Secondary battery state diagnostic method and state diagnostic device

Abstract

To provide a secondary battery state diagnosing method and a secondary battery state diagnosing device with which it is possible to diagnose the degradation state of a secondary battery with high accuracy, on the basis of information that can be acquirable with a simple operation.SOLUTION: The secondary battery state diagnosing method includes steps for: obtaining a calculation result that indicates a relationship between the charge state and the closed-circuit voltage of a secondary battery, on the basis of a relationship between the charge state and the open-circuit voltage of the secondary battery and a relationship between the charge state and the internal resistance of the secondary battery; and comparing a measurement result that indicates the relationship between the charge state and the closed-circuit voltage of the secondary battery with a calculation result that indicates the relationship between the charge state and the closed-circuit voltage of the secondary battery, the measurement result acquired by successively conducting measurement for each charge state of the secondary battery, in a charge process and a discharge process of the secondary battery. The secondary battery state diagnosing device comprises an acquisition unit for acquiring measured data that indicates the relationship between the charge state and the closed-circuit voltage of the secondary battery, a storage unit, and a computation unit. The measured data is inputted to the acquisition unit in the charge or discharge process of the secondary battery after being acquired by successively conducting measurement for each charge state of the secondary battery.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] It is known that secondary batteries such as lithium-ion batteries deteriorate in battery characteristics when repeatedly charged and discharged, when stored in a high-temperature environment, etc. As deterioration of a secondary battery progresses, a voltage drop and a capacity reduction occur. Therefore, the voltage and current are controlled according to the degree of deterioration of the secondary battery.

[0003] Conventionally, diagnosis of the state of health (SOH) has been performed to appropriately control secondary batteries. Deterioration of secondary batteries occurs due to irreversible reactions of the positive and negative electrodes, and alteration of elements other than the electrodes, such as electrolytes and current collectors. It is known that deterioration of secondary batteries is the result of individual deterioration of the electrodes and elements other than the electrodes. Since appropriate control according to the cause of deterioration is desired during the use of secondary batteries, a method for non-destructively diagnosing the deterioration state of secondary batteries is required.

[0004] Patent Document 1 describes a method for detecting internal information of a secondary battery. In this method, the state of the positive electrode and the state of the negative electrode are quantitatively evaluated nondestructively by using the charge / discharge curves of the positive electrode alone and the negative electrode alone. The charge / discharge curves of the positive electrode alone and the negative electrode alone are superimposed and calculated to reproduce the charge / discharge curve of the secondary battery.

[0005] Patent Document 2 describes an internal information detection device for a secondary battery. This device performs intermittent charging control so that the detected battery is intermittently charged by repeating charging at a fixed capacity and pausing charging. Information on the charging characteristics of the secondary battery, such as its voltage, is acquired during the process of intermittently charging the secondary battery. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2009-080093 A [Patent Document 2] International Publication No. 2014 / 147753 Summary of the Invention [Problem to be solved by the invention]

[0007] In diagnosing the deterioration state of a secondary battery, in Patent Document 1, the charge / discharge curve of the secondary battery is calculated based on the charge / discharge curve specific to the positive electrode material, the charge / discharge curve specific to the negative electrode material, and correction parameters, and then the charge / discharge curve of the secondary battery based on actual measurement is compared with the charge / discharge curve of the secondary battery based on measurement. However, the charge / discharge curve includes the relationship between the charge state such as the discharge amount and the potential and the potential change rate, and the influence of the voltage rise and voltage drop due to the internal resistance of the secondary battery. In the method using only the potential and the potential change rate as indicators, there is a problem that the accuracy of diagnosis is low when the change in internal resistance due to deterioration is large.

[0008] In Patent Document 2, intermittent charging is performed when obtaining information on the charging characteristics of the secondary battery to be diagnosed. However, the method of intermittent charging and discharging requires a charging and discharging device for charging and discharging under predetermined conditions, the task of removing the secondary battery from the circuit during use, or periodic switching. Since special equipment and tasks are required, it is not easy for the user of the secondary battery to obtain the information himself, and there is an issue that versatility is low. In addition, the method of intermittent charging and discharging takes time to obtain battery information.

[0009] Therefore, an object of the present invention is to provide a secondary battery status diagnosis method and a secondary battery status diagnosis device that can diagnose the deterioration state of a secondary battery with high accuracy based on information that can be obtained through simple operations. [Means for solving the problem]

[0010] In order to solve the above problems, a method for diagnosing a state of a secondary battery according to the present invention is a method for diagnosing a deterioration state of a secondary battery, comprising the steps of: determining a relationship between the state of charge of the secondary battery and the open circuit voltage corrected by the parameter representing the deterioration state, and a relationship between the state of charge of the secondary battery and the internal resistance corrected by the parameter representing the deterioration state; The relationship between the state of charge of the secondary battery and the open circuit voltage; The amended A step of obtaining a calculation result showing a relationship between the state of charge and the closed circuit voltage of the secondary battery based on the relationship between the state of charge and the internal resistance of the secondary battery, and a step of comparing a measurement result showing the relationship between the state of charge and the closed circuit voltage of the secondary battery with the calculation result showing the relationship between the state of charge and the closed circuit voltage of the secondary battery; identifying the parameter indicating a diagnosis result of the deterioration state of the secondary battery based on a result of the comparison; The measurement result indicating the relationship between the state of charge of the secondary battery and the closed circuit voltage is obtained by continuously measuring the secondary battery for each state of charge during a charging process or a discharging process of the secondary battery.

[0011] Further, a secondary battery state diagnostic device according to the present invention is a state diagnostic device for diagnosing a deterioration state of a secondary battery, comprising: an acquisition unit for acquiring measurement data indicating a relationship between a state of charge and a closed circuit voltage of the secondary battery; a memory unit for storing reference data indicating a relationship between a state of charge and an open circuit potential of a positive electrode that is specific to a positive electrode material, reference data indicating a relationship between a state of charge and an internal resistance of a positive electrode that is specific to a positive electrode material, reference data indicating a relationship between a state of charge and an open circuit potential of a negative electrode that is specific to a negative electrode material, and reference data indicating a relationship between a state of charge and an internal resistance of a negative electrode that is specific to a negative electrode material; and a correction unit for correcting the deterioration state using a parameter that indicates the deterioration state. a calculation unit that generates first calculated data indicating the relationship between the state of charge of the secondary battery and the open circuit voltage, and second calculated data indicating the relationship between the state of charge of the secondary battery and its internal resistance based on the reference data obtained, generates third calculated data indicating the relationship between the state of charge of the secondary battery and its closed circuit voltage based on the first calculated data and the second calculated data, and compares the measurement data with the third calculated data, wherein the measurement data is acquired by continuously measuring each state of charge of the secondary battery during the charging or discharging process of the secondary battery, and then inputs the measurement data to the acquisition unit. Effect of the Invention

[0012] According to the present invention, it is possible to provide a secondary battery state diagnosis method and a secondary battery state diagnosis device that can diagnose the deterioration state of a secondary battery with high accuracy based on information that can be obtained by simple operations. [Brief description of the drawings]

[0013] [Figure 1] 1 is a diagram showing a configuration of a secondary battery state diagnosis device according to an embodiment of the present invention; [Diagram 2] 4 is a flowchart showing a process for diagnosing a deterioration state of a secondary battery. [Diagram 3] FIG. 4 is a diagram showing an example of the relationship between the charged state of an electrode and the open circuit potential. [Figure 4] FIG. 4 is a diagram showing an example of the relationship between the charged state of an electrode and the open circuit potential. [Diagram 5] FIG. 4 is a diagram showing an example of the relationship between the charged state and the internal resistance of an electrode. [Figure 6] FIG. 4 is a diagram showing an example of the relationship between the charged state and the internal resistance of an electrode. [Figure 7] FIG. 4 is a diagram showing an example of the relationship between the state of charge and the open circuit potential of a secondary battery. [Figure 8] FIG. 4 is a diagram showing an example of the relationship between the state of charge and the internal resistance of a secondary battery. [Figure 9] FIG. 4 is a diagram showing an example of the relationship between the state of charge of a secondary battery and a closed circuit potential. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, a method and an apparatus for diagnosing a state of a secondary battery according to an embodiment of the present invention will be described. Note that the same reference numerals are used to designate the same components in the following drawings, and duplicated explanations will be omitted.

