POWER STORAGE DEVICE CONTROL APPARATUS, POWER STORAGE DEVICE CONTROL SYSTEM, AND POWER STORAGE DEVICE CONTROL METHOD

Abstract

To provide a power storage device controller, a power storage device control system, and a power storage device control method, capable of increasing available power storage capacity (battery capacity) of a deteriorated power storage device such as a secondary battery, without causing further deterioration of the power storage device.SOLUTION: A battery controller includes a control unit. The control unit lowers a lower limit voltage of discharge for the power storage device on the basis of a deteriorated state of the power storage device in a range in which positive electrode electric potential of the power storage device is not equal to or lower than a first threshold or in a range in which negative electrode electric potential of the power storage device is not equal to or higher than a second threshold.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an electricity storage device control device, an electricity storage device control system, and an electricity storage device control method. [Background technology]

[0002] A lower limit voltage and an upper limit voltage are set for lithium-ion secondary batteries so that they can be used within an appropriate voltage range. A control device for a lithium-ion secondary battery controls the terminal voltage of the lithium-ion secondary battery so that it is within the range from the lower limit voltage to the upper limit voltage. By controlling the lithium-ion secondary battery to be used within the appropriate voltage range, the control device prevents overcharging of the lithium-ion secondary battery and suppresses deterioration.

[0003] Furthermore, lithium ion secondary batteries have the problem that their battery capacity decreases due to degradation. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2015-110922 A Summary of the Invention [Problem to be solved by the invention]

[0005] The problem that the embodiments of the present invention aim to solve is to provide an energy storage device control device, an energy storage device control system, and an energy storage device control method that can increase the available storage capacity (battery capacity) of a deteriorated energy storage device without causing further deterioration of the energy storage device such as a secondary battery. [Means for solving the problem]

[0006] According to an embodiment, an electric storage device control apparatus includes a control unit that reduces a lower limit voltage of discharge of the electric storage device based on a degradation state of the electric storage device, within a range in which a positive electrode potential of the electric storage device does not become equal to or lower than a first threshold value, or within a range in which a negative electrode potential of the electric storage device does not become equal to or higher than a second threshold value. Effect of the Invention

[0007] The present invention can increase the available power storage capacity of a degraded power storage device without causing further degradation of the power storage device. [Brief description of the drawings]

[0008] [Figure 1] 1 is a block diagram showing an example of a configuration of a main part of a battery control system according to an embodiment; [Diagram 2] 2 is a flowchart showing an example of processing by a processor in FIG. 1 . [Diagram 3] 1 is a graph showing capacity characteristics of positive electrode potential and negative electrode potential in the initial state and at EOL. [Figure 4] 4 is a graph showing an example of terminal voltage vs. deterioration rate characteristics. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, a battery control system according to an embodiment will be described with reference to the drawings. Note that, for the sake of explanation, the drawings used in the following description of the embodiment may omit configurations. In addition, in each drawing and in this specification, the same reference numerals denote similar elements. FIG. 1 is a block diagram showing an example of a main configuration of a battery control system 1 according to an embodiment.

[0010] The battery control system 1 is a system that controls a battery 10. The battery control system 1 includes, as an example, a battery 10, a control device 20, a voltmeter 30, an ammeter 40, a thermometer 50, and a timer 60. The battery control system 1 is an example of an electricity storage device control system.

[0011] The battery 10 is, for example, a lithium ion secondary battery. Therefore, the battery 10 is capable of charging and discharging. The positive electrode material of the battery 10 is, for example, a ternary material. The battery 10 is an example of an electricity storage device.

[0012] The control device 20 is a computer that performs processes such as calculations and controls required for the operation of the battery control system 1. The control device 20 includes, as an example, a processor 21, a read-only memory (ROM) 22, a random-access memory (RAM) 23, and an auxiliary storage device 24. A bus 25 and the like connect these components together. The control device 20 is an example of an electricity storage device control device.

[0013] The processor 21 is a central part of the control device 20 and performs various calculations and processing. The processor 21 is, for example, a central processing unit (CPU), a micro processing unit (MPU), a system on a chip (SoC), a digital signal processor (DSP), an application specific integrated circuit (ASIC), a programmable logic device (PLD), or a field-programmable gate array (FPGA). Alternatively, the processor 21 is a combination of a plurality of these. The processor 21 may also be a combination of these with a hardware accelerator. The processor 21 controls each part to realize various functions of the battery control system 1 based on programs such as firmware, system software, and application software stored in the ROM 22 or the auxiliary storage device 24. The processor 21 also executes processing to be described later based on the programs. Note that a part or all of the programs may be incorporated in the circuit of the processor 21. Note that the processor 21 is an example of a control part.

