Degradation suppression control system, degradation suppression control method, degradation suppression control program, and recording medium on which degradation suppression control program is recorded

Abstract

In a deterioration suppression control system, a data acquisition unit acquires battery data including a voltage and a current of a secondary battery. The deterioration estimation unit estimates, on the basis of battery data of the secondary battery, a reduction rate of a current remaining capacity of the positive electrode with respect to an initial remaining capacity of the positive electrode and a reduction rate of a current remaining capacity of the negative electrode with respect to an initial remaining capacity of the negative electrode. When the reduction rate of the remaining capacity of the positive electrode is greater than the reduction rate of the remaining capacity of the negative electrode, the charge / discharge control unit switches to charge / discharge control that preferentially suppresses degradation of the positive electrode. When the rate of decrease in the remaining capacity of the negative electrode is greater than the rate of decrease in the remaining capacity of the positive electrode, the charge / discharge control is switched to a charge / discharge control in which deterioration suppression of the negative electrode is preferentially performed.

Description

Technical Field

[0001] The present disclosure relates to a degradation suppression control system, a degradation suppression control method, and a degradation suppression control program for suppressing degradation of a secondary battery. Background Art

[0002] In recent years, lithium-ion batteries have been used for a variety of purposes. In order to suppress the degradation of lithium-ion batteries, a common method is to directly use the voltage, current, and temperature of the lithium-ion battery to switch the charge and discharge control method. In this regard, a method of estimating the internal state of the lithium-ion battery (more specifically, the degradation state of the positive and negative electrodes) to switch the charge and discharge control method is proposed (for example, refer to patent document 1). Patent document 1 proposes the following method: when the difference between the capacity of the positive electrode and the capacity of the negative electrode, or the difference between the discharge end potential of the positive electrode and the discharge end potential of the negative electrode is reversed to a negative value, the operating conditions of the secondary battery are changed.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2017-54692 Summary of the invention

[0006] In the design of secondary batteries, the positive and negative electrodes are usually added with residual capacity outside the range of battery capacity that is not used in actual charging and discharging. When a large amount of residual capacity is added, the control based on the difference between the capacity of the positive electrode and the capacity of the negative electrode, or the difference between the discharge terminal potential of the positive electrode and the discharge terminal potential of the negative electrode does not necessarily ensure the maximum battery capacity.

[0007] The present disclosure has been made in view of such circumstances, and an object of the present disclosure is to provide a technology capable of suppressing the deterioration of a secondary battery to the greatest extent possible.

[0008] In order to solve the above-mentioned problem, a degradation suppression control system of a certain embodiment of the present invention comprises: an acquisition unit, which acquires battery data including voltage and current of a secondary battery; an estimation unit, which estimates, based on the battery data of the secondary battery, a reduction rate of a current remaining capacity of the positive electrode relative to an initial remaining capacity of the positive electrode and a reduction rate of a current remaining capacity of the negative electrode relative to an initial remaining capacity of the negative electrode; and a charge and discharge control unit, which switches to charge and discharge control that prioritizes degradation suppression of the positive electrode when the reduction rate of the remaining capacity of the positive electrode is greater than the reduction rate of the remaining capacity of the negative electrode, and switches to charge and discharge control that prioritizes degradation suppression of the negative electrode when the reduction rate of the remaining capacity of the negative electrode is greater than the reduction rate of the remaining capacity of the positive electrode.

[0009] Furthermore, arbitrary combinations of the above-described constituent elements and modes in which expressions of the present disclosure are converted between devices, systems, methods, computer programs, recording media, and the like are also applicable as modes of the present disclosure.

[0010] According to the present disclosure, it is possible to suppress the degradation of the secondary battery to the greatest extent possible. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a diagram for explaining a secondary battery degradation suppression control system.

[0012] Figure 2 It is a diagram showing an example of a storage degradation characteristic map.

[0013] Figure 3A It is a diagram showing an example of a charge / discharge degradation characteristic map.

[0014] Figure 3B It is a diagram showing an example of a charge / discharge degradation characteristic map.

[0015] Figure 4 It is a diagram showing an example of a charge and discharge curve and a dV / dQ curve of a secondary battery, a positive electrode, and a negative electrode.

[0016] Figure 5 This is a diagram showing another example of the dV / dQ curve of the secondary battery.

[0017] Figure 6 This is a diagram showing an example of charge and discharge curves of a secondary battery, a positive electrode, and a negative electrode in an initial state of a certain secondary battery.

[0018] Figure 7 It is a diagram showing a contraction example of the charge and discharge curves of a secondary battery, a positive electrode, and a negative electrode.

[0019] Figure 8 1 is a flowchart showing the flow of a process of switching the charge and discharge control method by the degradation suppression control system according to the embodiment.

[0020] Fig. 9 1 is a flowchart showing an example of degradation suppression control during charging performed by the degradation suppression control system according to the embodiment. DETAILED DESCRIPTION

[0021] Figure 1It is a diagram for explaining a degradation suppression control system 10 for a secondary battery. The degradation suppression control system 10 is a system for analyzing the degradation state of a secondary battery 21 mounted on an electric vehicle 20 and performing optimal degradation suppression control of the secondary battery 21. The degradation suppression control system 10 may, for example, be constructed on a self-owned server set up in a self-owned facility or data center of an operator that provides a degradation analysis service for a secondary battery 21 mounted on an electric vehicle 20. In addition, the degradation suppression control system 10 may also be constructed on a cloud server utilized based on a cloud service. In addition, the degradation suppression control system 10 may also be constructed on a plurality of servers dispersedly disposed at a plurality of locations (data centers, self-owned facilities). The plurality of servers may also be any combination of a combination of a plurality of self-owned servers, a combination of a plurality of cloud servers, or a combination of a self-owned server and a cloud server.

