Sign detection method, sign detection device, and computer program

Abstract

The present invention acquires measurement values of the charge capacity and voltage of a power storage element when the power storage element has been charged from the discharge end state, derives, when the rate at which the voltage changes in accordance with changes in the charge capacity is defined as dV / dQ, the charge capacity dependency of dV / dQ on the basis of the acquired measurement values, identifies, on the basis of the derivation result, the peak position of a peak appearing on a characteristic curve indicating the charge capacity dependence of dV / dQ, and detects, on the basis of the identified peak position, a sign of sudden deterioration of the power storage element.

Description

预兆检测方法、预兆检测装置、及计算机程序

[0001] The present disclosure relates to a预兆 detection method, a预兆 detection 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 at the time of engine startup 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 charge state.

[0004] Japanese Unexamined Patent Application Publication No. 2021-163627

[0005] However, with the technique disclosed in Patent Document 1, a预兆 of rapid deterioration in a power storage element cannot be detected.

[0006] An object of the present disclosure is to provide a预兆 detection method, a预兆 detection device, and a computer program that can detect a预兆 of rapid deterioration in a power storage element.

[0007] The预兆 detection method in the present disclosure acquires measurement values of the voltage and charge capacity of the power storage element when the power storage element is charged from a discharged state, and based on the acquired measurement values, when the ratio of change in the voltage in response to a change in the charge capacity is defined as dV / dQ, derives the charge capacity dependence of dV / dQ, specifies the peak position of a peak appearing in a characteristic curve showing the charge capacity dependence of dV / dQ based on the derived result, and causes a computer to execute a process of detecting a预兆 of rapid deterioration of the power storage element based on the specified peak position.

[0008] According to the above aspect, a预兆 of rapid deterioration in a power storage element can be detected.

[0009] This is an explanatory diagram illustrating the outline of the process performed by the predictive detection device according to Embodiment 1. This is an external perspective view showing an example of the configuration of a power storage element. This is a schematic diagram of the wound electrode body provided by the power storage element. This is a block diagram illustrating the internal configuration of the predictive detection device. This is a graph showing the change in capacity retention rate when a charge-discharge cycle test is performed. This is a graph showing the change in negative electrode potential E with increasing charge capacity Q. This is a graph showing the Q dependence of dV / dQ. This is a graph showing the Q dependence of dV / dQ. This is a graph showing the change in the peak position of the first peak with respect to the number of cycles. This is a graph showing the change in the area intensity of the first peak with respect to the number of cycles. This is a graph showing the change in the full width at half maximum of the first peak with respect to the number of cycles. This is a flowchart illustrating the procedure of the process performed by the predictive detection device according to Embodiment 1. This is a schematic diagram showing an example of the display when predictive detection occurs. 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 process performed by the predictive detection device according to Embodiment 2.

[0010] (1) The predictive detection method of the present disclosure acquires measured values ​​of the voltage and charge capacity of the energy storage element when the energy storage element is charged from a discharged state, derives the charge capacity dependence of dV / dQ when the rate at which the voltage changes in response to the change in charge capacity is dV / dQ based on the acquired measured values, identifies the peak position of the peak appearing in the characteristic curve showing the charge capacity dependence of dV / dQ based on the derived result, and performs a process by computer to detect the signs of rapid deterioration of the energy storage element based on the identified peak position.

[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. In rechargeable batteries, if charging and discharging are performed under inappropriate conditions, the reaction inside the battery may become uneven due to electrolyte depletion, separator clogging, etc., and rapid degradation may occur. When rapid degradation occurs, deposits such as lithium may form on the negative electrode surface, leading to abnormalities such as internal short circuits and battery swelling.

[0013] In recent years, there have been suggestions to reuse (repurpose) secondary batteries that have reached their End of Life (EOL) for automotive use for stationary applications. This means that secondary batteries may be used for longer periods than those guaranteed by the manufacturer at the time of manufacture. In such cases, the risk of rapid degradation also increases.

[0014] If signs of rapid degradation in secondary batteries could be detected, countermeasures such as lowering the charging voltage or charging rate could be taken, thereby easing the charging conditions and suppressing rapid degradation of secondary batteries. However, currently, there is no technology that can detect signs of rapid degradation in secondary batteries.

[0015] The inventors of this invention conducted a detailed analysis of the Q dependence (charge capacity dependence) of dV / dQ (the rate at which the voltage of the energy storage element changes in response to a change in charge capacity) and found that the peak position of the peak appearing in the Q dependence of dV / dQ may shift to the lower capacity side as the number of cycles increases. This shift in the peak position to the lower capacity side is thought to be due to the non-uniformity of the internal reaction of the battery and the decrease in the reaction area of ​​the positive and negative electrodes. The inventors of this invention found that this shift in the peak position to the lower capacity side occurs even before the energy storage element rapidly deteriorates.

[0016] In the predictive detection method described in (1) above, the Q dependence of dV / dQ is derived from the measured voltage and charge capacity of the energy storage element, and the peak position of the peak appearing in the derived dV / dQ Q dependence is identified. In the predictive detection method described in (1) above, the identified peak position can be used as an indicator to detect signs of degradation.

[0017] (2) In the predictive detection method described in (1) above, the area intensity of the peak may be calculated, and a precursor of rapid deterioration of the energy storage element may be detected based on the peak position and the calculated area intensity.

