Estimation device, energy storage device, estimation method, and computer program

Abstract

Providing an estimation device, an energy storage device, an estimation method, and a computer program. [Solution] An estimation device for estimating a post-degradation performance value, which indicates the performance of an energy storage element at any point in time of degradation, by constant current testing, comprising: a calculation unit that determines the DC resistance value of the energy storage element using the voltage change value over a time range from the start of the constant current test to the point immediately after the start and the current value in the constant current test; and an estimation unit that estimates the post-degradation performance value of the energy storage element by referring to the correlation relationship that exists between the DC resistance value and the post-degradation performance value.

Description

Technical Field

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[0001] The present disclosure relates to an estimation device, a power storage device, an estimation method, and a computer program.

Background Art

[0002] Secondary batteries such as lithium-ion batteries are widely used. For example, secondary batteries are mounted on vehicles such as automobiles and are used as a power supply for a starter at engine startup and as a power supply for various electrical components.

[0003] In recent years, due to social demands such as regulations, secondary utilization such as reuse and recycling of secondary batteries has been required. Information on secondary batteries targeted for secondary utilization is managed by a server and provided to operators as needed (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In order to determine whether a secondary battery is reusable, it is necessary to grasp the performance value after deterioration of the secondary battery. At present, after adjusting to a specific temperature, charging to SOC 100% and discharging to SOC 0% are performed for capacity measurement, and it is difficult to grasp the performance value after deterioration simply and quickly.

[0006] An object of the present disclosure is to provide an estimation device, a power storage device, an estimation method, and a computer program that can simply and quickly estimate the performance value after deterioration of a power storage element. ​​​​ The estimation device in this disclosure is an estimation device for estimating a post-degradation performance value indicating the performance of an energy storage element at an arbitrary point in time of degradation by a constant current test, and comprises a calculation unit that determines the DC resistance value of the energy storage element using the voltage change value over a time range from the start of the constant current test to the time immediately after the start and the current value in the constant current test, and an estimation unit that estimates the post-degradation performance value of the energy storage element by referring to the correlation relationship that exists between the DC resistance value and the post-degradation performance value. [Effects of the Invention]

[0008] According to the above embodiment, the performance value of the energy storage element after degradation can be easily and quickly estimated. [Brief explanation of the drawing]

[0009] [Figure 1] This is a block diagram showing the configuration of the vehicle and server according to the embodiment. [Figure 2] This block diagram shows the internal configuration of the BMU. [Figure 3] This is an explanatory diagram illustrating the outline of the deterioration diagnosis test. [Figure 4] This graph shows the measurement results for 1sDCR. [Figure 5] This graph shows the measurement results for ΔCCV. [Figure 6] This graph shows the relationship between 1s DCR and volume retention rate. [Figure 7] This graph shows the relationship between 10s DCR and volume retention rate. [Figure 8] This graph shows the relationship between ΔCCV and the volume maintenance rate. [Figure 9] This graph shows the relationship between ΔOCV and volume maintenance rate. [Figure 10] This flowchart shows the procedure for estimating the capacity retention rate using a BMU. [Modes for carrying out the invention]

[0010] (1) The estimation device of the present disclosure is an estimation device for estimating a post-degradation performance value that indicates the performance of an energy storage element at an arbitrary point in time of degradation by constant current testing, comprising: a calculation unit that determines the DC resistance value of the energy storage element using the voltage change value over a time range from the start of the constant current test to the time immediately after the start and the current value in the constant current test; and an estimation unit that estimates the post-degradation performance value of the energy storage element by referring to the correlation relationship that exists between the DC resistance value and the post-degradation performance value.

[0011] The energy storage element of this disclosure is a rechargeable secondary battery, such as a lithium-ion secondary battery, which is installed in electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and the like. Since secondary batteries are required to be reused, it is important to understand the performance values ​​of secondary batteries when they are reused.

[0012] According to the estimation device described in (1) above, the post-degradation performance value of the energy storage element can be estimated by determining the DC resistance value of the energy storage element using the voltage change value over a time range from the start of the constant current test to the time immediately after the start, and the current value in the constant current test. The post-degradation performance value is, for example, the capacity retention rate. Alternatively, the post-degradation performance value may be the discharge capacity, remaining service life, number of charge cycles, internal resistance value, etc. The estimation device described in (1) above can measure the voltage change value by measuring the voltage of the energy storage element at the start of the constant current test and the voltage of the energy storage element immediately after the start (for example, after 1 second). For the current value, the set value in the constant current test may be used. The estimation device described in (1) above only requires the use of measurements taken from the start of the constant current test to the time immediately after the start, so the post-degradation performance value of the energy storage element can be estimated simply and quickly.