[0022] In the present embodiment, as the electric vehicle 20 , an electric vehicle 20 used by a delivery company is assumed.

[0023] The secondary battery 21 mounted on the electric vehicle 20 supplies electric power to a driving motor (not shown). The secondary battery 21 is formed by connecting a plurality of cells or a plurality of parallel cell blocks in series.

[0024] Each parallel cell block is formed by connecting a plurality of cells in parallel.

[0025] As the cell, a lithium ion battery cell, a nickel metal hydride battery cell, a lead battery cell, etc. can be used. In the following, in this specification, an example of using a lithium ion battery cell (nominal voltage: 3.6V-3.7V) is assumed. The number of cells or parallel cell blocks connected in series is determined according to the voltage of the driving motor.

[0026] The voltage sensor 22 detects the voltage across both ends of the single cells or parallel single cell battery blocks (the voltage between the positive electrode and the negative electrode) respectively connected in series. A shunt resistor is connected in series with the multiple single cells connected in series or the multiple single cell battery blocks connected in parallel. The current sensor 23 detects the current flowing through the single cells or parallel single cell battery blocks connected in series based on the voltage across both ends of the shunt resistor. In addition, a Hall element can also be used instead of the shunt resistor. The temperature sensor 24 detects the temperature of the multiple single cells or parallel single cell battery blocks based on the divided voltage of the thermistor and the resistor provided in at least one of the multiple single cells or parallel single cell battery blocks.

[0027] The BMU (Battery Management Unit) and the ECU (Electronic Control Unit) jointly constitute the control unit 25. The BMU estimates the SOC (State Of Charge) by combining the OCV (Open Circuit Voltage) method with the current accumulation method. The OCV method is a method of estimating the SOC based on the measured OCV of each monomer and the SOC-OCV curve of the monomer. The current accumulation method is a method of estimating the SOC based on the OCV at the start of charge and discharge of each monomer and the cumulative value of the measured current. The current accumulation method accumulates the measurement error of the current as the charge and discharge time becomes longer. Therefore, it is preferred to use the SOC estimated by the OCV method to correct the SOC estimated by the current accumulation method.

[0028] The BMU samples the voltage, current, temperature, and SOC of multiple cells or multiple parallel cell blocks at regular intervals (e.g., every 10 seconds). The BMU sends the battery data including the voltage, current, temperature, and SOC of multiple cells or multiple parallel cell blocks to the ECU via the vehicle network. For example, CAN (Controller Area Network) and LIN (Local Interconnect Network) can be used as the vehicle network.

[0029] The communication unit 26 has a function of performing communication signal processing with the communication unit 33 of the charging station 30 and a function of performing wireless signal processing for connecting to the network 5. The communication unit 26 can access the network 5 using, for example, a mobile phone network (cellular network), a wireless LAN, V2I (Vehicle-to-Infrastructure), V2V (Vehicle-to-Vehicle), an ETC system (Electronic Toll Collection System), or DSRC (Dedicated Short Range Communications).

[0030] The network 5 is a general term for communication lines such as the Internet, dedicated lines, and VPN (Virtual Private Network), and its communication medium and protocol are not limited. As the communication medium, for example, a mobile phone network (cellular network), a wireless LAN, a wired LAN, an optical fiber network, an ADSL network, a CATV network, etc. can be used. As the communication protocol, for example, TCP (Transmission Control Protocol: Transmission Control Protocol) / IP (Internet Protocol: Internet Protocol), UDP (User Datagram Protocol: User Datagram Protocol) / IP, Ethernet (registered trademark), etc. can be used.

[0031] The ECU may send the sampled battery data to the degradation suppression control system 10 at any time, or may accumulate the sampled battery data in an internal memory and simultaneously send the sampled battery data in the memory to the degradation suppression control system 10 at a predetermined time. In addition, the ECU may send the sampled battery data in the memory to the degradation suppression control system 10 via the charging pile 30 when the electric vehicle 20 is connected to the charging pile 30 by a charging cable.

[0032] The electric vehicle 20 can be connected to the charging stand 30 by a charging cable, so that the secondary battery 21 in the electric vehicle 20 can be charged from the outside. The charging stand 30 is connected to the commercial power system 2 to charge the secondary battery 21 .

[0033] Generally speaking, in the case of normal charging, the battery is charged with AC, and in the case of fast charging, the battery is charged with DC. In the case of charging with AC (for example, single-phase 100V / 200V), the charging voltage or the charging current is controlled by the charger (not shown) in the electric vehicle 20. In the case of charging with DC, the charging voltage or the charging current is controlled by the power supply unit 31 of the charging pile 30. The power supply unit 31 includes a rectifier circuit, a filter, and a DC / DC converter. DC power is generated by full-wave rectifying the AC power supplied from the commercial power system 2 by the rectifier circuit and smoothing it by the filter. The DC / DC converter controls the voltage or current of the generated DC power.

[0034] As fast charging standards, for example, CHAdeMO (registered trademark), ChaoJi, GB / T, and Combo (Combined Charging System) can be used. In CHAdeMO2.0, the maximum output (specification) is specified as 1000V×400A=400kW. In CHAdeMO3.0, the maximum output (specification) is specified as 1500V×600A=900kW. In ChaoJi, the maximum output (specification) is specified as 1500V×600A=900kW. In GB / T, the maximum output (specification) is specified as 750V×250A=185kW. In Combo, the maximum output (specification) is specified as 900V×400A=350kW. In CHAdeMO, ChaoJi, and GB / T, CAN is used as the communication method. In Combo, PLC (Power Line Communication) is used as the communication method.

[0035] In the charging cable using the CAN method, in addition to the power line, a communication line is also included. When the electric vehicle 20 is connected to the charging pile 30 through the charging cable, the control unit 25 of the electric vehicle 20 establishes a communication channel with the control unit 32 of the charging pile 30. In addition, in the charging cable using the PLC method, the communication signal is superimposed on the power line to be transmitted.

