JP7660540B2 - Secondary battery state diagnostic method and state diagnostic device - Google Patents

Description

The present invention relates to a method and device for diagnosing the state of a secondary battery.

It is known that the battery characteristics of secondary batteries such as lithium-ion batteries deteriorate when they are repeatedly charged and discharged, or when they are stored in high-temperature environments. As deterioration of a secondary battery progresses, voltage drops and capacity reductions occur. For this reason, voltage and current are controlled according to the degree of deterioration of the secondary battery.

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 at the positive and negative electrodes, and alteration of elements other than the electrodes, such as the electrolyte 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 use of secondary batteries, a non-destructive method for diagnosing the deterioration state of secondary batteries is required.

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 evaluated non-destructively and quantitatively 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 charge/discharge curves of the negative electrode alone are superimposed and calculated to reproduce the charge/discharge curve of the secondary battery.

Patent document 2 describes a device for detecting internal information about a secondary battery. In this device, intermittent charging control is performed to intermittently charge the detected battery by repeatedly charging a fixed capacity and pausing charging. Information about the charging characteristics of the secondary battery, such as its voltage, is acquired during the process of intermittently charging the secondary battery.

JP 2009-080093 A International Publication No. 2014/147753

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 measurements is compared with the charge/discharge curve of the secondary battery based on measurements. However, the charge/discharge curve includes the relationship between the charge state (e.g., the discharge amount) and the potential and potential change rate, as well as the effects of voltage rise and voltage drop due to the internal resistance of the secondary battery. Methods that use only the potential and potential change rate as indicators have the problem that the accuracy of diagnosis is low when the change in internal resistance due to deterioration is large.

In Patent Document 2, intermittent charging is performed when obtaining information on the charging characteristics of the secondary battery to be diagnosed. However, methods of intermittent charging and discharging require a charging and discharging device for charging and discharging under specified conditions, the task of removing the secondary battery from the circuit when in use, or periodic switching operations. Because special equipment and operations are required, it is not easy for users of secondary batteries to obtain the information themselves, and there is an issue that versatility is low. Furthermore, with methods of intermittent charging and discharging, it takes time to obtain battery information.

The present invention aims to provide a method and device for diagnosing the condition of a secondary battery that can diagnose the deterioration state of a secondary battery with high accuracy based on information that can be obtained through simple operations.

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

In addition, the secondary battery state diagnostic device according to the present invention is a state diagnostic device for diagnosing the deterioration state of a secondary battery, and includes an acquisition unit for acquiring measurement data showing the relationship between the charge state and closed circuit voltage of the secondary battery, a memory unit for storing reference data showing the relationship between the charge state of the positive electrode and the open circuit potential of the positive electrode specific to the positive electrode material, reference data showing the relationship between the charge state of the positive electrode and the internal resistance of the positive electrode specific to the positive electrode material, reference data showing the relationship between the charge state of the negative electrode and the open circuit potential of the negative electrode specific to the negative electrode material, and reference data showing the relationship between the charge state of the negative electrode and the internal resistance of the negative electrode specific to the negative electrode material, and a correction unit for correcting the deterioration state with a parameter indicating the deterioration state. A calculation unit generates first calculation data indicating the relationship between the charge state of the secondary battery and the open circuit voltage, and second calculation data indicating the relationship between the charge state of the secondary battery and the internal resistance based on the reference data obtained, generates third calculation data indicating the relationship between the charge state of the secondary battery and the closed circuit voltage based on the first calculation data and the second calculation data, and compares the measurement data with the third calculation data, and the measurement data is input to the acquisition unit after being acquired by continuously measuring each charge state of the secondary battery during the charging or discharging process of the secondary battery.

The present invention provides a method and device for diagnosing the condition of a secondary battery that can diagnose the deterioration state of a secondary battery with high accuracy based on information that can be obtained through simple operations.

1 is a diagram showing a configuration of a secondary battery state diagnosis device according to an embodiment of the present invention; 4 is a flowchart showing a process for diagnosing a deterioration state of a secondary battery. FIG. 4 is a diagram showing an example of the relationship between the charged state of an electrode and the open circuit potential. FIG. 4 is a diagram showing an example of the relationship between the charged state of an electrode and the open circuit potential. FIG. 4 is a diagram showing an example of the relationship between the charged state and the internal resistance of an electrode. FIG. 4 is a diagram showing an example of the relationship between the charged state and the internal resistance of an electrode. 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. FIG. 4 is a diagram showing an example of the relationship between the state of charge and the internal resistance of a secondary battery. 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.

