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

Abstract

The purpose of the present invention is to provide a battery degradation state estimation method with which it is possible to highly accurately detect degradation due to reduction in battery capacity, and also provide a degradation suppression control method and a degradation suppression control system which are for suppressing degradation by using data of a result obtained by said battery degradation state estimation method. The present invention is configured to comprise: a degradation state estimation unit including a resistance value history acquisition unit that acquires a resistance value history of a battery in discharging for a predetermined time during traveling of a vehicle, and a degradation calculation unit that calculates the degradation state of the battery from the resistance value history of the battery; and a degradation suppression control unit for performing control on degradation suppression of the battery on the basis of the degradation state of the battery.

Description

[Technical field]

[0001] The present invention relates to a battery degradation state estimating device, degradation suppression system, degradation state estimating method, and degradation suppression method, and in particular to a degradation state estimating device, degradation suppression system, degradation state estimating method, and degradation suppression method for a lithium metal secondary battery that contains lithium metal in the negative electrode. [Background technology]

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

[0003] Furthermore, Patent Document 2 discloses a battery monitoring device for a secondary battery block consisting of multiple secondary batteries connected in parallel, which calculates the internal resistance from the voltage change and current change of the secondary battery block, and determines whether or not there is an abnormality in each secondary battery based on the internal resistance value.

[0004] [Patent Document 1] JP 2015-68783 A [Patent Document 2] JP 2006-138750 A Summary of the Invention [Problem to be solved by the invention]

[0005] Degradation of on-board batteries can be classified into degradation due to a decrease in capacity and degradation that reduces output due to an increase in internal resistance. In both Patent Document 1 and Patent Document 2, the determination of secondary battery degradation is performed by measuring the decrease in output due to an increase in internal resistance, but does not detect degradation due to a decrease in capacity.

[0006] Lithium metal batteries (LMB) that contain lithium metal in the negative electrode do not lose much capacity over time, especially in the initial state, making it difficult to accurately calculate the remaining capacity. As a result, the accuracy of the display of the EV's driving range decreases.

[0007] The present invention has been made in consideration of the above, and aims to provide a battery degradation state estimation device, degradation suppression system, degradation state estimation method, and degradation suppression method that are capable of setting with high accuracy the degradation due to a decrease in battery capacity for batteries (lithium metal batteries LMB) that contain lithium metal in the negative electrode. [Means for solving the problem]

[0008] In order to solve the above problems, the battery state of health (SOH) estimation device of the present invention is a state of health estimation device that estimates the capacity degradation state of a lithium metal secondary battery containing lithium metal in a negative electrode, and includes a resistance value history acquisition unit that acquires a history of the resistance value of the lithium metal secondary battery during a predetermined time of discharge, and a state of health 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 charging rate SOC of the lithium metal secondary battery falls within a predetermined range. The resistance value history acquisition unit acquires a history of a first resistance value (Ra) that is the resistance value of the lithium metal secondary battery during a first time of discharge, and a history of a second resistance value (Rb) that is the resistance value of the lithium metal secondary battery during a second time of discharge longer than the first time, and the state of health 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 state of charge (SOC) is in a range of less than 30%, because the deterioration state becomes more noticeable when the battery 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] The battery state of health (SOH) estimation device of the present invention further includes a state of health notification unit that notifies a user (driver) of the state of health SOH of the lithium metal secondary battery calculated by the state of health calculation unit. Notification methods include displaying on a display device, and warning by storing a fault code in a storage device when the state of health worsens.

[0014] Furthermore, the battery state of health (SOH) estimating device of the present invention constitutes a battery degradation suppression system together with a degradation suppression control unit that executes degradation suppression control for suppressing degradation of a lithium metal secondary battery. The degradation suppression control unit executes the degradation suppression control when a ratio of the second resistance value to the first resistance value, that is, a second resistance value / first resistance value, exceeds 3. Examples of degradation prevention means in the degradation suppression control unit include limiting charging or strengthening cooling.

[0015] The battery degradation state estimating method of the present invention is a degradation state estimating method for estimating the degradation state of a lithium metal secondary battery containing lithium metal in the negative electrode, and includes 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 period of time, and a degradation state calculation step of calculating the capacity 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 charging rate SOC of the lithium metal secondary battery falls within a predetermined range.