[0015] The secondary battery state diagnosis method according to the present embodiment relates to a method for diagnosing the deterioration state of a secondary battery. Examples of the secondary battery to be diagnosed include a lithium ion secondary battery, a sodium ion secondary battery, a magnesium ion secondary battery, a calcium ion secondary battery, a zinc secondary battery, an aluminum ion secondary battery, a nickel-metal hydride secondary battery, a lead secondary battery, etc. As the secondary battery to be diagnosed, a lithium ion secondary battery is particularly preferable.

[0016] In the secondary battery state diagnosis method according to the present embodiment, the relationship between the charge state and closed circuit voltage (CCV) of the secondary battery is used as information for diagnosing the deterioration state of the secondary battery to be diagnosed. Based on the measurement of the closed circuit voltage for each charge state of the secondary battery, the deterioration state of the secondary battery and the deterioration state of each electrode of the secondary battery can be diagnosed individually and non-destructively.

[0017] In the method for diagnosing the state of a secondary battery according to the present embodiment, the closed circuit voltage for each state of charge of the secondary battery to be diagnosed is continuously measured during the charging or discharging process of the secondary battery without switching between charging and discharging in between. The closed circuit voltage of the secondary battery is continuously measured with measurement intervals as necessary during the continuous charging or discharging process so as to include measurement results in different states of charge.

[0018] The relationship between the state of charge and the closed circuit voltage of the secondary battery can be calculated based on the relationship between the state of charge and the open circuit voltage (OCV) of the secondary battery and the relationship between the state of charge and the internal resistance of the secondary battery. The relationship between the state of charge and the open circuit voltage of the secondary battery can be calculated based on the relationship between the state of charge and the open circuit voltage 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 internal resistance of the secondary battery can be calculated based on the relationship between the state of charge and the internal resistance of the positive electrode, the relationship between the state of charge and the internal resistance of the negative electrode, and the resistance of elements other than the electrodes.

[0019] Therefore, in the method for diagnosing the state of a secondary battery according to the present embodiment, the relationship between the state of charge and the open circuit voltage for each electrode and the relationship between the state of charge and the internal resistance for each electrode are prepared in advance as reference information. These relationships are corrected by a deterioration state parameter that represents the deterioration state of elements other than the positive electrode, negative electrode, and electrodes. By combining relationships corrected by the deterioration state parameter, the relationship between the state of charge and the closed circuit voltage of a secondary battery assumed to be in a deteriorated state can be reproduced by calculation.

[0020] Therefore, by comparing the measurement result based on the actual measurement with the calculation result in which the deterioration state based on the reproduction is assumed, the actual deterioration state can be estimated based on the agreement between the measurement result and the calculation result. Based on the agreement between the measurement result and the calculation result, the deterioration state parameter set hypothetically is approximated toward the true value. Since the deterioration state parameter represents the degree of deterioration of elements other than the positive electrode, the negative electrode, and the electrodes, by finding a solution for the deterioration state parameter, the deterioration state of the secondary battery and the deterioration state of each electrode of the secondary battery can be evaluated.

[0021] Conventionally, a method is known for collecting information on a secondary battery to be diagnosed by intermittently charging and discharging. However, in the method of intermittently charging and discharging, it is necessary to repeatedly measure the voltage at a given state of charge while changing the state of charge of the secondary battery. In the conventional method, in order to collect information for each of a large number of discrete states of charge, it is necessary to repeat charging and discharging with a small current and pausing for electrochemical relaxation at each measurement point.

[0022] Such conventional methods require charging / discharging equipment and charging / discharging procedures to charge / discharge under specified conditions. In addition, since existing circuits in which secondary batteries are used often cannot be used, the secondary battery must be removed from the circuit when in use. In addition, methods that charge / discharge intermittently take time to collect battery information. Methods that collect information on secondary batteries to be diagnosed by intermittent charging / discharging require special equipment and procedures, and have the problem of requiring effort, skill, and measurement time.

[0023] In contrast, in the secondary battery state diagnosis method according to the present embodiment, the closed circuit voltage of the secondary battery to be diagnosed is continuously measured during the charging or discharging process and used for diagnosis. Therefore, the information on the secondary battery required for diagnosis can be collected with a simple operation. For example, it is possible to measure the closed circuit voltage for each charging state of the secondary battery on an existing circuit equipped with a voltmeter and an ammeter. Since no special equipment or operation is required, and no effort or skill is required, the deterioration state of the secondary battery to be diagnosed can be diagnosed non-destructively and with high accuracy based on information that can be obtained with a simple operation.

[0024] In this specification, the state of charge means an electrochemical state determined by the ratio of the amount of dischargeable electricity to the amount of electricity that can be discharged from a fully charged state. The state of charge can be expressed by an appropriate state quantity that can be converted between them, such as the state of charge (SOC) [%], where the fully charged state is 100% and the fully discharged state is 0%, the depth of charge (DOD) where the fully charged state is 0% and the fully discharged state is 100%, 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.

[0025] FIG. 1 is a diagram showing the configuration of a secondary battery state diagnosis device according to this embodiment. 1, the secondary battery state diagnostic device 100 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. The calculation unit 10, the storage unit 20, the input unit 30, the output unit 40, and the communication unit 50 of the state diagnostic device 100 are connected to a bus.

[0026] The condition diagnosis device 100 is a device that diagnoses the degradation state of a secondary battery, and can be configured by hardware such as a computer. The condition diagnosis device 100 executes a process for diagnosing the degradation state of a secondary battery in accordance with a predetermined program.

[0027] The condition diagnosis device 100 receives measurement data indicating the results of actual measurement, executes a predetermined program, and outputs diagnostic data indicating the results of diagnosing the deterioration state of the secondary battery. In the process of diagnosing the deterioration state of the secondary battery, calculation data for comparison with the measurement data is generated by referring to previously prepared reference data indicating electrode characteristics.

[0028] The calculation unit 10 reads various data and programs, executes the programs, calculates the state of the secondary battery, etc. The calculation unit 10 is configured by a calculation device such as a CPU (Central Processing Unit), for example.

[0029] The storage unit 20 stores various data and programs. The storage unit 20 is configured with storage devices such as a RAM (Random Access Memory) and a ROM (Read Only Memory). The various data and programs may be stored in a writable and readable hard disk, a flash memory, a magnetic disk, an optical disk, or the like.

[0030] The input unit 30 is a device that accepts input from an operator. The input unit 30 is configured with, for example, a keyboard, a mouse, a touch panel, etc. The input unit 30 can be connected via an input interface (not shown).

[0031] The output unit 40 is a device that outputs operation information, various data contents, diagnostic conditions, diagnostic results, etc. of the condition diagnostic device 100. The output unit 40 is configured, for example, with 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).

[0032] The communication unit 50 transmits and receives various data and control signals to and from external measuring devices, electric communication lines, etc. The communication unit 50 can be connected via a communication interface, an input / output interface, etc. (not shown).

[0033] Communication unit 50 may acquire measurement data of the secondary battery to be diagnosed from an external measuring device such as a voltmeter or ammeter, or may acquire the data via an electric communication line from a terminal at the source of use of the secondary battery, a terminal at a service center that maintains the secondary battery, etc. At the source of use of the secondary battery or at the service center, measurement data can be collected from the secondary battery to be diagnosed and input to a terminal, etc., and transmitted to condition diagnosis device 100 in response to a request to diagnose the deterioration state of the secondary battery.