The following describes a method and device for diagnosing the state of a secondary battery according to one embodiment of the present invention. Note that the same reference numerals are used to designate common components in the following figures, and duplicate descriptions will be omitted.

The secondary battery state diagnosis method according to this embodiment relates to a method for diagnosing the deterioration state of a secondary battery. Examples of secondary batteries to be diagnosed include lithium ion secondary batteries, sodium ion secondary batteries, magnesium ion secondary batteries, calcium ion secondary batteries, zinc secondary batteries, aluminum ion secondary batteries, nickel-hydrogen secondary batteries, and lead secondary batteries. As the secondary battery to be diagnosed, a lithium ion secondary battery is particularly preferable.

In the secondary battery state diagnosis method according to this embodiment, the relationship between the charge state of the secondary battery and the closed circuit voltage (CCV) 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.

In the secondary battery state diagnosis method according to this embodiment, the closed circuit voltage for each charge state 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. The closed circuit voltage of the secondary battery is continuously measured during the continuous charging or discharging process with measurement intervals as necessary so as to include measurement results in different charge states.

The relationship between the state of charge and the closed circuit voltage of a 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 a 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.

Therefore, in the secondary battery state diagnosis method according to this 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 with degradation state parameters that represent the degradation state of elements other than the positive electrode, negative electrode, and electrodes. By combining relationships corrected with the degradation state parameters, the relationship between the state of charge and the closed circuit voltage of a secondary battery assumed to be in a degraded state can be reproduced by calculation.

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

Conventionally, there is a known method for collecting information on a secondary battery to be diagnosed by intermittently charging and discharging. However, in a 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. With 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.

Conventional methods like these require charging and discharging equipment and procedures to charge and discharge under specified conditions. Also, because existing circuits in which secondary batteries are used often cannot be used, the secondary battery must be removed from the circuit when in use. Also, methods that charge and discharge intermittently take time to collect battery information. Methods that collect information on the secondary battery to be diagnosed by intermittent charging and discharging require special equipment and procedures, and have the problem of requiring effort, skill, and measurement time.

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 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.

In this specification, the state of charge refers to an electrochemical state determined by the ratio of the amount of electricity that can be discharged to the amount of electricity that can be discharged from a fully charged state. The state of charge can be expressed as an appropriate state quantity that can be converted between the two, 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 the charge carrier elements contained in the active material.

FIG. 1 is a diagram showing the configuration of a secondary battery state diagnosis device according to this embodiment.
1, the secondary battery state diagnosis 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 diagnosis device 100 are connected to a bus.

The condition diagnosis device 100 is a device that diagnoses the deterioration state of a secondary battery, and can be configured with hardware such as a computer. The condition diagnosis device 100 executes a process for diagnosing the deterioration state of a secondary battery according to a specified program.

The condition diagnosis device 100 executes a predetermined program using measurement data indicating the measurement results obtained by actual measurement as input, and outputs diagnostic data indicating the diagnosis results of 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 reference data indicating the electrode characteristics prepared in advance.

The calculation unit 10 reads various data and programs, executes 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.

The storage unit 20 stores various data and programs. The storage unit 20 is configured, for example, with storage devices such as RAM (Random Access Memory) and ROM (Read Only Memory). The various data and programs may be stored in a writable and readable hard disk, flash memory, magnetic disk, optical disk, etc.

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

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

The communication unit 50 transmits and receives various data and control signals between 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).

The 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 or a terminal at a service center that maintains the secondary battery. 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 the condition diagnosis device 100 in response to a request to diagnose the deterioration state of the secondary battery.

FIG. 2 is a flowchart showing the process of diagnosing the deterioration state of the secondary battery.
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.

The measurement data is data of the measurement results that indicates the relationship between the charge state of the secondary battery and the closed circuit voltage. The measurement data is collected by continuously measuring the closed circuit voltage for each charge state 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 equation or a data table.

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

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

When the charge/discharge current during measurement is at a low rate, the effects of resistance components due to large currents and the effects of degradation due to large currents are reduced, making it possible to accurately determine the relationship between the secondary battery's state of charge and closed circuit voltage. In addition, when the charge/discharge current during measurement is 0.01 C or higher, the time required to collect battery information is reduced.

