Electrodeposition reaction detection method, detection device, and computer program

Abstract

The present invention causes a computer to execute processing for acquiring time-series data of a charging current when a power storage element is charged while the charging current is reduced so as to maintain a set voltage, calculating a value pertaining to the amount of change in the charging current on the basis of the acquired time-series data, and detecting the occurrence of an electrodeposition reaction in the power storage element on the basis of an increase or decrease in the value at a specific current value accompanying an increase in the number of charge / discharge cycles.

Description

Method for Detecting Electrolysis Reaction, Detection Device, and Computer Program

[0001] The present disclosure relates to a method for detecting an electrolysis reaction, a 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 for a starter at the time of engine startup and a power supply 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 charging state.

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

[0005] However, the technique disclosed in Patent Document 1 cannot detect an electrolysis reaction in a power storage element.

[0006] An object of the present disclosure is to provide a method for detecting an electrolysis reaction, a detection device, and a computer program capable of detecting the occurrence of an electrolysis reaction.

[0007] The method for detecting an electrolysis reaction in the present disclosure acquires time-series data of the charging current when charging a power storage element while decreasing the charging current so as to maintain a set voltage, calculates a value related to the change amount of the charging current based on the acquired time-series data, and based on an increase or decrease of the value at a specific current value as the number of charge-discharge cycles increases, causes a computer to execute a process of detecting the occurrence of an electrolysis reaction in the power storage element.

[0008] According to the above aspect, the occurrence of an electrolysis reaction can be detected.

[0009] This is an explanatory diagram illustrating the outline of the processing performed by the detection device according to Embodiment 1. This is an external perspective view showing an example of the configuration of an energy storage element. This is a schematic diagram of the wound electrode body provided by the energy storage element. This is a block diagram illustrating the internal configuration of the detection device. This is a graph showing the time change of the C rate. This is a graph showing the time change of dI / dt. This is a graph showing the change of dI / dt with respect to the current value. This is a graph showing the change of dI / dQ with respect to the current value. This is a graph showing the cycle change of the value of dI / dt at a specific current value. This is a flowchart illustrating the procedure of the processing performed by the detection device according to Embodiment 1. This is an explanatory diagram illustrating an example of the configuration of a charge control system according to Embodiment 2. This is a flowchart illustrating the procedure of the processing performed by the detection device according to Embodiment 2.

[0010] (1) The electrodeposition reaction detection method of the present disclosure acquires time-series data of the charging current when charging an energy storage element while reducing the charging current to maintain a set voltage, calculates a value related to the amount of change in the charging current based on the acquired time-series data, and performs a process by computer to detect the occurrence of an electrodeposition reaction in the energy storage element based on the increase or decrease of the value at a specific current value with an increase in the number of charge-discharge cycles.

[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] Energy storage elements installed in power supplies degrade with repeated charging and discharging. It is empirically known that the capacity degradation of an energy storage element 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 energy storage elements. However, if charging and discharging are performed under inappropriate conditions in the power supply, the reaction inside the energy storage element may become non-uniform, and deposition and dissolution reactions of elemental metals (electrodeposition) may occur. For example, if alkali metal ions (such as lithium ions or sodium ions) are used as charge carriers in the energy storage element, fluctuations in the concentration distribution and electric field distribution near the negative electrode may cause alkali metals (such as lithium or sodium) to precipitate in a dendritic pattern. These dendritic crystals are also called dendrites. If dendrites deposited on the negative electrode surface grow and come into contact with the positive electrode, an internal short circuit will occur. It is difficult to predict the degradation of energy storage elements due to such dendrite growth using empirical rules such as the square root rule.

[0013] The inventors of this application have investigated the behavior of the charging current measured during CCCV charging and have found that by examining the increase or decrease in the value related to the change in the charging current, it is possible to detect the occurrence of an electrodeposition reaction even in cases where electrodeposition occurs non-uniformly in the planar direction.

