Evaluation device and evaluation method

Abstract

This method allows for a simpler assessment of the degradation status of energy storage devices. [Solution] The evaluation device of the present disclosure is a device for evaluating the degradation state of an energy storage device, comprising a control unit that acquires the voltage and / or SOC during charging and discharging of the energy storage device at predetermined intervals while the energy storage device is in use, derives a usage frequency distribution, and evaluates the degradation state of the energy storage device based on the difference between a determination frequency distribution including the initial value of the energy storage device and the derived usage frequency distribution.

Description

Technical Field

[0001] This specification discloses an evaluation apparatus and an evaluation method.

Background Art

[0002] Conventionally, as an evaluation method for evaluating a lithium secondary battery, by inputting the usage history of the target secondary battery included in the target secondary battery information and the internal resistance value increase information into a classification model, a tendency group of the target secondary battery is determined, and based on the target secondary battery information and the correlation information corresponding to the tendency group, an estimation of the capacity index value of the target secondary battery has been proposed (for example, see Patent Document 1). In this evaluation method, it is stated that even when the usage histories of secondary batteries are different, the capacity can be efficiently estimated from the state of the internal resistance of the secondary battery. Further, as an evaluation method, a battery system, a memory storing a capacity estimation model obtained by machine learning, and a processor for estimating the battery capacity maintenance rate using the capacity estimation model are provided, and the capacity estimation model is a learned model using, as teacher data, the usage pattern regarding the current, SOC, and temperature of the battery and the measured value of the capacity degradation rate per unit time of the battery (for example, see Patent Document 2). In this evaluation method, it is stated that the capacity of the battery can be estimated with high accuracy.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

[0005] This disclosure is made in view of these challenges and primarily aims to provide a novel evaluation apparatus and evaluation method that can evaluate the degradation state of energy storage devices using a simpler method. [Means for solving the problem]

[0006] Through diligent research to achieve the above-mentioned objectives, the inventors discovered that by acquiring the voltage and SOC of an energy storage device during charging and discharging and analyzing their frequency distribution, the degradation state of the energy storage device can be understood, leading to the completion of the invention disclosed herein.

[0007] That is, the evaluation apparatus disclosed herein is An evaluation device for evaluating the degradation state of energy storage devices, A control unit that acquires the voltage and / or SOC of a power storage device during charging and discharging at predetermined intervals to derive a usage frequency distribution, and evaluates the degradation state of the power storage device based on the difference between a determination frequency distribution including the initial value of the power storage device and the derived usage frequency distribution. It is something that is provided.

[0008] The evaluation methods disclosed herein are: An evaluation method for evaluating the degradation state of an energy storage device, A derivation step of obtaining the voltage and / or SOC during charging and discharging of the energy storage device at predetermined time intervals and deriving the usage frequency distribution, An evaluation step in which the degradation state of the energy storage device is evaluated based on the difference between the frequency distribution for determination, which includes the initial value of the energy storage device, and the frequency distribution during use that was derived, It includes. [Effects of the Invention]

[0009] In the evaluation device and evaluation method of the present disclosure, the deterioration state of the power storage device is evaluated based on the difference value between the usage frequency distribution obtained by acquiring the voltage and / or SOC during charging and discharging of the power storage device every predetermined time and the determination frequency distribution including the initial value of the power storage device. In this evaluation device, there is no need to perform machine learning or the like, and the deterioration state of the power storage device can be evaluated by a simpler method. In addition, in this evaluation method, any aspect of the evaluation device may be adopted, or steps for realizing the function of the evaluation device may be added.

Brief Description of the Drawings

[0010] [Figure 1] Explanatory diagram showing an example of the battery system 10. [Figure 2] Flowchart showing an example of the deterioration state evaluation processing routine. [Figure 3] Relationship diagram between the charge-discharge curve and the SOC. [Figure 4] Explanatory diagram showing an example of the relationship between the SOC and the count number. [Figure 5] Relationship diagram between the SOC and the frequency. [Figure 6] Relationship diagram between the voltage and the frequency. [Figure 7] Explanatory diagram of an example of the method for quantifying battery deterioration. [Figure 8] Explanatory diagram of an example of the method for quantifying battery deterioration. [Figure 9] Relationship diagram between the charging C rate and the data acquisition interval. [Figure 10] Schematic diagram showing the relationship between the battery usage example and the calculated frequency distribution.

