Charging control device

Abstract

The purpose of the present invention is to accurately assess the need for charging by a recovery charge / discharge mode. Thi charge control device charges a lithium metal battery, which is a secondary battery in which lithium metal is used in a negative electrode, using a prescribed normal charge mode and a recovery charge / discharge mode. In the recovery charge / discharge mode, the lithium metal battery is temporarily discharged and then is charged for a longer time than in the normal charge mode. A detection unit detects a battery voltage, which is the voltage of the lithium metal battery. A calculation unit calculates the self-discharge rate of the lithium metal battery on the basis of a change in the battery voltage. A recording unit records a history of the self-discharge rate. An assessment unit assesses the need for charging by the recovery charge / discharge mode on the basis of a change in the self-discharge rate in time series in the history.

Description

[Technical field]

[0001] The present invention relates to a charge control device that controls charging of a secondary battery. [Background technology]

[0002] In recent years, electric vehicles such as EVs and HEVs have become more widespread from the viewpoint of reducing carbon dioxide emissions and reducing adverse effects on the global environment. Lithium-ion batteries are often installed in electric vehicles. Lithium-ion batteries have an electrolyte solution containing lithium ions between a positive electrode and a negative electrode, and a separator that separates the electrolyte solution into a positive electrode side and a negative electrode side.

[0003] Currently, most lithium-ion batteries use carbon in the anode, but the use of lithium metal in the anode is being considered to improve the energy density. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent No. 10,727,545 Summary of the Invention [Problem to be solved by the invention]

[0005] Compared to conventional lithium ion batteries that use carbon in the anode, lithium metal batteries that use lithium metal in the anode have the following problems:

[0006] That is, in a conventional lithium ion battery, lithium ions in the electrolyte are stored between graphite layers during charging, and the stored lithium ions are released into the electrolyte during discharging. On the other hand, in a lithium metal battery, lithium ions in the electrolyte are deposited as lithium metal on the negative electrode during charging, and the lithium metal on the negative electrode is dissolved into the electrolyte as lithium ions during discharging. Therefore, repeated charging and discharging causes repeated deposition and dissolution of lithium metal.

[0007] This repeated precipitation and dissolution causes the lithium metal in the negative electrode, which was neatly and orderly crystallized when new, to become porous and grow into dendrites. This forms a micro-short circuit between the negative and positive electrodes, increasing the self-discharge rate of the lithium metal battery.

[0008] If this is left unchecked, the short circuit will progress and the self-discharge rate will accelerate. As a result, for example, when an electric vehicle is in operation, the voltage of the lithium metal battery will drop quickly, reducing the range of the electric vehicle.

[0009] One possible solution to this problem is to fully discharge the lithium metal battery, i.e., to fully dissolve the lithium metal in the negative electrode, and then charge the battery slowly over a period of time using a recovery charge-discharge mode, which allows the lithium metal in the negative electrode to crystallize into a larger size.

[0010] However, the rate at which a micro-short circuit forms varies depending on various conditions of the lithium metal battery, such as the negative electrode, positive electrode, electrolyte, separator, and charge / discharge conditions, etc. Therefore, it is difficult to determine when charging in the recovery charge / discharge mode should be performed, that is, to determine whether charging in the recovery charge / discharge mode is necessary at each time.

[0011] Specifically, for example, it is possible to determine that there is a micro-short circuit and that charging in a recovery charge / discharge mode is necessary on the condition that the battery voltage, such as the open circuit voltage of the lithium metal battery, is lower than a threshold value. However, in general, with various batteries including lithium metal batteries, when the storage capacity is large, the drop in open circuit voltage is small even if a micro-short circuit path is formed. Therefore, compared to the variation in battery voltage between lithium metal batteries, the magnitude of the voltage drop due to a micro-short circuit is not large enough, making it difficult to determine the presence of a micro-short circuit and therefore difficult to determine whether charging in a recovery charge / discharge mode is necessary.

