Diagnostic method, diagnostic device, and computer program

Abstract

According to the present invention, a computer executes a process for: acquiring measurement values of the voltage and capacity of a power storage element when the power storage element including a positive electrode and a negative electrode is charged to a charging end or discharged from the charging end; calculating, on the basis of the acquired measurement values, dV / dQ that is a ratio of a voltage change amount dV to a capacity change amount dQ at a capacity value at which the difference from a capacity value at the charging end becomes a set value; and diagnosing capacity deterioration of the positive electrode of the power storage element on the basis of the calculated dV / dQ.

Description

Diagnostic method, diagnostic device, and computer program

[0001] The present disclosure relates to a diagnostic method, a diagnostic device, and a computer program.

[0002] In recent years, power storage elements such as lithium-ion secondary batteries have been widely used. For example, the power storage element is mounted on a vehicle such as an automobile and is used as a power supply source for a starter when starting an engine and a power supply source for various electrical components.

[0003] As a technique for grasping the deterioration state of a power storage element, Patent Document 1 discloses a technique for determining a decrease in an electrolytic solution from a characteristic indicated by a ratio of a change amount of a battery voltage to a change amount of a state of charge.

[0004] Japanese Patent Application Laid-Open No. 2021-163627

[0005] However, with the technique disclosed in Patent Document 1, it is impossible to diagnose capacity deterioration in the positive electrode of a power storage element.

[0006] An object of the present disclosure is to provide a diagnostic method, a diagnostic device, and a computer program capable of diagnosing capacity deterioration in the positive electrode of a power storage element.

[0007] The diagnostic method in the present disclosure acquires measurement values of the voltage and capacity of a power storage element including a positive electrode and a negative electrode when the power storage element is charged to the end of charge or discharged from the end of charge, and based on the acquired measurement values, calculates dV / dQ, which is the ratio of the change amount of voltage dV to the change amount of capacity dQ at a capacity value where the difference from the capacity value at the end of charge becomes a set value, and based on the calculated dV / dQ, causes a computer to execute a process of diagnosing capacity deterioration in the positive electrode of the power storage element.

[0008] According to the above aspect, it is possible to diagnose capacity deterioration in the positive electrode of a power storage element.

[0009] This is an explanatory diagram illustrating the outline of the processing performed by the diagnostic device according to Embodiment 1. This is an external perspective view showing an example of the configuration of an energy storage element. This is a schematic diagram of the wound electrode body provided by the energy storage element. This is a block diagram showing the internal configuration of the diagnostic device. This is a graph showing the cycle change of the dV / dQ curve. This is a chart showing the relationship between the rate of change of dV / dQ and the capacity retention rate. This is a graph showing the relationship between the SOC of the energy storage element and the positive electrode OCP (Open Circuit Potential) obtained from simulation. This is a graph showing the change in the dE / dQ curve when the positive electrode capacity retention rate changes. This is a flowchart illustrating the procedure of the processing performed by the diagnostic device according to Embodiment 1. This is an explanatory diagram illustrating an example of the configuration of a charge control system according to Embodiment 2. This is a flowchart illustrating the procedure of the processing performed by the diagnostic device according to Embodiment 2.

[0010] (1) The diagnostic method of the present disclosure acquires measured values ​​of the voltage and capacity of an energy storage element including a positive electrode and a negative electrode when the energy storage element is charged to the end of charging or discharged from the end of charging, calculates dV / dQ, which is the ratio of the voltage change amount dV to the capacity change amount dQ, at a capacity value where the difference from the capacity value at the end of charging is a set value, based on the acquired measured values, and performs a process by computer to diagnose the capacity degradation of the positive electrode of the energy storage element based on the calculated dV / dQ.

[0011] The energy storage element of this disclosure is, for example, a battery cell used in an in-vehicle power supply such as an electric vehicle (EV), a hybrid electric vehicle (HEV), or a plug-in hybrid electric vehicle (PHEV). Alternatively, the energy storage element may be a battery cell used in a stationary power supply such as an Energy Storage System (ESS) or a backup power supply. The battery cell may be a rechargeable secondary battery such as a lithium-ion battery.

[0012] Rechargeable batteries, including lithium-ion batteries, generally degrade with repeated charging and discharging. It is empirically known that the capacity degradation of rechargeable batteries is proportional to the square root of the usage time (number of cycles). This empirical square root rule is often applied to predict the degradation of rechargeable batteries. However, if charging and discharging are performed under inappropriate conditions, the internal reactions of the battery may become non-uniform due to electrolyte depletion, separator clogging, etc. In this case, the empirical square root rule may not accurately predict the degradation of the rechargeable battery.

[0013] Understanding the degradation parameters of both the positive and negative electrodes is crucial for predicting the overall battery life. Currently, there are no known degradation parameters for the positive and negative electrodes that can be obtained non-destructively and easily.

