Predictive detection method, predictive detection device, and computer program

Abstract

Providing a predictive detection method, a predictive detection device, and a computer program. [Solution] When the energy storage element is charged from its discharged state, the voltage and charge capacity of the energy storage element are measured and obtained. Based on the obtained measured values, the charge capacity dependence of dV / dQ is derived, where dV / dQ is the rate at which the voltage changes in response to the change in charge capacity. Based on the derived result, the peak position of the peak appearing in the characteristic curve showing the charge capacity dependence of dV / dQ is identified, and based on the identified peak position, signs of rapid deterioration of the energy storage element are detected.

Description

Technical Field

[0001] The present disclosure relates to a预兆 detection method, a预兆 detection device, and a computer program.

Background Art

[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.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

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

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

Means for Solving the Problems

[0007] It should be noted that the term "预兆" is not a common English word in this context. It seems there might be a specific technical or misspelled term. If it's a specific technical term in Japanese related to battery deterioration prediction, it might need to be accurately translated based on the actual meaning in that field. Here I've just left it as "预兆" for the purpose of following the translation rules.The predictive detection method in this 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 defined as 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. [Effects of the Invention]

[0008] According to the above embodiment, it is possible to detect signs of rapid deterioration in the energy storage element. [Brief explanation of the drawing]

[0009] [Figure 1] This is an explanatory diagram illustrating the outline of the process performed by the predictive detection device according to Embodiment 1. [Figure 2] This is an external perspective view showing an example of the configuration of an energy storage element. [Figure 3] This is a schematic diagram of the wound electrode body of an energy storage element. [Figure 4] This is a block diagram showing the internal configuration of a predictive maintenance device. [Figure 5] This graph shows the change in capacity retention rate when a charge-discharge cycle test is performed. [Figure 6] This graph shows the change in the negative electrode potential E as the charging capacity Q increases. [Figure 7] This graph shows the Q dependence of dV / dQ. [Figure 8] This graph shows the Q dependence of dV / dQ. [Figure 9] This graph shows the change in the peak position of the first peak as the number of cycles increases. [Figure 10] This graph shows the change in the area intensity of the first peak as the number of cycles increases. [Figure 11] This graph shows the change in the full width at half maximum of the first peak as the number of cycles increases. [Figure 12]This is a flowchart illustrating the procedure for processing performed by the predictive detection device according to Embodiment 1. [Figure 13] This is a schematic diagram showing an example of a display when an anomaly is detected. [Figure 14] This is an explanatory diagram illustrating an example configuration of a charging control system according to Embodiment 2. [Figure 15] This is a flowchart illustrating the procedure for processing performed by the predictive detection device according to Embodiment 2. [Modes for carrying out the invention]

[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] Secondary batteries containing lithium-ion batteries generally deteriorate due to repeated charge and discharge. It is empirically known that the capacity degradation of secondary batteries is proportional to the square root of the usage time (number of cycles). Such empirical root rules are often applied to predict the degradation of secondary batteries. In secondary batteries, when charge and discharge are performed under inappropriate conditions, the reaction inside the battery may become non-uniform due to depletion of the electrolyte, clogging of the separator, etc., and rapid degradation may occur. When rapid degradation occurs, deposits such as lithium may precipitate on the surface of the negative electrode, leading to abnormalities such as internal short circuits and battery swelling.

[0013] In recent years, it has also been proposed to reuse (re-purpose) secondary batteries that have reached the end of life (EOL) for in-vehicle use for stationary use, and secondary batteries may be used longer than the period guaranteed by the manufacturer at the time of manufacture. In such cases, the risk of rapid degradation also increases.

[0014] If a sign of rapid degradation in a secondary battery can be detected, countermeasures such as lowering the charging voltage or the charging rate can be taken, and rapid degradation of the secondary battery can be suppressed by relaxing the charging conditions. However, at present, there is no technology that can detect a sign of rapid degradation in a secondary battery.