[0014] The ROM 22 and the RAM 23 are the main storage devices of the control device 20. The ROM 22 is a non-volatile memory used exclusively for reading data. The ROM 22 stores, for example, firmware among the above programs. The ROM 22 also stores data used by the processor 21 when performing various processes. The RAM 23 is a memory used for reading and writing data. The RAM 23 is used as a work area for storing data that is temporarily used when the processor 21 performs various processes. The RAM 23 is typically a volatile memory.

[0015] The auxiliary storage device 24 is an auxiliary storage device of the control device 20. The auxiliary storage device 24 is, for example, an EEPROM (electric erasable programmable read-only memory), a HDD (hard disk drive), or a flash memory. The auxiliary storage device 24 stores, for example, system software and application software among the above programs. The auxiliary storage device 24 also stores data used by the processor 21 in performing various processes, data generated by the processes in the processor 21, various setting values, and the like.

[0016] The auxiliary storage device 24 also stores a battery database 241. The battery database 241 is a database that stores and manages various data related to the battery 10. The various data includes data used to determine the degradation state of the battery 10.

[0017] The bus 25 includes a control bus, an address bus, a data bus, etc., and transmits signals exchanged among the various parts of the control device 20 .

[0018] The voltmeter 30 measures the terminal voltage (cell voltage, battery voltage) of the battery 10. In addition, the voltmeter 30 outputs, for example, a signal indicating the value of the measured voltage.

[0019] The ammeter 40 measures the charging and discharging current of the battery 10. The charging and discharging current includes a charging current and a discharging current. The ammeter 40 also outputs a signal indicating the value of the measured current, for example.

[0020] The thermometer 50 measures the temperature of the battery 10. Furthermore, the thermometer 50 outputs, for example, a signal indicating the value of the measured temperature.

[0021] The timer 60 measures time. Furthermore, the timer 60 outputs, for example, a signal indicating the measured time.

[0022] The processor 21 receives signals output by the voltmeter 30, ammeter 40, thermometer 50 and timer 60, and thereby obtains the terminal voltage, charge / discharge current, temperature and time of the battery 10. The processor 21 uses the timer 60 to measure the charging and discharging time of the battery 10. The charging and discharging time includes the charging time and the discharging time. The charging time is, for example, a time indicating the total length of the period during which the battery 10 is charging. The discharging time is, for example, a time indicating the total length of the period during which the battery 10 is discharging.

[0023] The operation of the battery control system 1 according to the embodiment will be described below with reference to Fig. 2 and other figures. Note that the contents of the processing in the following operation description are merely examples, and various processing that can obtain similar results can be used as appropriate. Fig. 2 is a flowchart showing an example of processing by the processor 21 of the control device 20. The processor 21 executes the processing of Fig. 2 based on a program stored in, for example, the ROM 22 or the auxiliary storage device 24.

[0024] The processor 21 starts the process in Fig. 2 at predetermined time intervals, for example. The processor 21 starts the process in Fig. 2 when, for example, there is an input instructing execution of the process in Fig. 2. The processor 21 starts the process in Fig. 2 when, for example, a predetermined condition based on at least one of the number of times the battery 10 has been charged, the number of times the battery 10 has been discharged, the charging time, and the discharging time is satisfied. The processor 21 starts the process in Fig. 2 when, for example, charging of the battery 10 is started.

[0025] In step ST11, the processor 21 determines the deviation amount G1 by calculation or the like. The processor 21 determines the deviation amount G1, for example, using the deterioration state. The processor 21 determines the deterioration state of the battery 10 by calculation or the like. The processor 21 determines the deterioration state of the battery 10, for example, using the method (A) or (B) shown below. Alternatively, the processor 21 determines the deterioration state of the battery 10 by using a method that combines the methods (A) and (B).

[0026] (A) The processor 21 calculates, for example, a state of health (SOH) as a value indicating the deterioration state of the battery 10. The SOH can be calculated, for example, by the following formula (1): SOH = (current battery capacity) / (initial battery capacity) × 100(%) (1) The smaller the SOH value, the more deteriorated the battery 10. In other words, the smaller the SOH value, the more deteriorated the battery 10 is.

[0027] The initial state (BOL (beginning of life)) is, for example, the state of battery 10 at the time of manufacture or at a certain point after manufacture. The certain point in time is, for example, at the time of inspection during manufacture, at the time of completion of manufacture, at the time of inspection after manufacture, or at the time of shipment from the factory. The battery capacity in the initial state may be a predetermined value rather than a value measured individually for each battery 10. The predetermined value is, for example, the battery capacity in the initial state measured using a battery having the same specifications as battery 10.

