Secondary battery state diagnosis method and state diagnosis device

Abstract

To provide a secondary battery state diagnosing method and a secondary battery state diagnosing device with which it is possible to diagnose a secondary battery or per-electrode degradation, even when an active material is used for electrodes of the secondary battery whose change of potential does not precisely correspond to a change of charge state.SOLUTION: Provided is a state diagnosis method for diagnosing the degradation state of a secondary battery, wherein a relationship of the charge state and open-circuit voltage of the secondary battery, and a relationship group composed of relationships of the charge state and internal resistance of the secondary battery for each of mutually different energization times are taken as input information, and the degradation state of the secondary battery, the degradation state of positive electrodes and the degradation state of negative electrodes are taken as output information. The secondary battery state diagnosing device takes, as input information, data that indicates a relationship of the charge state and open-circuit voltage of the secondary battery, and data that indicates a relationship group composed of relationships of the charge state and internal resistance of the secondary battery for each of mutual different energization times, and takes, as output information, data that indicates the degradation state of the secondary battery, data that indicates the degradation state of positive electrodes, and data that indicates the degradation of negative electrodes.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method and device for diagnosing the state of a secondary battery. [Background technology]

[0002] In recent years, secondary batteries such as lithium-ion batteries have been used as drive power sources in vehicles and as storage power sources for smart houses, etc. It is known that the battery characteristics of lithium-ion batteries and other batteries deteriorate when they are repeatedly charged and discharged or when stored in high-temperature environments. Because drive power sources and storage power sources are used for long periods of time, it is necessary to minimize deterioration and ensure reliability and safety.

[0003] The active materials used in lithium-ion batteries are sometimes selected not only for their performance, such as capacity and voltage, but also for their degradation prevention and safety. For example, Li(Ni,Mn,Co)O2 (NMC) and LiFePO4 (LFP) are used as positive electrode active materials. Graphite and Li4Ti5O 12 (LTO) and other formats are used.

[0004] It is known that the degradation of secondary batteries such as lithium-ion batteries progresses rapidly in high-potential regions where the state of charge is high and in low-potential regions where the state of charge is low. The degradation of secondary batteries occurs due to changes in the characteristics of the positive electrode, negative electrode, and elements other than the electrodes, such as the electrolyte and current collector. As degradation progresses, the charge / discharge curve and operating voltage range change, affecting safety. It is necessary to accurately detect the degradation of electrodes and elements other than the electrodes and select optimal control methods and operating conditions according to the degradation state.

[0005] Patent Document 1 describes a method for detecting internal information of a secondary battery. In this method, the charge / discharge curve of the secondary battery is reproduced by superimposing the charge / discharge curve of the positive electrode alone and the charge / discharge curve of the negative electrode alone. By reproducing the charge / discharge curve of the secondary battery, the deterioration state of the positive electrode and negative electrode can be quantitatively evaluated nondestructively. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-080093 Summary of the Invention [Problem to be solved by the invention]

[0007] In Patent Document 1, the charge / discharge curve of a secondary battery is reproduced based on the charge / discharge curve of the positive electrode alone and the charge / discharge curve of the negative electrode alone. In the reproduction process, the effective active material amounts of the positive and negative electrodes, an index for the relative positions of the charge / discharge curves of the positive and negative electrodes, and the open circuit potentials of the positive and negative electrodes are determined. It is said that detecting the status of the positive and negative electrodes can prevent a decrease in battery life and safety compared to conventional methods such as using changes in battery voltage.

[0008] However, the method of Patent Document 1 utilizes the change in open circuit potential in response to a change in the state of charge for diagnosis. This method has the problem that it cannot accurately diagnose the state of deterioration when an active material that shows little change in potential in response to a change in the state of charge is used. For example, LiFePO4, Li4Ti5O 12 are known to have a small change in open circuit potential when charged and discharged.

[0009] In the method of Patent Document 1, when one of the positive and negative electrodes uses an active material whose potential changes little with changes in the state of charge, the method can only diagnose the deterioration state of the electrode whose potential changes greatly, which causes the problem that deterioration of the electrode that is not diagnosed progresses in a latently progressing manner. If deterioration progresses in a latently progressing manner, the secondary battery will rapidly deteriorate when the degree of deterioration exceeds a certain threshold, thereby reducing the reliability and safety of the secondary battery.

[0010] Therefore, the present invention aims to provide a secondary battery condition diagnosis method and a secondary battery condition diagnosis device that can diagnose the deterioration of each secondary battery and electrode, even if the electrodes of the secondary battery use active materials that show little change in potential in response to changes in the charging state. [Means for solving the problem]

[0011] In order to solve the above-mentioned problems, a state diagnosis method for a secondary battery according to the present invention is a state diagnosis method for diagnosing a deterioration state of a secondary battery, the method comprising: a first step of evaluating the relationship between the state of charge and open circuit voltage of the secondary battery, and the relationship between the state of charge and internal resistance of the secondary battery for each different current-flow time, as input information; and a second step of evaluating the relationship between the state of charge and open circuit voltage of the secondary battery based on the relationship between the state of charge and open circuit potential of the positive electrode that is specific to a positive electrode material, and the relationship between the state of charge and open circuit potential of the negative electrode that is specific to a negative electrode material; and a second step of evaluating the relationship between the state of charge and internal resistance of the secondary battery based on the relationship between the state of charge and internal resistance of the positive electrode that is specific to a positive electrode material for each different current-flow time, and the relationship between the state of charge and internal resistance of the negative electrode that is specific to a negative electrode material for each different current-flow time, Indicates the deterioration state of the electrode a step of correcting the relationship between the state of charge of the positive electrode and the open circuit potential and the relationship between the state of charge of the negative electrode and the open circuit potential to generate a relationship between the state of charge and the open circuit voltage of the secondary battery assumed to be in a deteriorated state based on the corrected relationship between the state of charge of the positive electrode and the open circuit potential and the relationship between the state of charge of the negative electrode and the open circuit potential, and comparing the relationship between the state of charge of the secondary battery and the open circuit voltage, which is the input information, with the relationship between the state of charge of the secondary battery and the open circuit voltage to evaluate the agreement between the relationships; and the second step of correcting the relationship between the state of charge of the positive electrode and the internal resistance and the relationship between the state of charge of the negative electrode and the internal resistance to generate a relationship between the state of charge of the positive electrode and the internal resistance of the negative electrode based on the corrected relationship between the state of charge of the positive electrode and the open circuit potential and the relationship between the state of charge of the negative electrode and the open circuit potential to generate a relationship between the state of charge of the positive electrode and the open circuit potential of the secondary battery assumed to be in a deteriorated state and evaluate the agreement between the relationships. Indicates the deterioration state of electrodes and elements other than electrodesa step of correcting the relationship between the state of charge and the internal resistance of the secondary battery assumed to be in a deteriorated state by correcting the relationship between the state of charge and the internal resistance of the positive electrode and the relationship between the state of charge and the internal resistance of the negative electrode, and generating a relationship between the state of charge and the internal resistance of the secondary battery assumed to be in a deteriorated state based on the corrected relationship between the state of charge and the internal resistance of the positive electrode and the corrected relationship between the state of charge and the internal resistance of the negative electrode, and comparing the relationship between the state of charge and the internal resistance of the secondary battery assumed to be in a deteriorated state in the relationship group that is the input information with the relationship between the state of charge and the internal resistance of the secondary battery assumed to be in a deteriorated state to evaluate the agreement between the relationships, Each different energization time The aforementioned The relationship between the state of charge and internal resistance of a secondary battery The second step is performed while switching the relationship, and the magnitude of the resistance component excluding the reaction resistance component and the diffusion resistance component of the secondary battery is determined based on a comparison between the relationships. Indicates the deterioration state of electrodes and elements other than electrodes The output information is obtained by using the parameter.

[0012] Furthermore, a secondary battery state diagnosis device according to the present invention is a state diagnosis device for diagnosing a deterioration state of a secondary battery, and the device receives as input information data showing the relationship between the state of charge of the secondary battery and the open circuit voltage, and data showing a relationship group formed of the relationship between the state of charge of the secondary battery and the internal resistance for each different current application time, and outputs as output information data showing the deterioration state of the secondary battery, data showing the deterioration state of a positive electrode used in the secondary battery, and data showing the deterioration state of a negative electrode used in the secondary battery, and outputs a relationship between the state of charge of the positive electrode and the open circuit potential specific to the positive electrode material. a first step of evaluating the relationship between the state of charge of the secondary battery and the open circuit voltage based on the relationship between the state of charge of the negative electrode and the open circuit potential, which is specific to the negative electrode material; and a second step of evaluating a group of relationships formed by the relationship between the state of charge of the secondary battery and the internal resistance, based on the relationship between the state of charge of the positive electrode and the internal resistance, which is specific to the positive electrode material for each different current flow time, and the relationship between the state of charge of the negative electrode and the internal resistance, which is specific to the negative electrode material for each different current flow time, Indicates the deterioration state of the electrodea step of correcting the relationship between the state of charge of the positive electrode and the open circuit potential and the relationship between the state of charge of the negative electrode and the open circuit potential to generate a relationship between the state of charge and the open circuit voltage of the secondary battery assumed to be in a deteriorated state based on the corrected relationship between the state of charge of the positive electrode and the open circuit potential and the relationship between the state of charge of the negative electrode and the open circuit potential, and comparing the relationship between the state of charge of the secondary battery and the open circuit voltage, which is the input information, with the relationship between the state of charge of the secondary battery and the open circuit voltage to evaluate the agreement between the relationships; and the second step of correcting the relationship between the state of charge of the positive electrode and the internal resistance and the relationship between the state of charge of the negative electrode and the internal resistance to generate a relationship between the state of charge of the positive electrode and the internal resistance of the negative electrode based on the corrected relationship between the state of charge of the positive electrode and the open circuit potential and the relationship between the state of charge of the negative electrode and the open circuit potential to generate a relationship between the state of charge of the positive electrode and the open circuit potential of the secondary battery assumed to be in a deteriorated state and evaluate the agreement between the relationships. Indicates the deterioration state of electrodes and elements other than electrodes a step of correcting the relationship between the state of charge and the internal resistance of the secondary battery assumed to be in a deteriorated state by correcting the relationship between the state of charge and the internal resistance of the positive electrode and the relationship between the state of charge and the internal resistance of the negative electrode, and generating a relationship between the state of charge and the internal resistance of the secondary battery assumed to be in a deteriorated state based on the corrected relationship between the state of charge and the internal resistance of the positive electrode and the corrected relationship between the state of charge and the internal resistance of the negative electrode, and comparing the relationship between the state of charge and the internal resistance of the secondary battery assumed to be in a deteriorated state in the relationship group that is the input information with the relationship between the state of charge and the internal resistance of the secondary battery assumed to be in a deteriorated state to evaluate the agreement between the relationships, Each different energization time The aforementioned The relationship between the state of charge and internal resistance of a secondary battery The second step is performed while switching the relationship, and the magnitude of the resistance component excluding the reaction resistance component and the diffusion resistance component of the secondary battery is determined based on a comparison between the relationships. Indicates the deterioration state of electrodes and elements other than electrodes The output information is obtained by using the parameter. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a secondary battery condition diagnosis method and a secondary battery condition diagnosis device that can diagnose the deterioration of each secondary battery and electrode, even if the electrodes of the secondary battery use active materials that show little change in potential in response to changes in the charging state. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a diagram showing the configuration of a secondary battery state diagnosis device according to an embodiment of the present invention; [Figure 2] 4 is a flowchart showing a process for diagnosing the deterioration state of a secondary battery. [Figure 3] FIG. 10 is a diagram showing an example of the relationship between the state of charge of an electrode and the open circuit potential. [Figure 4] FIG. 10 is a diagram showing an example of the relationship between the state of charge of an electrode and the open circuit potential. [Figure 5] FIG. 4 is a diagram showing an example of the relationship between the state of charge of a secondary battery and the open circuit voltage. [Figure 6] FIG. 10 is a diagram showing an example of the relationship between the state of charge of an electrode and the internal resistance for each current application time. [Figure 7] FIG. 10 is a diagram showing an example of the relationship between the state of charge of an electrode and the internal resistance for each current application time. [Figure 8] FIG. 10 is a diagram showing an example of the relationship between the state of charge and the internal resistance of a secondary battery for each current-carrying time. [Figure 9] FIG. 10 is a diagram showing an example of the relationship between the state of charge and the open circuit voltage of a secondary battery assumed to be in a deteriorated state. [Figure 10] FIG. 10 is a diagram showing an example of the relationship between the state of charge and the internal resistance of a secondary battery assumed to be in a deteriorated state. DETAILED DESCRIPTION OF THE INVENTION

[0015] A secondary battery state diagnosis method and a secondary battery state diagnosis device according to one embodiment of the present invention will be described below. Note that common components in the following drawings will be assigned the same reference numerals, and duplicated explanations will be omitted. In the following description, the state quantity of the positive electrode will be given the subscript p, and the state quantity of the negative electrode will be given the subscript n. When the positive electrode and the negative electrode are not distinguished, they will be referred to as electrodes and will be given the subscript x.

