distance calculation unit 150 includes a reference space 151, a Mahalanobis distance calculation unit 150A for calculating the Mahalanobis distance of the charge transfer resistance of the AC impedance of the battery measured this time, and the charge transfer of the AC impedance of the battery measured last time. and a Mahalanobis distance calculation unit 150B that calculates the Mahalanobis distance of resistance.

The battery deterioration determination unit 160 includes a reference battery deterioration level AC impedance table 161 and a reference new battery AC impedance table 162 .

[Devices Connected to Battery Degradation Determining Device 100]
A battery 10 (target battery), a battery control unit 20 and a measurement unit 30 are connected to the battery deterioration determination device 100 .
<Battery 10>
Battery 10 is a lithium ion battery or an all solid state lithium ion battery.

<Battery control unit 20>
The battery control unit 20 includes a charge/discharge control unit 21 that charges and discharges the battery 10 and a cooling control unit 22 (battery temperature control means) that cools the battery 10 .
The charge/discharge control unit 21 charges or discharges the connected battery 10 (target battery). The charging/discharging control unit 21 includes a dummy resistor (not shown), a discharging unit that discharges the dummy resistor by heat generated by passing a current through the dummy resistor, and a charging unit that charges the battery 10 by supplying an external power source or the like. In the case of a drive battery used in hybrid electric vehicles (HEVs), the dummy resistor is the power motor and the charging unit is the onboard charger.

The cooling control unit 22 controls the temperature of the battery 10 to an appropriate temperature (preset temperature during measurement) by heating/cooling means (not shown).

The cooling control unit 22 controls the environmental temperature of the battery 10 so that the distribution ratio of the solution resistance or the ion transfer resistance (in the case of an all-solid-state lithium-ion battery, the ion transfer resistance) and the charge transfer resistance of a preset AC impedance are antagonistic. The measurement temperature is controlled to 15° C. or less (preferably 10° C.) in the front and rear regions (40% to 60% region) centering on the point where the temperature rises.
The cooling control unit 22 controls the environmental temperature of the battery 10 to a measurement temperature of 15°C or less, excluding 0°C.

<Measurement unit 30>
The measurement unit 30 includes a battery voltage/battery current detection unit 31 for detecting the battery voltage/battery current of the battery 10 to be measured, and a battery temperature detection unit 32 (battery temperature control means) for detecting the battery temperature of the battery 10 to be measured. ) and an outside air temperature detection unit 33 (battery temperature control means) that detects the outside air temperature around the battery 10 to be measured.

<Battery state setting unit 110>
Battery state setting unit 110 sets battery power, battery charge power amount, battery discharge power amount, SOC, and temperature conditions. The battery state setting unit 110 outputs the set temperature for measurement to the cooling control unit 22 .

<Battery AC impedance measuring device 120>
The battery AC impedance measuring device 120 applies a minute AC signal with a frequency ω(i) to the battery 10 and measures the AC impedance (real axis impedance Z ^′ (ω(i)), imaginary axis impedance Z ^″ ) of the battery 10 at the measurement temperature. (ω(i))) is measured.
Battery AC impedance measuring device 120 outputs the measured AC impedance (real axis impedance Z ^′ (ω(i)), imaginary axis impedance Z ^″ (ω(i))) to charge transfer resistance calculator 140 and charge transfer resistance calculator 140. Output to unit 140 .

The battery AC impedance measuring device 120 includes a voltmeter (not shown) for measuring the voltage of the battery 10 (target battery), an ammeter for measuring the current of the battery 10, and a sine wave AC signal to generate a sine wave AC signal. It comprises an alternating current source for applying a signal to the battery 10 and a complex impedance measuring section. This complex impedance measurement unit is configured by, for example, an impedance analyzer.
A complex impedance measurement unit (not shown) inputs the voltage value V measured by the voltmeter and the current value I measured by the ammeter for each measurement frequency, and calculates each measurement from the current value I and the voltage value V. Calculate the complex impedance at frequency.

Incidentally, the method of measuring the AC impedance is not limited to the above example, and various methods can be used. For example, a voltage waveform or current waveform in which multiple frequency signals are superimposed is applied, the current waveform or voltage waveform is measured, the voltage waveform and current waveform are respectively subjected to a discrete Fourier transform (DFT), and the ratio of each frequency component is calculated. may be requested.

<Solution resistance calculator 130>
^The solution resistance calculator 130 calculates the solution ^resistance ( Z ^' ( _ωm )''Z'^' ( _ωm )=0) is calculated and output to the battery deterioration determination unit 160. Z ^' ( _ωm ) is the real axis impedance of the solution resistance, Z'^' ( _ωm ) is the imaginary axis impedance of the solution resistance.

Based on the AC impedance measured by the impedance measuring device 120, the solution resistance calculator 130 calculates the point (real axis impedance Z ^' ( ω(i)>0, calculate the solution resistance represented by the imaginary axis impedance Z ^″ (ω(i)=0).

<Charge transfer resistance calculator 140>
The charge transfer resistance calculation unit 140 uses the setting information of the battery state setting unit 110 and the AC impedance (real axis impedance Z ^′ (ω(i)) and imaginary axis impedance Z ^″ (ω( Based on i))), the charge transfer resistance of the measured AC impedance of the battery is calculated.