[0015] The inventors of the present application have analyzed in detail 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 the charge capacity), and found that the peak position of the peak appearing in the Q-dependence of dV / dQ may shift to the low-capacity side as the number of cycles increases. The low-capacity shift of the peak position is considered to be due to the non-uniformity of the reaction inside the battery and the decrease in the reaction area of the positive and negative electrodes. The inventors of the present application have found that a low-capacity shift of the peak position occurs 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 detection 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 prediction 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 detection 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 enables the acquisition of reliable dV / dQ data. According to the predictive detection 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 reaction of the battery in actual use and enables 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 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 falls 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 dV / dQ Q dependence is identified. The predictive detection device described in (10) above can use the identified peak position 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 appearing in the characteristic curve showing the charge capacity dependence of dV / dQ, when the energy storage element is charged from a discharged state, based on the acquired measured values, based on the derived results, based on the identified peak position of the peak appearing in the characteristic curve showing the charge capacity dependence of dV / dQ, and 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 be described in detail below with reference to the drawings illustrating its embodiments. (Embodiment 1) Figure 1 is an explanatory diagram illustrating the outline of the processes performed by the predictive maintenance device according to Embodiment 1. The predictive maintenance device 1 according to Embodiment 1 is a device for detecting signs of rapid deterioration in the energy storage element 20 mounted on the power supply 2. The power supply 2 is installed in, for example, an electric vehicle (EV), a hybrid electric vehicle (HEV), or a plug-in hybrid electric vehicle (PHEV). 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 supply. 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 modules, or they may be mounted on the power supply 2 in the form of banks or domains.

[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 degradation 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 degradation in the energy storage element 20 based on the peak position of the peak appearing in the Q dependence of the derived dV / dQ.

[0044] In this specification, rapid degradation is distinguished from normal degradation in terms of degradation rate (the rate at which performance deteriorates per unit period). Normal degradation refers to a decrease in the performance of the energy storage element 20 at a rate expected by empirical rules such as the square root rule. In contrast, rapid degradation refers to a decrease in the performance of the energy storage element 20 at a rate faster than the rate expected by empirical rules such as the square root rule.

[0045] 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.

[0046] 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 the positive current collector 25 and the negative current collector 26, respectively. The battery case 22 is made of a lightweight metal material with high thermal conductivity, such as aluminum.

[0047] 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 sheets. 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.

[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 (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.

[0049] 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.

[0050] 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.

[0051] 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.

[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 components 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 source 2 (or a vehicle or power storage facility equipped with the power source 2). As the communication module, a communication module that performs wireless communication using known mobile communication standards such as 3G, 4G, 5G, or a wireless LAN method such as WiFi (registered trademark) is used. Alternatively, the communication module may be a communication module for short-range wireless communication such as Bluetooth (registered trademark) or ZigBee (registered trademark), or a communication module compliant with a wired communication standard such as Ethernet (registered trademark). The communication unit 13 communicates with the power source 20 (or a vehicle or power storage facility equipped with the power source 2) and acquires measurement values necessary for precursor detection. The communication unit 13 outputs the acquired measurement values to the control unit 11.

[0061] The operation unit 14 includes an input device such as a keyboard or a mouse, and receives user operations. The display unit 15 includes a display device such as a liquid crystal display device, and displays information to be notified to the user. Alternatively, the precursor detection device 1 may be configured to receive necessary operations through an external computer and transmit information to be notified to the user to the external computer. In this case, the precursor detection device 1 may not include the operation unit 114 and the display unit 115.