Embodiments for Carrying Out the Invention

[0011] (Battery System 10) Embodiments of the evaluation apparatus disclosed in this specification will be described below with reference to the drawings. FIG. 1 is a schematic explanatory diagram showing an example of a battery system 10. The battery system 10 may be, for example, a system that executes the usage management of a lithium-ion secondary battery as the power storage device 12. This battery system 10 includes an object 11, a power storage device 12, a voltmeter 13, and an evaluation apparatus 20. The object 11 is operated by the power supplied from the power storage device 12. The object 11 may be, for example, a drive source such as a motor. The voltmeter 13 measures the voltage of the power storage device 12. The voltmeter 13 outputs the measured voltage value to the evaluation apparatus 20 at predetermined intervals.

[0012] The power storage device 12 is not particularly limited as long as it can be charged and discharged, and may be any one of an alkali metal battery, an alkali metal ion battery, a capacitor, a hybrid capacitor, an air battery, and a nickel-hydrogen battery. Examples of the alkali metal include lithium, sodium, potassium, cesium, etc., among which lithium is preferable. The power storage device 12 is configured as, for example, a lithium-ion secondary battery. The power storage device 12 may include, for example, a positive electrode, a negative electrode, and an ion conduction medium that is interposed between the positive electrode and the negative electrode and conducts carrier ions. This power storage device 12 may have a structure in which a positive electrode formed with a positive electrode mixture on both sides of a current collector and a negative electrode formed with a negative electrode mixture on both sides of the current collector are laminated, or may have a bipolar structure in which electrode bodies formed with a positive electrode mixture on one side of the current collector and a negative electrode mixture on the other side are laminated. The positive electrode may include, as the positive electrode active material, a sulfide containing a transition metal element, an oxide containing lithium and a transition metal element, etc. The positive electrode active material is, for example, a lithium manganese composite oxide having a basic composition formula of Li (1-x) MnO2 (0 < x < 1, etc., the same below) or Li (1-x) Mn2O4, etc., a lithium cobalt composite oxide having a basic composition formula of Li (1-x) CoO2, etc., a lithium nickel composite oxide having a basic composition formula of Li (1-x) NiO2, etc., a basic composition formula of Li (1-x) Nia Co b Mn c Lithium nickel cobalt manganese composite oxides such as O2 (a + b + c = 1) can be used. Also, examples of the positive electrode active material include lithium iron phosphate. Note that the "basic composition formula" implies that other elements may be included. The negative electrode may include a carbon material or a composite oxide containing lithium as the negative electrode active material. Examples of the negative electrode active material include inorganic compounds such as lithium, lithium alloys, and tin compounds, carbon materials capable of occluding and releasing lithium ions, composite oxides containing a plurality of elements, and conductive polymers. Examples of the carbon material include cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, and carbon fibers. Among these, graphites such as artificial graphite and natural graphite are preferred. Examples of the composite oxide include lithium titanium composite oxide and lithium vanadium composite oxide. The ion conduction medium can be, for example, an electrolytic solution in which a supporting salt is dissolved. Examples of the supporting salt include lithium salts such as LiPF6 and LiBF4. Examples of the solvent of the electrolytic solution include carbonates, esters, ethers, nitriles, furans, sulfolanes, and dioxolanes, and these can be used alone or in combination. Specifically, examples of the carbonates include cyclic carbonates such as ethylene carbonate, propylene carbonate, vinylene carbonate, butylene carbonate, and chloroethylene carbonate, and chain carbonates such as dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl-n-butyl carbonate, methyl-t-butyl carbonate, di-i-propyl carbonate, and t-butyl-i-propyl carbonate. Also, the ion conduction medium can utilize a solid ion conductive polymer, an inorganic solid electrolyte, a mixed material of an organic polymer electrolyte and an inorganic solid electrolyte, or an inorganic solid powder bound by an organic binder. A separator may be disposed between the positive electrode and the negative electrode of this power storage device 12. This separator may be a solid electrolyte.

