JP2023139691A - Secondary battery state diagnosing method and state diagnosing device - Google Patents

Abstract

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

Description

The present invention relates to a method and apparatus for diagnosing the condition of a secondary battery.

In recent years, secondary batteries such as lithium ion batteries have been used as driving power sources installed in vehicles and as power storage power sources for smart houses and the like. It is known that the battery characteristics of lithium ion batteries etc. deteriorate when repeatedly charged and discharged or when stored in a high temperature environment. Drive power supplies and power storage power supplies are used for long periods of time, so they are required to minimize deterioration and ensure reliability and safety.

Active materials used in lithium ion batteries are selected not only from the viewpoint of performance such as capacity and voltage, but also from the viewpoint of suppressing deterioration and improving safety. For example, Li(Ni, Mn, Co)O ₂ (NMC), LiFePO ₄ (LFP), etc. are used as the positive electrode active material. As the negative electrode active material, graphite, Li ₄ Ti ₅ O ₁₂ (LTO), etc. are used.

It is known that deterioration of secondary batteries such as lithium ion batteries progresses quickly in high potential regions where the state of charge is high and in low potential regions where the state of charge is low. Deterioration of a secondary battery occurs due to changes in the characteristics of the positive electrode, negative electrode, and elements other than the electrodes, such as the electrolyte and the current collector. As deterioration progresses, the charge/discharge curve, operating voltage range, etc. change, which affects safety. It is necessary to accurately detect deterioration of electrodes and elements other than electrodes, and to select optimal control methods and usage conditions according to the state of deterioration.

Patent Document 1 describes a method for detecting internal information of a secondary battery. In this method, the charging and discharging curve of the positive electrode alone and the charging and discharging curve of the negative electrode alone are superimposed and calculated to reproduce the charging and discharging curve of the secondary battery. By reproducing the charge/discharge curve of a secondary battery, the state of deterioration of the positive and negative electrodes can be quantitatively evaluated in a non-destructive manner.

Japanese Patent Application Publication No. 2009-080093

In Patent Document 1, a charging/discharging curve of a secondary battery is reproduced based on a charging/discharging curve of a positive electrode alone and a charging/discharging curve of a negative electrode alone. In the process of reproduction, the effective amounts of active materials in the positive and negative electrodes, indicators regarding the positional relationship between the charge and discharge curves of the positive and negative electrodes, and the open circuit potentials of the positive and negative electrodes are determined. It is said that by detecting the status of the positive and negative electrodes, it is possible to avoid deterioration in battery life and safety, compared to conventional methods that use changes in battery voltage.

However, the method of Patent Document 1 utilizes changes in open circuit potential in response to changes in charging state for diagnosis. This method has a problem in that the deterioration state cannot be accurately diagnosed when an active material whose potential changes poorly with respect to changes in the state of charge is used. For example, it is known that LiFePO ₄ , Li ₄ Ti ₅ O ₁₂ , etc. used in lithium ion secondary batteries have small changes in open circuit potential when charged and discharged.

In the method of Patent Document 1, when one of the positive electrode and the negative electrode uses an active material whose potential changes poorly with changes in the state of charge, it is possible to diagnose only the deterioration state of the electrode where the potential changes significantly. Therefore, a problem arises in that electrode deterioration potentially progresses without being diagnosed. If the deterioration potentially progresses, the secondary battery will rapidly deteriorate when the degree of deterioration exceeds a certain threshold, resulting in lower reliability and safety of the secondary battery.

Therefore, the present invention makes it possible to diagnose the deterioration of each secondary battery or each electrode, even when the electrodes of the secondary battery use an active material whose potential changes poorly with changes in the state of charge. It is an object of the present invention to provide a secondary battery condition diagnosing method and a secondary battery condition diagnosing device.

In order to solve the above-mentioned problems, a secondary battery condition diagnosis method according to the present invention is a condition diagnosis method for diagnosing the deterioration condition of a secondary battery, and includes the relationship between the charging condition of the secondary battery and the open circuit voltage. , and a relationship group consisting of the relationship between the state of charge and the internal resistance of the secondary battery for each different energization time as input information, and the deterioration state of the secondary battery and the positive electrode used in the secondary battery. The deterioration state and the deterioration state of the negative electrode used in the secondary battery are output information.

Further, the secondary battery condition diagnosis device according to the present invention is a condition diagnosis device for diagnosing the deterioration condition of the secondary battery, and includes data indicating the relationship between the charging condition of the secondary battery and the open circuit voltage, and The input information is data indicating a relationship group consisting of the relationship between the state of charge and the internal resistance of the secondary battery for each different energization time, and data indicating the state of deterioration of the secondary battery, data indicating the state of deterioration of the secondary battery, and the data used for the secondary battery. Data indicating the deterioration state of the positive electrode used in the secondary battery and data indicating the deterioration state of the negative electrode used in the secondary battery are output information.

According to the present invention, even if the electrodes of a secondary battery use an active material whose potential changes poorly with changes in the state of charge, it is possible to diagnose deterioration of each secondary battery or electrode. A method for diagnosing the condition of a secondary battery and a device for diagnosing the condition of a secondary battery can be provided.

FIG. 1 is a diagram showing the configuration of a secondary battery condition diagnosis device according to the present embodiment. 3 is a flowchart showing a process for diagnosing a deterioration state of a secondary battery. FIG. 3 is a diagram showing an example of the relationship between the charging state of an electrode and an open circuit potential. FIG. 3 is a diagram showing an example of the relationship between the charging state of an electrode and an open circuit potential. FIG. 3 is a diagram showing an example of the relationship between the charging state of a secondary battery and an open circuit voltage. FIG. 3 is a diagram showing an example of the relationship between the charging state of an electrode and internal resistance for each current application time. FIG. 3 is a diagram showing an example of the relationship between the charging state of an electrode and internal resistance for each current application time. FIG. 3 is a diagram illustrating an example of the relationship between the charging state of a secondary battery and internal resistance for each energization time. FIG. 3 is a diagram illustrating an example of the relationship between the charging state of a secondary battery assumed to be in a deteriorated state and the open circuit voltage. FIG. 3 is a diagram illustrating an example of the relationship between the charging state and internal resistance of a secondary battery assumed to be in a deteriorated state.

Hereinafter, a secondary battery condition diagnosing method and a secondary battery condition diagnosing device according to an embodiment of the present invention will be described. Note that common components in the following figures are denoted by the same reference numerals, and redundant explanation will be omitted. In the following description, a subscript p is added to the state quantity of the positive electrode, and a subscript n is added to the state quantity of the negative electrode. When a positive electrode and a negative electrode are not distinguished, they are written as electrodes and a subscript x is added.

The method for diagnosing the state of a secondary battery according to the present embodiment relates to a method for diagnosing a deterioration state of a secondary battery. In this state diagnosis method, the deterioration state of a secondary battery is diagnosed in a non-destructive manner, using a secondary battery whose deterioration state is unknown as a diagnosis target. This condition diagnosis method uses the measurement results of open circuit voltage for each state of charge of the secondary battery to be diagnosed, and the measurement results of internal resistance for each energization time and state of charge. The deterioration state and the deterioration state of each electrode included in the secondary battery can be individually diagnosed.

The method for diagnosing the condition of a secondary battery according to the present embodiment is a secondary battery in which an active material whose open circuit potential is constant except near a fully charged state and near a fully discharged state is used for one of a positive electrode and a negative electrode. It can be applied to secondary batteries and secondary batteries that are used as both a positive electrode and a negative electrode. Furthermore, the present invention can also be applied to secondary batteries in which active materials with variable open circuit potentials are used for both the positive electrode and the negative electrode. Even if an active material whose open circuit potential is constant except near the fully charged state and near the fully discharged state is used, the deterioration state can be diagnosed with high accuracy.

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

Examples of electrodes whose potential changes poorly with respect to changes in charging state include electrodes using lithium iron phosphate (LiFePO ₄ ), lithium titanate (Li ₄ Ti ₅ O ₁₂ , Li ₂ TiO ₃ ), and the like. Examples of electrodes whose potential changes sufficiently with respect to changes in the state of charge include electrodes other than these using graphite, lithium cobalt oxide (LiCoO ₂ ), and the like.

In the method for diagnosing the state of a secondary battery according to the present embodiment, the open circuit voltage for each state of charge of the secondary battery to be diagnosed and the internal resistance for each state of charge of the secondary battery to be diagnosed are measured. The internal resistance is measured at different energization times by changing the length of the energization time during measurement into two or more types. By measuring the open circuit voltage and internal resistance, a group of relationships indicating the relationship between the charging state of the secondary battery and the open circuit voltage, and the dependence of the charging state of the secondary battery and the internal resistance on the energization time are determined. Note that the internal resistance may be measured during the discharging process by changing the length of the discharging time at the time of measurement into two or more types and for each different energization time during the discharging.

Information indicating the relationship between the charging state of the secondary battery and the open circuit voltage, and information indicating the relationship group indicating the energization time dependence between the charging state of the secondary battery and the internal resistance are input when diagnosing the deterioration state. Used as information. The output information obtained based on the input information includes information indicating the deterioration state of the secondary battery, information indicating the deterioration state of the positive electrode used in the secondary battery, and information indicating the deterioration state of the negative electrode used in the secondary battery. This is the information shown.

A relationship group indicating the dependence of the state of charge of the secondary battery on the energization time and the internal resistance is composed of the relationship between the state of charge of the secondary battery and the internal resistance for each different energization time. That is, the relationship between the state of charge and the internal resistance, which corresponds to a capacitance-resistance curve, is collected for each energization time while changing the length of the energization time when measuring the internal resistance. A plurality of relationships for each energization time are aggregated to form a relationship group.