[0012] The present invention has been made in consideration of the above circumstances, and has an object to accurately determine whether charging in a recovery charge / discharge mode is necessary. [Means for solving the problem]

[0013] The present inventors have found that the necessity of charging in the recovery charge / discharge mode can be accurately determined by judging the necessity based on the time series change in the self-discharge rate, rather than judging the necessity based on the magnitude of the battery voltage itself or the magnitude of the self-discharge rate itself, and have arrived at the present invention. The present invention is a charge control device as described below in (1) to (9).

[0014] (1) A charge control device for charging a lithium metal battery as a secondary battery using lithium metal as a negative electrode in a predetermined normal charge mode and a recovery charge / discharge mode in which the lithium metal battery is discharged once and then charged for a longer period of time than in the normal charge mode, A detection unit that detects a battery voltage as a voltage of the lithium metal battery; a calculation unit that calculates a self-discharge rate of the lithium metal battery based on the change in the battery voltage; A recording unit that records a history of the self-discharge rate; a determination unit that determines whether or not charging in the recovery charge / discharge mode is necessary based on a change in the self-discharge rate over time in the history; A charging control device comprising:

[0015] According to this configuration, the necessity of charging in the recovery charge / discharge mode is determined not based on the magnitude of the battery voltage itself or the magnitude of the self-discharge rate itself, but based on the change in the self-discharge rate over time. Therefore, since the object of comparison is the past self-discharge rate, the determination can be made with high accuracy even when there is a variation in the battery voltage between lithium metal batteries. As described above, according to this configuration, the necessity of charging in the recovery charge / discharge mode can be determined with high accuracy.

[0016] (2) The charge control device according to (1), wherein the determination unit determines that charging in the recovery charge / discharge mode is necessary on condition that the self-discharge rate is increasing.

[0017] Lithium metal batteries have a relatively high self-discharge rate when new, but as they begin to be used, the self-discharge rate often gradually decreases as the electrodes and other components gradually become familiar with each other. However, when a micro-short circuit begins to occur, the self-discharge rate begins to increase. With this configuration, it is possible to determine when this timing occurs and when charging in the recovery charge / discharge mode is necessary.

[0018] (3) a switching unit that allows switching from the normal charging mode to the recovery charging / discharging mode when the determination unit determines that charging in the recovery charging / discharging mode is necessary; The charging control device according to (1) or (2),

[0019] According to this configuration, switching from the normal charging mode to the recovery charging / discharging mode can be permitted only when charging in the recovery charging / discharging mode is necessary.

[0020] (4) a maintenance attention unit that issues a maintenance attention when the determination unit determines that charging in the recovery charge / discharge mode is necessary; The charging control device according to any one of (1) to (3), comprising:

[0021] According to this configuration, when charging in the recovery charge / discharge mode is necessary, it is possible to notify the user, etc., to that effect.

[0022] (5) A temperature detection unit that detects a battery temperature as the temperature of the lithium metal battery, the calculation unit calculates the self-discharge rate at a predetermined temperature and a predetermined state of charge based on the detected battery voltage and the detected battery temperature. The charging control device according to any one of (1) to (4).

[0023] According to this configuration, the error in the self-discharge rate caused by the temperature difference can be corrected, and therefore it is possible to more accurately determine whether charging in the recovery charge / discharge mode is necessary.

[0024] (6) The lithium metal battery is mounted on an electric vehicle, the determination unit determines whether or not charging in the recovery charge / discharge mode is necessary based on a change in the self-discharge rate in response to an increase in one of a traveling distance and an operating time of the electric vehicle. The charging control device according to any one of (1) to (5) above.

[0025] The self-discharge rate is likely to increase due to an increase in mileage or operation time. In this regard, the determination unit can determine whether charging in the recovery charge / discharge mode is necessary based on a change in the self-discharge rate with respect to an increase in either the mileage or the operation time, and can transition to the recovery charge / discharge mode. Therefore, compared to determining whether charging in the recovery charge / discharge mode is necessary based on a change in the self-discharge rate with a mere increase in the elapsed time since the battery was new, the determination unit can more accurately determine whether charging in the recovery charge / discharge mode is necessary and transition to the recovery charge / discharge mode.