Specifically, the charge transfer resistance calculation unit 140A combines the setting information of the battery measured this time by the battery state setting unit 110 and the AC impedance (real axis impedance Z ^′ (ω(i) ) and the imaginary axis impedance Z ^″ (ω(i))), the charge transfer resistance of the AC impedance of the battery measured this time is calculated and output to the Mahalanobis distance calculator 150A.
In addition, the charge transfer resistance calculation unit 140B combines the setting information of the battery measured last time by the battery state setting unit 110 and the AC impedance (real axis impedance Z ^′ (ω(i)) measured by the battery AC impedance measurement device 120, imaginary Based on the axial impedance Z ^″ (ω(i))), the charge transfer resistance of the AC impedance of the battery measured last time is calculated and output to the Mahalanobis distance calculator 150B.

Here, the AC impedance of the battery that was measured last time is data in which the state of deterioration of the battery is updated and recorded. The deterioration state of the battery progresses from the initial stage, but when the system determines that it has clearly deteriorated, the deterioration state of the battery is updated. The last deterioration judgment data is used), which is known data. The AC impedance of the battery measured this time is the AC impedance data of the battery measured this time when the deterioration state of the battery is updated when the system determines that the battery has clearly deteriorated by the same deterioration determination process as described above.

<Mahalanobis Distance Calculator 150>
The Mahalanobis distance calculator 150 calculates the Mahalanobis distance of the charge transfer resistance of the AC impedance of the battery calculated by the charge transfer resistance calculator 140 . In this embodiment, distance calculation including Mahalanobis distance is used as a statistical method. The AC impedance of the battery is analyzed by obtaining the Mahalanobis distance, which is one of the nonlinear discriminant analysis methods, and performing quantitative evaluation. Mahalanobis distance analysis transforms and evaluates events that are multivariate into the reference space 151 .

The Mahalanobis distance calculator 150 creates a reference space 151 by finding the average value and variance of the distribution from the measured AC impedance distribution. Calculate how far each measured frequency point is from the reference space 151, calculate the difference between the frequencies, compare this difference with the reference value "1", and from the reference value "1", For example, when the distance is "2" or more, it is determined as deterioration. For example, as shown by the symbol b in FIG. 4B, the measured frequency impedance of the battery is analyzed by the Mahalanobis distance, and in the battery (800) with 800 charge-discharge cycles, the behavior change of the measured frequency impedance is observed at the 8 Hz part. Check the state of deterioration of the battery.

The Mahalanobis distance calculation unit 150A converts the charge transfer resistance of the AC impedance of the battery measured this time calculated by the charge transfer resistance calculation unit 140A into a multivariate event in the reference space 151 by Mahalanobis distance calculation and uses it as an evaluation target, The Mahalanobis distance of the AC impedance of the battery measured this time is output to the battery deterioration determination unit 160 .

In addition, the Mahalanobis distance calculation unit 150B converts the charge transfer resistance of the AC impedance of the battery measured last time calculated by the charge transfer resistance calculation unit 140B into a multivariate event in the reference space 151 by Mahalanobis distance calculation, and evaluates it. , and the previously measured Mahalanobis distance of the AC impedance of the battery is output to the battery deterioration determination unit 160 .

<Battery deterioration determination unit 160>
The battery deterioration determination unit 160 sets the environmental temperature of the battery 10 to 15° C. or less, which is a region before and after a point at which the distribution ratio of the solution resistance or the ion transfer resistance and the charge transfer resistance of the preset AC impedance is competitive. When the measurement temperature is controlled to , the AC impedance measurement data of the battery 10 measured by the battery AC impedance measuring device 120 and the standard AC impedance data previously measured under the same conditions as the measurement conditions of the reference battery are compared. Determining the degree of deterioration of the battery or whether the battery is new.

The battery deterioration determination unit 160 compares the AC impedance measurement data of the battery 10 measured by the battery AC impedance measuring device 120 and the measurement conditions of the reference battery when the environmental temperature of the battery 10 is controlled to a measurement temperature other than 0°C. The degree of deterioration of the battery or whether the battery is new is determined by comparing with standard AC impedance data previously measured under the same conditions.

The battery deterioration determination unit 160 determines that the ambient temperature of the battery 10 is less than 0° C., which is a region before and after a point at which the distribution ratio of the solution resistance or the ion transfer resistance and the charge transfer resistance of the preset AC impedance is competitive. When the measurement temperature is controlled to , the measurement data measured by the battery AC impedance measuring device 120 is compared with the standard AC impedance data previously measured under the same conditions as the measurement conditions of the reference battery to determine whether the battery is a new battery or not. Determine whether the battery is dead or not.

The battery deterioration determination unit 160 compares the measurement data measured by the battery AC impedance measuring device 120 with the standard AC impedance data previously measured under the same conditions as the measurement conditions of the reference battery to determine the degree of deterioration of the battery. For a deteriorated battery determined to be deteriorated, battery life control information for reducing the charge level, temperature, or load current, which are deterioration factors of the battery, is output.

The battery deterioration determination unit 160 uses the AC impedance data of the applied frequency when the impedance delay due to the capacitance components of the solution resistance and the charge transfer resistance calculated by the solution resistance calculation unit 130 is maximum as comparison data.

The battery deterioration determination unit 160 uses a statistical method to compare the AC impedance measurement data of the battery 10 measured by the battery AC impedance measuring device 120 and the standard AC impedance data previously measured under the same conditions as the measurement conditions of the reference battery. The degree of deterioration of the battery or a new battery is determined by comparison.