In the process of diagnosing the deterioration state, first, the relationship between the charging state of the electrode and the open circuit potential, and the relationship between the charging state of the electrode and the internal resistance for each energization time are prepared in advance as reference information. These relationships are corrected using deterioration state parameters assuming the deterioration state of each electrode of the secondary battery to be diagnosed. The deterioration state parameter is a parameter representing the deterioration state of the positive electrode, the deterioration state of the negative electrode, and the deterioration state of elements other than the electrode.

Then, based on the relationship between the state of charge of the electrode and the open circuit potential corrected by the state of deterioration parameter, the relationship between the state of charge of the secondary battery assumed to be in a deteriorated state and the open circuit voltage is calculated. . Furthermore, based on the relationship between the state of charge of the electrode and the internal resistance corrected by the state of deterioration parameter, the relationship between the state of charge and internal resistance of the secondary battery assumed to be in a deteriorated state is calculated. The relationship between the charging state of the secondary battery and the internal resistance is reproduced based on the relationship for each energization time.

Next, calculation results showing the relationship between the state of charge of the secondary battery and the open circuit voltage based on the reproduction, and calculation results showing the relationship between the state of charge of the secondary battery and the internal resistance based on the reproduction, are used for diagnosis based on actual measurements. Comparison is made with measurement results showing the relationship between the state of charge of the target secondary battery and open circuit voltage, and measurement results showing the relationship between the state of charge and internal resistance of the secondary battery that is the target of diagnosis based on actual measurements. The relationship between the state of charge and internal resistance of the secondary battery is compared for each energization time using each relationship forming the relationship group.

When the measurement results and calculation results are compared and fitting is performed so that the measurement results and calculation results match, the hypothetically set deterioration state parameters are approximated to the true values. Therefore, a solution to the deterioration state parameter can be obtained based on the consistency between the measurement result and the calculation result. Based on the solution of the deterioration state parameters, the deterioration state of the secondary battery and the deterioration state of each electrode of the secondary battery can be quantitatively diagnosed.

The internal resistance of a secondary battery can be calculated as a combination of the internal resistance of the positive electrode that depends on the state of charge, the internal resistance of the negative electrode that depends on the state of charge, and the resistance of elements other than the electrode that does not depend on the state of charge. However, electrodes and elements other than electrodes have different degrees of deterioration. Therefore, it is necessary to set mutually independent deterioration state parameters for the positive and negative electrodes and for each element other than the electrodes. If the deterioration state parameters are set separately, there will be a large number of variables, so if there is little battery information, there is a problem that a single solution for the deterioration state parameters cannot be obtained.

On the other hand, in the method for diagnosing the state of a secondary battery according to the present embodiment, in diagnosing the state of deterioration, the state of charge of the secondary battery is determined based on the relationship between the state of charge and the internal resistance of the secondary battery for each different energization time. A relational group showing the dependence of the charging state and the internal resistance on the energization time is used. By using a plurality of relationships collected for each energization time while changing the length of energization time when measuring internal resistance, it is possible to obtain an independent solution for the deterioration state parameter set for each electrode and each element other than the electrode.

Specifically, in the method for diagnosing the condition of a secondary battery according to the present embodiment, the relationship between the state of charge and the internal resistance of the secondary battery for each different energization time is compared to determine whether the state of charge of the secondary battery depends on the state of charge. It is possible to determine the magnitude of the resistance component that does not depend on the state of charge, excluding the reaction resistance component and the diffusion resistance component that depends on the state of charge. Therefore, the deterioration state of the secondary battery and the deterioration state of each electrode of the secondary battery can be diagnosed with high accuracy.

In this specification, the state of charge means 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 is determined by mutual factors such as the state of charge SOC [%], the amount of discharge from a fully charged state [Ah], the amount of charge from a fully discharged state [Ah], and the composition ratio of charge carrier elements contained in the active material. It can be expressed as an appropriate state quantity that can be converted into .

FIG. 1 is a diagram showing the configuration of a secondary battery condition diagnosis device according to the present embodiment.
As shown in FIG. 1, a secondary battery condition diagnosis device 100 according to the present embodiment includes a calculation section 10, a storage section 20, an input section 30, an output section 40, and a communication section 50. There is.

The condition diagnosis device 100 is a device for diagnosing the deterioration condition of a secondary battery, and can be configured by hardware such as a computer. The state diagnosis device 100 executes processing for diagnosing the deterioration state of the secondary battery according to a predetermined program. As long as the condition diagnosis device 100 includes at least the calculation section 10, the storage section 20, the input section 30, the output section 40, the communication section 50, etc. can be configured as appropriate.

The calculation unit 10 reads various data and programs, executes programs, calculates states, and the like. The calculation unit 10 is configured by, for example, a calculation device such as a CPU (Central Processing Unit). In addition to the process of diagnosing the deterioration state of the secondary battery, the calculation unit 10 also performs the process of calculating the operating condition of the secondary battery based on the diagnosis result of the deterioration state, and the process of executing the operating condition of the secondary battery. A process of generating a control signal may also be performed.

The storage unit 20 stores various data and programs. The storage unit 20 is configured by a storage device such as a RAM (Random Access Memory) or a ROM (Read Only Memory). Various data and programs may be stored in writable and readable hard disks, flash memories, magnetic disks, optical disks, and the like.

The input unit 30 is a device that receives input from an operator. The input unit 30 includes, for example, a keyboard, a mouse, a touch panel, and the like. 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, contents of various data, diagnosis status, diagnosis results, etc. The output unit 40 is configured by, for example, a liquid crystal display, an organic EL display, a cathode ray tube, or the like. 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 to and from external measuring instruments and the like. The communication unit 50 can be connected to an external measuring device or the like via a communication interface, an input/output interface, etc. (not shown). As the measuring device, a charging/discharging tester or the like that can measure the voltage and current of a secondary battery that has a function of charging and discharging under predetermined conditions can be connected.

The condition diagnosis device 100 receives measurement data indicating the relationship between the state of charge of the secondary battery and the open circuit voltage, and measurement data indicating a relationship group indicating the current-carrying time dependence between the state of charge of the secondary battery and the internal resistance. , is input as input information. This input information may be input from an external measuring device or the like via the communication unit 50, or may be input from a writable and readable storage medium or external storage device. Further, the information may be stored in the storage unit 20 after being input.

Measurement data showing the relationship between the state of charge and open circuit voltage of the secondary battery is collected by intermittently measuring the open circuit voltage for each state of charge of the secondary battery being diagnosed. . Measurement data indicating the relationship between the state of charge of the secondary battery and the open circuit voltage is collected through actual measurement and then input to the state diagnostic device 100. Measured data indicating the relationship between the state of charge of the secondary battery and the open circuit voltage may be expressed as a relational expression or as a data table.

The measurement data showing the relational group showing the dependence of the charging state and internal resistance of the secondary battery on the current supply time is the measurement data that shows the internal resistance for each state of charge of the secondary battery to be diagnosed, for each current supply time and for each state of charge. Collected by intermittent measurements. Measurement data indicating a relational group indicating the dependence of the charging state of the secondary battery on the energization time and the internal resistance is input to the state diagnosis device 100 after being collected through actual measurements. The measurement data indicating a relational group indicating the current-carrying time dependence of the state of charge of the secondary battery and the internal resistance may be expressed as a relational expression or as a data table.

The measurement data indicating the relationship between the state of charge of the secondary battery and the open circuit voltage includes data indicating the state of charge and data indicating the open circuit voltage of the secondary battery for a predetermined state of charge. The measurement data showing the relationship group showing the dependence of the charging state and the internal resistance of the secondary battery on the energizing time are data showing the energizing time, data showing the charging state associated with the data showing the energizing time, and data showing the energizing time. and data indicating the internal resistance of the secondary battery for a predetermined state of charge associated with the data indicating.

The condition diagnostic device 100 also includes reference data indicating the relationship between the positive electrode charging state specific to the positive electrode material and the open circuit potential, reference data indicating the relationship between the negative electrode charging state specific to the negative electrode material and the open circuit potential, Reference data showing a relationship group showing the current-carrying time dependence between the positive electrode charge state and internal resistance specific to the positive electrode material, and a relationship showing the current-carrying time dependence between the negative electrode charge state and internal resistance specific to the negative electrode material. Reference data indicating the group is input as input information. These input information are input in advance of the process of diagnosing the deterioration state and are stored in the storage unit 20.

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

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

The reference data indicating a relational group indicating the current-carrying time dependence between the positive electrode state of charge and internal resistance specific to the positive electrode material is composed of the relationship between the positive electrode state of charge and internal resistance for each different current-carrying time. Reference data indicating the relationship between the charging state of the positive electrode and the internal resistance for each energizing time is collected by intermittently measuring the internal resistance of the positive electrode for each energizing time and charging state. A plurality of reference data for each energization time is collected to constitute reference data indicating a relation group.

The reference data showing the relationship group showing the current-carrying time dependence between the charging state of the positive electrode and the internal resistance specific to the positive electrode material includes data showing the current-carrying time, data showing the charging state associated with the data showing the current-carrying time, and , and data indicating the internal resistance of the positive electrode for a predetermined state of charge associated with the data indicating the energization time.