[0014] The inventors of this invention have found that the dV / dQ (the ratio of the voltage change dV to the capacity change dQ) at which the difference between the capacity value at the end of charging of the energy storage element and the set value is the set value can be used as a degradation parameter for the positive electrode.

[0015] In the diagnostic method described in (1) above, the dV / dQ is calculated from the measured voltage and capacity of the energy storage element at a capacity value where the difference from the capacity value at the end of charging is a set value, and the capacity degradation of the positive electrode is diagnosed based on the calculated dV / dQ. Therefore, in the diagnostic method described in (1) above, the dV / dQ value obtained by a non-destructive and simple method can be used as the degradation parameter of the positive electrode to diagnose the capacity degradation of the positive electrode.

[0016] (2) In the diagnostic method described in (1) above, the computer may perform a process to diagnose the capacity degradation by estimating the capacity maintenance rate of the positive electrode from the rate of change between the dV / dQ calculated at the start of operation of the energy storage element and the dV / dQ calculated at any point after the start of operation.

[0017] The inventors of this application have found that the rate of change between dV / dQ calculated at the start of operation of the energy storage element and dV / dQ calculated at any point after the start of operation is related to the capacity retention rate of the positive electrode. In the diagnostic method of (2) above, the capacity retention rate of the positive electrode can be estimated from the rate of change of dV / dQ from the start of operation to any point after the start of operation.

[0018] (3) In the diagnostic method described in (1) or (2) above, the set value may be set such that the capacity value used to calculate dV / dQ is a value near the end of charging.

[0019] In the diagnostic method described in (3) above, the capacitance degradation of the positive electrode can be estimated based on the dV / dQ value of the capacitance value near the end of charging.

[0020] (4) In the diagnostic method described in any one of (1) to (3) above, the set value may be set such that the capacity value used to calculate the dV / dQ is within the range of 70% to 90% of the capacity value at the end of charging.

[0021] According to the diagnostic method described in (4) above, the capacity degradation of the positive electrode can be estimated based on the dV / dQ at a capacity value within the range of 70% to 90% of the capacity value at the end of charging.

[0022] (5) In the diagnostic method described in any one of (1) to (4) above, if the diagnostic result of the energy storage element detects that capacity degradation has occurred in the positive electrode, the computer may execute a process to output a control command to the control device that controls the charging and discharging of the energy storage element to relax the charging and discharging conditions.

[0023] According to the diagnostic method described in (5) above, if the positive electrode capacity is degraded, a control command is output to relax the charging conditions, thereby suppressing the progression of capacity degradation.

[0024] (6) In the diagnostic method described in any one of (1) to (5) above, if the diagnostic result of the energy storage element detects that capacity degradation has occurred in the positive electrode, the computer may perform a process to output information indicating that capacity degradation has occurred in the positive electrode.

[0025] According to the diagnostic method described in (6) above, the user can be notified of capacity degradation in the positive electrode.

[0026] (7) The diagnostic device of the present disclosure comprises at least one calculation unit, the calculation unit acquires measured values ​​of the voltage and capacity of the energy storage element, including a positive electrode and a negative electrode, when the energy storage element is charged to the end of charging or discharged from the end of charging, and calculates dV / dQ, which is the ratio of the voltage change amount dV to the capacity change amount dQ, at a capacity value where the difference from the capacity value at the end of charging is a set value, based on the acquired measured values, and diagnoses the capacity degradation of the positive electrode of the energy storage element based on the calculated dV / dQ.

[0027] In the diagnostic device described in (7) above, the dV / dQ is calculated from the measured voltage and capacity of the energy storage element at a capacity value where the difference from the capacity value at the end of charging is a set value, and the capacity degradation of the positive electrode is diagnosed based on the calculated dV / dQ. Therefore, in the diagnostic device described in (7) above, the capacity degradation of the positive electrode can be diagnosed by using the dV / dQ value, which can be obtained by a non-destructive and simple method, as the degradation parameter of the positive electrode.

[0028] (8) The computer program of the present disclosure is a computer program that causes a computer to perform a process to diagnose the degradation of the positive electrode of the energy storage element, which includes a positive electrode and a negative electrode, by obtaining measured values ​​of the voltage and capacity of the energy storage element when the energy storage element is charged to the end of charging or discharged from the end of charging, and based on the obtained measured values, calculate dV / dQ, which is the ratio of the voltage change amount dV to the capacity change amount dQ at a capacity value where the difference from the capacity value at the end of charging is a set value, and based on the calculated dV / dQ.

[0029] In the computer program described in (8) above, the dV / dQ is calculated from the measured voltage and capacity of the energy storage element at a capacity value where the difference from the capacity value at the end of charging is a set value, and the capacity degradation of the positive electrode is diagnosed based on the calculated dV / dQ. Therefore, in the computer program described in (8) above, the dV / dQ value obtained by a non-destructive and simple method can be used as the positive electrode degradation parameter to diagnose the capacity degradation of the positive electrode.