[0013] The evaluation device 20 is a device that estimates and evaluates the degradation state of the energy storage device 12 from its voltage and / or state of charge (SOC). The evaluation device 20 comprises a control unit 21 and a storage unit 22. The evaluation device 20 is installed in a device that uses the energy storage device 12, and the control unit 21 may evaluate the degradation state of the energy storage device 12 in real time during charging and discharging while the energy storage device 12 is in use. Since this evaluation device 20 can evaluate the energy storage device 12 while it is in use, there is no need to perform separate charging, discharging, or measurements for the evaluation of the energy storage device 12. The control unit 21 is configured, for example, as a processor centered on a CPU, and controls the entire device. This control unit 21 acquires the voltage and / or SOC of the energy storage device 12 during charging and discharging at predetermined time intervals to derive a usage frequency distribution, and evaluates the degradation state of the energy storage device 12 based on the difference between the nth-time judgment frequency distribution, which is a reference value of the energy storage device 12 and includes the initial value, and the derived usage frequency distribution. The memory unit 22 is configured as a large-capacity storage device such as an HDD, and stores the frequency distribution 23 for the nth determination, the frequency distribution 24 during use, time-series data 25, and various programs. The frequency distribution 23 for the nth determination is the frequency distribution of the voltage and / or SOC of the energy storage device 12, where n=0 is the initial frequency distribution and n=1 is the frequency distribution used for the first degradation determination. The evaluation device 20 saves not only the initial frequency distribution but also all the frequency distributions for the nth (n is an integer greater than or equal to 0) degradation determination. For example, for the 5th degradation determination, the capacity degradation amount is calculated as "difference between n=0 and n=1" + "difference between n=1 and n=2" + "difference between n=2 and n=3" + "difference between n=3 and n=4" + "difference between n=4 and n=5", thus saving the capacity degradation amounts from previous degradation determinations. The frequency distribution 24 during use is the frequency distribution of the voltage and / or SOC in a predetermined period near the present when the energy storage device 12 is in use. The time-series data 25 consists of data acquired continuously for voltage and / or SOC. The usage frequency distribution 24 is derived by extracting data for a predetermined period from the data included in the time-series data 25.

[0014] The control unit 21 acquires the voltage and / or SOC of the energy storage device within a predetermined time range of 1 hour or less, 30 minutes or less, 15 minutes or less, 10 minutes or less, and 5 minutes or less. Since the acquisition of voltage and SOC is related to the amount of information in the usage frequency distribution, a relatively short time allows for more measurement points and more reliable evaluation of the degradation state. The control unit 21 may also derive a usage frequency distribution that includes the frequency for each predetermined voltage range and / or SOC range. This evaluation device 20 can obtain a usage frequency distribution accumulated within a predetermined range. The voltage range may be, for example, between the voltage at full charge and the voltage at discharge, in increments of 1V, 0.5V, 0.1V, etc. The SOC range may be in increments of 10%, 5%, 2.5%, etc.

[0015] The control unit 21 may evaluate the degradation state of the energy storage device 12 using a usage frequency distribution 24 accumulated over a predetermined period including a range of 10 days to 1 year. The usage frequency distribution 24 is preferably created using data accumulated over a predetermined period from the measurement point closest to the present time. In the usage frequency distribution 24, the predetermined period for accumulating data is preferably in the range of 10 days to 1 year, because if it is too short, the amount of information acquired will be small, and if it is too long, the changes in the usage environment may become too large. This predetermined period may be, for example, 10 days, 20 days, 1 month, 2 months, 3 months, 6 months, etc.

[0016] The control unit 21 may correct the voltage and / or SOC frequency of the nth-time determination frequency distribution 23 in a specific region where the effects of degradation are less pronounced, using the frequency of the usage frequency distribution 24 as a reference, and calculate the difference value. The specific region may be, for example, a lithium-ion secondary battery, a range of SOC = 50% to 65%. This correction is performed, for example, by multiplying the entire nth-time determination frequency distribution 23 by 1.1 when the specific region of the nth-time determination frequency distribution 23 is 1.1 times the value of the usage frequency distribution 24 (see Figures 5 and 6 below).

[0017] The control unit 21 may calculate the product of the range width and / or difference value of a predetermined voltage range and / or SOC range in the nth-time determination frequency distribution 23 and the usage frequency distribution 24 for each voltage range and / or SOC range, and use the accumulated value as the degree of degradation as the degradation state. To explain using SOC as an example, for example, if the frequency distribution is divided into 5% SOC intervals, the difference between the usage frequency distribution 24 and the nth-time determination frequency distribution 23 is normalized by dividing by the value of the usage frequency distribution 24, and this value is multiplied by this 5%, and the resulting value is accumulated (see Figures 7 and 8 below).