[0036] The communication unit 33 of the charging station 30 has a function of performing communication signal processing with the communication unit 26 of the electric vehicle 20 and a function of performing signal processing for connecting to the network 5. The communication unit 33 can access the network 5 using, for example, a wired LAN, a wireless LAN, or a mobile phone network (cellular network).

[0037] The degradation suppression control system 10 includes a control unit 11, a storage unit 12, and a communication unit 13. The communication unit 13 is a communication interface (for example, NIC: Network Interface Card) for connecting to the network 5 by wire or wirelessly.

[0038] The control unit 11 includes a data acquisition unit 111 , a degradation estimation unit 112 , and a charge and discharge control unit 113 .

[0039] The functions of the control unit 11 can be realized by the collaboration of hardware resources and software resources, or only by hardware resources. As hardware resources, CPU, ROM, RAM, GPU (Graphics Processing Unit), ASIC (Application Specific Integrated Circuit), FPGA (Field Programmable Gate Array), and other LSI can be used. As software resources, programs such as operating systems and application programs can be used. The program is pre-recorded in the memory of the storage unit 12 here, but it can also be provided through an electrical communication line such as the Internet, or recorded on a (non-transitory) recording medium such as a memory card.

[0040] The storage unit 12 includes a non-volatile recording medium such as an HDD or an SSD, and stores various data. The storage unit 12 includes a battery data storage unit 121 and a degradation characteristic storage unit 122. The battery data storage unit 121 accumulates the battery data acquired by the data acquisition unit 111 from the electric vehicle 20 or the charging station 30.

[0041] The degradation characteristic storage unit 122 stores the storage degradation characteristics, charge degradation characteristics, and discharge degradation characteristics of the positive electrode, and the storage degradation characteristics, charge degradation characteristics, and discharge degradation characteristics of the negative electrode for each type of the secondary battery.

[0042] The degradation characteristic storage unit 122 stores at least one of the information such as model, type, single body shape, positive electrode material, composition ratio of positive electrode material, negative electrode material, composition ratio of negative electrode material, energy weight density, energy volume density, etc. as battery information for determining the type of secondary battery. The data in the degradation characteristic storage unit 122 is updated every time a new type of secondary battery is registered. In addition, the data in the degradation characteristic storage unit 122 is also updated when the characteristic information of the registered secondary battery is updated.

[0043] Storage degradation of secondary batteries is a degradation that develops over time based on the temperature and SOC of the secondary battery at each time point. It develops over time regardless of whether it is being charged or discharged. Storage degradation is mainly caused by the formation of a film (SEI (Solid Electrolyte Interphase) film) on the negative electrode. Storage degradation depends on the SOC and temperature at each time point.

[0044] Generally speaking, the higher the SOC at each time point is, the faster the storage degradation rate is. Also, the higher the temperature at each time point is, the faster the storage degradation rate is.

[0045] The charge and discharge degradation of secondary batteries is a degradation that develops as the number of charge and discharge cycles increases. Charge and discharge degradation is mainly caused by cracks and peeling caused by the expansion or contraction of active materials. Charge and discharge degradation depends on the SOC range, temperature, and current rate used. Generally speaking, the larger the SOC range used, the faster the charge and discharge degradation rate increases. In addition, the higher the temperature, the faster the charge and discharge degradation rate increases. In addition, the higher the current rate, the faster the charge and discharge degradation rate increases.

[0046] The storage degradation characteristics, charge degradation characteristics, and discharge degradation characteristics of the positive electrode and the storage degradation characteristics, charge degradation characteristics, and discharge degradation characteristics of the negative electrode are derived in advance for each type of secondary battery through experiments and simulations performed by battery manufacturers.

[0047] Figure 2 This is a diagram showing an example of a storage degradation characteristic map. The horizontal axis represents SOC [%], and the vertical axis represents the storage degradation coefficient Ks. Generally speaking, storage degradation develops approximately linearly with respect to the value of the 0.5 power (square root) of the elapsed time (h). In addition, depending on the type of secondary battery, it may also develop approximately linearly with respect to the value of the 0.4 power, the 0.6 power, etc. of the elapsed time (h).

[0048] exist Figure 2 In the figure, for simplicity, only the storage degradation characteristics for two temperatures, 25°C and 45°C, are depicted, but in reality, storage degradation characteristics for many temperatures are generated. In addition, the storage degradation characteristics may be defined not by mapping but by a storage degradation characteristic model (function) with SOC and temperature as explanatory variables and storage degradation coefficient Ks as a target variable.

[0049] Figure 3A , Figure 3B It is a diagram showing an example of a charge / discharge degradation characteristic map. Figure 3A An example of a charge degradation characteristic map is shown. Figure 3B An example of a discharge degradation characteristic map is shown. The horizontal axis represents the usage range of SOC [%]. Figure 3A , Figure 3B In the figure, each SOC value represents the lower limit of the usage range of 10%. For example, SOC10% means that the charge and discharge are performed within the range of SOC 10% to 20%, and SOC11% means that the charge and discharge are performed within the range of SOC 11% to 21%. The vertical axis represents the charge / discharge degradation coefficients Kc and Kd.

[0050] Generally speaking, charge and discharge degradation develops approximately linearly with respect to the value of the 0.5 power (square root) of the total charge or discharge capacity (Ah). In addition, depending on the type of secondary battery, it may also develop approximately linearly with respect to the value of the 0.4 power, the 0.6 power, etc. of the total charge or discharge capacity (Ah).