[0016] The secondary battery state diagnosis method according to the present embodiment relates to a method for diagnosing the degradation state of a secondary battery. In this state diagnosis method, a secondary battery whose degradation state is unknown is used as a diagnosis target, and the degradation state of the secondary battery is diagnosed non-destructively. In this state diagnosis method, the degradation state of the secondary battery and the degradation state of each electrode of the secondary battery can be individually diagnosed using measurement results of the open circuit voltage for each state of charge of the secondary battery being diagnosed and measurement results of the internal resistance for each current flow time and for each state of charge.

[0017] The secondary battery state diagnosis method according to this embodiment can be applied to a secondary battery in which an active material whose open circuit potential is constant except near the fully charged state and near the fully discharged state is used in one of the positive and negative electrodes, or in which an active material whose open circuit potential is constant is used in both the positive and negative electrodes. It can also be applied to a secondary battery in which an active material whose open circuit potential is not constant is used in both the positive and negative electrodes. Even if an active material whose open circuit potential is constant except near the fully charged state and near the fully discharged state is used, the deterioration state can be diagnosed with high accuracy.

[0018] In this specification, "the open circuit potential is constant except near the fully charged state and near the fully discharged state" means that the change in open circuit potential with respect to the change in the state of charge is 50 mV or less within the operating voltage range of the secondary battery excluding near the fully charged state and near the fully discharged state. Using the state of charge (SOC) [%], the near fully charged state is defined as a region where the SOC is about 80% or more, and the near fully discharged state is defined as a region where the SOC is about 20% or less.

[0019] Electrodes that show little change in potential with changes in the state of charge include lithium iron phosphate (LiFePO4) and lithium titanate (Li4Ti5O 12 Examples of electrodes that have a sufficient change in potential in response to changes in the state of charge include electrodes that use graphite and lithium cobalt oxide (LiCoO2).

[0020] In the secondary battery state diagnosis method according to this embodiment, the open circuit voltage for each state of charge of the secondary battery to be diagnosed and the internal resistance for each state of charge of the secondary battery to be diagnosed are measured. The length of current flow during measurement is changed to two or more different lengths, and the internal resistance is measured for each different current flow time. By measuring the open circuit voltage and the internal resistance, a relationship between the state of charge of the secondary battery and the open circuit voltage, and a relationship group showing the current flow time dependency of the state of charge of the secondary battery and the internal resistance of the secondary battery are obtained. Note that the internal resistance may also be measured for each different current flow time during discharge, by changing the length of discharge time during measurement to two or more different lengths.

[0021] The information indicating the relationship between the state of charge of the secondary battery and the open circuit voltage, and the information indicating a relationship group showing the current-flow time dependency between the state of charge of the secondary battery and the internal resistance are used as input information in diagnosing the degradation state. The output information obtained based on the input information is information indicating the degradation state of the secondary battery, information indicating the degradation state of the positive electrode used in the secondary battery, and information indicating the degradation state of the negative electrode used in the secondary battery.

[0022] A relationship group showing the current flow time dependency of the state of charge and internal resistance of a secondary battery is composed of the relationship between the state of charge and internal resistance of the secondary battery for each different current flow time. That is, the relationship between the state of charge and internal resistance, which corresponds to the capacity-resistance curve, is collected for each current flow time while changing the length of current flow time when measuring the internal resistance. A relationship group is composed of a collection of multiple relationships for each current flow time.

[0023] In the process of diagnosing the deterioration state, the relationship between the electrode's state of charge and open circuit potential, and the relationship between the electrode's state of charge and internal resistance for each current flow time are first prepared as reference information. These relationships are corrected using deterioration state parameters assuming the deterioration state of each electrode of the secondary battery to be diagnosed. The deterioration state parameters are parameters that represent the deterioration state of the positive electrode, the deterioration state of the negative electrode, and the deterioration state of elements other than the electrodes.

[0024] Then, based on the relationship between the state of charge of the electrode and the open circuit potential corrected by the degradation state parameter, the relationship between the state of charge and the open circuit voltage of the secondary battery assumed to be in a degraded state is reproduced by calculation. Also, based on the relationship between the state of charge of the electrode and the internal resistance corrected by the degradation state parameter, the relationship between the state of charge and the internal resistance of the secondary battery assumed to be in a degraded state is reproduced by calculation. The relationship between the state of charge and the internal resistance of the secondary battery is reproduced based on the relationship for each current flow time.

[0025] Next, the calculation results showing the relationship between the state of charge of the secondary battery and the open circuit voltage based on the reproduction and the calculation results showing the relationship between the state of charge of the secondary battery and the internal resistance based on the reproduction are compared with the measurement results showing the relationship between the state of charge of the secondary battery that is the diagnosis target and the open circuit voltage based on actual measurements and the measurement results showing the relationship between the state of charge of the secondary battery that is the diagnosis target and the internal resistance based on actual measurements. The relationship between the state of charge of the secondary battery and the internal resistance is compared for each current flow time using each relationship constituting the relationship group.

[0026] By comparing the measurement results with the calculation results and performing fitting so that the measurement results and the calculation results match, the hypothetically set deterioration state parameters are approximated toward their true values. Therefore, a solution for the deterioration state parameters can be obtained based on the agreement between the measurement results and the calculation results. Based on the solution for the deterioration state parameters, the deterioration state of the secondary battery and the deterioration state of each electrode of the secondary battery can be quantitatively diagnosed.

[0027] The internal resistance of a secondary battery can be calculated as a combination of the internal resistance of the positive electrode, which depends on the state of charge, the internal resistance of the negative electrode, which depends on the state of charge, and the resistance of elements other than the electrodes, which do not depend on the state of charge. However, the degree of deterioration of the electrodes and elements other than the electrodes differs. Therefore, it is necessary to set independent deterioration state parameters for each of the positive and negative electrodes and elements other than the electrodes. Setting separate deterioration state parameters for each results in multiple variables, which poses a problem in that a single solution for the deterioration state parameters cannot be obtained when there is little battery information.

[0028] In contrast, the secondary battery state diagnosis method according to this embodiment uses a group of relationships indicating the current-flow time dependency of the secondary battery's state of charge and internal resistance, which are formed by relationships between the state of charge and internal resistance of the secondary battery for each different current-flow time, to diagnose the state of deterioration. Since the method uses multiple relationships collected for each current-flow time while changing the length of current-flow time when measuring the internal resistance, it is possible to obtain a single solution for the deterioration state parameters set for each electrode and element other than the electrodes.

[0029] Specifically, in the secondary battery state diagnosis method according to this embodiment, by comparing the relationship between the state of charge and the internal resistance of the secondary battery for each different current-flow time, it is possible to determine the magnitude of the resistance component that is independent of the state of charge, excluding the reaction resistance component of the secondary battery that depends on the state of charge and the diffusion resistance component that depends on the state of charge, and therefore it is possible to diagnose the deterioration state of the secondary battery and the deterioration state of each electrode of the secondary battery with high accuracy.

[0030] In this specification, the state of charge refers to an electrochemical state determined by the ratio of the amount of electricity that can be discharged to the amount of electricity that can be discharged from a fully charged state. The state of charge can be expressed by any appropriate state quantity that can be converted into any other state quantity, such as the state of charge (SOC) [%], the amount of discharge from a fully charged state [Ah], the amount of charge from a fully discharged state [Ah], or the composition ratio of charge carrier elements contained in the active material.

[0031] FIG. 1 is a diagram showing the configuration of a secondary battery state diagnosis device according to this embodiment. As shown in FIG. 1, a state diagnosis device 100 for a secondary battery according to this embodiment includes a calculation unit 10, a storage unit 20, an input unit 30, an output unit 40, and a communication unit 50.

[0032] The condition diagnosis device 100 is a device that diagnoses the degradation state of a secondary battery, and can be configured with hardware such as a computer. The condition diagnosis device 100 executes a process for diagnosing the degradation state of a secondary battery according to a predetermined program. As long as the condition diagnosis device 100 includes at least the calculation unit 10, the storage unit 20, input unit 30, output unit 40, communication unit 50, etc. can be configured as appropriate.

[0033] The calculation unit 10 reads various data and programs, executes programs, calculates states, etc. The calculation unit 10 is configured by a calculation device such as a CPU (Central Processing Unit). In addition to diagnosing the deterioration state of the secondary battery, the calculation unit 10 may also perform a process of calculating operating conditions for the secondary battery based on the diagnosis result of the deterioration state, and a process of generating a control signal for implementing the operating conditions for the secondary battery.

[0034] The storage unit 20 stores various data and programs. The storage unit 20 is configured by a storage device such as a RAM (Random Access Memory) or a ROM (Read Only Memory). The various data and programs may be stored in a writable and readable hard disk, flash memory, magnetic disk, optical disk, etc.

[0035] The input unit 30 is a device that accepts input from an operator. The input unit 30 is configured by, for example, a keyboard, a mouse, a touch panel, etc. The input unit 30 can be connected via an input interface (not shown).

[0036] The output unit 40 is a device that outputs operation information, various data contents, diagnostic status, diagnostic results, etc. of the condition diagnostic device 100. The output unit 40 is configured by, for example, a liquid crystal display, an organic EL display, a cathode ray tube, etc. The output unit 40 can be connected via an output interface (not shown).

[0037] The communication unit 50 transmits and receives various data and control signals to and from external measuring devices, etc. The communication unit 50 can be connected to external measuring devices, etc. via a communication interface, an input / output interface, etc. (not shown). As the measuring device, a charge / discharge tester or the like that can measure the voltage and current of a secondary battery that has the function of charging and discharging under predetermined conditions can be connected.

[0038] The condition diagnosis device 100 receives, as input information, measurement data showing the relationship between the state of charge of the secondary battery and the open circuit voltage, and measurement data showing a relationship group showing the current flow time dependency between the state of charge of the secondary battery and the internal resistance. This input information may be input from an external measuring device or the like via the communication unit 50, or may be input from a writable and readable storage medium or external storage device. Alternatively, the input information may be stored in the storage unit 20.

[0039] The measurement data showing the relationship between the state of charge and the open circuit voltage of the secondary battery is collected by intermittently measuring the open circuit voltage for each state of charge of the secondary battery to be diagnosed. The measurement data showing the relationship between the state of charge and the open circuit voltage of the secondary battery is collected by actual measurement and then input to the condition diagnosis device 100. The measurement data showing the relationship between the state of charge and the open circuit voltage of the secondary battery may be expressed as a relational equation or a data table.