In this embodiment, the battery deterioration determination unit 160 calculates the solution resistance (Z ^′ (ω _m ) ”Z ^″ (ω _m )=0) calculated by the solution resistance calculation unit 130, the current measurement calculated by the Mahalanobis distance calculation unit 150A Based on the Mahalanobis distance of the charge transfer resistance of the AC impedance of the battery obtained and the previously measured Mahalanobis distance of the charge transfer resistance of the AC impedance of the battery calculated by the Mahalanobis distance calculation unit 150B, the AC impedance for each reference battery deterioration degree is calculated. The degree of deterioration of the battery or the new battery is determined by referring to the table 161 or the reference new battery AC impedance table 162. The degree of deterioration can be expressed by the number of charge/discharge cycles.

In this way, the analysis of the AC impedance for each degree of battery deterioration is performed by obtaining the Mahalanobis distance of the nonlinear discriminant analysis method and performing quantitative evaluation. Mahalanobis distance analysis transforms and evaluates events that are multivariate into the reference space.

Further, in the present embodiment, the solution resistance calculator 130 calculates the solution resistance (Z ^′ (ω _m )″Z ^″ (ω _m )=0) and outputs it to the battery deterioration determiner 160. Battery deterioration determiner. 160 can use the AC impedance data of the applied frequency when the impedance delay due to the capacitance component of the charge transfer resistance is maximum as comparison data. A curve with a slope of 0 is selected using a statistical method, and the degree of deterioration of the battery is determined based on the selected reference Nyquist plot.

The battery deterioration determination unit 160 operates according to a computer program as well as a dedicated terminal device. It can be configured by an information processing device such as a PC (personal computer). The battery deterioration determination unit 160 can record the measurement results and analysis results in a recording medium such as an SSD (Solid State Drive) and output them to output means such as a monitor device.

<AC impedance table 161 for each reference battery deterioration degree>
The standard battery deterioration level AC impedance table 161 stores standard AC impedance data previously measured under the same conditions as those of the standard battery as the Mahalanobis distance of the standard battery AC impedance for each standard battery deterioration level.

The AC impedance table for each reference battery deterioration degree 161 stores AC impedance data for each charge/discharge frequency of a reference battery whose temperature is appropriately controlled, and is referred to by the battery deterioration determination unit 160 . The AC impedance table 161 for each reference battery deterioration degree is a matching table for each charge/discharge cycle.

FIG. 9 is a diagram showing an example of the AC impedance table 161 for each reference battery deterioration level.
The AC impedance table 161 for each reference battery deterioration degree is a standard at each measurement frequency (0.1 Hz, 0.2 Hz, . Store the Mahalanobis distance MD(n,x) of the AC impedance of the battery.
Note that the setting conditions such as the number of charge/discharge times and the measurement frequency are only examples and are not limited. In addition, an AC impedance table 161 for each reference battery deterioration level shown in FIG. 9 is stored as a database for each battery temperature interval.

<Reference New Battery AC Impedance Table 162>
The reference new battery AC impedance table 162 stores standard AC impedance data previously measured under the same conditions as those of the reference battery as Mahalanobis distances of AC impedance of the standard battery for each degree of deterioration of the standard battery.

The reference new battery AC impedance table 162 stores AC impedance data for each charge/discharge frequency of a reference battery whose temperature is appropriately controlled, and is referred to by the battery deterioration determination unit 160 .

FIG. 10 is a diagram showing an example of the reference new battery AC impedance table 162. As shown in FIG.
The reference new battery AC impedance table 162 shows the Mahalanobis distance MD (n, x) of the AC impedance of the new battery for each measurement frequency (0.2 Hz, . . . , 1 Hz, . . . , x Hz, . and store the threshold Th for .

The operation of the battery deterioration determination device 100 configured as described above will be described below.
First, the overall operation of the battery deterioration determination device 100 (see FIG. 8) will be described.
FIG. 11 is a flow chart showing the overall operation of the battery deterioration determination device 100. As shown in FIG.
In step S1, the battery deterioration determination unit 160 of the battery deterioration determination device 100 determines whether or not the system has been reset. If the system has been reset, the process proceeds to a new/deteriorated battery determination processing routine in step S2, and the system has been reset. If not, the process proceeds to the deterioration determination processing routine of step S3, which is normal deterioration processing.

In step S2, the battery deterioration determination unit 160 executes a new/used battery determination processing routine (see FIG. 12), and after executing the new/used battery determination processing routine, proceeds to step S3.

In step S3, the battery deterioration determination unit 160 executes a deterioration determination processing routine (see FIGS. 14A to 14C), and after executing the deterioration determination processing routine, ends the processing of this flow.

<New/Used Battery Judgment Processing Routine>
FIG. 12 is a flowchart showing the new/used battery determination process of the battery deterioration determination apparatus 100, which is called and executed by the subroutine call of step S2 in FIG.
As shown in FIG. 12, the outside air temperature detection unit 33 of the measurement unit 30 (see FIG. 8) inputs the environmental temperature to the cooling control unit 22 in step S101.
In step S102, the cooling control unit 22 determines whether or not the temperature is below 0°C.
If the environmental temperature is below 0° C. (step S102: Yes), the process proceeds to step S104.

In step S<b>103 , the battery temperature detection unit 32 of the measurement unit 30 inputs the battery temperature to the cooling control unit 22 .
If the battery temperature is below 0°C (step S104: Yes), the process proceeds to step S109.