[0051] exist Figure 3A , Figure 3B In the figure, for simplicity, only the charge / discharge degradation characteristics for two current rates of 0.1C and 0.8C are depicted, but in fact, the charge / discharge degradation characteristics for many current rates are generated. When charging, such as Figure 3A As shown in the figure, the charge / discharge degradation rate increases in the low and high areas of the SOC usage range. Figure 3B As shown in the figure, the charge / discharge degradation rate increases in a low region of the SOC usage range.

[0052] In addition, although temperature does not have the same effect as current rate, the charge / discharge degradation characteristics are also affected by temperature. Therefore, in order to improve the estimation accuracy of the charge / discharge degradation rate, it is preferable to prepare a charge / discharge degradation characteristic that specifies the relationship between the SOC usage range and the charge / discharge degradation coefficient for each combination of a plurality of current rates and a plurality of temperatures in two dimensions. On the other hand, when generating a simple charge / discharge degradation characteristic map, the temperature can be regarded as normal temperature, and only the charge / discharge degradation characteristics of each current rate of a plurality of current rates can be prepared.

[0053] Furthermore, the charge / discharge degradation characteristics may be defined not by mapping but by a charge / discharge degradation characteristics model (function) using the SOC usage range, current rate, and temperature as explanatory variables and the charge / discharge degradation coefficients Kc and Kd as target variables. Furthermore, the temperature may be a constant.

[0054] The storage degradation characteristics, charge degradation characteristics, and discharge degradation characteristics of the secondary battery described above are prepared for the positive electrode and the negative electrode, respectively. In this embodiment, the storage degradation characteristics, charge degradation characteristics, and discharge degradation characteristics of the secondary battery are used for the switching process of the degradation suppression control described later, and are not used for the degradation estimation process of the secondary battery.

[0055] In this embodiment, the degradation conditions of the positive and negative electrodes are analyzed independently by analyzing peak information appearing in a dV / dQ curve obtained by differentiating a charge and discharge curve of a secondary battery. The charge and discharge curve of a secondary battery is a curve that defines the relationship between the charge and discharge amount and the battery voltage.

[0056] Figure 4 The figure shows an example of a charge and discharge curve and a dV / dQ curve of a secondary battery, a positive electrode, and a negative electrode. The upper figure shows the charge and discharge curve. The horizontal axis represents the capacity [Ah], and the vertical axis on the left represents the battery voltage [V], the positive electrode potential [VvsL + / L], the vertical axis on the right represents the negative electrode potential [VvsL + / L]. Positive electrode potential [VvsL+ / L] and the negative electrode potential [VvsL + / L] is the potential when the lithium potential is set to 0 V. The battery voltage is the difference between the positive electrode potential and the negative electrode potential and is defined by OCV.

[0057] For example, the battery voltage at the lower limit of the battery capacity (SOC = 0%) is set to 2.5 V, and the battery voltage at the upper limit of the battery capacity (SOC = 100%) is set to 4.2 V. The lower figure shows the dV / dQ curve obtained by differentiating the charge and discharge curves of the secondary battery, the positive electrode, and the negative electrode. The horizontal axis represents the capacity [Ah], and the vertical axis represents the dV / dQ [V / Ah].

[0058] In lithium-ion batteries, lithium ions move back and forth between the positive electrode active material and the negative electrode active material during charging and discharging. During discharge, as lithium ions move from the negative electrode to the positive electrode, the negative electrode potential rises and the positive electrode potential decreases. The battery voltage decreases. During charging, as lithium ions move from the positive electrode to the negative electrode, the positive electrode potential rises and the negative electrode potential decreases. The battery voltage increases. The shape of the charge and discharge curve of a secondary battery varies depending on the type and amount of the positive electrode active material and the negative electrode active material.

[0059] In addition, the shape of the charge and discharge curve changes due to degradation.

[0060] Generally speaking, the charge and discharge curve of a secondary battery is as follows: Figure 4 It is difficult to extract the structural changes of the positive electrode active material and the negative electrode active material from the charge and discharge curve of the secondary battery due to the shape of the voltage gradually decreasing as shown. On the other hand, multiple peaks are observed in the dV / dQ curve of the secondary battery. It is possible to estimate whether each peak originates from the structure of the positive electrode active material or the structure of the negative electrode active material based on the shape of the dV / dQ curve of the positive electrode and the dV / dQ curve of the negative electrode at least in the initial state.

[0061] Each peak corresponds to the case where the rate of change of the positive electrode potential or the negative electrode potential takes a maximum value or a minimum value. The positive electrode potential and the negative electrode potential are determined by the lithium composition ratio in the active material. The lithium composition ratio in the active material when the rate of change of the potential becomes maximum or minimum has nothing to do with the battery capacity and is constant. Therefore, the rate of decrease of the distance between the two peaks originating from the positive electrode of the dV / dQ curve of the secondary battery corresponds to the rate of decrease of the positive electrode capacity. For example, if the distance between the two peaks originating from the positive electrode of the current dV / dQ curve is reduced to 80% of the distance between the two peaks originating from the positive electrode of the dV / dQ curve in the initial state, it can be estimated that the positive electrode capacity is reduced to 80% of the initial state. The same is true for the negative electrode.

[0062] Figure 5 Another example of a dV / dQ curve of a secondary battery is shown. Figure 5In the example shown, four peaks (maxima) are extracted from the dV / dQ curve of the secondary battery. The first peak N1 and the third peak N2 are peaks originating from the negative electrode, and the second peak P1 and the fourth peak P2 are peaks originating from the positive electrode. The reduction rate of the negative electrode capacity can be estimated based on the reduction rate of the distance between the first peak N1 and the third peak N2 (i.e., the amount of charge required to transform from the first peak N1 to the third peak N2). Similarly, the reduction rate of the positive electrode capacity can be estimated based on the reduction rate of the distance between the second peak P1 and the fourth peak P2.