[0014] In the detection method described in (1) above, a value related to the change in charging current is calculated from the time-series data of the charging current obtained when the energy storage element is charged while reducing the charging current to maintain the set voltage, and the occurrence of an electrodeposition reaction is detected based on the calculated value. Therefore, in the detection method described in (1) above, the occurrence of an electrodeposition reaction can be detected using a value related to the change in charging current obtained by a non-destructive and simple method.

[0015] (2) In the detection method described in (1) above, the computer may perform a process to calculate the amount of change in the charging current per unit time as the value.

[0016] According to the detection method described in (2) above, the occurrence of an electrodeposition reaction can be detected based on the change in charging current per unit time.

[0017] (3) In the detection method described in (1) above, the computer may perform a process to calculate the amount of change in the charging current per unit capacity as the value.

[0018] According to the detection method described in (3) above, the occurrence of an electrodeposition reaction can be detected based on the change in charging current per unit capacity.

[0019] (4) In the detection method described in any one of (1) to (3) above, the computer may perform a process to determine that an electrodeposition reaction has occurred if the value is greater than a threshold.

[0020] According to the detection method described in (4) above, if the calculated value exceeds the threshold, it can be determined that an electrodeposition reaction has occurred.

[0021] (5) In the detection method described in any one of (1) to (3) above, the computer may perform a process to determine that an electrodeposition reaction has occurred if the difference between the value at the time of the first charge-discharge cycle and the value at the time of the second charge-discharge cycle is greater than a threshold.

[0022] According to the detection method described in (5) above, if the calculated value increases sharply relative to the number of cycles, it can be determined that an electrodeposition reaction has occurred.

[0023] (6) In the detection method described in any one of (1) to (5) above, if it is determined that an electrodeposition reaction has occurred in the energy storage element, the computer may execute a process to output a control command to the charge control device that controls the charging of the energy storage element, thereby relaxing the charging conditions.

[0024] According to the detection method described in (6) above, if it is determined that an electrodeposition reaction has occurred, a control command is output to relax the charging conditions, thereby suppressing the progression of electrodeposition and the occurrence of internal short circuits.

[0025] (7) In the detection method described in any one of (1) to (5) above, if it is determined that an electrodeposition reaction has occurred in the energy storage element, the computer may execute a process to output a control command to the charge control device that controls the charging of the energy storage element to stop charging.

[0026] According to the detection method described in (7) above, if it is determined that an electrodeposition reaction has occurred, a control command to stop charging is output, thereby suppressing the progression of electrodeposition and the occurrence of internal short circuits.

[0027] (8) The detection device of the present disclosure comprises at least one calculation unit, the calculation unit acquires time-series data of the charging current when the energy storage element is charged while reducing the charging current to maintain a set voltage, calculates a value relating to the amount of change in the charging current based on the acquired time-series data, and detects the occurrence of an electrodeposition reaction in the energy storage element based on the increase or decrease of the value at a specific current value with an increase in the number of charge-discharge cycles.

[0028] In the detection device described in (8) above, a value related to the change in charging current is calculated from the time-series data of the charging current obtained when the energy storage element is charged while reducing the charging current to maintain the set voltage, and the occurrence of an electrodeposition reaction is detected based on the calculated value. Therefore, the detection device described in (8) above can detect the occurrence of an electrodeposition reaction using a value related to the change in charging current obtained by a non-destructive and simple method.

[0029] (9) The computer program of the present disclosure is a computer program that causes a computer to perform a process of detecting the occurrence of an electrodeposition reaction in the energy storage element based on an increase or decrease in the value at a specific current value that accompanies an increase in the number of charge-discharge cycles, by acquiring time-series data of the charging current when the energy storage element is charged while the charging current is reduced in order to maintain a set voltage, calculating a value relating to the amount of change in the charging current based on the acquired time-series data, and detecting the occurrence of an electrodeposition reaction in the energy storage element based on an increase or decrease in the value at a specific current value that accompanies an increase in the number of charge-discharge cycles.