[0018] The inventors of this application have found that as the number of cycles increases, not only does the peak position shift to a lower capacity, but the area intensity of the peak also decreases. The decrease in area intensity is thought to be due to a decrease in the amount of negative electrode active material contributing to the peak due to the non-uniformity of the internal reaction of the battery. In the predictive detection method described in (2) above, the peak position and area intensity can be used as indicators to detect signs of degradation.

[0019] (3) In the predictive detection method described in (1) or (2) above, the half-width of the peak may be calculated, and a precursor of rapid deterioration of the energy storage element may be detected based on the peak position and the calculated half-width.

[0020] The inventors of this application have found that as the number of cycles increases, not only does the peak position shift to a lower capacity, but the full width at half maximum (FWHM) of the peak also decreases. The decrease in FWHM is thought to be due to a decrease in the amount of negative electrode active material contributing to the peak, caused by the non-uniformity of the internal reaction of the battery. In the predictive detection method described in (3) above, the peak position and FWHM can be used as indicators to detect signs of degradation.

[0021] (4) In the predictive detection method described in any one of (1) to (3) above, the peak may be a peak that appears in response to a change in the stage structure of the negative electrode active material.

[0022] According to the prediction method described in (4) above, the peak position, area intensity, and full width at half maximum of the peak that appears in response to changes in the stage structure of the negative electrode active material can be used as indicators to detect signs of deterioration.

[0023] (5) In the predictive detection method described in (4) above, the peak position of the peak corresponding to the potential change between the potential flat region associated with the two-phase coexistence reaction of the high stage and the fourth stage and the potential flat region associated with the two-phase coexistence reaction of the third stage and the second stage may be identified.

[0024] According to the precursor detection method described in (5) above, the peak position, area intensity, and full width at half maximum of the peak observed between potential flat areas can be used as indicators to detect precursors to degradation.

[0025] (6) In the predictive detection method described in any one of (1) to (5) above, the voltage and charge capacity measurements may be obtained when the energy storage element is charged at a high rate of a second setting value or higher, which is higher than the first setting value, from the end of the discharge state in which the energy storage element has been deeply discharged at a low rate of less than the first setting value.

[0026] According to the predictive discharge method described in (6) above, deep discharge is performed at a low rate, which allows for the uniformity of the discharge state of the negative electrode and provides reliable dV / dQ data. According to the predictive discharge method described in (6) above, charging is performed at a high rate from the end of the discharge state after deep discharge at a low rate, which reflects the non-uniformity of the internal battery reaction in actual use and allows for the detection of signs of degradation.

[0027] (7) In the predictive detection method described in any one of (1) to (6) above, if the charging capacity corresponding to the identified peak position is less than the first threshold, it may be determined that a sign of rapid degradation has been detected.

[0028] The inventors of this application have found that under conditions where rapid degradation does not occur, the change in peak position accompanying the change in the number of cycles is small, and that a shift to a lower capacity at the peak position occurs only when rapid degradation occurs. In the prediction detection method of (7) above, by setting a threshold for the charging capacity corresponding to the peak position, signs of rapid degradation can be detected.

[0029] (8) In the predictive detection method described in (7) above, if it is determined that a sign of rapid deterioration has been detected, a control command may be output to the charge control device that controls the charging of the energy storage element to relax the charging conditions.

[0030] According to the warning detection method described in (8) above, if a warning of rapid degradation is detected, a control command is output to relax the charging conditions, thereby suppressing the occurrence of rapid degradation in the energy storage element.

[0031] (9) In the predictive detection method described in (8) above, if the charging capacity corresponding to the identified peak position is less than a second threshold which is lower than the first threshold, a control command to stop charging the energy storage element may be output to the charging control device.

[0032] According to the warning detection method described in (9) above, if the charging capacity corresponding to the peak position is below the second threshold, charging is stopped, thereby preventing abnormalities such as internal short circuits and battery swelling caused by rapid degradation.

[0033] (10) The predictive detection device of the present disclosure comprises at least one calculation unit, the calculation unit acquires measured values ​​of the voltage and charge capacity of the energy storage element when the energy storage element is charged from a discharged state, derives the charge capacity dependence of dV / dQ when the rate at which the voltage changes in accordance with the change in charge capacity is dV / dQ based on the acquired measured values, identifies the peak position of the peak appearing in the characteristic curve showing the charge capacity dependence of dV / dQ based on the derived result, and detects a sign of rapid deterioration of the energy storage element based on the identified peak position.

[0034] In the predictive detection device described in (10) above, the Q dependence of dV / dQ is derived from the measured voltage and charge capacity of the energy storage element, and the peak position of the peak appearing in the derived Q dependence of dV / dQ is identified. In the predictive detection device described in (10) above, the identified peak position can be used as an indicator to detect signs of degradation.

[0035] (11) The computer program of the present disclosure is a computer program that causes a computer to perform a process to detect signs of rapid deterioration of the energy storage element based on the identified peak position of the peak that appears on the characteristic curve showing the charge capacity dependence of dV / dQ, based on the identified peak position of the energy storage element when the energy storage element is charged from a discharged state, derives the voltage and charge capacity of the energy storage element when the rate of change of the voltage in accordance with the change in charge capacity is dV / dQ based on the acquired measured values, and causes a computer to perform a process to detect signs of rapid deterioration of the energy storage element based on the identified peak position.