[0013] (2) In the estimation device according to (1) above, the power storage element includes an electrode using a substance whose stage structure changes stepwise according to the stored charge amount as an active material, and the calculation unit may set a time range in which the voltage change of the power storage element should be measured so as not to be accompanied by the change of the stage structure.

[0014] As an example of performing the stage structure change, when graphite is used for the negative electrode, the negative electrode undergoes a structural change due to the amount of lithium ions (stored charge amount) present between the graphene planes that are inserted and removed during charge and discharge. This structural change affects the OCV change accompanying the SOC change. Based on this finding, the inventors discovered a method for excluding the ODV change.

[0015] When a life test or a storage test of the power storage element is carried out and continued, the battery performance deteriorates. At this time, inside the power storage element, it is considered that various deteriorations such as surface deterioration of the positive electrode active material, particle cracking of the positive electrode active material, film growth on the negative electrode, and electrolyte deterioration are progressing. Due to such deterioration, the ohmic resistance (electrical resistance, lithium ion resistance of the electrolyte), reaction resistance (charge transfer resistance, film resistance), diffusion resistance, etc. of the power storage element increase. It is considered that there is a correlation between the various resistances and the amount of decrease in battery performance, and it is considered that the performance value after deterioration can be estimated by measuring the amount of resistance change by an appropriate method.

[0016] When evaluating the battery performance, when using a voltage change value (=ΔV) or a DC resistance value (=ΔV / I) of about 10 seconds to 60 seconds, these values include, in addition to the above-mentioned ohmic resistance, reaction resistance, and diffusion resistance, the influence of the change in OCV (Open Circuit Voltage) accompanying the change in SOC (state of charge). Regarding the change in OCV, the influence of the change in the stage structure in the active material (for example, graphite used for the negative electrode active material) appears significantly in a certain specific voltage range. Therefore, in a specific voltage range, it has been difficult to obtain a clear correlation with the performance value after deterioration for ΔV and DCR (=ΔV / I) with a relatively long measurement time of about 10 seconds to 60 seconds.

[0017] In contrast, the inventors of the present application have found that there is a clearer correlation between the DCR with a relatively short measurement time of about 1 second and the performance value after deterioration. In the DCR with a relatively short measurement time, the influence of ohmic resistance and reaction resistance is the main factor, and the influence of the SOC change that appears significantly in the DCR from 10 seconds to about 60 seconds can be considered almost negligible. In the estimation device of (2) above, since the time range for measuring the voltage change is set so as not to accompany the change in the stage structure in the active material, the performance value after deterioration of the energy storage element can be estimated using the clear correlation that appears with the DCR.

[0018] (3) In the estimation device according to (1) or (2) above, a storage unit that stores a correlation relationship derived in advance from the relationship between the DC resistance values measured for a plurality of types of energy storage elements with different charge-discharge cycles and the performance values after deterioration of each energy storage element is provided, and the estimation unit may estimate the performance value after deterioration of the energy storage element for which the calculation unit has obtained the DC resistance value by referring to the correlation relationship stored in the storage unit.

[0019] According to the estimation device of (3) above, the performance value after deterioration can be estimated by referring to the correlation relationship derived in advance.

[0020] (4) In the estimation device according to any one of (1) to (3) above, a correction unit that corrects the estimated performance value after deterioration according to the charge state of the energy storage element may be provided.

[0021] According to the estimation device of (4) above, by correcting the correlation relationship using the charge state of the energy storage element, the performance value after deterioration can be estimated more accurately.

[0022] (5) In the estimation device according to any one of (1) to (4) above, a correction unit that corrects the estimated performance value after deterioration according to the temperature of the energy storage element may be provided.

[0023] According to the estimation device of (5) above, by correcting the correlation relationship using the temperature of the energy storage element, the performance value after deterioration can be estimated more accurately.

[0024] (6) The energy storage device of the present disclosure may include an energy storage element and an estimation device as described in any one of (1) to (5) above.

[0025] According to the energy storage device described in (6) above, the performance value after degradation can be estimated inside the energy storage device.