[0030] The present invention will now be described in detail based on the drawings illustrating its embodiments. (Embodiment 1) Figure 1 is an explanatory diagram illustrating the outline of the process performed by the diagnostic device according to Embodiment 1. The diagnostic device 1 according to Embodiment 1 is a device for diagnosing capacity degradation targeting the positive electrode of a power storage element 20 mounted on a power supply 2. The power supply 2 is mounted on, for example, an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), etc. The power supply 2 stores power supplied from an external source in the power storage element 20 and supplies the power stored in the power storage element 20 to various equipment of the vehicle, such as the electric motor, headlights, turn signals, interior lights, and power windows.

[0031] Alternatively, power source 2 may be a power source installed in an energy storage facility that is installed alongside a power generation facility such as a solar power generation facility or a wind power generation facility. The energy storage facility may be an ESS (Energy Storage System) or a backup power source. Power source 2 stores the electricity supplied from the power generation facility in an energy storage element 20 and supplies the electricity stored in the energy storage element 20 to power-consuming facilities such as factories, office buildings, schools, hospitals, restaurants, and airports.

[0032] Multiple energy storage elements 20 are mounted on the power supply 2. The multiple energy storage elements 20 may be mounted on the power supply 2 in the form of a module, or they may be mounted on the power supply 2 in the form of a bank or domain.

[0033] In this embodiment, the energy storage element 20 is a battery cell made of lithium-ion batteries. The total capacity of a secondary battery, including lithium-ion batteries, is determined by the combined design of the positive electrode capacity and the negative electrode capacity, and generally deteriorates with repeated charging and discharging. It is empirically known that the capacity degradation of a secondary battery is proportional to the square root of the usage time (number of cycles). This empirical square root rule is often applied to predict the degradation of secondary batteries. However, if charging and discharging are performed under inappropriate conditions in a secondary battery, the reaction inside the battery may become non-uniform due to electrolyte depletion, separator clogging, etc. Understanding the degradation parameters of the positive electrode and the negative electrode is important for predicting the lifespan of the battery as a whole.

[0034] In this embodiment, a method for diagnosing the capacity degradation of the positive electrode is proposed. As will be described in detail later, the diagnostic device 1 acquires measured values ​​of the voltage and capacity of the energy storage element 20 (voltage value V and capacity value Q), and calculates dV / dQ at a specific capacity value based on the acquired measured values. dV / dQ represents the ratio of the voltage change amount dV to the capacity change amount dQ. The diagnostic device 1 uses the calculated dV / dQ as the positive electrode degradation parameter to diagnose the capacity degradation of the positive electrode of the energy storage element 20.

[0035] Figure 2 is an external perspective view showing an example configuration of the energy storage element 20, and Figure 3 is a schematic diagram of the wound electrode body 21 provided by the energy storage element 20. The energy storage element 20 according to this embodiment is a battery cell made of a lithium-ion battery. The energy storage element 20 is constructed by housing a flat-shaped wound electrode body 21 and an electrolyte (not shown in the figure) in a hollow rectangular parallelepiped-shaped battery case 22. In Figure 2, the wound electrode body 21 is shown as if viewed through the inside of the battery case 22.

[0036] The top surface of the battery case 22 is provided with a positive terminal 23 and a negative terminal 24 for external connection. The positive terminal 23 and the negative terminal 24 are electrically connected to a positive current collector 25 and a negative current collector 26, respectively. The battery case 22 is made of a lightweight metal material with high thermal conductivity, such as aluminum.

[0037] The wound electrode body 21 is constructed by overlapping a sheet-shaped positive electrode 211, on which a positive electrode active material layer 211A is formed, and a sheet-shaped negative electrode 212, on which a negative electrode active material layer 212A is formed, via two sheet-shaped separators 213, and winding them together. The positive electrode 211 and the negative electrode 212 are arranged offset from each other in the width direction of the sheet. At one end of the positive electrode 211 in the width direction, there is a region where the positive electrode active material layer 211A is not formed, and a positive electrode current collector 25 is joined to this region. For example, aluminum foil is used for the positive electrode current collector 25. Similarly, at the other end of the negative electrode 212 in the width direction, there is a region where the negative electrode active material layer 212A is not formed, and a negative electrode current collector 26 is joined to this region. For example, copper foil is used for the negative electrode current collector 26.

[0038] The positive electrode active material layer 211A contains a positive electrode active material. A lithium metal composite oxide is used as the positive electrode active material. The lithium metal composite oxide contains lithium, oxygen, and other elements (e.g., Mn, Ni, Co, Fe, Nb, W, P, Si, etc.). There may be one or more elements other than lithium and oxygen. The positive electrode active material layer 211A may further contain a conductive additive, a binder, etc. As a conductive additive, carbon black such as acetylene black (AB) or other carbon materials (such as graphite) are preferably used. As a binder, polyvinylidene fluoride (PVDF), etc., is used.