[0036] The computer program described in (11) above derives the Q dependence of dV / dQ from the measured voltage and charge capacity of the energy storage element, and identifies the peak position of the peak appearing in the derived Q dependence of dV / dQ. The computer program described in (1) above can use the identified peak position as an indicator to detect signs of degradation.

[0037] 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 predictive detection device according to Embodiment 1. The predictive detection device 1 according to Embodiment 1 is a device for detecting signs of rapid deterioration targeting the energy storage element 20 mounted on a power supply 2. The power supply 2 is mounted, for example, on 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 energy storage element 20 and also supplies the power stored in the energy storage element 20 to various equipment of the vehicle, such as the electric motor, headlights, turn signals, interior lights, and power windows.

[0038] 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.

[0039] The power supply 2 is equipped with multiple energy storage elements 20. 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.

[0040] In this embodiment, the energy storage element 20 is a battery cell made of lithium-ion battery. Secondary batteries, including lithium-ion batteries, generally degrade with repeated charging and discharging. It is empirically known that the capacity degradation of secondary 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 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., and rapid degradation may occur. When rapid degradation occurs, deposits such as lithium may precipitate on the negative electrode surface, which can lead to abnormalities such as internal short circuits and battery swelling.

[0041] In recent years, there have been suggestions to reuse (repurpose) secondary batteries that have reached their End of Life (EOL) for automotive use for stationary applications. This means that secondary batteries may be used for longer periods than those guaranteed by the manufacturer at the time of manufacture. In such cases, the risk of rapid degradation also increases.

[0042] If signs of rapid degradation in secondary batteries could be detected, countermeasures such as lowering the charging voltage or charging rate could be taken, thereby easing the charging conditions and suppressing rapid degradation of secondary batteries. However, currently, there is no technology that can detect signs of rapid degradation in secondary batteries.

[0043] In this embodiment, a method for detecting signs of rapid deterioration in the energy storage element 20 is proposed. As will be described in detail later, the predictive detection device 1 acquires measured values ​​related to the energy storage element 20 (voltage V and charge capacity Q of the energy storage element 20) and derives the Q dependence of dV / dQ based on the acquired measured values. The predictive detection device 1 detects signs of rapid deterioration in the energy storage element 20 based on the peak position of the peak that appears in the Q dependence of the derived dV / dQ.

[0044] In this specification, sudden degradation is distinguished from normal degradation from the perspective of the degradation rate (the rate at which performance deteriorates per unit period). Normal degradation refers to the performance of the power storage element 20 deteriorating at a rate assumed by an empirical rule such as the root rule. In contrast, sudden degradation refers to the performance of the power storage element 20 deteriorating at a rate faster than that assumed by an empirical rule such as the root rule.

[0045] FIG. 2 is an external perspective view showing a configuration example of the power storage element 20, and FIG. 3 is a schematic diagram of the wound electrode body 21 included in the power storage element 20. The power storage element 20 according to the embodiment is a battery cell using a lithium-ion battery. The power storage element 20 is configured by housing a flat wound electrode body 21 and an electrolyte (not shown in the figure) in a hollow rectangular parallelepiped battery case 22. In FIG. 2, the wound electrode body 21 is shown in a state where the inside of the battery case 22 is seen through.

[0046] On the upper surface of the battery case 22, a positive electrode terminal 23 and a negative electrode terminal 24 for external connection are provided. The positive electrode terminal 23 and the negative electrode terminal 24 are electrically connected to a positive electrode current collector 25 and a negative electrode current collector 26, respectively. As the material of the battery case 22, for example, a lightweight and highly thermally conductive metal material such as aluminum is used.

[0047] The wound electrode body 21 is formed by overlapping a sheet-like positive electrode 211 with a positive electrode active material layer 211A and a sheet-like negative electrode 212 with a negative electrode active material layer 212A through two sheet-like separators 213 and winding them. The positive electrode 211 and the negative electrode 212 are arranged in a state shifted from each other in the width direction of the sheet. At one end in the width direction of the positive electrode 211, a region where the positive electrode active material layer 211A is not formed is provided, and the positive electrode current collector 25 is joined to this region. For example, an aluminum foil is used for the positive electrode current collector 25. Similarly, at the other end in the width direction of the negative electrode 212, a region where the negative electrode active material layer 212A is not formed is provided, and the negative electrode current collector 26 is joined to this region. For example, a copper foil is used for the negative electrode current collector 26.

[0048] 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 (for example, Mn, Ni, Co, Fe, Nb, W, P, Si, etc.). The elements other than lithium and oxygen may be of one kind or a plurality of kinds. The positive electrode active material layer 211A may further contain a conductive assistant, a binder, etc. As the conductive assistant, for example, carbon black such as acetylene black (AB) and other carbon materials (such as graphite) are preferably used. As the binder, for example, polyvinylidene fluoride (PVDF) etc. are used.

[0049] The negative electrode active material layer 212A contains a negative electrode active material. As the negative electrode active material, for example, 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) etc. are used. As the thickener, for example, carboxymethyl cellulose (CMC) etc. are used.

