Battery diagnostic method, diagnostic device, diagnostic system, and diagnostic program

Abstract

To provide a battery diagnosis method with which an increase in the data quantity that is used for determining a battery state is suppressed, and the battery state is appropriately determined on the basis of the measurement results of frequency responses of impedance.SOLUTION: A battery diagnosis method according to an embodiment determines, for each of a plurality of SOC values, whether the absolute value of change rate of first impedance with respect to the SOC is equal to or below a reference value, on the basis of the measurement results of the first impedance of a battery at a first frequency. The diagnosis method measures the second battery impedance at a second frequency that is higher than the first frequency, with regard to the target SOC value among the plurality of SOC values the absolute value of change rate of which is equal to or below the reference value. The diagnosis method determines the battery state on the basis of the measurement results of first and second impedances at the target SOC value.SELECTED DRAWING: Figure 11

Description

Technical Field

[0001] Embodiments of the present invention relate to a battery diagnosis method, a diagnosis apparatus, a diagnosis system, and a diagnosis program.

Background Art

[0002] In recent years, for batteries such as secondary batteries, the frequency characteristics of the battery impedance are measured, and the state of the battery including the deterioration state of the battery is diagnosed based on the measurement results of the frequency characteristics of the impedance. In such diagnosis, a current waveform whose current value changes periodically, such as an alternating current waveform, is input to the battery at each of a plurality of frequencies, and the impedance of the battery at each of the plurality of frequencies is measured, thereby measuring the frequency characteristics of the battery impedance. The frequency characteristics of impedance are measured for each of a plurality of SOC values of the battery. Then, for each of the plurality of SOC values for which the frequency characteristics of impedance have been measured, using the measurement results of the frequency characteristics of impedance, the resistance related to each of the positive electrode and the negative electrode is calculated, for example, the charge transfer resistance of at least one of the positive electrode and the negative electrode is calculated. Then, based on the resistance calculated for each of the plurality of SOC values and the relationship between the calculated resistance and the SOC of the battery, the state of the battery such as the deterioration state of the battery is determined.

[0003] When diagnosing the state of a battery as described above, there is a demand for suppressing an increase in the amount of data used for determining the battery state, for example, by reducing the number of SOC values for which impedance measurement at high frequencies is performed. There is also a demand that even if the amount of data used for determining the battery state is reduced, the battery state such as the deterioration state of the battery can be appropriately determined based on the measurement results of the frequency characteristics of impedance.

Prior Art Literature

Patent Literature

[0004]

Patent Literature 1

[0005] [Non-Patent Document 1] JP Schmidt et al., “Studies on LiFePO4 as cathode materials using impedance spectrometry” Journal of power Sources. 196, (2011), pp5342-pp5348 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The problem that the present invention aims to solve is to provide a battery diagnostic method, diagnostic device, diagnostic system, and diagnostic program that suppress the increase in the amount of data used to determine the state of the battery and appropriately determine the state of the battery based on the measurement results of the impedance frequency characteristics. [Means for solving the problem]

[0007] In the battery diagnostic method of the embodiment, the rate of change of the first impedance with respect to the battery's SOC is calculated for each of the battery's multiple SOC values, based on the measurement result of the first impedance, which is the impedance of the battery at a first frequency that is in any frequency range of 0.1 Hz or higher and 100 Hz or lower. In the diagnostic method, the reference value is set as either half the absolute value of the rate of change of the first impedance at the lowest SOC value among multiple SOC values, or half the absolute value of the rate of change of the first impedance at the highest SOC value among multiple SOC values. The diagnostic method uses the rate of change of the first impedance at each of the multiple SOC values ​​to determine which of the multiple SOC values... Then, the SOC value in which the absolute value of the rate of change of the first impedance is less than or equal to the reference value is selected as the target SOC value. In the diagnostic method, if two or more SOC values ​​are selected as target SOC values ​​from among multiple SOC values, for each of the two or more selected target SOC values... The second impedance is the impedance of the battery at a second frequency that is higher than the first frequency and within the frequency range of 100 Hz or higher and 10 kHz or lower. S In addition to the first impedance, the second impedance is also measured. The diagnostic method determines the state of the battery based on the measurement results of the first and second impedances for each of two or more target SOC values. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic diagram showing an example of the relationship between the charge state of a battery and the potentials of the positive and negative electrodes in an embodiment of the battery to be diagnosed. [Figure 2] Figure 2 is a schematic diagram showing an example of the relationship between the charge state of the first electrode and the charge transfer resistance of the first electrode for a battery to be diagnosed in the embodiment. [Figure 3] Figure 3 is a schematic diagram showing an example of the relationship between the state of charge (SOC) of a battery and the charge transfer resistance of the first electrode in the embodiment. [Figure 4] Figure 4 is a schematic diagram showing an example of a battery diagnostic system according to this embodiment. [Figure 5] Figure 5 is a schematic diagram showing an example of the current waveform input to the battery in the measurement of the battery impedance according to the embodiment. [Figure 6] Figure 6 is a schematic diagram showing a different example from Figure 5 of the current waveform input to the battery in the measurement of the battery impedance according to the embodiment. [Figure 7] Figure 7 is a schematic diagram showing an example of a process for calculating the rate of change of the first impedance with respect to the battery's SOC for each of a plurality of SOC values ​​in an embodiment. [Figure 8] Figure 8 is a schematic circuit diagram showing an example of a battery 5 equivalent circuit used in fitting calculations in this embodiment. [Figure 9] Figure 9 is a schematic diagram showing an example of a process for calculating the reference SOC value at which the charge transfer resistance of the first electrode is minimized, in an embodiment. [Figure 10] Figure 10 is a schematic diagram showing an example of the relationship between the charge transfer resistance of the first electrode and the state of charge (SOC) of the battery, calculated in the embodiment, for each of the first period and the second period following the first period. [Figure 11]Figure 11 is a flowchart illustrating an example of the process performed by the processing circuit of the diagnostic device when it executes a diagnostic program in this embodiment. [Figure 12] Figure 12 is a schematic diagram illustrating three calculation patterns used to calculate the trajectory showing the relationship between the charge transfer resistance of the positive electrode and the state of charge (SOC) of the battery in a verification related to the embodiment. [Modes for carrying out the invention]

[0009] The embodiments will be described below with reference to the drawings.

[0010] (Embodiment) First, the battery to be diagnosed in the embodiment will be described. The battery to be diagnosed is a secondary battery such as a lithium-ion secondary battery, a lead-acid battery, and a nickel-metal hydride battery. The battery may be formed from single cells (single cells), or it may be a battery module or cell block formed by electrically connecting a plurality of single cells. When the battery is formed from a plurality of single cells, the plurality of single cells may be electrically connected in series, or they may be electrically connected in parallel. In addition, the battery may have both a series connection structure in which a plurality of single cells are connected in series, and a parallel connection structure in which a plurality of single cells are connected in parallel. Furthermore, the battery may be a battery string, a battery array, or a storage battery in which a plurality of battery modules are electrically connected. In addition, in a battery module in which a plurality of single cells are electrically connected, each of the plurality of single cells may be diagnosed as the battery to be diagnosed.

[0011] In the aforementioned type of battery, the battery charge (amount of charge) and State of Charge (SOC) are defined as parameters indicating the battery's charge state. The real-time battery charge is calculated based on the battery charge at a predetermined point in time and the time change of the current flowing through the battery from that predetermined point in time. For example, the real-time battery charge can be calculated by adding the time-integrated value of the current flowing through the battery from a predetermined point in time to the battery charge at that predetermined point in time.

[0012] For a battery, a lower limit voltage Vmin and an upper limit voltage Vmax are specified for the voltage. Further, an SOC value is defined as the SOC value of the battery. In the battery, the state where the voltage during discharging or charging under predetermined conditions reaches the lower limit voltage Vmin is specified as the state where the SOC value is 0 (0%), and the state where the voltage during discharging or charging under predetermined conditions reaches the upper limit voltage Vmax is specified as the state where the SOC value is 1 (100%). In addition, for the battery, the charging capacity (charge amount) required for the SOC value to change from 0 to 1 during charging under predetermined conditions, or the discharging capacity (discharge charge amount) required for the SOC value to change from 1 to 0 during discharging under predetermined conditions, is specified as the battery capacity. Then, the ratio of the remaining charge amount (remaining capacity) to the full battery capacity when the SOC value is 0 is the SOC of the battery.

[0013] In addition, the battery includes a positive electrode and a negative electrode as electrodes, and the polarities of the positive electrode and the negative electrode are opposite to each other. On each of the positive electrode and the negative electrode of the battery, the potential changes in response to changes in the state of charge. Each of the positive electrode and the negative electrode has a predetermined relationship between the potential and the state of charge. Therefore, for each electrode of the battery, the potential can be calculated based on the state of charge, and the state of charge can be calculated based on the potential. For a battery such as a secondary battery, repeated charging and discharging causes the relationship between the potential of each electrode (the positive electrode and the negative electrode) relative to the charge amount and SOC of the battery to change compared to that when the battery starts being used. In the embodiment, for the battery to be diagnosed, the real-time relationship between the potential of at least one of the positive electrode and the negative electrode relative to the SOC of the battery is estimated. Then, regarding the relationship between the potential of at least one of the positive electrode and the negative electrode relative to the SOC of the battery, by comparing the relationship at the start of use of the battery with the real-time relationship, the degradation state of at least one of the positive electrode and the negative electrode is determined.

[0014] FIG. 1 is a schematic diagram showing an example of the relationship between the state of charge of a battery to be diagnosed in an embodiment and the respective potentials of a positive electrode and a negative electrode. In FIG. 1, the horizontal axis represents the charge amount (state of charge) of the battery, and the vertical axis represents potential. In FIG. 1, relationships Vp1 and Vp2 between the charge amount of the battery and the potential of the positive electrode, and a relationship Vn between the charge amount of the battery and the potential of the negative electrode are shown. In the battery 5 of the example in FIG. 1, by repeating charging and discharging, the relationship between the charge amount of the battery and the potential of the positive electrode changes from the relationship Vp1 to the relationship Vp2. When compared under the condition that the charge amount of the battery is the same, in the relationship Vp2, the potential of the positive electrode is higher than that in the relationship Vp1. Therefore, in the example of FIG. 1, due to deterioration of the positive electrode, the potential of the positive electrode after deterioration shifts to a higher potential side relative to the potential of the positive electrode before deterioration when compared under the same condition of the same charge amount of the battery. Since the relationship between the charge amount of the battery and the potential of the positive electrode changes as described above, in the example of FIG. 1, the relationship between the potential of the positive electrode and the SOC of the battery changes from the start of use of the battery or the like.