[0039] The negative electrode active material layer 212A contains a negative electrode active material. As the negative electrode active material, carbon materials such as graphite, hard carbon, and soft carbon are used. The negative electrode active material layer 212A may further contain a binder, a thickener, etc. As the binder, for example, styrene-butadiene rubber (SBR) is used. As the thickener, for example, carboxymethylcellulose (CMC) is used.

[0040] The separator 213 is formed from a porous resin film. As the porous resin film, a porous resin film made of resin such as polyethylene (PE) or polypropylene (PP) can be used. The separator 213 may be formed from a single-layer resin film or from a resin film having a multi-layer structure of two or more layers. The separator 213 may also be provided with a heat-resistant layer.

[0041] The electrolyte housed in the battery case 22 together with the wound electrode body 21 can be the same as that used in existing lithium-ion batteries. For example, an electrolyte containing a supporting salt in an organic solvent can be used. As the organic solvent, aprotic solvents such as carbonates, esters, and ethers can be used. As the supporting salt, lithium salts such as LiPF6, LiBF4, and LiClO4 are preferably used. The electrolyte may also contain various additives such as gas generators, film-forming agents, dispersants, and thickeners.

[0042] The energy storage element 20 may be equipped with a reference electrode for measuring the potentials of the positive electrode 211 and the negative electrode 212. The reference electrode is placed, for example, between the wound electrode body 21 and the battery case 22. The reference electrode may be made of any material that exhibits a stable potential, such as metallic lithium, lithium-aluminum alloy, or lithium-tin alloy. If the battery case 22 is electrically insulated from the positive electrode terminal 23 and the negative electrode terminal 24, the battery case 22 may be used as the reference electrode. Since the potential of the reference electrode can be treated as known, the positive electrode potential is measured by measuring the potential difference between the positive electrode 211 and the reference electrode, and the negative electrode potential is measured by measuring the potential difference between the negative electrode 212 and the reference electrode.

[0043] Figures 2 and 3 illustrate a rectangular lithium-ion battery equipped with a wound electrode body 21 as an example of an energy storage element 20. Alternatively, the energy storage element 20 may be a lithium-ion battery equipped with a stacked electrode body, or a cylindrical lithium-ion battery, a laminated lithium-ion battery, or the like.

[0044] FIG. 4 is a block diagram showing the internal configuration of the diagnostic device 1. The diagnostic device 1 is a dedicated or general-purpose computer for diagnosing the capacity degradation of the positive electrode in the energy storage element 20. As shown in FIG. 1, the diagnostic device 1 is installed outside the power supply 2 and diagnoses the capacity degradation of the positive electrode of the energy storage element 20 externally. For example, the diagnostic device 1 may be installed at a remote location sufficiently far from the power supply 2 and perform diagnosis remotely, or may be installed within a range where wired communication is possible and perform diagnosis on-site. Alternatively, the diagnostic device 1 may be provided in the power supply 2 (or the vehicle or energy storage facility on which the power supply 2 is mounted) to diagnose the capacity degradation of the positive electrode of the energy storage element 20.

[0045] The diagnostic device 1 includes a control unit 11, a storage unit 12, a communication unit 13, an operation unit 14, a display unit 15, and the like. The control unit 11 is, for example, an arithmetic circuit including a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like. The CPU included in the control unit 11 reads and executes various computer programs stored in the ROM or the storage unit 12 to control each part of the hardware and realize the function of diagnosing the capacity degradation of the positive electrode of the energy storage element 20.

[0046] The control unit 11 may be any arithmetic circuit including a plurality of CPUs, a multi-core CPU, a GPU (Graphics Processing Unit), a microcomputer, a volatile or non-volatile memory, and the like. The control unit 11 may include functions such as a timer for measuring the elapsed time from when a measurement start instruction is given until a measurement end instruction is given, a counter for counting numbers, and a clock for outputting date and time information. <******><******>The storage unit 12 includes a storage device such as a flash memory or a hard disk. Various computer programs and data are stored in the storage unit 12. The computer program (program product) stored in the storage unit 12 includes a diagnostic program PG that diagnoses the capacitance degradation at the positive electrode of the power storage element 20 based on the measured values related to the power storage element 20. The data stored in the storage unit 12 includes various parameters used in the diagnostic program PG and data input through the communication unit 13 or the like.

[0048] The diagnostic program PG may be a single computer program or may be composed of a plurality of computer programs. The diagnostic program PG may be executed by a single computer or may be executed in cooperation by a plurality of computers. Furthermore, the diagnostic program PG may partially use an existing library.