[0040] The measurement data showing the relationship group indicating the current-flow time dependency between the state of charge and internal resistance of the secondary battery is collected by intermittently measuring the internal resistance for each state of charge of the secondary battery to be diagnosed for each current-flow time. The measurement data showing the relationship group indicating the current-flow time dependency between the state of charge and internal resistance of the secondary battery is collected by actual measurement and then input to the condition diagnosis device 100. The measurement data showing the relationship group indicating the current-flow time dependency between the state of charge and internal resistance of the secondary battery may be expressed as a relational equation or a data table.

[0041] The measurement data indicating the relationship between the state of charge and the open circuit voltage of the secondary battery includes data indicating the state of charge and data indicating the open circuit voltage of the secondary battery for a predetermined state of charge. The measurement data indicating a relationship group indicating the current flow time dependency of the state of charge and internal resistance of the secondary battery includes data indicating the current flow time, data indicating the state of charge associated with the data indicating the current flow time, and data indicating the internal resistance of the secondary battery for a predetermined state of charge associated with the data indicating the current flow time.

[0042] Furthermore, the condition diagnosis device 100 receives, as input information, reference data showing the relationship between the state of charge of the positive electrode and the open-circuit potential that is specific to the positive electrode material, reference data showing the relationship between the state of charge of the negative electrode and the open-circuit potential that is specific to the negative electrode material, reference data showing a relationship group showing the current-flow time dependency between the state of charge of the positive electrode and the internal resistance that is specific to the positive electrode material, and reference data showing a relationship group showing the current-flow time dependency between the state of charge of the negative electrode and the internal resistance that is specific to the negative electrode material. These pieces of input information are input and stored in the memory unit 20 before the process of diagnosing the deterioration state.

[0043] The reference data is used as basic data for generating calculation data assuming a deterioration state. The reference data is collected by measuring the open circuit potential and internal resistance for each state of charge of the electrode using a half cell or the like. The reference data is stored in the memory unit 20 of the condition diagnosis device 100. The reference data may be expressed as a relational expression or a data table.

[0044] The reference data indicating the relationship between the state of charge and the open circuit potential of the positive electrode, which is specific to the positive electrode material, includes data indicating the state of charge and data indicating the open circuit potential of the positive electrode for a predetermined state of charge. The reference data indicating the relationship between the state of charge and the open circuit potential of the negative electrode, which is specific to the negative electrode material, includes data indicating the state of charge and data indicating the open circuit potential of the negative electrode for a predetermined state of charge.

[0045] The reference data showing the relationship group indicating the current-flow time dependency of the positive electrode's state of charge and internal resistance, which is specific to the positive electrode material, is composed of the relationship between the positive electrode's state of charge and internal resistance for each different current-flow time. The reference data showing the relationship between the positive electrode's state of charge and internal resistance for each current-flow time is collected by intermittently measuring the positive electrode's internal resistance for each current-flow time and for each state of charge. The reference data showing the relationship group is composed of a collection of multiple reference data for each current-flow time.

[0046] The reference data indicating a group of relationships showing the current flow time dependency between the state of charge and internal resistance of the positive electrode specific to the positive electrode material includes data indicating the current flow time, data indicating the state of charge associated with the data indicating the current flow time, and data indicating the internal resistance of the positive electrode for a predetermined state of charge associated with the data indicating the current flow time.

[0047] The reference data showing the relationship group indicating the current-flow time dependency of the negative electrode's state of charge and internal resistance, which is specific to the negative electrode material, is composed of the relationship between the negative electrode's state of charge and internal resistance for each different current-flow time. The reference data showing the relationship between the negative electrode's state of charge and internal resistance for each current-flow time is collected by intermittently measuring the negative electrode's internal resistance for each current-flow time and for each state of charge. The reference data showing the relationship group is composed of a collection of multiple reference data for each current-flow time.

[0048] The reference data showing a group of relationships indicating the current flow time dependency between the charge state and internal resistance of the negative electrode specific to the negative electrode material includes data indicating the current flow time, data indicating the charge state associated with the data indicating the current flow time, and data indicating the internal resistance of the negative electrode for a predetermined charge state associated with the data indicating the current flow time.

[0049] As the reference data, for example, data on an electrode in an initial state where degradation has not progressed substantially can be used. For example, after a half cell is produced using the produced electrode, data on the electrode in the initial state can be collected based on actual measurements during the first to fifth charge and discharge processes. Because irreversible reactions may occur on the electrode during the first charge and discharge processes, it is preferable to collect data during the second to fifth charge and discharge processes.

[0050] As the reference data, it is preferable to prepare a plurality of data for each type of active material used in the electrode. As the reference data, it is preferable to prepare data for various electrodes according to the type of active material used in the secondary battery to be diagnosed or the type of active material expected to be used. Even if the type of active material used in the secondary battery to be diagnosed is unknown, the degradation state can be diagnosed with high accuracy by performing fitting while replacing the reference data.

[0051] The measurement data of the secondary battery and the reference data of the electrodes may be acquired during a charging process or a discharging process. However, there is generally a hysteresis between the behavior during a charging process and the behavior during a discharging process. Therefore, it is preferable that the measurement data of the secondary battery and the reference data of the electrodes are acquired during the same charging and discharging process.

[0052] Measurement data for secondary batteries and reference data for electrodes can be collected by repeatedly measuring the open circuit voltage at any state of charge and the internal resistance at any state of charge while changing the state of charge. It is preferable to measure the open circuit voltage and the internal resistance at multiple states of charge within the operating voltage range of the secondary battery.

[0053] Measurement data for secondary batteries and reference data for electrodes can be collected during intermittent charge / discharge cycles, for example, by charging or discharging a secondary battery or half-cell to a predetermined state of charge, then charging or discharging at a constant, small current for a predetermined period of time, followed by a predetermined rest period, and repeating this cycle until another predetermined state of charge is reached, while measuring the open circuit voltage and current at each state of charge.

[0054] In the intermittent charge / discharge process, the rest time between charge and discharge is preferably 10 minutes or more, more preferably 30 minutes or more. If the rest time between charge and discharge is sufficient, the electrochemical state of the active material and the movement of charge carriers become closer to equilibrium, allowing for more accurate measurements of the open circuit voltage and internal resistance.

[0055] During the intermittent charge / discharge process, the charge / discharge current applied to adjust the battery to a predetermined state of charge is preferably at least 10 C or less, and more preferably 1 C or less. The lower the charge / discharge rate, the more accurate the open circuit voltage and internal resistance can be measured. From the viewpoint of shortening the measurement time, the charge / discharge current applied to adjust the battery to a predetermined state of charge is preferably 0.1 C or more.

[0056] The open circuit voltage is preferably measured for a plurality of different states of charge. From the viewpoint of accurate diagnosis, the number of measurement points at which the open circuit voltage is measured is preferably 10 or more. From the viewpoint of reducing the number of measurements, the number of measurement points at which the open circuit voltage is measured is preferably 50 or less.

[0057] Measurement data showing the relationship between the current flow time dependence of the state of charge and internal resistance of a secondary battery can be obtained based on actual measurements of the internal resistance of the secondary battery for each different current flow time. By starting to pass a charge / discharge current through the secondary battery to be diagnosed and measuring the voltage V and current I after a predetermined time has passed, the internal resistance R = ΔV / ΔI for each state of charge can be obtained.

[0058] The internal resistance of the secondary battery is preferably determined based on the open circuit voltage and the closed circuit voltage of the secondary battery. Based on the open circuit voltage and the closed circuit voltage, measurement data for each state of charge can be collected collectively during the intermittent charge and discharge process.

[0059] The internal resistance Rc(Q) [Ω] of a secondary battery at the state of charge Q can be calculated using the following formula (1), where the open circuit voltage of the secondary battery at the state of charge Q is OCVc(Q) [V], the closed circuit voltage of the secondary battery at the state of charge Q is CCVc(Q) [V], and the amount of current flowing up to the state of charge Q is ΔI [A]. Rc(Q)={OCVc(Q)-CCVc(Q)} / ΔI···(1)

[0060] The current flow time t during measurement of the internal resistance must be at least two types in order to obtain data with different current flow amounts ΔI. From the viewpoint of reducing the amount of data, the number of types of current flow times t is preferably 10 or less, more preferably 5 or less. The current flow times t are preferably separated by 5 seconds or more, more preferably 10 seconds or more, so that the measured internal resistance values ​​are significantly different from each other.

[0061] The current-flow time t when measuring the internal resistance is preferably 5 seconds or more, more preferably 30 seconds or more. If the current-flow time t is too short, the internal resistance will be measured immediately after the start of current flow. The internal resistance immediately after the start of current flow is significantly affected by IR loss caused by factors other than the electrodes and cannot be measured accurately, so it is preferable not to use this data.

[0062] The measurement of the internal resistance is preferably performed within a single charge / discharge process, either during a continuous charge process toward a fully charged state or during a continuous discharge process toward a fully discharged state. The measurement timing of the internal resistance, i.e., the period of the current flow time t for acquiring data for each current flow amount ΔI, is preferably after T / 2, more preferably after 2T / 3, of the total current flow time T for completing the collection of all data. This is because the longer the time passes, the larger the internal resistance becomes, which is suitable for accurate measurement.

[0063] The measurement data of the secondary battery and the reference data of the electrode may be data showing the relationship between the state of charge and the numerical value of the open-circuit potential, data showing the relationship between the state of charge and the numerical value of the internal resistance, data showing the relationship between the state of charge and the differential value of the open-circuit potential, or data showing the relationship between the state of charge and the differential value of the internal resistance. Using the differential value of the open-circuit potential provides a relationship that is inversely proportional to the amount of effective active material, thereby ensuring the accuracy of the amount of effective active material. Using the differential value of the internal resistance can reduce the contribution of voltage drop due to factors other than the electrode.

[0064] After processing to diagnose the degradation state, the condition diagnosis device 100 outputs, as output information, diagnosis result data indicating the degradation state of the secondary battery, diagnosis result data indicating the degradation state of the positive electrode used in the secondary battery, and diagnosis result data indicating the degradation state of the negative electrode used in the secondary battery. As long as the condition diagnosis device 100 has the function of outputting these pieces of output information, it may output any one type of data or multiple types of data. The output information may be displayed as an image on the output unit 40 or may be stored as a database in the storage unit 20.

[0065] FIG. 2 is a flowchart showing a process for diagnosing the deterioration state of a secondary battery. As shown in FIG. 2, a first step (steps S1 to S6) of performing an evaluation based on an open circuit voltage and a second step (steps S7 to S18) of performing an evaluation based on an internal resistance are performed in this order.

[0066] In the first step (steps S1 to S6), the relationship between the state of charge and the open circuit voltage of a secondary battery assumed to be in a deteriorated state is evaluated based on reference data showing the relationship between the state of charge of the positive electrode and the open circuit potential, which is specific to the positive electrode material, and reference data showing the relationship between the state of charge of the negative electrode and the open circuit potential, which is specific to the negative electrode material.

[0067] In the second step (steps S7 to S18), the relationship between the state of charge and internal resistance of a secondary battery assumed to be in a deteriorated state is evaluated based on the reference data constituting the relationship group, which includes reference data showing the relationship between the state of charge and internal resistance of the positive electrode specific to the positive electrode material for each current flow time, and reference data showing the relationship between the state of charge and internal resistance of the negative electrode specific to the negative electrode material for each current flow time.

[0068] In the first step (steps S1 to S6) and the second step (steps S7 to S18), the reference data is corrected with the degradation state parameters to assume a degradation state, and calculation data for the secondary battery in the assumed degradation state is generated based on the corrected reference data. Then, the measurement data based on the actual measurement is compared with the calculation data based on the reproduction in which the degradation state is assumed, and the agreement between the data is evaluated. By performing fitting so that the data agree with each other, a solution for the degradation state parameters is found.