[0026] (7) The estimation method of the present disclosure is an estimation method for estimating a post-degradation performance value that indicates the performance of an energy storage element at an arbitrary point in time of degradation by constant current testing, wherein the method involves using the voltage change value over a time range from the start of the constant current testing to the time immediately after the start of the testing and the current value in the constant current testing to determine the DC resistance value of the energy storage element, and then using a computer to perform a process of estimating the post-degradation performance value of the energy storage element by referring to the correlation between the DC resistance value and the post-degradation performance value.

[0027] According to the estimation method described in (7) above, the performance value after degradation can be estimated by measuring the DC resistance value using the voltage change value and current value over a time range from the start of the constant current test to the time immediately after the start.

[0028] (8) The computer program of the present disclosure is a computer program that causes a computer to estimate a post-degradation performance value indicating the performance of an energy storage element at an arbitrary point in time of degradation by constant current testing, and is a computer program that causes a computer to perform a process of determining the DC resistance value of the energy storage element using the voltage change value over a time range from the start of the constant current test to the time immediately after the start and the current value in the constant current test, and then estimating the post-degradation performance value of the energy storage element by referring to the correlation between the DC resistance value and the post-degradation performance value.

[0029] According to the computer program described in (8) above, the performance value after degradation can be estimated by measuring the DC resistance value using the voltage change value and current value over a time range from the start of the constant current test to the moment immediately after the start.

[0030] The following explanation will use a vehicle-mounted energy storage device as an example of the application of this disclosure. Figure 1 is a block diagram showing the configuration of a vehicle 1 and a server 2 according to an embodiment. The vehicle 1 includes an energy storage element 11 consisting of multiple battery cells 10, a BMU (Battery Management Unit) 12, a load 13, an integrated ECU (Electronic Control Unit) 14, a communication unit 15, a voltage sensor 16, and a current sensor 17.

[0031] Vehicle 1 is an electric vehicle (EV), hybrid electric vehicle (HEV), plug-in hybrid electric vehicle (PHEV), etc. Vehicle 1 is equipped with a high-voltage battery to drive the electric motor for propulsion, a 12V battery for starting the vehicle and auxiliary equipment, etc. Vehicle 1 may also be equipped with a 12V battery as a backup power source. Reusable secondary batteries such as lithium-ion batteries are used for the high-voltage battery and the 12V battery.

[0032] The energy storage element 11 is the high-voltage battery or 12V battery described above. The energy storage element 11 is configured by connecting a plurality of battery cells 10 in series. An example of a battery cell 10 is a lithium-ion battery. Alternatively, the battery cell 10 may be a rechargeable battery cell such as an all-solid-state battery, lead-acid battery, redox flow battery, zinc-air battery, alkaline manganese battery, lithium-sulfur battery, sodium-sulfur battery, silver-zinc oxide battery, nickel-metal hydride battery, or molten salt thermal battery.

[0033] The BMU12 is a device for managing the state of the energy storage element 11. The BMU12 acquires time-series measurement data obtained from various sensors such as a voltage sensor 16 and a current sensor 17, and stores the acquired measurement data as history in the storage unit 122 (see Figure 2). The measurement data includes the voltage value of the energy storage element 11, the current value flowing through the energy storage element 11, etc. The measurement data may also include the temperature (also called ambient temperature or environmental temperature) measured by a temperature sensor placed around the energy storage element 11. The BMU12 may also count the number of charge-discharge cycles and store the counted number of cycles as history in the storage unit 122.

[0034] In this embodiment, the BMU 12 estimates the post-degradation performance value, which indicates the performance value of the energy storage element 11 at an arbitrary point in degradation, using measurement data obtained from various sensors. The correlation between the DC resistance value (1sDCR, described later) and the capacity retention rate (SOH: State of Health), which is necessary for estimating the post-degradation performance value, is assumed to have been derived in advance and stored in the memory unit 122 within the BMU 12. The BMU 12 measures the 1sDCR using measurement data obtained from various sensors and estimates the capacity retention rate by referring to the above correlation.

[0035] Load 13 is an electric motor that generates the driving torque necessary to move vehicle 1. Load 13 may also include various equipment installed in vehicle 1, such as headlights, turn signals, interior lights, and power windows.