On the other hand, in step S105, the battery AC impedance measuring device 120 (see FIG. 8) measures the AC impedance plot, and uses the measured impedance measurement data (Z ^′ (ω), Z ^″ (ω)) of the battery 10 to calculate the solution resistance. It outputs to the section 130 and the charge transfer resistance calculation section 140 (see FIG. 8).
In step S107, the charge transfer resistance calculation unit 140 (see FIG. 8) sets the setting information of the battery state setting unit 110 and the AC impedance measured by the battery AC impedance measuring device 120 (real axis impedance Z ^′ (ω(i)), Based on the imaginary axis impedance Z ^″ (ω(i))), a Nyquist plot is obtained by plotting on the complex plane represented by the impedance real number component Z ^′ and the imaginary number component Z ^″ (Z ^″ peak_measure f_Z ^″ peak_measure ) and output to the Mahalanobis distance calculator 150 (see FIG. 8).

Specifically, the charge transfer resistance calculation unit 140A combines the setting information of the battery measured this time by the battery state setting unit 110 and the AC impedance (real axis impedance Z ^′ (ω(i) ) and the imaginary axis impedance Z ^″ (ω(i))), the charge transfer resistance of the AC impedance of the battery measured this time is calculated and output to the Mahalanobis distance calculator 150A.
In addition, the charge transfer resistance calculation unit 140B combines the setting information of the battery measured last time by the battery state setting unit 110 and the AC impedance (real axis impedance Z ^′ (ω(i)) measured by the battery AC impedance measurement device 120, imaginary Based on the axial impedance Z ^″ (ω(i))), the charge transfer resistance of the AC impedance of the battery measured last time is calculated and output to the Mahalanobis distance calculator 150B.

In step S108, the charge transfer resistance calculator 140 calculates the top of the arc drawn by the Nyquist plot of the battery plotted on the complex plane represented by the real component Z ^' and the imaginary component Z ^' ' of the impedance (where the slope becomes 0). ) is obtained (Z ^″ peak_model f_Z ^″ peak_model), and this impedance curve is corrected by the correction coefficient (K_Z ^″ peak K_f_Z ^″ peak) shown in the dashed box h in FIG. Calculation of part (Z ^″ peak_model f_Z ^″ peak_model) will be described with reference to FIG.

FIG. 13 is a diagram showing the number of charging/discharging times and AC impedance characteristics of a new battery (Active) and partially deteriorated batteries (80, 800) when the measured environmental temperature is -5°C. The horizontal axis is the impedance real component Z ^' [mΩ], and the vertical axis is the impedance imaginary component Z ^″ [mΩ].
Symbol e in FIG. 13 represents an AC impedance plot of a new battery (Active), and symbol f in FIG. 13 represents AC impedance plots of halfway deteriorated batteries (80) and (800). The arrow i in FIG. 13 indicates the magnitude of the impedance imaginary component Z ^″ [mΩ] up to the top (Z ^″ peak_model) of the arc drawn by the Nyquist plot of the new battery (Active), and the symbol j in FIG. Fig. 3 shows the measurement frequency (f_Z ^{" peak_model) of the AC impedance curve when (Z" peak_model} ).

As shown in Fig. 13, by comparing the peaks (Z ^″ peak_model) of the arcs drawn by the Nyquist plots of the new battery (Active) and the halfway deteriorated batteries (80 and 800), the measurement environment temperature was further lowered below 0°C. In the state (here, when the measured environmental temperature is −5° C.), it becomes possible to distinguish between a new battery (Active) and a halfway deteriorated battery (80) (800), which has not been known until now.However, in this embodiment, In identifying the new battery (Active) and the halfway deteriorated battery (80) (800), the charge transfer resistance of the AC impedance is obtained as described later, and the Mahalanobis distance analysis is performed by the Mahalanobis distance calculation unit 150. As a result, Improve judgment accuracy.

Returning to the flow of FIG. 12, in step S109, the battery deterioration determination unit 160 determines whether or not the frequency and imaginary axis impedance conditions are satisfied. That is, battery deterioration determination unit 160 determines whether or not expression (1) is satisfied.
Z ^″ peak_measure＜Z ^″ peak_model＋K_Z ^″ peak
f_Z ^″ peak_measure＞f_Z ^″ peak_model＋K_f_Z ^″ peak … (1)

Here, in the present embodiment, the battery deterioration determination unit 160 determines whether the battery is new based on the impedance condition of the above equation (1) and further by the Mahalanobis distance analysis by the Mahalanobis distance calculation unit 150 . That is, the battery deterioration determination unit 160 combines the AC impedance measurement data processed by the complex impedance processing unit 132 with the apex (Z ^″ peak_model) using the Mahalanobis distance.

Specifically, the Mahalanobis distance MD(n, x) of the reference new battery AC impedance in the reference new battery AC impedance table 162 shown in FIG. 10 is compared with the threshold value Th for new battery determination. If the Mahalanobis distance MD(n,x) is less than or equal to the threshold Th, the battery deterioration determination unit 160 determines that the battery is new in step S110, and if the Mahalanobis distance MD(n,x) is greater than the threshold Th, step S111. is determined to be a used product, and the processing of this flow ends.

When the measurement environment temperature is lowered below 0°C, as shown in FIG ^. It was found that the difference in the measurement frequency (f_Z ^″ peak_model) of the AC impedance curve is remarkable. Therefore, in the case of new battery determination, the new battery determination may be performed based on whether or not the condition of the above formula (1) is satisfied without using Mahalanobis distance analysis.