[0030] In the computer program described in (9) above, a value related to the change in charging current is calculated from the time-series data of the charging current obtained when the energy storage element is charged while decreasing the charging current to maintain the set voltage, and the occurrence of an electrodeposition reaction is detected based on the calculated value. Therefore, the computer program described in (9) above can detect the occurrence of an electrodeposition reaction using a value related to the change in charging current obtained by a non-destructive and simple method.

[0031] The present invention will be described in detail below based on the drawings illustrating its embodiments. (Embodiment 1) Figure 1 is an explanatory diagram illustrating the outline of the process performed by the detection device according to Embodiment 1. The detection device 1 according to Embodiment 1 is a device for detecting the occurrence of an electrodeposition reaction in an energy storage element 20 mounted on a power supply 2.

[0032] Power source 2 is a power source installed in vehicles such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs). Power source 2 stores power supplied from an external source in an 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.

[0033] 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.

[0034] Multiple energy storage elements 20 are mounted on the power supply 2. The multiple energy storage elements 20 may be mounted on the power supply 2 in the form of a module, or they may be mounted on the power supply 2 in the form of a bank or domain.

[0035] The energy storage element 20 mounted on power supply 2 deteriorates due to repeated charging and discharging. It is empirically known that the capacity degradation of the energy storage element 20 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 the energy storage element 20. However, if charging and discharging are performed under inappropriate conditions in power supply 2, the reaction inside the energy storage element 20 may become non-uniform, and deposition and dissolution reactions (electrodeposition reactions) of elemental metals may occur. For example, if alkali metal ions (such as lithium ions or sodium ions) are used as charge carriers in the energy storage element 20, fluctuations in the concentration distribution and electric field distribution near the negative electrode may cause alkali metals (such as lithium or sodium) to precipitate in a dendritic pattern. These dendritic crystals are also called dendrites. If dendrites deposited on the surface of the negative electrode grow and come into contact with the positive electrode, an internal short circuit will occur. It is difficult to predict the degradation of the energy storage element 20 due to such dendrite growth using empirical rules such as the square root rule.

[0036] Therefore, in this embodiment, a method for detecting the occurrence of an electrodeposition reaction in the energy storage element 20 is proposed. As will be described in detail later, the detection device 1 acquires time-series data of the charging current when the energy storage element 20 is charged while decreasing the charging current to maintain a set voltage, and calculates a value related to the change in the charging current based on the acquired time-series data. For example, if the change in charging current at a certain current value is denoted as dI, the detection device 1 calculates the change in charging current per unit time, dI / dt. Alternatively, the detection device 1 may calculate the change in charging current per unit capacity, dI / dQ. The detection device 1 detects the occurrence of an electrodeposition reaction in the energy storage element 20 based on the increase or decrease of the above value (dI / dt or dI / dQ) accompanying the increase in the number of charge-discharge cycles.

[0037] Figure 2 is an external perspective view showing an example of the configuration of the energy storage element 20, and Figure 3 is a schematic diagram of the wound electrode body 21 provided in the energy storage element 20. The energy storage element 20 is, for example, 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.

[0038] The top surface of the battery case 22 is provided with a positive terminal 23 and a negative terminal 24 for external connection. The positive terminal 23 and the negative terminal 24 are electrically connected to a positive current collector 25 and a negative current collector 26, respectively. The battery case 22 is made of a lightweight metal material with high thermal conductivity, such as aluminum.

[0039] The wound electrode body 21 is constructed by overlapping a sheet-shaped positive electrode 211, on which a positive electrode active material layer 211A is formed, and a sheet-shaped negative electrode 212, on which a negative electrode active material layer 212A is formed, via two sheet-shaped separators 213, and winding them together. The positive electrode 211 and the negative electrode 212 are arranged offset from each other in the width direction of the sheet. At one end of the positive electrode 211 in the width direction, there is a region where the positive electrode active material layer 211A is not formed, and a positive electrode current collector 25 is joined to this region. For example, aluminum foil is used for the positive electrode current collector 25. Similarly, at the other end of the negative electrode 212 in the width direction, there is a region where the negative electrode active material layer 212A is not formed, and a negative electrode current collector 26 is joined to this region. For example, copper foil is used for the negative electrode current collector 26.