The reference data indicating a relationship group indicating the current-carrying time dependence between the negative electrode state of charge and internal resistance specific to the negative electrode material is constituted by the relationship between the negative electrode state of charge and internal resistance for different current-carrying times. Reference data indicating the relationship between the state of charge of the negative electrode and the internal resistance for each energizing time is collected by intermittently measuring the internal resistance of the negative electrode for each energizing time and each charging state. A plurality of reference data for each energization time is collected to constitute reference data indicating a relation group.

The reference data showing the relationship group showing the current-carrying time dependence between the charging state of the negative electrode and the internal resistance specific to the negative electrode material includes data showing the current-carrying time, data showing the charging state associated with the data showing the current-carrying time, and , and data indicating the internal resistance of the negative electrode for a predetermined state of charge associated with the data indicating the energization time.

As the reference data, for example, data of an electrode in an initial state in which deterioration has not substantially progressed can be used. For example, after a half cell is manufactured using the manufactured electrode, data on the electrode in the initial state can be collected based on actual measurements during the first to fifth charging or discharging processes. Since an irreversible reaction may occur on the electrode during the first charging or discharging process, it is preferable to collect it during the second to fifth charging and discharging processes.

As the reference data, it is preferable to prepare a plurality of data for each type of active material used in the electrode. As reference data, prepare data for various electrodes depending on the type of active material used in the secondary battery being diagnosed and the type of active material expected to be used. It is preferable. Even if the type of active material used in the secondary battery to be diagnosed is unknown, the deterioration state can be diagnosed with high accuracy by performing fitting while replacing reference data.

The measurement data of the secondary battery and the reference data of the electrodes may be acquired during the charging process or during the 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 that the measurement data of the secondary battery and the reference data of the electrodes be acquired in the same charging/discharging process.

Measurement data of secondary batteries and reference data of electrodes can be collected by repeatedly measuring the open circuit voltage at any charging state or measuring the internal resistance at any charging state while changing the charging state. . It is preferable to measure the open circuit voltage and internal resistance for a plurality of states of charge within the working voltage range of the secondary battery.

Measurement data of the secondary battery and reference data of the electrodes can be collected during the intermittent charging and discharging process. For example, after a secondary battery or half cell is charged or discharged to a predetermined state of charge, it is charged or discharged for a certain period of time with a small constant current, and then paused for a predetermined period of time to reach another predetermined state of charge. The open circuit voltage and current can be measured and collected at each charging state while repeating up to 30 seconds.

In the process of intermittent charging and discharging, the charging and discharging pause time is preferably 10 minutes or more, more preferably 30 minutes or more. If sufficient time is allowed for charging and discharging pauses, the electrochemical state of the active material and the movement of charge carriers will be closer to equilibrium, resulting in more accurate open circuit voltage and internal resistance. can be measured.

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

It is preferable to measure the open circuit voltage for a plurality of charging states that are different from each other. From the viewpoint of accurate diagnosis, the number of measurement points for measuring open circuit voltage is preferably 10 or more. The number of measurement points for measuring open circuit voltage is preferably 50 or less from the viewpoint of reducing the number of measurements.

Measurement data indicating a relational group indicating the dependence of the charging state of the secondary battery on the energization time and the internal resistance can be obtained based on actual measurements of the internal resistance of the secondary battery for different energization times. By starting to supply a charging/discharging current to the secondary battery to be diagnosed and measuring the voltage V and current I after a predetermined period of time, the internal resistance R = ΔV/ΔI for each charging state can be calculated. You can ask for it.

The internal resistance of the secondary battery is preferably determined based on the open circuit voltage of the secondary battery and the closed circuit voltage of the secondary battery. Based on the open-circuit voltage and the closed-circuit voltage, measurement data for each state of charge can be collected all at once during the intermittent charging and discharging process.

The internal resistance Rc (Q) [Ω] of the secondary battery in the state of charge Q is the open circuit voltage of the secondary battery in the state of charge Q, OCVc (Q) [V], and the closed circuit voltage of the secondary battery in the state of charge Q. When CCVc (Q) [V] is CCVc (Q) and ΔI [A] is the amount of current up to charging state Q, calculation can be performed using the following equation (1).
Rc(Q)={OCVc(Q)-CCVc(Q)}/ΔI...(1)

The energization time t when measuring the internal resistance needs to be set to at least two types in order to obtain data with different energization amounts ΔI. From the viewpoint of reducing the number of data, the number of types of energization time t is preferably 10 or less, more preferably 5 or less. The types of energization time t are preferably separated by 5 seconds or more, and more preferably 10 seconds or more, so that the measured internal resistance values are significantly different.

The current application time t when measuring the internal resistance is preferably 5 seconds or more, more preferably 30 seconds or more. If the energization time t is too short, the internal resistance will be measured immediately after the start of energization. The internal resistance immediately after the start of energization is largely influenced by IR loss caused by elements other than the electrodes and cannot be measured accurately, so it is preferable not to use it as data.

It is preferable that the internal resistance is measured during one charging/discharging process, either in a continuous charging process towards a fully charged state or in a continuous discharging process towards a fully discharged state. The measurement timing of the internal resistance, that is, the cycle of the energization time t for acquiring data for each energization amount ΔI is preferably T/2 or later, and 2T/ 3 or later is more preferable. This is because as time elapses, an internal resistance with a larger absolute value suitable for accurate measurement occurs.

The measurement data of the secondary battery and the reference data of the electrodes may be data indicating the relationship between the state of charge and the numerical value of the open circuit potential, or data indicating the relationship between the state of charge and the numerical value of the internal resistance. The data may be data indicating the relationship between the state of charge and the differential value of the open circuit potential, or data indicating the relationship between the state of charge and the differential value of the internal resistance. When the differential value of the open circuit potential is used, a relationship that is inversely proportional to the amount of effective active material is obtained, so the correctness of the amount of effective active material can be ensured. By using the differential value of the internal resistance, it is possible to reduce the contribution of voltage drops caused by elements other than the electrodes.

After the process of diagnosing the deterioration state, the condition diagnosis device 100 provides diagnosis result data indicating the deterioration condition of the secondary battery, diagnosis result data indicating the deterioration condition of the positive electrode used in the secondary battery, and diagnostic result data indicating the deterioration condition of the positive electrode used in the secondary battery. Diagnosis result data indicating the deterioration state of the used negative electrode is output as output information. The condition diagnostic device 100 may output any one type of data, or may output multiple types of data, as long as it has the function of outputting these output information. The output information may be displayed as an image on the output unit 40 or may be stored in the storage unit 20 as a database.

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

In the first step (steps S1 to S6), reference data indicating the relationship between the positive electrode charging state and open circuit potential specific to the positive electrode material and the relationship between the negative electrode charging state and open circuit potential specific to the negative electrode material are obtained. Based on the reference data shown, the relationship between the charging state of the secondary battery assumed to be in a deteriorated state and the open circuit voltage is evaluated.

In the second step (steps S7 to S18), among the reference data constituting the relation group, reference data indicating the relationship between the state of charge of the positive electrode and the internal resistance specific to the positive electrode material for each energization time, and reference data for each energization time are selected. The relationship between the state of charge and internal resistance of a secondary battery assumed to be in a deteriorated state is evaluated based on reference data indicating the relationship between the state of charge and internal resistance of the negative electrode specific to the negative electrode material.

In the first step (steps S1 to S6) and the second step (steps S7 to S18), the reference data is corrected with the deterioration state parameter to assume the deterioration state, and the deterioration state is assumed based on the corrected reference data. generate calculation data for the secondary battery. Then, the measured data based on the actual measurement is compared with the calculated data based on the reproduction assuming a deteriorated state, and the consistency between the data is evaluated. By performing fitting so that the data match each other, a solution to the deterioration state parameters is obtained.

<First step: Evaluation based on open circuit voltage>
As shown in FIG. 2, the state diagnosis device 100 first reads measurement data indicating the relationship between the state of charge and open circuit voltage of the secondary battery to be diagnosed. The measurement data can be read from the storage unit 20, an external measuring device connected to the communication unit 50, a storage medium, or an external storage device.

Subsequently, the condition diagnosis device 100 generates reference data indicating the relationship between the positive electrode charging state specific to the positive electrode material and the open circuit potential, and reference data indicating the relationship between the negative electrode charging state specific to the negative electrode material and the open circuit potential. The data is read (step S2). The reference data can be read from the storage unit 20, a storage medium, or an external storage device.

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

FIG. 3 is a diagram showing an example of the relationship between the charged state of the electrode and the open circuit potential.
FIG. 3 corresponds to reference data for a positive electrode using LiFePO ₄ (LFP) as an active material. 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 with respect to the reference electrode.

FIG. 4 is a diagram showing an example of the relationship between the charged state of the electrode and the open circuit potential.
FIG. 4 corresponds to reference data of a negative electrode using graphite as an active material. 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 with respect to the reference electrode.

As shown in FIGS. 3 and 4, the relationship between the charged state of the electrode and the open circuit potential is unique to the active material used as the electrode material. It is preferable to prepare reference data indicating such a relationship as a relational expression or a data table for each of the positive and negative electrodes and for each active material used in the electrode.

As shown in FIG. 3, in an electrode using LFP or the like, the open circuit potential does not substantially fluctuate and remains flat even when the state of charge changes. It is difficult to evaluate the deterioration state of an electrode using such an active material based on the relationship between the charging state of the electrode and the open circuit potential. On the other hand, as shown in FIG. 4, in an electrode using graphite or the like, the open circuit potential fluctuates greatly in response to changes in the state of charge. The state of deterioration of an electrode using such an active material can be evaluated based on the relationship between the state of charge of the electrode and the open circuit potential.