[0015] Further, in the battery to be diagnosed, one of the positive electrode and the negative electrode is defined as a first electrode, and one of the positive electrode and the negative electrode having a polarity opposite to that of the first electrode is defined as a second electrode. In the battery, the first electrode contains a first electrode active material as an electrode active material, and the second electrode contains a second electrode active material different from the first electrode active material as an electrode active material. When the SOC value of the battery changes in a range of 0 to 1 (0% to 100%), the first electrode active material undergoes a single-phase reaction (solid solution reaction) in each of insertion and extraction of lithium. Further, when the SOC value of the battery 5 changes in a range of 0 to 1, the second electrode active material may undergo a two-phase coexistence reaction or a single-phase reaction in each of insertion and extraction of lithium. When the second electrode contains the second electrode active material that undergoes a two-phase coexistence reaction, the second electrode has a plateau region where the potential is constant or substantially constant even if the state of charge changes. In the example of FIG. 1, the negative electrode serves as the second electrode containing the second electrode active material that undergoes a two-phase coexistence reaction, and the negative electrode has a plateau region ε.

[0016] In one example, the battery being diagnosed is a lithium-ion secondary battery that charges and discharges through the movement of lithium ions between the positive and negative electrodes. The first electrode active material of the first electrode undergoes a single-phase reaction for both the intercalation and release of lithium, while the second electrode active material of the second electrode undergoes a two-phase coexistence reaction for both the intercalation and release of lithium. When the positive electrode is the first electrode, the first electrode active material (positive electrode active material) that undergoes a single-phase reaction is one of the following: lithium nickel cobalt manganese oxide, lithium cobalt oxide, or lithium nickel cobalt aluminum oxide. The negative electrode, which is the second electrode, uses one of the following as the second electrode active material (negative electrode active material) that undergoes a two-phase coexistence reaction: lithium titanate, titanium oxide, or niobium titanium oxide. On the other hand, when the negative electrode is the first electrode, the first electrode active material (negative electrode active material) that undergoes a single-phase reaction is one of the following: carbon-based active material, etc. Then, in the positive electrode, which serves as the second electrode, either lithium iron phosphate or lithium manganese oxide is used as the second electrode active material (positive electrode active material) that undergoes a two-phase coexistence reaction.

[0017] In the embodiments, the real-time relationship between the potential of the first electrode and the battery's SOC is estimated for the battery to be diagnosed. Furthermore, in the battery diagnosis, the relationship between the potential of the second electrode and the battery's SOC may be estimated based on the estimated relationship between the potential of the first electrode and the battery's SOC. When estimating the real-time relationship between the potential of the first electrode and the battery's SOC, the impedance and frequency characteristics of the impedance of the battery to be diagnosed are measured. Then, the resistance component of the battery's impedance is calculated based on the measurement results of the frequency characteristics of the battery's impedance.

[0018] Here, the impedance components of the battery include ohmic resistance, which includes resistance during the lithium transfer process in the electrolyte, the charge transfer impedance of the positive and negative electrodes, impedance due to the film, which includes film resistance of the film formed on the positive or negative electrode by reactions, etc., Warburg impedance, which includes diffusion resistance, and the inductance component of the battery. In the positive and negative electrodes, the resistance component of the charge transfer impedance becomes the charge transfer resistance. The impedance components of the battery, including the charge transfer resistance of the first and second electrodes, can be calculated using the frequency characteristics of the battery's impedance.

[0019] In the embodiments, the frequency characteristics of the impedance are measured for each of several target SOC values ​​of the battery to be diagnosed. Then, for each of the multiple target SOCs, the charge transfer resistance of the first electrode is calculated as the resistance related to the first electrode based on the measurement results of the impedance frequency characteristics. This allows the real-time relationship between the charge transfer resistance of the first electrode and the battery's SOC to be calculated. Furthermore, the charge transfer resistance of the first electrode has a predetermined relationship with respect to the potential and charge state of the first electrode. In the embodiments, the real-time relationship between the potential of the first electrode and the battery's SOC is calculated using the calculation results of the relationship between the charge transfer resistance of the first electrode and the battery's SOC, and the predetermined relationship between the potential of the first electrode and the charge transfer resistance of the first electrode. Then, the degradation state of the first electrode is determined based on the calculation results of the relationship between the charge transfer resistance of the first electrode and the battery's SOC, and the calculation results of the relationship between the potential of the first electrode and the battery's SOC, etc.

[0020] Figure 2 is a schematic diagram showing an example of the relationship between the charge state of the first electrode and the charge transfer resistance of the first electrode for a battery to be diagnosed in the embodiment. In Figure 2, the horizontal axis represents the stoichiometry of the first electrode as the charge state of the first electrode, and the vertical axis represents the charge transfer resistance of the first electrode. In the battery of the embodiment, the first electrode contains a first electrode active material that undergoes a single-phase reaction, as described above. Therefore, as shown in Figure 2, when the charge state of the first electrode changes, the charge transfer resistance of the first electrode changes in accordance with the charge state of the first electrode. The relationship between the stoichiometry of the first electrode and the charge transfer resistance of the first electrode shown in Figure 2 takes the shape of a convex curve toward the side with lower charge transfer resistance (downward).

[0021] Figure 3 is a schematic diagram showing an example of the relationship between the battery's State of Charge (SOC) and the charge transfer resistance of the first electrode for a battery being diagnosed in this embodiment. In Figure 3, the horizontal axis represents the battery's SOC, and the vertical axis represents the charge transfer resistance of the first electrode. In the battery being diagnosed, the relationship between the stoichiometry of the first electrode and the charge transfer resistance of the first electrode takes on a convex shape toward the side with lower charge transfer resistance, as shown in Figure 2, etc. Therefore, the relationship between the battery's SOC and the charge transfer resistance of the first electrode, as shown in Figure 3, etc., also takes on a convex shape toward the side with lower charge resistance. Furthermore, the charge transfer resistance of the first electrode tends to be lower in the range where the SOC value is between 30% and 70% compared to the range where the SOC value is between 20% and 80% and 70% respectively.

[0022] Furthermore, the rate of change of the charge transfer resistance of the first electrode with respect to the State of Charge (SOC) of the battery is defined. At SOC values ​​where the charge transfer resistance increases with increasing SOC, the rate of change of the charge transfer resistance is a positive value, and at SOC values ​​where the charge transfer resistance decreases with increasing SOC, the rate of change of the charge transfer resistance is a negative value. In a battery, the absolute value of the rate of change of the charge transfer resistance of the first electrode with respect to SOC is smaller in the range where the SOC value is 20% or less, and in the range where the SOC value is 80% or more, when the SOC value is between 30% and 70%.

[0023] Furthermore, if the second electrode active material contained in the second electrode undergoes a single-phase reaction, the relationship between the charge state of the second electrode and the charge transfer resistance of the second electrode will follow a similar trend to the relationship between the charge state of the first electrode and the charge transfer resistance of the first electrode shown in Figure 2, etc., resulting in a convex shape towards the lower charge transfer resistance side. For this reason, the relationship between the battery's SOC and the charge transfer resistance of the second electrode will follow a similar trend to the relationship between the battery's SOC and the charge transfer resistance of the first electrode shown in Figure 3, etc., resulting in a convex shape towards the lower charge transfer resistance side. Moreover, if the second electrode active material contained in the second electrode undergoes a two-phase coexistence reaction, the charge transfer resistance of the second electrode will remain constant or nearly constant even if the charge state of the second electrode changes. For this reason, even if the battery's SOC changes, the charge transfer resistance of the second electrode will not change or will hardly change.

[0024] In the battery being diagnosed, the relationship between the charge transfer resistance of the first and second electrodes relative to the battery's State of Charge (SOC) is as described above. Therefore, the relationship between the battery's SOC and its impedance (absolute value of impedance) follows a similar trend to the relationship between the battery's SOC and the charge transfer resistance of the first electrode. In other words, the relationship between the battery's SOC and its impedance has a convex shape towards the lower impedance side. Furthermore, the battery's impedance tends to be lower in the range where the SOC value is between 30% and 70% compared to the range where the SOC value is below 20% and the range where the SOC value is above 80%.

[0025] Furthermore, it defines the rate of change of the battery's impedance with respect to the battery's State of Charge (SOC). For SOC values ​​where the impedance increases with increasing SOC, the rate of change of impedance is positive, and for SOC values ​​where the impedance decreases with increasing SOC, the rate of change of impedance is negative. In batteries, the absolute value of the rate of change of impedance with respect to SOC is smaller in the range where the SOC value is 20% or less, and in the range where the SOC value is 80% or more, when the SOC value is between 30% and 70%.

[0026] The aforementioned trend, shown in the relationship between the battery's SOC and its impedance, becomes particularly pronounced in impedances at relatively low frequency ranges, for example, between 0.1 Hz and 100 Hz. This frequency range varies depending on the type and combination of active materials contained in the electrodes. In one example, the positive electrode is a first electrode containing lithium nickel cobalt manganese oxide, which undergoes a single-phase reaction, as the positive electrode active material, and the negative electrode is a second electrode containing lithium titanate, which undergoes a two-phase coexistence reaction, as the negative electrode active material. In this case, the aforementioned trend, shown in the relationship between the battery's SOC and its impedance, becomes particularly pronounced at impedances around 1 Hz. The embodiments utilize the aforementioned trend, shown in the relationship between the battery's SOC and its impedance, to determine whether or not to measure the battery's impedance in a relatively high frequency range between 100 Hz and 10 kHz for each of several SOC values.

[0027] The following describes a diagnostic system for diagnosing the battery described above. Figure 4 is a schematic diagram showing an example of a diagnostic system 1 for battery 5 according to the embodiment. As shown in Figure 4, the diagnostic system 1 comprises a battery-mounted device 2 and a diagnostic device 3. The battery-mounted device 2 is equipped with a battery 5, a control circuit 6, a storage medium 7, and a communication module 8. The battery-mounted device 2 is also equipped with a drive circuit 11, a current detection circuit 12, and a voltage detection circuit 13. Examples of battery-mounted devices 2 include large-scale energy storage devices for power grids, smartphones, vehicles, stationary power supply devices, robots, and drones. Examples of vehicles that can be used as battery-mounted devices 2 include railway cars, electric buses, electric vehicles, plug-in hybrid vehicles, and electric motorcycles. The battery 5 is the battery described above. Therefore, the battery 5 is equipped with a first electrode containing a first electrode active material that undergoes a single-phase reaction, and the relationship between the battery's SOC and the battery's impedance shows the aforementioned trend in the impedance range of a relatively low frequency between 0.1 Hz and 100 Hz.