[0026] (7) a temperature detection unit that detects a battery temperature as the temperature of the lithium metal battery; a table storing a discharge current value as a current value during discharge in the recovery charge / discharge mode and a discharge time as a time required for the discharge, for each of a plurality of self-discharge rate categories and for each of a plurality of battery temperature categories; a setting unit that sets the discharge current value and the discharge time in the recovery charge / discharge mode based on the self-discharge rate calculated by the calculation unit, the battery temperature detected by the temperature detection unit, and the table; The charging control device according to any one of (1) to (6), comprising:

[0027] The optimal discharge current value and discharge time differ depending on the self-discharge rate and the battery temperature. In this regard, the setting unit sets the discharge current value and discharge time based on the table in accordance with the self-discharge rate and the battery temperature, making it easier to set the optimal discharge current value and discharge time.

[0028] (8) a temperature control unit that allows charging in the recovery charge / discharge mode on condition that the temperature of the lithium metal battery is equal to or higher than a predetermined temperature; The charging control device according to any one of (1) to (7) above, comprising:

[0029] From the viewpoint of protecting the lithium metal battery, it is preferable that discharging in the recovery charge / discharge mode is performed at a temperature equal to or higher than a predetermined temperature. In this regard, the temperature control unit allows charging in the recovery charge / discharge mode on the condition that the temperature of the lithium metal battery is equal to or higher than a predetermined temperature, so that the lithium metal battery can be efficiently protected.

[0030] (9) a maintenance attention unit that issues a maintenance attention when the determination unit determines that charging in the recovery charge / discharge mode is necessary, and releases the maintenance attention when discharging in the recovery charge / discharge mode is completed; The charging control device according to any one of (1) to (8), comprising:

[0031] According to this configuration, the maintenance attention unit can automatically send and cancel a maintenance attention. Effect of the Invention

[0032] As described above, the configuration of (1) makes it possible to accurately determine whether charging in the recovery charge / discharge mode is necessary. Furthermore, the configurations of (2) to (9) that refer to (1) above provide additional effects. [Brief description of the drawings]

[0033] [Figure 1] 1 is a configuration diagram showing an electric vehicle according to a first embodiment. [Diagram 2] 4 is a graph showing an example of a change in battery voltage. [Diagram 3] 1 is a graph showing an example of a change in self-discharge rate. [Figure 4] 10 is a flowchart showing a flow of charging in a recovery charge / discharge mode. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiment, and can be appropriately modified and implemented without departing from the spirit of the invention.

[0035] [First embodiment] 1 is a configuration diagram showing an electric vehicle 200 of this embodiment. The electric vehicle 200 includes a motor 220 that serves as a power source for the electric vehicle 200, a lithium metal battery 210 that serves as a secondary battery that supplies power to the motor 220, and a charge control device 100 that controls charging of the lithium metal battery 210.

[0036] The lithium metal battery 210 has a positive electrode, a negative electrode, an electrolyte disposed between the positive electrode and the negative electrode, and a separator that separates the electrolyte into a positive electrode side and a negative electrode side.

[0037] The positive electrode is composed of a layer containing a positive electrode active material, a binder, and a conductive additive. The positive electrode active material is, for example, lithium cobalt oxide (LiCoO 2 ), lithium nickel oxide (LiNiO 2 ), LiNi p Mnq Co r O 2 (p+q+r=1), LiNi p Al q Co r O 2 (p+q+r=1), lithium manganate (LiMn 2 O 4 ) In addition, other positive electrode active materials include, for example, Li 1 +xMn 2 -x-yMyO 4 (x+y=2, M=at least one selected from Al, Mg, Co, Fe, Ni, and Zn). Other examples of the positive electrode active material include lithium titanate (oxide containing Li and Ti), lithium metal phosphate (LiMPO 4 , M=at least one selected from Fe, Mn, Co, and Ni). Preferably, the positive electrode active material is Li 1 Ni 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) is used.