Thus, at room temperature, the AC impedance hardly changes, but when the environmental temperature of the battery is lowered below 0° C., the AC impedance of the battery increases. In particular, it was found that the behavior of the battery (80), which had been subjected to even a few charge-discharge cycles, and the new battery (Active) changed greatly when the measurement frequency was lowered to 4 Hz or less. As shown in FIG. 13, in the environmental temperature range below 0° C., it is possible to distinguish between a new battery (Active) (see symbol e in FIG. 13) and a slightly used battery (80) (see symbol f in FIG. 13). . The new battery determination device 100A can distinguish between new and used batteries, which have been indistinguishable until now, and can determine the authenticity even if the battery is intentionally faked as new, for example.

<Degradation determination processing routine>
FIGS. 14A to 14C are flowcharts showing deterioration determination processing of the battery deterioration determination device 100, which are called and executed by the subroutine call of step S3 in FIG.
As shown in FIG. 14A, elapsed time is counted in step S201.
In step S202, battery AC impedance measuring device 120 inputs a sampling voltage.
In step S203, battery AC impedance measuring device 120 inputs the sampling current.
In step S204, the charge/discharge control unit 21 of the battery control unit 20 calculates the amount of power.
In step S205, the charge/discharge control unit 21 integrates the charge power amount.
In step S206, the charge/discharge control unit 21 integrates the amount of discharged power.

When measuring the AC impedance, the impedance characteristics may be measured differently even if the deterioration state is the same. Therefore, it is necessary to match the battery states of the batteries to be compared. Battery state setting unit 110 sets the battery state of the battery with respect to battery power, battery charge power amount, battery discharge power amount, SOC, and temperature conditions.

In step S207, battery state setting unit 110 determines whether or not a predetermined period of time has elapsed, and if the predetermined period of time has elapsed, determines in step S208 whether or not the charged power amount has exceeded a predetermined value.
In step S209, battery state setting unit 110 determines whether or not the amount of discharged power exceeds a predetermined value.If the amount of discharged power exceeds the predetermined value, in step S210 it determines whether power input/output has not occurred for a predetermined time or longer. determine whether
In step S211, the battery state setting unit 110 determines whether or not the battery SOC is within a predetermined value, and if the battery SOC exceeds the predetermined value, determines in step S212 whether or not the outside temperature is within a predetermined range. .
In step S213, battery state setting unit 110 determines whether the battery temperature is within a predetermined range. If the battery temperature exceeds the predetermined range, the process proceeds to step S214 (see FIG. 14B).

If the predetermined time has not elapsed in step S207, if the charged power amount does not exceed the predetermined value in step S208, and if the discharged power amount does not exceed the predetermined value in step S209, the power is discharged in step S210. input/output is less than a predetermined time, if the SOC of the battery is outside the predetermined value in step S211, if the outside air temperature is out of the predetermined range in step S212, or if the battery temperature is out of the predetermined range in step S213, Return to step S201.

Here, even if the battery has deteriorated in capacity, the process does not jump to the END process and end. When a predetermined time has passed, or when a predetermined charging power amount has been charged, the process proceeds to the routine after step S214 (see FIG. 14B). Normally, the process returns to step S201 again and does not proceed to the routine after step S214, so Mahalanobis distance calculation is not performed either.

In step S214, the battery AC impedance measuring device 120 applies a minute AC signal with a frequency ω(i) (i=1, 2, . . . , n) to the battery 10 to Z ^' (ω(i)), imaginary axis impedance Z ^″ (ω(i))) curves are measured.

In step S215, the solution resistance calculator 130 performs an interpolation calculation to obtain the real axis impedance Z ^′ (ω _{m )} from ω _m when the imaginary axis impedance Z ^″ (ω _m )=0. If ≠ω(i), the real axis impedance Z ^' ( _ωm ) is calculated by interpolation from ω(i)< _ωm <ω(i+1).

In step S216, the solution resistance calculator 130 temporarily records the real axis impedance Z ^' (ω _m ) obtained by the interpolation calculation in a recording means (not shown) as the solution resistance of the battery.

In step S217, the Mahalanobis distance calculator 150 sets the reference space 151 before obtaining the Mahalanobis distance. The Mahalanobis distance calculator 150 obtains the average value and variance of the distribution from the distribution of the measured AC impedance to set the reference space 151 .

In step S218, the Mahalanobis distance calculation unit 150A calculates the Mahalanobis distance of the AC impedance curve (here, charge transfer resistance of AC impedance) of the battery measured this time. That is, the Mahalanobis distance calculator 150A calculates the Mahalanobis distance between the AC impedance curve of the battery measured this time and the set reference space 151 .

In step S219, the Mahalanobis distance calculation unit 150B reads out the calculation result of the AC impedance curve of the battery measured last time. That is, the Mahalanobis distance calculator 150B reads out the calculation result of the Mahalanobis distance between the previously measured AC impedance curve of the battery and the set reference space 151 .

In step S220, the battery deterioration determination unit 160 detects the minute AC signal of the same frequency ω(i) (i=1, 2, . . . , n) applied to the battery 10, and the AC The Mahalanobis distance of the impedance curve and the Mahalanobis distance of the AC impedance curve previously measured and recorded by the Mahalanobis distance calculator 150B are compared for each measurement frequency, and it is determined whether the comparison result exceeds a predetermined value.

If the comparison result exceeds the predetermined value (step S220: Yes), the process proceeds to step S221. If the comparison result does not exceed the predetermined value (step S220: No), the process of this flow ends.