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

Subsequently, the condition diagnosis device 100 sets the deterioration condition parameters of the positive electrode (step S3). In step S3, a deterioration state parameter related to the capacity is set for correcting the relationship between the charging state of the positive electrode and the open circuit potential.

Subsequently, the condition diagnostic device 100 sets the deterioration condition parameter of the negative electrode (step S4). In step S4, a deterioration state parameter regarding the capacity is set for correcting the relationship between the charge state of the negative electrode and the open circuit potential. Note that either step S3 or step S4 may be executed first.

As the deterioration state parameter related to capacity, a coefficient or a constant of a state quantity representing the state of charge can be set in a function indicating the relationship between the state of charge and the open circuit potential or internal resistance. For example, the active material utilization rate mrx of the positive electrode and the negative electrode, the out-of-range capacity δx [Ah] of the positive electrode and the negative electrode, etc. can be set.

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

The out-of-range capacity δx represents a capacity that can only be obtained outside the upper limit voltage and lower limit voltage of the secondary battery, out of the total capacity of the electrode. The total capacitance of the electrode, Qx [Ah], is calculated as expressed.

The total capacitance Qx [Ah] of the electrode can be expressed by the following equation (2), assuming deterioration that causes out-of-range capacitance δx.
Qx=qx×mx−δx...(2)

The deterioration state parameter related to capacity is defined as an arbitrary numerical value at a predetermined interval between an upper limit value and a lower limit value representing a state in which there is no deterioration of the electrode or a state in which the electrode has completely deteriorated. The deterioration state parameter related to the capacity may be linked in data to a coefficient or constant of a state quantity representing the state of charge or a degree of deterioration representing the deterioration state of the electrode. Such deterioration state parameters can be stored in the storage unit 20 as a parameter table.

In step S3 and step S4, any value can be provisionally set as the deterioration state parameter related to capacity. Since the deterioration state of the electrode is unknown at this stage, an arbitrary value is temporarily set and subsequent calculations are performed. By performing fitting while exchanging the deterioration state parameters, the deterioration state parameters can be approximated toward their true values.

Next, the condition diagnosis device 100 uses the reference data indicating the relationship between the positive electrode charge state and the open circuit potential, the reference data indicating the relationship between the negative electrode charge state and the open circuit potential, and the set deterioration state parameter. Based on this, calculation data indicating the relationship between the charging state of the secondary battery and the open circuit voltage is generated (step S5).

The relationship between the state of charge and the open circuit voltage of the secondary battery can be determined by using the relationship between the state of charge of the positive electrode and the open circuit potential, and the relationship between the state of charge of the negative electrode and the open circuit potential. It can be calculated by combining the functions of . The relationship between the state of charge and open circuit potential for each electrode is corrected using the deterioration state parameter. By using the relationship corrected by the deterioration state parameter, calculation data indicating the behavior of the open circuit voltage for each state of charge of the secondary battery in which the deterioration state is assumed is generated.

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

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

As shown in Figure 5, the relationship between the state of charge of the secondary battery and the open circuit voltage is determined by the relationship between the state of charge of the positive electrode and the open circuit potential, which is specific to the positive electrode material, and the state of charge of the negative electrode, which is specific to the negative electrode material. It is determined based on the relationship with the open circuit potential. Using the relationship corrected with the degradation state parameter, the capacitance-open circuit voltage curve will shift up and down due to overvoltage and the flat voltage region will shrink. It is preferable to save measured data showing such a relationship and calculated data reproduced for comparison with the measured data as a relational expression or a data table.

Next, the condition diagnosis device 100 calculates calculation data indicating the relationship between the state of charge of the secondary battery and the open circuit voltage calculated assuming a deteriorated state, and the state of charge and the open circuit voltage of the secondary battery to be diagnosed. It is determined whether the calculated data assuming a deteriorated state and the measured data based on actual measurements match each other (step S6).

Determination as to whether the data match each other can be performed using any determination method. For example, it can be performed based on the sum of squared residuals between data. By calculating the sum of squares of the differences between the calculated data and the measured data, and comparing the sum of squares of the differences with an arbitrarily set threshold, it is possible to determine the consistency between the data.

As the sum of squares of the difference, Σ(Vcc_i-Vce_i) ² is expressed as =1 to N.

The calculated sum of squared differences can be compared with a preset threshold for consistency. As the threshold regarding the consistency of the open circuit potential, an arbitrary value that increases the degree of similarity between the data can be set depending on the accuracy required for diagnosis, the number of repetitions of calculation, and the like. When calculating the sum of squares of differences, if there is no calculated data of the discharge state corresponding to the measured data, the calculated data corresponding to the measured data may be interpolated by interpolation.

As a result of the comparison, if the sum of squares of the difference between the calculated data and the measured data exceeds a preset threshold, the relationship between the state of charge of the secondary battery calculated assuming a deteriorated state and the open circuit voltage is calculated. It can be determined that the calculated data shown and the measured data showing the relationship between the state of charge of the secondary battery to be diagnosed and the open circuit voltage do not match each other. In this case (step S6; NO), another deterioration state parameter is reset, and the calculation data is regenerated and recompared.

On the other hand, as a result of the comparison, if the sum of squares of the difference between the calculated data and the measured data is less than or equal to a preset threshold, the relationship between the charging state of the secondary battery and the open circuit voltage calculated assuming a deteriorated state It can be determined that the calculated data indicating the relationship between the charging state of the secondary battery to be diagnosed and the open circuit voltage match each other. In this case (step S6; YES), the set deterioration state parameter is adopted and the process moves to a second step (steps S7 to S18) in which evaluation is performed based on internal resistance.

The adopted deterioration state parameter is registered in the storage unit 20 in association with an identifier for identifying the secondary battery to be diagnosed and an identifier for identifying the electrode. In the first step (steps S1 to S6), deterioration state parameters are set assuming a deterioration state. Therefore, the registered deterioration state parameters can be updated according to the results of the second step (steps S7 to S18).

In addition, in the first step (S1 to S6), resetting the deterioration state parameters and regenerating and recomparing the calculated data based on the reset deterioration state parameters is performed so that the calculated data and the measured data match each other. This can be repeated any number of times until it is determined that As the deterioration state parameters, values that have not been set in previous calculations can be set in order.

To determine whether calculated data and measured data match each other, instead of comparing the sum of squares of the difference between calculated data and measured data with a predetermined threshold, The determination can also be made by comparing the amount of decrease for each calculation of the sum with a predetermined threshold. For repeated regeneration and re-comparison of calculation data, when the decrease in the sum of squares of the current difference from the sum of squares of the previous difference becomes less than a predetermined value, it is determined that the data match each other. be able to.

In diagnosis based on open circuit voltage, if calculated data and measured data do not match each other for a predetermined number of calculations or for a predetermined calculation time, the diagnostic process can be stopped. Alternatively, by replacing the reference data with the reference data of an electrode using a different active material, it is possible to reset the deterioration state parameters, and to regenerate and recompare the calculated data based on the reset deterioration state parameters.

The reference data regarding the open circuit potential is preferably stored in the storage unit 20 as a database in association with an identifier that identifies the positive electrode and the negative electrode, and an identifier that identifies the type of active material used in the electrode. . By preparing such a database, even if the type of active material used in the secondary battery that is the subject of diagnosis is unknown, it is possible to regenerate and re-comparison the calculated data by replacing the reference data. It is possible to conduct a thorough evaluation.

<Second step: Evaluation based on internal resistance>
As shown in FIG. 2, after the evaluation based on the open circuit voltage, the state diagnostic device 100 generates measurement data showing a relationship group showing the current-carrying time dependence between the state of charge and the internal resistance of the secondary battery to be diagnosed. Read (step S7). The measurement data can be read from the storage unit 20, an external measuring device connected to the communication unit 50, a storage medium, or an external storage device.

Subsequently, the condition diagnosis device 100 obtains reference data indicating a relational group indicating the energization time dependence between the positive electrode charging state and internal resistance specific to the positive electrode material, and the negative electrode charging state and internal resistance specific to the negative electrode material. Reference data indicating a relational group indicating the energization time dependence of is read (step S8). The reference data can be read from the storage unit 20, a storage medium, or an external storage device.

Reference data of an electrode using any active material can be read as the reference data indicating a relational group indicating the dependence of the charging state of the electrode and the internal resistance on the current application time. Even if the type of electrode or active material is unknown at this stage, the state of deterioration can be appropriately evaluated by performing fitting while replacing reference data. However, if the type of active material is known or can be predicted, it is preferable to read the reference data of the corresponding electrode.

As reference data showing the relational group showing the current-carrying time dependence between the charging state of the electrode and the internal resistance, the data of the electrode for each current-carrying time constituting the relational group showing the current-carrying time dependence between the charging state of the electrode and the internal resistance is used. Data corresponding to part or all of the relationship between the state of charge and the internal resistance may be read. If the reference data of the energization time corresponding to the energization time of the measurement data is read, appropriate evaluation can be performed based on the energization time dependence of the internal resistance.

Subsequently, the state diagnostic device 100 starts analysis based on the energization time dependence of the charging state and internal resistance (step S9). The state diagnosis device 100 specifies which energization time data is to be analyzed and the energization time to be analyzed.

As the energization time to be analyzed, any energization time among the energization times for which measurement data was acquired can be specified. The energization times to be analyzed can be specified, for example, in ascending order or descending order from the measurement data. Among the reference data indicating the relationship group, measurement data and reference data of the energization time of the identified analysis target are extracted, and analysis is performed based on the energization time dependence of the state of charge and internal resistance.