[0034] FIG. 2 is a flowchart showing the process of diagnosing the deterioration state of the secondary battery. As shown in Figure 2, in the process of diagnosing the deterioration state of a secondary battery, reference data showing the relationship between the state of charge and the open circuit voltage for each electrode and reference data showing the relationship between the state of charge and the internal resistance for each electrode are read, deterioration state parameters are set, and calculation data showing the relationship between the state of charge and the closed circuit voltage of a secondary battery assumed to be in a deteriorated state is generated. Then, the measurement data based on actual measurement and the calculation data based on reproduction are compared to determine whether the data match each other.

[0035] The measurement data is data of the measurement result showing the relationship between the state of charge of the secondary battery and the closed circuit voltage. The measurement data is collected by continuously measuring the closed circuit voltage for each state of charge of the secondary battery to be diagnosed during the charging or discharging process of the secondary battery. After being collected by actual measurement, the measurement data is input to an acquisition unit that acquires the measurement data of the condition diagnosis device 100 and stored in the memory unit 120. The acquisition unit may acquire the measurement data via the communication unit 50, or via the input unit 30 or a storage medium. The measurement data may be expressed as a relational expression or a data table.

[0036] The measurement data is obtained by continuously measuring the closed circuit voltage for each charge state of the secondary battery during the charging process toward the fully charged state of the secondary battery to be diagnosed or during the discharging process toward the fully discharged state, without switching between charge and discharge in between. The measurement of the closed circuit voltage may be performed with a time interval between the measurement points, as long as there is no switching between charge and discharge between the measurement points.

[0037] The closed circuit voltage is preferably measured during a charging process in which the battery is charged with a low rate charging current, or during a discharging process in which the battery is discharged with a low rate discharging current. The charge / discharge current during the measurement is preferably 0.3 C or less, more preferably 0.2 C or less, and even more preferably 0.1 C or less. The charge / discharge current during the measurement is preferably 0.01 C or more. The charge / discharge current during the measurement may be a constant current or a variable current.

[0038] If the charge / discharge current during measurement is low, the effect of resistance components due to large current and the effect of degradation due to large current are small, so the relationship between the charge state of the secondary battery and the closed circuit voltage can be accurately obtained. Also, if the charge / discharge current during measurement is 0.01C or more, the time required to collect battery information is shortened.

[0039] The closed circuit voltage can be measured over any range of charge states as long as sufficient measurement data for diagnosis can be obtained. It is most desirable to obtain measurement data over the entire range from SOC 100% (fully charged state) to SOC 0% (fully discharged state), but it can also be measured over a partial range such as SOC 80-20%, SOC 100-50%, or SOC 50-0%.

[0040] The closed circuit voltage may be measured, for example, during a charging process of a secondary battery in use from a current charged state to a fully charged state, or during a discharging process of a secondary battery in use from a current charged state to a fully discharged state. Also, the closed circuit voltage may be measured during a charging process in the next charge / discharge cycle of the secondary battery in use, or during a discharging process in the next charge / discharge cycle. However, from the viewpoint of performing an accurate diagnosis, it is preferable that the measurement data be collected during one continuous charging process or one continuous discharging process.

[0041] The closed circuit voltage is preferably measured for a plurality of different charging states. The number of measurement points for measuring the closed circuit voltage is preferably two or more, more preferably five or more, and even more preferably ten or more. With a large number of measurement points, a precise comparison between the measured data and the calculated data can be made, improving the accuracy of the diagnosis of the deterioration state.

[0042] 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 charging state 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.

[0043] The reference data are prepared in advance in the condition diagnosis device 100, and include reference data showing the relationship between the charge state of the positive electrode and the open circuit potential, which is specific to the positive electrode material, reference data showing the relationship between the charge state of the positive electrode and the internal resistance, which is specific to the positive electrode material, reference data showing the relationship between the charge state of the negative electrode and the open circuit potential, which is specific to the negative electrode material, and reference data showing the relationship between the charge state of the negative electrode and the internal resistance, which is specific to the negative electrode material.

[0044] FIG. 3 is a diagram showing an example of the relationship between the charged state of an electrode and the open circuit potential. Figure 3 corresponds to the reference data for the positive electrode. The horizontal axis shows the discharge amount qp [Ah / g] from a fully charged state per unit mass of the positive electrode active material as an example of the charged state of the electrode. The vertical axis shows the open circuit potential Vp [V] of the positive electrode relative to the reference electrode.

[0045] FIG. 4 is a diagram showing an example of the relationship between the charged state of an electrode and the open circuit potential. Figure 4 corresponds to the reference data for the negative electrode. 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 charged state of the electrode. The vertical axis shows the open circuit potential Vn [V] of the negative electrode relative to the reference electrode.

[0046] As shown in Figures 3 and 4, the relationship between the state of charge of an electrode and the open circuit potential is a relationship specific to the active material used as the material of the electrode. It is preferable to prepare reference data showing such a relationship between the state of charge and the open circuit potential as a relational expression or a data table for each electrode, that is, the positive electrode and the negative electrode, and for each active material used in the electrode. By preparing reference data for a plurality of types of active materials, even if the type of active material used in the secondary battery to be diagnosed is unknown, the deterioration state of the secondary battery can be properly diagnosed by converging the calculation while replacing the reference data.

[0047] As shown in Figure 3, the curve of the state of charge of the electrode vs. the open circuit potential may have a plateau region in which the open circuit potential does not substantially change with the change in the state of charge of the electrode. The curve shown in Figure 3 is obtained, for example, when LiFePO4 is used. On the other hand, as shown in Figure 4, the curve of the state of charge of the electrode vs. the open circuit potential may have a change in the open circuit potential with the change in the state of charge of the electrode.

[0048] As shown in Figures 3 and 4, when an active material whose open circuit potential does not substantially change with respect to the change in the state of charge of the electrode is used, the deterioration state of the electrode is difficult to be reflected in the electrode potential. Although the curve shifts up or down due to the deterioration of the electrode, the amount of shift is small relative to the change in the state of charge. Therefore, it is difficult to perform a highly accurate diagnosis based only on the relationship between the state of charge of the electrode and the open circuit potential.

[0049] FIG. 5 is a diagram showing an example of the relationship between the charged state and the internal resistance of an electrode. Figure 5 corresponds to the reference data for the positive electrode. The horizontal axis shows the discharge amount qp [Ah / g] from a fully charged state per unit mass of the positive electrode active material as an example of the charged state of the electrode. The vertical axis shows the internal resistance rp [mΩ·g] of the positive electrode active material. Figure 5 shows data for a positive electrode using the same type of active material as Figure 3.

[0050] FIG. 6 is a diagram showing an example of the relationship between the charged state and the internal resistance of an electrode. Figure 6 corresponds to the reference data for the negative electrode. 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 charged state of the electrode. The vertical axis shows the internal resistance rn [mΩ·g] of the negative electrode active material. Figure 6 shows data for a negative electrode using the same type of active material as Figure 4.

[0051] As shown in Figures 5 and 6, the relationship between the state of charge of an electrode and the internal resistance is a relationship specific to the active material used as the material of the electrode. It is preferable to prepare reference data showing such a relationship between the state of charge and the internal resistance as a relational expression or a data table for each electrode (positive electrode and negative electrode) and for each active material used in the electrode. By preparing reference data for a plurality of types of active materials, even if the type of active material used in the secondary battery to be diagnosed is unknown, the deterioration state of the secondary battery can be properly diagnosed by converging the calculation while replacing the reference data.

[0052] As shown in Figure 5, the curve of the state of charge of the electrode versus the internal resistance often fluctuates with changes in the state of charge of the electrode, even when an active material having a plateau region in which the open circuit potential does not substantially change with changes in the state of charge of the electrode is used. On the other hand, as shown in Figure 6, the curve of the state of charge of the electrode versus the internal resistance has a characteristic point near 0.18 Ah / g. The characteristic point near 0.18 Ah / g also appears in the curve of the state of charge versus the open circuit potential shown in Figure 4.