[0028] In this embodiment, the lower limit voltage of the battery 10 changes. For this reason, the current battery capacity in the SOH is preferably the battery capacity when the upper limit voltage and the lower limit voltage are the same as the upper limit voltage and the lower limit voltage in the initial state. Here, the lower limit voltage and the upper limit voltage indicate the lower limit and the upper limit of the terminal voltage of the battery 10. The processor 21 stops discharging the battery 10 when the terminal voltage of the battery 10 becomes equal to or lower than the lower limit voltage. For example, the processor 21 determines that the terminal voltage is equal to or lower than the lower limit voltage when the terminal voltage becomes equal to or lower than the lower limit voltage, the voltage obtained by adding a predetermined value VA1 to the lower limit voltage, or the value obtained by multiplying the lower limit voltage by a predetermined value VA2. The processor 21 stops charging when the terminal voltage of the battery 10 becomes equal to or higher than the upper limit voltage. For example, the processor 21 determines that the terminal voltage is likely to become equal to or lower than the lower limit voltage when the terminal voltage becomes equal to or lower than the upper limit voltage, the voltage obtained by subtracting a predetermined value VA3 from the upper limit voltage, or the value obtained by multiplying the upper limit voltage by a predetermined value VA4. The values ​​VA1 to VA4 are positive numbers. The value VA2 is a value greater than 1. The value VA4 is a value less than 1.

[0029] Fig. 3 shows the positive electrode potential and the negative electrode potential in the initial state and the positive electrode potential and the negative electrode potential in the deteriorated state. Fig. 3 is a graph showing the capacity characteristics of the positive electrode potential and the negative electrode potential in the initial state and at EOL (end of life). Note that Fig. 3 shows an example, and the measurement results of this embodiment may be different from those shown in Fig. 3. Curve C11 is an example of a capacity-potential curve of a positive electrode in an initial state. Curve C12 is an example of a capacity-potential curve of a negative electrode in an initial state. The unit of potential in FIG. 3 is, for example, volts (V vs. Li / Li+). The unit of capacity in FIG. 3 is, for example, ampere-hours (Ah) or %. As shown in FIG. 3, when the capacity Q increases, the positive electrode potential increases and the negative electrode potential decreases. When the capacity Q decreases, the positive electrode potential decreases and the negative electrode potential increases.

[0030] The potential difference V11 indicates the lower limit voltage in the initial state. The potential difference V12 indicates the upper limit voltage in the initial state. The potential difference V11 and the potential difference V12 are the positive electrode potentials when the negative electrode potential is taken as a reference. The capacity Q11 indicates the capacity of the battery 10 at the lower limit voltage V11 in the initial state. In the initial state, the capacity Q11 is 0% in SOC. That is, the capacity Q11 is the capacity in a fully discharged state in the initial state. The capacity Q12 indicates the capacity of the battery 10 at the upper limit voltage V12 in the initial state. In the initial state, the capacity Q12 is 100% in SOC. That is, the capacity Q12 is the fully charged capacity in the initial state. From the above, the battery capacity F11 indicates the battery capacity of the battery 10 in the initial state. Note that F11=Q12-Q11.

[0031] When the battery 10 deteriorates, the positive electrode potential and the negative electrode potential become as shown by curves C21 and C22, for example. For comparison, curves C11 and C12 are also shown by two-dot chain lines in the same graph as curves C21 and C22. Curve C21 is a capacity-potential curve of the positive electrode at the EOL when deterioration of the battery 10 has progressed. Curve C22 is a capacity-potential curve of the negative electrode at the EOL. In this way, curve C21 has a shape that is like a curve C11 that has been contracted in the horizontal axis direction due to deterioration of the positive electrode active material of the battery 10. This contraction amount becomes larger as deterioration of the battery 10 progresses. In addition, curve C22 becomes a graph that is like a curve C12 that has been translated in the positive direction of the horizontal axis due to a shift in the charge-discharge balance of the battery 10. The amount of this parallel movement (shift amount G1) becomes larger as deterioration of the battery 10 progresses. As a result, the battery capacity of the battery 10 at EOL is battery capacity F22 when the upper limit voltage and the lower limit voltage are the same as those in the initial state. The potential difference V22 indicates the lower limit voltage at EOL when the lower limit voltage of EOL is the same as that in the initial state. Therefore, the value of the potential difference V22 is equal to the value of the potential difference V11. The potential difference V23 indicates the upper limit voltage at EOL when the upper limit voltage of EOL is the same as that in the initial state. Therefore, the value of the potential difference V23 is equal to the value of the potential difference V12. Furthermore, the capacity Q22 indicates the capacity of the battery 10 at the lower limit voltage V22 at EOL when the lower limit voltage of EOL is the same as that in the initial state. At EOL, the capacity Q22 is 0% in terms of SOC. That is, the capacity Q22 is the capacity in a fully discharged state at EOL when the lower limit voltage of EOL is the same as that in the initial state. Capacity Q23 indicates the capacity of the battery 10 at the upper limit voltage V23 at EOL when the upper limit voltage at EOL is the same as the upper limit voltage at the initial state. At EOL, capacity Q23 is 100% in terms of SOC. That is, capacity Q23 is the full charge capacity at EOL when the upper limit voltage at EOL is the same as the upper limit voltage at the initial state. Note that F22=Q23-Q22. The deviation amount G1 is an example of the deviation amount with respect to the capacity of the battery 10.