[0069] <Step 1: Evaluation based on open circuit voltage> 2, first, the condition diagnosis device 100 reads measurement data indicating the relationship between the state of charge and the open circuit voltage of the secondary battery to be diagnosed. The measurement data can be read from the memory unit 20, an external measuring device connected to the communication unit 50, a storage medium, or an external storage device.

[0070] Next, the condition diagnosis device 100 reads reference data indicating the relationship between the state of charge of the positive electrode and the open circuit potential, which is specific to the positive electrode material, and reference data indicating the relationship between the state of charge of the negative electrode and the open circuit potential, which is specific to the negative electrode material (step S2). The reference data can be read from the storage unit 20, a storage medium, or an external storage device.

[0071] As the reference data showing the relationship between the state of charge and the open circuit potential, reference data for an electrode using any active material can be read. Even if the type of electrode or the type of active material is unknown at this stage, the deterioration state can be properly evaluated by performing fitting while changing the reference data. However, if the type of active material is known or can be predicted, it is preferable to read the reference data for the corresponding electrode.

[0072] FIG. 3 is a diagram showing an example of the relationship between the state of charge of an electrode and the open circuit potential. Figure 3 shows reference data for a positive electrode using LiFePO4 (LFP) as the active material. The horizontal axis shows the discharge rate qp [Ah / g] from a fully charged state per unit mass of the positive electrode active material, as an example of the state of charge of the electrode. The vertical axis shows the open circuit potential Vp [V] of the positive electrode relative to the reference electrode.

[0073] FIG. 4 is a diagram showing an example of the relationship between the state of charge of an electrode and the open circuit potential. Figure 4 shows reference data for a negative electrode using graphite as the active material. The horizontal axis shows the discharge capacity (qn [Ah / g]) from a fully charged state per unit mass of the negative electrode active material, as an example of the state of charge of the electrode. The vertical axis shows the open circuit potential (Vn [V]) of the negative electrode relative to the reference electrode.

[0074] 3 and 4, the relationship between the state of charge of an electrode and the open circuit potential is specific to the active material used as the electrode material. Reference data showing such a relationship is preferably prepared as a relational expression or a data table for each positive and negative electrode and for each active material used in the electrode.

[0075] As shown in Figure 3, for electrodes using LFP or other active materials, the open-circuit potential does not change substantially with changes in the state of charge and remains flat. It is difficult to evaluate the deterioration state of electrodes using such active materials based on the relationship between the state of charge and the open-circuit potential of the electrode. On the other hand, as shown in Figure 4, for electrodes using graphite or other active materials, the open-circuit potential changes significantly with changes in the state of charge. The deterioration state of electrodes using such active materials can be evaluated based on the relationship between the state of charge and the open-circuit potential of the electrode.

[0076] Therefore, even if an active material whose open circuit potential is constant except near the fully charged state and near the fully discharged state is used for at least one of the positive and negative electrodes, fitting can be performed efficiently by combining the first step (steps S1 to S6) of performing an evaluation based on the open circuit voltage and the second step (steps S7 to S18) of performing an evaluation based on the internal resistance.

[0077] Subsequently, the condition diagnostic device 100 sets a deterioration state parameter for the positive electrode (step S3). In step S3, a deterioration state parameter related to capacity is set to correct the relationship between the state of charge of the positive electrode and the open circuit potential.

[0078] Next, the condition diagnosis device 100 sets a deterioration state parameter for the negative electrode (step S4). In step S4, a deterioration state parameter related to capacity is set to correct the relationship between the state of charge of the negative electrode and the open circuit potential. Note that either step S3 or step S4 may be executed first.

[0079] The capacity degradation parameters can be set as coefficients or constants of state quantities representing the state of charge in functions that show the relationship between the state of charge and the open circuit potential or internal resistance, such as the active material utilization rate mrx of the positive and negative electrodes, and the out-of-range capacity δx [Ah] of the positive and negative electrodes.

[0080] The active material utilization rate mrx represents the proportion of the active material contained in the electrode that contributes to the charge-discharge reaction. When the amount of active material contained in the electrode is mx0 [g] and the amount of active material used that contributes to the charge-discharge reaction is mx [g], the active material utilization rate mrx is expressed as mrx = mx / mx0.

[0081] The out-of-range capacity δx represents the total capacity of the electrode that can only be obtained outside the upper and lower voltage limits of the secondary battery. The total capacity of the electrode, Qx [Ah], is expressed as Qx = mx × qx, where mx [g] is the amount of active material used in the charge / discharge reaction, and qx [Ah / g] is the capacity per unit mass of the electrode.

[0082] The total capacity Qx [Ah] of the electrodes can be expressed by the following equation (2), assuming that deterioration occurs that causes an out-of-range capacity Δx. Qx = qx × mx - δx (2)

[0083] The capacity-related degradation state parameter is defined as an arbitrary numerical value at a predetermined interval between an upper limit value and a lower limit value representing a state in which the electrodes are not degraded or a state in which the electrodes are completely degraded. The capacity-related degradation state parameter may be linked in data to a coefficient or constant of a state quantity representing the state of charge or a degradation degree representing the degradation state of the electrodes. Such degradation state parameters can be stored in the storage unit 20 as a parameter table.

[0084] In steps S3 and S4, any value can be provisionally set as the deterioration state parameter related to capacity. Since the deterioration state of the electrode is unknown at this stage, any value is provisionally set and subsequent calculations are performed. By performing fitting while replacing the deterioration state parameter, the deterioration state parameter can be approximated toward the true value.

[0085] Next, the condition diagnosis device 100 generates calculation data showing the relationship between the charge state and the open circuit voltage of the secondary battery based on reference data showing the relationship between the charge state and the open circuit potential of the positive electrode, reference data showing the relationship between the charge state and the open circuit potential of the negative electrode, and the set deterioration state parameters (step S5).

[0086] The relationship between the state of charge and the open circuit voltage of a secondary battery can be calculated by combining functions of the open circuit potential with respect to the state of charge, using the relationship between the state of charge and the open circuit potential of the positive electrode and the relationship between the state of charge and the open circuit potential of the negative electrode. The relationship between the state of charge and the open circuit potential of each electrode is corrected using a deterioration state parameter. Using the relationship corrected using the deterioration state parameter, calculation data is generated that shows the behavior of the open circuit voltage for each state of charge of a secondary battery assumed to be in a deteriorated state.

[0087] The open circuit potential Vc(Q) [V] of a secondary battery in the state of charge Q can be calculated using the following equation (3) where Qc = Qp + δp = Qn + δn, where Vp(Q) [V] is the open circuit potential of the positive electrode in the state of charge Q, Vn(Q) [V] is the open circuit potential of the negative electrode in the state of charge Q, Qc [Ah] is the discharge amount of the secondary battery from the fully charged state, Qp [Ah] is the discharge amount of the positive electrode from the fully charged state, and Qn [Ah] is the discharge amount of the negative electrode from the fully charged state. Vc(Qc)=Vp(Qp)-Vn(Qn) (3)

[0088] FIG. 5 is a diagram showing an example of the relationship between the state of charge of a secondary battery and the open circuit voltage. Figure 5 shows the measurement data for a secondary battery using LFP as the positive electrode active material and graphite as the negative electrode active material. The horizontal axis shows the discharge amount Qc [Ah / g] from the fully charged state of the secondary battery, which is an example of the state of charge of the secondary battery. The vertical axis shows the open circuit voltage Vc [V].

[0089] As shown in Figure 5, the relationship between the state of charge and open-circuit voltage of a secondary battery is determined based on the relationship between the state of charge and open-circuit potential of the positive electrode, which is specific to the positive electrode material, and the relationship between the state of charge and open-circuit potential of the negative electrode, which is specific to the negative electrode material. When a relationship corrected using the state-of-degradation parameter is used, the capacity-open-circuit voltage curve will shift up or down due to overpotential and the flat voltage region will be reduced. It is preferable to save measured data showing this relationship, as well as calculated data reproduced for comparison with the measured data, as a relational equation or a data table.

[0090] Next, the condition diagnosis device 100 compares the calculation data showing the relationship between the charge state and open circuit voltage of the secondary battery calculated assuming a deteriorated state with the measurement data showing the relationship between the charge state and open circuit voltage of the secondary battery being diagnosed, and determines whether the calculation data assuming a deteriorated state and the measurement data based on actual measurements match each other (step S6).

[0091] The determination of whether or not the data match each other can be performed using any determination method. For example, it can be performed based on the residual sum of squares between the data. The sum of squares of the differences between the calculated data and the measured data is calculated, and the sum of squares of the differences is compared with an arbitrarily set threshold value to determine the match between the data.

[0092] The sum of squares of the differences is Σ(Vcc_i-Vce_i), where Vcc_1 to Vcc_N are the calculated values ​​of the open circuit voltages in the calculation data, and Vce_1 to Vce_N are the measured values ​​of the open circuit voltages in the measurement data. 2 can be calculated for i=1 to N.

[0093] The calculated sum of squares of the differences can be compared with a preset threshold for consistency. The threshold for consistency of the open circuit potential can be set to any value that increases the similarity between the data, depending on the accuracy required for diagnosis, the number of calculation iterations, etc. When calculating the sum of squares of the differences, if there is no calculated data for the discharge state corresponding to the measured data, calculated data corresponding to the measured data can be interpolated.

[0094] If the comparison result shows that the sum of squares of the differences between the calculated data and the measured data exceeds a preset threshold, it can be determined that the calculated data indicating the relationship between the state of charge and the open circuit voltage of the secondary battery calculated assuming a deteriorated state and the measured data indicating the relationship between the state of charge and the open circuit voltage of the secondary battery being diagnosed do not match. In this case (step S6; NO), another deteriorated state parameter is reset, and the calculated data is regenerated and compared again.

[0095] On the other hand, if the comparison result shows that the sum of squares of the differences between the calculated data and the measured data is equal to or less than a preset threshold, it can be determined that the calculated data indicating the relationship between the state of charge and the open circuit voltage of the secondary battery calculated assuming a deteriorated state and the measured data indicating the relationship between the state of charge and the open circuit voltage of the secondary battery being diagnosed match each other. In this case (step S6; YES), the set deteriorated state parameters are adopted and the process proceeds to the second step (steps S7 to S18) of performing an evaluation based on internal resistance.

[0096] The adopted degradation state parameters are linked to an identifier for identifying the secondary battery to be diagnosed and an identifier for identifying the electrodes, and are registered in the storage unit 20. In the first step (steps S1 to S6), degradation state parameters assuming a degradation state are set. Therefore, the registered degradation state parameters can be updated according to the results of the second step (steps S7 to S18).

[0097] In the first step (S1 to S6), the resetting of the deterioration state parameters and the regeneration and recomparison of the calculation data based on the reset deterioration state parameters can be repeated any number of times until it is determined that the calculation data and the measurement data match each other. Values ​​that were not set in previous calculations can be set as the deterioration state parameters in order.

[0098] Whether the calculated data and the measured data match can also be determined by comparing the sum of squares of the differences between the calculated data and the measured data with a predetermined threshold value, instead of comparing the sum of squares of the differences between the calculated data and the measured data with a predetermined threshold value. When the sum of squares of the differences between the calculated data and the measured data is repeatedly regenerated and recompared, it can be determined that the data match when the sum of squares of the differences between the calculated data and the measured data decreases by a predetermined value or less from the sum of squares of the differences between the previous data.

[0099] In the diagnosis based on the open circuit voltage, if the calculated data and the measured data do not match after a predetermined number of calculations or a predetermined calculation time, the diagnosis process can be stopped, or the reference data can be replaced with reference data for an electrode using a different active material, and the deterioration state parameters can be reset, and the calculation data can be regenerated and compared again based on the reset deterioration state parameters.

