Battery degradation state estimation device, degradation suppression system, degradation state estimation method, and degradation suppression method

Abstract

To provide a battery degradation state estimation method for accurately detecting battery degradation due to reduction in battery capacity, and to provide a degradation suppression control method and degradation suppression control system for suppressing degradation using result data obtained form the battery degradation state estimation method.SOLUTION: A degradation suppression system is provided, comprising: a degradation state estimation unit including a resistance history acquisition unit for acquiring a history of battery resistance during a predetermined period of discharge while a vehicle is running, and a degradation computation unit for deriving the state of battery degradation from the history of the battery resistance; and a degradation suppression control unit for providing battery degradation suppression control based on the state of battery degradation.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a battery degradation state estimation device, a degradation suppression system, a degradation state estimation method, and a degradation suppression method, and particularly to a degradation state estimation device, a degradation suppression system, a degradation state estimation method, and a degradation suppression method for a lithium metal secondary battery containing lithium metal in a negative electrode.

Background Art

[0002] Patent Document 1 discloses a means for measuring the terminal voltage of each secondary battery for the purpose of monitoring the degradation state of each secondary battery when the secondary batteries are connected in series, and determining the degradation state of each secondary battery based on the change over time of each terminal voltage.

[0003] Further, Patent Document 2 discloses a battery monitoring device for a secondary battery block composed of a plurality of secondary batteries connected in parallel, which calculates an internal resistance from the voltage change amount and current change amount of the secondary battery block, and determines an abnormality of each secondary battery based on the internal resistance value.

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Degradation of in-vehicle batteries includes degradation due to a decrease in capacity and degradation that causes a decrease in output due to an increase in internal resistance. The determination of the degradation of the secondary batteries in Patent Documents 1 and 2 both measure the decrease in output caused by the increase in internal resistance and make a degradation determination, and do not detect degradation due to a decrease in capacity.

[0006] A battery (lithium metal battery LMB) containing lithium metal in the negative electrode has a small decrease in capacity over time, especially in the initial state, and it is difficult to accurately calculate the remaining capacity. As a result, the display accuracy of the driving range of the EV decreases.

[0007] The present invention has been made in view of the above, and aims to present a battery degradation state estimation device, a degradation suppression system, a degradation state estimation method, and a degradation suppression method that can accurately set the degradation due to the decrease in the capacity of a battery (lithium metal battery LMB) containing lithium metal in the negative electrode.

Means for Solving the Problems

[0008] In order to solve the above problems, the battery degradation state (SOH) estimation device of the present invention is a degradation state estimation device that estimates the capacity degradation state of a lithium metal secondary battery containing lithium metal in the negative electrode, and includes a resistance value history acquisition unit that acquires the history of the resistance value of the lithium metal secondary battery in discharge for a predetermined time, and a degradation state calculation unit that calculates the capacity degradation state SOH of the lithium metal secondary battery based on the history of the resistance value acquired by the resistance value history acquisition unit when the state of charge SOC of the lithium metal secondary battery is within a predetermined range. The resistance value history acquisition unit acquires the history of the first resistance value (Ra), which is the resistance value of the lithium metal secondary battery in discharge for the first time, and the history of the second resistance value (Rb), which is the resistance value of the lithium metal secondary battery in discharge for the second time longer than the first time, and the degradation state calculation unit calculates the SOH of the capacity degradation state of the lithium metal secondary battery based on the history of the first resistance value (Ra) and the history of the second resistance value (Rb) acquired by the resistance value history acquisition unit.

[0009] From the battery resistance value (Ra) during discharge for a first time when the battery's state of charge (SOC) falls within a predetermined range, and the battery resistance value (Rb) during discharge for a second time different from the first time when the battery's state of charge (SOC) falls within the predetermined range, it is possible to determine the range of deterioration of the battery's remaining capacity, as will be described in detail later.

[0010] In the battery state of health (SOH) estimating device of the present invention, it is effective that the resistance value history acquisition unit acquires the history of the first resistance value and the history of the second resistance value while the vehicle is running. Discharge while the vehicle is running is related to accelerator operation by the driver, and resistance values ​​at various discharge times can be acquired by normal driving, and the driver can also obtain the battery resistance at a predetermined time of discharge by consciously operating the accelerator for a predetermined time.