[0049] The computer program including the diagnostic program PG is provided by a non-temporary recording medium RM on which the computer program is recordable in a readable manner. The recording medium RM is a portable memory such as a CD-ROM, a USB memory, or an SD (Secure Digital) card. The control unit 11 reads a desired computer program from the recording medium RM using a reading device not shown in the figure and stores the read computer program in the storage unit 12. Alternatively, the computer program including the diagnostic program PG may be provided by communication.

[0050] The communication unit 13 includes a communication module for communicating with the power supply 2 (or the vehicle or energy storage equipment on which the power supply 2 is installed). The communication module is a communication module that wirelessly transmits data using known mobile communication standards such as 3G, 4G, or 5G, or a wireless LAN method such as Wi-Fi®. Alternatively, the communication module may be a communication module for short-range wireless communication such as Bluetooth® or ZigBee®, or a communication module that conforms to a wired communication standard such as Ethernet®. The communication unit 13 communicates with the power supply 2 (or the vehicle or energy storage equipment on which the power supply 2 is installed) and acquires measurement values ​​necessary for diagnosing capacity degradation. The communication unit 13 outputs the acquired measurement values ​​to the control unit 11.

[0051] The operation unit 14 is equipped with an input device such as a keyboard or mouse and accepts user input. The display unit 15 is equipped with a display device such as a liquid crystal display and displays information to be notified to the user. Alternatively, the diagnostic device 1 may be configured to accept necessary operations via an external computer and transmit information to be notified to the user to the external computer. In this case, the diagnostic device 1 does not need to be equipped with an operation unit 14 and a display unit 15.

[0052] The evaluation tests conducted by the inventors of this application are described below. Figure 5 is a graph showing the cycle change of the dV / dQ curve. The vertical axis of the graph represents dV / dQ (V / Ah), and the horizontal axis represents the amount of charged electricity (Ah). The inventors conducted a cycle degradation test under a temperature condition of 45°C, changing the SOC (State of Charge) in the range of 20% to 100%, and performed a capacity confirmation test by adjusting the temperature to 25°C each time during the 45°C cycle. In the capacity confirmation test, the energy storage element 20 was charged at a rate of 1C from SOC 0% to 100% using the CCCV (Constant Current, Constant Voltage) method, and then discharged at a rate of 1 / 3C. The voltage value V and capacity value (amount of charged electricity) Q of the energy storage element 20 were measured during this process. In order to sufficiently charge the energy storage element 20, a low rate of 0.05C or less may be used at the end of charging. The voltage value V is measured using an existing voltage sensor, and the capacitance value Q is measured using existing methods such as current integration. Figure 5 shows the dV / dQ curve (solid line graph) obtained from the measurement results at 0 cycles and the dV / dQ curve (dashed line graph) obtained from the measurement results at 3500 cycles. In Figure 5, each graph is shown with the end of the charge aligned to the right end.

[0053] The inventors found that information regarding the capacity degradation of the positive electrode 211 of the energy storage element 20 can be obtained from the changes in such a dV / dQ curve. More specifically, they found that by taking the point where the capacity difference from the end of charging is constant (for example, point A shown in Figure 5), information regarding the capacity degradation of the positive electrode 211 can be obtained from the dV / dQ at this point.

[0054] Figure 6 is a chart showing the relationship between the rate of change of dV / dQ and the capacity retention rate. In the chart in Figure 6, the rate of change of dV / dQ represents the rate of change of dV / dQ at the capacity value where the capacity difference from the end of charging is constant. For example, in Figure 5, if B1 is the dV / dQ at point A obtained from the dV / dQ curve for 0 cycles, and B2 is the dV / dQ at point A obtained from the dV / dQ curve for 3500 cycles, the rate of change is calculated as (B2 - B1) / B1 × 100. When actually calculated, the rate of change of dV / dQ from 0 cycles to 3500 cycles was 12.1%, and 100 - rate of change was 87.9%.

[0055] On the other hand, the energy storage element 20 was disassembled, and the positive electrode single-electrode capacity was measured using a two-electrode cell with the working electrode as the positive electrode and the counter electrode as lithium metal. When this was compared with the initial product, the capacity retention rate of the positive electrode single-electrode (1 / 3C discharge capacity retention rate) was found to be 86.2%. The capacity retention rate represents the ratio of the capacity at any given point in degradation to the initial capacity.

[0056] As shown in Figure 6, the value calculated based on dV / dQ (100 - rate of change) and the capacity retention rate of the positive electrode unipolar show good agreement. Therefore, it can be seen that the capacity degradation at the positive electrode 211 of the energy storage element 20 can be diagnosed by determining the dV / dQ at a capacity value where the difference from the capacity value at the end of charging is constant. Here, the capacity value at which the difference from the capacity value at the end of charging is constant (point A in Figure 5) is set appropriately within the range of capacity values ​​near the end of charging (for example, within the range of 70% to 90% of the capacity value at the end of charging).