[0018] (Evaluation method) The evaluation method disclosed herein is an evaluation method for evaluating the degradation state of an energy storage device, and includes: a derivation step of acquiring the voltage and / or SOC of the energy storage device 12 during charging and discharging at predetermined time intervals to derive a usage frequency distribution; and an evaluation step of evaluating the degradation state of the energy storage device 12 based on the difference between a frequency distribution 23 for n-th determination including the initial value of the energy storage device 12 and the derived usage frequency distribution 24. This evaluation method may be performed by the evaluation device 20 described above. In this evaluation method, similar to the evaluation device described above, the degradation state of the energy storage device is evaluated based on the difference between the usage frequency distribution and the determination frequency distribution including the initial value, so the degradation state of the energy storage device can be evaluated using a simpler method. In this evaluation method, any embodiment of the evaluation device described above may be adopted, or steps that realize the functions of the evaluation device described above may be added.

[0019] Figure 2 is a flowchart showing an example of a degradation state evaluation processing routine executed by the control unit 21 of the evaluation device 20. This flowchart is stored in the memory unit 22 and executed when the battery system 10 is put into use. When this routine starts, the control unit 21 determines whether or not it is the timing to acquire the frequency factor (S100), and if it is the timing to acquire it, it acquires the voltage from the voltmeter 13 and obtains the SOC from the acquired voltage value (S110). This timing is set to the acquisition time, 5 minutes, 10 minutes, 15 minutes, 30 minutes, 1 hour, etc. Next, the control unit 21 updates the time series data 25 with the acquired voltage and SOC (S120). After S120, or if it is not the timing to acquire the frequency factor in S100, it determines whether or not it is the timing to determine the degradation state (S130). Examples of the timing for determining the degradation state include user input or the passage of a predetermined period, such as 6 months or 1 year. When it is time to determine the degradation state, the control unit 21 determines whether the number of measurement points in the time series data 25 is within a divisible number (S140). The divisible number can be, for example, one hundred, several hundred, one thousand, or several thousand points. If the number of measurement points is within a divisible number, the control unit 21 derives a usage frequency distribution 24 using the measurement points from the most recent predetermined period (S150). The control unit 21 places the measurement points into one of the predetermined SOC widths (for example, 5%) and creates a frequency (see Figure 4 below). Next, the control unit 21 reads and acquires the nth-time determination frequency distribution 23 from the storage unit 22 (S160), and acquires the degradation state of the energy storage device 12 based on the nth-time determination frequency distribution 23 and the usage frequency distribution 24 (S170). At this time, the control unit 21 corrects the frequency distribution 23 for n-th determination to match the usage frequency distribution 24 based on a specific region where the effect of degradation is small, obtains the difference value between the usage frequency distribution 24 and the frequency distribution 23 for n-th determination for each predetermined range width, normalizes it by dividing it by the value of the usage frequency distribution 24, calculates the product of the normalized difference value and the range width for each predetermined range width, and takes the value obtained by accumulating these as the degree of degradation. The "capacity degradation amount" as the degree of degradation can be obtained by accumulating the capacity degradation amount at the time of the previous degradation determination and the estimated capacity degradation amount at the time of the current determination. Subsequently, the control unit 21 outputs the obtained degree of degradation to an external device such as a display or a management device (S180).Then, after S180, or if it is not the timing for determining the deterioration state in S130, or if the number of measurement points is not the number that can be determined in S140, the control unit 21 determines whether the deterioration determination process has finished or not (S190). If the deterioration determination process has not finished, the control unit 21 executes the processes from S100 onwards, while if the deterioration determination process has finished, it terminates this routine.

[0020] Here, the correspondence between the components of this embodiment and the components of the present disclosure will be clarified. The energy storage device 12 of this embodiment corresponds to an example of the energy storage device of the present disclosure, the evaluation device 20 corresponds to an example of the evaluation device, and the control unit 21 corresponds to an example of the control unit. In addition, in this embodiment, an example of the evaluation method of the present disclosure is also clarified by describing the operation of the evaluation device 20.

[0021] In the evaluation apparatus 20 and evaluation method of this embodiment described above, the degradation state of the energy storage device is evaluated based on the difference between the usage frequency distribution obtained by acquiring the voltage and / or SOC during charging and discharging of the energy storage device at predetermined time intervals and the determination frequency distribution including the initial value of the energy storage device. This evaluation apparatus and evaluation method does not require machine learning or the like, and the degradation state of the energy storage device can be evaluated using a simpler method.