[0032] As described above, the battery capacity of the battery 10 decreases due to deterioration of the battery 10. In addition, the SOH at the EOL is expressed as follows: SOH = F22 / F11 × 100(%) (2) It can be expressed as:

[0033] The processor 21 uses dV / dQ to determine the deterioration state of the battery 10. Here, dV / dQ is a value obtained by differentiating the capacity Q of the battery 10 with respect to the terminal voltage V of the battery 10. In other words, dV / dQ is the ratio of the amount of change in the terminal voltage V to the amount of change in the capacity Q.

[0034] The processor 21 measures the capacity Q using, for example, the charge / discharge current I and the charge / discharge time of the battery 10. The processor 21 calculates the capacity Q by, for example, acquiring a measurement value of the charge / discharge current I at predetermined time intervals and integrating the charge / discharge current I over time. The processor 21 finds dV / dQ using the measurement value of the terminal voltage V of the battery 10 acquired at predetermined time intervals and the calculated capacity Q.

[0035] The processor 21 calculates the SOH from, for example, dV / dQ. A known method can be used to calculate the SOH from dV / dQ. The processor 21 calculates the SOH from dV / dQ by using, for example, a table or a map included in the battery database 241.

[0036] The processor 21 may use dQ / dV instead of dV / dQ to determine the degradation state of the battery 10. dQ / dV is a value obtained by differentiating the terminal voltage V with the capacity Q.

[0037] (B) The processor 21 obtains, for example, a positive electrode deterioration amount K1, a negative electrode deterioration amount K2, and a lithium trap amount TK1 as values ​​indicating the deterioration state of the battery 10. The positive electrode deterioration amount K1, the negative electrode deterioration amount K2, and the lithium trap amount TK1 indicate that the larger the values ​​are, the more deteriorated the battery 10 is. In other words, the positive electrode deterioration amount K1, the negative electrode deterioration amount K2, and the lithium trap amount TK1 are, the worse the deterioration state of the battery 10 is.

[0038] The positive electrode deterioration amount K1 is a value indicating the degree of deterioration of the positive electrode of the battery 10. The positive electrode of the battery 10 deteriorates over time and due to charging and discharging, etc. Also, the more the positive electrode of the battery 10 deteriorates, the less the amount of lithium ions that the positive electrode active material can release or absorb.

[0039] The negative electrode deterioration amount K2 is a value indicating the degree of deterioration of the negative electrode of the battery 10. The negative electrode of the battery 10 deteriorates over time and due to charging and discharging, etc. Also, the more the negative electrode of the battery 10 deteriorates, the less the amount of lithium ions that the negative electrode active material can release or absorb.

[0040] The lithium trap amount TK1 is a value indicating the amount of lithium that contributes to the battery reaction. When the battery 10 is charged, lithium ions are released from the positive electrode and the negative electrode absorbs the lithium ions. This causes the negative electrode to store electric charge. Then, the lithium ions stored in the negative electrode of the battery 10 are released and the lithium ions return to the positive electrode. In this way, lithium ions move between the positive electrode and the negative electrode due to charging and discharging. However, some of the lithium ions are taken up or precipitated in the coating over time and during charging and discharging. The lithium ions taken up or precipitated in the coating no longer contribute to the battery reaction.

[0041] The processor 21 obtains the positive electrode deterioration amount K1, the negative electrode deterioration amount K2, and the lithium trap amount TK1, for example, using the state of the battery 10 and time. The state of the battery 10 includes, for example, temperature, SOC (state of charge), and current-carrying state. The current-carrying state of the battery 10 includes, for example, three types of states: a charging state, a discharging state, and a no-current-carrying state. Alternatively, the current-carrying state of the battery 10 may include two types of states: a charging / discharging state, and a no-current-carrying state.