[0063] In order to estimate the current charge and discharge curve of the secondary battery, it is necessary to perform maintenance charging at a low rate from SOC = 0% to SOC = 100%. The current rate is set low to reduce the influence of the voltage drop IR caused by the current and make the detection voltage close to the ideal OCV. For example, it is ideal to perform maintenance charging for 20 hours at a current rate of 0.05C. In addition, it is also possible to estimate the charge and discharge curve of the secondary battery with 7 hours of maintenance charging by repeatedly charging at a current rate of 0.2C for 3 minutes and detecting the voltage after a 1-minute pause.

[0064] If the reference electrode of metal lithium is introduced into the secondary battery, the positive electrode potential and the negative electrode potential can be detected. In this case, the charge and discharge curve of the positive electrode, the charge and discharge curve of the negative electrode, the dV / dQ curve of the positive electrode, and the dV / dQ curve of the negative electrode can be estimated. Thus, the reduction rate of the distance between the two peaks of the dV / dQ curve of the positive electrode can be directly calculated. Similarly, the reduction rate of the distance between the two peaks of the dV / dQ curve of the negative electrode can be directly calculated.

[0065] However, a general secondary battery sold on the market does not have a reference electrode. Therefore, as described above, in this embodiment, the peaks originating from the positive electrode and the peaks originating from the negative electrode among the multiple peaks of the dV / dQ curve of the secondary battery are determined to find the reduction rate of the positive electrode capacity and the reduction rate of the negative electrode capacity.

[0066] In the design of secondary batteries, residual capacity is usually added to the positive electrode and the negative electrode in advance. The designer fills the positive electrode with more positive electrode active material than the positive electrode active material used in actual charge and discharge, and fills the negative electrode with more negative electrode active material than the negative electrode active material used in actual charge and discharge. The more positive electrode active material is added, the wider the width of the positive electrode charge and discharge curve is, and the more negative electrode active material is added, the wider the width of the negative electrode charge and discharge curve is. The width of the charge and discharge curve of the positive and negative electrodes shrinks due to deterioration.

[0067] The area where the positive electrode charge and discharge curve overlaps with the negative electrode charge and discharge curve is the battery capacity. The designer sets the lower limit of the battery capacity to SOC=0% (for example, battery voltage=2.5V) and the upper limit to SOC=100% (for example, battery voltage=4.2V).

[0068] Figure 6 This is a diagram showing an example of charge and discharge curves of a secondary battery, a positive electrode, and a negative electrode in the initial state of a certain secondary battery. The horizontal axis represents the capacity [Ah], and the vertical axis represents the battery voltage [V], the positive electrode potential [VvsL + / L], negative electrode potential [VvsL + / L]. Figure 6 In the example shown, the lower limit capacity of the positive electrode is set lower than the lower limit capacity of the battery, and it is actually possible to discharge again from the state of SOC = 0%. The difference between the lower limit capacity of the positive electrode and the lower limit capacity of the battery is the positive electrode remaining capacity. The upper limit capacity of the negative electrode is set higher than the upper limit capacity of the battery, and it is actually possible to charge again from the state of SOC = 100%. The difference between the upper limit capacity of the negative electrode and the upper limit capacity of the battery is the negative electrode remaining capacity.

[0069] Figure 7 It is a diagram showing an example of contraction of the charge and discharge curves of a secondary battery, a positive electrode, and a negative electrode. The upper diagram shows a state in which the width of the charge and discharge curve of the positive electrode has contracted by 10% due to the deterioration of the positive electrode. The lower diagram shows a state in which the width of the charge and discharge curve of the negative electrode has contracted by 10% due to the deterioration of the negative electrode. The BMU of the secondary battery sets the range between the lower limit voltage and the upper limit voltage of the secondary battery as the battery capacity. Regardless of whether the positive electrode capacity is reduced by 10% as shown in the upper diagram or the negative electrode capacity is reduced by 10% as shown in the lower diagram, the battery capacity is reduced by 10%.

[0070] Figure 8 It is a flowchart showing the process of switching processing of the charging and discharging control method performed by the degradation suppression control system 10 involved in the embodiment. When the maintenance implementation period arrives ("Yes" in S10), the charging and discharging control unit 113 sends a maintenance charging instruction to the control unit 32 of the charging pile 30. For example, maintenance charging can also be performed every few months. The power supply unit 31 charges the secondary battery 21 with a constant current at a current rate specified by the degradation suppression control system 10. The control unit 25 of the electric vehicle 20 sends battery data including voltage, current, temperature, and SOC during maintenance charging to the control unit 32 of the charging pile 30. After the maintenance charging is completed, the control unit 32 of the charging pile 30 sends the battery data during maintenance charging to the degradation suppression control system 10.

[0071] The data acquisition unit 111 of the degradation suppression control system 10 acquires the battery data during maintenance charging from the charging station 30 and accumulates it in the battery data holding unit 121. The degradation estimation unit 112 statistically processes the battery data of a plurality of cells included in the secondary battery 21 during maintenance charging to generate battery data of a representative cell.

[0072] The degradation estimation unit 112 generates a charge and discharge curve of the representative cell based on the capacity and voltage included in the battery data of the representative cell. The capacity can be obtained by integrating the current. The degradation estimation unit 112 estimates the capacity charged during the period from SOC = 0% (lower limit voltage) to SOC = 100% (upper limit voltage) as the current battery capacity (S11).

[0073] The degradation estimation unit 112 calculates the reduction rate of the battery capacity during this maintenance charge relative to the battery capacity during the previous maintenance charge, and compares the reduction rate with a threshold value (S12). If the reduction rate is below the threshold value (No in S12), the charging and discharging control method is not switched and the processing ends.