[0053] As shown in Figures 5 and 6, the internal resistance often fluctuates with the change in the state of charge of the electrode. By referring to the relationship between the state of charge of the electrode and the internal resistance in addition to the relationship between the state of charge of the electrode and the open circuit potential, the relationship between the state of charge of the secondary battery and the closed circuit voltage can be accurately reproduced by calculation, taking into account the resistance increase behavior specific to the electrode material, unlike the case where it is based only on the relationship between the state of charge and the open circuit potential. Therefore, the deterioration state of the secondary battery can be diagnosed with high accuracy based on the information of the closed circuit voltage, which can be obtained by simple operations.

[0054] As the reference data, for example, data of 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 of the electrode in the initial state can be collected during about the first to fifth charge and discharge processes. Since an irreversible reaction may occur on the electrode during the first charge and discharge process, it is preferable to collect data during about the second to fifth charge and discharge processes.

[0055] The measurement data and the reference data may be obtained during a charging process or during a discharging process. However, in general, there is hysteresis between the behavior during the charging process and the behavior during the discharging process. Therefore, it is preferable to use data obtained during a common charging and discharging process as the measurement data and the reference data for the same diagnosis.

[0056] The measurement data and the reference data may be data showing the relationship between the state of charge and the voltage value, data showing the relationship between the state of charge and the internal resistance value, data showing the relationship between the state of charge and the differential value of the voltage, or data showing the relationship between the state of charge and the differential value of the internal resistance. When the differential value of the voltage is used, a relationship that is inversely proportional to the amount of active material used can be obtained, so that the accuracy of the amount of active material used can be ensured.

[0057] 2, first, the calculation unit 10 reads measurement data indicating the relationship between the state of charge and the closed circuit voltage of the secondary battery to be diagnosed from the storage unit 20 (step S1). As the measurement data, data of a predetermined diagnosis target can be selected in response to a request to diagnose the deterioration state of the secondary battery.

[0058] Next, the calculation unit 10 reads from the memory unit 20 reference data indicating the relationship between the charge state 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 charge state of the negative electrode and the open circuit potential, which is specific to the negative electrode material (step S2).

[0059] For example, the calculation unit 10 can read from the memory unit 20 data on the discharge amount qp per unit mass of the positive electrode from a fully charged state and data on the open circuit potential OCVp of the positive electrode corresponding to the discharge amount qp, or data on the charge amount qp per unit mass of the positive electrode from a fully discharged state and data on the open circuit potential OCVp of the positive electrode corresponding to the charge amount qp, as reference data indicating the relationship between the charge state of the positive electrode specific to the positive electrode material and the open circuit potential.

[0060] In addition, the calculation unit 10 can read from the memory unit 20 data on the discharge amount qn per unit mass of the negative electrode from a fully charged state and data on the open circuit potential OCVn of the negative electrode corresponding to the discharge amount qn, or data on the charge amount qn per unit mass of the negative electrode from a fully discharged state and data on the open circuit potential OCVn of the negative electrode corresponding to the charge amount qn, as reference data showing the relationship between the charge state of the negative electrode specific to the negative electrode material and the open circuit potential.

[0061] Next, the calculation unit 10 reads from the memory unit 20 reference data indicating the relationship between the charge state and internal resistance of the positive electrode, which is specific to the positive electrode material, and reference data indicating the relationship between the charge state and internal resistance of the negative electrode, which is specific to the negative electrode material (step S3).

[0062] For example, the calculation unit 10 can read from the memory unit 20 data on the discharge amount qp per unit mass of the positive electrode from a fully charged state and data on the internal resistance Rp of the positive electrode corresponding to the discharge amount qp, or data on the charge amount qp per unit mass of the positive electrode from a fully discharged state and data on the internal resistance Rp of the positive electrode corresponding to the charge amount qp, as reference data indicating the relationship between the charge state and internal resistance of the positive electrode specific to the positive electrode material.

[0063] In addition, the calculation unit 10 can read from the memory unit 20 data on the discharge amount qn per unit mass of the negative electrode from a fully charged state and data on the internal resistance Rn of the negative electrode corresponding to the discharge amount qn, or data on the charge amount qn per unit mass of the negative electrode from a fully discharged state and data on the internal resistance Rn of the negative electrode corresponding to the charge amount qn, as reference data showing the relationship between the charge state and internal resistance of the negative electrode specific to the negative electrode material.

[0064] The order of execution of steps S1, S2, and S3 is not particularly limited. In steps S2 and S3, the reference data may be selected from the reference database according to the measurement data loaded in step S1. Alternatively, the measurement data for each diagnosis request may be selected from the measurement database according to the loaded reference data.

[0065] The reference data can also be selected from a reference database based on information associated with the measurement data, for example, information on the type of active material used in the secondary battery to be diagnosed, information on the upper and lower limit voltages of the secondary battery to be diagnosed, etc. The measurement database can also be formed by collecting measurement data from various secondary batteries to be diagnosed.

[0066] In steps S2 and S3, it is preferable to read data of an electrode using the same type of active material as the secondary battery to be diagnosed as the reference data. However, if the type of active material used in the secondary battery to be diagnosed is unknown, data of any electrode can be read. Even if the type of active material is unknown, the deterioration state of the secondary battery can be properly diagnosed by converging the subsequent calculations while replacing the reference data.

[0067] Next, the calculation unit 10 sets deterioration state parameters that represent the deterioration states of the electrodes and elements other than the electrodes, with respect to the relationship indicated by the reference data (step S4).

[0068] Specifically, the calculation unit 10 performs a process of correcting the relationships indicated by the reference data, i.e., the relationship between the charge state of the positive electrode and the open circuit potential that is specific to the positive electrode material, the relationship between the charge state of the positive electrode and the internal resistance that is specific to the positive electrode material, the relationship between the charge state of the negative electrode and the open circuit potential that is specific to the negative electrode material, and the relationship between the charge state of the negative electrode and the internal resistance that is specific to the negative electrode material, using deterioration state parameters set to arbitrary values.

[0069] The deterioration state parameters are parameters that quantitatively 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. As the deterioration state parameters, individual parameters are set for each of the positive electrode, the negative electrode, and elements other than the electrodes. The deterioration state parameters are defined between a predetermined upper limit value and a predetermined lower limit value that correspond to no deterioration or complete deterioration.

[0070] By correcting the relationship shown by the reference data with the degradation state parameters, it is possible to generate calculation data showing the relationship between the state of charge and the open circuit voltage of a secondary battery assumed to be in a predetermined degradation state, and calculation data showing the relationship between the state of charge and the internal resistance of a secondary battery assumed to be in a predetermined degradation state. From these calculation data, calculation data showing the relationship between the state of charge and the closed circuit voltage of the secondary battery is generated, and fitting to the measurement data provides a solution for the degradation state parameters that are approximated to the true value.

[0071] As the deterioration state parameters, it is preferable to set a plurality of parameters corresponding to the electrodes and elements other than the electrodes that cause deterioration. As the deterioration state parameters, a deterioration state parameter related to the capacitance and a deterioration state parameter related to the resistance can be set.

[0072] As the deterioration state parameters related to the capacity, the coefficients and constants of the state quantities representing the state of charge can be set in the function showing the relationship between the state of charge and the open circuit potential, or in the function showing the relationship between the state of charge and the internal resistance. For example, for the positive electrode, the amount of positive electrode active material used mp, the positive electrode side position shift δp, etc. can be set. For the negative electrode, the amount of negative electrode active material used mn, the negative electrode side position shift δn, etc. can be set.

[0073] The amount of positive electrode active material used mp represents the amount of positive electrode active material used in the charge / discharge reaction among the positive electrode active material contained in the positive electrode. The amount of positive electrode active material used mp [g] satisfies mp = mp0 × mpr, where mp0 [g] is the amount of positive electrode active material contained in the positive electrode and mpr is the proportion of positive electrode active material used in the charge / discharge reaction.

[0074] The positive electrode side positional deviation δp means the deviation of the curve along the capacity axis due to the deterioration of the positive electrode on the voltage-capacity curve of the positive electrode. The positive electrode side positional deviation δp corresponds to the decrease in the capacity of the positive electrode due to the deterioration of the positive electrode. The positive electrode side positional deviation δp corresponds to the capacity of the positive electrode that can only be obtained on the higher potential side than the upper limit of the operating voltage range of the secondary battery.