[0011] Moreover, in the battery state of health (SOH) estimating device of the present invention, it is effective to implement the estimation when the battery's state of charge (SOC) is in a range of less than 30%, because the deterioration state becomes more noticeable when the battery's state of charge (SOC) is low.

[0012] In addition, in the battery state of health (SOH) estimation device of the present invention, in addition to estimating the state of health (SOH) of the battery during discharge, it also includes estimating the state of health (SOH) of the battery during charging. Specifically, the degradation state is estimated by temporarily stopping the current during charging and acquiring a history of charging efficiency. Also, by performing discharging and charging for a predetermined time within a range of 1 to 10 seconds before and after temporarily stopping the current during charging and acquiring a history of charging efficiency, degradation can be estimated with higher accuracy. Estimating the state of health (SOH) of the battery during charging is efficient when the battery's state of charge (SOC) is in the range of 50 to 90%.

[0013] In addition, the apparatus for estimating the state of deterioration (SOH) of the battery according to the present invention further includes a state-of-deterioration notification unit that notifies the user (driver) of the state of deterioration SOH of the lithium metal secondary battery calculated by the state-of-deterioration calculation unit. Examples of the notification method include display on a display device, and a cautionary advice by storing a failure code when the state of deterioration worsens in a storage device.

[0014] In addition, the apparatus for estimating the state of deterioration (SOH) of the battery according to the present invention constitutes a battery deterioration suppression system together with a deterioration suppression control unit that executes deterioration suppression control for suppressing the deterioration of the lithium metal secondary battery. The deterioration suppression control unit executes the deterioration suppression control when the value of the second resistance value / the first resistance value, which is the ratio of the second resistance value to the first resistance value, exceeds 3. Examples of the deterioration prevention means in the deterioration suppression control unit include charging restriction or enhanced cooling.

[0015] The method for estimating the state of deterioration of the battery according to the present invention is a method for estimating the state of deterioration of a lithium metal secondary battery containing lithium metal in a negative electrode, the method including: a resistance value history acquisition step of acquiring a history of the resistance value of the lithium metal secondary battery in discharge for a predetermined time; and a state-of-deterioration calculation step of calculating a capacity deterioration state SOH of the lithium metal secondary battery based on the history of the resistance value acquired in the resistance value history acquisition step when the state of charge SOC of the lithium metal secondary battery is within a predetermined range.

[0016] The method for suppressing the deterioration of the battery according to the present invention includes a deterioration suppression control step of executing deterioration suppression control for suppressing the deterioration of the lithium metal secondary battery based on the resistance value history acquisition step and the state-of-deterioration calculation step in the state-of-deterioration estimation method, and the state of deterioration SOH calculated in the state-of-deterioration calculation step.

Advantages of the Invention

[0017] Thus, the present invention can accurately determine the state of deterioration (SOH) of a battery from the resistance value (Ra) of the battery during discharge at a first time when the state of charge (SOC) of the battery is within a predetermined range and the resistance value (Rb) of the battery during discharge at a second time different from the first time when the state of charge (SOC) of the battery is within the predetermined range. Further, by performing deterioration prevention control based on the accurate determination result of the state of deterioration (SOH) of the battery, it is possible to gently lead to the deterioration of the battery.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0019] The present invention assumes that a lithium-metal secondary battery is used as the battery. The lithium-metal secondary battery includes a positive electrode, a negative electrode, a separator and an electrolyte disposed between the positive electrode and the negative electrode, and is characterized by having a lithium-metal layer as the negative electrode. The lithium-metal layer is formed by depositing lithium-metal particles on a negative electrode current collector or a lithium foil. The lithium-metal secondary battery has a very high energy density compared to a conventional lithium-ion secondary battery and is expected to be put into practical use.