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

The closed circuit voltage may be measured, for example, during a charging process of a secondary battery in use from its current charged state to a fully charged state, or during a discharging process of a secondary battery in use from its current charged state to a fully discharged state. It may also be measured during a charging process in the next charge/discharge cycle of a 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 a single continuous charging process or a single continuous discharging process.

It is preferable to measure the closed circuit voltage for multiple charging states that are different from each other. The number of measurement points at which the closed circuit voltage is measured is preferably two or more, more preferably five or more, and even more preferably ten or more. With more measurement points, a more precise comparison can be made between the measured data and the calculated data, improving the accuracy of diagnosis of the deterioration state.

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 equation or a data table.

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

FIG. 3 is a diagram showing an example of the relationship between the charged state of an electrode and the open circuit potential.
3 corresponds to the reference data for the positive electrode. The horizontal axis indicates 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 indicates the open circuit potential Vp [V] of the positive electrode relative to the reference electrode.

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

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 equation or a data table for each positive and negative electrode and for each active material used in the electrode. By preparing reference data for multiple 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 calculations while replacing the reference data.

As shown in Fig. 3, the curve of the charge state 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 charge state of the electrode. The curve shown in Fig. 3 is obtained, for example, when _LiFePO4 is used. On the other hand, as shown in Fig. 4, the curve of the charge state of the electrode vs. the open circuit potential may have a change in the open circuit potential with the change in the charge state of the electrode.

As shown in Figures 3 and 4, when an active material is used whose open circuit potential does not substantially change with changes in the state of charge of the electrode, the deterioration state of the electrode is unlikely to be reflected in the electrode potential. Although the curve shifts up or down due to electrode deterioration, 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.

FIG. 5 is a diagram showing an example of the relationship between the charged state and the internal resistance of an electrode.
5 corresponds to the reference data of 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. FIG. 5 shows the data of a positive electrode using the same type of active material as FIG. 3.

FIG. 6 is a diagram showing an example of the relationship between the charged state and the internal resistance of an electrode.
6 corresponds to the reference data of 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. FIG. 6 shows data of a negative electrode using the same type of active material as FIG. 4.

As shown in Figures 5 and 6, the relationship between the state of charge of an electrode and its internal resistance is 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 equation or a data table for each positive and negative electrode and for each active material used in the electrode. By preparing reference data for multiple 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 calculations while replacing the reference data.

As shown in Figure 5, the curve of the electrode's state of charge vs. internal resistance often fluctuates in response to changes in the state of charge of the electrode, even when an active material is used that has a plateau region in which the open circuit potential does not substantially change in response to changes in the state of charge of the electrode. On the other hand, as shown in Figure 6, the curve of the electrode's state of charge vs. 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 vs. open circuit potential shown in Figure 4.

As shown in Figures 5 and 6, the internal resistance often fluctuates with changes in the state of charge of the electrode. By looking at 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 precisely reproduced by calculation, taking into account the resistance increase behavior specific to the electrode material, unlike when 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 information on the closed circuit voltage, which can be obtained by simple operations.

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

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

The measurement data and reference data may be data showing the relationship between the state of charge and a voltage value, data showing the relationship between the state of charge and an internal resistance value, data showing the relationship between the state of charge and a differential value of the voltage, or data showing the relationship between the state of charge and a 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, thereby ensuring the accuracy of the amount of active material used.

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

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

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 showing the relationship between the charge state of the positive electrode specific to the positive electrode material and the open circuit potential.

The calculation unit 10 can also 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.

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

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 showing the relationship between the charge state and internal resistance of the positive electrode specific to the positive electrode material.

The calculation unit 10 can also 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.

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

The reference data can also be selected from a reference database based on information associated with the measurement data, such as information on the type of active material used in the secondary battery to be diagnosed, or information on the upper and lower voltage limits of the secondary battery to be diagnosed. Measurement data can also be collected from various secondary batteries to be diagnosed to form a measurement database.

In steps S2 and S3, it is preferable to read data on an electrode that uses 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 on 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.

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

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

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. Individual parameters are set as deterioration state parameters 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.

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 specified 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 specified 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 measured data provides a solution for the degradation state parameters that are approximated to the true value.

As the deterioration state parameters, it is preferable to set multiple 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 capacity and a deterioration state parameter related to the resistance can be set.