[0075] The capacity of the positive electrode Qp [Ah] is expressed as Qp = qp × mp, where mp [g] is the amount of positive electrode active material used in the charge / discharge reaction, and qp [Ah / g] is the capacity per unit mass of the positive electrode. If we assume that the positive electrode is degraded by a positional shift δp, the capacity of the positive electrode Qp [Ah] can be expressed by the following formula (1). Qp = qp × mp - δp (1)

[0076] The amount of negative electrode active material used mn represents the amount of the negative electrode active material contained in the negative electrode that is used in the charge / discharge reaction. The amount of negative electrode active material used mn [g] satisfies mn = mn0 × mnr, where mn0 [g] is the amount of negative electrode active material contained in the negative electrode and mnr is the proportion of the negative electrode active material used in the charge / discharge reaction.

[0077] The negative electrode side positional deviation δn means the deviation of the curve along the capacity axis due to the deterioration of the negative electrode on the voltage-capacity curve of the negative electrode. The negative electrode side positional deviation δn corresponds to the decrease in the capacity of the negative electrode due to the deterioration of the negative electrode. The negative electrode side positional deviation δn corresponds to the capacity of the negative electrode that can only be obtained at a lower potential side than the lower limit of the operating voltage range of the secondary battery.

[0078] The capacity of the negative electrode, Qn [Ah], is expressed as Qn = qn × mn, where mn [g] is the amount of negative electrode active material used in the charge / discharge reaction, and qn [Ah / g] is the capacity per unit mass of the negative electrode. If we assume that deterioration occurs due to a negative electrode position shift δn, the capacity of the negative electrode, Qn [Ah], can be expressed by the following formula (2). Qn = qn × mn - δn (2)

[0079] As the deterioration state parameters related to resistance, in the function showing the relationship between the state of charge and the internal resistance, the coefficient of the resistance term corresponding to the internal resistance of each electrode that depends on the state of charge, and the constant corresponding to the resistance of elements other than the electrodes that does not depend on the state of charge can be set. For example, for the internal resistance of the positive electrode, the positive electrode resistance coefficient ap can be set, and for the internal resistance of the negative electrode, the negative electrode resistance coefficient an can be set. For the resistance of elements other than the electrodes, the resistance constant Ro can be set.

[0080] Assuming degradation of the positive electrode resistance coefficient ap, the internal resistance Rp [Ω] of the positive electrode in the state of charge x can be expressed by the following equation (3), where the amount of positive electrode active material used in the charge / discharge reaction is mp [g] and the internal resistance of the positive electrode active material in the state of charge x is rp(x) [Ω g]. Rp(Qp) = ap / mp × rp(qp) (3)

[0081] Assuming degradation of the negative electrode resistance coefficient an, the negative electrode internal resistance Rp [Ω] in the state of charge x can be expressed by the following equation (4), where the amount of negative electrode active material used in the charge / discharge reaction is mn [g] and the negative electrode active material internal resistance in the state of charge x is rn(x) [Ω g]. Rn(Qn) = an / mn × rn(qn) (4)

[0082] The deterioration state parameter can be defined as any value at any interval between a predetermined upper limit value and a predetermined lower limit value corresponding to no deterioration or complete deterioration. The deterioration state parameter is preferably normalized according to the relational expression to be corrected. The deterioration state parameter can be prepared as a parameter table in association with data indicating the state of health (SOH) [%]. Using such a table makes it possible to set deterioration state parameters corresponding to the same state of health (SOH) [%].

[0083] In step S4, the deterioration state parameter can be set to any value between a predetermined upper limit and lower limit, assuming the deterioration state of the positive electrode, the deterioration state of the negative electrode, and the deterioration state of elements other than the electrodes. If any value is set and the subsequent calculations are allowed to converge, a solution for the deterioration state parameter that is approximated to the true value is obtained. If the subsequent calculations do not converge, the deterioration state parameter is updated to an unset value and recalculated.

[0084] Specifically, the calculation unit 10 performs a process of calculating an OCV (qp×mp-δp) corrected with a deterioration state parameter from data of the open circuit potential OCVp (Qp) of the positive electrode for each state of charge based on reference data showing the relationship between the state of charge and the open circuit potential of the positive electrode specific to the positive electrode material. Similarly, the calculation unit 10 performs a process of calculating an OCV (qn×mn-δn) corrected with a deterioration state parameter from data of the open circuit potential OCVn (Qn) of the negative electrode for each state of charge based on reference data showing the relationship between the state of charge and the open circuit potential of the negative electrode specific to the negative electrode material.

[0085] The calculation unit 10 also performs a process of calculating ap / mp×rp(qp) corrected with the degradation state parameter from data on the positive electrode internal resistance Rp(Qp) for each state of charge based on reference data showing the relationship between the positive electrode's state of charge and internal resistance specific to the positive electrode material. Similarly, the calculation unit 10 performs a process of calculating an / mn×rn(qn) corrected with the degradation state parameter from data on the negative electrode internal resistance Rn(Qn) for each state of charge based on reference data showing the relationship between the negative electrode's state of charge and internal resistance specific to the negative electrode material.

[0086] Next, the calculation unit 10 generates calculation data (first calculation data) indicating 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 positive electrode corrected by the deterioration state parameter and the open circuit potential, and the relationship between the state of charge of the negative electrode corrected by the deterioration state parameter and the open circuit potential (step S5).

[0087] The calculated data indicating the relationship between the charge state of the secondary battery and the open circuit voltage is used to generate the calculated data indicating the relationship between the charge state of the secondary battery and the closed circuit voltage. The calculated data indicating the relationship between the charge state of the secondary battery and the open circuit voltage can be generated by calculation and then stored in the storage unit 120. The calculated data indicating the relationship between the charge state of the secondary battery and the open circuit voltage may be expressed by a relational equation or a data table.

[0088] The open circuit potential OCVc(x) [V] of a secondary battery in the state of charge x can be calculated by the following formula (5) where Qc = Qp + δp = Qn + δn, where OCVp(x) [V] is the open circuit potential of the positive electrode in the state of charge x, OCVn(x) [V] is the open circuit potential of the negative electrode in the state of charge x, Qc [Ah] is the discharge capacity of the secondary battery from the fully charged state, Qp [Ah] is the discharge capacity of the positive electrode from the fully charged state, and Qn [Ah] is the discharge capacity of the negative electrode from the fully charged state. OCVc(Qc)=OCVp(Qp)-OCVn(Qn)...(5)

[0089] FIG. 7 is a diagram showing an example of the relationship between the state of charge and the open circuit potential of a secondary battery. 7, the horizontal axis indicates the discharge amount [Ah / g] from a fully charged state per unit mass of active material as an example of the state of charge of a secondary battery. The vertical axis indicates potential [V]. The dashed and dotted line indicates the open circuit potential OCVp of the positive electrode, the solid line indicates the open circuit potential OCVc of the secondary battery, and the dashed line indicates the open circuit potential OCVn of the negative electrode.

[0090] As shown in Fig. 7, the relationship between the state of charge and the open circuit potential of a secondary battery is obtained by combining 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. Calculation data showing such a relationship between the state of charge and the open circuit potential is generated from reference data corrected with the deterioration state parameters, and stored as a relational expression or a data table.

[0091] Next, the calculation unit 10 generates calculation data (second calculation data) indicating the relationship between the charge state and internal resistance of the secondary battery based on the relationship between the charge state and internal resistance of the positive electrode corrected by the correction parameter and the relationship between the charge state and internal resistance of the negative electrode corrected by the correction parameter (step S6).

[0092] The calculated data indicating the relationship between the charge state and the internal resistance of the secondary battery is used to generate the calculated data indicating the relationship between the charge state and the closed circuit voltage of the secondary battery. The calculated data indicating the relationship between the charge state and the internal resistance of the secondary battery can be generated by calculation and then stored in the storage unit 120. The calculated data indicating the relationship between the charge state and the internal resistance of the secondary battery may be represented by a relational equation or a data table.