[0100] The reference data for the open circuit potential is preferably linked to identifiers for identifying the positive and negative electrodes and identifiers for identifying the types of active materials used in the electrodes, and stored as a database in the storage unit 20. By preparing such a database, even if the type of active material used in the secondary battery to be diagnosed is unknown, appropriate evaluation can be performed by regenerating and recomparing the calculation data with the reference data replaced.

[0101] <Second step: Evaluation based on internal resistance> 2, after the evaluation based on the open circuit voltage, the condition diagnosis device 100 reads measurement data indicating a relationship group showing the current flow time dependency between the state of charge and internal resistance of the secondary battery to be diagnosed (step S7). The measurement data can be read from the memory unit 20, an external measuring device connected to the communication unit 50, a storage medium, or an external storage device.

[0102] Next, the condition diagnosis device 100 reads reference data indicating a relationship group that indicates the current-flow time dependency between the state of charge and internal resistance of the positive electrode, which is specific to the positive electrode material, and reference data indicating a relationship group that indicates the current-flow time dependency between the state of charge and internal resistance of the negative electrode, which is specific to the negative electrode material (step S8). The reference data can be read from the storage unit 20, a storage medium, or an external storage device.

[0103] Reference data for an electrode using any active material can be loaded as reference data showing a relationship group indicating the current-flow time dependence between the state of charge and internal resistance of the electrode. Even if the type of electrode or active material is unknown at this stage, fitting can be performed while changing the reference data to properly evaluate the state of deterioration. However, if the type of active material is known or can be predicted, it is preferable to load the reference data for the corresponding electrode.

[0104] As the reference data indicating the relationship group showing the current-flow time dependency of the electrode's state of charge and internal resistance, data corresponding to some or all of the relationships between the electrode's state of charge and internal resistance for each current-flow time that constitute the relationship group showing the current-flow time dependency of the electrode's state of charge and internal resistance may be read in. If the reference data for the current-flow time corresponding to the current-flow time of the measurement data is read in, an appropriate evaluation can be made based on the current-flow time dependency of the internal resistance.

[0105] Subsequently, the condition diagnosis device 100 starts an analysis based on the current flow time dependency of the state of charge and the internal resistance (step S9). The condition diagnosis device 100 specifies the current flow time to be analyzed, that is, the current flow time data to be analyzed.

[0106] The current flow time to be analyzed can be any current flow time among the current flow times for which measurement data has been acquired. The current flow times to be analyzed can be identified, for example, in ascending or descending order from the measurement data. The measurement data and reference data for the identified current flow time to be analyzed are extracted from the reference data indicating the relationship group, and an analysis based on the current flow time dependency of the state of charge and internal resistance is performed.

[0107] FIG. 6 is a diagram showing an example of the relationship between the state of charge of the electrode and the internal resistance for each current application time. Figure 6 corresponds to reference data for a positive electrode using LiFePO4 (LFP) as the active material. The horizontal axis shows the discharge rate qp [Ah / g] from a fully charged state per unit mass of the positive electrode active material, as an example of the state of charge of the electrode. The vertical axis shows the internal resistance Rp [mΩ·g] of the positive electrode. The circle plots show the results for a current flow time of t = 40 seconds, the black circles show the results for a current flow time of t = 50 seconds, the triangle plots show the results for a current flow time of t = 60 seconds, and the triangle plots show the results for a current flow time of t = 72 seconds.

[0108] FIG. 7 is a diagram showing an example of the relationship between the state of charge of the electrode and the internal resistance for each current application time. Figure 7 corresponds to reference data for a negative electrode using graphite as the active material. The horizontal axis shows the discharge amount qn [Ah / g] from a fully charged state per unit mass of the negative electrode active material, as an example of the state of charge of the electrode. The vertical axis shows the internal resistance Rn [mΩ·g] of the negative electrode. The circle plots show the results for a current flow time of t = 40 seconds, the black circles show the results for a current flow time of t = 50 seconds, the triangle plots show the results for a current flow time of t = 60 seconds, and the triangle plots show the results for a current flow time of t = 72 seconds.

[0109] 6 and 7, the relationship between the state of charge of an electrode and its internal resistance is specific to the active material used as the electrode material. Reference data showing this relationship is preferably prepared as a relational expression or a data table for each positive and negative electrode, for each active material used in the electrode, and for each current-flow time during measurement of the internal resistance.

[0110] As shown in Figure 6, even for active materials whose open-circuit potential does not substantially change with changes in the state of charge, the internal resistance of the electrode generally changes with changes in the state of charge. The deterioration state of an electrode using such an active material can be evaluated by looking at the relationship between the state of charge and the internal resistance of the electrode. However, if there are no characteristic points on the curves, it is difficult to compare curves based on the characteristic points. Because direct fitting of curves to each other cannot be performed in the section with characteristic points, more battery information is required.

[0111] If there is insufficient battery information for the secondary battery to be diagnosed, even if fitting is performed, it may not be possible to converge the degradation state parameters to a single solution. Therefore, in the subsequent analysis, calculated data showing the relationship between the state of charge and internal resistance of the secondary battery to be diagnosed for each current-flow time is fitted to measured data showing the relationship between the state of charge and internal resistance of the secondary battery to be diagnosed for each current-flow time.

[0112] The condition diagnosis device 100 extracts, as basic data, reference data that indicates the relationship between the electrode's state of charge and internal resistance corresponding to the current-flow time of the identified analysis object from among reference data that indicate a relationship group that indicates the current-flow time dependency between the electrode's state of charge and internal resistance specific to the electrode material. Furthermore, from measurement data that indicate a relationship group that indicates the current-flow time dependency between the state of charge and internal resistance of the secondary battery that is the diagnosis object, the device extracts, as the analysis object, measurement data that indicates the relationship between the secondary battery's state of charge and internal resistance corresponding to the current-flow time of the identified analysis object. If there is no reference data that corresponds to the current-flow time of the identified analysis object, the reference data may be interpolated.

[0113] Subsequently, the condition diagnosis device 100 sets a deterioration state parameter for the positive electrode (step S10). In step S10, a deterioration state parameter related to resistance is set to correct the relationship between the state of charge of the positive electrode and the internal resistance.

[0114] Next, the condition diagnosis device 100 sets a deterioration state parameter for the negative electrode (step S11). In step S11, a deterioration state parameter related to resistance is set to correct the relationship between the state of charge of the negative electrode and the internal resistance. Note that either step S10 or step S11 may be performed first. The deterioration state parameters for elements other than the electrodes may be set at any stage.

[0115] As the deterioration state parameter for resistance, in the function showing the relationship between the state of charge and the internal resistance, the coefficient of the resistance term for each electrode that depends on the state of charge, or a constant corresponding to the resistance of elements other than the electrodes can be set. For example, the resistance R0 of elements other than the electrodes, the resistance coefficient ax of the internal resistance of the positive electrode and the negative electrode, etc. can be set.

[0116] Assuming degradation represented by the resistance coefficient ax, the internal resistance Rx(Q) [Ω] of the electrode at the state of charge Q can be expressed by the following equation (4), where the amount of active material used that contributes to the charge / discharge reaction is mx [g], the internal resistance of the active material at the state of charge Q is rx(Q) [Ω g], the total capacity of the electrode is Qx [Ah], and the capacity per unit mass of the electrode is qx [Ah / g]. Rx(Qx)=ax / mx×rx(qx) (4)

[0117] The deterioration state parameter for resistance is defined as any numerical value in a predetermined interval between an upper limit value and a lower limit value representing a state in which the electrode is not deteriorated or a state in which the electrode is completely deteriorated. The deterioration state parameter for resistance may be linked in data to a coefficient or constant of a state quantity representing the state of charge or a deterioration degree representing the deterioration state of the electrode. Such deterioration state parameters can be stored in the storage unit 20 as a parameter table.

[0118] In steps S10 and S11, any value can be provisionally set as the deterioration state parameter related to resistance. Since the deterioration state of the electrode is unknown at this stage, any value is provisionally set and subsequent calculations are performed. By performing fitting while replacing the deterioration state parameter, the deterioration state parameter can be approximated toward the true value.

[0119] Next, the condition diagnosis device 100 generates calculation data showing the relationship between the charge state and internal resistance of the secondary battery for each predetermined current flow time based on reference data showing the relationship between the charge state and internal resistance of the positive electrode for each predetermined current flow time, reference data showing the relationship between the charge state and internal resistance of the negative electrode for each predetermined current flow time, and the set deterioration state parameters (step S12).

[0120] The relationship between the state of charge and internal resistance of a secondary battery can be calculated by combining functions of internal resistance with respect to the state of charge, using the relationship between the state of charge and internal resistance of the positive electrode and the relationship between the state of charge and internal resistance of the negative electrode. The relationship between the state of charge and internal resistance of each electrode is corrected using a deterioration state parameter. Using the relationship corrected using the deterioration state parameter, calculation data is generated that shows the behavior of the internal resistance for each state of charge of a secondary battery assumed to be in a deteriorated state.

[0121] The internal resistance Rc(t,Q) [Ω] of a secondary battery at the state of charge Q occurring at current flow time t can be calculated using the following equation (5), where the internal resistance of the positive electrode at the state of charge Q occurring at current flow time t is rp(t,Q) [Ω g], the internal resistance of the negative electrode at the state of charge Q occurring at current flow time t is rn(t,Q) [Ω g], the resistance of elements other than the electrodes is R0 [mΩ], the resistance coefficient of the positive electrode internal resistance is ap, and the resistance coefficient of the negative electrode internal resistance is an. Rc(t,Qc)=ap / mp×rp(t,qp) +an / mn×rn(t,qn)+R0 (5)

[0122] FIG. 8 is a diagram showing an example of the relationship between the state of charge and the internal resistance of a secondary battery for each current-carrying time. Figure 8 shows the measurement data for a secondary battery using LFP as the positive electrode active material and graphite as the negative electrode active material. The horizontal axis shows the discharge amount Qc [Ah] from a fully charged state of the secondary battery as an example of the state of charge of the secondary battery. The vertical axis shows the internal resistance Rc [mΩ] of the secondary battery. The circle plots show the results for a current flow time of t = 40 seconds, the black circles show the results for a current flow time of t = 50 seconds, the triangle plots show the results for a current flow time of t = 60 seconds, and the triangle plots show the results for a current flow time of t = 72 seconds.

[0123] As shown in Figure 8, the relationship between the state of charge and internal resistance of a secondary battery is determined based on the relationship between the state of charge and internal resistance of the positive electrode, which is specific to the positive electrode material, and the relationship between the state of charge and internal resistance of the negative electrode, which is specific to the negative electrode material. When a relationship corrected using a degradation state parameter is used, the capacity-resistance curve shifts up or down depending on the assumed degradation state. It also shifts up or down depending on the current flow time. It is preferable to save measurement data showing this relationship, as well as calculation data reproduced for comparison with the measurement data, as a relational expression or a data table.

[0124] In step S12, the calculation data showing the relationship between the state of charge and the internal resistance of the secondary battery for each current-carrying time is preferably calculated for the current-carrying time converted by a weighting function ρ(t) corresponding to the estimated deterioration rate, i.e., it is preferably calculated based on reference data in which the current-carrying time t is replaced by the weighting function ρ(t).

[0125] The weighting function ρ(t) is ρ(t)=exp(-k A t), ρ(t)=k B (t) -1 / 2 , ρ(t)=exp(-k A t)+k B (t) -1 / 2 etc. can be used. Here, k A ,k B is a constant. The constant k A ,k B can be obtained by a preliminary test in which the internal resistance is actually measured.