[0042] The battery database 241 includes data (deterioration amount data) indicating how much the positive electrode deterioration amount K1, the negative electrode deterioration amount K2, and the lithium trap amount TK1 increase when the battery 10 continues in a certain state for a unit time. The deterioration amount data is in the form of, for example, a table or a map. Alternatively, the deterioration amount data may be in the form of a function such as a mathematical formula.

[0043] As an example, the deterioration amount data in the form of a table includes information such as how much the positive electrode deterioration amount K1 increases per unit time when the current-carrying state is a charging state, the temperature is 20° C., and the SOC is 40%. In this way, the deterioration amount data in the form of a table stores the increase amounts per unit time of the positive electrode deterioration amount K1, the negative electrode deterioration amount K2, and the lithium trap amount TK1 in association with various temperatures and various SOCs for each current-carrying state.

[0044] The deterioration amount data in the form of a function indicates, for example, the increase in the positive electrode deterioration amount K1, the negative electrode deterioration amount K2, and the lithium trap amount TK1 as a function of the state of the battery 10 and time.

[0045] The processor 21 acquires the current state of the battery 10 at predetermined time intervals, and uses the deterioration amount data to determine the increase in each of the positive electrode deterioration amount K1, the negative electrode deterioration amount K2, and the lithium trap amount TK1 from the state of the battery 10 and the time that the state of the battery 10 has continued, and calculates the positive electrode deterioration amount K1, the negative electrode deterioration amount K2, and the lithium trap amount TK1 by integrating each of the increase amounts.

[0046] The processor 21 updates the positive electrode deterioration amount K1, the negative electrode deterioration amount K2, and the lithium trap amount TK1 in real time by, for example, determining the positive electrode deterioration amount K1, the negative electrode deterioration amount K2, and the lithium trap amount TK1 at predetermined time intervals. Alternatively, the processor 21 stores the history of the temperature change, the SOC change, and the change in the current-carrying state of the battery 10 in the battery database 241 of the auxiliary storage device 24 or the RAM 23, and determines the positive electrode deterioration amount K1, the negative electrode deterioration amount K2, and the lithium trap amount TK1 as necessary.

[0047] The processor 21 may obtain the positive electrode deterioration amount K1, the negative electrode deterioration amount K2, and the lithium trap amount TK1 by using the capacity Q instead of the SOC. The processor 21 may obtain the positive electrode deterioration amount K1, the negative electrode deterioration amount K2, and the lithium trap amount TK1 by using other known methods.

[0048] Next, the processor 21 calculates the amount of deviation G1 using the SOH. The processor 21 calculates the deviation G1 using, for example, the SOH calculated in (A). The processor 21 also calculates the deviation G1 using a table or a function indicating the relationship between the SOH and the deviation G1. The battery database 241 includes the table or the function. The table stores the deviation G1 for each SOH value, for example, by associating the deviation G1 with each SOH value. The function is, for example, a function of SOH indicating the value of the deviation G1.

[0049] Alternatively, the processor 21 calculates the deviation amount G1 using, for example, at least one of the positive electrode deterioration amount K1, the negative electrode deterioration amount K2, and the lithium trap amount TK1 calculated in (B). The processor 21 also calculates the deviation amount G1 using a table or function or the like showing the relationship between at least one of the positive electrode deterioration amount K1, the negative electrode deterioration amount K2, and the lithium trap amount TK1 and the deviation amount G1. The battery database 241 includes the table or function or the like. The table stores the deviation amount G1 for at least one value of the negative electrode deterioration amount K2 and the lithium trap amount TK1 by associating the deviation amount G1 with at least one value of the positive electrode deterioration amount K1, the negative electrode deterioration amount K2, and the lithium trap amount TK1, for example. As an example, the table stores the deviation amount G1 for each value of the negative electrode deterioration amount K2 by associating the deviation amount G1 with each value of the negative electrode deterioration amount K2. The function is, for example, a function of at least one of the positive electrode deterioration amount K1, the negative electrode deterioration amount K2, and the lithium trap amount TK1, which indicate the value of the deviation amount G1. As an example, the function is a function of the negative electrode deterioration amount K2, which indicates the value of the deviation amount G1. It is considered that the deviation amount G1 increases as the negative electrode deterioration amount K2 increases.

[0050] The processor 21 may obtain the deviation amount G1 from dV / DQ or dQ / dV without obtaining SOH in (A). The processor 21 can indirectly estimate the deviation amount G1 by calculating a peak shift due to deterioration, for example, by utilizing the fact that the peak of the dV / dQ plot indicates the oxidation-reduction reaction of the battery. The processor 21 may also obtain the deviation amount G1 by other known methods.