[0093] The internal resistance Rc(x) [Ω] of a secondary battery in the state of charge x can be calculated by the following equation (6) where Qc = Qp + δp = Qn + δn, where Rp(x) [Ω] is the internal resistance of the positive electrode in the state of charge x, Rn(x) [Ω] is the internal resistance of the negative electrode in the state of charge x, Ro [Ω] is the resistance of elements other than the electrodes, Qc [Ah] is the discharge capacity of the secondary battery from the fully charged state, Qp [Ah] is the discharge capacity of the positive electrode from the fully charged state, and Qn [Ah] is the discharge capacity of the negative electrode from the fully charged state. Rc(Qc)=Ro+Rp(Qp)+Rn(Qn)...(6)

[0094] FIG. 8 is a diagram showing an example of the relationship between the state of charge and the internal resistance of a secondary battery. In Fig. 8, the horizontal axis indicates the discharge amount [Ah / g] from a fully charged state per unit mass of active material as an example of the charged state of a secondary battery. The vertical axis indicates DC internal resistance [mΩ]. The solid line indicates the internal resistance Rc of the secondary battery, the dashed line indicates the internal resistance Rp of the positive electrode, and the dashed line indicates the internal resistance Rn of the negative electrode.

[0095] As shown in Figure 8, the relationship between the state of charge and the internal resistance of a secondary battery is obtained by combining the relationship between the state of charge and the internal resistance of the positive electrode, which depends on the state of charge, the relationship between the state of charge and the internal resistance of the negative electrode, which depends on the state of charge, and the resistance of elements other than the electrodes, which does not depend on the state of charge, but since it strongly depends on the individual deterioration states of the electrodes and elements other than the electrodes, appropriate selection of reference data is required. Calculation data showing such a relationship between the state of charge and the internal resistance is generated from reference data corrected with deterioration state parameters, and stored as a relational expression or a data table.

[0096] If the internal resistance of the secondary battery in the reference data used as the basic data is 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 does not depend on the state of charge, the deterioration state of each electrode, which has a different degree of deterioration, can be accurately reproduced by calculation, making it possible to evaluate the deterioration state of each electrode of the secondary battery with high accuracy.

[0097] Next, the calculation unit 10 generates calculation data (third calculation data) indicating the relationship between the charge state of the secondary battery and the closed circuit voltage based on the calculation data indicating the relationship between the charge state of the secondary battery and the open circuit voltage and the calculation data indicating the relationship between the charge state of the secondary battery and the internal resistance (step S7).

[0098] The calculated data indicating the relationship between the charge state of the secondary battery and the closed circuit voltage is used for comparison with the measured data indicating the relationship between the charge state of the secondary battery and the closed circuit voltage. The calculated data indicating the relationship between the charge state of the secondary battery and the closed circuit voltage can be generated by calculation and then stored in the storage unit 120. The calculated data indicating the relationship between the charge state of the secondary battery and the closed circuit voltage may be expressed by a relational equation or a data table.

[0099] The closed circuit potential CCVc(x) [V] of a secondary battery in the state of charge x can be calculated using the following equations (7) to (9), where the closed circuit potential of the positive electrode in the state of charge x is CCVp(x) [V], the closed circuit potential of the negative electrode in the state of charge x is CCVn(x) [V], and the discharge amount of the secondary battery from the fully charged state is I [A]. CCVc(Qc)=CCVp(Qp)-CCVn(Qn)-I×Rc (7) CCVp(Qp)=OCVp(Qp)-I×Rp(Qp)...(8) CCVn(Qn)=OCVn(Qn)-I×Rn(Qn)...(9)

[0100] FIG. 9 is a diagram showing an example of the relationship between the state of charge of a secondary battery and the closed circuit potential. In FIG. 9, the horizontal axis indicates the discharge amount [Ah / g] from a fully charged state per unit mass of active material, as an example of the state of charge of a secondary battery. The vertical axis indicates potential [V]. The thick solid line indicates the open circuit potential OCVp of the positive electrode, the center solid line indicates the open circuit voltage OCVc of the secondary battery, the thick dashed line indicates the closed circuit potential CCVp of the positive electrode, the center solid line indicates the closed circuit voltage CCVc of the secondary battery, the thin solid line indicates the open circuit potential OCVn of the negative electrode, and the thin dashed line indicates the closed circuit potential CCVn of the negative electrode. The plots show measurement data based on actual measurements.

[0101] As shown in FIG. 9, the relationship between the state of charge of the secondary battery and the closed circuit voltage is obtained by combining the relationship between the state of charge of the secondary battery and the open circuit voltage, and the relationship between the state of charge of the secondary battery and the internal resistance. The simultaneous equations of Equations (5) to (9) can be used to obtain the calculated data of the closed circuit voltage for each state of charge of the secondary battery assuming a degraded state, as shown by the dashed line. The calculated data showing the relationship between the state of charge and the closed circuit voltage is generated from the calculated data corrected with the degraded state parameters, and is stored as a relational equation or a data table. Then, fitting is performed by setting the degraded state parameters so that the calculated data shown by the dashed line matches the measured data based on the actual measurement shown by the ● plot.

[0102] Next, the calculation unit 10 compares the measurement data showing the relationship between the state of charge and the closed circuit voltage of the secondary battery based on the actual measurement with the calculation data showing the relationship between the state of charge and the closed circuit voltage of the secondary battery, the deterioration state of which is assumed based on the reproduction (step S8). In the comparison process, it is determined whether the measurement data based on the actual measurement and the calculation data assuming the deterioration state match each other (step S9).

[0103] The measured data and the calculated data can be compared by any method that determines the similarity between the data, such as regression analysis that determines the sum of squares of residuals or correlation coefficients under linear or nonlinear regression, weighted regression analysis that assigns weights according to the state of charge, or cluster analysis that assigns data by comparing with a clustered database. The measured data and calculated data may be clustered by associating them with data of additional variables such as temperature.

[0104] The comparison between the measured data and the calculated data may be performed for data corresponding to a part of the section of the state of charge, or may be performed for data corresponding to the entire section of the state of charge. Performing fitting for the entire section can improve the accuracy of diagnosis of the deterioration state. On the other hand, if there is a feature point in a part of the section of the state of charge, fitting can be performed only for the part of the section that includes the feature point.

[0105] For example, the comparison between the measured data and the calculated data can be performed based on the residual sum of squares between the data. The sum of squares of the difference between the measured data and the calculated data is calculated, and the sum of squares of the difference is compared with an arbitrarily set threshold. The agreement between the measured data and the calculated data can be determined based on the magnitude relationship between the sum of squares of the difference and the threshold.

[0106] When the discharge capacity Qc from the fully charged state of the secondary battery is used as the charge state, the measurement data indicating the relationship between the state of charge and the closed circuit voltage of the secondary battery to be diagnosed is a set of discrete data consisting of a combination of the measured value Qce of the discharge capacity from the fully charged state of the secondary battery and the measured value CCVce of the closed circuit voltage of the secondary battery. The set of measurement data can be stored in the memory unit 20 as a data table. The data table of measurement data includes data such as (Qce_1, CCVce_1), (Qce_2, CCVce_2), . . ., (Qce_N, CCVce_N).

[0107] To determine whether the data match each other, calculation data corresponding to the charge state of the measurement data is extracted from the data table of calculation data. For the measurement data (Qce_1, CCVce_1), (Qce_2, CCVce_2), ..., (Qce_N, CCVce_N), calculation data (Qcc_1, CCVcc_1), (Qcc_2, CCVcc_2), ..., (Qcc_N, CCVcc_N) with the same or similar discharge capacity Qc can be extracted.