[0020] The positive electrode is composed of a layer containing a positive electrode active material, a binder, and a conductive assistant. Examples of the positive electrode active material include lithium cobaltate (LiCoO2), lithium nickelate (LiNiO2), LiNipMnqCorO2 (p + q + r = 1), LiNipAlqCorO2 (p + q + r = 1), lithium manganate (LiMn2O4), heteroatom-substituted Li-Mn spinel represented by Li1+xMn2-x-yMyO4 (x + y = 2, M is at least one selected from Al, Mg, Co, Fe, Ni, and Zn), lithium titanate (oxide containing Li and Ti), lithium metal phosphate (LiMPO4, M is at least one selected from Fe, Mn, Co, and Ni), etc. Preferably, Li1Ni0.8Co0.1Mn0.1O2 (NCM811) is used as the positive electrode active material.

[0021] The electrolytic solution contains an organic solvent and an electrolyte. As the organic solvent, for example, as the first organic solvent, hydrofluoroethers such as 1,1,2,2-tetrafluoro-1-(2,2,2-trifluoroethoxy)ethane, methyl nonafluoroisobutyl ether, and methyl nonafluorobutyl ether, which are fluorine-substituted chain hydrocarbons, can be used. Also, for example, as the second organic solvent, 1,2-dimethoxyethane (DME), ethylene carbonate (EC), propylene carbonate (PC), sulfolane (SL), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC), etc. can be used. These first organic solvent and second organic solvent can be used in combination. The electrolyte is a source of lithium ions, which are charge carriers, and contains a lithium salt. As the lithium salt, at least one selected from the group consisting of LiFSI, LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, LiC(CF3SO2)3, LiN(CF3SO2)2 (LiTFSI), LiN(FSO2)2 (LiFSI), and LiBC4O8 can be used. Among them, LiFSI can be preferably used as the electrolyte.

[0022] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0023] Figure 1 is a block diagram of the degradation control system of the present invention. The degradation control system 1 of the present invention includes a degradation state estimation unit 10 including a resistance value history acquisition unit 11, a degradation state calculation unit 12, and a degradation state notification unit 13, and a degradation suppression control unit 20.

[0024] The resistance value history acquisition unit 11 of the degradation state estimation unit 10 sequentially obtains the internal resistance value of the battery during charging or discharging while the vehicle is running. The method of obtaining the internal resistance value will be described later. The open circuit voltage can be estimated from the obtained resistance value and the closed circuit voltage of the battery, and the state of charge (SOC) of the battery can be estimated.

[0025] When the estimated state of charge (SOC) of the battery becomes less than 30%, the internal resistance value R is obtained during each of two discharges with different discharge times. Generally, when the discharge time is different, the internal resistance value during that discharge is also different, and the longer the discharge time, the larger the resistance value. For example, let the resistance value when the discharge time is 1 second be Ra, and let the resistance value when the discharge time is 30 seconds be Rb. If the respective resistance values Ra0 and Rb0 at the initial state of the battery are known, the rate of increase of the respective resistance values Ra and Rb of the current battery from the initial state can be obtained.

[0026] The history data of the resistance value R (Ra, Rb) acquired by the resistance value history acquisition unit 11 is sent to the degradation state calculation unit 12. In the degradation state calculation unit 12, data indicating the relationship between the classification of the degradation state (SOH) of the remaining capacity of the battery in the operation time of the battery, the rate of increase of the resistance value Ra when the discharge time is 1 second, and the rate of increase of the resistance value Rb when the discharge time is 30 seconds is held. By collating the history data of the resistance value R (Ra, Rb) sent from the resistance value history acquisition unit 11, it is possible to determine which classification the degradation state (SOH) of the remaining capacity of the current battery belongs to among the classifications divided by the degradation state (SOH). The data of the result obtained by the degradation state calculation unit 12 is sent to the degradation state notification unit 13, the effective remaining capacity is calculated from the SOC at that time, and the travelable distance and the battery capacity degradation rate are calculated and notified to the user (driver).

[0027] Further, the data of the result obtained by the deterioration state calculation unit 12 is sent to the deterioration suppression control unit 20, and deterioration suppression control is performed according to the category of the deterioration state (SOH) to which the current battery belongs and the ratio of Ra to Rb (the value of Rb / Ra).