In step S221 (see FIG. 14C), the battery deterioration determination unit 160 determines whether the comparison result satisfies the relationship ω ₁ <ω ₀ . Here, ω ₀ is the frequency exceeding a predetermined value in the comparison result between the Mahalanobis distance of the AC impedance curve measured and recorded last time and the Mahalanobis distance of the AC impedance curve measured and recorded the time before last. Also, ω1 is the frequency exceeding _a predetermined value in the comparison result between the Mahalanobis distance of the AC impedance curve measured this time and the Mahalanobis distance of the AC impedance curve measured and recorded last time.

As described above, since it is known from the experimental results that the measurement frequency decreases as the deterioration progresses, the determination is made in the direction of decreasing the measurement frequency.

_If the comparison result satisfies the relationship ω ₁ <ω ₀ (step S221 _: Yes), the process proceeds to step S222; finish.

In step S222, battery deterioration determination unit 160 reads the Mahalanobis distance of the AC impedance curve of the reference battery. Specifically, the battery deterioration determining unit 160 reads the Mahalanobis distance of the AC impedance curve of the reference battery from the AC impedance table for each reference battery deterioration degree 161 (see FIG. 9).

In step S223, the battery deterioration determination unit 160 interpolates to calculate the degree of deterioration of the Mahalanobis distance of the AC impedance curve measured this time with respect to the Mahalanobis distance of the AC impedance curve of the reference battery.

Step S224 is a <deterioration level updating step>. In step S224, the battery deterioration determination unit 160 updates the battery deterioration position. That is, the degree of deterioration of the battery is updated and this result is recorded.

In this way, the Mahalanobis distance of the AC impedance curve measured this time and the Mahalanobis distance of the AC impedance curve measured and recorded last time are compared for each measurement frequency, and the comparison result exceeds a predetermined value (step S220) and ω ₁ If there is a relationship of <ω ₀ (step S221), the battery deterioration position is updated, and the AC impedance curve is updated by the following processing.

Step S225 is <step of updating solution resistance>. In step S225, the battery deterioration determination unit 160 updates the real axis impedance Z ^' ( _ωm ) as the solution resistance of the battery.

The update of solution resistance is described.
When the AC impedance curve draws a rising Nyquist diagram from the real axis, from ω _m when the imaginary axis impedance Z ^″ (ω _m )=0, the real axis impedance Z ^′ (ω _m ) is the solution resistance of the battery. The solution resistance of the battery is updated to the new battery deterioration position, and this is recorded.This update of the solution resistance is performed by replacing the data temporarily recorded in the recording means in step S216 (see FIG. 14B) with the data that satisfies the conditions. It is to update as the solution resistance of time.

Steps S226 and S227 are <steps for updating the charge transfer resistance>. First, in step S226, the battery deterioration determination unit 160 updates the AC impedance curve of the battery. Specifically, the battery deterioration determination unit 160 replaces the AC impedance curve measured this time with the AC impedance curve measured and recorded last time and updates the record.

In step S227, battery deterioration determination unit 160 updates the Mahalanobis distance of the AC impedance curve, and ends the processing of this flow. Specifically, the battery deterioration determination unit 160 updates the Mahalanobis distance between the AC impedance curve measured this time and the set reference space instead of the Mahalanobis distance of the AC impedance curve measured and recorded last time.

[effect]
As described above, the battery deterioration determination device 100 according to the present embodiment determines the point at which the distribution ratio of the solution resistance or the ion transfer resistance and the charge transfer resistance of the preset AC impedance is competitive with the environmental temperature of the battery. A cooling control unit 22 that controls the measurement temperature to be 15 ° C. or less, which is the front and back region of the center, a battery AC impedance measurement device 120 that measures the battery AC impedance data at the measurement temperature, and the battery AC impedance measurement device 120 measured. A battery deterioration determination unit 160 that determines the degree of deterioration of the battery by comparing the measurement data with standard AC impedance data previously measured under the same conditions as the measurement conditions of the reference battery.

Then, in the method for determining battery deterioration according to the present embodiment, the environmental temperature of the battery is set in a range before and after a point at which the distribution ratio of the solution resistance or ion transfer resistance of the preset AC impedance and the charge transfer resistance is competitive. A step of controlling the measurement temperature to 15 ° C. or less and excluding 0 ° C., a step of measuring the AC impedance data of the battery at the measurement temperature, and the measured measurement data and the measurement conditions of the reference battery in advance under the same conditions and determining the degree of deterioration of the battery by comparing it with the measured standard AC impedance data.

Here, the calculation and arithmetic processing of the battery deterioration determination device and the battery deterioration determination method can be executed by a computer program.

As described in the problem to be solved, like the lead-acid battery described in Patent Document 4, the internal resistance of the AC impedance rises linearly with respect to the deterioration state, and the deterioration state can be easily grasped by measuring the internal resistance. Lithium-ion batteries, on the other hand, differ in their constituent elements (storage principle) themselves, and their behavior is also different, such as the impedance value being lower than the initial value when measured at room temperature or higher.
It is difficult to diagnose deterioration of a lithium-ion battery including all-solid-state batteries, and it is difficult to judge deterioration unless the battery has reached the end of its life.

The conventional method for judging the deterioration of a battery is to perform it in the normal temperature range where the battery state is stable.

In this embodiment, the measurement is performed at an ambient temperature of, for example, nearly 10° C., which is lower than room temperature. A temperature range near 10° C. is a temperature range in which the battery state is relatively stable and deterioration behavior is easily confirmed. In the temperature range near 10° C., the ratio of charge transfer resistance and solution resistance, which constitute the impedance of the battery, is about half.
By lowering the environmental temperature, it is possible to diagnose the battery in the middle of deterioration without requiring a large-scale device, and it is possible to realize a battery deterioration determination device that can determine even a moderate degree of deterioration.