[0050] The separator 213 is formed of a porous resin film. As the porous resin film, a porous resin film made of a resin such as polyethylene (PE) or polypropylene (PP) can be used. The separator 213 may be formed of a resin film having a single-layer structure, or may be formed of a resin film having a multi-layer structure of two or more layers. The separator 213 may be provided with a heat-resistant layer.

[0051] For the electrolyte accommodated in the battery case 22 together with the wound electrode body 21, the same ones as those of existing lithium ion batteries can be used. For example, as the electrolyte, an electrolyte in which a supporting salt is contained in an organic solvent can be used. As the organic solvent, for example, aprotic solvents such as carbonates, esters, and ethers are used. As the supporting salt, for example, lithium salts such as LiPF6, LiBF4, and LiClO4 are preferably used. The electrolyte may contain various additives such as a gas generating agent, a film forming agent, a dispersant, and a thickener.

[0052] 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.

[0053] Figures 2 and 3 illustrate a rectangular lithium-ion battery equipped with a wound electrode body 210 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, etc.

[0054] Figure 4 is a block diagram showing the internal configuration of the predictive maintenance device 1. The predictive maintenance device 1 is a dedicated or general-purpose computer for detecting signs of rapid deterioration in the energy storage element 20. As shown in Figure 1, the predictive maintenance device 1 is installed outside the power supply 2 and detects signs of rapid deterioration in the energy storage element 20 from an external location. For example, the predictive maintenance device 1 may be installed in a remote location sufficiently far from the power supply 2 and detect signs of rapid deterioration by remote diagnosis, or it may be installed within a range where wired communication is possible and detect signs of rapid deterioration by on-site diagnosis. Alternatively, the predictive maintenance device 1 may be installed in the power supply 2 (or the vehicle or energy storage equipment on which the power supply 2 is installed) and detect signs of rapid deterioration by self-diagnosis.

[0055] The predictive detection device 1 comprises 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 equipped with a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), and the like. The CPU in the control unit 11 controls various hardware parts by reading and executing various computer programs stored in the ROM or storage unit 12, thereby realizing a function to detect signs of rapid deterioration in the energy storage element 20.

[0056] The control unit 11 may be any arithmetic circuit equipped with multiple CPUs, a multi-core CPU, a GPU (Graphics Processing Unit), a microcontroller, volatile or non-volatile memory, etc. The control unit 11 may also include functions such as a timer for measuring the elapsed time from the time 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.

[0057] The storage unit 12 includes a storage device such as flash memory or a hard disk. Various computer programs and data are stored in the storage unit 12. The computer programs stored in the storage unit 12 include a predictive detection program PG that causes the computer to execute a process to detect signs of rapid deterioration in the energy storage element 20 based on measured values ​​related to the energy storage element 20. The data stored in the storage unit 12 includes various parameters used in the predictive detection program PG and data input through the communication unit 13, etc.

[0058] The predictive maintenance program PG may be a single computer program or may consist of multiple computer programs. The predictive maintenance program PG may run on a single computer or may run collaboratively by multiple computers. Furthermore, the predictive maintenance program PG may partially utilize existing libraries.

[0059] The computer program, including the predictive maintenance program PG, is provided on a non-temporary recording medium RM on which the computer program is recorded in a readable format. The recording medium RM is a portable memory such as a CD-ROM, USB memory, or SD (Secure Digital) card. The control unit 11 reads the 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 predictive maintenance program PG, may be provided via communication.

[0060] 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 predictive detection. The communication unit 13 outputs the acquired measurement values ​​to the control unit 11.

[0061] 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 predictive detection 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 predictive detection device 1 does not need to be equipped with an operation unit 14 and a display unit 15.

[0062] The evaluation tests conducted by the present inventors are described below. Figure 5 is a graph showing the change in capacity retention rate when a charge-discharge cycle test is performed. In the graph of Figure 5, the horizontal axis is the number of cycles, and the vertical axis is the capacity retention rate (%). The graph of Figure 5 shows the change in capacity retention rate when a charge-discharge cycle test is performed by adjusting the temperature of the energy storage element 20 to T1, T2, and T3 (T1 < T2 < T3). The graphs for temperatures T1 and T3 show that the performance of the energy storage element 20 (capacity retention rate in this example) decreases in roughly proportion to the number of cycles, indicating normal degradation behavior. On the other hand, the graph for temperature T2 shows that a rapid decline in performance begins when the number of cycles exceeds Na, indicating rapid degradation behavior.

[0063] By evaluating the performance of the energy storage element 20 over a long period and plotting its performance against the number of cycles, information can be obtained from the plotted graph regarding whether or not rapid degradation has occurred in the energy storage element 20. However, as shown in the change in capacity retention rate at temperature T2, the behavior before rapid degradation occurs is almost the same as the behavior of normal degradation without rapid degradation, and it can be seen that the performance decreases in roughly proportion to the number of cycles. In other words, although the graph shown in Figure 5 confirms that rapid degradation has actually occurred and has occurred after some time has passed, no information indicating signs of rapid degradation can be obtained at the time before rapid degradation occurs.

[0064] The inventors of the present invention examined the relationship between the charging capacity Q and voltage V of the energy storage element 20 in order to detect signs of rapid deterioration in the energy storage element 20.