[0036] The main ECU 14 is a control device that comprehensively controls the vehicle 1, and performs functions such as charging and discharging control of the energy storage elements 11 and driving control of the load 13. The main ECU 14 is connected to the BMU 12 and the communication unit 15 for communication. Communication within the vehicle 1 uses CAN (Controller Area Network), LIN (Local Interconnect Network), ECHONET (registered trademark), ECHONETLight (registered trademark), etc. The main ECU 14 acquires data from the energy storage elements 11 managed by the BMU 12 at appropriate times and uploads the acquired data from the energy storage elements 11 to the server 2 via the communication unit 15. The main ECU 14 receives various data transmitted from the server 2 via the communication unit 15 and performs processing according to the received data.

[0037] The communication unit 15 includes an in-vehicle communication interface for communicating with the central ECU 14 and an external communication interface for communicating with the server 2 via the communication network NW. The external communication interface uses wireless communication interfaces such as WiFi (registered trademark), 3G, 4G, 5G, and LTE (Long Term Evolution). The communication unit 15 communicates with the central ECU 14 via the in-vehicle communication network described above, and also sends and receives various data with the server 2 via the communication network NW.

[0038] The voltage sensor 16 is an existing voltage sensor and is connected in parallel to the energy storage element 11. The voltage sensor 16 measures the voltage of the energy storage element 11 at an appropriate sampling period (e.g., every second) and outputs the measurement result to the BMU 12. The voltage sensor 16 may also be connected in parallel to each battery cell 10. In this case, the sum of the cell voltages measured for each battery cell 10 may be output to the BMU 12 as the voltage value of the energy storage element 11.

[0039] The current sensor 17 is an existing current sensor such as a Hall sensor and is connected in series with the energy storage element 11. The current sensor 17 measures the current flowing through the energy storage element 11 at an appropriate sampling period (for example, in units of 1 second) and outputs the measurement result to the BMU 12.

[0040] Server 2 comprises a control unit 21, a storage unit 22, a communication unit 23, and the like. The control unit 21 of Server 2 includes a CPU (Central Processing Unit) and the like, and performs control of the entire server. The storage unit 22 includes a storage device such as an HDD (Hard Disk Drive) and stores data from the energy storage element 11 received from the vehicle 1 via the communication network NW. The communication unit 23 includes a wired or wireless communication interface for communicating with the vehicle 1 via the communication network NW.

[0041] Figure 2 is a block diagram showing the internal configuration of the BMU12. The BMU12 includes a control unit 121, a storage unit 122, a connection unit 123, a communication unit 124, and the like.

[0042] The control unit 121 is an arithmetic circuit or processing circuit equipped with a CPU, ROM (Read Only Memory), RAM (Random Access Memory), etc. The CPU of the control unit 121 controls each part of the hardware by reading and executing a computer program stored in the ROM or storage unit 122, thereby causing the entire device to function as an estimation device in this disclosure.

[0043] Alternatively, the control unit 121 may be any arithmetic circuit or processing circuit equipped with multiple CPUs, multi-core CPUs, GPUs (Graphics Processing Units), microcontrollers, volatile or non-volatile memory, etc. The control unit 121 may also include functions such as a timer for measuring the elapsed time from the time a measurement start instruction is given until a measurement end instruction is given, a counter for counting numbers, and a clock for outputting date and time information.

[0044] The storage unit 122 includes a storage device such as flash memory or a hard disk. Various computer programs and data are stored in the storage unit 122. The computer programs stored in the storage unit 122 include an estimation program PG that causes the computer to perform a process to estimate the post-degradation performance value, which indicates the performance of the energy storage element 11 at an arbitrary degradation point, based on the 1sDCR of the energy storage element 11. The storage unit 122 may also include a history database DB that stores measurement data such as voltage, current, and temperature of the energy storage element 11.

[0045] The computer program (program product) including the estimated program PG is provided on a non-temporary recording medium RM on which the computer program is recorded in a readable format. The recording medium RM is a portable memory such as a CD-ROM, USB memory, or SD (Secure Digital) card. The control unit 121 reads the desired computer program from the recording medium RM using a reading device (not shown in the figure) and stores the read computer program in the storage unit 122. Alternatively, the computer program including the estimated program PG may be provided via communication.

[0046] The estimation program PG may be a single computer program or a group of programs composed of multiple computer programs. The estimation program PG may be executed collaboratively by multiple computers. The estimation program PG may partially utilize existing libraries.

[0047] The connection section 123 is equipped with connection terminals for connecting various sensors such as a voltage sensor 16 and a current sensor 17. The control unit 121 acquires various measurement data measured by the sensors connected to the connection section 123 through the connection section 123.