[0062] Hereinafter, an evaluation test conducted by the inventors of the present application will be described. FIG. 5 is a graph showing the transition of the capacity retention rate when a charge-discharge cycle test is performed. In the graph of FIG. 5, the horizontal axis represents the number of cycles, and the vertical axis represents the capacity retention rate (%). The graph of FIG. 5 shows the transition of the capacity retention rate when the charge-discharge cycle test is performed by adjusting the temperature of the power storage element 20 to T1, T2, T3 (T1 < T2 < T3). In the graphs of temperature T1 and temperature T3, the performance of the power storage element 20 (in this example, the capacity retention rate) decreases generally proportionally to the number of cycles, showing the behavior of normal deterioration. On the other hand, in the graph of temperature T2, a rapid performance decline starts when the number of cycles exceeds Na, showing the behavior of rapid deterioration.

[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 about whether or not rapid degradation occurred in the energy storage element 20 can be obtained from the plotted graph. 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 proportional proportion to the number of cycles. In other words, although the graph shown in Figure 5 confirms that rapid degradation actually occurred and after some time has passed, no information indicating a precursor to rapid degradation can be obtained at the time before rapid degradation occurs.

[0064] The inventors of this application 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 hexagonal carbon lattices (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, 4th stage, 3rd stage, 2nd stage, and 1st stage. The 1st 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 difficult-to-obtain negative electrode potential E, 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, on 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 desorbed, or when Li crystallizes (dendriticizes) on 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 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 (e.g., 0.02CA) to equalize the discharge state of the negative electrode 212, and then charged at a high rate above the second set value (e.g., 1CA), 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 0.02CA, and then charged at a high rate such as 1CA. 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] The first peak appears in both graphs of FIGS. 7 and 8, but the second peak does not appear. As shown in FIG. 7, in the charge-discharge cycle test at temperature T1, even if the cycle numbers are increased in the order of N1, N2, N3, N4, the peak position of the first peak hardly changes. On the other hand, as shown in FIG. 8, in the charge-discharge cycle test at temperature T2, when the cycle numbers are increased in the order of N1, N2, N3, N4, the peak position of the first peak shifts to the low-capacity side.

[0072] The peak position of the first peak is specified by fitting the first peak using an appropriate function such as a Gaussian function. For example, the least squares method is used for fitting. In order to specify the peak position accurately, fitting with a Gaussian function or the like may be performed after removing the background from dV / dQ. The background is represented by, for example, a linear function passing through two points at both ends of the peak. From the function obtained by fitting the first peak, not only the peak position but also information on the area intensity and the full width at half maximum (FWHM or half-width at half maximum) of the peak can be obtained.

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

[0074] Typically, capacity degradation in lithium-ion batteries is mainly due to lithium trapping in the negative electrode coating. This type of 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 cycle number 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 cases where only the first peak appears, but the Q dependence of dV / dQ may also include a second peak in addition to the first. 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] FIG. 10 is a graph showing the change in the area intensity of the first peak with the number of cycles. The horizontal axis represents the number of cycles, and the vertical axis represents the area intensity (V). The graph in FIG. 10 shows the change in the area intensity (peak area) when charge-discharge cycle tests are performed at temperatures T1, T2, T3 (T1 < T2 < T3). The graph in FIG. 10 shows that the area intensity tends to decrease with an increase in the number of cycles, but the rate of decrease in the area intensity from cycle Nb is the largest in the cycle at temperature T2 where rapid deterioration occurred.

[0079] FIG. 11 is a graph showing the change in the full width at half maximum of the first peak with 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 FIG. 11 shows the change in the full width at half maximum when charge-discharge cycle tests are performed at temperatures T1, T2, T3 (T1 < T2 < T3). The graph in FIG. 11 shows that the full width at half maximum tends to decrease with an increase in the number of cycles, but the rate of decrease in the full width at half maximum from cycle Nb is the largest in the cycle at temperature T2 where rapid deterioration occurred. Although FIG. 11 shows the change in the full width at half maximum, it is needless to say that the same information can also be obtained from the change in the half width at half maximum.