[0028] In the battery-equipped device 2, the battery management unit (BMU) is composed of a control circuit 6 and a storage medium 7. The control circuit 6 manages the battery 5 by controlling its charging and discharging, etc. The control circuit 6 is composed of a processor or integrated circuit, and the processor etc. that constitutes the control circuit 6 includes any of the following: CPU (Central Processing Unit), ASIC (Application Specific Integrated Circuit), microcontroller, FPGA (Field Programmable Gate Array), and DSP (Digital Signal Processor). The control circuit 6 may be composed of one processor etc. or multiple processor etc. The storage medium 7 is either a main memory such as memory or an auxiliary memory. Examples of storage mediums 7 include magnetic disks, optical disks (CD-ROM, CD-R, DVD, etc.), magneto-optical disks (MO, etc.), and semiconductor memory. The battery-equipped device 2 may be provided with only one memory etc. that serves as the storage medium 7, or it may be provided with multiple memory etc.

[0029] The communication module 8 consists of the communication interface of the battery-equipped device 2, etc. The control circuit 6 communicates with an external processing device of the battery-equipped device 2, including the diagnostic device 3, via the communication module 8. The control circuit 6 performs processing by executing a program stored on a storage medium, etc. The program executed by the control circuit 6 may also be stored on a computer (server) connected via a network such as the Internet, or on a server in a cloud environment. In this case, the control circuit 6 downloads the program via the network. The control circuit 6 also performs processing based on commands, etc. received from the outside via the communication module 8.

[0030] The control circuit 6 controls the charging and discharging of the battery 5 by controlling the operation of the drive circuit 11, for example. The control circuit 6 switches between a state in which the battery 5 is being charged and a state in which the battery 5 is being discharged by switching the operation state of the drive circuit 11. When the battery 5 is being charged, the control circuit 6 adjusts the magnitude of the current input to the battery 5 by controlling the operation of a power source (not shown) that supplies power to the battery 5 and the operation of the drive circuit 11. The power source that supplies power to the battery 5 may be installed in the battery-equipped device 2 or may be provided outside the battery-equipped device 2.

[0031] The current detection circuit 12 and the voltage detection circuit 13 constitute a measurement unit 10 that detects and measures parameters related to the battery 5. The measurement unit 10 periodically measures parameters related to the battery 5 when the battery 5 is being charged or discharged. In the measurement unit 10, the current detection circuit 12 periodically detects and measures the current flowing through the battery 5, and the voltage detection circuit 13 periodically detects and measures the voltage applied to the battery 5 as parameters related to the battery 5. In one example, the measurement unit 10 includes a temperature sensor (not shown) in addition to the current detection circuit 12 and the voltage detection circuit 13. In this case, the temperature sensor periodically detects and measures the temperature of the battery 5 as a parameter related to the battery 5.

[0032] The diagnostic device 3 diagnoses the state of the battery 5, including its degradation status. In an example shown in Figure 4, the diagnostic device 3 is a processing unit (computer) such as a server located outside the battery-equipped device 2, and can communicate with the battery-equipped device 2 via a network. The diagnostic device 3 includes a processing circuit 21, a storage medium 22, a communication module 23, and a user interface 25. The processing circuit 21 is composed of a processor or integrated circuit, and the processor or other components constituting the processing circuit 21 include any of the following: CPU, ASIC, microcontroller, FPGA, and DSP. The processing circuit 21 may be composed of one processor or multiple processors. The storage medium 22 is either a main memory such as a memory device or an auxiliary memory device. The diagnostic device 3 may be provided with only one memory device that serves as the storage medium 22, or it may be provided with multiple memory devices.

[0033] The processing circuit 21 performs processing by executing programs stored in the storage medium 22. In the example shown in Figure 4, the storage medium 22 stores a data management program 27 and a diagnostic program 28 as programs to be executed by the processing circuit 21. The processing circuit 21 writes data to the storage medium 22 and reads data from the storage medium 22 by executing the data management program 27. The processing circuit 21 also performs the processing described later in the diagnosis of the battery 5 by executing the diagnostic program 28. The diagnostic program 28 includes an impedance measurement program 31, a rate of change determination program 32, a resistance calculation program 33, and a state determination program 35.

[0034] In one example, the diagnostic device 3 is composed of multiple processing units (computers), such as multiple servers, and the processors of the multiple processing units cooperate to perform the processing described later in the diagnosis of the battery 5. In another example, the diagnostic device 3 is composed of a cloud server in a cloud environment. The infrastructure of the cloud environment is composed of virtual processors such as virtual CPUs and cloud memory. Therefore, when the diagnostic device 3 is composed of a cloud server, the virtual processor performs the processing described later in the diagnosis of the battery 5 in place of the processing circuit 21. The cloud memory has the function of storing programs and data, similar to the storage medium 22.

[0035] In one example, the program executed by the processing circuit 21 and the storage medium 22 that stores the data used for processing by the processing circuit 21 are located in a separate computer from the battery-powered device 2 and the diagnostic device 3. In this case, the diagnostic device 3 is connected to the computer where the storage medium 22 is located via a network. In another example, the diagnostic device 3 is mounted on the battery-powered device 2. In this case, the processor and other components mounted on the battery-powered device 2 perform the processing described later in the diagnosis of the battery 5, instead of the processing circuit 21.

[0036] The communication module 23 consists of a communication interface and the like for the processing unit that constitutes the diagnostic device 3. The processing circuit 21 communicates with external devices of the diagnostic device 3, including the battery-equipped device 2, via the communication module 23. The user interface 25 receives input from users of the diagnostic device 3 and the diagnostic system 1 regarding operations related to the diagnosis of the battery 5. For this reason, the user interface 25 is provided with an operation unit that receives input from users, such as a button, mouse, touch panel, and keyboard. The user interface 25 is also provided with a notification unit that provides information related to the diagnosis of the battery 5. The notification unit provides information through either a screen display or sound emission. The user interface 25 may be provided separately from the processing unit that constitutes the diagnostic device 3.

[0037] In this embodiment, in diagnosing the state of the battery 5, including its degradation state, the diagnostic device 3 performs the following processing. The control circuit 6 of the battery-equipped device 2 transmits measurement data, including the measurement results of the aforementioned parameters related to the battery 5 from the measurement unit 10, to the diagnostic device 3 via the communication module 8. The processing circuit 21 of the diagnostic device 3 receives the measurement data transmitted from the battery-equipped device 2 via the communication module 23. The measurement data received by the processing circuit 21 shows the measured values ​​and time changes (time history) for parameters related to the battery 5, including the current and voltage of the battery 5, at each of multiple measurement points. For this reason, the measurement data may show the time changes (time history) of the current of the battery 5 and the time changes (time history) of the voltage of the battery 5, and may also show the time changes (time history) of the temperature of the battery 5.

[0038] At least one of the control circuit 6 of the battery-equipped device 2 and the processing circuit 21 of the diagnostic device 3 calculates the real-time charge amount (amount of charge) and state of charge (SOC) of the battery 5 based on measurement data, including measurement results from the measurement unit 10 of parameters related to the battery 5. In addition, at least one of the control circuit 6 and the processing circuit 21 calculates the time-dependent changes (time history) of the charge amount and SOC of the battery 5 based on the time-dependent changes (time history) of parameters related to the battery 5. The real-time charge amount and SOC of the battery 5 are calculated as described above.

[0039] The processing circuit 21 executes the diagnostic program 28 to diagnose the state of the battery 5. The processing circuit 21 then measures the impedance of the battery 5 by executing the impedance measurement program 31 included in the diagnostic program 28. During the measurement of the impedance of the battery 5, the processing circuit 21 sends a command to the control circuit 6 of the battery-equipped device 2. The control circuit 6 then controls the operation of the drive circuit 11 and the power supply based on the command from the processing circuit 21, and supplies current to the battery 5 with a current waveform in which the current value changes periodically. As a result, a current waveform in which the current value changes periodically is input to the battery 5.

[0040] Figure 5 is a schematic diagram showing an example of the current waveform input to battery 5 during impedance measurement according to the embodiment. Figure 6 is a schematic diagram showing a different example of the current waveform input to battery 5 during impedance measurement according to the embodiment. In both Figure 5 and Figure 6, the horizontal axis represents time t and the vertical axis represents current I. In the example in Figure 5 and the example in Figure 6, the impedance of battery 5 at the frequency of the input current waveform is measured.

[0041] In the example shown in Figure 5, the control circuit 6, etc., inputs an alternating current Ia(t), whose waveform changes periodically in direction, to the battery 5. On the other hand, in the example shown in Figure 6, a superimposed current Ib(t), which is obtained by superimposing the alternating current waveform onto a reference DC current trajectory Ibref(t), is input to the battery 5. In the superimposed current Ib(t) input to the battery 5, the current value changes periodically around the reference current trajectory Ibref(t). Furthermore, the superimposed current Ib(t) is a DC current whose direction of flow does not change. The reference current trajectory Ibref(t) is, for example, the trajectory of the time change of the charging current set as a charging condition in charging the battery 5.

[0042] In one example, the impedance of battery 5 is measured in parallel with the charging of battery 5 (adjustment of the State of Charge of battery 5). In this case, similar to the superimposed current Ib(t) in the example in Figure 6, a superimposed current is input to battery 5, which is obtained by superimposing the current waveform of an AC current onto a reference current trajectory of a DC current that is set as the trajectory of the time change of the charging current. The superimposed current is a DC current whose current value changes periodically around the reference current trajectory in charging. In the reference current trajectory in charging, the current value of the charging current may be constant over time, or it may change over time. Also, although the current waveform of the AC current Ia(t) in Figure 5 and the current waveform of the superimposed current Ib(t) in Figure 6 are both sine waves, the current waveforms of the AC current and the superimposed current may be current waveforms other than sine waves, such as triangular waves and sawtooth waves.

[0043] The measurement unit 10, using the current detection circuit 12 and the voltage detection circuit 13, measures the current and voltage of the battery 5 at multiple measurement points while a current waveform with periodically changing current values ​​is input to the battery 5 as described above. The control circuit 6 then transmits measurement data, including the measurement results of the current and voltage of the battery 5 while a current waveform with periodically changing current values ​​is input to the battery 5, to the diagnostic device 3 via the communication module 8. The processing circuit 21 receives the measurement data transmitted from the control circuit 6 via the communication module 23. The measurement data received by the processing circuit 21 shows the measured values ​​of the current and voltage of the battery 5 at each of the multiple measurement points, as well as the time changes (time history) of the current and voltage of the battery 5, while a current waveform with periodically changing current values ​​is input to the battery 5.

[0044] The processing circuit 21 executes the impedance measurement program 31 to calculate the impedance of the battery 5 at the frequency of the input current waveform based on the measurement data received from the control circuit 6. In one example, the processing circuit 21 calculates the peak-to-peak value (variation range) in the periodic change of the current of the battery 5 based on the time change of the current of the battery 5, and calculates the peak-to-peak value (variation range) in the periodic change of the voltage of the battery 5 based on the time change of the voltage of the battery 5. Then, the processing circuit 21 calculates the impedance of the battery 5 from the ratio of the peak-to-peak value of the voltage to the peak-to-peak value of the current.