FIG. 6 is a diagram illustrating an example of the relationship between the charging state of the electrode and the internal resistance for each energization time.
FIG. 6 corresponds to reference data of a positive electrode using LiFePO ₄ (LFP) as an active material. 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 internal resistance Rp [mΩ·g] of the positive electrode. The 〇 plot is the result of energization time t = 40 seconds, the ● plot is the result of energization time t = 50 seconds, the △ plot is the result of energization time t = 60 seconds, and the ▲ plot is the result of energization time t =72 seconds.

FIG. 7 is a diagram illustrating an example of the relationship between the charging state of the electrode and the internal resistance for each energization time.
FIG. 7 corresponds to reference data of a negative electrode using graphite as an active material. 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 internal resistance Rn [mΩ·g] of the negative electrode. The 〇 plot is the result of energization time t = 40 seconds, the ● plot is the result of energization time t = 50 seconds, the △ plot is the result of energization time t = 60 seconds, and the ▲ plot is the result of energization time t =72 seconds.

As shown in FIGS. 6 and 7, the relationship between the charged state of the electrode and the internal resistance is unique to the active material used as the electrode material. Reference data showing such relationships can be prepared as a relational formula or data table for each positive and negative electrode, each active material used in the electrode, and each energization time when measuring internal resistance. preferable.

As shown in Figure 6, even for active materials whose open circuit potential does not substantially change with changes in the state of charge, the internal resistance generally changes with changes in the state of charge of the electrode. . The state of deterioration of an electrode using such an active material can be evaluated by referring to the relationship between the state of charge and internal resistance of the electrode. However, if there are no feature points on the curves, it is difficult to compare the curves using the feature points as a reference. Since direct fitting between curves cannot be performed in sections where there are feature points, more battery information is required.

If battery information about the secondary battery to be diagnosed is insufficient, even if fitting is performed, it may not be possible to converge the deterioration state parameters to a single solution. Therefore, in the analysis that follows, we will use measurement data that shows the relationship between the state of charge and internal resistance of the secondary battery to be diagnosed for each energization time, and the relationship between the state of charge and internal resistance of the secondary battery for each energization time. Fit the calculated data that shows the relationship.

The state diagnosis device 100 determines the state of charge of the electrode corresponding to the specified energization time of the analysis target from among the reference data indicating a relational group indicating the energization time dependence between the state of charge of the electrode unique to the electrode material and the internal resistance. Reference data showing the relationship between the internal resistance and the internal resistance is extracted as basic data. In addition, among the measurement data showing the relationship group showing the dependence of the charging state of the secondary battery to be diagnosed and the internal resistance on the current-on time, the charging state of the secondary battery corresponding to the current-on time of the specified analysis target is determined. Measured data showing the relationship with internal resistance is extracted as an analysis target. If there is no reference data corresponding to the specified energization time of the analysis target, the reference data may be interpolated by interpolation.

Subsequently, the condition diagnosis device 100 sets the deterioration condition parameters of the positive electrode (step S10). In step S10, a deterioration state parameter regarding the resistance is set for correcting the relationship between the charging state of the positive electrode and the internal resistance.

Subsequently, the condition diagnostic device 100 sets the deterioration condition parameter of the negative electrode (step S11). In step S11, a deterioration state parameter regarding the resistance is set for correcting the relationship between the charging state of the negative electrode and the internal resistance. Note that either step S10 or step S11 may be executed first. Deterioration state parameters for elements other than electrodes may be set at any stage.

As deterioration state parameters related to resistance, it is possible to set a coefficient of the resistance term for each electrode that depends on the state of charge in a function that shows the relationship between the state of charge and internal resistance, and a constant corresponding to the resistance of elements other than the electrodes. can. For example, the resistance R0 of elements other than the electrode, the resistance coefficient ax of the internal resistance of the positive electrode and the negative electrode, etc. can be set.

The internal resistance Rx(Q) [Ω] of the electrode in the state of charge Q is calculated by assuming the deterioration represented by the resistance coefficient ax, the amount of active material used that contributes to the charge/discharge reaction, mx [g], and the amount of active material used in the state of charge Q. When the internal resistance of the material is rx (Q) [Ω・g], the total capacitance of the electrode is Qx [Ah], and the capacitance per unit mass of the electrode is qx [Ah/g], it can be expressed by the following equation (4). I can do it.
Rx(Qx)=ax/mx×rx(qx)...(4)

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

In step S10 and step S11, any value can be provisionally set as the deterioration state parameter regarding the resistance. Since the deterioration state of the electrode is unknown at this stage, an arbitrary value is temporarily set and subsequent calculations are performed. By performing fitting while exchanging the deterioration state parameters, the deterioration state parameters can be approximated toward their true values.

Subsequently, the condition diagnosis device 100 generates reference data indicating the relationship between the state of charge of the positive electrode and internal resistance for each predetermined energization time, and reference data indicating the relationship between the state of charge of the negative electrode and the internal resistance for each predetermined energization time. Based on the data and the set deterioration state parameters, calculation data indicating the relationship between the charging state of the secondary battery and the internal resistance for each predetermined energization time is generated (step S12).

The relationship between the state of charge and internal resistance of a secondary battery is determined by using the relationship between the state of charge and internal resistance of the positive electrode and the state of charge and internal resistance of the negative electrode. It can be calculated by composition. The relationship between the state of charge and internal resistance for each electrode is corrected using the deterioration state parameter. By using the relationship corrected with the deterioration state parameter, calculation data indicating the behavior of the internal resistance for each state of charge of the secondary battery in which the deterioration state is assumed is generated.

The internal resistance Rc (t, Q) [Ω] of the secondary battery in the state of charge Q that occurs during the energization time t is the internal resistance of the positive electrode in the state of charge Q that occurs during the energization time t as rp (t, Q) [Ω・g ], the internal resistance of the negative electrode in the state of charge Q that occurs at the energization time t is rn (t, Q) [Ω・g], the resistance of elements other than the electrode is R0 [mΩ], the resistance coefficient of the internal resistance of the positive electrode is ap, When the resistance coefficient of the internal resistance of the negative electrode is an, it can be calculated using the following equation (5).
Rc (t, Qc) = ap/mp x rp (t, qp)
+an/mn×rn(t, qn)+R0...(5)

FIG. 8 is a diagram showing an example of the relationship between the charging state of the secondary battery and the internal resistance for each energization time.
FIG. 8 corresponds to measurement data of a secondary battery using LFP as a positive electrode active material and graphite as a negative electrode active material. The horizontal axis indicates the discharge amount Qc [Ah] from a fully charged state of the secondary battery, as an example of the charging state of the secondary battery. The vertical axis indicates the internal resistance Rc [mΩ] of the secondary battery. The 〇 plot is the result of energization time t = 40 seconds, the ● plot is the result of energization time t = 50 seconds, the △ plot is the result of energization time t = 60 seconds, and the ▲ plot is the result of energization time t =72 seconds.

As shown in Figure 8, the relationship between the state of charge and internal resistance of a secondary battery is the relationship between the state of charge of the positive electrode and internal resistance specific to the positive electrode material, and the state of charge of the negative electrode and internal resistance specific to the negative electrode material. It is determined based on the relationship between Using the relationship corrected by the state of deterioration parameter, the capacitance-resistance curve shifts up and down depending on the assumed state of deterioration. Further, a vertical shift occurs depending on the energization time. It is preferable to save measured data showing such a relationship and calculated data reproduced for comparison with the measured data as a relational expression or a data table.

In step S12, calculation data indicating the relationship between the state of charge and internal resistance of the secondary battery for each energization time is calculated for the energization time converted by a weighting function ρ(t) according to the estimated deterioration rate. It is preferable that That is, it is preferable to calculate based on reference data in which the energization time t is replaced with a weighting function ρ(t).

The weighting function ρ(t) is ρ(t)=exp(-k _A t), ρ(t)=k _B (t) ^-1/2 , ρ(t)=exp(-k _A t)+k _B (t) ^-1/2 etc. can be used. Here, k _A and k _B are constants. The constants k _A and k _B can be determined by a preliminary test based on actual measurement of internal resistance.

The reference data is data in which the dependence of the internal resistance value on the energization time t does not change. On the other hand, the measured data to be compared with the calculated data is data in which the dependence of the internal resistance value on the energization time t changes due to capacity deterioration or the like. If calculation data is generated by converting with a weighting function ρ(t) according to the estimated deterioration rate, changes in internal resistance depending on the energization time t can be reflected in the calculation data, so it is necessary to prepare the calculation data for each energization time. Accurate diagnosis can be made while suppressing the number of reference data.

Subsequently, the condition diagnosis device 100 calculates calculation data indicating the relationship between the state of charge and internal resistance of the secondary battery for each predetermined energization time calculated assuming a deteriorated state, and the diagnosis target for each predetermined energization time. Compare measured data showing the relationship between the state of charge and internal resistance of a certain secondary battery to determine whether calculated data assuming a deteriorated state and measured data based on actual measurements match each other. (Step S13).

Determination as to whether the data match each other can be performed using any determination method. For example, it can be performed based on the sum of squared residuals between data. By calculating the sum of squares of the differences between the calculated data and the measured data, and comparing the sum of squares of the differences with an arbitrarily set threshold, it is possible to determine the consistency between the data.

As the sum of squares of the difference, when the calculated values of internal resistance in the calculation data are Rcc_1 to Rcc_N and the measured values of internal resistance in the measured data are Rce_1 to Rce_N, Σ(Rcc_i-Rce_i) ² is defined as i=1 ~N can be calculated.