[0048] The communication unit 124 is equipped with a communication interface for sending and receiving various types of data. The communication interface provided by the communication unit 124 uses a communication interface compliant with CAN, LIN, ECHONET®, ECHONETLight®, etc., as described above. The communication unit 124 sends and receives necessary data with the control ECU 14.

[0049] Figure 3 is an explanatory diagram illustrating the outline of the degradation diagnosis test. The inventors of this application conducted a constant current test using multiple energy storage elements with different capacity retention rates in order to investigate the correlation between various measured values ​​of the energy storage element and the capacity retention rate. Specifically, the inventors set the voltage and temperature of the energy storage element to predetermined values, then performed charging or discharging at a constant current for a certain period of time, and then measured the voltage of the energy storage element at appropriate sampling intervals (e.g., 1-second intervals) while the charging or discharging was stopped and the element was left idle for a certain period of time. In the graph shown in Figure 3, the horizontal axis represents the elapsed time (seconds) from the start of the test, and the vertical axis represents the voltage of the energy storage element (V). The graph in Figure 3 shows the change in voltage when the initial voltage is set to V0, discharge is performed for 60 seconds at a discharge rate of 1C, and then the discharge is stopped and the element is left idle for 60 seconds.

[0050] From such a constant current test, values ​​such as 1sDCR, 10sDCR, ΔCCV, and ΔOCV can be obtained. Here, 1sDCR represents the DC resistance value obtained by dividing the voltage change value during the time range from the start of the constant current test to the time immediately after the start by the current value. In this embodiment, the time immediately after the start is set to the point 1 second after the start of the constant current test. The voltage change value is the difference (=V0-V1) between the voltage value V0 at the start of the constant current test and the voltage value V1 at the time immediately after the start, and is measured by the voltage sensor 16. The current value may be an actual measured value measured by the current sensor 17, or it may be the set value of the current in the constant current test. In this embodiment, the DC resistance value is determined based on the voltage change value for 1 second after the start of the test, so it is written as 1sDCR, but the measurement time of the voltage change is not limited to 1 second. The measurement time of the voltage change may be less than 1 second or more than 1 second. The measurement time for voltage changes can be arbitrarily set, as long as it does not involve a change in the stage structure of the active material used in the electrodes of the energy storage element (for example, graphite used as the negative electrode active material).

[0051] The 10sDCR used for comparison represents the DC resistance value obtained by dividing the voltage change value at 10 seconds after the start of the constant current test by the current value. ΔCCV represents the voltage change value from the start of the constant current test to just before the discharge is stopped (60 seconds after the example in Figure 3). ΔOCV represents the difference between the initial voltage V0 and the voltage of the energy storage element after the pause (the voltage at 120 seconds after the example in Figure 3).

[0052] The inventors of the present application conducted a constant current test while variously changing conditions such as the starting voltage and temperature for a plurality of power storage elements having different capacity retention rates, and examined the relationship between the above measurement values and the capacity retention rate. FIG. 4 is a graph showing the measurement results of 1sDCR. The horizontal axis of the graph represents the pre-discharge voltage (V), and the vertical axis represents 1sDCR (mΩ). The example of FIG. 4 shows the measurement results when three power storage elements with different capacity retention rates were prepared, the temperature was adjusted to -10°C, 0°C, 25°C, 45°C, and 60°C, and then 1sDCR was measured. In FIG. 4, the capacity retention rates are denoted by the letters A, B, and C. The order of the capacity retention rates from high to low is A < B < C. From the graph of FIG. 4, it can be seen that the measured value of 1sDCR changes depending on the value of the pre-discharge voltage, but at any temperature, the lower the capacity retention rate, the higher the 1sDCR, and there is a correlation between 1sDCR and the capacity retention rate.

[0053] FIG. 5 is a graph showing the measurement results of ΔCCV. The horizontal axis of the graph represents the pre-discharge voltage (V), and the vertical axis represents ΔCCV (V). The example of FIG. 5 shows the measurement results when three power storage elements with different capacity retention rates were prepared, the temperature was adjusted to -10°C, 0°C, 25°C, 45°C, and 60°C, and then ΔCCV was measured. In FIG. 5, the capacity retention rates are denoted by the letters A, B, and C. The order of the capacity retention rates from high to low is A < B < C. In the graph of FIG. 5, although generally the lower the capacity retention rate, the higher the ΔCCV, at some pre-discharge voltages, the ΔCCV of the power storage element with a capacity retention rate of C is higher than the ΔCCV of the power storage element with a capacity retention rate of B, and it can be seen that there is no correlation between ΔCCV and the capacity retention rate. Although the measurement results of ΔCCV are shown in FIG. 5, the measurement results of 10sDCR and ΔOCV were the same as those of ΔCCV.