[0045] In diagnosing the battery 5 to be diagnosed, the processing circuit 21 first executes the impedance measurement program 31 to measure the first impedance, which is the impedance of the battery 5 at a first frequency, for each of the multiple SOC values ​​of the battery 5. The first impedance for each of the multiple SOC values ​​is measured as described above. That is, the processing circuit 21 measures the first impedance for each of the multiple SOC values ​​by inputting a current waveform to the battery 5 in which the current value changes periodically at a first frequency.

[0046] In one example, the State of Charge (SOC) of battery 5 is adjusted by charging or other means for each of the multiple SOC values ​​to be measured, and then an AC current similar to the example in Figure 5 is input to battery 5 at a first frequency, and the impedance of battery 5 is measured for each of the multiple SOC values. In another example, a superimposed current similar to the example in Figure 6 is input to battery 5 at a first frequency, and the impedance of battery 5 is measured for each of the multiple SOC values ​​while charging battery 5. In this case, a superimposed current, in which the current waveform of the AC current is superimposed on the reference current trajectory of the DC current at a first frequency, is input to battery 5.

[0047] The first frequency is a relatively low frequency, and is one of the frequencies in the frequency range of 0.1 Hz or higher and 100 Hz or lower (the first frequency range). In one example, in battery 5, the positive electrode is a first electrode containing lithium nickel cobalt manganese oxide, which undergoes a single-phase reaction, as the positive electrode active material, and the negative electrode is a second electrode containing lithium titanate, which undergoes a two-phase coexistence reaction, as the negative electrode active material. In this case, the first frequency is preferably around 1 Hz.

[0048] Furthermore, the measurement results of the first impedance at each of the multiple SOC values ​​can be shown, for example, in a complex impedance plot (Cole-Cole plot) for battery 5. In the complex impedance plot, the real and imaginary components of the impedance of battery 5, including the first impedance at each of the multiple SOC values, are shown. Also, in the complex impedance plot, the distance from the origin becomes the magnitude of the impedance (absolute value of the impedance). A method for measuring the frequency characteristics of the impedance of a battery by inputting a current waveform with periodically changing current values ​​to the battery, and complex impedance plots, etc., are shown in Non-Patent Literature 1 (JP Schmidt et al., “Studies on LiFePO4as cathode materials using impedance spectrometry” Journal of power Sources. 196, (2011), pp5342-pp5348), etc.

[0049] As described above, when the first impedance, which is the impedance of the battery 5 at the first frequency, is measured for each of the multiple SOC values ​​to be measured, the processing circuit 21 executes the rate of change determination program 32 to calculate the rate of change β of the first impedance with respect to the SOC of the battery 5 for each of the multiple SOC values ​​for which the first impedance has been measured. In calculating the rate of change β, the absolute value of the first impedance (magnitude of the first impedance), that is, the distance from the origin in the complex impedance plot, is used as the value of the first impedance for each of the multiple SOC values. Furthermore, for SOC values ​​in which the first impedance increases with increasing SOC, the rate of change β of the first impedance will be a positive value, and for SOC values ​​in which the first impedance decreases with increasing SOC, the rate of change β of the first impedance will be a negative value.

[0050] Figure 7 is a schematic diagram showing an example of a process for calculating the rate of change β of the first impedance with respect to the battery's SOC for each of a plurality of SOC values ​​in an embodiment. In Figure 7, the horizontal axis represents the SOC of battery 5, and the vertical axis represents the first impedance (absolute value of the first impedance). In the example in Figure 7, 0 (0%) is set as the lowest minimum SOC value and 1 (100%) as the highest maximum SOC value, and the first impedance of battery 5 is measured at intervals of 0.1 (10%) in terms of the battery's SOC. Therefore, for each of the 11 SOC values, the first impedance, which is the impedance at the first frequency, is measured. In Figure 7, the first impedances for the 11 SOC values ​​are plotted as points M0, M1, M2, M3, M4, M5, M6, M7, M8, M9, and M10.

[0051] When calculating the rate of change β of the first impedance with respect to SOC for each of the 11 SOC values, the processing circuit 21 calculates the trajectory X of a function that shows the relationship between the SOC of battery 5 and the first impedance by fitting a function such as a quadratic or cubic function to points M0 to M10, for example. Then, for each of the 11 SOC values, the processing circuit 21 calculates the slope of the tangent line in the trajectory X as the rate of change β of the first impedance with respect to SOC of battery 5. For example, the slopes of the tangent lines T0, T3, T5, T7, and T10 are calculated as the rate of change β of the first impedance when the SOC values ​​are 0, 0.3, 0.5, 0.7, and 1, respectively. Similarly, the rate of change β of the first impedance when the SOC values ​​are 0.1, 0.2, 0.4, 0.6, 0.8, and 0.9 are also calculated from the slope of the tangent line in the trajectory X. Furthermore, in calculating the trajectory X, interpolation such as spline interpolation may be performed instead of fitting using a function such as a quadratic function.

[0052] As described above, when the rate of change β of the first impedance with respect to the SOC is calculated for each of the multiple SOC values ​​for which the first impedance has been measured, the processing circuit 21 executes the rate of change determination program 32 to determine whether the absolute value |β| of the calculated rate of change β for each of the multiple SOC values ​​is less than or equal to the reference value βref. Then, the processing circuit 21 sets the SOC value among the multiple SOC values ​​for which the absolute value |β| of the rate of change β is less than or equal to the reference value βref as the target SOC value for measuring the impedance of the battery 5 at a second frequency higher than the first frequency. The reference value βref may be a fixed value, or it may be set to an appropriate value by the processing circuit 21.

[0053] In one example, the reference value βref is set based on the rate of change βL at the lowest SOC value among multiple SOC values ​​for which the first impedance was measured, or the rate of change βH at the highest SOC value among multiple SOC values ​​for which the first impedance was measured. For example, half the absolute value |βL| of the rate of change βL at the lowest SOC value, or half the absolute value |βH| of the rate of change βH at the highest SOC value, is set as the reference value βref. In this case, in the example in Figure 7, half the absolute value |β0| of the rate of change β0 when the SOC value is 0, or half the absolute value |β10| of the rate of change β10 when the SOC value is 1, is set as the reference value βref.

[0054] Here, the first frequency is one of the frequencies in the frequency range of 0.1 Hz or higher and 100 Hz or lower (the first frequency range). Therefore, the absolute value |β| of the rate of change β of the first impedance with respect to SOC is smaller in the range where the SOC value is 20% or lower and in the range where the SOC value is 80% or higher than 30% or higher and 70% or lower. For this reason, in one example, when determining whether the absolute value |β| of the rate of change β is less than or equal to the reference value βref, SOC values ​​in the range of 30% or higher and 70% or lower are determined to be target SOC values ​​whose absolute value |β| is less than or equal to the reference value βref. SOC values ​​lower than 30% and SOC values ​​higher than 70% are determined to be not target SOC values ​​because their absolute value |β| is greater than the reference value βref.

[0055] For example, as shown in the example in Figure 7, suppose the rate of change β of the first impedance with respect to SOC is calculated for each of the 11 SOC values. In this case, for SOC values ​​0.3, 0.4, 0.5, 0.6, and 0.7, the absolute value |β| of the rate of change β is determined to be less than or equal to the reference value βref, and is determined to be a target SOC value. On the other hand, for SOC values ​​0, 0.1, 0.2, 0.8, 0.9, and 1, the absolute value |β| of the rate of change β is determined to be greater than the reference value βref, and is determined not to be a target SOC value. In one example, the aforementioned reference value βref may be set to an appropriate value so that only SOC values ​​in the range of 30% or more and 70% or less among multiple SOC values ​​are target SOC values. Furthermore, it is preferable that two or more of the SOC values ​​for which the first impedance was measured are determined to be target SOC values, and it is even more preferable that three or more of the SOC values ​​for which the first impedance was measured are determined to be target SOC values.

[0056] As described above, when an SOC value is set as the target SOC value such that the absolute value |β| of the rate of change β of the first impedance with respect to the SOC is less than or equal to the reference value βref, for each target SOC value, the second impedance, which is the impedance of the battery 5 at a second frequency higher than the first frequency, is measured in addition to the first impedance. In one example, among multiple SOC values, only SOC values ​​in the range of 30% or more and 70% or less are determined to be the target SOC value, and the processing circuit 21 executes the impedance measurement program 31 to measure the second impedance only for SOC values ​​in the range of 30% or more and 70% or less among the SOC values ​​for which the first impedance has been measured.

[0057] The second impedance for each of the target SOC values ​​is measured in the same manner as the first impedance for each of the multiple SOC values. That is, the processing circuit 21 measures the second impedance for each of the target SOC values ​​by inputting a current waveform to the battery 5 in which the current value changes periodically at a second frequency. In one example, the SOC of the battery 5 is adjusted for each of the target SOC values ​​by charging, etc., and then an AC current similar to the example in Figure 5 is input to the battery 5 at a second frequency, and the impedance of the battery 5 is measured for each of the target SOC values. In another example, a superimposed current similar to the example in Figure 6 is input to the battery 5 at a second frequency, and the impedance of the battery 5 is measured for each of the target SOC values ​​while the battery 5 is being charged. In this case, a superimposed current, in which the current waveform of the AC current is superimposed on the reference current trajectory of the DC current at a second frequency, is input to the battery 5.

[0058] The second frequency is higher than the first frequency and is a relatively high frequency. Furthermore, the second frequency is one of the frequencies within the frequency range of 100 Hz or higher and 10 kHz or lower (the second frequency range). The lower limit of the frequency range of 100 Hz or higher and 10 kHz or lower (the second frequency range), which may include the second frequency, is higher than the upper limit of the frequency range of 0.1 Hz or higher and 20 Hz or lower (the first frequency range), which may include the first frequency. In one example, in battery 5, the positive electrode is a first electrode containing lithium nickel cobalt manganese oxide, which undergoes a single-phase reaction, as the positive electrode active material, and the negative electrode is a second electrode containing lithium titanate, which undergoes a two-phase coexistence reaction, as the negative electrode active material. In this case, the second frequency is preferably around 1000 Hz (1 kHz).

[0059] As described above, by measuring the impedance of battery 5, for SOC values ​​where the absolute value |β| of the rate of change β of the first impedance is greater than the reference value βref, only the first impedance is measured. On the other hand, for target SOC values ​​where the absolute value |β| of the rate of change β of the first impedance is less than or equal to the reference value βref, both the first and second impedances are measured, and the impedance at each of multiple frequencies is measured. For example, in the example in Figure 7, among the 11 SOC values, the first and second impedances are measured only for five SOC values: 0.3, 0.4, 0.5, 0.6, and 0.7.