[0028] The reasons why the capacity deterioration of the lithium metal battery LMB is different from that of the lithium ion battery LIB will be compared and explained. As described above, in the conventional lithium ion battery LIB, graphite or the like is used as the negative electrode member, whereas in the lithium metal battery LMB, lithium is used as the negative electrode member.

[0029] FIG. 2 is a diagram showing the capacity deterioration characteristics of the lithium ion battery LIB. In the lithium ion battery LIB, SEI is generated on the electrode due to the use of the battery. However, in the initial stage of battery use, the decrease in active lithium in the battery due to the generation of SEI is the main cause of the deterioration of the remaining capacity of the battery. Therefore, even in the initial stage of battery use, the deterioration progresses at a specific rate, and it is relatively easy to detect the deterioration state of the remaining capacity. When the capacity reduction of the positive electrode exceeds the growth of SEI, the deterioration progresses greatly.

[0030] FIG. 3 is a diagram showing the capacity deterioration characteristics of the deterioration of the lithium metal battery LMB. Also in the lithium metal battery LMB, a film is generated on the electrode due to the use of the battery. However, in the initial stage of battery use, the decrease in active lithium in the battery due to film formation is compensated by the excess lithium in the negative electrode, and in the initial stage of battery use, the capacity change is small and the capacity deterioration state is difficult to detect. The reduction width of the remaining capacity is smaller than that of the lithium ion battery LIB. However, thereafter, the deposited metallic lithium becomes isolated and loses its conductivity, and the battery capacity rapidly decreases to reach the end of life EOL.

[0031] Thus, it can be said that the lithium metal battery LMB has the property that, throughout the period of battery use, the degree of deterioration of the remaining capacity is small up to a certain period and it is difficult to detect the progress of deterioration with differential capacity, but after a certain time, the deterioration progresses and it reaches the end of life EOL. Therefore, in the lithium metal battery LMB, it can be said that monitoring the deterioration situation from the initial state where the degree of deterioration of the remaining capacity is small is further required compared to the conventional lithium ion battery LIB. In that sense, it can be said that the method for estimating the deterioration state of the battery of the present invention is a method that is strongly required in the deterioration monitoring of the lithium metal battery LMB with high accuracy of estimating the deterioration state of the battery.

[0032] Next, the method for estimating the deterioration state of the battery of the present invention will be described in detail with reference to FIG. 4.

[0033] During the running of the vehicle, due to the driver's operations such as accelerator and brake operations, various discharge states and charge states of different time lengths occur in the battery mounted on the vehicle. The characteristics of the relationship between the closed-circuit voltage and the current value (I-V characteristics) are automatically detected by the system in the vehicle in correspondence with the discharge or charge time (length) and stored in the storage device. The resistance value R is sequentially calculated from the I-V characteristics of discharge and charge during running.

[0034] From the resistance value R obtained as described above and the closed-circuit voltage CCV of the battery, the open-circuit voltage OCV of the battery can be obtained, and finally, the state of charge (SOC) of the battery can be estimated from the OCV-SOC relationship. When the state of charge (SOC) of the battery becomes less than 30%, two resistance values during discharge with different discharge time lengths are obtained. The discharge time length can be made different by varying the output time during running, specifically, the length of depressing the accelerator.

[0035] For example, the resistance value Ra when the discharge time length is 1 second and the resistance value Rb when the discharge time length is 30 seconds are obtained from the I-V characteristics during discharge. Assuming that the values of the resistance value Ra0 when the discharge time length at the initial stage of battery use is 1 second and the resistance value Rb0 when the discharge time length is 30 seconds have been acquired in advance, the increase rates of the current battery resistance values Ra and Rb from the battery resistance values Ra0 and Rb0 at the initial stage of battery use can be obtained.

[0036] On the other hand, within the vehicle system, data on the relationship between the battery usage time (operation time), the increase rates of the resistance values Ra and Rb, and the state of health (SOH) degradation of the remaining battery capacity are retained. Figure 4 is a graph showing the relationship between the battery usage time (operation time), the increase rates of the resistance values Ra and Rb, and the state of health (SOH) degradation of the remaining battery capacity. According to this graph, there is a specific relationship between the battery operation time and the resistance values Ra and Rb, and the range of the state of health (SOH) degradation of the remaining battery capacity can be known based on the respective value ranges of the resistance values Ra and Rb.