[0126] The reference data is data that does not change the dependency of the internal resistance value on the current-flow time t. On the other hand, the measured data that is compared with the calculated data is data in which the dependency of the internal resistance value on the current-flow time t changes due to factors such as capacity degradation. If the calculated data is generated by converting it with a weighting function ρ(t) that corresponds to the estimated degradation rate, the change in internal resistance that depends on the current-flow time t can be reflected in the calculated data, thereby enabling accurate diagnosis while reducing the amount of reference data prepared for each current-flow time.

[0127] Next, the condition diagnosis device 100 compares the calculation data showing the relationship between the charge state and internal resistance of the secondary battery for each predetermined current flow time, calculated assuming a degraded state, with the measurement data showing the relationship between the charge state and internal resistance of the secondary battery being diagnosed for each predetermined current flow time, and determines whether the calculation data assuming a degraded state and the measurement data based on actual measurements match each other (step S13).

[0128] The determination of whether or not the data match each other can be performed using any determination method. For example, it can be performed based on the residual sum of squares between the data. The sum of squares of the differences between the calculated data and the measured data is calculated, and the sum of squares of the differences is compared with an arbitrarily set threshold value to determine the match between the data.

[0129] The sum of squares of the difference is Σ(Rcc_i-Rce_i), where Rcc_1 to Rcc_N are the calculated values ​​of the internal resistance in the calculation data and Rce_1 to Rce_N are the measured values ​​of the internal resistance in the measurement data. 2 can be calculated for i=1 to N.

[0130] The calculated sum of squares of the differences can be compared with a preset threshold value for consistency. The threshold value for consistency of the internal resistance can be set to any value that increases the similarity between the data, depending on the accuracy required for the diagnosis, the number of calculation iterations, etc. When calculating the sum of squares of the differences, if there is no calculated data for the discharge state corresponding to the measured data, the calculated data corresponding to the measured data may be interpolated.

[0131] If the comparison result shows that the sum of squares of the differences between the calculated data and the measured data exceeds a preset threshold, it can be determined that the calculated data indicating the relationship between the state of charge and internal resistance of the secondary battery calculated assuming a deteriorated state and the measured data indicating the relationship between the state of charge and internal resistance of the secondary battery being diagnosed do not match. In this case (step S13; NO), another deteriorated state parameter is reset, and the calculated data is regenerated and compared again.

[0132] On the other hand, if the comparison result indicates that the sum of squares of the differences between the calculated data and the measured data is equal to or less than a preset threshold, it can be determined that the calculated data indicating the relationship between the state of charge and internal resistance of the secondary battery calculated assuming a deteriorated state and the measured data indicating the relationship between the state of charge and internal resistance of the secondary battery being diagnosed match each other. In this case (step S13; YES), the set deteriorated state parameters are adopted, and the process proceeds to step S14.

[0133] Next, based on the comparison result, the condition diagnosis device 100 determines whether or not a single solution corresponding to the true value of the degradation state parameter can be determined (step S14). In step S14, it is evaluated whether or not a single solution has been obtained for the resistance R0 of the element other than the electrode that does not depend on the discharge state, among the degradation state parameters.

[0134] Whether a single solution can be determined is determined by comparing the past deterioration state parameters adopted in the analysis in which the current flow time is specified with the latest deterioration state parameters adopted in the analysis in which the current flow time is changed. Based on the similarity between the past deterioration state parameters and the latest deterioration state parameters, it can be evaluated whether the solution of the deterioration state parameters has converged to a single solution.

[0135] The internal resistance of a secondary battery varies depending on the current flow time. Similarly, the internal resistance of the positive electrode, which depends on the state of charge, and the internal resistance of the negative electrode, which depends on the state of charge, vary depending on the current flow time. On the other hand, the resistance R0 of elements other than the electrodes, which does not depend on the state of charge, is essentially independent of the current flow time, except immediately after the start of current flow. Therefore, by comparing the past deterioration state parameters with the latest deterioration state parameters while changing the current flow time, a common solution that is independent of the current flow time can be obtained as a single solution.

[0136] The determination of whether a single solution corresponding to the true value of the degradation state parameter can be made by comparing the difference between the past degradation state parameter and the latest degradation state parameter with a preset threshold. When the difference exceeds the preset threshold, it can be determined that a single solution corresponding to the true value cannot be determined. On the other hand, when the difference is less than the preset threshold, it can be determined that a single solution corresponding to the true value can be determined.

[0137] The threshold value is preferably a value that makes the difference between the past degradation state parameter and the latest degradation state parameter less than 10%, more preferably less than 5%, of the past degradation state parameter. The resistance R0 of elements other than the electrodes is usually 10 mΩ or more. Using such a value allows for determination with an error of less than 1 mΩ.

[0138] Furthermore, whether or not a single solution corresponding to the true value of the degradation state parameter can be determined can be determined by cluster analysis. For example, by repeating an analysis specifying the power-on time, calculation results of the degradation state parameter can be collected, and the calculation results can be clustered using the power-on time as one of the variables. When the latest degradation state parameter is clustered with a predetermined number of samples within a predetermined distance, it can be determined that a single solution corresponding to the true value can be determined. On the other hand, when the latest degradation state parameter is not clustered with a predetermined number of samples within a predetermined distance, it can be determined that a single solution corresponding to the true value cannot be determined.

[0139] In the case of cluster analysis, the representative value of the cluster to which the sample belongs under predetermined conditions can be used as the single solution corresponding to the true value of the degradation state parameter. Examples of the representative value include the mean, median, and mode value. Furthermore, when multiple clusters to which the samples belong are formed, the representative value of the cluster to which the sample with the longest current flow time belongs can be used. This is because the longer the current flow time, the larger the absolute value of the internal resistance, resulting in higher accuracy.

[0140] If it is determined as a result of the analysis that a single solution corresponding to the true value of the degradation state parameter cannot be determined (step S14; NO), the analysis for each power supply time is insufficient, so the process proceeds to step S15.

[0141] On the other hand, if it is determined as a result of the analysis that a single solution corresponding to the true value of the degradation state parameter can be determined (step S14; YES), the analysis for each power supply time is sufficient, and the process proceeds to step S17.

[0142] If it is determined that a single solution cannot be determined, the condition diagnosis device 100 determines whether or not the data corresponding to all current-on times has been analyzed as the analysis target (step S15). In step S15, it determines whether or not the analysis has been performed based on the measurement data corresponding to all current-on times among the measurement data of the secondary battery collected for each current-on time.

[0143] If it is determined that the data corresponding to all current-carrying times have not been analyzed (step S15; NO), the process proceeds to step S16. Next, the condition diagnosis device 100 changes the current-carrying time to be analyzed (step S16). Then, the measurement data and reference data for the changed current-carrying time to be analyzed are extracted, and the analysis based on the current-carrying time dependency of the state of charge and the internal resistance is resumed. The current-carrying time to be analyzed can be changed, for example, in ascending or descending order from the measurement data.

[0144] On the other hand, if it is determined that the data corresponding to all the current-carrying times have been analyzed (step S15; YES), analysis for each current-carrying time is sufficient, and the process proceeds to step S17.

[0145] If it is determined that a single solution can be determined or if it is determined that data corresponding to all current flow times have been analyzed, the analysis based on the current flow time dependency of the state of charge and the internal resistance is terminated (step S17). Next, the state diagnosis device 100 determines the remaining degradation state parameters based on the single solution corresponding to the true value of the degradation state parameter (R0) (step S18). Thereafter, the processing for diagnosing the degradation state is terminated.

[0146] The remaining degradation state parameters, such as the resistance coefficient ax of the internal resistance of the positive and negative electrodes, can be recalculated based on the true value R0 and equation (4) when the resistance R0 of elements other than the electrodes converges to a single solution corresponding to the true value. In addition, the active material utilization mrx of the positive and negative electrodes and the out-of-range capacity δx of the positive and negative electrodes can be recalculated.

[0147] Alternatively, the remaining deterioration state parameters, such as the resistance coefficient ax of the positive and negative electrode internal resistance, can be extracted from a database in which the adopted deterioration state parameters are stored as data corresponding to the deterioration state parameter (R0) equivalent to the true value. When extracted from a database, there may be multiple pieces of data, such as the resistance coefficient ax, corresponding to the deterioration state parameter (R0) equivalent to the true value. In this case, the data for which the maximum current flow time is specified can be used. This is because the longer the current flow time, the larger the absolute value of the internal resistance, and the higher the fitting accuracy.

[0148] The degradation state parameter (R0) corresponding to the true value and the remaining degradation state parameters (ax, mrx, δx, etc.) are linked to an identifier for identifying the secondary battery to be diagnosed and an identifier for identifying the electrodes, and are registered in the storage unit 20. The degradation state parameter related to the capacity and the degradation state parameter related to the internal resistance are registered linked to each other.

[0149] In the second step (S7 to S18), the resetting of the deterioration state parameters and the regeneration and recomparison of the calculation data based on the reset deterioration state parameters can be repeated any number of times until it is determined that the calculation data and the measurement data match each other. Values ​​that were not set in previous calculations can be set as the deterioration state parameters in order.

[0150] Whether the calculated data and the measured data match can also be determined by comparing the sum of squares of the differences between the calculated data and the measured data with a predetermined threshold value, instead of comparing the sum of squares of the differences between the calculated data and the measured data with a predetermined threshold value. When the sum of squares of the differences between the calculated data and the measured data is repeatedly regenerated and recompared, it can be determined that the data match when the sum of squares of the differences between the calculated data and the measured data decreases by a predetermined value or less from the sum of squares of the differences between the previous data.

[0151] Whether the calculated data and the measured data match can also be determined by comparing the minimum value of the sum of squares of the differences between the calculated data and the measured data with a predetermined threshold value. When the minimum value of the sum of squares of the differences calculated over a predetermined number of calculations or a predetermined calculation time is equal to or less than a predetermined value, it can be determined that the data match.

[0152] In the diagnosis based on the internal resistance, if the calculated data and the measured data do not match after a predetermined number of calculations or a predetermined calculation time, the diagnosis process can be stopped. Alternatively, the reference data can be replaced with reference data for an electrode using a different active material, and the deterioration state parameters can be reset, and the calculation data based on the reset deterioration state parameters can be regenerated and compared again. The diagnosis based on the open circuit voltage can also be restarted using the deterioration state parameters set in the diagnosis based on the internal resistance.

[0153] The reference data for the internal resistance is preferably linked to identifiers for identifying the positive and negative electrodes and identifiers for identifying the types of active materials used in the electrodes, and stored as a database in the storage unit 20. By preparing such a database, even if the type of active material used in the secondary battery to be diagnosed is unknown, appropriate evaluation can be performed by regenerating and recomparing the calculation data with the reference data replaced.

[0154] FIG. 9 is a diagram showing an example of the relationship between the state of charge and the open circuit voltage of a secondary battery assumed to be in a deteriorated state. Figure 9 shows the results of fitting calculated data for a secondary battery using LFP as the positive electrode active material and graphite as the negative electrode active material, generated based on reference data corrected with degradation state parameters, to measured data. The horizontal axis represents the discharge amount Qc [Ah] from the fully charged state of the secondary battery, as an example of the state of charge of the secondary battery. The vertical axis represents the open circuit voltage Vc [V]. The dashed line corresponds to the reference data of the positive electrode corrected with the deterioration state parameters, the dotted line corresponds to the reference data of the negative electrode corrected with the deterioration state parameters, the solid line corresponds to the calculated data of the secondary battery, and the circle plot corresponds to the measured data of the secondary battery.

[0155] FIG. 10 is a diagram showing an example of the relationship between the state of charge and the internal resistance of a secondary battery assumed to be in a deteriorated state. Figure 10 shows the results of fitting calculated data for a secondary battery using LFP as the positive electrode active material and graphite as the negative electrode active material to measured data, generated based on reference data corrected with degradation state parameters. The horizontal axis shows the discharge amount Qc [Ah] from a fully charged state of the secondary battery as an example of the state of charge of the secondary battery. The vertical axis shows the internal resistance Rc [mΩ] of the secondary battery. The dashed line shows the reference data for the positive electrode corrected with the degradation state parameters, the dotted line shows the reference data for the negative electrode corrected with the degradation state parameters, the solid line shows the calculated data for the secondary battery, and the circles show the measured data for the secondary battery.