[0016] The battery deterioration suppression method of the present invention comprises the resistance value history acquisition process and the deterioration state calculation process in the deterioration state estimation method, and a deterioration suppression control process for executing deterioration suppression control to suppress deterioration of the lithium metal secondary battery based on the state of deterioration SOH calculated in the deterioration state calculation process. Effect of the Invention

[0017] In this way, the present invention has the effect of being able to accurately determine the battery's state of health (SOH) from the battery's 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's 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, and also being able to gently induce battery deterioration by performing deterioration prevention control based on the accurate determination result of the battery's state of health (SOH). [Brief description of the drawings]

[0018] [Figure 1] FIG. 2 is a block diagram of the deterioration control system of the present invention. [Diagram 2] FIG. 1 is a graph showing the capacity degradation characteristics of a lithium-ion battery LIB. [Diagram 3] FIG. 1 is a diagram showing the capacity degradation characteristics of a lithium metal battery LMB. [Figure 4] FIG. 2 is a graph showing the history of resistance Ra and resistance Rb of the battery of the present invention. [Diagram 5] FIG. 4 is a diagram showing a flow of deterioration suppression control according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The present invention is premised on the use of a lithium metal secondary battery as the battery. The lithium metal secondary battery is characterized by comprising a positive electrode, a negative electrode, a separator and an electrolyte solution disposed between the positive electrode and the negative electrode, and 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 lithium foil. The lithium metal secondary battery has a very high energy density compared to conventional lithium ion secondary batteries, and is expected to be put to practical use.

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

[0021] 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. The electrolyte is a source of lithium ions, which are charge transfer media, and includes a lithium salt. The lithium salt may be 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. Among them, LiFSI is preferably used as the electrolyte.

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

[0023] 1 is a block diagram of a deterioration control system according to the present invention. The deterioration control system 1 according to the present invention comprises a deterioration state estimation unit 10 having a resistance value history acquisition unit 11, a deterioration state calculation unit 12, and a deterioration state notification unit 13, and a deterioration 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 when it is charged or discharged while the vehicle is running. How to obtain 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 falls below 30%, the internal resistance value R is obtained during two discharges with different discharge times. In general, if the discharge time differs, the internal resistance value during the discharge also differs, and the longer the discharge time, the larger the resistance value. For example, the resistance value when the discharge time is 1 second is Ra, and the resistance value when the discharge time is 30 seconds is Rb. If the resistance values ​​Ra0 and Rb0 in the initial state of the battery are known, the rate of increase from the initial state of the current resistance values ​​Ra and Rb of the battery 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 deterioration state calculation unit 12. The deterioration state calculation unit 12 holds data indicating the classification of the deterioration state (SOH) of the remaining capacity of the battery during the operation time of the battery, and the relationship between the increase rate of the resistance value Ra when the discharge time is 1 second and the increase rate of the resistance value Rb when the discharge time is 30 seconds, and can determine which classification of the deterioration state (SOH) the current remaining capacity of the battery belongs to by collating the history data of the resistance value R (Ra, Rb) sent from the resistance value history acquisition unit 11. The result data obtained by the deterioration state calculation unit 12 is sent to the deterioration state notification unit 13, which calculates the effective remaining capacity from the SOC at that time, and calculates the drivable distance and the capacity deterioration rate of the battery and notifies the user (driver).

[0027] In addition, the result data 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 classification of the state of health (SOH) to which the current battery belongs and the ratio of Ra to Rb (the value of Rb / Ra).

[0028] The reason why the capacity degradation of the lithium metal battery LMB differs from that of the lithium ion battery LIB will be explained below. As mentioned above, the conventional lithium ion battery LIB uses graphite as the negative electrode material, whereas the lithium metal battery LMB uses lithium as the negative electrode material.

[0029] Figure 2 shows the capacity degradation characteristics of a lithium-ion battery LIB. In a lithium-ion battery LIB, SEI is generated in the electrodes as the battery is used. In the early stages of battery use, the active lithium in the battery decreases due to the generation of SEI, which is the main cause of the degradation of the remaining capacity of the battery. Therefore, even in the early stages of battery use, degradation progresses at a certain rate, and it is relatively easy to detect the degradation state of the remaining capacity. When the capacity loss of the positive electrode exceeds the growth of SEI, the degradation progresses significantly.

[0030] FIG. 3 is a diagram showing the capacity degradation characteristics of the lithium metal battery LMB. In the lithium metal battery LMB, a film is also formed on the electrodes as the battery is used. However, in the early stages of battery use, the reduction in active lithium in the battery due to the film formation is compensated for by the surplus lithium in the negative electrode, and in the early stages of battery use, the capacity change is small and the capacity degradation state is difficult to detect. The reduction in remaining capacity is smaller than that of the lithium ion battery LIB. However, thereafter, the precipitated metallic lithium loses conductivity and becomes isolated, causing a sudden decrease in battery capacity and leading to the EOL.

[0031] In this way, the lithium metal battery LMB has a property that, throughout the duration of battery use, the degree of deterioration of the remaining capacity is small until a certain period, and it is difficult to detect the progress of deterioration by differential capacity, but after a certain period, the deterioration progresses and the battery reaches its end of life. Therefore, it can be said that it is more necessary to monitor the deterioration status of the lithium metal battery LMB from the initial state where the degree of deterioration of the remaining capacity is small, compared to the conventional lithium ion battery LIB. In that sense, the method of estimating the deterioration state of a battery of the present invention has high accuracy in estimating the deterioration state of the battery, and is a method that is more highly desired in monitoring the deterioration of the lithium metal battery LMB.