[0057] The inventors used simulations to deduce a mechanism that allows for the diagnosis of positive electrode unipolar capacitance degradation from the dV / dQ of an energy storage element.

[0058] Figure 7 is a graph showing the relationship between the SOC of an energy storage element and the positive electrode OCP (Open Circuit Potential) obtained from simulation. The horizontal axis of the graph represents SOC (%), and the vertical axis represents the positive electrode OCP (V). The SOC-positive electrode OCP curve is obtained by performing simulations using existing models such as equivalent circuit models and mathematical models of the energy storage element. The inventors performed simulations with different positive electrode capacity retention rates and obtained the SOC-positive electrode OCP curve when the positive electrode potential at the end of charging was matched. Assuming that the SOC-positive electrode OCP curve maintains a similar shape even when the positive electrode capacity retention rate decreases, the SOC-positive electrode OCP curve shown in Figure 7 was obtained.

[0059] Figure 8 is a graph showing the change in the dE / dQ curve when the positive electrode capacity retention rate changes. The vertical axis represents dE / dQ (V / Ah), and the horizontal axis represents capacity (Ah). dE / dQ represents the ratio of the change in positive electrode potential dE to the change in capacity dQ. dE / dQ is calculated from the SOC-positive electrode OCP curve in Figure 7. As shown in Figure 8, near the end of charging, the value of dE / dQ increased as the positive electrode capacity retention rate decreased. This behavior of dE / dQ is thought to be reflected in the dV / dQ curve in Figure 5, which shows the combined behavior of the positive and negative electrodes.

[0060] From the above inferences, it can be seen that the capacity degradation of the positive electrode 211 can be diagnosed by using the dV / dQ of the energy storage element 20 near the end of charging (for example, in the range of 70% to 90% of the capacity value at the end of charging). As mentioned above, the rate of change between the dV / dQ calculated at the start of operation of the energy storage element 20 (at cycle 0) and the dV / dQ calculated at any point after the start of operation is closely related to the capacity retention rate of the positive electrode 211. Therefore, by determining the rate of change of dV / dQ, the capacity retention rate of the positive electrode 211 can be estimated with high accuracy without disassembling the energy storage element 20.

[0061] The following describes the processes performed by the diagnostic device 1. Figure 9 is a flowchart illustrating the procedure for the processes performed by the diagnostic device 1 according to Embodiment 1. The diagnostic device 1 reads and executes the diagnostic program PG from the storage unit 12 at an appropriate timing after the power supply 2 (energy storage element 20) has started operation, and performs the following processes based on the diagnostic program PG. For example, if the power supply 2 is for stationary use, the processes may be executed at regular intervals, or if the power supply 2 is for vehicle use, the processes may be executed at timings instructed by the user, such as during vehicle inspections.

[0062] The control unit 11 of the diagnostic device 1 instructs the charge / discharge control device of the energy storage element 20 to perform a capacity verification test via the communication unit 13 (step S101). Upon receiving the instruction to perform the capacity verification test, the charge / discharge control device charges the energy storage element 20 to its limit (or discharges the energy storage element 20 from its limit). It is preferable to charge (or discharge) the energy storage element 20 at a low rate (for example, 0.05C or less) at the limit of charging.

[0063] The control unit 11 acquires measured values ​​of the voltage and capacity of the energy storage element 20 when the energy storage element 20 is charged to its limit (or discharged from its limit) (step S102). The voltage (cell voltage) of the energy storage element 20 is measured as the potential difference between the positive and negative electrodes. The capacity of the energy storage element 20 is measured as the time integral of the charging current (or discharge current). Sensors necessary for measuring the voltage and capacity of the energy storage element 20 (e.g., a voltage sensor and a current sensor) are provided on at least one energy storage element 20 provided by the power supply 2. The diagnostic device 1 may acquire measured values ​​of voltage and capacity from the energy storage element 20 in real time, or it may acquire them from an external device after they have been recorded on that external device. Both voltage and capacity are obtained as time-series measured values ​​and stored in the storage unit 12.

[0064] The control unit 11 calculates dV / dQ at a capacity value where the difference between the capacity value at the end of charging and the set value is the acquired voltage and capacity measurement values ​​(step S103). If the capacity value at the end of charging is Q0 and the capacity value used to calculate dV / dQ (the capacity value corresponding to point A in Figure 5) is Q1, the capacity value Q1 is determined such that the difference between them (Q0 - Q1) is the set value. The set value is set appropriately so that the capacity value Q1 is within a range near the end of charging (for example, within a range of 70% to 90% of the capacity value Q0 at the end of charging). Depending on the charging rate and battery design, the upper limit of the range may change in particular. As explained in Figure 8, the value of dV / dQ increases as the capacity retention rate of the positive electrode decreases near the end of charging, so it is preferable to set the set value so that the capacity value Q1 is within a range in which such behavior occurs. If V1 is the voltage of the energy storage element 20 at a capacity value Q1, and V2 is the voltage when the capacity value increases by ΔQ from Q1, then dV / dQ at a capacity value Q1 is calculated as (V2 - V1) / ΔQ.