[0038] The negative electrode has a negative electrode base material such as a negative electrode current collector or lithium foil, and a lithium metal layer formed by depositing lithium metal on the negative electrode base material. The lithium metal battery 210 has a much higher energy density than conventional lithium ion batteries.

[0039] The electrolytic solution includes an organic solvent and an electrolyte. For example, the organic solvent may be a hydrofluoroether such as 1,1,2,2-tetrafluoro-1-(2,2,2-trifluoroethoxy)ethane, methyl nonafluoroisobutyl ether, or methyl nonafluorobutyl ether, which is a fluorine-substituted chain hydrocarbon, as the first organic solvent. For example, the organic solvent may be 1,2-dimethoxyethane (DME), ethylene carbonate (EC), propylene carbonate (PC), sulfolane (SL), dimethyl carbonate (DMC), diethyl carbonate (DEC), or ethyl methyl carbonate (EMC). These first and second organic solvents may be used in combination.

[0040] The electrolyte is a source of lithium ions, which are a charge transfer medium, and contains a lithium salt. Examples of the lithium salt include LiFSI and LiPF 6 , LiBF 4 , LiClO 4 , LiAsF 6 , LiCF 3 SO 3 , LiC(CF 3 SO 2 ) 3 , LiN(CF 3 SO 2 ) 2 (LiTFSI), LiN(FSO 2 ) 2 (LiFSI), and LiBC 4 O 8 Among them, LiFSI can be preferably used as the electrolyte.

[0041] The lithium metal battery 210 supplies power to the motor 220 during power running, such as when accelerating the electric vehicle 200 or maintaining the vehicle speed on an uphill road, etc. On the other hand, during regeneration, such as when the electric vehicle 200 decelerates or when acceleration is suppressed on a downhill road, the lithium metal battery 210 is charged by the power supplied from the motor 220.

[0042] The charge control device 100 controls charging when the lithium metal battery 210 is charged by a charging facility. Specifically, the charge control device 100 charges the lithium metal battery 210 in a predetermined normal charging mode and a predetermined recovery charging / discharging mode.

[0043] Charging in normal charging mode is performed using charging equipment at home, at a charging spot, etc. In normal charging mode, CC charging is performed with a constant charging current, and then CV charging is performed with a constant charging voltage.

[0044] Charging in the recovery charge / discharge mode is performed by charging equipment at a dealer or the like. In the recovery charge / discharge mode, a control program is executed for performing maintenance to recover the capacity, resistance, and self-discharge performance of the lithium metal battery 210, or for performing maintenance to prevent performance degradation. Specifically, in the recovery charge / discharge mode, a charge / discharge control program and a battery temperature control program are executed as programs separate from programs that perform current limiting and temperature control during vehicle running or charging.

[0045] Specifically, in the recovery charge / discharge mode, the lithium metal battery 210 is first fully discharged, and then the lithium metal battery 210 is charged for a longer period of time than in the normal charge mode. Specifically, in the recovery charge / discharge mode, discharge is performed, CC charging is performed, and then CV charging is performed. The charging current in the CC charging in the recovery charge / discharge mode is smaller than the charging current in the CC charging in the normal charge mode. More specifically, in the recovery charge / discharge mode, the lithium metal battery 210 is fully discharged at about 0.2 to 1 C until the SOC is about 20 to 0%, and then charged at about 0.05 to 0.3 C until the SOC is 100%.

[0046] The charging control device 100 is mainly composed of an ECU equipped with a CPU, RAM, ROM, etc., and has a detection unit 10, a calculation unit 20, a recording unit 30, a determination unit 40, a control unit 50, and a maintenance attention unit 60.

[0047] The detection unit 10 has a voltage detection unit 11, a current detection unit 12, and a temperature detection unit 13. The voltage detection unit 11 has a voltage sensor and detects a "battery voltage" as the terminal voltage of the lithium metal battery 210. The current detection unit 12 has a current sensor and detects a "battery current" as the current flowing through the lithium metal battery 210. The temperature detection unit 13 has a temperature sensor and detects a "battery temperature" as the temperature of the lithium metal battery 210.