[0037] For example, if the increase rates of the resistance values Ra and Rb are in the range of 100 - 120%, it can be known that the state of health (SOH) degradation of the remaining battery capacity is in the range of 100 - 97. Also, if the increase rate of the resistance value Rb is in the range of 120 - 160%, it can be known that the state of health (SOH) degradation of the remaining battery capacity is in the range of 97 - 95. Similarly, if the increase rate of the resistance value Ra is in the range of 140% or less and the increase rate of the resistance value Rb is in the range of 160% or more, it can be known that the state of health (SOH) degradation of the remaining battery capacity is in the range of 95 - 90. Similarly, if the increase rate of the resistance value Ra is in the range of 140 - 180%, it can be known that the state of health (SOH) degradation of the remaining battery capacity is in the range of 90 - 80. Finally, if the increase rate of the resistance value Ra is in the range of 180% or more, it can be known that the state of health (SOH) degradation of the remaining battery capacity is in the range of 80 - 70.

[0038] The system in the vehicle determines the range of the current state of health (SOH) of the battery's remaining capacity by comparing the resistance value Ra when the discharge time length obtained above is 1 second and the resistance value Rb when the discharge time length is 30 seconds with the data on the relationship between the increase rate of the resistance values Ra and Rb shown in FIG. 4 and the degradation of the battery's remaining capacity SOH, which are pre-stored in the vehicle's system.

[0039] The data on the determination result regarding the range of the current state of health (SOH) of the battery's remaining capacity obtained can be known to the user, for example, by being displayed on a display device. Note that since it is not necessary for the user such as the driver to always know the state of health (SOH) of the battery's remaining capacity, instead of displaying it on the display device, it may be notified to the user by a caution display on an alarm device, for example, when it is necessary to notify the user of the degradation state.

[0040] Also, the system in the vehicle performs degradation suppression control based on the range of the current state of health (SOH) of the battery's remaining capacity and the value of the ratio (Rb / Ra) of the resistance value Ra to the resistance value Rb. Examples of degradation suppression methods include methods such as charging restriction and enhanced cooling. In particular, when the value of the ratio (Rb / Ra) of the resistance value Ra to the resistance value Rb exceeds 3, protection control such as rapid cooling of the battery is performed assuming that the remaining capacity of the battery is approaching the end of life (EOL).

[0041] In the above, the state of health (SOH) of the battery's remaining capacity is estimated by obtaining the resistance values Ra and Rb during discharge, but it is also possible to estimate the state of health (SOH) of the battery's remaining capacity during charging. In this case, the charging current is temporarily stopped to obtain the history of the charging efficiency. By performing discharge and charging for a predetermined time within the range of 1 to 10 seconds before and after temporarily stopping the charging current during charging, the history of the charging efficiency can be obtained more efficiently. Note that in the estimation of the state of health (SOH) of the battery's remaining capacity during charging, it is more efficient to temporarily stop the charging current when the state of charge (SOC) of the battery is in the range of 50 to 90%.

[0042] Next, the deterioration suppression control of the present invention will be described using the flowchart of FIG. 5. The flowchart of FIG. 5 first stores the I-V characteristics of charging and discharging during vehicle travel, sequentially calculates and stores the resistance values for various discharge times (step S11), and starts by obtaining the state of charge SOC of the battery using the method described above (step S12).

[0043] Next, it is determined whether the state of charge of the battery has fallen below 30% (step S13). If the answer is NO, that is, if it is determined that the state of charge is 30% or more, the process returns to step S11, and the loop of step S11, step S12, step S13, step S11... is repeated until the answer is YES in step S13.