The calculated sum of squared differences can be compared with a preset threshold for consistency. As the threshold value regarding the consistency of internal resistance, an arbitrary value that increases the degree of similarity between data can be set depending on the accuracy required for diagnosis, the number of repetitions of calculation, etc. When calculating the sum of squares of differences, if there is no calculated data of the discharge state corresponding to the measured data, the calculated data corresponding to the measured data may be interpolated by interpolation.

As a result of the comparison, when the sum of squares of the difference between the calculated data and the measured data exceeds a preset threshold, the relationship between the state of charge and internal resistance of the secondary battery calculated assuming a deteriorated state is shown. It can be determined that the calculated data and the measured data indicating the relationship between the state of charge and internal resistance of the secondary battery to be diagnosed do not match each other. In this case (step S13; NO), another deterioration state parameter is reset, and the calculation data is regenerated and recompared.

On the other hand, as a result of the comparison, if the sum of squares of the difference between the calculated data and the measured data is less than or equal to a preset threshold, the relationship between the state of charge and internal resistance of the secondary battery calculated assuming a deteriorated state is It can be determined that the calculated data shown and the measured data showing the relationship between the state of charge and internal resistance of the secondary battery to be diagnosed are in agreement with each other. In this case (step S13; YES), the set deterioration state parameter is adopted and the process moves to step S14.

Next, the condition diagnosis device 100 determines whether a single solution corresponding to the true value of the degraded condition parameter can be determined based on the comparison result (step S14). In step S14, it is evaluated whether a single solution has been obtained for the resistance R0 of elements other than the electrodes that do not depend on the discharge state among the deterioration state parameters.

To determine whether a single solution can be determined, compare the past deterioration state parameters adopted in the analysis that specified the energization time with the latest deterioration state parameters adopted in the analysis that changed the energization time. done by. Based on the degree of similarity between the past deterioration state parameters and the latest deterioration state parameters, it can be evaluated whether the solutions of the deterioration state parameters have converged to one.

The internal resistance of a secondary battery takes different values depending on the energization time. Similarly, the internal resistance of the positive electrode, which depends on the state of charge, and the internal resistance of the negative electrode, which depends on the state of charge, take different values depending on the current application time. On the other hand, the resistance R0 of the elements other than the electrodes, which does not depend on the state of charge, does not substantially depend on the energization time except immediately after the start of energization. Therefore, by comparing the past deterioration state parameters and the latest deterioration state parameters while changing the energization time, a common solution that does not depend on the energization time can be obtained as a single solution.

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

As the threshold value, it is preferable to use a value such that the difference between the past deterioration state parameter and the latest deterioration state parameter is less than 10% of the past deterioration state parameter, and preferably less than 5%. is more preferable. The resistance R0 of elements other than electrodes is usually 10 mΩ or more. When such numerical values are used, determination can be made with an error of less than 1 mΩ.

Further, it is possible to determine whether a single solution corresponding to the true value of the deterioration state parameter can be determined by cluster analysis. For example, by repeating an analysis that specifies the energization time, calculation results of deterioration state parameters can be collected, and the calculation results can be clustered using the energization time as one of the variables. When the latest degraded state parameters are clustered within a predetermined distance and with a predetermined number of samples, it can be determined that a single solution corresponding to the true value can be determined. On the other hand, when the latest degraded state parameters are not clustered within a predetermined distance with a predetermined number of samples, it can be determined that a single solution corresponding to the true value cannot be determined.

In the case of cluster analysis, a representative value of a cluster to which a sample is assigned under predetermined conditions may be employed as a single solution corresponding to the true value of the deterioration state parameter. Representative values include average values, median values, mode values, and the like. Further, when a plurality of clusters to which samples are assigned are formed, the representative value of the cluster to which the sample with the longest energization time is assigned can be employed. This is because the longer the current application time, the larger the absolute value of the internal resistance, and the higher the accuracy.

As a result of the analysis, if it is determined that a single solution corresponding to the true value of the deterioration state parameter cannot be determined (step S14; NO), the process moves to step S15 because analysis for each energization time is insufficient.

On the other hand, if it is determined as a result of the analysis that a single solution corresponding to the true value of the deterioration state parameter can be determined (step S14; YES), the analysis for each energization time is sufficient, so the process moves to step S17.

If it is determined that a single solution cannot be determined, the state diagnostic device 100 determines whether data corresponding to all energization times has been analyzed as an analysis target (step S15). In step S15, it is determined whether analysis has been performed based on the measurement data corresponding to all the energization times among the measurement data of the secondary battery collected for each energization time.

As a result of the determination, if it is determined that the data corresponding to all the energization times have not been analyzed (step S15; NO), the process moves to step S16. Next, the state diagnosis device 100 changes the energization time of the analysis target (step S16). Then, the measurement data and reference data of the changed energization time of the analysis target are extracted, and the analysis based on the energization time dependence of the state of charge and internal resistance is restarted. The energization times to be analyzed can be changed, for example, in ascending order or descending order from the measured data.

On the other hand, as a result of the determination, if it is determined that the data corresponding to all the energization times have been analyzed as analysis targets (step S15; YES), the analysis for each energization time is sufficient, so the process moves to step S17. .

If it is determined that a single solution can be determined, or if it is determined that data corresponding to all energization times are analyzed, an analysis based on the energization time dependence of the state of charge and internal resistance is performed. The process ends (step S17). Next, the state diagnosis device 100 determines the remaining deteriorated state parameters based on the single solution corresponding to the true value of the deteriorated state parameter (R0) (step S18). Thereafter, the processing for diagnosing the deterioration state ends.

The remaining deterioration state parameters, such as the resistance coefficient ax of the internal resistance of the positive electrode and negative electrode, are calculated by combining R0 corresponding to the true value and the formula (4 ) etc. can be recalculated based on Further, the active material utilization rate mrx of the positive electrode and the negative electrode and the out-of-range capacity δx of the positive electrode and the negative electrode can be recalculated.

Alternatively, for the remaining deterioration state parameters such as the resistance coefficient ax of the internal resistance of the positive electrode and the negative electrode, data corresponding to the deterioration state parameter (R0) corresponding to the true value can be obtained from the database in which the adopted deterioration state parameters are stored. It can also be extracted as When extracting from the database, there may be a plurality of data such as the resistance coefficient ax corresponding to the deterioration state parameter (R0) corresponding to the true value. In this case, data specifying the maximum energization time can be employed. This is because the longer the energization time is, the larger the absolute value of the internal resistance becomes, and the higher the accuracy of fitting becomes.

The deterioration state parameter (R0) corresponding to the true value and the remaining deterioration state parameters (ax, mrx, δx, etc.) are linked with an identifier that identifies the secondary battery to be diagnosed and an identifier that identifies the electrode. , are registered in the storage unit 20. The deterioration state parameters related to capacity and the deterioration state parameters related to internal resistance are registered in association with each other.

Note that in the second step (S7 to S18), the resetting of the deterioration state parameters and the regeneration and recomparison of the calculated data based on the reset deterioration state parameters are performed so that the calculated data and the measured data match each other. This can be repeated any number of times until it is determined that As the deterioration state parameters, values that have not been set in previous calculations can be set in order.

To determine whether calculated data and measured data match each other, instead of comparing the sum of squares of the difference between calculated data and measured data with a predetermined threshold, The determination can also be made by comparing the amount of decrease for each calculation of the sum with a predetermined threshold. For repeated regeneration and re-comparison of calculation data, when the decrease in the sum of squares of the current difference from the sum of squares of the previous difference becomes less than a predetermined value, it is determined that the data match each other. be able to.

Further, whether or not the calculated data and the measured data match each other can also be determined by comparing the minimum value of the sum of squares of the difference between the calculated data and the measured data with a predetermined threshold value. It is also possible to determine that the data match each other when the minimum value of the calculation results of the sum of squares of differences becomes equal to or less than a predetermined value after a predetermined number of calculations or a predetermined calculation time.

In the diagnosis based on internal resistance, if the calculated data and the measured data do not match each other after a predetermined number of calculations or a predetermined calculation time, the diagnostic processing can be stopped. Alternatively, by replacing the reference data with the reference data of an electrode using a different active material, it is possible to reset the deterioration state parameters, and to regenerate and recompare the calculated data based on the reset deterioration state parameters. The diagnosis based on the open circuit voltage may be redone using the deterioration state parameters set in the diagnosis based on the internal resistance.

The reference data regarding the internal resistance is preferably stored in the storage unit 20 as a database in association with an identifier that identifies the positive electrode and the negative electrode, and an identifier that identifies the type of active material used for the electrode. By preparing such a database, even if the type of active material used in the secondary battery that is the subject of diagnosis is unknown, it is possible to regenerate and re-comparison the calculated data by replacing the reference data. It is possible to conduct a thorough evaluation.

FIG. 9 is a diagram illustrating an example of the relationship between the charging state of a secondary battery assumed to be in a deteriorated state and the open circuit voltage.
Figure 9 shows the results of calculation data for a secondary battery using LFP as the positive electrode active material and graphite as the negative electrode active material, generated based on reference data corrected with deterioration state parameters, and fitted to the measured data. be. The horizontal axis indicates the discharge amount Qc [Ah] from a fully charged state of the secondary battery, as an example of the charging state of the secondary battery. The vertical axis indicates the open circuit voltage Vc [V].
The broken line is the reference data of the positive electrode corrected with the deterioration state parameter, the dotted line is the reference data of the negative electrode corrected with the deterioration state parameter, the solid line is the calculated data of the secondary battery, and the plot of ○ is the measured data of the secondary battery. handle.