[0048] The calculation unit 20 calculates a "self-discharge rate Ds" as the self-discharge rate of the lithium metal battery 210 at a predetermined temperature, such as 25°C, and at a predetermined charge state, such as a fully charged state, based on the battery voltage and battery temperature detected by the detection unit 10. The self-discharge rate Ds may be, for example, the amount of voltage decrease per unit time, i.e., the voltage decrease rate, or may be the amount of decrease in the amount of stored electricity per unit time, i.e., the rate of decrease in the amount of stored electricity.

[0049] The calculation unit 20 has a provisional calculation unit 21 and a correction unit 22. The provisional calculation unit 21 calculates a "provisional self-discharge rate Dst" as a self-discharge rate at the current battery temperature and a predetermined charge state, based on a change in the battery voltage Vb. The correction unit 22 calculates the self-discharge rate Ds described above by correcting the provisional self-discharge rate Dst based on the current battery temperature.

[0050] The recording unit 30 records the history of the self-discharge rate Ds by sequentially storing the self-discharge rate Ds or information related thereto.

[0051] The determination unit 40 determines whether or not charging in the recovery charge / discharge mode is necessary based on the change in the self-discharge rate Ds over time in the history. Hereinafter, "charging in the recovery charge / discharge mode is necessary" will simply be referred to as "recovery charge / discharge is necessary." The determination unit 40 determines that recovery charge / discharge is necessary on the condition that, for example, in the most recent specified period, the change in the self-discharge rate Ds with respect to an increase in the travel distance or operation time of the electric vehicle 200 can be determined to be positive even taking into account errors, etc., that is, on the condition that it can be determined that the self-discharge rate Ds is increasing even taking into account errors, etc. The reason for this determination will be described later.

[0052] The control unit 50 controls so that charging is performed in the normal charging mode when the determination unit 40 does not determine that recovery charging / discharging is necessary, and so that charging is performed in the recovery charging / discharging mode when the determination unit 40 determines that recovery charging / discharging is necessary. Specifically, the control unit 50 has a switching unit 51, a setting unit 52, and a temperature control unit 53. The switching unit 51 turns on a recovery charging / discharging flag on the condition that the determination unit 40 determines that recovery charging / discharging is necessary. This allows switching from the normal charging mode to the recovery charging / discharging mode.

[0053] The setting unit 52 sets a "discharge current value" as the current value during discharge in the recovery charge / discharge mode, and a "discharge time" as the time required for the discharge. Specifically, the setting unit 52 has a table 52a that stores the discharge current value and the discharge time for each of a plurality of self-discharge rate Ds categories and each of a plurality of battery temperature categories. The setting unit 52 sets the discharge current value and the discharge time based on the self-discharge rate Ds calculated by the calculation unit 20, the battery temperature detected by the temperature detection unit 13, and the table 52a.

[0054] Temperature control unit 53 allows charging in the recovery charge / discharge mode on condition that the battery temperature is equal to or higher than a predetermined temperature, such as equal to or higher than 20° C. More specifically, temperature control unit 53 allows charging in the recovery charge / discharge mode on condition that the battery temperature is within a predetermined temperature range, such as 20° C. to 25° C.

[0055] The maintenance attention unit 60 issues a maintenance attention when the determination unit 40 determines that recovery charging / discharging is required. The maintenance attention may be, for example, a visual one such as a maintenance attention lamp, or an auditory one, or both. An auditory one may, for example, sound a maintenance attention sound or announce the need for recovery charging / discharging at a predetermined timing, such as when the main power supply of the electric vehicle 200 is turned on. The maintenance attention unit 60 cancels the maintenance attention when discharging in the recovery charging / discharging mode is completed.

[0056] Next, the reason why the determining unit 40 determines that recovery charge / discharge is required based on an increase in the self-discharge rate Ds will be described with reference to FIG. 2 and FIG.