[0051] In step ST12, the processor 21 determines whether or not to change the lower limit voltage of the battery 10. The processor 21 determines whether or not to change the lower limit voltage of the battery 10 by using, for example, the deviation amount G1 obtained in step ST11. For example, if the number of times the lower limit voltage has been changed is 0 and the deviation amount G1 is equal to or less than the threshold value TH1, the processor 21 determines to change the lower limit voltage of the battery 10. For example, the processor 21 determines whether or not to change the lower limit voltage of the battery 10 by using the SOH obtained in (A). For example, if the number of times the lower limit voltage has been changed is 0 and the SOH is equal to or less than the threshold value TH2, the processor 21 determines to change the lower limit voltage of the battery 10. In addition, the processor 21 determines whether or not to change the lower limit voltage of the battery 10 by using at least one of the positive electrode deterioration amount K1, the negative electrode deterioration amount K2, and the lithium trap amount TK1 obtained in (B). The processor 21 determines to change the lower limit voltage of the battery 10 when, for example, any one of the following three conditions is satisfied: the number of times the lower limit voltage has been changed is 0, and the positive electrode deterioration amount K1 is equal to or greater than a threshold value TH3, the negative electrode deterioration amount K2 is equal to or greater than a threshold value TH4, and the lithium trap amount TK1 is equal to or greater than a threshold value TH5. Alternatively, the processor 21 determines to change the lower limit voltage of the battery 10 when, for example, the number of times the lower limit voltage has been changed is 0, and all of the above-mentioned three conditions are satisfied. The threshold values ​​TH1 to TH5 are determined in advance by, for example, a designer or manager of the battery control system 1. In addition, the processor 21 may determine to change the lower limit voltage when the lower limit voltage has been changed at least once and the deviation G1 from the previous change in the lower limit voltage or the deterioration state of the battery 10 has deteriorated to a predetermined level or more. If the processor 21 does not determine that the lower limit voltage of the battery 10 is to be changed, it determines No in step ST12 and ends the processing shown in Fig. 2. On the other hand, if the processor 21 determines that the lower limit voltage of the battery 10 is to be changed, it determines Yes in step ST12 and proceeds to step ST13.

[0052] In step ST13, the processor 21 determines an offset amount from the deviation amount G1 obtained in step ST11. The offset amount indicates how many volts the lower limit voltage should be reduced. The processor 21 determines an offset amount that satisfies at least one of the following conditions: the positive electrode potential does not enter the positive electrode deterioration range and the negative electrode potential does not enter the negative electrode deterioration range when the terminal voltage of the battery 10 is at the lower limit voltage in the current deterioration state of the battery 10. Preferably, the processor 21 determines an offset amount that does not enter the positive electrode deterioration range and does not enter the negative electrode deterioration range when the terminal voltage of the battery 10 is at the lower limit voltage. The positive electrode deterioration range indicates a range of the positive electrode potential of the battery 10 in which the positive electrode deteriorates particularly quickly. The positive electrode deterioration range is, for example, a range in which the positive electrode potential [V vs. Li / Li+] is equal to or less than a threshold value TH6. The negative electrode deterioration range indicates a range of the negative electrode potential of the battery 10 in which the negative electrode deteriorates particularly quickly. The negative electrode deterioration range is, for example, a range in which the potential of the negative electrode [V vs. Li / Li+] is equal to or greater than a threshold value TH7. The processor 21 obtains the offset amount by using, for example, the deviation amount G1 and a table or function included in the battery database 241. The table stores the offset amount for each value of the deviation amount G1 by, for example, associating the offset amount with each value of the deviation amount G1. The offset value in the table is, for example, a value such that the potential of the positive electrode of the battery 10 does not fall within the positive electrode deterioration range or the potential of the negative electrode of the battery 10 does not fall within the negative electrode deterioration range. Preferably, the offset value in the table is, for example, a value such that the potential of the positive electrode of the battery 10 does not fall within the positive electrode deterioration range and the potential of the negative electrode of the battery 10 does not fall within the negative electrode deterioration range. The function is, for example, a function of the deviation amount G1 indicating the offset amount. The offset value calculated by the function is a value such that the potential of the negative electrode of the battery 10 does not fall within the negative electrode deterioration range, or the potential of the positive electrode of the battery 10 does not fall within the positive electrode deterioration range. Preferably, the offset value calculated by the function is a value such that the potential of the positive electrode of the battery 10 does not fall within the positive electrode deterioration range, and the potential of the negative electrode of the battery 10 does not fall within the negative electrode deterioration range. The offset amount is, for example, a value such that when the lower limit voltage is lowered by the offset amount in the initial state, the potential of the positive electrode of the battery 10 enters the positive electrode deterioration range or the potential of the negative electrode of the battery 10 enters the negative electrode deterioration range. The offset amount is, for example, a value such that when the lower limit voltage is lowered by the offset amount in the initial state, the potential of the positive electrode of the battery 10 enters the positive electrode deterioration range and the potential of the negative electrode of the battery 10 enters the negative electrode deterioration range. Even if the lower limit voltage is lowered by the offset amount in the initial state and the potential of the positive electrode enters the positive electrode deterioration range or the potential of the negative electrode enters the negative electrode deterioration range, there are cases in which the potential of the positive electrode does not enter the positive electrode deterioration range and the potential of the negative electrode does not enter the negative electrode deterioration range even if the lower limit voltage is lowered by the offset amount at EOL. Therefore, the offset amount may be such a value. In addition, since the larger the offset amount, the larger the usable battery capacity, the offset amount is preferably a value such that when the lower limit voltage is lowered by the offset amount in the initial state, the potential of the positive electrode of the battery 10 falls within the positive electrode deterioration range, and the potential of the negative electrode falls within the negative electrode deterioration range. Note that the threshold value TH6 is an example of a first threshold value. The threshold value TH7 is an example of a second threshold value.