[0108] Then, for each corresponding piece of charge state data, the square of the difference between the measured value in the measurement data and the calculated value in the calculation data is calculated, and the square of the difference is summed up for a predetermined range of data. The sum of the squares of the differences between the measured values ​​CCVce_1 to CCVce_N in the measurement data and the calculated values ​​CCVcc_1 to CCVcc_N in the calculation data is calculated as Σ(CCVce_i-CCVcc_i). 2 can be calculated for i=1 to N.

[0109] The calculated sum of squares of the differences is compared with a preset threshold value for consistency. The threshold value for consistency of the closed circuit potential can be set to any value that increases the similarity between the data, depending on the accuracy required for the diagnosis, the number of iterations of the calculation with the deterioration state parameters changed, etc. If there is no calculated data of the discharge state corresponding to the measured data, the calculated data may be interpolated by interpolation.

[0110] If the comparison result shows that the sum of squares of the difference between the measured data and the calculated data exceeds a preset threshold, it can be determined that the measured data indicating the relationship between the state of charge and the closed circuit voltage of the secondary battery to be diagnosed and the calculated data indicating the relationship between the state of charge and the closed circuit voltage of the secondary battery calculated assuming a deteriorated state do not match each other. In this case (step S9; NO), the deteriorated state parameters are reset, and the calculated data is regenerated and recompared.

[0111] In regeneration and recomparison of the calculation data, the state-of-degradation parameters may be set to unset values. The state-of-degradation parameters may be set, for example, in ascending or descending order with respect to the state of degradation represented by the state-of-degradation parameters. The state-of-degradation parameters related to the capacitance and the state-of-degradation parameters related to the resistance may be selected independently of each other, regardless of the estimated state of degradation.

[0112] On the other hand, when the comparison result shows that the sum of squares of the difference between the measured data and the calculated data is equal to or less than the preset threshold, it can be determined that the measured data showing the relationship between the state of charge and the closed circuit voltage of the secondary battery to be diagnosed and the calculated data showing the relationship between the state of charge and the closed circuit voltage of the secondary battery calculated assuming a deteriorated state match each other. In this case (step S9; YES), the set deteriorated state parameters are adopted and registered in the memory unit 20, and the diagnosis process is terminated.

[0113] The resetting of the degradation state parameters and the regeneration and recomparison of the calculation data based on the reset degradation state parameters can be repeated any number of times until it is determined that the measurement data and the calculation data match each other. The process of diagnosing the degradation state of the secondary battery can be terminated according to the result of the determination of the match between the measurement data and the calculation data or a predetermined stop condition.

[0114] For example, the diagnosis process can be terminated when the number of calculation repetitions reaches a predetermined number, when the similarity between the calculation data corrected with the deterioration state parameters converged by the calculation and the measurement data does not reach a predetermined similarity, or when the setting of all previously prepared deterioration state parameters has been completed.

[0115] In regeneration and recomparison of the calculation data, if the measurement data and the calculation data do not match each other after a specified number of calculations or a specified calculation time, the deterioration state parameters may be replaced with reference data of an electrode using a different active material, and the deterioration state parameters may be reset, and the calculation data may be regenerated and recompared based on the reset deterioration state parameters.

[0116] When the process of diagnosing the deterioration state of the secondary battery is completed, the output unit 40 displays the diagnosis results of the deterioration state of the secondary battery and the diagnosis results of the deterioration state of each electrode. The output unit 40 can display data showing the diagnosis results in response to the diagnosis request as graphs such as a curve of state of charge vs. voltage or a curve of state of charge vs. internal resistance, or as a table.

[0117] Data indicating the diagnosis results of the deterioration state of the secondary battery include the adopted deterioration state parameters, calculation data indicating the relationship between the charge state and open circuit voltage of the secondary battery generated using calculation data for each electrode, calculation data indicating the relationship between the charge state and internal resistance of the secondary battery generated using calculation data for each electrode, and calculation data indicating the relationship between the charge state and closed circuit voltage of the secondary battery generated using these calculation data.

[0118] Examples of data showing the diagnosis results of the deterioration state of each electrode include calculation data showing the relationship between the state of charge of the electrode corrected by the adopted correction parameter and the open circuit potential, and calculation data showing the relationship between the state of charge of the electrode corrected by the adopted correction parameter and the internal resistance. These data can be displayed for each of the positive and negative electrodes.

[0119] The output unit 40 may display information such as the type of active material used in the electrodes and the similarity indicating the agreement between the measured data and the calculated data together with the data indicating the diagnosis result. It may also display the state of health (SOH) corresponding to the value of the state of health parameter. It may also display only the final result based on the state of health parameter adopted, or may display intermediate results for each iteration of the calculation together with the final result.

[0120] In the process of diagnosing the deterioration state of a secondary battery, after a deterioration state parameter that is approximated to a true value is specified based on the agreement between the measured data and the calculated data, the state of health (SOH) of the secondary battery can be estimated from the calculated data corrected with the specified deterioration state parameter. The state of health (SOH) can be expressed as a capacity maintenance rate SOHQ of the secondary battery relative to its initial state, or a resistance rise rate SOHR of the secondary battery or electrodes relative to their initial states.

[0121] The capacity retention rate SOHQ [%] can be calculated by the following formulas (10) to (11) when the capacity of a secondary battery in an initial state when fully charged is Qmax0 [Ah], the capacity of a secondary battery in a fully charged state when degraded 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[%]...(10) Qmax1=∫Idt / ((SOC1-SOC2) / 100)...(11)

[0122] The resistance rise rate SOHRc [%] of the secondary battery, the resistance rise rate SOHRp [%] of the positive electrode, and the resistance rise rate SOHRn [%] of the negative electrode can be calculated using the following formulas (12) to (14) when the internal resistance of the secondary battery in the initial state is Rc0 [Ω], the internal resistance of the secondary battery in a degraded state is Rc1 [Ω], the internal resistance of the positive electrode in the initial state is Rp0 [Ω], the internal resistance of the secondary battery in a degraded state is Rp1 [Ω], the internal resistance of the negative electrode in the initial state is Rn0 [Ω], and the internal resistance of the negative electrode in a degraded state is Rn1 [Ω]. SOHRc=Rc1 / Rc0×100[%] (12) SOHRp=Rp1 / Rp0×100[%] (13) SOHRn=Rn1 / Rn0×100[%] (14)

[0123] According to the above-mentioned secondary battery state diagnosis method and secondary battery state diagnosis device, the relationship between the charge state and the closed circuit voltage of the secondary battery is used as information for diagnosing the deterioration state of the secondary battery, so there is no need to adjust the secondary battery to a specified charge state and measure the open circuit voltage, etc. When collecting information used for diagnosis, no charge / discharge device or charge / discharge operation for charging / discharging under specified conditions is required, and no effort or skill is required. Therefore, the deterioration state of the secondary battery to be diagnosed can be diagnosed non-destructively and with high accuracy based on information that can be obtained by simple operations.

[0124] 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.

[0125] For example, a potential range in which the positive electrode material can be properly used and a potential range in which the negative electrode material can be properly used are determined in advance, and when the open circuit potential fluctuates 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 the capacity is ensured within the potential range in which they can be properly used.

[0126] Furthermore, the diagnosis results of the deterioration state of the secondary battery can be stored as a database for each diagnosis request. The diagnosis result data may be collected for different secondary batteries, or may be collected by performing diagnosis on the same secondary battery at different times. These diagnosis results can be stored in a storage device as chronological diagnosis result data for each diagnosis request.

[0127] The diagnosis request is received via an electric communication line from a terminal at the user's side of the secondary battery, a terminal at a service center, etc. The diagnosis result data indicating the diagnosis result of the deterioration state of the secondary battery can be stored in a storage device in association with an identifier for identifying the diagnosis request, data indicating additional information sent from the user's side such as the usage time of the secondary battery and the accumulated amount of power supplied to the secondary battery, and data indicating the date and time of the diagnosis.

[0128] The usage time of the secondary battery can be registered and stored as the time from the first charge / discharge of the secondary battery to be diagnosed to the present, the number of charge / discharge cycles, etc. The cumulative current flow to the secondary battery can be registered and stored as the usage time of the secondary battery and the total current flow from the first charge / discharge of the secondary battery to the present, which is calculated based on the rated current, etc.