[0156] 9 and 10, the calculated data showing the relationship between the state of charge of the secondary battery and the open circuit voltage, and the calculated data showing the relationship between the state of charge of the secondary battery and the internal resistance are fitted to match the measured data. The fitted calculated data and the degradation state parameters used in the fitting can be saved as a relational expression or a data table showing the diagnosis results.

[0157] <Output information> When the first step (steps S1 to S6) and the second step (steps S7 to S18) are completed, the output unit 40 can output the adopted deterioration state parameters, the diagnosis results of the deterioration state for each electrode, and the diagnosis results of the deterioration state of the secondary battery. The diagnosis results of the deterioration state for each electrode and the diagnosis results of the deterioration state of the secondary battery can be displayed as a graph, a table, etc.

[0158] The diagnosis results of the deterioration state for each electrode include calculated data showing the relationship between the state of charge of the electrode and the open circuit potential, corrected using the deterioration state parameters, and calculated data showing the relationship between the state of charge of the electrode and the internal resistance, corrected using the deterioration state parameters. The calculated data showing the relationship between the state of charge of the electrode and the internal resistance may be displayed independently as data for each current flow time, or may be displayed collectively for each current flow time. These data can be displayed for each positive electrode and negative electrode.

[0159] The diagnosis results of the deterioration state of the secondary battery include data on the deterioration state (State of Health: SOH) of the secondary battery, calculation data showing the relationship between the state of charge of the secondary battery and the open circuit voltage synthesized from the calculation data for each electrode, and calculation data showing the relationship between the state of charge of the secondary battery and the internal resistance synthesized from the calculation data for each electrode. The calculation data showing the relationship between the state of charge of the secondary battery and the internal resistance may be displayed independently as data for each current flow time, or the data for each current flow time may be displayed together.

[0160] The state of health (SOH) can be output as a capacity retention rate SOHQ, a resistance increase rate SOHR, etc. The state of health (SOH) is expressed as a capacity ratio relative to a predetermined reference state, a rate of change of a state of health parameter relative to a predetermined reference state, etc.

[0161] The capacity retention rate SOHQ [%] can be calculated using the following equations (6) to (7), where the capacity of a secondary battery in an initial state when fully charged is Qmax0 [Ah], the capacity of a secondary battery in a degraded state when fully charged is Qmax1 [Ah], and the states of charge at the upper and lower limits of the integration interval of a secondary battery in a degraded state are SOC1 [%] and SOC2 [%]. SOHQ=Qmax1 / Qmax0×100[%]...(6) Qmax1=∫Idt / ((SOC1-SOC2) / 100)···(7)

[0162] The resistance increase rate SOHRc [%] of the secondary battery, the resistance increase rate SOHRp [%] of the positive electrode, and the resistance increase rate SOHRn [%] of the negative electrode can be calculated using the following equations (8) to (10), where the internal resistance of the secondary battery in its initial state is Rc0 [Ω], the internal resistance of the secondary battery in its degraded state is Rc1 [Ω], the internal resistance of the positive electrode in its initial state is Rp0 [Ω], the internal resistance of the secondary battery in its degraded state is Rp1 [Ω], the internal resistance of the negative electrode in its initial state is Rn0 [Ω], and the internal resistance of the negative electrode in its degraded state is Rn1 [Ω]. SOHRc=Rc1 / Rc0×100[%]...(8) SOHRp=Rp1 / Rp0×100[%] (9) SOHRn=Rn1 / Rn0×100[%] (10)

[0163] The diagnosis result of the deterioration state of the secondary battery can be used to change the operating condition range of the secondary battery. Depending on the diagnosis result of the deterioration state of the secondary battery, the upper and lower limits of the charge state of the secondary battery, the upper and lower limits of the charging current to the secondary battery, the upper and lower limits of the discharging current from the secondary battery, etc. can be changed.

[0164] For example, a potential range in which a positive electrode material can be properly used and a potential range in which a negative electrode material can be properly used are determined in advance, and then, when a change in open circuit potential occurs due to deterioration of either the positive electrode or the negative electrode, the upper limit voltage value and the lower limit voltage value can be changed so that capacity is secured within the potential range in which they can be properly used.

[0165] Furthermore, the diagnosis results of the deterioration state of the secondary battery can be saved as a database for each diagnosis request. The diagnosis result data may be collected for each different secondary battery, or may be collected by performing diagnoses on the same secondary battery at different times. These diagnosis results can be saved in the condition diagnosis device 100 as time-series diagnosis result data for each diagnosis request.

[0166] The diagnostic result data indicating the diagnostic result of the secondary battery's degradation state can be linked to an identifier for identifying the diagnostic request, data indicating the date and time of the diagnosis, and data indicating the usage history of the secondary battery. The usage history of the secondary battery can include history of the usage time of the secondary battery, the cumulative amount of current flowing through the secondary battery, the number of charge / discharge cycles of the secondary battery, the voltage, current, temperature, etc. The data indicating the usage history of the secondary battery can be input via the input unit 30. These linked data can be output as output information together with the diagnostic result.

[0167] The diagnostic results of the deterioration state of the secondary battery stored as a database can be used to change the operating conditions of the secondary battery. The operating conditions of the secondary battery include the upper and lower limits of the charge state of the secondary battery, the upper and lower limits of the charging current to the secondary battery, and the upper and lower limits of the discharging current from the secondary battery. One or more of these operating conditions can be changed based on the stored diagnostic result data.

[0168] The operating conditions of the secondary battery can be changed using (1) the deterioration state of each electrode, (2) the rate of change in the deterioration state of each electrode, or (3) the remaining life of the secondary battery as indicators. These indicators are compared with predetermined thresholds, and when it is determined that the deterioration of each electrode or the deterioration of the secondary battery is likely to progress, the operating condition range of the secondary battery can be changed to conditions that ensure safety.

[0169] (1) The latest degradation state parameter obtained as output information can be used as an index for the degradation state of each electrode. When the degradation state of the positive electrode represented by the degradation state parameter or the degradation state of the negative electrode represented by the degradation state parameter is equal to or greater than a preset threshold, the operating condition range of the secondary battery can be changed to a condition that ensures safety.

[0170] (2) The rate of change of the deterioration state of each electrode can be determined by the rate of change (rate of change) of the deterioration state of the positive electrode relative to the cumulative load, or the rate of change (rate of change) of the deterioration state of the negative electrode relative to the cumulative load. When the deterioration state of the positive electrode represented by the deterioration state parameter or the deterioration state of the negative electrode represented by the deterioration state parameter is equal to or greater than a preset threshold value with respect to the application of a predetermined cumulative load, the operating condition range of the secondary battery can be changed to a condition that ensures safety.

[0171] The cumulative load can be calculated from the usage time of the secondary battery, the amount of current flowing through the secondary battery, or a combination of two or more of the usage time, amount of current flowing through the secondary battery, temperature, and current. Using two or more of these variables, a model function is formulated that shows the relationship between the cumulative load and the electrode degradation state. Then, the electrode degradation state for various cumulative loads is measured, and the coefficients and constants of the model function can be determined by fitting based on the measurements.

[0172] (3) The remaining life of a secondary battery can be determined by the length of time the secondary battery is used until its discharge capacity drops to a predetermined value due to deterioration. When the remaining life of the secondary battery is equal to or less than a predetermined threshold value relative to the expected predetermined use time, the operating condition range of the secondary battery can be changed to a range that ensures safety.

[0173] The discharge capacity of a secondary battery after a predetermined period of use can be estimated based on the rate of change (rate of change) of the deterioration state of the secondary battery with respect to the cumulative load, the current discharge capacity of the secondary battery, and information on the period of use. The rate of change (rate of change) of the deterioration state of the secondary battery with respect to the cumulative load can be calculated based on the rate of change (rate of change) of the deterioration state of the positive electrode with respect to the cumulative load and the rate of change (rate of change) of the deterioration state of the negative electrode with respect to the cumulative load.

[0174] Examples of operations for changing the operating conditions of the secondary battery to ensure safety include lowering the upper limit of the state of charge of the secondary battery, raising the lower limit of the state of charge of the secondary battery, lowering the upper or lower limit of the charging current to the secondary battery, and lowering the upper or lower limit of the discharging current from the secondary battery. The calculation unit 10 may perform processing to generate a control signal for performing one or more of these operations.

[0175] By changing the range of operating conditions of the secondary battery after such a diagnosis, the progression of deterioration of the secondary battery can be suppressed, thereby extending the life of the secondary battery. The history of diagnosis results used to change the range of operating conditions of the secondary battery is obtained as data indicating the deterioration state of each electrode by the above-mentioned secondary battery state diagnosis method and secondary battery state diagnosis device, so that deterioration of either the positive electrode or the negative electrode can be detected early, ensuring the safety of the secondary battery.

[0176] The above-described secondary battery state diagnosis method and secondary battery state diagnosis device use the relationship between the state of charge of the secondary battery and its open-circuit potential, and a set of relationships formed by the relationship between the state of charge of the secondary battery and its internal resistance for different current-carrying times, as input information for diagnosing the state of deterioration. Therefore, the state of deterioration of the secondary battery and the state of deterioration of each of its positive and negative electrodes can be individually diagnosed through diagnoses based on the open-circuit potential and the internal resistance. By using the set of relationships formed by the relationship between the state of charge of the secondary battery and its internal resistance for different current-carrying times, the multivariable internal resistance can be approximated to its true value in calculations based on the internal resistance. Therefore, even if one of the positive and negative electrodes uses an active material whose potential changes little with changes in the state of charge, the state of deterioration of the secondary battery and each of its electrodes can be diagnosed with high accuracy. The state of deterioration of each electrode is diagnosed using measurements of the open-circuit voltage of the secondary battery being diagnosed and the internal resistance of the secondary battery being diagnosed, allowing for non-destructive diagnosis of the state of deterioration of the secondary battery and each of its electrodes.

[0177] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the present invention. For example, the present invention is not necessarily limited to those having all of the configurations of the above-described embodiments. It is possible to replace part of the configuration of an embodiment with another configuration, add part of the configuration of an embodiment to another form, or omit part of the configuration of an embodiment. [Example]

[0178] The present invention will be specifically explained below by showing examples, but the technical scope of the present invention is not limited to these examples.

[0179] <Getting input information> For LFP-Li metal half-cells, graphite-Li metal half-cells, and LFP-graphite secondary batteries, the relationship between the state of charge and open-circuit potential (voltage), as well as the relationship between the state of charge and internal resistance depending on the current flow time, were determined based on actual measurements during the discharge process.

[0180] Measurements of the open circuit potential (voltage) and internal resistance were performed using the Galvanostatic Intermittent Titration Technique (GITT). The discharge current was 1 CA. During the discharge process, a 72-second discharge followed by a 30-minute rest was repeated intermittently until the discharge end potential (voltage).

[0181] Data showing the relationship between state of charge and open-circuit potential (voltage) were collected by measuring the open-circuit potential (voltage) after a 30-minute rest period for a given discharge capacity during intermittent charge-discharge cycling. Figure 3 corresponds to the reference data collected on the LFP-Li metal half-cell. Figure 4 corresponds to the reference data collected on the graphite-Li metal half-cell. Figure 5 corresponds to the measured data collected on the LFP-graphite secondary battery.