[0040] 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.

[0041] 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.

[0042] 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 include a heat-resistant layer.

[0043] 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.

[0044] In FIGS. 2 and 3, as an example of the power storage element 20, a rectangular lithium-ion battery including a wound electrode body 21 has been described. Alternatively, the power storage element 20 may be a lithium-ion battery including a laminated electrode body, or may be a cylindrical lithium-ion battery, a laminated lithium-ion battery, etc.

[0045] Figure 4 is a block diagram showing the internal configuration of the detection device 1. The detection device 1 is a dedicated or general-purpose computer for detecting the occurrence of an electrodeposition reaction in the energy storage element 20. As shown in Figure 1, the detection device 1 is installed outside the power supply 2 and detects the occurrence of the electrodeposition reaction in the energy storage element 20 from an external location. For example, the detection device 1 may be installed in a remote location sufficiently far from the power supply 2 to detect the occurrence of the electrodeposition reaction remotely, or it may be installed within a range where wired communication is possible to detect the occurrence of the electrodeposition reaction on-site. Alternatively, the detection device 1 may be installed on the power supply 2 (or the vehicle or energy storage equipment on which the power supply 2 is installed) to detect the occurrence of the electrodeposition reaction in the energy storage element 20.

[0046] The detection device 1 includes a control unit 11, a storage unit 12, a communication unit 13, an operation unit 14, a display unit 15, and the like. The control unit 11 is, for example, an arithmetic circuit 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 the function of detecting the occurrence of an electrodeposition reaction in the energy storage element 20.

[0047] 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.

[0048] The storage unit 12 includes a storage device such as a flash memory or a hard disk. Various computer programs and data are stored in the storage unit 12. The computer program (program product) stored in the storage unit 12 includes a detection program PG for detecting the occurrence of an electrolysis reaction based on the time-series data of the charging current. The data stored in the storage unit 12 includes various parameters used in the detection program PG and data input through the communication unit 13 and the like.

[0049] The detection program PG may be a single computer program or may be composed of a plurality of computer programs. The detection program PG may be executed by a single computer or may be executed in cooperation by a plurality of computers. Furthermore, the detection program PG may partially use an existing library.

[0050] The computer program including the detection program PG is provided by a non-temporary recording medium RM on which the computer program is recordable in a readable manner. The recording medium RM is a portable memory such as a CD-ROM, a USB memory, or an SD (Secure Digital) card. The control unit 11 reads a desired computer program from the recording medium RM using a reading device not shown in the figure and stores the read computer program in the storage unit 12. Alternatively, the computer program including the detection program PG may be provided by communication.

[0051] 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 detecting the occurrence of the electrodeposition reaction. The communication unit 13 outputs the acquired measurement values ​​to the control unit 11.

[0052] 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 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 detection device 1 does not need to be equipped with an operation unit 14 and a display unit 15.

[0053] The verification tests conducted by the inventors of the present invention are described below. The inventors conducted a cycle degradation test under temperature conditions of 25°C and a charge / discharge rate of 1C, varying the State of Charge (SOC) from 0% to 100%. Upon disassembly and inspection at 2000 cycles, non-uniform deposition of lithium metal in the planar direction was confirmed. During the cycle degradation test, capacity verification tests at 25°C were conducted as appropriate. In the capacity verification test, the energy storage element 20 was charged from SOC 0% to 100% using the CCCV (Constant Current, Constant Voltage) method at a charge rate of 1C, and then discharged at a discharge rate of 1 / 3C. In the capacity verification test, the charging current I and capacity value (charged amount Q) to the energy storage element 20 were measured in a time series.