[0065] The control unit 11 diagnoses the capacity degradation of the positive electrode 211 of the energy storage element 20 based on the calculated dV / dQ (step S104). The control unit 11 calculates the rate of change between the dV / dQ at the start of operation of the energy storage element 20 and the dV / dQ calculated in step S103 (dV / dQ calculated at any point after the start of operation). Here, the dV / dQ at the start of operation of the energy storage element 20 is assumed to have been calculated in advance using the method described above and stored in the memory unit 12. The control unit 11 estimates the capacity maintenance rate of the positive electrode unipolar of the energy storage element 20 based on the calculated rate of change. Specifically, the control unit 11 can estimate 100 - rate of change as the capacity maintenance rate of the positive electrode unipolar of the energy storage element 20.

[0066] Alternatively, the control unit 11 may set a threshold for the rate of change of dV / dQ from the start of operation, and diagnose that capacity degradation has occurred if the calculated rate of change is greater than or equal to the threshold, and diagnose that capacity degradation has not occurred if the calculated rate of change is less than the threshold.

[0067] The control unit 11 outputs the diagnostic result from step S104 (step S105). Specifically, the control unit 11 displays the diagnostic result on the display unit 15. If the control unit 11 performs the diagnosis at multiple timings after the start of operation, it may display the cycle change of the positive electrode single electrode capacity retention rate in a graph. Alternatively, the control unit 11 may notify the battery manufacturer of the estimated capacity retention rate information via the communication unit 13.

[0068] As described above, in Embodiment 1, the capacitance degradation of the positive electrode unipolar of the energy storage element 20 can be estimated in a non-destructive and simple manner.

[0069] (Embodiment 2) Embodiment 2 describes a configuration in which charging control is performed according to the detection result of the diagnostic device 1.

[0070] Figure 10 is an explanatory diagram illustrating an example configuration of a charging control system according to Embodiment 2. The charging control system according to Embodiment 2 includes a diagnostic device 1 and a power supply 2, as well as a charging control device 3. The diagnostic device 1 and power supply 2 are the same as those described in Embodiment 1, so their description will be omitted.

[0071] The charging control device 3 is, for example, a BMU (Battery Management Unit). The charging control device 3 is installed inside or outside the power supply 2 and performs charging control for the power supply 2. In addition to charging control, the charging control device 3 may also perform discharge control.

[0072] The charging control device 3 is connected to the diagnostic device 1 and the power supply 2 in a communication manner. Communication between the charging control device 3 and the diagnostic device 1 uses wireless communication via mobile communication standards such as 3G, 4G, or 5G, or wireless LAN methods such as Wi-Fi®. Alternatively, communication conforming to wired communication standards such as Ethernet® may be used. Communication between the charging control device 3 and the power supply 2 uses communication standards such as CAN (Controller Area Network) or LIN (Local Interconnect Network).

[0073] The charging control device 3 acquires the measured voltage and capacity values ​​of the energy storage element 20 by communicating with the power supply 2. The charging control device 3 transmits the acquired voltage and capacity values ​​to the diagnostic device 1.

[0074] The diagnostic device 1 acquires the voltage and capacity measurements of the energy storage element 20 by communicating with the charge control device 3. Based on the acquired voltage and capacity measurements, the diagnostic device 1 diagnoses the degradation of the positive electrode capacity of the energy storage element 20. The diagnostic method is the same as in Embodiment 1.

[0075] If the diagnostic device 1 determines that capacity degradation has occurred in the positive electrode 211 of the energy storage element 20, it sends a control command to the charging control device 3 to relax the charging conditions. For example, the charging conditions can be relaxed by reducing at least one of the charging rate, charging current, and charging voltage.

[0076] The diagnostic device 1 may set a first threshold and a second threshold (first threshold < second threshold) for the rate of change of dV / dQ. In this case, if the rate of change of dV / dQ becomes equal to or greater than the first threshold, the diagnostic device 1 sends a control command to the charge control device 3 to relax the charging conditions, and if dV / dQ becomes equal to or greater than the second threshold, the diagnostic device 1 sends a control command to the charge control device 3 to stop charging.

[0077] The charging control device 3 can suppress the degradation of the positive electrode capacity in the energy storage element 20 by performing charging control to the power supply 2 in response to a control command from the diagnostic device 1.

[0078] Figure 11 is a flowchart illustrating the procedure of the diagnostic device 1 according to Embodiment 2. If the power supply 2 is for stationary use, the diagnostic device 1 performs the same procedure as in the flowchart of Figure 9 at periodic intervals, or if the power supply 2 is for vehicle use, at intervals instructed by the user, such as during vehicle inspections, to diagnose the capacity degradation of the positive electrode 211 of the energy storage element 20 (steps S201 to S204).