[0065] Figure 6 is a graph showing the change in negative electrode potential E as the charging capacity Q increases. The horizontal axis represents the charging capacity Q (Ah), and the left vertical axis represents the negative electrode potential E (V). The solid line graph shows the change in negative electrode potential E as the charging capacity Q changes. The right vertical axis in Figure 6 is dE / dQ (V / Ah). The Q dependence of dE / dQ is shown by a dashed line in Figure 6.

[0066] For the negative electrode 212 of the energy storage element 20, graphite is used as the negative electrode active material. Graphite is a layered material in which carbon hexagonal network planes (graphene) are stacked in parallel. Various chemical species (intercalants) are inserted between the graphite layers. One example of an inserted chemical species is lithium ions. The insertion of chemical species between the graphite layers forms a graphite intercalation compound (GIC). The graphite intercalation compound takes on a unique structure called a stage structure. A structure in which chemical species are regularly inserted every n graphite layers is called the nth stage stage structure. When the energy storage element 20 is charged from the discharged state, the stage structure of the graphite intercalation compound changes in the following order: high stage, fourth stage, third stage, second stage, and first stage. The first stage structure is a saturated structure in which inserted species are inserted between all layers. Such chemical species insertion reactions into layered materials can occur not only between graphite and lithium ions, but also between various layered materials and chemical species.

[0067] The charge-discharge curve shown in Figure 6 exhibits potential flats associated with two-phase coexistence reactions. In the example in Figure 6, three potential flats are visible: a potential flat associated with the two-phase coexistence reaction between the high stage and the fourth stage (first potential flat), a potential flat associated with the two-phase coexistence reaction between the third stage and the second stage (second potential flat), and a potential flat associated with the two-phase coexistence reaction between the second stage and the first stage (third potential flat).

[0068] When the negative electrode potential E is differentiated with respect to the charging capacity Q, the potential change between potential flat regions is observed as a peak in dE / dQ. In the example in Figure 6, a first peak is observed corresponding to the potential change between the first and second potential flat regions, and a second peak is observed corresponding to the potential change between the second and third potential flat regions. Since the potential change between the second and third potential flat regions is small, the second peak is not clearly observed unless charging is done at a low rate. On the other hand, at low rates, it may not be possible to evaluate the non-uniformity at rates that are relevant to actual use. If the non-uniformity of the internal reaction of the battery progresses, the second peak may not be observed at all.

[0069] In this embodiment, instead of the negative electrode potential E, which is difficult to obtain, the relationship between the charging capacity Q and the voltage V was examined using the voltage (cell voltage) V of the energy storage element 20, which can be measured relatively easily in actual operation. That is, in this embodiment, the first peak appearing in the characteristic curve showing the Q dependence of dV / dQ was the target of analysis. In order to obtain reliable data on the Q dependence of dV / dQ, it is necessary to ensure that the discharge state of the negative electrode 212 is consistent before the start of charging. In particular, in order to suppress the shift of the peak to the high-capacity side due to imbalance, it is necessary to discharge the negative electrode 212 as deeply as possible. Imbalance refers to the fact that Li that is not used for charging and discharging is trapped (deposited) on the negative electrode, which reduces the amount of Li ions that are originally the carriers of charging and discharging, and thus reduces the apparent amount of charge. In other words, at the negative electrode, the amount of Li ions that can be used for charging and discharging decreases when Li is incorporated into the electrode film (thin film) and cannot be detached, or when Li crystallizes (dendriticizes) at the negative electrode. On the other hand, in order to evaluate the non-uniformity of the internal reaction of the battery at a practical rate, it is necessary to charge it at a relatively high rate. Therefore, in this embodiment, the dV / dQ was analyzed when the battery was deeply discharged at a low rate below the first set value (for example, 0.02 CA) to equalize the discharge state of the negative electrode 212, and then charged at a high rate above the second set value (for example, 1 CA), which is higher than the first set value.

[0070] Figures 7 and 8 are graphs showing the Q dependence of dV / dQ. In the graphs of Figures 7 and 8, the horizontal axis represents the charging capacity Q (Ah), and the vertical axis represents dV / dQ (V / Ah). Figures 7 and 8 show the Q dependence of dV / dQ when the energy storage element 20 is discharged to the end of its discharge state at a low rate such as 0.02 CA, and then charged at a high rate such as 1 CA. Figure 7 shows the Q dependence of dV / dQ at temperature T1, and Figure 8 shows the Q dependence of dV / dQ at temperature T2.

[0071] In both Figure 7 and Figure 8, the first peak is visible, but the second peak is not. As shown in Figure 7, in the charge-discharge cycle test at temperature T1, the peak position of the first peak remains virtually unchanged even when the number of cycles is increased in the order of N1, N2, N3, and N4. On the other hand, as shown in Figure 8, in the charge-discharge cycle test at temperature T2, when the number of cycles is increased in the order of N1, N2, N3, and N4, the peak position of the first peak shifts towards the lower capacity side.

[0072] The peak position of the first peak is determined by fitting the first peak to an appropriate function, such as a Gaussian function. For example, the least squares method can be used for fitting. To accurately determine the peak position, it is preferable to remove the background from dV / dQ before performing fitting with a Gaussian function or the like. The background can be represented, for example, by a linear function passing through two points at both ends of the peak. From the function obtained by fitting the first peak, information on the peak position, as well as the peak area intensity and half-width (full width at half maximum) can be obtained.