[0054] Figure 5 is a graph showing the time change of the C rate, and Figure 6 is a graph showing the time change of dI / dt. The graphs in Figures 5 and 6 show the time changes of the current value (C rate) and dI / dt when the energy storage element 20 is charged using the CCCV method. In the graph in Figure 5, the vertical axis is the C rate and the horizontal axis is time. In the graph in Figure 6, the vertical axis is dI / dt and the horizontal axis is time. In CCCV charging, the energy storage element 20 is charged with a constant current (1C in this embodiment), and when the voltage of the energy storage element 20 reaches a set voltage, the charging current is reduced while charging the energy storage element 20 to maintain that set voltage. The graphs in Figures 5 and 6 show the behavior of the current value (C rate) and dI / dt when transitioning from CC charging (constant current charging) to CV charging (constant voltage charging) in CCCV charging.

[0055] As an example, the conventional method disclosed in "Koseoglou, Markos, et al. "Lithium plating detection using differential charging current analysis in lithium-ion batteries." Journal of Energy Storage 54 (2022): 105345" reveals that when lithium metal deposition occurs inside a lithium-ion battery, the behavior associated with this lithium metal deposition (LP: lithium plating) is reflected in the time-series data of the charging current and dI / dt. Specifically, it shows that when lithium metal deposition occurs, the time-series data of the charging current shows a shift from a decrease to an increase, and the time-series data of dI / dt shows a peak.

[0056] However, according to the inventors' verification results, as shown in Figure 5, the charging current decreases monotonically over time, and no behavior of shifting from a decrease to an increase can be observed. Furthermore, as shown in Figure 6, dI / dt increases monotonically over time, and no peak can be found.

[0057] This suggests that if electrodeposition occurs non-uniformly in the planar direction, the behavior of the electrodeposition itself may be masked by the overall behavior of the battery and therefore undetectable.

[0058] The inventors of this application have investigated the behavior of the above-mentioned current value (C rate) and dI / dt and have found that the occurrence of an electrodeposition reaction can be detected by examining the increase or decrease in the amount of change in the charging current per unit time at a specific current value, or the amount of change in the charging current per unit capacity at a specific current value.

[0059] Figure 7 is a graph showing the change in dI / dt with respect to the current value, and Figure 8 is a graph showing the change in dI / dQ with respect to the current value. In the graph of Figure 7, the vertical axis represents dI / dt, and the horizontal axis represents the C rate normalized by the rated capacity instead of the charging current value. In the graph of Figure 8, the vertical axis represents dI / dQ, and the horizontal axis represents the C rate normalized by the rated capacity instead of the charging current value, similar to Figure 7. The value of dI / dt for each C rate can be calculated from time-series data of current values ​​as shown in Figure 5. Also, since capacity Q can be calculated as the integrated value of current I, the value of dI / dQ for each C rate can similarly be calculated from time-series data of current values.

[0060] As shown in Figures 7 and 8, an increase in the values ​​of dI / dt and dI / dQ is observed, especially at high rates. Figure 9 is a graph showing the cycle change of the dI / dt value at a specific current value. In the graph of Figure 9, the vertical axis represents the dI / dt value at 0.9C, and the horizontal axis represents the number of cycles. As shown in the graph of Figure 9, it can be seen that the dI / dt value rises sharply from before 2000 cycles, when non-uniform deposition of lithium metal in the planar direction was confirmed. Therefore, by setting an appropriate threshold for the dI / dt value, the occurrence of the electrodeposition reaction can be detected. The threshold may be set to a relatively low value (e.g., TH1) to detect signs of electrodeposition, or to a relatively high value (e.g., TH2) to detect that electrodeposition has occurred. Figure 9 shows the cycle change of the dI / dt value at a specific current value, but a similar trend is observed in the cycle change of the dI / dQ value at a specific current value, so by setting an appropriate threshold for the dI / dQ value, the occurrence of the electrodeposition reaction can be detected.