[0054] Figure 6 is a graph showing the relationship between 1sDCR and capacity retention rate. The horizontal axis of the graph represents capacity retention rate (%), and the vertical axis represents 1sDCR (mΩ). The graph in Figure 6 shows the relationship between the capacity retention rate of energy storage elements that have undergone cycle degradation under various temperature conditions and the 1sDCR measured by constant current testing. The capacity retention rate of the degraded energy storage elements was measured using existing methods before conducting the constant current testing. The 1sDCR was derived by constant current testing after the energy storage elements under measurement were adjusted to a specific temperature (e.g., 25°C) and a specific charge state (e.g., SOC 50%).

[0055] As shown in the graph in Figure 6, a clear correlation is observed between 1sDCR and capacity retention rate. By calculating the 1sDCR for multiple energy storage elements with known capacity retention rates and deriving the correlation between 1sDCR and capacity retention rate in advance, the capacity retention rate of the target energy storage element 11 can be estimated from the correlation by measuring its 1sDCR.

[0056] Figure 7 is a graph showing the relationship between 10sDCR and capacity retention rate. The horizontal axis of the graph represents capacity retention rate (%), and the vertical axis represents 10sDCR (mΩ). The graph in Figure 7 shows the relationship between the capacity retention rate of energy storage elements that have undergone cycle degradation under various temperature conditions and the 10sDCR measured by constant current testing. The capacity retention rate of the degraded energy storage elements was measured using existing methods before conducting the constant current testing. The 10sDCR was derived by constant current testing after the energy storage elements under measurement were adjusted to a specific temperature (e.g., 25°C) and a specific charge state (e.g., SOC 50%).

[0057] Figure 8 is a graph showing the relationship between ΔCCV and capacity retention rate. The horizontal axis of the graph represents capacity retention rate (%), and the vertical axis represents ΔCCV (V). The graph in Figure 8 shows the relationship between the capacity retention rate of energy storage elements that have undergone cycle degradation under various temperature conditions and the ΔCCV measured by constant current testing. The capacity retention rate of the degraded energy storage elements was measured using existing methods before conducting the constant current testing. ΔCCV was derived by constant current testing after the energy storage elements under measurement were adjusted to a specific temperature (e.g., 25°C) and a specific charge state (e.g., SOC 50%).

[0058] Figure 9 is a graph showing the relationship between ΔOCV and capacity retention rate. The horizontal axis of the graph represents capacity retention rate (%), and the vertical axis represents ΔOCV (V). The graph in Figure 9 shows the relationship between the capacity retention rate of energy storage elements that have undergone cycle degradation under various temperature conditions and the ΔOCV measured by constant current testing. The capacity retention rate of the degraded energy storage elements was measured using an existing method before conducting the constant current testing. ΔOCV was derived by constant current testing after the energy storage elements under measurement were adjusted to a specific temperature (e.g., 25°C) and a specific charge state (e.g., SOC 50%).

[0059] As shown in the graphs in Figures 7 to 9, no correlation is observed between the measured values ​​of 10sDCR, ΔCCV, and ΔOCV and the capacity retention rate. In particular, for energy storage elements with a capacity retention rate of 80% or less, even if the capacity retention rate is the same, the measured values ​​of 10sDCR, ΔCCV, and ΔOCV will differ if the usage history (temperature conditions) up to that point is different. Therefore, even if the values ​​of 10sDCR, ΔCCV, and ΔOCV are obtained, the capacity retention rate cannot be accurately estimated from these values.

[0060] Even when a constant current test like the one described above is performed, the battery performance of the energy storage element deteriorates. Inside the energy storage element, various types of deterioration progress, such as surface degradation of the positive electrode active material, particle cracking of the positive electrode active material, film growth on the negative electrode, and electrolyte degradation. Due to such deterioration, the ohmic resistance, reaction resistance, diffusion resistance, etc. of the energy storage element increase. It is thought that there is a correlation between these various resistances and the amount of deterioration in battery performance, and it is believed that the performance value after deterioration (capacity retention rate in this embodiment) can be estimated by determining the amount of resistance change using an appropriate method.