[0022] It goes without saying that this disclosure is not limited in any way to the embodiments described above, and can be implemented in various forms as long as they fall within the technical scope of this disclosure.

[0023] For example, in the embodiment described above, voltage and SOC were used as frequency factors, but voltage alone or SOC alone may also be used.

[0024] Although not described in the embodiments described above, the evaluation method of this disclosure may also be used to evaluate the SOH estimate obtained from the battery history. If there is a discrepancy between the degree of degradation of this disclosure and the SOH estimate, the SOH estimate may not be adopted.

[0025] In the embodiment described above, the frequency distribution 23 for n-th determination also preserves the frequency distribution for the nth time, but it is not limited to this and may include only the initial frequency distribution.

[0026] This disclosure may be any of the following [1] to [9]. [1] An evaluation device for evaluating the degradation state of an energy storage device, A control unit that acquires the voltage and / or SOC of a power storage device during charging and discharging at predetermined intervals to derive a usage frequency distribution, and evaluates the degradation state of the power storage device based on the difference between a determination frequency distribution including the initial value of the power storage device and the derived usage frequency distribution. An evaluation device equipped with the following features. [2] The evaluation apparatus according to [1], wherein the control unit acquires the voltage and / or SOC of the energy storage device within a predetermined time range of 1 hour or less, 30 minutes or less, 15 minutes or less, 10 minutes or less, and 5 minutes or less. [3] The evaluation apparatus according to [1] or [2], wherein the control unit derives the usage frequency distribution including the frequency for each predetermined voltage range and / or SOC range. [4] The control unit evaluates the degradation state of the energy storage device using the usage frequency distribution accumulated over a predetermined period including a range of 10 days to 1 year, according to any one of [1] to [3]. [5] The control unit corrects the usage frequency distribution based on the voltage and / or SOC of the initial values ​​of the determination frequency distribution in a specific region where the effects of degradation are less pronounced, and obtains the difference value, as described in any one of [1] to [4]. [6] The control unit calculates the product of the range width of a predetermined voltage range and / or SOC range in the determination frequency distribution and the usage frequency distribution and the difference value for each voltage range and / or SOC range, and the value obtained by integrating these is the degree of deterioration as the deterioration state, as described in any one of [1] to [5]. [7] The evaluation device is installed in the device that uses the energy storage device, The control unit evaluates the degradation state of the energy storage device in real time during charging and discharging while the energy storage device is in use, as described in any one of [1] to [6]. [8] The energy storage device is a lithium secondary battery, an evaluation apparatus according to any one of [1] to [7]. [9] An evaluation method for evaluating the degradation state of an energy storage device, A derivation step of obtaining the voltage and / or SOC during charging and discharging of the energy storage device at predetermined time intervals and deriving the usage frequency distribution, An evaluation step in which the degradation state of the energy storage device is evaluated based on the difference between the frequency distribution for determination, which includes the initial value of the energy storage device, and the frequency distribution during use that was derived, An evaluation method that includes this. [Examples]

[0027] The following describes an example of an experimental case in which the evaluation apparatus and evaluation method disclosed herein were specifically examined.

[0028] For the degradation evaluation test, a lithium-ion secondary battery (Panasonic NCR18650B) was used as the energy storage device. The energy storage devices used were battery 1 (new), battery 2 (with a capacity reduced to 90.5%), and battery 3 (with a capacity reduced to 2.6%). Figure 3 shows the relationship between the OCV charge / discharge curve and the State of Charge (SOC) at 20°C - 0.1CC discharge using batteries 1 and 2. Since the capacity of the degraded battery 2 has decreased to 90.5% compared to the new battery 1, the discharge time of the degraded battery is shorter than that of the new battery. 3.00V was defined as SOC=0% and 4.20V as SOC=100%, and each voltage was defined in 5% increments relative to the initial capacity. Data was acquired once every 5 minutes, and a frequency distribution was created by counting voltages between 3.00V (SOC0%) and 3.23V (SOC5%) as having a frequency of SOC0%. Figure 4 is an explanatory diagram of the histogram showing the relationship between the count number and the state of charge (SOC) obtained from the discharge OCV in Figure 3. Figure 5 is a relationship diagram between SOC and frequency, where the sum of all count numbers on the vertical axis equals "1" compared to Figure 4. Figure 6 is a relationship diagram between voltage and frequency, using batteries 1 and 2, where the sum of all count numbers on the vertical axis equals "1". In the degraded battery 2, the capacity has decreased by 30% to 45% of the SOC, so the SOC frequency has also decreased by 30% to 45% of the SOC. As the capacity decreases in this way, the capacity does not decrease uniformly across all SOC ranges, so the shape of the SOC frequency distribution changes.