[0053] Processor 21 may obtain the offset amount from SOH obtained in (A) without obtaining deviation amount G1. Processor 21 obtains the offset amount from SOH by using a table or a function included in battery database 241, for example. Moreover, the processor 21 may not calculate the deviation amount G1, but may calculate the offset amount from at least one of the positive electrode deterioration amount K1, the negative electrode deterioration amount K2, and the lithium trap amount TK1 calculated in (B). The processor 21 calculates the offset amount using at least one of the positive electrode deterioration amount K1, the negative electrode deterioration amount K2, and the lithium trap amount TK1, using a table or a function included in the battery database 241, for example.

[0054] In step ST14, the processor 21 sets the lower limit voltage of the battery 10 to the voltage obtained by subtracting the offset amount calculated in step ST13 from the lower limit voltage in the initial state. FIG. 3 shows a potential difference V21 as an example of the lower limit voltage set in step ST14. The potential difference V21 can be expressed by the following formula (3). V21 = V11 - (offset amount) (3)

[0055] Note that the capacitance Q21 indicates the capacitance of the battery 10 at the lower limit voltage V21 at EOL when the lower limit voltage is V21. At EOL, when the lower limit voltage is V21, the capacitance Q21 is 0% in terms of SOC. That is, the capacitance Q21 is the capacitance in the fully discharged state at EOL when the lower limit voltage at EOL is V21. The battery capacitance F21 indicates the battery capacitance of the battery 10 at EOL when the lower limit voltage is V21. Note that F21 = Q23 - Q21. Also, in FIG. 3, the magnitude relationship between Q11 and Q21 is Q11 < Q21, but this is not always the case.

[0056] The relationship between the terminal voltage and the degradation rate in the initial state and at EOL is shown in FIG. 4. FIG. 4 is a graph showing an example of the terminal voltage - degradation rate characteristics. The curve C31 is an example of the terminal voltage - degradation rate curve in the initial state. The curve C32 is an example of the terminal voltage - degradation rate curve at EOL. The voltage V31 indicates the difference between the upper limit voltage and the lower limit voltage in the initial state, and V31 = V12 - V11. The voltage V32 indicates the difference between the upper limit voltage and the lower limit voltage at EOL, and V32 = V23 - V21.

[0057] As shown in FIG. 4, at EOL, compared with the initial state, the degradation rate in the low voltage range is slow. Thus, the battery 10 has a slower degradation rate in the low voltage range as the degradation progresses. Therefore, if the lower limit voltage is V21 in the initial state, the degradation rate will become fast. In contrast, at EOL, even if the lower limit voltage is V21, the degradation rate is the same as when the lower limit voltage is V11 in the initial state.

[0058] The battery control system 1 of the embodiment lowers the lower limit voltage when the battery 10 is degraded more than a predetermined level. Thereby, the battery control system 1 of the embodiment can increase the battery capacitance of the degraded battery 10.

[0059] Furthermore, the battery control system 1 of the embodiment lowers the lower limit voltage to a range in which the positive electrode potential of the battery 10 does not fall into the positive electrode deterioration range even when the terminal voltage of the battery 10 is at the lower limit voltage. In this way, the battery control system 1 of the embodiment suppresses an increase in the deterioration rate of the battery 10 caused by lowering the lower limit voltage.