[0080] Therefore, it is shown that the area intensity and the full width at half maximum of the peak appearing in the Q-dependence of dV / dQ can be indicators for detecting signs of rapid deterioration in the energy storage element 20. The sign detection device 1 may determine whether there is a sign of rapid deterioration 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 the full width at half maximum in addition to the peak position of the peak appearing in the derived Q-dependence of dV / dQ. For example, the sign detection device 1 predicts the number of cycles Nx at which rapid deterioration starts from the peak position of the peak appearing in the Q-dependence of dV / dQ, calculates the rate of decrease in the area intensity or the full width at half maximum from the predicted number of cycles Nx, and determines whether a sign of rapid deterioration has been detected based on whether the rate of decrease exceeds a threshold value.

[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 setpoint (e.g., 0.02CA), and then charged at a high rate above a second setpoint (e.g., 1CA). 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 measurement 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 to step S101 and repeats the process 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 communicative 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 (registered trademark). Alternatively, communication conforming to wired communication standards such as Ethernet (registered trademark) 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 sends 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 degradation 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 to step S201 and repeats the process 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 13 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 13 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. [Explanation of Symbols]

[0106] 1. Predictive detection device 2 Power supply 11 Control Unit 12 Storage section 13 Communications Department 14 Control section 15 Communications Department 20 Energy storage elements 211 Positive electrode 212 Negative electrode PG Predictive Detection Program RM recording media

Claims

1. When the energy storage element is charged from its discharged state, the measured values ​​of the voltage and charge capacity of the energy storage element are obtained. Based on the acquired measurement values, the dependence of dV / dQ on the charging capacity is derived when dV / dQ is defined as the rate at which the voltage changes in response to the change in the charging capacity. Based on the derived results, the peak position of the peak appearing in the characteristic curve showing the charge capacity dependence of dV / dQ is identified. Based on the identified peak position, the system detects signs of rapid deterioration of the energy storage element. A predictive detection method that uses a computer to perform the processing.

2. The area intensity of the aforementioned peak is calculated, Based on the aforementioned peak position and the calculated area intensity, the system detects signs of rapid deterioration of the energy storage element. The predictive detection method according to claim 1, wherein the processing is performed by the computer.

3. The full width at half maximum of the aforementioned peak is calculated, Based on the aforementioned peak position and the calculated full width at half maximum, the system detects signs of rapid deterioration of the energy storage element. The predictive detection method according to claim 1, wherein the processing is performed by the computer.

4. The aforementioned peak is a peak that appears in response to changes in the stage structure of the negative electrode active material. The predictive behavior detection method according to claim 1.

5. Identify the peak position of the peak corresponding to the potential change between the potential flat region associated with the two-phase coexistence reaction in the high-stage and fourth-stage, and the potential flat region associated with the two-phase coexistence reaction in the third-stage and second-stage. The predictive detection method according to claim 4, wherein the processing is performed by the computer.

6. The voltage and charging capacity are measured 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 after deep discharge at a low rate below a first setting value. The predictive detection method according to claim 1, wherein the processing is performed by the computer.

7. If the charging capacity corresponding to the identified peak position is below the first threshold, it is determined that a sign of rapid degradation has been detected. The predictive detection method according to claim 1, wherein the processing is performed by the computer.

8. If it is determined that signs of rapid deterioration have been detected, a control command is output to the charge control device that controls the charging of the energy storage element to relax the charging conditions. The predictive detection method according to claim 7, wherein the processing is performed by the computer.

9. 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 is output to the charging control device. The predictive detection method according to claim 8, wherein the processing is performed by the computer.

10. It comprises at least one arithmetic unit, The aforementioned arithmetic unit, When the energy storage element is charged from its discharged state, the measured values ​​of the voltage and charge capacity of the energy storage element are obtained. Based on the acquired measurement values, the dependence of dV / dQ on the charging capacity is derived when dV / dQ is defined as the rate at which the voltage changes in response to the change in the charging capacity. Based on the derived results, the peak position of the peak appearing in the characteristic curve showing the charge capacity dependence of dV / dQ is identified. Based on the identified peak position, the system detects signs of rapid deterioration of the energy storage element. Predictive detection device.

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

Images