[0073] Figure 9 is a graph showing the change in the peak position of the first peak with respect to the number of cycles. The horizontal axis represents the number of cycles, and the vertical axis represents the peak position (Ah). The graph in Figure 9 shows the change in the peak position when charge-discharge cycle tests were performed at temperatures T1, T2, and T3 (T1 < T2 < T3). From the graphs for temperatures T1 and T3, it can be seen that the peak position of the first peak remains approximately constant regardless of the increase or decrease in the number of cycles. On the other hand, from the graph for temperature T2, it can be seen that the peak position of the first peak shifts to the lower capacity side as the number of cycles increases.

[0074] Typically, capacity degradation in lithium-ion batteries is mainly due to Li-trapping in the negative electrode coating. This type of capacity degradation is normal and can be explained by an empirical root rule, and the peak position of the first peak does not shift towards the lower capacity side. On the other hand, degradation mainly caused by a decrease in the positive electrode unipolar capacity, a decrease in the negative electrode unipolar capacity, or a decrease in the positive and negative electrode reaction area (non-uniformity of the internal battery reaction) is abnormal degradation in which the charging capacity decreases. It is thought that the peak position of the first peak shifts towards the lower capacity side due to this type of abnormal degradation.

[0075] As explained using the graph in Figure 5, the energy storage element 20 exhibited rapid degradation behavior when the number of cycles exceeded Na in the cycle at temperature T2. In contrast, in the same energy storage element 20 cycle at temperature T2, the peak position began to shift towards the lower capacity side from around the number of cycles Nb, before the number of cycles exceeded Na.

[0076] This indicates that the peak position of the peak appearing in the Q dependence of dV / dQ can be used as an indicator for detecting signs of rapid degradation in the energy storage element 20. In other words, the predictive detection device 1 can determine whether or not there are signs of rapid degradation in the energy storage element 20 by deriving the Q dependence of dV / dQ of the energy storage element 20 and analyzing the peak position of the peak appearing in the derived Q dependence of dV / dQ.

[0077] Figures 7 and 8 show a case where only the first peak appears, but in the Q dependence of dV / dQ, a second peak may also appear in addition to the first peak. In this case, the predictive detection device 1 may analyze the peak positions of the first and second peaks and detect signs of rapid degradation in the energy storage element 20 based on the peak position of each peak, the distance between peaks, etc.

[0078] Figure 10 is a graph showing the change in area intensity of the first peak with respect to the number of cycles. The horizontal axis represents the number of cycles, and the vertical axis represents area intensity (V). The graph in Figure 10 shows the change in area intensity (peak area) when charge-discharge cycle tests were conducted at temperatures T1, T2, and T3 (T1 < T2 < T3). The graph in Figure 10 shows that the area intensity tends to decrease with increasing cycle numbers, but the rate of decrease in area intensity from cycle number Nb is largest in the cycle at temperature T2 where rapid degradation occurred.

[0079] Figure 11 is a graph showing the change in the full width at half maximum (FMAX) of the first peak with respect to the number of cycles. The horizontal axis represents the number of cycles, and the vertical axis represents the full width at half maximum (Ah). The graph in Figure 11 shows the change in the full width at half maximum when charge-discharge cycle tests were performed at temperatures T1, T2, and T3 (T1 < T2 < T3). The graph in Figure 11 shows that the full width at half maximum tends to decrease with increasing cycle numbers, but the rate of decrease in the full width at half maximum from cycle number Nb is largest in the cycle at temperature T2 where rapid degradation occurred. Although Figure 11 shows the change in full width at half maximum, similar information can of course be obtained from the change in half width at half maximum.

[0080] Therefore, the area intensity and full width at half maximum of the peak appearing in the Q dependence of dV / dQ can serve as indicators for detecting signs of rapid degradation in the energy storage element 20. The predictive detection device 1 may determine whether or not there are signs of rapid degradation in the energy storage element 20 by deriving the Q dependence of dV / dQ of the energy storage element 20 and analyzing at least one of the area intensity and full width at half maximum in addition to the peak position of the peak appearing in the Q dependence of dV / dQ. For example, the predictive detection device 1 may predict the number of cycles Nx at which rapid degradation will begin from the peak position of the peak appearing in the Q dependence of dV / dQ, calculate the rate of decrease in area intensity or full width at half maximum from the predicted number of cycles Nx, and determine whether or not signs of rapid degradation have been detected based on whether or not the rate of decrease exceeds a threshold.

[0081] Figure 12 is a flowchart illustrating the procedure of processing performed by the predictive maintenance device 1 according to Embodiment 1. The predictive maintenance device 1 performs the following processing at the timing of vehicle inspections if the power supply 2 is for vehicle use, or at periodic timings if the power supply 2 is for stationary use.

[0082] The energy storage element 20 is deeply discharged to its final discharge state at a low rate below a first set value (e.g., 0.02 CA), and then charged at a high rate above a second set value (e.g., 1 CA). The control unit 11 of the predictive detection device 1 acquires the measured values ​​of voltage and charge capacity measured during charging, for example, through the communication unit 13 (step S101). The voltage (cell voltage) of the energy storage element 20 is measured as the potential difference between the positive and negative electrodes. The charge capacity of the energy storage element 20 is measured as the time integral of the charging current. Sensors (e.g., voltage sensor and current sensor) for measuring the voltage and charge capacity of the energy storage element 20 are provided on at least one energy storage element 20 provided by the power supply 2. The predictive detection device 1 may acquire the measured values ​​of voltage and charge 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 device.