[0060] In diagnosing the battery 5 to be diagnosed, the processing circuit 21 determines the state of the battery 5, such as its degradation state, based on the measurement results of the first impedance and the second impedance for each target SOC value. At this time, the processing circuit 21 calculates the resistance component of the impedance of the battery 5 for each target SOC value for which the first impedance and the second impedance have been measured by executing the resistance calculation program 33. Then, for each target SOC value, the charge transfer resistance of the first electrode, which is one of the impedance resistance components, is calculated as the resistance related to the first electrode. In addition, for each target SOC value, the charge transfer resistance of the second electrode may also be calculated in addition to the charge transfer resistance of the first electrode.

[0061] The storage medium 22 stores an equivalent circuit model containing information about the equivalent circuit of the battery 5. In the equivalent circuit of the equivalent circuit model, several electrical characteristic parameters (circuit constants) corresponding to the impedance component of the battery 5 are set. Electrical characteristic parameters are parameters that indicate the electrical characteristics of the circuit elements provided in the equivalent circuit. Examples of electrical characteristic parameters include resistance, capacitance, inductance, and impedance. Furthermore, if a CPE (constant phase element) is used instead of a capacitor as a circuit element in the equivalent circuit, capacitance and Debye's empirical parameter are set as the electrical characteristic parameters of the CPE. The resistance shown as an electrical characteristic parameter in the equivalent circuit may include the charge transfer resistance of the first electrode and may also include the charge transfer resistance of the second electrode.

[0062] Furthermore, the equivalent circuit model stored in the storage medium 22 includes data showing the relationship between the electrical characteristic parameters of the equivalent circuit and the impedance of the battery 5. The data showing the relationship between the electrical characteristic parameters and the impedance of the battery 5 includes, for example, calculation formulas for calculating the real and imaginary components of the impedance from the electrical characteristic parameters (circuit constants). In this case, the calculation formula uses the electrical characteristic parameters and frequency to calculate the real and imaginary components of the impedance of the battery 5.

[0063] The processing circuit 21 calculates the charge transfer resistance of the first electrode for each target SOC value for which both the first and second impedances have been measured as frequency characteristics of the impedance, using an equivalent circuit model as follows. That is, in calculating the charge transfer resistance of the first electrode for each target SOC value, the processing circuit 21 performs a fitting calculation using an equivalent circuit model including the equivalent circuit, and the measurement results of the first and second impedances. In this case, the electrical characteristic parameters of the equivalent circuit including the charge transfer resistance of the first electrode are used as variables in the fitting calculation, and the variable electrical characteristic parameters are calculated. Furthermore, in the fitting calculation, for example, at the first frequency for which the first impedance was measured and the second frequency for which the second impedance was measured, the values ​​of the variable electrical characteristic parameters are determined to minimize the difference between the impedance calculation result using the calculation formula included in the equivalent circuit model and the impedance measurement result.

[0064] As described above, the charge transfer resistance of the first electrode, which is set as one of the electrical characteristic parameters in the equivalent circuit, is calculated by performing a fitting calculation. Furthermore, if the charge transfer resistance of the second electrode is set as one of the electrical characteristic parameters in the equivalent circuit, the charge transfer resistance of the second electrode is also calculated. The equivalent circuit of the battery, etc., is shown in Non-Patent Document 1. In addition, the measurement results of the frequency characteristics of the battery impedance, and the method of performing a fitting calculation using the equivalent circuit model of the battery to calculate the electrical characteristic parameters (circuit constants) of the equivalent circuit are also shown in Non-Patent Document 1.

[0065] Figure 8 is a schematic circuit diagram showing an example of an equivalent circuit of battery 5 used in fitting calculations in the embodiment. In the example equivalent circuit of Figure 8, resistors Ro1, Ro2, Rc1, Rc2, Rc3, capacitances C1, C2, C3, inductance L1, impedances Zw1, Zw2, and Debye empirical parameters α1, α2, α3 are set as electrical characteristic parameters corresponding to the impedance components of battery 5. Here, resistors Ro1 and Ro2 correspond to the resistance components that become ohmic resistances, inductance L1 corresponds to the inductance component of battery 5, and impedances Zw1 and Zw2 correspond to the impedance components that become Warburg impedances. Furthermore, resistor Rc3 corresponds to the film resistance of the film formed on the positive or negative electrode by a reaction, etc., and resistor Rc3, capacitance C3, and Debye empirical parameter α3 correspond to the impedance caused by the film, including the film resistance. Capacitance C3 and Debye empirical parameter α3 become the electrical characteristic parameters of CPEQ3.

[0066] Furthermore, in the equivalent circuit example shown in Figure 8, resistance Rc1, capacitance C1, and Debye's empirical parameter α1 are set as electrical characteristic parameters corresponding to the impedance component of the charge transfer impedance of the first electrode, and capacitance C1 and Debye's empirical parameter α1 become the electrical characteristic parameters of CPEQ1. Then, in the equivalent circuit example shown in Figure 8, resistance Rc2, capacitance C2, and Debye's empirical parameter α2 are set as electrical characteristic parameters corresponding to the impedance component of the charge transfer impedance of the second electrode, and capacitance C2 and Debye's empirical parameter α2 become the electrical characteristic parameters of CPEQ2. By calculating the electrical characteristic parameters of the equivalent circuit example shown in Figure 8 as described above through fitting calculations, resistance Rc1 is calculated as the charge transfer resistance of the first electrode, and resistance Rc2 is calculated as the charge transfer resistance of the second electrode.

[0067] The processing circuit 21 calculates the charge transfer resistance of the first electrode for each of the multiple target SOC values, for which the first and second impedances are measured as frequency characteristics of impedance, as described above. This calculates the relationship between the charge transfer resistance of the first electrode, which is the resistance related to the first electrode, and the SOC of the battery 5. The relationship between the charge transfer resistance of the first electrode and the SOC of the battery 5 is shown, for example, by a curve on a graph where the horizontal axis is the SOC of the battery 5 and the vertical axis is the charge transfer resistance of the first electrode. In calculating the curve showing the relationship between charge transfer resistance and SOC, points representing the charge transfer resistance of the first electrode for each of the multiple target SOC values ​​are plotted on the aforementioned graph. Then, a curve showing the relationship between charge transfer resistance and SOC is calculated by fitting a function such as a quadratic or cubic function to the plotted points. Note that in calculating the curve showing the relationship between the charge transfer resistance of the first electrode and SOC, interpolation such as spline interpolation may be performed instead of fitting using a function.

[0068] The processing circuit 21 executes the state determination program 35 and uses the relationship between the charge transfer resistance of the first electrode and the state of charge (SOC) of the battery 5, calculated as described above, to determine the SOC value at which the charge transfer resistance of the first electrode is minimized, which is then used as the reference SOC value. The reference SOC value at which the charge transfer resistance of the first electrode is minimized changes from the time the battery 5 is first used, due to a change in the relationship between the potential of the first electrode and the SOC of the battery 5. Therefore, by calculating the reference SOC value at which the charge transfer resistance of the first electrode is minimized, it becomes possible to determine the degradation state of the first electrode and thus the state of the battery 5. Based on the calculated reference SOC value, the processing circuit 21 determines the state of the battery 5, including the degradation state of the first electrode.

[0069] Figure 9 is a schematic diagram showing an example of a process for calculating a reference SOC value in which the charge transfer resistance of the first electrode is minimized in an embodiment. In Figure 9, the horizontal axis represents the SOC of battery 5, and the vertical axis represents the charge transfer resistance of the first electrode. In the example in Figure 9, among several SOC values ​​for which the first impedance has been measured, five SOC values ​​of 0.3, 0.4, 0.5, 0.6, and 0.7 are determined to be target SOCs in which the absolute value |β| of the aforementioned rate of change β is less than or equal to the reference value βref. Then, the second impedance is measured for each of the five target SOC values, and the charge transfer resistance of the first electrode is calculated as described above based on the measurement results of the first and second impedances. In Figure 9, the charge transfer resistance of the first electrode for the five target SOC values ​​is plotted as points N1, N2, N3, N4, and N5. Then, by fitting the function to points N1 to N5, the trajectory Y of the function showing the relationship between the SOC of battery 5 and the charge transfer resistance of the first electrode is calculated.

[0070] As shown in the example trajectory Y in Figure 9, the trajectory showing the relationship between the charge transfer resistance of the first electrode and the state of charge (SOC) of the battery 5 has a convex shape towards the side with lower charge transfer resistance (downward). The SOC value at the peak of the convex shape in the trajectory showing the relationship between the charge transfer resistance of the first electrode and the SOC of the battery 5 is calculated as the reference SOC value at which the charge transfer resistance of the first electrode is at its lowest. In the example in Figure 9, the SOC value at the peak of the convex shape of trajectory Y is 0.5 (50%), and 0.5 is calculated as the reference SOC value at which the charge transfer resistance of the first electrode is at its lowest.

[0071] Furthermore, the processing circuit 21 may calculate the real-time relationship between the potential of the first electrode and the SOC of the battery 5 based on the relationship between the charge transfer resistance of the first electrode and the SOC of the battery 5 by executing the state determination program 35. In this case, data showing a predetermined relationship between the potential of the first electrode and the charge transfer resistance of the first electrode is stored in the storage medium 22. The processing circuit 21 calculates the real-time relationship between the potential of the first electrode and the SOC of the battery 5 based on the calculation result of the relationship between the charge transfer resistance of the first electrode and the SOC of the battery 5, and the predetermined relationship between the charge transfer resistance of the first electrode and the potential. At this time, for example, the relationship between the potential of the first electrode and the SOC of the battery 5 is calculated by calculating the corresponding value of the potential of the first electrode for each of a plurality of SOC values, including the target SOC value for which the second impedance was measured.

[0072] The processing circuit 21 calculates the potential value of the first electrode corresponding to each of several SOC values ​​by calculating the relationship between the potential of the first electrode and the SOC of the battery 5 as described above. For example, it calculates the potential value of the first electrode corresponding to the state where the SOC value of the battery 5 is 0 (the state where the battery 5 is at its lower limit voltage Vmin), and the potential value of the first electrode corresponding to the state where the SOC value of the battery 5 is 1 (the state where the battery 5 is at its upper limit voltage Vmax). Then, the processing circuit 21 calculates the range between the potential value of the first electrode corresponding to the state where the SOC value is 0 (0%) and the potential value of the first electrode corresponding to the state where the SOC value is 1 (100%) as the real-time usable potential range for the first electrode.