[0060] Furthermore, the battery control system 1 of the embodiment lowers the lower limit voltage to a range in which the negative electrode potential of the battery 10 does not fall into the negative electrode deterioration range even when the terminal voltage of the battery 10 is at the lower limit voltage. In this way, the battery control system 1 of the embodiment suppresses an increase in the deterioration rate of the battery 10 caused by lowering the lower limit voltage.

[0061] Furthermore, the battery control system 1 of the embodiment determines the offset amount using the deviation amount G1, thereby improving the accuracy with which the battery control system 1 of the embodiment determines the offset amount, and preventing the lower limit voltage of the battery 10 from being lowered too much.

[0062] The above embodiment can be modified as follows. The battery 10 may be a secondary battery other than a lithium ion secondary battery. For example, the battery control system of the embodiment is considered to be similarly practicable in the case where a rocking chair type secondary battery or the like is used instead of a lithium ion secondary battery. The battery control system of the embodiment may also include an electricity storage device other than a secondary battery instead of the battery 10. For example, the battery control system of the embodiment is considered to be similarly practicable in the case where a lithium ion capacitor or the like is used instead of a secondary battery.

[0063] The processor 21 may also change the upper limit voltage of the battery 10. The processor 21 may use known conditions as conditions for changing the upper limit voltage. The processor 21 may use a known method as a method for determining the value of the upper limit voltage after the change.

[0064] The processor 21 may implement part or all of the processes implemented by the programs in the above-described embodiments by using a hardware circuit configuration.

[0065] The program for implementing the process of the embodiment is transferred, for example, in a state stored in the device. However, the device may be transferred without the program stored therein. The program may then be transferred separately and written to the device. The program may be transferred, for example, by recording it on a removable storage medium or by downloading it via a network such as the Internet or a LAN (local area network).

[0066] Although the embodiment of the present invention has been described above, it is merely an example and does not limit the scope of the present invention. The embodiment of the present invention can be implemented in various forms without departing from the gist of the present invention. [Explanation of symbols]

[0067] 1 Battery control system 10 batteries 20 Control device 21 Processors 22 ROM 23 RAM 24 Auxiliary storage 25 Bus 30 Voltmeter 40 ammeter 50 thermometer 60 Timer 241 Battery Database

Claims

1. A control unit is provided which calculates a deviation of a negative electrode potential due to deterioration of a power storage device relative to a capacity of the power storage device, and lowers a lower limit voltage of discharge of the power storage device based on a deterioration state of the power storage device within a range in which the positive electrode potential of the power storage device does not become equal to or lower than a first threshold value, or within a range in which the negative electrode potential of the power storage device does not become equal to or higher than a second threshold value; The power storage device control device, wherein the first threshold value is a range of potential of a positive electrode of the power storage device in which deterioration of the positive electrode occurs particularly quickly at EOL, and the second threshold value is a range of potential of a negative electrode of the power storage device in which deterioration of the negative electrode occurs particularly quickly at EOL.

2. The power storage device control device according to claim 1 , wherein the control unit lowers the lower limit voltage within a range in which the positive electrode potential does not become equal to or lower than the first threshold value.

3. The power storage device control device according to claim 2 , wherein the control unit lowers the lower limit voltage in a range in which the positive electrode potential does not become equal to or lower than a first threshold value and the negative electrode potential does not become equal to or higher than a second threshold value.

4. A power storage device; an electricity storage device control device that calculates a deviation amount of a negative electrode potential of the electricity storage device due to deterioration of the electricity storage device with respect to a capacity of the electricity storage device, and reduces a lower limit voltage of discharge of the electricity storage device based on a deterioration state of the electricity storage device within a range in which a positive electrode potential of the electricity storage device does not become equal to or lower than a first threshold value or within a range in which a negative electrode potential of the electricity storage device does not become equal to or higher than a second threshold value; The first threshold is a range of potential of a positive electrode of the power storage device in which deterioration of the positive electrode occurs particularly quickly at EOL, and the second threshold is a range of potential of a negative electrode of the power storage device in which deterioration of the negative electrode occurs particularly quickly at EOL.

5. A deviation of a negative electrode potential due to deterioration of a power storage device relative to a capacity of the power storage device is calculated, and a lower limit voltage of discharge of the power storage device is lowered based on a deterioration state of the power storage device within a range in which the positive electrode potential of the power storage device does not become equal to or lower than a first threshold value, or within a range in which the negative electrode potential of the power storage device does not become equal to or higher than a second threshold value; A method for controlling an electricity storage device, wherein the first threshold value is a range of potential of a positive electrode of the electricity storage device in which deterioration of the positive electrode occurs particularly quickly at EOL, and the second threshold value is a range of potential of a negative electrode of the electricity storage device in which deterioration of the negative electrode occurs particularly quickly at EOL.

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