[0083] The control unit 11 derives the Q dependence of dV / dQ, which is the rate at which the voltage V changes in response to a change in the charging capacity Q, based on the acquired measured values ​​(step S102). If V1 is the voltage when the charging capacity is Q1, and V2 is the voltage when the charging capacity increases by ΔQ from Q1, then dV / dQ at charging capacity Q1 is calculated, for example, as (V2 - V1) / ΔQ. The control unit 11 derives the Q dependence of dV / dQ by calculating dV / dQ for each value of charging capacity Q.

[0084] The control unit 11 identifies the peak position of the peak appearing in the Q dependence of the derived dV / dQ (step S103). Under the above charging conditions (charging at a low rate), a first peak appears in the characteristic curve showing the Q dependence of dV / dQ, corresponding to the potential change from the first potential flat to the second potential flat. The control unit 11 identifies the peak position of the first peak by fitting dV / dQ using an appropriate fitting function (e.g., a Gaussian function) that has the peak position of the first peak as a parameter. If a second peak appears in the characteristic curve, the control unit 11 may similarly identify the peak position of the second peak.

[0085] The control unit 11 determines whether or not there are signs of rapid degradation in the energy storage element 20 based on the peak position identified in step S103 (step S104). As described above, if rapid degradation does not occur, the peak position of the first peak remains largely unchanged, and if rapid degradation occurs, the peak position of the first peak shifts to the lower capacity side. The control unit 11 sets a threshold for the charging capacity corresponding to the peak position of the first peak, and if the peak position of the first peak is above the threshold, it determines that there are no signs of rapid degradation, and if it is below the threshold (when the first peak has shifted to the lower capacity side), it determines that there are signs of rapid degradation.

[0086] If it is determined that there are no signs of rapid deterioration (S104: NO), the control unit 11 returns the process to step S101 and repeats the processes from steps S101 to S104.

[0087] If the control unit 11 determines in step S104 that there are signs of rapid deterioration in the energy storage element 20 (S104: YES), it outputs information indicating that signs of rapid deterioration have been detected (step S105). Specifically, the control unit 11 displays information indicating that signs of rapid deterioration have been detected on the display unit 15. Figure 13 is a schematic diagram showing an example of the display when signs are detected. Figure 13 shows an example in which text information indicating that signs of rapid deterioration have been detected is displayed on the display unit 15 along with a graph showing the Q dependence of dV / dQ. Alternatively, the control unit 11 may notify the user's terminal device of the information indicating that signs of rapid deterioration have been detected via the communication unit 13. If the signs detection device 1 is equipped with an audio output unit, the control unit 11 may also announce the detection of signs of rapid deterioration by voice.

[0088] In the flowchart of Figure 12, a threshold is set for the charging capacity corresponding to the peak position of the first peak, and the presence or absence of signs of rapid degradation is determined based on the comparison result between the peak position and the threshold. Alternatively, the control unit 11 may set a threshold for the amount (or shift rate) of shift of the peak position of the first peak to the lower capacity side, and if the calculated amount (or shift rate) of the peak position is less than or equal to the threshold, it may be determined that there are no signs of rapid degradation, and if it exceeds the threshold, it may be determined that there are signs of rapid degradation.

[0089] Furthermore, the control unit 11 may detect signs of rapid degradation by analyzing at least one of the area intensity and full width at half maximum, in addition to the peak position of the peak appearing in the Q dependence of dV / dQ.

[0090] As described above, in Embodiment 1, it is possible to detect signs of rapid deterioration of the energy storage element 20 at a time before the rapid deterioration of the energy storage element 20 actually begins.

[0091] (Embodiment 2) Embodiment 2 describes a configuration in which charging control is performed according to the detection result of the predictive detection device 1.

[0092] Figure 14 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 predictive detection device 1 and a power supply 2, as well as a charging control device 3. The predictive detection device 1 and the power supply 2 are the same as those described in Embodiment 1, so their description will be omitted.

[0093] 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.

[0094] The charging control device 3 is connected to the predictive detection device 1 and the power supply 2 in a communication manner. Communication between the charging control device 3 and the predictive detection 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).

[0095] The charging control device 3 acquires the measured voltage and charging capacity values ​​of the energy storage element 20 by communicating with the power supply 2. The charging control device 3 transmits the acquired measured voltage and charging capacity values ​​to the predictive detection device 1.

[0096] The predictive detection device 1 acquires measured voltage and charge capacity values ​​measured with respect to the energy storage element 20 by communicating with the charge control device 3. Based on the acquired voltage and charge capacity values, the predictive detection device 1 detects signs of deterioration in the energy storage element 20. The predictive detection judgment method performed by the predictive detection device 1 is the same as in Embodiment 1.

[0097] When the predictive detection device 1 detects signs of deterioration in the energy storage element 20, it transmits a control command to the charge 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.