[0073] In one example, the processing circuit 21 executes the state determination program 35 to calculate the real-time relationship between the potential of the second electrode and the SOC of the battery 5, based on the calculation result of the real-time relationship between the potential of the first electrode and the SOC of the battery 5. At this time, the calculation is performed using the measurement results of the battery 5 voltage for each of several SOC values, including the target SOC value for which the second impedance was measured. Then, for each of the multiple SOC values, the corresponding value of the potential of the second electrode is calculated based on the measurement result of the battery 5 voltage and the calculation result of the potential of the first electrode.

[0074] The processing circuit 21 calculates the relationship between the potential of the second electrode and the state of charge (SOC) of the battery 5 as described above. For example, it calculates the potential value of the second electrode corresponding to the state where the SOC value of the battery 5 is 0 (the state where the battery 5 is at its lower limit voltage Vmin), and the potential value of the second electrode corresponding to the state where the SOC value of the battery 5 is 1 (the state where the battery 5 is at its upper limit voltage Vmax). The processing circuit 21 then calculates the range between the potential value of the second electrode corresponding to the state where the SOC value is 0 (0%) and the potential value of the second electrode corresponding to the state where the SOC value is 1 (100%) as the real-time usable potential range for the second electrode.

[0075] The processing circuit 21 executes the state determination program 35 to determine the state of the battery 5 based on one or more of the following: the relationship between the charge transfer resistance of the first electrode and the state of charge (SOC) of the battery 5, the reference SOC value at which the charge transfer resistance of the first electrode is minimized, the relationship between the potential of the first electrode and the SOC of the battery 5, and the relationship between the potential of the second electrode and the SOC of the battery 5. At this time, the degradation state of the first electrode and the second electrode, as well as the overall degradation state of the battery 5, are determined.

[0076] In one example, the processing circuit 21 executes the state determination program 35 to compare past data with real-time data regarding the relationship between the charge transfer resistance of the first electrode and the state of charge (SOC) of the battery 5, the reference SOC value at which the charge transfer resistance of the first electrode is minimized, and the relationship between the potential of the first electrode and the SOC of the battery 5. The processing circuit 21 then compares the past data, which is data from a first period, with the real-time data, which is data from a second period that follows the first period, to determine the real-time state of the battery 5, including the real-time degradation state of the first electrode.

[0077] In this case, the processing circuit 21 performs the following in both the first and second periods: measurement of the first impedance for multiple SOC values, determination of whether the absolute value |β| of the rate of change β is less than or equal to the reference value βref, measurement of the second impedance for the target SOC value, and determination of the state of the battery 5. In addition, the data from the first period, which is historical data, is stored in the storage medium 22 or the like. In determining the state of the battery 5 in the second period, the processing circuit 21 reads the data from the first period from the storage medium 22 and compares the data from the first period with the real-time data from the second period.

[0078] For example, the processing circuit 21 calculates the relationship between the charge transfer resistance of the first electrode and the State of Charge (SOC) of the battery 5 for a first period, such as when the battery 5 is first put into use, and for a second period, such as after the first period, as described above. The processing circuit 21 then calculates the reference SOC value of the battery 5 at which the charge transfer resistance of the first electrode is minimized for each of the first and second periods, as described above. The processing circuit 21 then compares the calculation result for the reference SOC value of the battery 5 at which the charge transfer resistance of the first electrode is minimized for the first period with the calculation result for the second period. Based on the comparison result for the reference SOC value, the processing circuit 21 then calculates the change in the relationship between the SOC of the battery 5 and the potential of the first electrode during the second period compared to the first period.

[0079] Figure 10 is a schematic diagram showing an example of the relationship between the charge transfer resistance of the first electrode and the State of Charge (SOC) of the battery 5, calculated in the embodiment, for both the first period and the second period following the first period. In Figure 10, the horizontal axis represents the SOC of the battery 5, and the vertical axis represents the charge transfer resistance of the first electrode. In Figure 10, the relationship for the first period is shown by a solid line, and the relationship for the second period is shown by a dashed line. In the example in Figure 10, for both the first and second periods, among the multiple SOC values ​​for which the first impedance was measured, five SOC values ​​of 0.3, 0.4, 0.5, 0.6, and 0.7 are determined to be target SOCs where the absolute value |β| of the aforementioned rate of change β is less than or equal to the reference value βref. Then, for each of the five target SOC values, the second impedance is measured, and based on the measurement results of the first and second impedances, the charge transfer resistance of the first electrode is calculated as described above.

[0080] In the example shown in Figure 10, the calculated charge transfer resistance of the first electrode for five target SOC values ​​during the first period is plotted as points Na1, Na2, Na3, Na4, and Na5, and the calculated charge transfer resistance of the first electrode for five target SOC values ​​during the second period is plotted as points Nb1, Nb2, Nb3, Nb4, and Nb5. Then, by fitting the function to points Na1 to Na5, a trajectory Ya showing the relationship between the SOC of battery 5 and the charge transfer resistance of the first electrode during the first period is calculated, and by fitting the function to points Nb1 to Nb5, a trajectory Yb showing the relationship between the SOC of battery 5 and the charge transfer resistance of the first electrode during the second period is calculated. In the example shown in Figure 10, the SOC value at the apex of the convex shape of trajectory Ya is 0.6 (60%), and 0.6 is calculated as the reference SOC value at which the charge transfer resistance of the first electrode is lowest during the first period. Similarly, the SOC value at the apex of the convex shape of trajectory Yb is 0.5 (50%), and 0.5 is calculated as the reference SOC value at which the charge transfer resistance of the first electrode is lowest during the first period.

[0081] As described above, a reference SOC value is calculated for each of the first and second periods at which the charge transfer resistance of the first electrode is at its lowest. Therefore, in the example shown in Figure 10, it is calculated that the reference SOC value is approximately 10% (0.1) lower in the second period than in the first period. Consequently, the processing circuit 21 calculates that the relationship between the potential of the first electrode and the SOC of battery 5 in the second period is shifted by approximately 10% in terms of SOC of battery 5, compared to the relationship between the potential of the first electrode and the SOC of battery 5 in the first period, with the SOC value of battery 5 shifting towards the higher potential side when compared under the same conditions. Thus, by comparing the relationship between the charge transfer resistance of the first electrode and the SOC of battery 5 with data from a past period (first period) and real-time data (second period), the change in the relationship between the potential of the first electrode and the SOC of battery 5 from a past period can be calculated.

[0082] Figure 11 is a flowchart schematically showing an example of the processing performed by the processing circuit 21 of the diagnostic device 3 when it executes the diagnostic program 28 in the embodiment. Figure 11 shows the processing in the diagnosis of the battery 5, and the processing in Figure 11 is performed each time the battery 5 is diagnosed. When the processing in Figure 11 is started, the processing circuit 21 measures the first impedance, which is the impedance of the battery 5 at the first frequency, for each of the multiple SOC values ​​as described above (S101). At this time, an alternating current or the superimposed current described above is input to the battery 5 at the first frequency, and the first impedance of the battery 5 is measured for each of the multiple SOC values ​​to be measured. Then, for each of the multiple SOC values ​​for which the first impedance has been measured, the processing circuit 21 calculates the rate of change β of the first impedance with respect to the SOC of the battery 5 as described above (S102).

[0083] The processing circuit 21 then sets the SOC value among the multiple SOC values ​​for which the first impedance has been measured as the target SOC value, such that the absolute value of the rate of change β|| is less than or equal to the reference value βref (S103). In this case, the reference value βref is set in the same manner as in any of the examples described above. In addition, in S103, the processing circuit may determine that the SOC values ​​in the range of 30% or more and 70% or less among the multiple SOC values ​​are the target SOC values ​​for which the absolute value of the rate of change β||| is less than or equal to the reference value βref. Then, for each of the target SOC value and the set SOC value, the processing circuit measures the second impedance, which is the impedance of the battery 5 at a second frequency higher than the first frequency, in addition to the first impedance (S104). In this case, an AC current or the superimposed current described above is input to the battery 5 at the second frequency, and the second impedance of the battery 5 is measured for each of the target SOC values.

[0084] Then, for each target SOC value, the processing circuit 21 calculates the charge transfer resistance of the first electrode as the resistance related to the first electrode based on the first impedance and the second impedance (S105). At this time, as described above, the charge transfer resistance of the first electrode is calculated for each target SOC value by performing a fitting calculation using an equivalent circuit model in which the charge transfer resistance of the first electrode is used as an electrical characteristic parameter. Then, from the calculation results of the charge transfer resistance of the first electrode for each target SOC value, the processing circuit 21 calculates the real-time relationship between the charge transfer resistance of the first electrode and the SOC of the battery 5, and a reference SOC value which is the SOC value in which the charge transfer resistance of the first electrode is minimized, as described above (S106).

[0085] Then, based on the calculation results regarding the relationship between the charge transfer resistance of the first electrode and the state of charge (SOC) of the battery 5, the processing circuit 21 calculates the real-time relationship between the SOC of the battery 5 and the potential of the first electrode, as described above, and calculates the real-time usable potential range of the first electrode (S107). Then, based on the calculation results regarding the relationship between the SOC of the battery 5 and the potential of the first electrode, and the measurement results regarding the voltage of the battery 5, the processing circuit 21 calculates the real-time relationship between the SOC of the battery 5 and the potential of the second electrode, as described above, and calculates the real-time usable potential range of the second electrode (S108).

[0086] The processing circuit 21 then compares past data (first period) with real-time data (second period) regarding one of the following: the relationship between the charge transfer resistance of the first electrode and the state of charge (SOC) of the battery 5; the reference SOC value at which the charge transfer resistance of the first electrode is minimized; the relationship between the potential of the first electrode and the SOC of the battery 5; and the relationship between the potential of the second electrode and the SOC of the battery 5. Based on the comparison with past data, the processing circuit then performs calculations and determines the state of the battery (S109). In this case, for example, based on the reference SOC value at which the charge transfer resistance of the first electrode is minimized, the change in the state of the battery 5 from a certain period in the past is calculated, for example, the change in the relationship between the potential of the first electrode and the SOC of the battery 5 from a certain period in the past.

[0087] As described above, in this embodiment, for each of the multiple SOC values ​​for which the first impedance has been measured, it is determined whether the absolute value |β| of the rate of change β of the first impedance with respect to the SOC of the battery 5 is less than or equal to a reference value βref. Then, for the target SOC value among the multiple SOC values ​​for which the absolute value |β| of the rate of change β is less than or equal to the reference value βref, the second impedance is measured, and the state of the battery 5 is determined based on the measurement results of the first and second impedances for the target SOC value. As described above, since the frequency characteristics of the impedance are measured, the number of SOC values ​​for which the second impedance, which is the impedance at high frequencies, is measured decreases. By reducing the number of SOC values ​​for which the impedance at high frequencies is measured, the increase in the amount of data used to determine the state of the battery 5 is suppressed.