[0057] 2 is a graph showing an example of the transition of the battery voltage Vb. In CC charging in normal charging mode, a predetermined amount of electricity is stored per unit time, and the battery voltage Vb increases. In the subsequent CV charging, the charging speed slows down as the battery voltage Vb approaches the full charge voltage, and the battery voltage Vb gradually reaches the full charge voltage. When the full charge voltage is reached, charging is stopped and the voltage detection unit 11 detects the open circuit voltage as the battery voltage Vb.

[0058] After charging is stopped, the charge control device 100 detects the open circuit voltage as the battery voltage Vb again by the voltage detection unit 11, and then stops. After that, even if the power of the lithium metal battery 210 is not used, the battery voltage Vb gradually decreases due to self-discharge. During this time, the charge control device 100 temporarily starts up every predetermined time ti, such as every few hours, and detects the open circuit voltage as the battery voltage Vb by the voltage detection unit 11. Based on the changes in the open circuit voltage, the calculation unit 20 calculates the self-discharge rate Ds. After that, when the user turns on the main power switch of the electric vehicle 200, the power of the lithium metal battery 210 is consumed, and the battery voltage Vb decreases.

[0059] FIG. 3 is a graph showing an example of the transition of the self-discharge rate Ds of the lithium metal battery 210. When the lithium metal battery 210 is new, the self-discharge rate Ds is relatively high, but when it starts to be used, the electrodes and the like gradually become familiar, and the self-discharge rate Ds gradually decreases. However, as the battery is repeatedly charged and discharged, the lithium metal of the negative electrode, which was crystallized neatly and beautifully when it was new, becomes porous, causing dendritic growth, and a micro-short circuit is formed between the negative electrode and the positive electrode. As the micro-short circuit progresses, the self-discharge rate Ds starts to increase. Therefore, as described above, the determination unit 40 determines that recovery charge / discharge is required based on the increase in the self-discharge rate Ds. In other words, the determination unit 40 determines that recovery charge / discharge is required at the timing of the inflection point where the slope of the self-discharge rate Ds changes from negative to positive.

[0060] 3 indicates the number of years elapsed, but preferably indicates the travel distance or operation time of the electric vehicle 200. In other words, it is preferable to determine whether charging in the recovery charge / discharge mode is necessary based on the slope of the change in the self-discharge rate Ds relative to the increase in the travel distance or operation time. Therefore, the determination unit 40 employs this preferable aspect as described above.

[0061] 4 is a flow chart showing the flow of charging in the recovery charge / discharge mode. Note that the charging mode in the initial setting of this flow is the normal charging mode. In this flow, first, in S11, the detection unit 10 detects the battery voltage Vb and the battery temperature.

[0062] Next, in S21, the provisional calculation unit 21 of the calculation unit 20 calculates a provisional self-discharge rate Dst based on the detected change in the battery voltage Vb. Next, in S22, the correction unit 22 of the calculation unit 20 corrects the provisional self-discharge rate Dst based on the battery temperature to calculate a self-discharge rate Ds.

[0063] Next, in S31, the recording unit 30 stores the self-discharge rate Ds. In this way, the history of the self-discharge rate Ds is successively stored.

[0064] Next, in S41, the determination unit 40 calculates the slope of the self-discharge rate Ds based on the history of the self-discharge rate Ds. Next, in S42, the determination unit 40 determines whether the slope is positive or not, that is, whether the self-discharge rate Ds is increasing or not. If the determination in S42 is negative, the flow ends without switching the charging mode from the normal charging mode to the recovery charging / discharging mode, that is, while maintaining the charging mode in the normal charging mode. On the other hand, if the determination in S42 is positive, the flow proceeds to S51.

[0065] In S51, the switching unit 51 of the control unit 50 turns on the recovery charge / discharge flag. This allows charging in the recovery charge / discharge mode. In the following S61, the maintenance attention unit 60 issues a maintenance attention. Note that the order of S51 and S61 may be reversed, or they may be performed simultaneously.

[0066] Then, in S71, the user brings the electric vehicle 200 to a dealer. At this time, since the recovery charge / discharge flag is ON, a dealer worker can perform charging in the recovery charge / discharge mode by performing a predetermined operation. Then, the charging actually starts.