[0182] Data showing the relationship between the state of charge and internal resistance and the current-time dependence was collected by calculating the internal resistance after a specified discharge time during intermittent charge-discharge cycles. Data for each current-time period was collected as discharge-time-dependent data for each discharge time period. The internal resistance was calculated by dividing the difference between the open-circuit potential (voltage) before discharge and the open-circuit potential (voltage) after a specified discharge time by the discharge current. The discharge time, t, was set to 40, 50, 60, and 72 seconds. Figure 6 corresponds to the reference data collected for the LFP-Li metal half cell. Figure 7 corresponds to the reference data collected for the graphite-Li metal half cell. Figure 8 corresponds to the measurement data collected for the LFP-graphite secondary battery.

[0183] <Step 1: Evaluation based on open circuit voltage> Calculated data showing the relationship between the state of charge and the open circuit voltage of the secondary battery was generated based on reference data showing the relationship between the state of charge and the open circuit potential of the positive electrode, whose state of degradation is known, reference data showing the relationship between the state of charge and the open circuit potential of the negative electrode, whose state of degradation is known, and the degradation state parameters. Then, the calculated data calculated assuming a degraded state was fitted to measured data showing the relationship between the state of charge and the open circuit voltage of the secondary battery to be diagnosed.

[0184] The open-circuit voltage data was fitted using the solver function in Excel (Microsoft). The root mean squared error (RMSE) between the measured data and the calculated data was calculated. Then, fitting was performed so that the relative error, calculated by dividing the root mean squared error by the average value, was minimized. As a result of the calculation, the degradation state parameters mrn = 0.864 and δn = 0.499 [Ah] were obtained. Figure 9 corresponds to the calculated data for the open-circuit potential obtained for the LFP-graphite secondary battery.

[0185] <Step 2: Evaluation based on internal resistance> Calculated data showing the relationship between the state of charge and internal resistance of a secondary battery was generated based on reference data showing the relationship between the state of charge and internal resistance of a positive electrode whose state of degradation is known, reference data showing the relationship between the state of charge and internal resistance of a negative electrode whose state of degradation is known, and degradation state parameters. Regarding the relationship between the state of charge and internal resistance, multiple pieces of data for each current flow time were prepared and used in the calculation, with the current flow time being varied during the measurement of the internal resistance. Then, the calculated data, calculated assuming a degraded state, was fitted to the measured data showing the relationship between the state of charge and internal resistance of the secondary battery to be diagnosed for each current flow time.

[0186] Fitting of the internal resistance data was performed using the solver function installed in Excel (manufactured by Microsoft). The root mean squared error (RMSE) between the measured data and the calculated data was calculated. Then, fitting was performed so that the relative error obtained by dividing the root mean squared error by the average value was minimized. In the examples, since an equivalent degradation state was assumed between the measured data and the reference data, correction by the weighting function ρ(t) was not performed.

[0187] Initial values of mrp and ap were each set in three ways. Then, fitting was performed for each elapsed discharge time at each initial value. When performing fitting, as a constraint condition for R0, 0 < R0 [mΩ] < 20 was provided. The upper limit of 20 mΩ is the minimum value of the calculation result of R0 at the energization time t = 1 sec.

[0188] [Table 1] Table 1 shows the calculation results of R0 at t = 72 sec. As R0, four solutions of 1, 6, 10, 14 [mΩ] were obtained.

[0189] [Table 2] Table 2 shows the calculation results of R0 at t = 60 sec. As R0, three solutions of 10, 13, 16 [mΩ] were obtained.

[0190] [Table 3] Table 3 shows the calculation results of R0 at t = 50 sec. As R0, four solutions of 5, 10, 12, 18 [mΩ] were obtained.

[0191] [Table 4] Table 4 shows the calculation results for R0 at t = 40 seconds. Two solutions were obtained for R0: 8 and 12 mΩ.

[0192] Here, R0 = 20 [mΩ] means that the calculation has not converged within the range of the constraints, so the true value of R0 was set to 10 mΩ, which is the common solution at current flow times t = 50, 60, and 72 "sec."

[0193] Next, the remaining degradation state parameters were calculated under R0 = 10 [mΩ] at a current flow time of t = 72 sec, resulting in the following degradation state parameters: mrp = 0.820, δp = 0.00035 [Ah], ap = 0.0128, an = 0.00270. Figure 10 corresponds to the calculated data for the internal resistance after fitting obtained for the LFP-graphite secondary battery. [Explanation of symbols]

[0194] 100 Status diagnostic device (secondary battery status diagnostic device) 10 Arithmetic section 20 Memory section 30 Input section 40 Output section 50 Communications Department

Claims

1. A state diagnosis method for diagnosing a deterioration state of a secondary battery, comprising: a relationship group consisting of a relationship between a state of charge of a secondary battery and an open circuit voltage, and a relationship between a state of charge of the secondary battery and an internal resistance for each different current-carrying time is used as input information, and a deterioration state of the secondary battery, a deterioration state of a positive electrode used in the secondary battery, and a deterioration state of a negative electrode used in the secondary battery are used as output information; a first step of evaluating the relationship between the state of charge and the open circuit voltage of the secondary battery based on a relationship between the state of charge and the open circuit potential of the positive electrode that is specific to the positive electrode material and a relationship between the state of charge and the open circuit potential of the negative electrode that is specific to the negative electrode material; a second step of evaluating a group of relationships formed by the relationships between the state of charge and the internal resistance of the secondary battery based on the relationships between the state of charge of the positive electrode and the internal resistance specific to the positive electrode material for each different current-flow time and the relationships between the state of charge of the negative electrode and the internal resistance specific to the negative electrode material for each different current-flow time, the first step is a step of correcting the relationship between the state of charge and the open circuit potential of the positive electrode and the relationship between the state of charge and the open circuit potential of the negative electrode by a parameter representing a degraded state of the electrode to assume a degraded state, generating a relationship between the state of charge and the open circuit voltage of the secondary battery assumed to be in a degraded state based on the corrected relationship between the state of charge and the open circuit potential of the positive electrode and the corrected relationship between the state of charge and the open circuit potential of the negative electrode, and comparing the relationship between the state of charge and the open circuit voltage of the secondary battery, which is the input information, with the relationship between the state of charge and the open circuit voltage of the secondary battery assumed to be in a degraded state to evaluate the agreement between the relationships; the second step is a step of correcting the relationship between the state of charge and the internal resistance of the positive electrode and the relationship between the state of charge and the internal resistance of the negative electrode with parameters representing the degradation states of the electrodes and elements other than the electrodes to assume a degradation state, generating a relationship between the state of charge and the internal resistance of the secondary battery assumed to be in a degradation state based on the corrected relationship between the state of charge and the internal resistance of the positive electrode and the corrected relationship between the state of charge and the internal resistance of the negative electrode, and comparing the relationship between the state of charge and the internal resistance of the secondary battery in the relationship group that is the input information with the relationship between the state of charge and the internal resistance of the secondary battery assumed to be in a degradation state to evaluate the agreement between the relationships; a second step of performing the second step while switching between the relationships between the state of charge and the internal resistance of the secondary battery for each different current-flow time in the relationship group that is the input information after the first step; determining the magnitude of a resistance component excluding the reaction resistance component and the diffusion resistance component of the secondary battery based on a comparison of the relationships; and obtaining the output information by using the determined resistance component as one of the parameters that represent the deterioration state of the electrodes and elements other than the electrodes.

2. 2. The secondary battery state diagnosis method according to claim 1, A method for diagnosing the state of a secondary battery, in which a group of relationships consisting of the relationship between the charge state and internal resistance of the secondary battery for each different current flow time is collected by changing the length of the current flow time when measuring the internal resistance to two or more different lengths.

3. 2. The secondary battery state diagnosis method according to claim 1, A secondary battery state diagnosis method, wherein the relationship between the state of charge of the secondary battery and the internal resistance for each different current-carrying time is calculated for the current-carrying time converted using a weighting function.

4. 2. The secondary battery state diagnosis method according to claim 1, A secondary battery state diagnosis method, wherein the internal resistance of the secondary battery is determined based on an open circuit voltage of the secondary battery and a closed circuit voltage of the secondary battery.

5. 2. The secondary battery state diagnosis method according to claim 1, A method for diagnosing the state of a secondary battery in which the open circuit potential of one of the positive electrode and the negative electrode is constant except near a fully charged state and near a fully discharged state.

6. 2. The secondary battery state diagnosis method according to claim 1, A secondary battery state diagnosis method that changes one or more of the upper and lower limit voltages during charging and discharging of the secondary battery, and the upper and lower limit currents during charging and discharging of the secondary battery, based on the output information.

7. A state diagnosis device for diagnosing a deterioration state of a secondary battery, comprising: data indicating the relationship between the state of charge of a secondary battery and an open circuit voltage, and data indicating a relationship group configured with the relationship between the state of charge of the secondary battery and the internal resistance for each different current-carrying time, as input information; data indicating the deterioration state of the secondary battery, data indicating the deterioration state of a positive electrode used in the secondary battery, and data indicating the deterioration state of a negative electrode used in the secondary battery as output information; a first step of evaluating the relationship between the state of charge and the open circuit voltage of the secondary battery based on a relationship between the state of charge and the open circuit potential of the positive electrode that is specific to the positive electrode material and a relationship between the state of charge and the open circuit potential of the negative electrode that is specific to the negative electrode material; a second step of evaluating a group of relationships formed by the relationships between the state of charge and the internal resistance of the secondary battery based on the relationships between the state of charge of the positive electrode and the internal resistance specific to the positive electrode material for each different current-flow time and the relationships between the state of charge of the negative electrode and the internal resistance specific to the negative electrode material for each different current-flow time; the first step is a step of correcting the relationship between the state of charge and the open circuit potential of the positive electrode and the relationship between the state of charge and the open circuit potential of the negative electrode by a parameter representing a degraded state of the electrode to assume a degraded state, generating a relationship between the state of charge and the open circuit voltage of the secondary battery assumed to be in a degraded state based on the corrected relationship between the state of charge and the open circuit potential of the positive electrode and the corrected relationship between the state of charge and the open circuit potential of the negative electrode, and comparing the relationship between the state of charge and the open circuit voltage of the secondary battery, which is the input information, with the relationship between the state of charge and the open circuit voltage of the secondary battery assumed to be in a degraded state to evaluate the agreement between the relationships; the second step is a step of correcting the relationship between the state of charge and the internal resistance of the positive electrode and the relationship between the state of charge and the internal resistance of the negative electrode with parameters representing the degradation states of the electrodes and elements other than the electrodes to assume a degradation state, generating a relationship between the state of charge and the internal resistance of the secondary battery assumed to be in a degradation state based on the corrected relationship between the state of charge and the internal resistance of the positive electrode and the corrected relationship between the state of charge and the internal resistance of the negative electrode, and comparing the relationship between the state of charge and the internal resistance of the secondary battery in the relationship group that is the input information with the relationship between the state of charge and the internal resistance of the secondary battery assumed to be in a degradation state to evaluate the agreement between the relationships; a secondary battery state diagnosis device that, after the first step, performs the second step while switching between the relationships between the state of charge and internal resistance of the secondary battery for each different current-flow time in the relationship group that is the input information, determines the magnitude of the resistance component excluding the reaction resistance component and diffusion resistance component of the secondary battery based on a comparison of the relationships, and obtains the output information by using the determined resistance component as one of the parameters that represent the deterioration state of the electrodes and elements other than the electrodes.

8. The secondary battery state diagnosis device according to claim 7, A secondary battery state diagnosis device comprising: a calculation unit that reads data indicating the relationship between the charge state and open circuit voltage of the secondary battery and data indicating a relationship group consisting of the relationship between the charge state and internal resistance of the secondary battery, and calculates data indicating the deterioration state of the secondary battery, data indicating the deterioration state of a positive electrode used in the secondary battery, and data indicating the deterioration state of a negative electrode used in the secondary battery.

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