[0088] By suppressing the increase in the amount of data used to determine the state of the battery 5, the increase in communication capacity between the battery-equipped device 2 and the diagnostic device 3 is also appropriately suppressed. Furthermore, the increase in the amount of data processed in the control circuit 6 of the battery-equipped device 2 and the processing circuit 21 of the diagnostic device 3 is appropriately suppressed, and the increase in load on the processors of the battery-equipped device 2 and the diagnostic device 3 is appropriately suppressed. In addition, the increase in the amount of data that needs to be managed by the diagnostic device 3 is also appropriately suppressed. Moreover, by suppressing the increase in the amount of data used to determine the state of the battery 5, the time required for data analysis is shortened, and the time required for processing in diagnosing the battery 5 is shortened.

[0089] Furthermore, in this embodiment, for each of the multiple SOC values, it is determined that the SOC value is the target SOC value for measuring the second impedance, based on the fact that the absolute value |β| of the rate of change β of the first impedance with respect to SOC is less than or equal to the reference value βref. As described above, the target SOC values ​​for measuring both the first and second impedances are determined, and based on the measurement results of the first and second impedances for each of the determined target SOC values, the relationship between the SOC of the battery 5 and the charge transfer resistance of the first electrode, and the reference SOC value at which the charge transfer resistance of the first electrode is minimized are appropriately calculated, as described above. Then, based on the calculation results regarding the relationship between the SOC of the battery 5 and the charge transfer resistance of the first electrode, the relationship between the potentials of the first and second electrodes and the SOC of the battery 5 is appropriately calculated.

[0090] Therefore, in this embodiment, even if the number of SOC values ​​used to measure impedance at high frequencies is reduced, the state of the battery 5, including the relationship between the SOC of the battery 5 and the charge transfer resistance of the first electrode, can be appropriately determined in real time based on the measurement results of the impedance frequency characteristics. In other words, in this embodiment, the increase in the amount of data used to determine the state of the battery 5 is suppressed, and the state of the battery 5 can be appropriately determined based on the measurement results of the impedance frequency characteristics.

[0091] Furthermore, in one embodiment, half of the absolute value |βL| of the rate of change βL at the lowest SOC value, or half of the absolute value |βH| of the rate of change βH at the highest SOC value, is used as the reference value βref, and for each of the multiple SOC values, it is determined whether the absolute value |β| of the rate of change β is less than or equal to the reference value βref. For this reason, for example, for SOC values ​​that fall within an SOC range where a reference SOC value exists that minimizes the charge transfer resistance of the first electrode, such as an SOC range of 30% or more and 70% or less, the second impedance is measured.

[0092] As a result, based on the measurement results of the first and second impedances at each target SOC value, the relationship between the SOC of battery 5 and the charge transfer resistance of the first electrode, and the reference SOC value at which the charge transfer resistance of the first electrode is minimized, can be calculated more appropriately. Therefore, based on the calculation results of the reference SOC value, etc., the changes in the state of battery 5, including the relationship between the potential of the first electrode and the SOC of battery 5, from a certain period in the past, such as the start of use, can be calculated more appropriately. This allows for more accurate determination of the state of battery 5.

[0093] (Verification related to the embodiment) Furthermore, the following verifications were performed in relation to the embodiments described above. In the verifications, a battery was diagnosed in which the positive electrode was a first electrode containing lithium nickel cobalt manganese oxide, which undergoes a single-phase reaction, as the positive electrode active material, and the negative electrode was a second electrode containing lithium titanate, which undergoes a two-phase coexistence reaction, as the negative electrode active material. The frequency characteristics of the battery impedance were measured at intervals of 0.1 (10%) in terms of the battery's SOC value, with 0 (0%) being the lowest minimum SOC value and 1 (100%) being the highest maximum SOC value. In other words, the frequency characteristics of the battery impedance were measured for each of the 11 SOC values. For each of the 11 SOC values, the impedance was measured at multiple different frequencies relative to each other, and the frequency characteristics of the impedance were measured.

[0094] Furthermore, in the verification, the charge transfer resistance of the positive electrode, which is the first electrode, was calculated for each of the 11 SOC values ​​based on the measurement results of the impedance frequency characteristics. The charge transfer resistance of the positive electrode was calculated by performing a fitting calculation using an equivalent circuit model in which the charge transfer resistance of the positive electrode is an electrical characteristic parameter, as described above in the embodiments. In addition, in the verification, points representing the charge transfer resistance of the positive electrode for each of the 11 SOC values ​​were plotted on a graph in which the horizontal axis is the battery's SOC and the vertical axis is the charge transfer resistance of the positive electrode. Then, using the plotted points, a curve representing the trajectory showing the relationship between the charge transfer resistance of the positive electrode and the battery's SOC was calculated for each of the three calculation patterns γ0, γ1, and γ2.

[0095] Figure 12 is a schematic diagram illustrating three calculation patterns γ0 to γ2 used to calculate the trajectory showing the relationship between the charge transfer resistance of the positive electrode and the state of charge (SOC) of the battery in a verification related to the embodiment. In Figure 12, the horizontal axis represents the SOC of the battery, and the vertical axis represents the charge transfer resistance of the positive electrode. In addition, in Figure 12, the charge transfer resistance of the positive electrode is plotted as points P0, P1, P2, P3, P4, P5, P6, P7, P8, P9, and P10 for 11 SOC values ​​for which the impedance frequency characteristics were measured.

[0096] In calculation pattern γ0, the relationship between the charge transfer resistance of the positive electrode and the battery's SOC was calculated using only the charge transfer resistance of the positive electrode at five SOC values ​​within the range of 30% to 70% out of 11 SOC values. In this process, a curve Y0, representing the relationship between the charge transfer resistance of the positive electrode and the battery's SOC, was calculated by fitting a quadratic function to five points P3 to P7. Therefore, in calculation pattern γ0, similar to one example of the embodiment described above, the relationship between the charge transfer resistance of the positive electrode and the battery's SOC was calculated using only the charge transfer resistance of the positive electrode at SOC values ​​within the range of 30% to 70%. In Figure 12, curve Y0 is shown as a solid line.

[0097] Furthermore, in calculation pattern γ1, unlike the embodiments described above, the trajectory showing the relationship between the charge transfer resistance of the positive electrode and the battery's SOC was calculated using all 11 SOC values. In this case, a curve Y0, which represents the trajectory showing the relationship between the charge transfer resistance of the positive electrode and the battery's SOC, was calculated by fitting a quadratic function to the 11 points P0 to P10. Furthermore, in calculation pattern γ2, unlike the embodiments described above, the trajectory showing the relationship between the charge transfer resistance of the positive electrode and the battery's SOC was calculated using only six SOC values ​​out of the 11 SOC values: 0, 0.2, 0.4, 0.6, 0.8, and 1. In this case, a curve Y2, which represents the trajectory showing the relationship between the charge transfer resistance of the positive electrode and the battery's SOC, was calculated by fitting a quadratic function to the six points P0, P2, P4, P6, P8, and P10. In Figure 12, curve Y1 is shown as a dashed line, and curve Y2 is shown as a dotted line.

[0098] As described above, by calculating the trajectory showing the relationship between the charge transfer resistance of the positive electrode and the battery's SOC using each of the calculation patterns γ0 to γ2, the amount of data used to calculate the relationship between the charge transfer resistance of the positive electrode and the battery's SOC was reduced in each of the calculation patterns γ0 and γ2 compared to calculation pattern γ1. Furthermore, in the SOC range where a reference SOC value that minimizes the charge transfer resistance of the positive electrode can exist, i.e., in the SOC range of 30% to 70%, the deviation from curve Y1 calculated in calculation pattern γ1 was smaller than that of curve Y2 calculated in calculation pattern γ2. In other words, in calculation patterns γ0 and γ2, the amount of data used to calculate the relationship between the charge transfer resistance of the positive electrode and the battery's SOC is reduced compared to calculation pattern γ1, but in the SOC range of 30% to 70%, curve Y0 calculated in calculation pattern γ0 is closer to curve Y1 calculated in calculation pattern γ1 than curve Y2 calculated in calculation pattern γ2.

[0099] From the above verification, it was demonstrated that even if the second impedance is measured only at the target SOC value where the absolute value |β| of the rate of change β of the first impedance is less than or equal to the reference value βref, as in the embodiment, and only the charge transfer resistance of the first electrode at the target SOC value is used, the reference SOC value at which the charge transfer resistance of the first electrode is minimized, and the relationship between the charge transfer resistance of the first electrode and the SOC of the battery can be appropriately calculated. Therefore, it was demonstrated that by measuring the first and second impedances only at the target SOC value where the absolute value |β| of the rate of change β of the first impedance is less than or equal to the reference value βref, and using the measurement results of the first and second impedances at the target SOC value to determine the state of the battery, it is possible to suppress the increase in the amount of data used to determine the state of the battery and improve the accuracy of the determination of the state of the battery.

[0100] In at least one embodiment or example described above, for each of the multiple SOC values ​​for which the first impedance has been measured, it is determined whether the absolute value of the rate of change of the first impedance with respect to the SOC is less than or equal to a reference value. Then, for the target SOC value for which the absolute value of the rate of change is less than or equal to the reference value, the second impedance is measured, and the state of the battery is determined based on the measurement results of the first impedance and the second impedance at the target SOC value. This suppresses the increase in the amount of data used to determine the state of the battery, and provides a battery diagnostic method, diagnostic device, diagnostic system, and diagnostic program that appropriately determines the state of the battery based on the measurement results of the impedance frequency characteristics.