[0044] When the answer is YES in step S13, that is, when the state of charge of the battery has fallen below 30%, the process proceeds to the next steps S14 and S15, and the internal resistance (Ra) of the battery during 1-second discharge and the internal resistance (Rb) of the battery during 30-second discharge are respectively obtained (step S14 and step S15). This is because it is known that the deterioration state of the battery becomes more prominent as the state of charge of the battery is lower, and in order to accurately detect the deterioration state with high precision, it waits for the state of charge of the battery to fall below 30%.

[0045] And since the values of the internal resistance (Ra) of the battery during 1-second discharge and the internal resistance (Rb) of the battery during 30-second discharge at the initial stage of battery use are known in advance, it is possible to obtain the rate of increase of the internal resistance (Ra) of the battery during 1-second discharge and the internal resistance (Rb) of the battery during 30-second discharge of the current battery, which are obtained in step S14 and step S15, respectively, with respect to the initial state.

[0046] According to the obtained internal resistance (Ra) of the battery during 1-second discharge and the internal resistance (Rb) of the battery during 30-second discharge of the current battery, and their respective increase rates, if within the range of Ra increase rate < 120% and Rb increase rate < 120% (step S21), the state of health (SOH) of the remaining capacity of the battery is 97 < SOH < 100, and a display indicating this is made on the display device (step S31). In this case, the state of degradation is considered not to have advanced, and no measures such as charge limitation are taken (step S51).

[0047] Similarly, if within the range of 120% < Rb increase rate < 160% (step S22), a display indicating that 95 < SOH < 97 is made on the display device (step S32), and in this case as well, no measures such as charge limitation are taken (step S51). Similarly, if within the range of Ra increase rate < 120% and 160% < Rb increase rate (step S23), a display indicating that 90 < SOH < 95 is made on the display device (step S33), and in this case as well, no measures such as charge limitation are taken (step S51).

[0048] Also, if within the range of 140% < Ra increase rate < 180% (step S24), a display indicating that 80 < SOH < 90 is made on the display device (step S34). Here, it is determined whether the value of Rb / Ra exceeds 3 (step S41). If the answer is NO, that is, if the value of Rb / Ra does not exceed 3, deterioration prevention control is performed (step S52). On the other hand, if the answer is YES, that is, if the value of Rb / Ra exceeds 3, protection control is performed (step S53). Note that in the case of 80 < SOH < 90, the possibility that the value of Rb / Ra exceeds 3 is low, and in this range, it can be said that in most cases, the process mostly shifts to step S52 where deterioration prevention control is performed.

[0049] Finally, if it is within the range of 180% < rate of increase in Ra (step S25), the display device will display that 70 < SOH < 80 (step S35). Also in this case, next, it is determined whether the value of Rb / Ra exceeds 3 (step S41). If the answer is NO, that is, if the value of Rb / Ra does not exceed 3, deterioration prevention control is performed (step S52). On the other hand, if the answer is YES, that is, if the value of Rb / Ra exceeds 3, protection control is performed (step S53). Note that when 70 < SOH < 80, the value of Rb / Ra is likely to exceed 3, and it can be said that protection control is likely to be required within this range.

[0050] In the deterioration prevention control (step S52), a relatively gentle method for preventing deterioration is adopted. Specifically, measures such as charge limitation, temperature control, and recovery charging mode are taken. The recovery charging mode is a measure of temporarily interrupting discharge and performing low-rate charging. In contrast, in the protection control (step S53), a strong and forced method for preventing deterioration is adopted. Specifically, the starting temperature of cooling is changed, for example, rapid cooling is performed at a temperature of 35°C or higher, and regarding charging, a strong limitation on the allowable current value is also imposed. By these deterioration prevention control (step S52) and protection control (step S53), the progress of battery deterioration can be slowed down.

[0051] As described above, the embodiments for implementing the present invention have been described using examples. However, the present invention is not limited to such examples at all, and it goes without saying that the present invention can be implemented in various modes without departing from the spirit of the present invention.