As deterioration state parameters related to capacity, coefficients and constants of state quantities representing the state of charge can be set in a function showing the relationship between the state of charge and the open circuit potential, or in a 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.

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 x 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.

The positive electrode side position shift δp means the shift in the curve along the capacity axis due to deterioration of the positive electrode on the voltage-capacity curve of the positive electrode. The positive electrode side position shift δp corresponds to the decrease in the capacity of the positive electrode due to deterioration of the positive electrode. The positive electrode side position shift 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.

The capacity Qp [Ah] of the positive electrode is expressed as Qp = qp × mp, where mp [g] is the amount of the 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 deterioration that causes a positive electrode position shift δp is assumed, the capacity Qp [Ah] of the positive electrode can be expressed by the following formula (1).
Qp=qp×mp−δp...(1)

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 x 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.

The negative electrode side position shift δn means the shift in the curve along the capacity axis due to deterioration of the negative electrode on the voltage-capacity curve of the negative electrode. The negative electrode side position shift δn corresponds to the decrease in the capacity of the negative electrode due to deterioration of the negative electrode. The negative electrode side position shift 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.

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

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

Assuming that the positive electrode resistance coefficient ap deteriorates, the internal resistance Rp [Ω] of the positive electrode in the state of charge x can be expressed by the following formula (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)

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

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

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, or 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 close 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.

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

The calculation unit 10 also performs a process of calculating ap/mp×rp(qp) corrected with the degradation state parameters from the data on the internal resistance Rp(Qp) of the positive electrode for each charging state based on reference data showing the relationship between the charging state and internal resistance of the positive electrode 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 parameters from the data on the internal resistance Rn(Qn) of the negative electrode for each charging state based on reference data showing the relationship between the charging state and internal resistance of the negative electrode specific to the negative electrode material.

Next, the calculation unit 10 generates calculation data (first calculation data) indicating the relationship between the charge state of the secondary battery and the open circuit voltage based on the relationship between the charge state of the positive electrode corrected by the degradation state parameters and the open circuit potential, and the relationship between the charge state of the negative electrode corrected by the degradation state parameters and the open circuit potential (step S5).

The calculated data showing the relationship between the charge state of the secondary battery and the open circuit voltage is used to generate calculated data showing the relationship between the charge state of the secondary battery and the closed circuit voltage. The calculated data showing 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 memory unit 120. The calculated data showing 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.

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

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 charged state of the secondary battery. The vertical axis indicates potential [V]. The dashed 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.

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 is stored as a relational equation or a data table.

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

Calculation data showing the relationship between the charge state and the internal resistance of the secondary battery is used to generate calculation data showing the relationship between the charge state and the closed circuit voltage of the secondary battery. After being generated by calculation, the calculation data showing the relationship between the charge state and the internal resistance of the secondary battery can be stored in the memory unit 120. The calculation data showing the relationship between the charge state and the internal resistance of the secondary battery may be expressed by a relational equation or a data table.

The internal resistance Rc(x) [Ω] of the secondary battery in the state of charge x is expressed as follows: 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. Under this condition, Qc = Qp + δp = Qn + δn, the internal resistance Rc(x) [Ω] of the secondary battery in the state of charge x is expressed as follows:
Rc(Qc)=Ro+Rp(Qp)+Rn(Qn)...(6)

FIG. 8 is a diagram showing an example of the relationship between the state of charge and the internal resistance of a secondary battery.
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 the secondary battery. The vertical axis indicates the 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.

As shown in Figure 8, the relationship between the state of charge and internal resistance of a secondary battery is determined by combining the relationship between the state of charge and internal resistance of the positive electrode, which depends on the state of charge, the relationship between the state of charge and 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. However, 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 internal resistance is generated from reference data corrected with deterioration state parameters, and stored as a relational equation or a data table.

If the internal resistance of the secondary battery in the reference data used as 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 precisely reproduced by calculation. Therefore, it becomes possible to evaluate the deterioration state of each electrode of the secondary battery with high accuracy.

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).

The calculated data showing the relationship between the charge state of the secondary battery and the closed circuit voltage is used for comparison with the measured data showing the relationship between the charge state of the secondary battery and the closed circuit voltage. The calculated data showing 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 memory unit 120. The calculated data showing 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.

The closed circuit potential CCVc(x) [V] of a secondary battery in a state of charge x can be calculated by the following formulas (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 x Rc
...(7)
CCVp (Qp) = OCVp (Qp) - I × Rp (Qp) (8)
CCVn(Qn)=OCVn(Qn)-I×Rn(Qn)...(9)

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 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 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.