[0079] Based on the diagnosis in step S204, the control unit 11 determines whether or not capacity degradation has occurred in the positive electrode 211 of the energy storage element 20 (step S205). If it is determined that no capacity degradation has occurred in the positive electrode 211 (S205: NO), the control unit 11 terminates the process according to this flowchart.

[0080] If the control unit 11 determines that the positive electrode 211 has undergone capacity degradation (S205: YES), it outputs a control command to the charge control device 3 to relax the charging conditions (step S206). Specifically, the control unit 11 generates a control command to reduce at least one of the charging rate, charging current, and charging voltage, and transmits the generated control command to the charge control device 3 via the communication unit 13. Alternatively, the control unit 11 may generate a control command to stop charging and transmit the generated control command to the charge control device 3 via the communication unit 13.

[0081] As described above, in Embodiment 2, if capacity degradation occurs in the positive electrode 211 of the energy storage element 20, a control command to relax the charging conditions is output to the charging control device, thereby suppressing capacity degradation in the positive electrode 211 of the energy storage element 20.

[0082] The degradation analysis of the positive electrode 211 shown in Embodiments 1 and 2 is performed under conditions that are less susceptible to the degradation of the negative electrode 212's capacity. However, if an influence is suspected, the degradation of the positive electrode 211's capacity can be estimated by excluding the influence using separate simulation values, theoretical values, or experimental values.

[0083] The disclosed embodiments are illustrative in all respects and not restrictive. The scope of the invention is defined by the claims and includes all modifications in the sense and scope equivalent to the claims.

[0084] For example, in this embodiment, the energy storage element 20 is a battery cell made of a lithium-ion battery. Alternatively, the energy storage element 20 may be a battery cell made of an all-solid-state battery, a lead-acid battery, a redox flow battery, a zinc-air battery, an alkaline manganese battery, a lithium-sulfur battery, a sodium-sulfur battery, a silver-zinc oxide battery, a nickel-metal hydride battery, a molten salt thermal battery, or the like.

[0085] 1 Diagnostic device 2 Power supply 11 Control unit 12 Memory unit 13 Communication unit 14 Operation unit 15 Display unit 20 Energy storage element 211 Positive electrode 212 Negative electrode PG Diagnostic program RM Recording medium

Claims

1. A diagnostic method that uses a computer to perform a process to diagnose the degradation of the positive electrode of an energy storage element, including a positive electrode and a negative electrode, by obtaining measured values ​​of the voltage and capacity of the energy storage element when the energy storage element is charged to its end or discharged from its end, calculating dV / dQ, which is the ratio of the voltage change dV to the capacity change dQ, at a capacity value where the difference from the capacity value at the end of charging is a set value, based on the obtained measured values, and diagnose the degradation of the capacity of the positive electrode of the energy storage element based on the calculated dV / dQ.

2. The diagnostic method according to claim 1, wherein the computer performs a process to diagnose the capacity degradation by estimating the capacity maintenance rate of the positive electrode from the rate of change between dV / dQ calculated at the start of operation of the energy storage element and dV / dQ calculated at any point after the start of operation.

3. The diagnostic method according to claim 1, wherein the setting value is set such that the capacity value used in calculating the dV / dQ is a value near the end of charging.

4. The diagnostic method according to claim 3, wherein the set value is set such that the capacity value used in calculating the dV / dQ is within the range of 70% to 90% of the capacity value at the end of charging.

5. The diagnostic method according to claim 1, wherein, as a result of diagnosing the energy storage element, the computer executes a process to output a control command to the control device that controls the charging and discharging of the energy storage element, which relaxes the charging and discharging conditions.

6. The diagnostic method according to claim 1, wherein, as a result of diagnosing the energy storage element, the computer performs a process to output information indicating that capacity degradation has occurred in the positive electrode.

7. A diagnostic device comprising at least one calculation unit, wherein the calculation unit acquires measured values ​​of the voltage and capacity of an energy storage element including a positive electrode and a negative electrode when the energy storage element is charged to the end of its charge or discharged from the end of its charge, calculates dV / dQ, which is the ratio of the voltage change amount dV to the capacity change amount dQ, at a capacity value where the difference from the capacity value at the end of the charge is a set value, based on the acquired measured values, and diagnoses the capacity degradation of the positive electrode of the energy storage element based on the calculated dV / dQ.

8. A computer program that causes a computer to perform a process to diagnose the degradation of the positive electrode of an energy storage element, including a positive electrode and a negative electrode, by obtaining measured values ​​of the voltage and capacity of the energy storage element when the energy storage element is charged to its limit or discharged from its limit, calculating dV / dQ, which is the ratio of the voltage change dV to the capacity change dQ, at a capacity value where the difference from the capacity value at the end of charging is a set value, based on the obtained measured values, and based on the calculated dV / dQ.

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