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

[0033] When the vehicle is running, the driver's operation of the accelerator and brakes causes the battery mounted on the vehicle to enter a discharged state or a charged state of various lengths of time. The system inside the vehicle automatically detects the characteristics (IV characteristics) of the relationship between the closed circuit voltage and the current value in correspondence with the time (length) of discharging or charging, and stores them in a memory device. The resistance value R is calculated successively from the IV characteristics of discharging and charging while the vehicle is running.

[0034] The open circuit voltage OCV of the battery is calculated from the resistance value R and the closed circuit voltage CCV of the battery calculated as above, and the state of charge (SOC) of the battery can be estimated from the OCV-SOC relationship. Then, when the state of charge (SOC) of the battery falls below 30%, two resistance values ​​during discharge with different discharge times are calculated. The length of discharge time can be varied by changing the output time during driving, specifically, the length of time the accelerator is pressed.

[0035] For example, the resistance value Ra when the discharge time is 1 second and the resistance value Rb when the discharge time is 30 seconds are obtained from the IV characteristics during discharge. If the resistance value Ra0 when the discharge time is 1 second in the initial stage of battery use and the resistance value Rb0 when the discharge time is 30 seconds are previously obtained, the rate of increase of the current battery resistance values ​​Ra and Rb from the resistance values ​​Ra0 and Rb0 in the initial stage of battery use can be obtained.

[0036] Meanwhile, data on the relationship between the battery usage time (driving time), the rate of increase in the resistance values ​​Ra and Rb, and the deterioration state of health of the battery remaining capacity is stored within the vehicle system. Figure 4 is a graph showing the relationship between the battery usage time (driving time), the rate of increase in the resistance values ​​Ra and Rb, and the deterioration state of health of the battery remaining 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 deterioration state of health of the battery remaining capacity can be known depending on the range of the respective values ​​of the resistance values ​​Ra and Rb.

[0037] For example, if the rate of increase of the resistance values ​​Ra and Rb is in the range of 100-120%, the deterioration state SOH of the remaining capacity of the battery is in the range of 100-97. If the rate of increase of the resistance value Rb is in the range of 120-160%, the deterioration state SOH of the remaining capacity of the battery is in the range of 97-95. Similarly, if the rate of increase of the resistance value Ra is in the range of 140% or less and the rate of increase of the resistance value Rb is in the range of 160% or more, the deterioration state SOH of the remaining capacity of the battery is in the range of 95-90. Similarly, if the rate of increase of the resistance value Ra is in the range of 140-180%, the deterioration state SOH of the remaining capacity of the battery is in the range of 90-80. Finally, if the rate of increase of the resistance value Ra is in the range of 180% or more, the deterioration state SOH of the remaining capacity of the battery is in the range of 80-70.

[0038] The in-vehicle system compares the resistance value Ra when the discharge time is 1 second and the resistance value Rb when the discharge time is 30 seconds obtained above with data stored in advance in the vehicle system showing the relationship between the rate of increase of the resistance values ​​Ra and Rb and the deterioration state of the battery remaining capacity SOH shown in Figure 4, thereby making it possible to determine the range in which the current deterioration state of the battery remaining capacity SOH falls.

[0039] The acquired data of the determination result regarding the range of the deterioration state SOH of the current remaining capacity of the battery can be notified to the user, for example, by being displayed on a display device. Note that since the deterioration state SOH of the remaining capacity of the battery is not something that users such as drivers need to know all the time, it is also possible to notify the user of the deterioration state by displaying a warning on an alarm device, for example, without displaying it on a display device.

[0040] In addition, the system inside the vehicle controls deterioration suppression based on the range of the current state of health (SOH) of the remaining capacity of the battery and the value of the ratio (Rb / Ra) of the resistance value Ra to the resistance value Rb. Methods of deterioration suppression include limiting charging and strengthening cooling. In particular, when the value of the ratio (Rb / Ra) of the resistance value Ra to the resistance value Rb exceeds 3, it is determined that the remaining capacity of the battery is approaching the EOL, and protection control such as rapid cooling of the battery is performed.

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

[0042] Next, the deterioration suppression control of the present invention will be described with reference to the flow diagram of Fig. 5. The flow of Fig. 5 starts by storing the IV characteristics of charging and discharging while the vehicle is running, sequentially calculating and saving the resistance values ​​for various discharge times (step S11), and then calculating the charging rate SOC of the battery using the method described above (step S12).