FIG. 10 is a diagram illustrating an example of the relationship between the state of charge and internal resistance of a secondary battery assumed to be in a deteriorated state.
Figure 10 shows the results of calculation data for a secondary battery using LFP as the positive electrode active material and graphite as the negative electrode active material, generated based on reference data corrected with deterioration state parameters, and fitted to the measured data. be. The horizontal axis indicates the discharge amount Qc [Ah] from a fully charged state of the secondary battery, as an example of the charging state of the secondary battery. The vertical axis indicates the internal resistance Rc [mΩ] of the secondary battery. The broken line is the reference data of the positive electrode corrected with the deterioration state parameter, the dotted line is the reference data of the negative electrode corrected with the deterioration state parameter, the solid line is the calculated data of the secondary battery, and the plot of ○ is the measured data of the secondary battery. handle.

As shown in Figures 9 and 10, the calculated data showing the relationship between the charging state of the secondary battery and the open circuit voltage, and the calculated data showing the relationship between the charging state of the secondary battery and the internal resistance, are different from the measured data. Fitted to match. The fitted calculation data and the deterioration state parameters employed in the fitting can be saved as a relational expression or data table indicating the diagnosis result.

<Output information>
When the first process (steps S1 to S6) and the second process (steps S7 to S18) are completed, the output unit 40 outputs the adopted deterioration state parameters, the deterioration state diagnosis results for each electrode, and the It is possible to output the diagnosis result of the deterioration state. The diagnosis results of the deterioration state of each electrode and the deterioration state of the secondary battery can be displayed as a graph, a table, or the like.

Diagnosis results of the deterioration state of each electrode include calculation data showing the relationship between the electrode state of charge and open circuit potential corrected by the adopted deterioration state parameters, and calculation data showing the relationship between the electrode state of charge and open circuit potential corrected by the adopted deterioration state parameters. Calculated data showing the relationship between the state of charge and internal resistance can be cited. The calculated data indicating the relationship between the charging state of the electrode and the internal resistance may be displayed independently as data for each energization time, or the data for each energization time may be displayed all at once. These data can be displayed for each positive electrode and negative electrode.

Diagnosis results of the deterioration state of the secondary battery include data on the state of health (SOH) of the secondary battery and the state of charge of the secondary battery synthesized from calculation data for each electrode and the open circuit voltage. Examples include calculated data showing the relationship, and calculated data showing the relationship between the state of charge of the secondary battery and the internal resistance synthesized from calculated data for each electrode. The calculated data indicating the relationship between the state of charge of the secondary battery and the internal resistance may be displayed independently as data for each energization time, or the data for each energization time may be displayed all at once.

The state of deterioration (SOH) can be output as a capacity retention rate SOHQ, a resistance increase rate SOHR, etc. The state of deterioration (SOH) is expressed by a capacity ratio with respect to a predetermined reference state, a rate of change of a deterioration state parameter with respect to a predetermined reference state, and the like.

The capacity maintenance rate SOHQ [%] is the capacity of the secondary battery in the initial state in the fully charged state, Qmax0 [Ah], the capacity of the secondary battery in the deteriorated state in the fully charged state as Qmax1 [Ah], and the capacity of the secondary battery in the deteriorated state in the fully charged state as Qmax0 [Ah]. When the charging states of the upper and lower limits of the integration interval of the battery are SOC1 [%] and SOC2 [%], calculation can be performed using the following equations (6) to (7).
SOHQ=Qmax1/Qmax0×100[%]...(6)
Qmax1=∫Idt/((SOC1-SOC2)/100)...(7)

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

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, change the upper and lower limits of the state of charge 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 do.

For example, a potential range in which the positive electrode material can be appropriately used and a potential range in which the negative electrode material can be appropriately used are determined in advance. If the open circuit potential changes due to deterioration of either the positive or negative electrode, the upper and lower voltage limits can be changed to ensure capacity within the potential range that can be used properly. can.

Further, the diagnosis result of the deterioration state of the secondary battery can be saved as a database for each diagnosis request. Diagnosis result data may be collected for each different secondary battery, or may be collected by performing diagnosis on the same secondary battery at different times. These diagnostic results can be stored in the condition diagnostic device 100 for each diagnostic request and as time-series diagnostic result data.

Diagnosis result data indicating the diagnosis result of the deterioration state of the secondary battery can be linked with an identifier for identifying the diagnosis request, data indicating the date and time of diagnosis, and data indicating the usage history of the secondary battery. The usage history of the secondary battery includes history of usage time of the secondary battery, cumulative amount of current applied to the secondary battery, number of charge/discharge cycles of the secondary battery, voltage, current, temperature, and the like. Data indicating the usage history of the secondary battery can be input via the input unit 30. These linked data can be output together with the diagnosis results as output information.

The diagnostic results of the deterioration state of the secondary battery stored as a database can be used for processing to change the operating conditions of the secondary battery. The operating conditions for the secondary battery include the upper and lower limits of the state of charge 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 discharge current from the secondary battery. One or more of these operating conditions can be changed based on accumulated diagnostic result data.

The operating conditions of the secondary battery can be changed using (1) the deterioration state of each electrode, (2) the rate of change of the deterioration state of each electrode, or (3) the remaining life of the secondary battery as an index. These indicators are compared with predetermined threshold values, and when it is determined that there is a high possibility that deterioration of each electrode or deterioration of the secondary battery will progress, the operating condition range of the secondary battery is changed to a condition that ensures safety. Can be changed.

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

(2) The rate of change of the deterioration state of each electrode is determined by the rate of change (rate of change) of the deterioration state of the positive electrode with respect to the cumulative load, or the rate of change (rate of change) of the deterioration state of the negative electrode with respect to the cumulative load. Can be used. When the deterioration state of the positive electrode represented by the deterioration state parameter or the deterioration state of the negative electrode represented by the deterioration state parameter is greater than or equal to a preset threshold for application of a predetermined cumulative load amount, secondary The operating condition range of the battery can be changed to conditions that ensure safety.

The cumulative load amount can be calculated from the usage time of the secondary battery, the amount of current applied to the secondary battery, or a combination of two or more of the usage time, the amount of current applied, the temperature, and the current. A model function representing the relationship between the cumulative load amount and the deterioration state of the electrode is formulated using two or more of these as variables. Then, the deterioration state of the electrode with respect to various accumulated loads is actually measured, and the coefficients and constants of the model function can be determined by fitting based on the actual measurements.

(3) As the remaining life of the secondary battery, the usage time of the secondary battery until the discharge capacity of the secondary battery decreases to a predetermined discharge capacity due to progress of deterioration can be used as an index. When the remaining life of the secondary battery is less than or equal to a preset threshold for a given expected usage time, the operating condition range of the secondary battery can be changed to conditions that ensure safety. .

The discharge capacity of a secondary battery after a predetermined usage time has elapsed is determined by the rate of change (rate of change) of the deterioration state of the secondary battery with respect to the cumulative load, the current discharge capacity of the secondary battery, and information on the usage time. It can be estimated based on The rate of change (rate of change) of the deterioration state of the secondary battery with respect to the cumulative load is the rate of change (rate of change) of the deterioration state of the positive electrode with respect to the cumulative load, and the rate of change (rate of change) of the deterioration state of the negative electrode with respect to the cumulative load. ) and can be calculated based on

Operations that change the operating conditions of the secondary battery to ensure safety include, for example, lowering the upper limit of the charging state of the secondary battery, increasing the lower limit of the charging state of the secondary battery, and changing the operating conditions of the secondary battery to ensure safety. Changes that lower the upper or lower limit of the charging current to the secondary battery, and changes that lower the upper or lower limit of the discharge current from the secondary battery. The calculation unit 10 may perform a process of generating a control signal for executing one or more of these.

If the operating condition range of the secondary battery is changed after such diagnosis, it is possible to suppress the progress of deterioration of the secondary battery, and thus the life of the secondary battery can be extended. The history of diagnostic results used to change the operating condition range of a 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 the positive electrode The safety of the secondary battery can be ensured by detecting deterioration of either of the negative electrode and the negative electrode at an early stage.

According to the above secondary battery state diagnosis method and secondary battery state diagnosis device, the relationship between the state of charge of the secondary battery and the open circuit potential, and the state of charge and internal resistance of the secondary battery for each different energization time are determined. Since the relationship group consisting of the relationship between the The deterioration state of each positive electrode and negative electrode can be individually diagnosed. Since we use a relation group consisting of the relationship between the charging state of the secondary battery and the internal resistance for each different energization time, in calculations based on internal resistance, the internal resistance consisting of multiple variables can be approximated toward the true value. can. Therefore, even if one of the positive and negative electrodes is equipped with an electrode that uses an active material whose potential changes poorly with changes in the state of charge, the deterioration state of the secondary battery and the deterioration of each electrode The condition can be diagnosed with high accuracy. Diagnosis of the deterioration state of each electrode uses the measurement results of the open circuit voltage of the secondary battery to be diagnosed and the measurement results of the internal resistance of the secondary battery to be diagnosed. It is possible to non-destructively diagnose the deterioration state of

Although the embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various changes can be made without departing from the spirit of the present invention. For example, the present invention is not necessarily limited to having all the configurations of the embodiments described above. Replacing part of the configuration of one embodiment with another configuration, adding part of the configuration of one embodiment to another form, or omitting part of the configuration of one embodiment I can do it.