[0098] The predictive detection device 1 may set a first threshold and a second threshold (provided that the first threshold > the second threshold) for the peak position of the peak appearing in the Q dependence of dV / dQ. In this case, if the charging capacity corresponding to the peak position falls below the first threshold, the preventive detection device 1 sends a control command to the charging control device 3 to relax the charging conditions, and if the charging capacity corresponding to the peak position falls below the second threshold, it sends a control command to the charging control device 3 to stop charging.

[0099] The charging control device 3 can suppress the occurrence of rapid deterioration in the energy storage element 20 by performing charging control to the power supply 2 in response to a control command from the predictive detection device 1.

[0100] Figure 15 is a flowchart illustrating the procedure performed by the predictive maintenance device 1 according to Embodiment 2. If the power supply 2 is for vehicle use, the predictive maintenance device 1 performs the same procedure as in the flowchart of Figure 12 at the timing of vehicle inspections, or at periodic timings if the power supply 2 is for stationary use, to determine whether or not there are signs of deterioration in the energy storage element 20 (steps S201 to S204).

[0101] If it is determined that there are no signs of rapid deterioration (S204: NO), the control unit 11 returns the process to step S201 and repeats the processes from steps S201 to S204.

[0102] If the control unit 11 determines in step S204 that there are signs of rapid deterioration in the energy storage element 20 (S204: YES), it outputs a control command to the charge control device 3 to relax the charging conditions (step S205). 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.

[0103] As described above, in Embodiment 2, if there are signs of deterioration in the energy storage element 20, a control command to relax the charging conditions is output to the charging control device, thereby suppressing the occurrence of rapid deterioration in the energy storage element 20.

[0104] 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.

[0105] 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.

[0106] 1. Predictive detection device 2. Power supply 11. Control unit 12. Memory unit 13. Communication unit 14. Operation unit 15. Communication unit 20. Energy storage element 211. Positive electrode 212. Negative electrode PG. Predictive detection program RM. Recording medium

Claims

1. A predictive maintenance method for a storage element, comprising: obtaining measured values ​​of the voltage and charge capacity of the storage element when it is charged from a discharged state; deriving the charge capacity dependence of dV / dQ, where dV / dQ is the rate at which the voltage changes in response to a change in the charge capacity, based on the obtained measured values; identifying the peak position of the peak appearing in the characteristic curve showing the charge capacity dependence of dV / dQ, based on the derived result; and executing a process by computer to detect signs of rapid deterioration of the storage element based on the identified peak position.

2. The method for detecting signs of rapid deterioration of the energy storage element according to claim 1, wherein the computer performs a process to detect signs of rapid deterioration of the energy storage element based on the peak position and the calculated area intensity.

3. The method for detecting signs of rapid deterioration of the energy storage element according to claim 1, wherein the computer performs a process to detect signs of rapid deterioration of the energy storage element based on the peak position and the calculated half-width of the peak.

4. The predictive detection method according to claim 1, wherein the peak is a peak that appears in conjunction with a change in the stage structure of the negative electrode active material.

5. The predictive detection method according to claim 4, wherein the computer performs a process to identify the peak position of the peak corresponding to the potential change between the potential flat region associated with the two-phase coexistence reaction of the high stage and the fourth stage and the potential flat region associated with the two-phase coexistence reaction of the third stage and the second stage.

6. The predictive detection method according to claim 1, wherein the computer performs a process to obtain measured values ​​of voltage and charge capacity when the energy storage element is charged at a high rate of a second setting value or higher, which is higher than the first setting value, from the discharge end state in which the energy storage element has been deeply discharged at a low rate of less than a first setting value.

7. The predictive maintenance method according to claim 1, wherein the computer performs a process to determine that a sign of rapid degradation has been detected if the charging capacity corresponding to the identified peak position is below a first threshold.

8. The predictive maintenance method according to claim 7, wherein, when it is determined that a sign of rapid deterioration has been detected, the computer executes a process to output a control command to the charge control device that controls the charging of the energy storage element, thereby easing the charging conditions.

9. The predictive detection method according to claim 8, wherein the computer performs a process of outputting a control command to the charging control device to stop charging the energy storage element when the charging capacity corresponding to the identified peak position is less than a second threshold which is lower than the first threshold.

10. A predictive device comprising at least one calculation unit, wherein the calculation unit acquires measured values ​​of the voltage and charge capacity of the energy storage element when the energy storage element is charged from a discharged state, derives the charge capacity dependence of dV / dQ when dV / dQ is the rate at which the voltage changes in accordance with the change in charge capacity based on the acquired measured values, identifies the peak position of the peak appearing in the characteristic curve showing the charge capacity dependence of dV / dQ based on the derived result, and detects signs of rapid deterioration of the energy storage element based on the identified peak position.

11. A computer program that causes a computer to perform a process to detect signs of rapid deterioration of the energy storage element based on the identified peak position, based on the identified peak position, based on the identified peak position, based on the measured values ​​obtained, the voltage and charge capacity of the energy storage element when the energy storage element is charged from a discharged state, the rate at which the voltage changes in response to the change in charge capacity is defined as dV / dQ, based on the derived results, the peak position of the peak appearing in the characteristic curve showing the charge capacity dependence of dV / dQ, and the voltage and charge capacity of the energy storage element when the energy storage element is charged from a discharged state.

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