[0061] When evaluating battery performance, if voltage change values ​​or DC resistance values ​​over a period of 10 to 60 seconds are used, these values ​​are thought to include the effects of ohmic resistance, reaction resistance, and diffusion resistance, as well as the effect of OCV changes accompanying changes in SOC. Regarding changes in OCV, the effect of changes in the stage structure of the active material (e.g., graphite used as the negative electrode active material) becomes particularly pronounced within a certain voltage range. Therefore, when using measurements with relatively long measurement times of 10 to 60 seconds (e.g., 10sDCR, ΔCCV, ΔOCV) within a specific voltage range, it is difficult to obtain a clear correlation between the measured values ​​and the capacity retention rate.

[0062] In contrast, when using a DCR with a relatively short measurement time of about 1 second (1sDCR), a clearer correlation is observed between 1sDCR and the capacity retention rate, as shown in the graph in Figure 6. In 1sDCR, the effects of ohmic resistance and reaction resistance are the main factors, and the effect of SOC change, which becomes prominent in DCRs of about 10 to 60 seconds, can be considered almost negligible.

[0063] In this embodiment, an approximation curve approximating each point is derived in advance from the graph showing the relationship between 1sDCR and capacity retention rate in Figure 6, and the function form representing the derived approximation curve, or a table showing the input / output relationship of the approximation curve, is stored in, for example, the storage unit 122. The control unit 121 of the BMU 12 measures the 1sDCR of the energy storage element 11 and estimates the capacity retention rate of the energy storage element 11 by referring to the function form or table stored in the storage unit 122.

[0064] The function shape or table of the approximation curve may be stored in the storage unit 22 of server 2. In this case, server 2 can estimate the capacity retention rate of the energy storage element 11 by acquiring the 1sDCR measured for the energy storage element 11 while it is mounted on vehicle 1 via the communication network NW. Server 2 may also acquire the 1sDCR measured for the energy storage element 11 while it is removed from vehicle 1 and estimate the capacity retention rate of the energy storage element 11 based on the acquired 1sDCR. Even if the usage history of the energy storage element 11 is unknown, server 2 can estimate the capacity retention rate of the energy storage element 11.

[0065] Figure 10 is a flowchart showing the procedure for estimating the capacity retention rate using the BMU12. Before executing the estimation procedure according to this flowchart, it is assumed that the correlation between the 1sDCR of the energy storage element and the capacity retention rate has been derived in advance, and that a function or table showing these correlations is stored in the storage unit 122 of the BMU12.

[0066] The control unit 121 of BUM12 starts the constant current test after the energy storage element 11 has stopped functioning (step S101). As described above, it may not be possible to correctly estimate the capacity retention rate if more than 10 seconds have elapsed since the start of charging and discharging of the energy storage element 11, or if a relaxation process is occurring after the end of charging and discharging. For this reason, it is preferable for the control unit 121 to stop charging and discharging of the energy storage element 11 and start the constant current test after it has been idle for a certain period of time.

[0067] The control unit 121 acquires measurement data output from the voltage sensor 16 and current sensor 17 at an appropriate sampling period (e.g., every second) (step S102). Based on the acquired measurement data, the control unit 121 calculates the 1sDCR of the energy storage element 11 (step S103). Specifically, the control unit 121 calculates the difference |V0-V1| between the voltage value V0 of the energy storage element 11 at the start of the constant current test and the voltage value V1 of the energy storage element 11 immediately after the start (e.g., after 1 second), and calculates the 1sDCR by dividing the calculated difference |V0-V1| by the measured value of the current I. Instead of the measured value of the current I, the set value of the current in the constant current test may be used.

[0068] The control unit 121 refers to the function form or table stored in the memory unit 122 and estimates the capacity retention rate of the energy storage element 11 based on the 1sDCR measured in step S103 (step S104).

[0069] The control unit 121 outputs the estimated capacity retention rate of the energy storage element 11 (step S105). The control unit 121 outputs the estimated capacity retention rate of the energy storage element 11 to the general ECU 14, and through the general ECU 14, causes the capacity retention rate of the energy storage element 11 to be displayed on the display device of the vehicle 1. Alternatively, the control unit 121 may output the estimated capacity retention rate of the energy storage element 11 to the general ECU 14, and transmit the capacity retention rate of the energy storage element 11 to the server 2 through the general ECU 14 and the communication unit 15.