Explanation of Reference Numerals

[0052] 1 Deterioration suppression system 10 Deterioration state estimation unit 11 Resistance value history acquisition unit 12 Deterioration state calculation unit 13 Deterioration state notification unit 20 Deterioration suppression control unit

Claims

1. A state-of-deterioration estimation device for estimating the state of deterioration of a lithium metal secondary battery containing lithium metal in a negative electrode, comprising: a resistance value history acquisition unit that acquires a history of the resistance value of the lithium metal secondary battery in discharge for a predetermined time; a state-of-deterioration calculation unit that calculates the state of health (SOH) of the lithium metal secondary battery based on the history of the resistance value acquired by the resistance value history acquisition unit when the state of charge (SOC) of the lithium metal secondary battery is within a predetermined range. The resistance value history acquisition unit acquires, during running of the vehicle, a history of a first resistance value that is the resistance value of the lithium metal secondary battery in discharge for a first time, and a history of a second resistance value that is the resistance value of the lithium metal secondary battery in discharge for a second time longer than the first time. The state-of-deterioration calculation unit calculates the state of health (SOH) of the lithium metal secondary battery based on the history of the first resistance value and the history of the second resistance value acquired by the resistance value history acquisition unit. A state-of-deterioration estimation device.

2. The state-of-deterioration estimation device according to claim 1, further comprising a state-of-deterioration notification unit that notifies the state of health (SOH) of the lithium metal secondary battery calculated by the state-of-deterioration calculation unit.

3. The data of the result obtained by the state-of-deterioration calculation unit is sent to the state-of-deterioration notification unit, and at the same time, the effective remaining capacity is calculated from the state of charge (SOC) of the lithium metal secondary battery at that time, and the travelable distance and the capacity deterioration rate of the battery are calculated. The state-of-deterioration estimation device according to claim 2.

4. The data of the result obtained by the state-of-deterioration calculation unit is sent to the state-of-deterioration notification unit, and at the same time, the effective remaining capacity is calculated from the state of charge (SOC) of the lithium metal secondary battery at that time, and the travelable distance and the capacity deterioration rate of the battery are calculated and notified to the driver of the vehicle. The state-of-deterioration estimation device according to claim 2.

5. The resistance value history acquisition unit acquires the history of the first resistance value and the history of the second resistance value. The state-of-deterioration calculation unit calculates the state of health (SOH) when the state of charge (SOC) of the lithium metal secondary battery becomes 30% or less. The state-of-deterioration estimation device according to claim 1.

6. In the state-of-deterioration estimation device according to claim 1, the first time is 1 second, and the second time is 5 to 30 seconds.

7. The state-of-deterioration estimation device according to any one of claims 1 to 6, and A degradation suppression system comprising: a degradation suppression control unit that executes degradation suppression control for suppressing degradation of the lithium metal secondary battery based on the degradation state SOH calculated by the degradation state calculation unit of the degradation state estimation device.

8. A method for estimating the degradation state of a lithium metal secondary battery containing lithium metal in the negative electrode, comprising: a resistance value history acquisition step of acquiring a history of the resistance value of the lithium metal secondary battery during discharge for a predetermined time; a degradation state calculation step of calculating the degradation state SOH of the lithium metal secondary battery based on the history of the resistance value acquired in the resistance value history acquisition step when the state of charge SOC of the lithium metal secondary battery is within a predetermined range. The resistance value history acquisition step acquires a history of a first resistance value, which is the resistance value of the lithium metal secondary battery during discharge for a first time, and a history of a second resistance value, which is the resistance value of the lithium metal secondary battery during discharge for a second time longer than the first time, while the vehicle is running. The degradation state calculation step calculates the degradation state SOH of the lithium metal secondary battery based on the history of the first resistance value and the history of the second resistance value acquired in the resistance value history acquisition step. A method for estimating the degradation state.

9. The degradation state calculation step calculates the degradation state SOH when the state of charge SOC of the lithium metal secondary battery is 30% or less. The method for estimating the degradation state according to Claim 8.

10. The first time is 1 second and the second time is 30 seconds. The method for estimating the degradation state according to Claim 8.

11. In the resistance value history acquisition step and the degradation state calculation step in the method for estimating the degradation state according to any one of Claims 8 to 10, and a degradation suppression control step of executing degradation suppression control for suppressing degradation of the lithium metal secondary battery based on the degradation state SOH calculated in the degradation state calculation step. A method for suppressing degradation.

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