As shown in Figure 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. Using the simultaneous equations of equations (5) to (9), it is possible to obtain calculated data for the closed circuit voltage for each state of charge of the secondary battery assuming a degraded state, as shown by the dashed line. Such calculated data showing the relationship between the state of charge and the closed circuit voltage is generated from calculated data corrected with the degraded state parameters, and 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 actual measurements shown by the ● plot.

Then, the calculation unit 10 compares the measurement data showing the relationship between the charge state and the closed circuit voltage of the secondary battery based on the actual measurement with the calculation data showing the relationship between the charge state and the closed circuit voltage of the secondary battery, which is assumed to be in a deteriorated state 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 a deteriorated state match each other (step S9).

The measured data and the calculated data can be compared by any method that determines the similarity between the data. For example, the measured data can be compared by 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 on additional variables such as temperature.

The comparison between the measured data and the calculated data may be performed for data corresponding to a portion of the charging state, or for data corresponding to the entire charging state. Performing fitting for the entire range can improve the accuracy of diagnosis of the deterioration state. On the other hand, if there is a feature point in some of the charging state ranges, fitting can be performed only for the portion of the range that includes the feature point.

For example, the comparison between measured data and calculated data can be made based on the residual sum of squares between the data. The sum of squares of the differences between the measured data and calculated data is calculated, and the sum of squares of the differences is compared with an arbitrarily set threshold value. The consistency between the measured data and calculated data can be determined based on the relationship between the sum of squares of the differences and the threshold value.

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 charge state of the secondary battery to be diagnosed and the closed circuit voltage is a set of discrete data that combines 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).

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 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) of the same or similar discharge capacity Qc can be extracted.

Then, for each corresponding piece of state-of-charge 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. Σ(CCVce_i-CCVcc_i) ² can be calculated for i=1 to N as 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.

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

When the comparison result shows that the sum of squares of the differences 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 degraded state do not match each other. In this case (step S9; NO), the degraded state parameters are reset, and the calculated data is regenerated and recompared.

When regenerating and recomparing the calculation data, unset values can be set as the deterioration state parameters. The deterioration state parameters can be selected and set, for example, in ascending or descending order with respect to the deterioration state represented by the deterioration state parameters. The deterioration state parameters related to the capacity and the deterioration state parameters related to the resistance may be selected independently of each other, regardless of the estimated deterioration state.

On the other hand, if the comparison result indicates that the sum of squares of the differences between the measured data and the calculated data is equal to or less than 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 degraded state match each other. In this case (step S9; YES), the set degraded state parameters are adopted and registered in the memory unit 20, and the diagnosis process is terminated.

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 measured data and the calculated data match each other. The process of diagnosing the degradation state of the secondary battery can be terminated depending on the result of the determination of the match between the measured data and the calculated data or on a specified stop condition.

For example, the diagnosis process can be terminated when the number of calculation iterations 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 the deterioration state parameters prepared in advance is completed.

When the calculation data is regenerated and recompared, if the measurement data and the calculation data do not match after a specified number of calculations or a specified calculation time, the deterioration state parameters may be replaced with reference data for an electrode using a different active material, and the calculation data may be regenerated and recompared again based on the re-set deterioration state parameters.

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 charge state vs. voltage or a curve of charge state vs. internal resistance, or as a table, etc.

Data showing the diagnosis results of the deterioration state of the secondary battery include the deterioration state parameters used, calculation data showing the relationship between the charge state and the open circuit voltage of the secondary battery generated from calculation data for each electrode, calculation data showing the relationship between the charge state and the internal resistance of the secondary battery generated from calculation data for each electrode, and calculation data showing the relationship between the charge state and the closed circuit voltage of the secondary battery generated from these calculation data.

Data showing the diagnosis results of the deterioration state of each electrode include calculated data showing the relationship between the state of charge of the electrode corrected with the adopted correction parameters and the open circuit potential, and calculated data showing the relationship between the state of charge of the electrode corrected with the adopted correction parameters and the internal resistance. These data can be displayed for each positive and negative electrode.

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 deterioration state parameter. It may also display only the final result based on the deterioration state parameter adopted, or may display intermediate results for each iteration of the calculation together with the final result.