[0074] When the reduction rate exceeds the threshold value ("Yes" in S12), the degradation estimation unit 112 differentiates the charge and discharge curve of the representative cell to generate a dV / dQ curve of the representative cell. The degradation estimation unit 112 estimates the reduction rate of the current positive electrode remaining capacity relative to the initial positive electrode remaining capacity based on the reduction rate of the distance between the two peaks originating from the positive electrode of the dV / dQ curve. In this embodiment, the reduction rate of the positive electrode remaining capacity is defined as the positive electrode relative degradation degree [%] as shown in the following (Formula 1) (S13).

[0075] Positive electrode relative degradation degree [%] = 100 - (current positive electrode capacity - current battery capacity) / (initial positive electrode capacity - initial battery capacity) (Formula 1).

[0076] The degradation estimation unit 112 estimates the reduction rate of the current negative electrode remaining capacity relative to the initial negative electrode remaining capacity based on the reduction rate of the distance between the two peaks originating from the negative electrode of the dV / dQ curve. In this embodiment, the reduction rate of the negative electrode remaining capacity is defined as the negative electrode relative degradation degree [%] (S14) as shown in the following (Formula 2).

[0077] Negative electrode relative degradation degree [%] = 100 - (current negative electrode capacity - current battery capacity) / (initial negative electrode capacity - initial battery capacity) (Formula 2).

[0078] When the relative degradation degree of the positive electrode is greater than the relative degradation degree of the negative electrode ("Yes" in S15), the charge and discharge control unit 113 switches to the charge and discharge control that prioritizes the suppression of degradation of the positive electrode (S16); when the relative degradation degree of the negative electrode is greater than the relative degradation degree of the positive electrode ("No" in S15), the charge and discharge control unit 113 switches to the charge and discharge control that prioritizes the suppression of degradation of the negative electrode (S17).

[0079] The situation where the relative degradation degree of the positive electrode is greater than that of the negative electrode is equivalent to Figure 7In the example of the upper graph, since the negative electrode has a relatively larger remaining capacity, the charge and discharge control that prioritizes the suppression of the positive electrode's degradation is selected.

[0080] On the contrary, the situation where the relative degradation degree of the negative electrode is greater than that of the positive electrode is equivalent to Figure 7 In the example of the lower graph, since the positive electrode has a relatively larger remaining capacity, the charge and discharge control that prioritizes the suppression of the deterioration of the negative electrode is selected.

[0081] Fig. 9 1 is a flowchart showing an example of degradation suppression control during charging performed by the degradation suppression control system 10 according to the embodiment. The charge and discharge control unit 113 generates a plurality of charge profiles before charging the secondary battery 21 (S20).

[0082] For example, the charge and discharge control unit 113 obtains the target SOC, charge start time, and charge end time of the secondary battery 21 based on the user's operation, and obtains the current SOC of the secondary battery 21 from the control unit 25 of the electric vehicle 20. The charge and discharge control unit 113 sets a plurality of slots at a predetermined step length within the chargeable time between the acquired charge start time and charge end time. The charge and discharge control unit 113 generates a charging profile in which a plurality of patterns of current rates are allocated to each slot within a range that satisfies the condition that the SOC of the secondary battery 21 reaches the target SOC at the charge end time.

[0083] The current rate allocated to one slot may be 0 (during the pause period). The charge and discharge control unit 113 may comprehensively generate charge profiles of hundreds of patterns.

[0084] When the charge and discharge control that prioritizes the suppression of degradation of the positive electrode is selected (“positive electrode” in S21), the charge and discharge control unit 113 refers to the storage degradation characteristics and charge degradation characteristics of the positive electrode to select a charge profile with the least degradation of the positive electrode from among the multiple charge profiles (S22). Specifically, the charge and discharge control unit 113 inputs the current rate and SOC of each slot of the charge profile to calculate the storage degradation coefficient of the positive electrode and the charge degradation coefficient of the positive electrode of each slot. The charge and discharge control unit 113 selects the charge profile with the smallest sum of the storage degradation coefficient of the positive electrode and the charge degradation coefficient of the positive electrode.

[0085] When the charge and discharge control that prioritizes the suppression of degradation of the negative electrode is selected ("negative electrode" in S21), the charge and discharge control unit 113 refers to the storage degradation characteristics and charge degradation characteristics of the negative electrode to select a charge profile with the least degradation of the negative electrode from among the multiple charge profiles (S23). Specifically, the charge and discharge control unit 113 inputs the current rate and SOC of each slot of the charge profile to calculate the storage degradation coefficient of the negative electrode and the charge degradation coefficient of the negative electrode of each slot. The charge and discharge control unit 113 selects the charge profile with the smallest sum of the storage degradation coefficient of the negative electrode and the charge degradation coefficient of the negative electrode.

[0086] In addition, when the electric vehicle 20 is an autonomous driving vehicle, a discharge plan with degradation suppression can be generated based on the delivery plan. The charge and discharge control unit 113 generates a plurality of discharge profiles before the electric vehicle 20 sets off. When the charge and discharge control that prioritizes degradation suppression of the positive electrode is selected, the charge and discharge control unit 113 refers to the storage degradation characteristics and charging degradation characteristics of the positive electrode to select a discharge profile with the least degradation of the positive electrode from among the plurality of discharge profiles. When the charge and discharge control that prioritizes degradation suppression of the negative electrode is selected, the charge and discharge control unit 113 refers to the storage degradation characteristics and charging degradation characteristics of the negative electrode to select a discharge profile with the least degradation of the negative electrode from among the plurality of discharge profiles.

[0087] As described above, according to the present embodiment, the relative degradation degree of the positive electrode and the relative degradation degree of the negative electrode are calculated based on the change in the peak position of the dV / dQ curve where the structural changes of the positive electrode active material and the negative electrode active material occur, and the change in the battery capacity. The relative degradation degree of the positive electrode and the relative degradation degree of the negative electrode are used as a scale to perform charge and discharge control to maintain the balance between the relative degradation degree of the positive electrode and the relative degradation degree of the negative electrode, that is, to maximize the area where the charge and discharge curve of the positive electrode overlaps with the charge and discharge curve of the negative electrode. In this way, the progression of degradation at the cell level (reduction in SOH (State Of Health)) can be suppressed to the maximum extent.