[0029] Figure 7 is an explanatory diagram of an example of a method for quantifying battery degradation using batteries 1 and 2. An example of a method for quantifying battery degradation will be explained using Figure 7. First, the frequency (baseline) is adjusted to the SOC range in which capacity degradation is presumed not to have occurred. In this case, this corresponds to SOC 50% to 65%, so the frequency of new batteries was multiplied by 1.1 (see Figures 5 and 6). Since the frequency is obtained at 5% SOC intervals, the decrease in frequency is accumulated. As for the calculation method, for example, the capacity decrease in "(1)" is calculated by dividing the frequency difference on the vertical axis by the frequency of the degraded product and multiplying by the SOC range, specifically, (0.0474 - 0.0381) / 0.0474 × 5% = 0.981%. Similarly, the capacity decrease in "(2)" is calculated as (0.0571 - 0.0667) / 0.0667 × 5% = -0.714%. The capacity reduction can be calculated by adding up the calculated values ​​(1) to (13), and the result was 10.1%. This result suggests that the 10.1% capacity reduction of the degraded product is close to the actual 9.5%, indicating that the estimation was accurate. Furthermore, according to the quantification of battery degradation of the SOC frequency distribution during discharge in battery 3 shown in Figure 8, the estimated capacity reduction was calculated to be 4.9%, which is close to the actual capacity reduction of 2.6%. As shown in Figure 6, which is included for reference, the same considerations can be applied to the acquired data for voltage frequency. Generally, battery usage and environment vary, but if the user is the same, similar conditions are likely to occur. For example, the battery temperature reflects the temperature of the region where the user lives, and the SOC range used tends to be higher for those who charge frequently. Therefore, by selecting data with similar battery usage and environment, and observing the time-series changes in the SOC frequency distribution during charging and discharging as described above, it is possible to estimate battery degradation (e.g., capacity degradation).

[0030] As shown in Figure 2, the flowchart of the degradation state evaluation processing routine assumes the acquisition of battery usage history data, including the SOC frequency distribution (voltage frequency distribution) during charging or discharging. Regarding the SOC frequency distribution, in Figure 3, data was acquired once every 5 minutes. However, if the acquisition frequency is, for example, once every hour, only 0 to 1 data point will be recorded for each SOC in 5% increments during a single charge / discharge cycle at 0.1C, making it difficult to properly distribute the frequency to each SOC. Figure 9 is a diagram showing the relationship between the charge C rate and the data acquisition interval. Figure 9 shows the data acquisition interval that allows for the acquisition of at least one data point for each SOC band with respect to the charge / discharge C rate when creating an SOC frequency distribution in 5% increments. For a battery used at an average of 0.1C, an acquisition frequency of at least once every 30 minutes is desirable to obtain a comparable SOC frequency distribution, and more preferably at least once every 15 minutes or at least once every 5 minutes. For a general solution, it is desirable to have at least one charge / discharge cycle per minute [(SOC step value / 100) × (60 / C rate)] minutes relative to the average C rate during use. More preferably, it is estimated to be at least one charge / discharge cycle per minute [2 × (SOC step value / 100) × (60 / C rate)] minutes, and even more preferably, at least one charge / discharge cycle per minute [3 × (SOC step value / 100) × (60 / C rate)] minutes. However, since the frequency distribution is data from multiple charge / discharge cycles, the above conditions are not necessary but are desirable. Figure 10 is a schematic diagram showing the relationship between battery usage examples and the calculated frequency distribution. In the flowchart of the degradation state evaluation processing routine, for the first time, after a certain period has elapsed, the acquired data is saved for battery degradation determination. From the second time onward, if a certain period has elapsed since the previous saving for battery degradation determination, the acquired data at that time is saved for battery degradation determination. As a result, time-series data for battery degradation determination is created. A "certain period" refers to the minimum number of days necessary to avoid significant variations in frequency or biases in usage due to a small number of charge / discharge cycles. Since one day may include days of non-use, a period of 10 days or more is desirable. From the time-series data used for battery degradation assessment, data with similar environmental and usage characteristics (e.g., average temperature calculated from battery sample history data, average SOC, average C-rate during charging and discharging, etc.) are extracted. The extracted data are compared, and the degree of battery degradation is quantified using methods such as those explained in Figures 7 and 8 to determine battery degradation.Regarding the SOC frequency distribution, cumulative data since measurement is acceptable, but cumulative data within each period is preferable. For example, if the previous data was taken on January 1st and the current data on February 1st, cumulative data from January 1st to February 1st is preferable because it more clearly shows shape changes. In some cases, SOH is estimated from battery history data, so if there is a discrepancy between the estimated SOH value and the battery degradation judgment, it is presumed that the SOH estimation is misdiagnosed, and it can be used as a countermeasure against misdiagnosis, such as adopting the battery degradation judgment. To accurately measure capacity, it is necessary to charge and discharge from SOC 0% to 100% under specified conditions such as temperature and C rate, but this would waste power and time, making it inefficient to actually do. Therefore, as a general method, SOH is estimated based on usage history from an SOH estimation model formula constructed based on test results. However, actual SOH varies greatly depending on the usage history, so the model formula cannot be said to be universally applicable to diverse usage. In particular, errors tend to be large for extreme usage. Also, for long-term use, the model formula is extrapolated based on test results, so errors tend to be large. Furthermore, a problem arises because errors may not be detected. On the other hand, this SOC frequency distribution-based degradation assessment is a statistical distribution within a period, and the information is similar to a rough OCV curve with time information removed. By selecting the data, the actual battery degradation status can be directly determined. In addition, because it contains statistical information while being lightweight, it is suitable for handling large amounts of battery data, such as automotive batteries. [Industrial applicability]