EXAMPLES The present invention will be specifically described below with reference to Examples, but the technical scope of the present invention is not limited thereto.

<Acquisition of input information>
For LFP-Li metal half cells, graphite-Li metal half cells, and LFP-graphite secondary batteries, the relationship between the state of charge and open circuit potential (voltage), and the dependence of the state of charge and internal resistance on energization time The relationship groups indicating the characteristics were determined based on actual measurements during the discharge process.

The open circuit potential (voltage) and internal resistance were measured by galvanostatic intermittent titration technique (GITT). The discharge current was 1 CA. In the discharge process, 72 seconds of discharge and 30 minutes of rest were intermittently repeated until the discharge end potential (voltage) was reached.

Data showing the relationship between state of charge and open circuit potential (voltage) was collected by measuring the open circuit potential (voltage) after a 30 minute pause for a given discharge capacity during intermittent charge/discharge cycles. FIG. 3 corresponds to reference data collected on an LFP-Li metal half cell. FIG. 4 corresponds to reference data collected on a graphite-Li metal half cell. FIG. 5 corresponds to measurement data collected from an LFP-graphite secondary battery.

Data showing a relationship group showing the dependence of charging state and internal resistance on current application time was collected by calculating the internal resistance when a predetermined discharging time elapsed in intermittent charge/discharge cycles. Data for each energization time was collected as discharge time-dependent data for each discharge time. The internal resistance was calculated by dividing the difference between the open circuit potential (voltage) before the start of discharge and the open circuit potential (voltage) after a predetermined discharge time by the discharge current. The discharge time t was set to t=40, 50, 60, and 72 seconds. FIG. 6 corresponds to reference data collected on an LFP-Li metal half cell. FIG. 7 corresponds to reference data collected on a graphite-Li metal half cell. FIG. 8 corresponds to measurement data collected with an LFP-graphite secondary battery.

<Step 1: Evaluation based on open circuit voltage>
Reference data showing the relationship between the state of charge of the positive electrode and the open circuit potential whose state of deterioration is known, reference data showing the relationship between the state of charge of the negative electrode whose state of deterioration is known and the open circuit potential, and the state of deterioration parameter. Based on this, calculation data showing the relationship between the charging state of the secondary battery and the open circuit voltage was generated. Calculated data calculated assuming a degraded state was then fitted to measured data showing the relationship between the state of charge and open circuit voltage of the secondary battery to be diagnosed.

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

<Step 2: Evaluation based on internal resistance>
Based on the reference data showing the relationship between the charging state of the positive electrode whose deterioration state is known and the internal resistance, the reference data showing the relationship between the charging state of the negative electrode and the internal resistance whose deterioration state is known, and the deterioration state parameter. , we generated calculation data showing the relationship between the state of charge and internal resistance of a secondary battery. Regarding the relationship between the state of charge and internal resistance, the energization time when measuring the internal resistance was varied, and a plurality of data for each energization time was prepared and used in calculations. Then, calculation data calculated assuming a deteriorated state was fitted to measurement data showing the relationship between the state of charge and internal resistance of the secondary battery to be diagnosed for each energization time.

Fitting of the internal resistance data was performed using a solver function installed in Excel (manufactured by Microsoft). The root mean squared error (RMSE) between the measured data and the calculated data was calculated. Then, fitting was performed so that the relative error obtained by dividing the root mean square error by the average value was minimized. Note that in the example, since the measurement data and the reference data are assumed to be in the same state of deterioration, correction using the weighting function ρ(t) was not performed.

Three initial values of mrp and ap were each set. Then, fitting was performed for each discharge elapsed time using each initial value. During fitting, 0<R0 [mΩ]<20 was set as a constraint condition for R0. The upper limit of 20 mΩ is the minimum value of the calculation result of R0 at the current application time t=1 sec.

表１は、ｔ＝７２ｓｅｃにおけるＲ０の計算結果である。Ｒ０として、１、６、１０、１４［ｍΩ］の４つの解が得られた。

Table 1 shows the calculation results of R0 at t=72 seconds. Four solutions were obtained for R0: 1, 6, 10, and 14 [mΩ].

表２は、ｔ＝６０ｓｅｃにおけるＲ０の計算結果である。Ｒ０として、１０、１３、１６［ｍΩ］の３つの解が得られた。

Table 2 shows the calculation results of R0 at t=60 seconds. Three solutions were obtained for R0: 10, 13, and 16 [mΩ].

表３は、ｔ＝５０ｓｅｃにおけるＲ０の計算結果である。Ｒ０として、５、１０、１２、１８［ｍΩ］の４つの解が得られた。

Table 3 shows the calculation results of R0 at t=50 seconds. Four solutions were obtained for R0: 5, 10, 12, and 18 [mΩ].

表４は、ｔ＝４０ｓｅｃにおけるＲ０の計算結果である。Ｒ０として、８、１２［ｍΩ］の２つの解が得られた。

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

Here, R0 = 20 [mΩ] means that the calculation has not converged within the range of the constraint conditions, so 10 mΩ, which is a common solution for the energization time t = 50, 60, and 72 "sec", is It was taken as the true value.

Next, as a result of calculating the remaining deterioration state parameters under R0 = 10 [mΩ] and energization time t = 72 seconds, the deterioration state parameters were mrp = 0.820, δp = 0.00035 [Ah], Ap=0.0128 and an=0.00270 were obtained. FIG. 10 corresponds to calculated data of internal resistance after fitting obtained for an LFP-graphite secondary battery.

100 Condition diagnosis device (secondary battery condition diagnosis device)
10 Arithmetic unit 20 Storage unit 30 Input unit 40 Output unit 50 Communication unit

Claims (10)

A condition diagnosis method for diagnosing a deterioration condition of a secondary battery,
A relationship group consisting of the relationship between the state of charge of the secondary battery and the open circuit voltage, and the relationship between the state of charge and internal resistance of the secondary battery for each different energization time is used as input information, A method for diagnosing the condition of a secondary battery, in which output information is a deterioration state, a deterioration state of a positive electrode used in the secondary battery, and a deterioration state of a negative electrode used in the secondary battery. The method for diagnosing the condition of a secondary battery according to claim 1,
The state of charge and open circuit voltage of the secondary battery are determined based on the relationship between the state of charge of the positive electrode and the open circuit potential specific to the positive electrode material, and the relationship between the state of charge of the negative electrode and the open circuit potential specific to the negative electrode material. A first step of evaluating the relationship between
Based on the relationship between the charging state of the positive electrode and the internal resistance specific to the positive electrode material for each different energizing time, and the relationship between the charging state of the negative electrode and the internal resistance specific to the negative electrode material for each different energizing time, A method for diagnosing the condition of a secondary battery, comprising: a second step of evaluating a relationship group consisting of a relationship between the state of charge and internal resistance of the battery. The method for diagnosing the condition of a secondary battery according to claim 1,
The relationship group consisting of the relationship between the charging state of the secondary battery and the internal resistance for each different energizing time is a relationship group consisting of the relationship between the charging state of the secondary battery and the internal resistance for each different energizing time. How to diagnose battery condition. The method for diagnosing the condition of a secondary battery according to claim 1,
The magnitude of the resistance component of the secondary battery excluding the reaction resistance component and the diffusion resistance component is determined by comparing the relationship between the state of charge and internal resistance of the secondary battery for each different energization time. How to diagnose the condition. The method for diagnosing the condition of a secondary battery according to claim 1,
A method for diagnosing the condition of a secondary battery, in which the relationship between the state of charge and internal resistance of the secondary battery for each different energization time is calculated for the energization time converted by a weighting function. The method for diagnosing the condition of a secondary battery according to claim 1,
The internal resistance of the secondary battery is determined based on the open circuit voltage of the secondary battery and the closed circuit voltage of the secondary battery. The method for diagnosing the condition of a secondary battery according to claim 1,
the open circuit potential of one of the positive electrode and the negative electrode is constant except near a fully charged state and near a fully discharged state;
The open circuit potential is determined to be full based on a relationship group consisting of the relationship between the state of charge and internal resistance of the positive electrode and the negative electrode, and the relationship between the state of charge and internal resistance of the secondary battery for each different energization time. A secondary battery condition diagnosing method for diagnosing a deterioration condition of the electrode, which is constant except near a charged state and near a fully discharged state. The method for diagnosing the condition of a secondary battery according to claim 1,
A secondary battery that changes one or more of the upper limit voltage and lower limit voltage during charging and discharging of the secondary battery, and the upper limit current and lower limit current during charging and discharging of the secondary battery, based on the output information. How to diagnose battery condition. A condition diagnostic device for diagnosing a deterioration condition of a secondary battery,
The input information includes data showing the relationship between the charging state of the secondary battery and the open circuit voltage, and data showing a relationship group consisting of the relationship between the charging state of the secondary battery and internal resistance for each different energization time. , data representing a deterioration state of the secondary battery, data representing a deterioration state of a positive electrode used in the secondary battery, and data representing a deterioration state of a negative electrode used in the secondary battery are output information. Secondary battery condition diagnosis device. The secondary battery condition diagnostic device according to claim 9,
Loading data indicating the relationship between the state of charge of the secondary battery and the open circuit voltage, and data indicating a relationship group consisting of the relationship between the state of charge of the secondary battery and the internal resistance, A secondary battery comprising a calculation unit that calculates data indicating a state of deterioration, data showing a state of deterioration of a positive electrode used in the secondary battery, and data showing a state of deterioration of a negative electrode used in the secondary battery. Condition diagnosis device.

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