[0129] The diagnosis results of the deterioration state of the secondary battery stored as a database can be used in a process of changing 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 diagnosis result data.

[0130] The operating conditions of the secondary battery can be changed using as indicators (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. When these indicators are compared with predetermined thresholds and it is determined that there is a high possibility that deterioration of each electrode or deterioration of the secondary battery will progress, the control conditions of the controller of the secondary battery are presented in order to change the operating condition range of the secondary battery to conditions that ensure safety.

[0131] (1) The latest degradation state parameters registered in the above process can be used as an index for the degradation state of each electrode. When the degree of degradation of the positive electrode represented by the degradation state parameters, the degree of degradation of the negative electrode represented by the degradation state parameters, or the degree of increase in resistance represented by the degradation state parameters 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.

[0132] (2) As the rate of change of the deterioration state of each electrode, the rate of change (rate of change) of the deterioration state of the positive electrode with respect to the cumulative load amount, or the rate of change (rate of change) of the deterioration state of the negative electrode with respect to the cumulative load amount can be used as an index. When the degree of deterioration of the positive electrode represented by the deterioration state parameter, the degree of deterioration of the negative electrode represented by the deterioration state parameter, or the degree of increase in resistance 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 amount, the operating condition range of the secondary battery can be changed to a condition that ensures safety.

[0133] 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 multiple types of parameters among the usage time, the amount of current flowing through the secondary battery, the temperature, and the current. A model function showing the relationship between the cumulative load and the deterioration state of the electrode is formulated using multiple types of parameters. Then, the deterioration state of the electrode for various cumulative loads is actually measured, and the coefficients and constants of the model function can be found by fitting using the actual measurement results.

[0134] (3) The remaining life of the secondary battery can be the usage time of the secondary battery until the discharge capacity of the secondary battery decreases to a predetermined discharge capacity due to the progression of deterioration. When the remaining life of the secondary battery is equal to or less than a preset threshold value for the expected predetermined usage time, the operating condition range of the secondary battery can be changed to a condition that ensures safety.

[0135] The usage time of the secondary battery until the discharge capacity drops to a predetermined value can be estimated by calculating the rate of change (rate of change) of the deterioration state of the secondary battery with respect to the cumulative load amount based on the rate of change (rate of change) of the deterioration state of the positive electrode with respect to the cumulative load amount and the rate of change (rate of change) of the deterioration state of the negative electrode with respect to the cumulative load amount, and based on the rate of change (rate of change) of the deterioration state of the secondary battery with respect to the cumulative load amount, the current discharge capacity of the secondary battery, and the discharge capacity at the end of the secondary battery's life.

[0136] Examples of operations for changing the operating conditions of the secondary battery to ensure safety include lowering the upper limit of the charge state of the secondary battery, raising the lower limit of the charge state 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. It is possible to present control conditions for the controller of the secondary battery for controlling one or more of these.

[0137] By changing the range of operating conditions of the secondary battery after such diagnosis, the progress of deterioration of the secondary battery can be suppressed, and the life of the secondary battery can be extended. 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 to ensure the safety of the secondary battery.

[0138] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible within the scope of the present invention. For example, the present invention is not necessarily limited to having all the configurations of the above embodiment. It is possible to replace a part of the configuration of an embodiment with another configuration, add a part of the configuration of an embodiment to another form, or omit a part of the configuration of an embodiment. [Explanation of symbols]

[0139] 100 Status diagnostic device (secondary battery status diagnostic device) 10 Arithmetic section 20 Memory section 30 Input section 40 Output section 50 Communication Department (Acquisition Department)

Claims

1. A state diagnosis method for diagnosing a deterioration state of a secondary battery, comprising: determining a relationship between the state of charge of the secondary battery corrected by the parameter representing the deterioration state and the open circuit voltage, and a relationship between the state of charge of the secondary battery corrected by the parameter representing the deterioration state and the internal resistance; determining a calculation result indicating a relationship between the state of charge of the secondary battery and the closed circuit voltage based on the corrected relationship between the state of charge of the secondary battery and the open circuit voltage and the corrected relationship between the state of charge of the secondary battery and the internal resistance; A step of comparing a measurement result indicating a relationship between a charge state of a secondary battery and a closed circuit voltage with a calculation result indicating a relationship between a charge state of the secondary battery and a closed circuit voltage; and identifying the parameter indicating a diagnosis result of the deterioration state of the secondary battery based on a result of the comparison. A secondary battery status diagnosis method in which measurement results indicating the relationship between the charging state of the secondary battery and the closed circuit voltage are obtained by continuously measuring each charging state of the secondary battery during the charging or discharging process of the secondary battery.

2. A method for diagnosing a state of a secondary battery according to claim 1, comprising: a step of correcting a relationship between the charge state of the positive electrode and the open circuit potential, which is specific to the positive electrode material, a relationship between the charge state of the positive electrode and the internal resistance, which is specific to the positive electrode material, a relationship between the charge state of the negative electrode and the open circuit potential, which is specific to the negative electrode material, and a relationship between the charge state of the negative electrode and the internal resistance, which is specific to the negative electrode material, with a parameter representing a deterioration state; determining a calculation result showing a relationship between the state of charge and the open circuit voltage of a secondary battery 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 determining a calculation result indicating the relationship between the state of charge and the internal resistance of the secondary battery 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.

3. A method for diagnosing a state of a secondary battery according to claim 1 or 2, comprising: A secondary battery status diagnosis method, in which, in the process of identifying the parameter, the parameter is identified based on the consistency between the measurement result and the calculation result, and the deterioration state of the secondary battery is estimated from the calculation result corrected by the identified parameter.

4. A method for diagnosing a state of a secondary battery according to any one of claims 1 to 3, comprising: The method for diagnosing a state of a secondary battery, wherein the measurement for each state of charge of the secondary battery is performed during the charging process or the discharging process at a low rate of 0.3 C or less.

5. A method for diagnosing a state of a secondary battery according to any one of claims 1 to 4, comprising: A method for diagnosing the state of a secondary battery, wherein the internal resistance of the secondary battery is a combination of the internal resistance of a positive electrode which depends on the state of charge, the internal resistance of a negative electrode which depends on the state of charge, and the resistance of elements other than the electrodes which does not depend on the state of charge.

6. A state diagnosis device for diagnosing a deterioration state of a secondary battery, comprising: an acquisition unit that acquires measurement data indicating a relationship between a state of charge of the secondary battery and a closed circuit voltage; a memory unit that stores reference data indicating a relationship between a state of charge of a positive electrode and an open circuit potential that is specific to a positive electrode material, reference data indicating a relationship between a state of charge of a positive electrode and an internal resistance that is specific to a positive electrode material, reference data indicating a relationship between a state of charge of a negative electrode and an open circuit potential that is specific to a negative electrode material, and reference data indicating a relationship between a state of charge of a negative electrode and an internal resistance that is specific to a negative electrode material; a calculation unit that generates first calculated data indicating a relationship between a state of charge and an open circuit voltage of the secondary battery and second calculated data indicating a relationship between the state of charge and an internal resistance of the secondary battery based on the reference data corrected by a parameter indicating a degradation state, generates third calculated data indicating a relationship between the state of charge and a closed circuit voltage of the secondary battery based on the first calculated data and the second calculated data, and compares the measurement data with the third calculated data, A secondary battery status diagnosis device in which the measurement data is acquired by continuously measuring each charging state of the secondary battery during a charging or discharging process of the secondary battery, and then input to the acquisition unit.

7. The secondary battery state diagnosis device according to claim 6, a display unit that displays a diagnosis result of the deterioration state of the secondary battery, the calculation unit identifies the parameter based on a match between the measurement data and the third calculation data, and estimates a degradation state of the secondary battery from the third calculation data corrected by the identified parameter; The display unit is a secondary battery condition diagnosis device that displays a diagnosis result of the estimated deterioration state of the secondary battery.

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