[0061] The following describes the processes performed by the detection device 1. Figure 10 is a flowchart illustrating the procedure for the processes performed by the detection device 1 according to Embodiment 1. The detection device 1 reads the detection program PG from the storage unit 12 at an appropriate timing after the power supply 2 (energy storage element 20) has started operation and executes it, and performs the following processes based on the detection program PG. For example, if the power supply 2 is for stationary use, the process may be executed at periodic intervals, or if the power supply 2 is for vehicle use, the process may be executed at a timing instructed by the user, such as during vehicle inspection.

[0062] The control unit 11 of the detection device 1 instructs the charge control device of the power supply 2 to perform CCCV charging via the communication unit 13 (step S101). Upon receiving the instruction to perform CCCV charging, the charge control device charges the energy storage element 20 with a constant current (e.g., 1C) until the set voltage is reached. Once the voltage of the energy storage element 20 reaches the set voltage, it continues to charge the energy storage element 20 while reducing the charging current to maintain the set voltage. The power supply 2 measures the charging current I during charging in a time series and outputs the time series data to the detection device 1. A sensor (current sensor) necessary for measuring the charging current of the energy storage element 20 is provided on at least one of the energy storage elements 20 provided by the power supply 2.

[0063] The control unit 11 acquires time-series data of the charging current I in the energy storage element 20 from the power supply 2 (step S102). The control unit 11 may acquire the measured value of the current from the power supply 2 in real time, or it may acquire it from an external device after it has been recorded in an external device. The acquired time-series data of the charging current I is stored in the storage unit 12.

[0064] The control unit 11 calculates a value related to the change in charging current at a specific current value based on the acquired time-series data of charging current (step S103). The control unit 11 calculates the change in charging current per unit time (i.e., dI / dt) as the value related to the change in charging current. Alternatively, the control unit 11 may calculate the change in charging current per unit capacity (i.e., dI / dQ) as the value related to the change in charging current. The current value used to calculate the change in charging current is set to an appropriate value such as 0.9C.

[0065] The control unit 11 detects the occurrence of an electrodeposition reaction based on the value calculated in step S103 (step S104). The control unit 11 compares the value calculated in step S103 with a pre-set threshold value. If the calculated value exceeds the threshold value, it determines that an electrodeposition reaction has occurred; otherwise, it determines that no electrodeposition reaction has occurred. The threshold value may be a pre-set threshold value (=TH1) for detecting signs of electrodeposition, or a pre-set threshold value (=TH2) for detecting that electrodeposition has occurred.

[0066] Alternatively, the control unit 11 may calculate the difference between the value calculated at the time of the first charge-discharge cycle (for example, the previous value) and the value calculated at the time of the second charge-discharge cycle (for example, the current value). If the absolute value of the calculated difference exceeds a threshold, it may determine that the electrodeposition reaction has occurred. If it does not exceed the threshold, it may determine that the electrodeposition reaction has not occurred.

[0067] The control unit 11 outputs the detection result from step S104 (step S105). Specifically, the control unit 11 displays the detection result on the display unit 15. Alternatively, the control unit 11 may notify an external terminal of the detection result via the communication unit 13.

[0068] As described above, in Embodiment 1, a value related to the change in charging current is calculated based on time-series data of the charging current, and the occurrence of an electrodeposition reaction is detected by comparing the calculated value with a threshold value. Therefore, in Embodiment 1, the occurrence of an electrodeposition reaction can be detected using a value related to the change in charging current, which can be obtained by a non-destructive and simple method without disassembling the energy storage element 20. Even in cases where electrodeposition occurs non-uniformly in the planar direction and the behavior of the electrodeposition is hidden by the behavior of the entire battery, Embodiment 1 can detect the occurrence of an electrodeposition reaction using the value related to the change in charging current as a clue.

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

[0070] Figure 11 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 detection device 1 and a power supply 2, as well as a charging control device 3. The detection device 1 and power supply 2 are the same as those described in Embodiment 1, so their description will be omitted.

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

[0072] The charging control device 3 is connected to the detection device 1 and the power supply 2 in a communication manner. Communication between the charging control device 3 and the 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).