[0067] In the recovery charge / discharge mode, first, in S52, the setting unit 52 of the control unit 50 sets a discharge current value and a discharge time. Next, in S53, the control unit 50 causes discharging to be performed based on the set discharge current value and discharge time. At this time, the charging is started by the temperature control unit 53 on the condition that the battery temperature is within a predetermined temperature range, such as 20 to 25°C. This discharging causes most of the lithium metal layer in the negative electrode of the lithium metal battery 210 to dissolve into the electrolyte.

[0068] When the discharge is completed, in S54, the switching unit 51 turns off the recovery charge / discharge flag, and in S62, the maintenance attention unit 60 cancels the maintenance attention. Next, in S55, the control unit 50 causes charging to be performed for a longer time than in the normal charging mode, that is, at a slower rate than in the normal charging mode. This causes lithium metal to crystallize to a larger size in the negative electrode. After charging is completed, the flow ends.

[0069] The configuration and effects of this embodiment are summarized below.

[0070] The determination unit 40 determines whether charging in the recovery charge / discharge mode is necessary based on the change in the self-discharge rate Ds over time, rather than based on the magnitude of the battery voltage Vb itself or the magnitude of the self-discharge rate Ds itself. Therefore, since the object to be compared is the past self-discharge rate Ds, the determination can be made with high accuracy even when there is variation in the battery voltage Vb between the lithium metal batteries 210.

[0071] When the lithium metal battery 210 is new, the self-discharge rate Ds is relatively high, but as the battery begins to be used, the electrodes and other components gradually become familiar with each other, and the self-discharge rate Ds often gradually decreases. However, when a micro-short circuit begins to occur, the self-discharge rate Ds starts to increase. In this regard, the determination unit 40 determines that recovery charging and discharging is necessary on the condition that the self-discharge rate Ds is increasing. Therefore, the occurrence of a micro-short circuit can be detected based on the self-discharge rate Ds changing from a decrease to an increase.

[0072] The switching unit 51 allows switching from the normal charging mode to the recovery charging / discharging mode when the determining unit 40 determines that recovery charging / discharging is required. Therefore, switching from the normal charging mode to the recovery charging / discharging mode can be permitted only when charging in the recovery charging / discharging mode is required.

[0073] The maintenance attention unit 60 issues a maintenance attention when the determination unit 40 determines that recovery charging / discharging is necessary. Therefore, when charging in the recovery charging / discharging mode is necessary, it is possible to inform the user, etc., of this fact.

[0074] The calculation unit 20 calculates the self-discharge rate Ds at a predetermined temperature such as 25°C and a predetermined charge state such as a fully charged state based on the detected battery voltage Vb and the detected battery temperature. This makes it possible to correct errors in the self-discharge rate Ds caused by differences in battery temperature. This makes it possible to more accurately determine whether charging in the recovery charge / discharge mode is necessary.

[0075] The self-discharge rate Ds is likely to increase due to an increase in the travel distance or operation time of the electric vehicle 200. In this regard, the determination unit 40 determines whether charging in the recovery charge / discharge mode is necessary based on a change in the self-discharge rate with respect to an increase in either the travel distance or the operation time. This allows for a more accurate determination than when determining whether charging in the recovery charge / discharge mode is necessary based on a change in the self-discharge rate Ds with a mere increase in the elapsed time since the battery was new.

[0076] The optimal discharge current value and discharge time during discharge in the recovery charge / discharge mode vary depending on the self-discharge rate Ds and the battery temperature. In this regard, the setting unit 52 sets the discharge current value and discharge time based on the self-discharge rate Ds calculated by the calculation unit, the battery temperature detected by the temperature detection unit 13, and table 52a. This makes it easier to set the optimal discharge current value and discharge time.

[0077] From the viewpoint of protecting the lithium metal battery 210, it is preferable that discharging in the recovery charge / discharge mode is performed at a predetermined temperature or higher. In this regard, the temperature control unit 53 allows charging in the recovery charge / discharge mode on the condition that the battery temperature is at a predetermined temperature or higher, so that the lithium metal battery 210 can be protected efficiently.