[0088] The present disclosure has been described above based on the embodiments. It should be understood by those skilled in the art that the embodiments are illustrative only, and that the combinations of the constituent elements and the processing procedures can have various modifications, and such modifications are also within the scope of the present disclosure.

[0089] The above-described degradation suppression control system 10 may be installed in the control unit 25 of the electric vehicle 20 or the control unit 32 of the charging station 30 .

[0090] In the above embodiment, a four-wheeled electric vehicle is envisioned as the electric vehicle 20. In this regard, it may also be an electric motorcycle (electric scooter), an electric bicycle, or an electric foot scooter. In addition, electric vehicles include not only full-size electric vehicles, but also low-speed electric vehicles such as golf carts and land cars. In addition, the object equipped with the secondary battery 21 is not limited to the electric vehicle 20. The object equipped with the secondary battery 21 also includes electric mobile bodies such as electric ships, railway vehicles, multi-rotor aircraft (drones), fixed power storage systems, and consumer electronic devices (smartphones, laptops, etc.).

[0091] Furthermore, the embodiment can also be determined by the following items.

[0092] [Project 1]

[0093] A degradation suppression control system (10), characterized by comprising:

[0094] an acquisition unit (111) for acquiring battery data including voltage and current of the secondary battery (21);

[0095] an estimating unit (112) that estimates a reduction rate of a current positive electrode remaining capacity relative to an initial positive electrode remaining capacity and a reduction rate of a current negative electrode remaining capacity relative to an initial negative electrode remaining capacity based on battery data of the secondary battery (21); and

[0096] A charge and discharge control unit (113) switches to a charge and discharge control that prioritizes the suppression of degradation of the positive electrode when the rate of decrease in the residual capacity of the positive electrode is greater than the rate of decrease in the residual capacity of the negative electrode, and switches to a charge and discharge control that prioritizes the suppression of degradation of the negative electrode when the rate of decrease in the residual capacity of the negative electrode is greater than the rate of decrease in the residual capacity of the positive electrode.

[0097] Thus, deterioration of the secondary battery (21) can be suppressed to the greatest extent possible.

[0098] [Project 2]

[0099] The degradation suppression control system (10) according to item 1 is characterized in that:

[0100] The estimation unit (112) generates a dV / dQ curve by differentiating a charge / discharge curve that defines the relationship between the capacity and the voltage of the secondary battery (21).

[0101] The estimation unit (112) estimates a reduction rate of the remaining capacity of the positive electrode based on a reduction rate of a distance between two peaks of the dV / dQ curve originating from the positive electrode.

[0102] The estimation unit (112) estimates a reduction rate of the remaining capacity of the negative electrode based on a reduction rate of a distance between two peaks of the dV / dQ curve originating from the negative electrode.

[0103] Thus, the reduction rate of the remaining capacity of the positive electrode and the reduction rate of the remaining capacity of the negative electrode can be estimated with high accuracy based on the charge and discharge curve of the secondary battery (21).

[0104] [Item 3]

[0105] The degradation suppression control system (10) according to item 1, wherein:

[0106] When the rate of decrease in capacity of the secondary battery (21) exceeds a threshold value,

[0107] The estimation unit (112) estimates a reduction rate of the remaining capacity of the positive electrode and a reduction rate of the remaining capacity of the negative electrode,

[0108] The charge and discharge control unit (113) performs switching control of the charge and discharge control based on the relationship between the two.

[0109] This makes it possible to optimize the switching frequency of the charge and discharge control.

[0110] [Item 4]

[0111] The degradation suppression control system (10) according to item 1, wherein:

[0112] The invention also comprises a degradation characteristic holding unit (122) for holding the storage degradation characteristic and charge degradation characteristic of the positive electrode and the storage degradation characteristic and charge degradation characteristic of the negative electrode of the secondary battery (21).

[0113] When the secondary battery (21) is charged,

[0114] The charge and discharge control unit (113) selects a charge profile with the least degradation of the positive electrode from among a plurality of charge profile candidates by referring to the storage degradation characteristics and the charge degradation characteristics of the positive electrode when the charge and discharge control with priority to the suppression of degradation of the positive electrode is selected.

[0115] When the charge and discharge control prioritizing the suppression of degradation of the negative electrode is selected, the charge and discharge control unit (113) refers to the storage degradation characteristics and charge degradation characteristics of the negative electrode to select a charge profile with the least degradation of the negative electrode from among a plurality of charge profile candidates.

[0116] Thus, a charging plan can be prepared that minimizes the deterioration of the secondary battery (21).

[0117] [Item 5]

[0118] A degradation suppression control method, characterized by comprising the following steps:

[0119] Acquiring battery data including voltage and current of the secondary battery (21);

[0120] Based on the battery data of the secondary battery (21), estimating the reduction rate of the current remaining capacity of the positive electrode relative to the initial remaining capacity of the positive electrode and the reduction rate of the current remaining capacity of the negative electrode relative to the initial remaining capacity of the negative electrode; and

[0121] When the rate of decrease in the remaining capacity of the positive electrode is greater than the rate of decrease in the remaining capacity of the negative electrode, the charge and discharge control is switched to prioritize the suppression of degradation of the positive electrode. When the rate of decrease in the remaining capacity of the negative electrode is greater than the rate of decrease in the remaining capacity of the positive electrode, the charge and discharge control is switched to prioritize the suppression of degradation of the negative electrode.

[0122] Thus, deterioration of the secondary battery (21) can be suppressed to the greatest extent possible.