In this embodiment, the cooling control unit 22 controls the environmental temperature of the battery to a measured temperature other than 0°C.

Lithium-ion batteries and all-solid-state lithium-ion batteries are manufactured in an inert environment with no air, but when the temperature reaches freezing, a small amount of moisture mixed in the constituent materials may cause condensation. If the AC impedance is measured in this state, the measured value may fluctuate, leading to an erroneous determination. For this reason, the region sandwiching 0° C., which is a temperature region inappropriate for deterioration degree determination and life deterioration control, is excluded from the temperature region. This makes it possible to ensure the accuracy of deterioration degree determination and life deterioration control.

In this embodiment, the battery deterioration determining unit 160 uses, as comparison data, AC impedance data at the applied frequency when the delay in impedance due to the capacitance component of the charge transfer resistance is maximized.

With this configuration, the measured AC impedance value at the applied frequency (around 5 Hz, not much dependent on the number of charge/discharge cycles) when the delay in impedance due to the capacitance component of the load transfer resistance is maximized in the measurement temperature range is Compare with standard data under the same conditions. This makes it possible to determine the degree of deterioration (degradation level).

Battery deterioration determination unit 160 uses distance calculation including Mahalanobis distance as a statistical method.

With such a configuration, it is possible to identify changes in AC impedance that indicate deterioration of the battery by using Mahalanobis distance analysis.

In this embodiment, the battery AC impedance measuring device 120 inputs battery impedance measurement data measured at a plurality of frequencies, and plots them on a complex plane represented by impedance real component Z ^′ and imaginary component Z ^″ . is a complex impedance processing unit that obtains a Nyquist plot, and the battery deterioration determination unit 160 selects the apex of the arc drawn by the Nyquist plot or the curve whose slope is 0 using a statistical method, and the selected reference Nyquist plot The degree of deterioration of the battery is determined based on

With this configuration, the degree of deterioration of the battery can be quantitatively diagnosed by a simple method. Since the degree of deterioration of the battery can be appropriately determined, the remaining life of the battery can be estimated, and an appropriate battery system can be realized and maintained.

<New battery judgment>
In the new battery determination apparatus 100 according to the present embodiment, the cooling control unit 22 determines the environmental temperature of the battery centering on the point at which the distribution ratio of the solution resistance or ion transfer resistance and the charge transfer resistance of the preset AC impedance is competitive. The battery deterioration determination unit 160 controls the measurement temperature to be less than 0 ° C., which is the region before and after , and the battery deterioration determination unit 160 measures the measurement data measured by the battery AC impedance measurement device 120 and the standard AC measured in advance under the same conditions as the measurement conditions of the reference battery It is determined whether the battery is a new battery or a used battery by comparing with the impedance data.

In the environmental temperature range below 0° C., it is possible to determine whether the battery is new or slightly used. That is, when the environmental temperature of the battery is lowered below 0° C., the AC impedance of the battery increases. If the measurement frequency is lowered to 4 Hz or less, the behavior of a battery that has undergone even a few charge-discharge cycles and that of a new battery will change significantly. At room temperature, the AC impedance does not change at all. Thus, by setting the AC impedance measurement temperature to less than 0° C., it becomes possible to determine whether the battery is new or has been used. It has a unique effect of being able to distinguish between new and used products, which was previously indistinguishable.

<Battery life control>
In the new battery determination apparatus 100 according to the present embodiment, the cooling control unit 22 determines the environmental temperature of the battery centering on the point at which the distribution ratio of the solution resistance or ion transfer resistance and the charge transfer resistance of the preset AC impedance is competitive. The measurement temperature is controlled to 15 ° C. or less, which is the region before and after , and the battery deterioration determination unit 160 determines the measurement data measured by the battery AC impedance measurement device 120 and the standard AC measured in advance under the same conditions as the measurement conditions of the reference battery. It judges the degree of deterioration of the battery by comparing it with the impedance data, and outputs battery life control information for reducing the charge level, temperature, or load current, which are deterioration factors of the battery, for the deteriorated battery judged to be deteriorated. .

By configuring in this way, it is possible to extend the life of the battery by reviewing the environmental temperature control range of the battery according to the state of deterioration of the battery. Conventionally, since the current value of deterioration of the battery is unknown, the temperature control range of the battery is not reviewed from the initial value. When the battery was new, there was no problem because the battery did not deteriorate even if it was operated in the general temperature control range. can be eliminated.

When the deterioration level of the battery in the middle of deterioration is obtained, the battery management temperature range is reviewed from the initial value, and the SOC, temperature, or load current, which are deterioration factors of the battery, are lowered. By appropriately controlling the battery in this way, it is possible to extend the life of the battery.
Also, when the deterioration diagnosis is performed in an appropriate temperature range (for example, 10° C.), it is possible to appropriately control the battery life over the entire range.

The present invention is not limited to the above-described embodiments, and includes other modifications and applications without departing from the gist of the present invention described in the claims.
For example, batteries to be subjected to deterioration determination can be widely applied to secondary batteries such as all solid state lithium ion batteries.

The battery deterioration determination method, the battery deterioration determination device, the new battery determination device, and the battery life control device may be hardware with independent calculation functions, or may be software in the battery system. Calculations and arithmetic processing of the battery deterioration determination method, the battery deterioration determination device, and the program may be performed using an ASIC (Application Specific Integrated Circuit) or the like instead of a computer program.