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

[0044] If the answer to step S13 is YES, that is, when the battery charging rate falls below 30%, the process proceeds to the next steps S14 and S15, where the battery's internal resistance (Ra) during 1 second of discharging is obtained (step S14), and the battery's internal resistance (Rb) during 30 seconds of discharging is obtained (step S15). This is because it is known that the lower the battery charging rate is, the more noticeable the deterioration state of the battery becomes, and in order to accurately and precisely detect the deterioration state, it is awaited until the battery charging rate falls below 30%.

[0045] Since the values ​​of the battery's internal resistance (Ra) during 1 second discharge and the battery's internal resistance (Rb) during 30 seconds discharge at the beginning of battery use are known in advance, it is possible to determine the rate of increase from the initial state of the current battery's internal resistance (Ra) during 1 second discharge and the battery's internal resistance (Rb) during 30 seconds discharge obtained in steps S14 and S15.

[0046] According to 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 required current battery, and according to the increase rate of each, if it is within the range of Ra increase rate < 120% and Rb increase rate < 120% (step S21), the degradation state (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 degradation state is considered not to have advanced, and no measures such as charge restriction are taken (step S51).

[0047] Similarly, if it is 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 restriction are taken (step S51). Similarly, if it is 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 restriction are taken (step S51).

[0048] Also, if it is 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 judged 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, degradation 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, it mostly shifts to step S52 where degradation prevention control is performed.

[0049] Finally, if it is within the range of 180% < rate of increase of Ra (step S25), the display device will display that 70 < SOH < 80 (step S35). Even 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 in this range.

[0050] In the deterioration prevention control (step S52), relatively gentle methods for preventing deterioration are 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), strong and mandatory methods for preventing deterioration are adopted. Specifically, the start temperature of cooling is changed, for example, rapid cooling is performed at a temperature of 35°C or higher, and for charging as well, a strong limit on the allowable current value is 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 degradation state estimation device that estimates a degradation state of a lithium metal secondary battery that includes 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 during a predetermined period of discharge; a deterioration state calculation unit that calculates a 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 charging rate (SOC) of the lithium metal secondary battery falls within a predetermined range, the resistance value history acquisition unit acquires a history of a first resistance value, which is a resistance value of the lithium metal secondary battery during discharging for a first time, and a history of a second resistance value, which is a resistance value of the lithium metal secondary battery during discharging for a second time longer than the first time; the degradation state calculation unit calculates a 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 degradation suppression control unit that executes degradation suppression control to suppress degradation of the lithium metal secondary battery based on the state of health (SOH) calculated by the degradation state calculation unit, A degradation suppression system, wherein the degradation suppression control unit executes the degradation suppression control when a ratio of the second resistance value to the first resistance value, that is, a value of second resistance value / first resistance value, exceeds 3.

2. the resistance value history acquisition unit acquires a history of the first resistance value and a history of the second resistance value while the vehicle is traveling; 2 . The degradation suppression system according to claim 1 , wherein the degradation state calculation unit calculates the state of degradation SOH when a charging rate SOC of the lithium metal secondary battery becomes 30% or less.

3. 3. The degradation suppression system according to claim 1, wherein the first time period is 1 second, and the second time period is 5 to 30 seconds.

4. 4. The degradation suppression system according to claim 1, further comprising a degradation state notifying unit that notifies the state of health (SOH) of the lithium metal secondary battery calculated by the degradation state calculating unit.

5. A method for estimating a state of deterioration of a lithium metal secondary battery including a lithium metal in a negative electrode, comprising: a resistance value history acquisition step of acquiring a history of the resistance value of the lithium metal secondary battery during a predetermined period of discharge; and a deterioration state calculation step of calculating a state of health (SOH) of the lithium metal secondary battery based on the resistance value history acquired in the resistance value history acquisition step when the charging rate (SOC) of the lithium metal secondary battery falls within a predetermined range. the resistance value history acquisition step acquires a history of a first resistance value, which is a resistance value of the lithium metal secondary battery during discharging for a first time, and a history of a second resistance value, which is a resistance value of the lithium metal secondary battery during discharging for a second time longer than the first time; the state of health calculation step calculates a 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 in the resistance value history acquisition step; and a degradation suppression control step of performing degradation suppression control to suppress degradation of the lithium metal secondary battery based on the state of health (SOH) calculated in the degradation state calculation step. A degradation state estimating method, in which the degradation suppression control process executes the degradation suppression control when a ratio of the second resistance value to the first resistance value, that is, second resistance value / first resistance value, exceeds 3.

6. the resistance value history acquisition step includes acquiring a history of the first resistance value and a history of the second resistance value while the vehicle is traveling; 6. The method according to claim 5, wherein the step of calculating the state of health calculates the state of health SOH when a charging rate SOC of the lithium metal secondary battery becomes 30% or less.

7. 7. The degradation state estimating method according to claim 5, wherein the first time period is 1 second and the second time period is 30 seconds.

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