[0101] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be implemented in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. For example, the terms "less than or equal to" and "greater than or equal to" used to express SOC values ​​and frequency ranges can be replaced as appropriate with terms such as "less than," "smaller than," and "greater than." The following are additional notes. [1] Based on the measurement result of the first impedance, which is the impedance of the battery at a first frequency, it is determined whether the absolute value of the rate of change of the first impedance with respect to the SOC of the battery is less than or equal to a reference value for each of the multiple SOC values ​​of the battery, For a target SOC value among the plurality of SOC values ​​in which the absolute value of the rate of change is less than or equal to the reference value, the second impedance, which is the impedance of the battery at a second frequency higher than the first frequency, is measured in addition to the first impedance; and a determination is made regarding the state of the battery based on the measurement results of the first impedance and the second impedance at the target SOC value. A battery diagnostic method comprising the following features. [2] The diagnostic method of [1], wherein, in determining whether the absolute value of the rate of change is less than or equal to the reference value, the reference value is half the absolute value of the rate of change at the lowest SOC value among the plurality of SOC values, or half the absolute value of the rate of change at the highest SOC value among the plurality of SOC values, and the determination is made for each of the plurality of SOC values. [3] The diagnostic method of [1], wherein, in determining whether the absolute value of the rate of change is less than or equal to the reference value, SOC values ​​in the range of 30% or more and 70% or less among the plurality of SOC values ​​are determined to be the target SOC values ​​whose absolute value is less than or equal to the reference value. [4] The diagnostic method of [1], wherein, in determining the state of the battery, the resistance of a first electrode, which is one of the positive and negative electrodes, is calculated based on the measurement results of the first impedance and the second impedance for the target SOC value whose absolute value is less than or equal to the reference value. [5] In determining whether the absolute value of the rate of change is less than or equal to the reference value, two or more of the multiple SOC values ​​are determined to be the target SOC values ​​whose absolute value is less than or equal to the reference value, In the determination of the state of the battery, the resistance of the first electrode is calculated for each of the two or more target SOC values, and the relationship between the resistance of the first electrode and the SOC of the battery is calculated. [4] Diagnostic method. [6] The diagnostic method of [5], wherein, in determining the state of the battery, the SOC value at which the resistance of the first electrode is minimized is calculated as a reference SOC value based on the relationship between the resistance of the first electrode and the SOC of the battery. [7] The determination of whether the absolute value of the rate of change is less than or equal to the reference value, the measurement of the second impedance with respect to the target SOC value, and the determination of the state of the battery are each performed in the first period and in the second period following the first period. In the determination of the battery state during the second period, the degradation state of the first electrode is determined by comparing the reference SOC value at which the resistance of the first electrode is minimized during the first period and the second period. [6] Diagnostic method. [8] The diagnostic method of [5], wherein in the determination of the state of the battery, the relationship between the potential of the first electrode and the SOC of the battery is calculated based on the relationship between the resistance of the first electrode and the SOC of the battery, and the usable potential range of the first electrode is calculated based on the relationship between the potential of the first electrode and the SOC of the battery. [9] The diagnostic method of [8], in determining the state of the battery, based on the relationship between the potential of the first electrode and the SOC of the battery, calculates the relationship between the potential of a second electrode, which is one of the positive and negative electrodes and has the opposite polarity to the first electrode, and the SOC of the battery, and calculates the usable potential range of the second electrode.

[10] The first impedance is measured at each of the plurality of SOC values ​​by inputting a superimposed current, obtained by superimposing the current waveform of an alternating current at the first frequency onto the reference current locus of a direct current, to the battery, In the measurement of the second impedance, the second impedance is measured at the target SOC value by inputting a superimposed current, obtained by superimposing the current waveform of an AC current at the second frequency onto the reference current trajectory, to the battery. [1] Diagnostic method.

[11] Based on the measurement result of the first impedance, which is the impedance of the battery at a first frequency, it is determined whether the absolute value of the rate of change of the first impedance with respect to the SOC of the battery is less than or equal to a reference value for each of the multiple SOC values ​​of the battery. For the target SOC value among the plurality of SOC values ​​whose absolute value of the rate of change is less than or equal to the reference value, the second impedance, which is the impedance of the battery at a second frequency higher than the first frequency, is measured in addition to the first impedance. Based on the measurement results of the first impedance and the second impedance in the target SOC value, a determination is made regarding the state of the battery. A diagnostic device equipped with a processor.

[12]

[11] diagnostic device, The battery diagnosed by the diagnostic device, A diagnostic system for the battery comprising the above.

[13] The battery comprises a first electrode which is a positive electrode and a negative electrode, and a second electrode which is the positive electrode and the negative electrode which has the opposite polarity to the first electrode, The first electrode comprises a first electrode active material that undergoes a single-phase reaction. The second electrode comprises a second electrode active material that undergoes a two-phase coexistence reaction.

[12] Diagnostic system.

[14] Computers, Based on the measurement result of the first impedance, which is the impedance of the battery at a first frequency, it is determined whether the absolute value of the rate of change of the first impedance with respect to the SOC of the battery is less than or equal to a reference value for each of the multiple SOC values ​​of the battery. For the target SOC value among the plurality of SOC values ​​whose absolute value of the rate of change is less than or equal to the reference value, the second impedance, which is the impedance of the battery at a second frequency higher than the first frequency, is measured in addition to the first impedance. Based on the measurement results of the first impedance and the second impedance in the target SOC value, a determination is made regarding the state of the battery. Battery diagnostic program. [Explanation of Symbols]

[0102] 1...Diagnostic system, 2...Battery-equipped device, 3...Diagnostic device, 5...Battery, 6...Control circuit, 10...Measurement unit, 21...Processing circuit, 22...Storage medium, 28...Diagnostic program, 31...Impedance measurement program, 32...Change rate determination program, 33...Resistance calculation program, 35...State determination program, β...Change rate, βref...Reference value.

Claims

1. Based on the measurement results of the first impedance, which is the impedance of the battery at a first frequency that is in the frequency range of 0.1 Hz or higher and 100 Hz or lower, the rate of change of the first impedance with respect to the SOC of the battery is calculated for each of the multiple SOC values ​​of the battery. The reference value is set to be half the absolute value of the rate of change of the first impedance at the lowest SOC value among the plurality of SOC values, or half the absolute value of the rate of change of the first impedance at the highest SOC value among the plurality of SOC values. Based on the rate of change of the first impedance at each of the plurality of SOC values, an SOC value is selected as the target SOC value among the plurality of SOC values ​​such that the absolute value of the rate of change of the first impedance is less than or equal to the reference value. When two or more of the aforementioned multiple SOC values ​​are selected as the target SOC values, for each of the two or more selected target SOC values, the second impedance, which is the impedance of the battery at a second frequency that is higher than the first frequency and within the frequency range of 100 Hz or more and 10 kHz or less, is measured in addition to the first impedance. The state of the battery is determined based on the measurement results of the first impedance and the second impedance at each of the two or more target SOC values. A battery diagnostic method comprising the following features.

2. The diagnostic method according to claim 1, wherein, in determining the state of the battery, the resistance relating to the first electrode, which is one of the positive and negative electrodes, is calculated for each of the two or more target SOC values ​​based on the measurement results of the first impedance and the second impedance.

3. The diagnostic method of claim 2, wherein, in the determination of the state of the battery, the relationship between the resistance of the first electrode and the SOC of the battery is calculated based on the calculation result of the resistance of the first electrode at each of two or more target SOC values.

4. The diagnostic method of claim 3, wherein, in the determination of the state of the battery, the SOC value at which the resistance of the first electrode is minimized is calculated as a reference SOC value based on the relationship between the resistance of the first electrode and the SOC of the battery.

5. The calculation of the rate of change of the first impedance for each of the plurality of SOC values, the setting of the reference value, the selection of the target SOC value from the plurality of SOC values ​​based on the reference value, the measurement of the second impedance for each of the two or more target SOC values ​​when two or more of the plurality of SOC values ​​are selected as the target SOC values, and the determination regarding the state of the battery are each performed in the first period and in the second period following the first period. In the determination of the battery state during the second period, the degradation state of the first electrode is determined by comparing the reference SOC value at which the resistance of the first electrode is minimized during the first period and the second period. The diagnostic method according to claim 4.

6. The diagnostic method of claim 3, wherein, in the determination of the state of the battery, the relationship between the potential of the first electrode and the SOC of the battery is calculated based on the relationship between the resistance of the first electrode and the SOC of the battery, and the usable potential range of the first electrode is calculated based on the relationship between the potential of the first electrode and the SOC of the battery.

7. The diagnostic method of claim 6, wherein, in the determination of the state of the battery, the relationship between the potential of the first electrode and the state of charge (SOC) of the battery is calculated based on the relationship between the potential of the first electrode and the SOC of the battery, and the relationship between the potential of the second electrode, which is one of the positive and negative electrodes and has the opposite polarity to the first electrode, and the usable potential range of the second electrode is calculated.

8. The system further comprises measuring the first impedance at each of the plurality of SOC values ​​by inputting a superimposed current, obtained by superimposing the current waveform of an AC current at the first frequency onto the reference current trajectory of a DC current, to the battery, In the measurement of the second impedance, the second impedance is measured for each of the two or more target SOC values ​​by inputting a superimposed current, obtained by superimposing the current waveform of an AC current at the second frequency onto the reference current trajectory, into the battery. The diagnostic method according to claim 1.

9. Based on the measurement results of the first impedance, which is the impedance of the battery at a first frequency that is in the frequency range of 0.1 Hz or higher and 100 Hz or lower, the rate of change of the first impedance with respect to the SOC of the battery is calculated for each of the multiple SOC values ​​of the battery. The reference value is set to be half the absolute value of the rate of change of the first impedance at the lowest SOC value among the plurality of SOC values, or half the absolute value of the rate of change of the first impedance at the highest SOC value among the plurality of SOC values. Based on the rate of change of the first impedance at each of the plurality of SOC values, an SOC value is selected as the target SOC value among the plurality of SOC values ​​such that the absolute value of the rate of change of the first impedance is less than or equal to the reference value. When two or more of the aforementioned multiple SOC values ​​are selected as the target SOC values, for each of the two or more selected target SOC values, the second impedance, which is the impedance of the battery at a second frequency that is higher than the first frequency and within the frequency range of 100 Hz or more and 10 kHz or less, is measured in addition to the first impedance. Based on the measurement results of the first impedance and the second impedance in each of the two or more target SOC values, a determination is made regarding the state of the battery. A diagnostic device equipped with a processor.

10. The diagnostic device according to claim 9, The battery diagnosed by the diagnostic device, A diagnostic system for the battery comprising the above.

11. The battery comprises a first electrode which is either a positive or negative electrode, and a second electrode which is one of the positive and negative electrodes and has the opposite polarity to the first electrode. The first electrode comprises a first electrode active material that undergoes a single-phase reaction. The second electrode includes a second electrode active material that undergoes a two-phase coexistence reaction. A diagnostic system according to claim 10.

12. On the computer, Based on the measurement results of the first impedance, which is the impedance of the battery at a first frequency that is in the frequency range of 0.1 Hz or higher and 100 Hz or lower, the rate of change of the first impedance with respect to the SOC of the battery is calculated for each of the multiple SOC values ​​of the battery. The reference value is set to be half the absolute value of the rate of change of the first impedance at the lowest SOC value among the plurality of SOC values, or half the absolute value of the rate of change of the first impedance at the highest SOC value among the plurality of SOC values. Based on the rate of change of the first impedance at each of the plurality of SOC values, the SOC value at which the absolute value of the rate of change of the first impedance is less than or equal to the reference value is selected as the target SOC value. When two or more of the aforementioned plurality of SOC values ​​are selected as the target SOC values, for each of the two or more selected target SOC values, the second impedance, which is the impedance of the battery at a second frequency that is higher than the first frequency and within the frequency range of 100 Hz or more and 10 kHz or less, is measured in addition to the first impedance. Based on the measurement results of the first impedance and the second impedance in each of the two or more target SOC values, a determination is made regarding the state of the battery. Battery diagnostic program.

Images