Moreover, the above-described embodiment has been described in detail in order to explain the present invention in an easy-to-understand manner, and is not necessarily limited to those having all the described configurations. Further, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. . Moreover, it is possible to add, delete, or replace a part of the configuration of each embodiment with another configuration.

Further, each of the above configurations, functions, processing units, processing means, and the like may be realized by hardware, for example, by designing them in an integrated circuit. Further, as shown in FIG. 6, each of the above configurations, functions, etc. may be realized by software for a processor to interpret and execute a program for realizing each function. Information such as programs, tables, files, etc. that realize each function can be stored in recording devices such as memory, hard disks, SSD (Solid State Drives), IC (Integrated Circuit) cards, SD (Secure Digital) cards, optical discs, etc. It can be held on a recording medium. In addition, in this specification, processing steps describing time-series processing refer to processing performed in time-series according to the described order, as well as processing performed in parallel or individually, even if processing is not necessarily performed in time-series. It also includes processing (eg, parallel processing or processing by objects) that is executed in parallel.
In addition, the control lines and information lines indicate those considered necessary for explanation, and not all control lines and information lines are necessarily indicated on the product. In practice, it may be considered that almost all configurations are interconnected.

10 battery (target battery)
20 battery control unit 21 charge/discharge control unit 22 cooling control unit (battery temperature control means)
30 measurement unit 31 battery voltage/battery current detection unit 32 battery temperature detection unit (battery temperature control means)
33 outside air temperature detector (battery temperature control means)
100 battery deterioration determination device 110 battery state setting unit (battery temperature control means)
120 battery AC impedance measuring device (impedance measuring means)
130 solution resistance calculation unit (solution resistance calculation means)
140, 140A, 140B charge transfer resistance calculator (charge transfer resistance calculator)
150, 150A, 150B Mahalanobis distance calculation unit (distance calculation means)
151 reference space 160 battery deterioration determination unit (battery deterioration determination means)
161 AC impedance table for each reference battery deterioration degree 162 AC impedance table for reference new battery

Claims (10)

The environmental temperature of the battery is controlled to a measurement temperature of 15 ° C. or less, which is a region before and after the point where the distribution ratio of the solution resistance or ion transfer resistance and charge transfer resistance of the preset AC impedance is antagonistic. Battery temperature a control means;
impedance measuring means for measuring AC impedance data of the battery at the measurement temperature;
battery deterioration determination means for determining the degree of deterioration of the battery by comparing the measurement data measured by the impedance measurement means with standard AC impedance data previously measured under the same conditions as the measurement conditions of a reference battery. A battery deterioration determination device characterized by: The battery temperature control means is
The battery deterioration determination device according to claim 1, wherein the environmental temperature of the battery is controlled to the measured temperature except 0°C. The battery temperature control means is
Control the environmental temperature of the battery to a measured temperature of less than 0 ° C,
The battery deterioration determination means includes:
It is characterized in that whether the battery is a new battery or a used battery is determined by comparing the measurement data measured by the impedance measuring means with standard AC impedance data previously measured under the same conditions as the measurement conditions of a reference battery. The battery deterioration determination device according to claim 1. The battery temperature control means is
The environmental temperature of the battery is controlled to a measurement temperature of 15 ° C. or less, which is a region before and after the point where the distribution ratio of the solution resistance or ion transfer resistance of the preset AC impedance and the charge transfer resistance is antagonistic,
The battery deterioration determination means includes:
Determining the degree of deterioration of the battery by comparing the measurement data measured by the impedance measuring means with the standard AC impedance data previously measured under the same conditions as the measurement conditions of the reference battery,
2. The battery deterioration determination device according to claim 1, wherein, for a deteriorated battery determined to be deteriorated, battery life control information for reducing a charge level, temperature, or load current, which are deterioration factors of the battery, is output. A solution resistance calculation means for calculating a solution resistance represented by a point where the real axis impedance and the imaginary axis impedance of the AC impedance cross zero when the measurement frequency is lowered based on the AC impedance measured by the impedance measurement means. The battery deterioration determination device according to claim 1, characterized in that: charge transfer resistance calculation means for calculating the charge transfer resistance of the measured AC impedance of the battery based on the AC impedance measured by the impedance measurement means;
a distance calculation means for calculating a distance using a statistical method for the charge transfer resistance calculated by the charge transfer resistance calculation means,
The battery deterioration determination means includes:
The battery deterioration determination device according to any one of claims 1 to 4, wherein the deterioration degree of the battery is determined based on the distance calculation result calculated by the distance calculation means. The battery deterioration determination device according to claim 6, wherein the distance calculation means uses distance calculation including Mahalanobis distance as a statistical method. The impedance measuring means is
A complex impedance processing unit that obtains a Nyquist plot by inputting battery impedance measurement data measured at a plurality of frequencies and plotting it on a complex plane represented by impedance real number component Z ^' and imaginary number component Z ^' ',
The battery deterioration determination means includes:
2. The apex of the arc drawn by the Nyquist plot or a curve whose slope is 0 is selected using a statistical method, and the degree of deterioration of the battery is determined based on the selected reference Nyquist plot. battery deterioration determination device. The battery deterioration determination device according to claim 1, wherein the battery is an all-solid lithium ion battery or a lithium ion battery. The environmental temperature of the battery is 15 ° C. or less, and excluding 0 ° C. controlling to the measured temperature;
measuring AC impedance data of the battery at the measured temperature;
and determining the degree of deterioration of the battery by comparing the measured data with standard AC impedance data previously measured under the same conditions as the measurement conditions of a reference battery.

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