[0073] The charging control device 3 acquires the measured value of the charging current measured with respect to the energy storage element 20 by communicating with the power supply 2. The charging control device 3 transmits the acquired measured value of the charging current to the detection device 1.

[0074] The detection device 1 acquires the measured value of the charging current measured with respect to the energy storage element 20 by communicating with the charging control device 3. Based on the acquired measured value of the charging current, the detection device 1 detects the occurrence of an electrodeposition reaction in the energy storage element 20. The detection method is the same as in Embodiment 1.

[0075] If the detection device 1 determines that an electrodeposition reaction is occurring in the energy storage element 20, it sends a control command to the charging control device 3 to relax the charging conditions. For example, the charging conditions can be relaxed by reducing at least one of the charging rate, charging current, and charging voltage.

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

[0077] The charging control device 3 can suppress internal short circuits caused by electrodeposition by performing charging control to the power supply 2 in response to control commands from the detection device 1.

[0078] Figure 12 is a flowchart illustrating the procedure performed by the detection device 1 according to Embodiment 2. If the power supply 2 is for stationary use, the detection device 1 performs the same procedure as in the flowchart of Figure 10 at periodic intervals, or if the power supply 2 is for vehicle use, at intervals instructed by the user, such as during vehicle inspections, to detect the electrodeposition reaction (steps S201 to S204).

[0079] The control unit 11 determines in step S204 whether an electrodeposition reaction was detected (step S205). If it determines that no electrodeposition reaction was detected (S205: NO), the control unit 11 terminates the process according to this flowchart.

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

[0081] As described above, in Embodiment 2, when an electrodeposition reaction is detected, a control command to relax the charging conditions is output to the charging control device, thereby suppressing internal short circuits associated with electrodeposition of the energy storage element 20.

[0082] 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.

[0083] 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.

[0084] 1. Detection device 2. Power supply 11. Control unit 12. Storage unit 13. Communication unit 14. Operation unit 15. Display unit 20. Energy storage element PG. Detection program RM. Recording medium

Claims

1. A method for detecting electrodeposition reactions, which involves acquiring time-series data of the charging current when charging an energy storage element while reducing the charging current to maintain a set voltage, calculating a value related to the change in the charging current based on the acquired time-series data, and using a computer to perform a process to detect the occurrence of an electrodeposition reaction in the energy storage element based on the increase or decrease of the value at a specific current value accompanying the increase in the number of charge-discharge cycles.

2. The detection method according to claim 1, wherein the computer performs a process to calculate the amount of change in the charging current per unit time as the value.

3. The detection method according to claim 1, wherein the computer performs a process to calculate the amount of change in the charging current per unit capacity as the value.

4. The detection method according to claim 1, wherein the computer performs a process to determine that an electrodeposition reaction has occurred if the value is greater than a threshold.

5. The detection method according to claim 1, wherein the computer performs a process to determine that an electrodeposition reaction has occurred if the difference between the value at the time of the first charge-discharge cycle and the value at the time of the second charge-discharge cycle is greater than a threshold.

6. The detection method according to claim 1, wherein, when it is determined that an electrodeposition reaction has occurred in the energy storage element, the computer executes a process to output a control command to a charge control device that controls the charging of the energy storage element, thereby easing the charging conditions.

7. The detection method according to claim 1, wherein, when it is determined that an electrodeposition reaction has occurred in the energy storage element, the computer executes a process to output a control command to a charge control device that controls the charging of the energy storage element to stop charging.

8. A detection device comprising at least one calculation unit, wherein the calculation unit acquires time-series data of the charging current when charging an energy storage element while decreasing the charging current to maintain a set voltage, calculates a value related to the amount of change in the charging current based on the acquired time-series data, and detects the occurrence of an electrodeposition reaction in the energy storage element based on the increase or decrease of the value at a specific current value accompanying the increase in the number of charge-discharge cycles.

9. A computer program that causes a computer to perform a process to detect the occurrence of an electrodeposition reaction in the energy storage element based on the increase or decrease of the value at a specific current value that accompanies the increase in the number of charge-discharge cycles.

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