[0123] [Item 6]

[0124] A degradation suppression control program is characterized by causing a computer to execute the following processing:

[0125] Acquiring battery data including voltage and current of the secondary battery (21);

[0126] Based on the battery data of the secondary battery (21), estimating the reduction rate of the current remaining capacity of the positive electrode relative to the initial remaining capacity of the positive electrode and the reduction rate of the current remaining capacity of the negative electrode relative to the initial remaining capacity of the negative electrode; and

[0127] When the rate of decrease in the remaining capacity of the positive electrode is greater than the rate of decrease in the remaining capacity of the negative electrode, the charge and discharge control is switched to prioritize the suppression of degradation of the positive electrode. When the rate of decrease in the remaining capacity of the negative electrode is greater than the rate of decrease in the remaining capacity of the positive electrode, the charge and discharge control is switched to prioritize the suppression of degradation of the negative electrode.

[0128] Thus, deterioration of the secondary battery (21) can be suppressed to the greatest extent possible.

[0129] Description of Reference Numerals

[0130] 2: Commercial power system; 5: Network; 10: Degradation suppression control system; 11: Control unit; 12: Storage unit; 13: Communication unit; 20: Electric vehicle; 21: Secondary battery; 22: Voltage sensor; 23: Current sensor; 24: Temperature sensor; 25: Control unit; 26: Communication unit; 30: Charging pile; 31: Power supply unit; 32: Control unit; 33: Communication unit; 111: Data acquisition unit; 112: Degradation estimation unit; 113: Charge and discharge control unit; 121: Battery data retention unit; 122: Degradation characteristic retention unit.

Claims

1. A degradation suppression control system, characterized in that: have: an acquisition unit that acquires battery data including a voltage and a current of the secondary battery; an estimating unit that estimates a reduction rate of a current remaining capacity of the positive electrode relative to an initial remaining capacity of the positive electrode and a reduction rate of a current remaining capacity of the negative electrode relative to an initial remaining capacity of the negative electrode based on the battery data of the secondary battery; and A charge and discharge control unit, which switches to a charge and discharge control that prioritizes the suppression of degradation of the positive electrode when the rate of decrease in the remaining capacity of the positive electrode is greater than the rate of decrease in the remaining capacity of the negative electrode, and switches to a charge and discharge control that prioritizes the suppression of degradation of the negative electrode when the rate of decrease in the remaining capacity of the negative electrode is greater than the rate of decrease in the remaining capacity of the positive electrode.

2. The degradation suppression control system according to claim 1, characterized in that: the estimating unit generates a dV / dQ curve by differentiating a charge and discharge curve defining a relationship between a capacity and a voltage of the secondary battery, The estimation unit estimates a reduction rate of the remaining capacity of the positive electrode based on a reduction rate of a distance between two peaks of the dV / dQ curve originating from the positive electrode, The estimation section estimates a reduction rate of a remaining capacity of the negative electrode based on a reduction rate of a distance between two peaks of the dV / dQ curve originating from the negative electrode.

3. The degradation suppression control system according to claim 1, wherein: When the rate of reduction in capacity of the secondary battery exceeds a threshold, The estimating unit estimates a reduction rate of the remaining capacity of the positive electrode and a reduction rate of the remaining capacity of the negative electrode, The charge and discharge control unit performs switching control of the charge and discharge control based on the relationship between the two.

4. The degradation suppression control system according to claim 1, wherein: further comprising a degradation characteristic holding unit for holding the storage degradation characteristic and charge degradation characteristic of the positive electrode of the secondary battery and the storage degradation characteristic and charge degradation characteristic of the negative electrode, When the secondary battery is charged, The charge and discharge control unit selects a charge profile that causes the least degradation of the positive electrode from among a plurality of charge profile candidates, referring to the storage degradation characteristics and the charge degradation characteristics of the positive electrode, when the charge and discharge control that prioritizes the suppression of degradation of the positive electrode is selected. When the charge and discharge control prioritizing suppression of degradation of the negative electrode is selected, the charge and discharge control unit selects a charge profile with the least degradation of the negative electrode from among a plurality of charge profile candidates, referring to the storage degradation characteristics and charge degradation characteristics of the negative electrode.

5. A degradation suppression control method, characterized in that: The following steps are involved: acquiring battery data including voltage and current of the secondary battery; estimating a reduction rate of a current remaining capacity of the positive electrode relative to an initial remaining capacity of the positive electrode and a reduction rate of a current remaining capacity of the negative electrode relative to an initial remaining capacity of the negative electrode based on the battery data of the secondary battery; and When the rate of decrease in the remaining capacity of the positive electrode is greater than the rate of decrease in the remaining capacity of the negative electrode, the charge and discharge control is switched to prioritize the suppression of degradation of the positive electrode. When the rate of decrease in the remaining capacity of the negative electrode is greater than the rate of decrease in the remaining capacity of the positive electrode, the charge and discharge control is switched to prioritize the suppression of degradation of the negative electrode.

6. A degradation suppression control program, characterized in that: Causes the computer to perform the following processing: acquiring battery data including voltage and current of the secondary battery; estimating a reduction rate of a current remaining capacity of the positive electrode relative to an initial remaining capacity of the positive electrode and a reduction rate of a current remaining capacity of the negative electrode relative to an initial remaining capacity of the negative electrode based on the battery data of the secondary battery; and When the rate of decrease in the remaining capacity of the positive electrode is greater than the rate of decrease in the remaining capacity of the negative electrode, the charge and discharge control is switched to prioritize the suppression of degradation of the positive electrode. When the rate of decrease in the remaining capacity of the negative electrode is greater than the rate of decrease in the remaining capacity of the positive electrode, the charge and discharge control is switched to prioritize the suppression of degradation of the negative electrode. 7 . A non-transitory recording medium recording the charging control program according to claim 6 .

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