[0031] The evaluation apparatus and evaluation method disclosed herein are applicable to the technical field of detecting the state of lithium-ion secondary batteries. [Explanation of Symbols]

[0032] 10 Battery system, 11 Object, 12 Energy storage device, 13 Voltmeter, 20 Evaluation device, 21 Control unit, 22 Memory unit, 23 Frequency distribution for nth determination, 24 Frequency distribution during use, 25 Time series data.

Claims

1. An evaluation device for evaluating the degradation state of energy storage devices, A control unit that acquires the voltage and / or SOC of a power storage device during charging and discharging at predetermined intervals to derive a usage frequency distribution, and evaluates the degradation state of the power storage device based on the difference between a determination frequency distribution including the initial value of the power storage device and the derived usage frequency distribution. An evaluation device equipped with the following features.

2. The evaluation apparatus according to claim 1, wherein the control unit acquires the voltage and / or SOC of the energy storage device within any of the ranges of 1 hour or less, 30 minutes or less, 15 minutes or less, 10 minutes or less, and 5 minutes or less as the predetermined time.

3. The evaluation apparatus according to claim 1 or 2, wherein the control unit derives the usage frequency distribution including the frequency for each predetermined voltage range and / or SOC range.

4. The evaluation apparatus according to claim 1 or 2, wherein the control unit evaluates the deterioration state of the energy storage device using the usage frequency distribution accumulated over a predetermined period including a range of 10 days to 1 year.

5. The evaluation apparatus according to claim 1 or 2, wherein the control unit corrects the frequency of the voltage and / or SOC in the determination frequency distribution in a specific region where the effect of degradation is less, based on the frequency of the usage frequency distribution, and calculates the difference value.

6. The evaluation apparatus according to claim 1 or 2, wherein the control unit calculates the product of the range width of a predetermined voltage range and / or SOC range in the determination frequency distribution and the usage frequency distribution and the difference value for each voltage range and / or SOC range, and the value obtained by integrating these is the degree of deterioration as the deterioration state.

7. The evaluation device is installed in the device that uses the energy storage device, The evaluation apparatus according to claim 1 or 2, wherein the control unit evaluates the degradation state of the energy storage device in real time during charging and discharging while the energy storage device is in use.

8. The evaluation apparatus according to claim 1 or 2, wherein the energy storage device is a lithium secondary battery.

9. An evaluation method for evaluating the degradation state of an energy storage device, A derivation step of obtaining the voltage and / or SOC during charging and discharging of the energy storage device at predetermined time intervals and deriving the usage frequency distribution, An evaluation step in which the degradation state of the energy storage device is evaluated based on the difference between the frequency distribution for determination, which includes the initial value of the energy storage device, and the frequency distribution during use that was derived, An evaluation method that includes this.

Images