In the process of diagnosing the deteriorated state of a secondary battery, after a deteriorated state parameter that is approximated to a true value is identified based on the consistency between the measured data and the calculated data, the deteriorated state (SOH) of the secondary battery can be estimated from the calculated data corrected with the identified deteriorated state parameter. The deteriorated state (SOH) can be expressed as the capacity maintenance rate SOHQ relative to the initial state of the secondary battery, or the resistance rise rate SOHR relative to the initial state of the secondary battery or electrodes.

The capacity maintenance rate SOHQ [%] can be calculated by the following formulas (10) to (11) when the capacity of the fully charged state of the initial secondary battery is Qmax0 [Ah], the capacity of the fully charged state of the degraded secondary battery is Qmax1 [Ah], and the charge states of the upper and lower limits of the integration interval of the degraded secondary battery are SOC1 [%] and SOC2 [%].
SOHQ=Qmax1/Qmax0×100[%]...(10)
Qmax1=∫Idt/((SOC1-SOC2)/100)...(11)

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 by 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)

According to the above-mentioned secondary battery state diagnosis method and secondary battery state diagnosis device, the relationship between the charge state of the secondary battery and the closed circuit voltage 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 is required to charge/discharge under specified conditions, 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 with simple operations.

The diagnosis results 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 results 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 discharge current from the secondary battery, etc. can be changed.

For example, the potential range in which the positive electrode material can be used properly and the potential range in which the negative electrode material can be used properly are determined in advance. Then, if the open circuit potential fluctuates due to deterioration of either the positive or negative electrode, the upper and lower voltage limits can be changed so that capacity is ensured within the potential range in which they can be used properly.

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 for each diagnosis request as chronological diagnosis result data.

The diagnosis request is received via a telecommunications line from the terminal where the secondary battery is used, a terminal at a service center, etc. The diagnosis result data indicating the diagnosis result of the secondary battery's deterioration state can be stored in a storage device in association with an identifier that identifies the diagnosis request, data indicating additional information sent from the user, such as the usage time of the secondary battery and the cumulative amount of power flowing through the secondary battery, and data indicating the date and time of the diagnosis.

As the usage time of the secondary battery, the time from the first charge/discharge of the secondary battery to be diagnosed to the present, the number of charge/discharge cycles, etc. can be registered and stored. As the cumulative current flowing to the secondary battery, the usage time of the secondary battery and the total current flowing from the first charge/discharge of the secondary battery to the present, calculated based on the rated current, etc. can be registered and stored.

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

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 secondary battery controller are presented in order to change the operating condition range of the secondary battery to conditions that ensure safety.

(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, or the degree of degradation of the negative electrode represented by the degradation state parameters, or the degree of resistance increase 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 conditions that ensure safety.

(2) The rate of change of the deterioration state of each electrode can be 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. When the degree of deterioration of the positive electrode represented by the deterioration state parameter, or the degree of deterioration of the negative electrode represented by the deterioration state parameter, or the degree of resistance increase represented by the deterioration state parameter, is equal to or greater than a preset threshold value for 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.

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 including usage time, amount of current flowing through the secondary battery, temperature, and current. Using multiple types of parameters, a model function is formulated that shows the relationship between the cumulative load and the deterioration state of the electrodes. The deterioration state of the electrodes for various cumulative loads is then measured, and the coefficients and constants of the model function can be found by fitting using the actual measurement results.

(3) The remaining life of the secondary battery can be determined by the usage time of the secondary battery until the discharge capacity of the secondary battery drops 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.

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 accumulated load of the deterioration state of the secondary battery based on the rate of change (rate of change) of the accumulated load of the deterioration state of the positive electrode and the rate of change (rate of change) of the accumulated load of the deterioration state of the negative electrode, and based on the rate of change (rate of change) of the accumulated load of the deterioration state of the secondary battery, the current discharge capacity of the secondary battery, and the discharge capacity at the end of the life of the secondary battery.

Examples of operations that change the operating conditions of the secondary battery to ensure safety include lowering the upper limit of the secondary battery's state of charge, raising the lower limit of the secondary battery's state of charge, 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 secondary battery controller to control one or more of these.

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

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

100 Status diagnostic device (secondary battery status diagnostic device)
10 Calculation unit 20 Storage unit 30 Input unit 40 Output unit 50 Communication unit (acquisition unit)

Claims (7)

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. 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. 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. 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. 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. 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. 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.