[0078] The maintenance attention unit 60 issues a maintenance attention when the determination unit 40 determines that recovery charging / discharging is required, and cancels the maintenance attention when discharging in the recovery charging / discharging mode is completed. Therefore, the maintenance attention unit 60 can automatically issue and cancel the maintenance attention.

[0079] [Modification form] The above embodiment can be modified as follows. The determination unit 40 may determine that recovery charge / discharge is necessary at a timing slightly earlier or later than the inflection point. That is, the determination unit 40 may determine that recovery charge / discharge is necessary on the condition that the slope of the self-discharge rate Ds is greater than a threshold value that is slightly smaller or slightly larger than zero. [Explanation of symbols]

[0080] 10. Detection unit 11 Voltage detection section 13 Temperature detection unit 20 Arithmetic section 21 Temporary Calculation Section 22 Correction section 30 Recording Section 40 Judgment section 50 Control section 51 Switching section 52 Setting section 52a Table 53 Temperature control unit 60 Maintenance Attention Department 100 Charging control device 200 Electric Vehicles 210 Lithium metal battery Vb Battery voltage Ds self-discharge rate

Claims

1. A charge control device for charging a lithium metal battery as a secondary battery using lithium metal as a negative electrode in a predetermined normal charging mode and a recovery charge / discharge mode in which the lithium metal battery is discharged once and then charged for a longer period of time than in the normal charging mode, A detection unit that detects a battery voltage as a voltage of the lithium metal battery; a calculation unit that calculates a self-discharge rate of the lithium metal battery based on the change in the battery voltage; A recording unit that records a history of the self-discharge rate; a determination unit that determines whether or not charging in the recovery charge / discharge mode is necessary based on a change in the self-discharge rate over time in the history; A charging control device comprising:

2. The charge control device according to claim 1 , wherein the determination unit determines that charging in the recovery charge / discharge mode is necessary on condition that the self-discharge rate is increasing.

3. a switching unit that allows switching from the normal charging mode to the recovery charging / discharging mode when the determination unit determines that charging in the recovery charging / discharging mode is necessary; The charge control device according to claim 1 or 2, further comprising:

4. a maintenance attention unit that issues a maintenance attention when the determination unit determines that charging in the recovery charge / discharge mode is necessary; The charge control device according to claim 1 or 2, further comprising:

5. a temperature detection unit that detects a battery temperature as the temperature of the lithium metal battery; the calculation unit calculates the self-discharge rate at a predetermined temperature and a predetermined state of charge based on the detected battery voltage and the detected battery temperature. The charge control device according to claim 1 or 2.

6. The lithium metal battery is mounted on an electric vehicle, the determination unit determines whether or not charging in the recovery charge / discharge mode is necessary based on a change in the self-discharge rate in response to an increase in one of a traveling distance and an operating time of the electric vehicle. The charge control device according to claim 1 or 2.

7. a temperature detection unit that detects a battery temperature as the temperature of the lithium metal battery; a table storing a discharge current value as a current value during discharge in the recovery charge / discharge mode and a discharge time as a time required for the discharge, for each of a plurality of self-discharge rate categories and for each of a plurality of battery temperature categories; a setting unit that sets the discharge current value and the discharge time in the recovery charge / discharge mode based on the self-discharge rate calculated by the calculation unit, the battery temperature detected by the temperature detection unit, and the table; The charge control device according to claim 1 or 2, further comprising:

8. a temperature control unit that allows charging in the recovery charge / discharge mode on condition that the temperature of the lithium metal battery is equal to or higher than a predetermined temperature; The charge control device according to claim 1 or 2, further comprising:

9. a maintenance attention unit that issues a maintenance attention when the determination unit determines that charging in the recovery charge / discharge mode is necessary, and releases the maintenance attention when discharging in the recovery charge / discharge mode is completed; The charge control device according to claim 1 or 2, further comprising:

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