[0070] The control unit 121 may correct the estimated capacity retention rate according to the charge state of the energy storage element 11 before starting the constant current test in step S101. The correction coefficient may be determined based on prior experimental results. Alternatively, the control unit 121 may measure the temperature of the energy storage element 11 and correct the estimated capacity retention rate according to the measured temperature. The correction coefficient may be predetermined, for example, such that the capacity retention rate is lower when the temperature is high and higher when the temperature is low.

[0071] As described above, in this embodiment, the only measurement required to estimate the capacity retention rate is the voltage change value of the energy storage element over one second. Compared to the conventional method of determining the capacity retention rate by charging to 100% SOC and discharging to 0% SOC to measure capacity, this method allows for a simpler and faster estimation of the capacity retention rate. As shown in the graph of Figure 6, a correlation is observed between 1sDCR and the capacity retention rate over a wide range of capacity retention rates from 60% to 100%. Therefore, even for energy storage elements with an unknown usage history and an unknown degree of degradation, the capacity retention rate can be estimated accurately using the method described in this embodiment. Of course, the capacity retention rate estimation method according to this embodiment can also be applied to energy storage elements 11 whose usage history is known.

[0072] The disclosed embodiments are illustrative in all respects and not restrictive. The scope of the invention is defined by the claims and includes all modifications in the sense and scope equivalent to the claims.

[0073] In this embodiment, the capacity retention rate is estimated as the post-degradation performance value of the energy storage element 11. Alternatively, the control unit 121 of the BMU 12 may estimate the discharge capacity that can be discharged from the energy storage element 11, and the discharge capacity may be estimated as the post-degradation performance value, such as the remaining service life, the number of charge cycles, the driving distance, or the internal resistance value. [Explanation of symbols]

[0074] 1 vehicle 2 servers 10 battery cells 11 Energy storage element 12 BMU 13 Load 14. General ECU 15 Communications Department 121 Control Unit 122 Storage section 123 Connection part 124 Communications Department PG Estimation Program RM recording media

Claims

1. An estimation device for estimating the post-degradation performance value, which indicates the performance of an energy storage element at any point in time of degradation, by constant current testing, A calculation unit that uses the voltage change value during the time range from the start of the constant current test to the time immediately after the start, and the current value during the constant current test, to determine the DC resistance value of the energy storage element. An estimation unit that estimates the degraded performance value of the energy storage element by referring to the correlation between the DC resistance value and the degraded performance value. An estimation device equipped with the following features.

2. The aforementioned energy storage element includes electrodes that use a material as the active material whose stage structure changes in stages according to the amount of stored energy. The calculation unit sets a time range for measuring the voltage change of the energy storage element so as not to involve any change in the stage structure. The estimation device according to claim 1.

3. A memory unit that stores the correlation between the DC resistance values ​​measured for multiple types of energy storage elements with different charge / discharge cycles and the post-degradation performance values ​​of each energy storage element, which was derived in advance. Equipped with, The estimation unit estimates the degraded performance value of the energy storage element for which the calculation unit has determined the DC resistance value, by referring to the correlation stored in the memory unit. The estimation device according to claim 1.

4. Correction unit corrects the estimated post-degradation performance value according to the charge state of the energy storage element. The estimation device according to claim 1, comprising:

5. Correction unit corrects the estimated post-degradation performance value according to the temperature of the energy storage element. The estimation device according to claim 1, comprising:

6. Energy storage element, An estimation device according to any one of claims 1 to 5 and A power storage device equipped with the following features.

7. An estimation method for estimating the post-degradation performance value, which indicates the performance of an energy storage element at an arbitrary point in time of degradation, by constant current testing, Using the voltage change values ​​during the time range from the start of the constant current test to the time immediately after the start, and the current values ​​in the constant current test, the DC resistance value of the energy storage element is determined. The performance value of the energy storage element after degradation is estimated by referring to the correlation between the DC resistance value and the performance value after degradation. An estimation method that uses a computer to perform the processing.

8. A computer program that estimates the post-degradation performance value, which indicates the performance of an energy storage element at any point in time of degradation, through a constant current test. Using the voltage change values ​​during the time range from the start of the constant current test to the time immediately after the start, and the current values ​​in the constant current test, the DC resistance value of the energy storage element is determined. The performance value of the energy storage element after degradation is estimated by referring to the correlation between the DC resistance value and the performance value after degradation. A computer program that causes a computer to perform a process.

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