Battery deterioration estimation device

Abstract

The present invention addresses the problem of making it possible to estimate the degree of deterioration of a secondary battery having a lithium metal layer on the negative electrode with high accuracy. In order to solve the problem, this battery degradation estimation device is provided with a current measurement unit, a voltage measurement unit, a calculation unit, and an estimation unit. The current measuring unit measures the discharge current of the secondary battery at a predetermined timing immediately after the discharge of the secondary battery begins. The voltage measuring unit measures a droop voltage, which is a difference between the voltage of the secondary battery before the start of discharge and the voltage of the secondary battery at the prescribed time. The calculation unit calculates the internal impedance of the secondary battery at the predetermined time on the basis of the measured discharge current and the measured dropout voltage. The estimation unit estimates the degree of deterioration of the secondary battery on the basis of the calculated internal impedance.

Description

Technical Field

[0001] The present invention relates to a battery degradation estimation device for estimating the degree of degradation of a secondary battery. Background Art

[0002] In recent years, from the viewpoints of reducing carbon dioxide emissions and minimizing adverse impacts on the global environment, electric vehicles such as electric vehicles (EVs) and hybrid electric vehicles (HEVs) have been gaining popularity. Some secondary batteries installed in electric vehicles and the like are configured as follows. That is, the secondary battery includes a positive electrode, a negative electrode having a metallic lithium layer, and an electrolyte disposed between the positive electrode and the negative electrode.

[0003] [Prior Art Documents]

[0004] (Patent Document)

[0005] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2023-87844 Summary of the Invention

[0006] [Problems to be Solved by the Invention]

[0007] In such a secondary battery, as charging and discharging are repeated, an SEI film is formed on the metallic lithium layer of the negative electrode and gradually grows. Here, "SEI" is an abbreviation for "Solid Electrolyte Interphase".

[0008] The inventor considered estimating the degree of degradation of the secondary battery based on the growth degree of the SEI film. This is because the growth of the SEI film means a decrease in the activity of metallic lithium in the negative electrode. Therefore, if the growth degree of the SEI film is known, the degree of decrease in the activity of metallic lithium can be estimated, and thus the degree of degradation of the secondary battery can be estimated.

[0009] As the SEI film grows, the resistance of the SEI layer gradually increases. And in a state where the SEI layer has grown to a certain extent or more, the resistance of the SEI film occupies a large proportion of the internal impedance of the entire secondary battery. Therefore, the growth degree of the SEI film can be estimated based on the internal impedance of the secondary battery. The degree of degradation of the secondary battery can be estimated based on the growth degree.

[0010] However, the present inventors also focused on the following problems. When the secondary battery discharges, the dissolution and precipitation of metallic lithium are stabilized within the metallic lithium layer. That is, the following situation is stabilized: The metallic lithium in the part of the metallic lithium layer closer to the negative electrode than the SEI film temporarily dissolves, passes through the SEI film, and then inserts into the positive electrode active material. During this process, the diffusion resistance accounts for a larger proportion in the internal impedance of the secondary battery. Therefore, the resistance of the SEI film cannot be measured with high precision. Consequently, the growth degree of the SEI film cannot be accurately estimated. As a result, the degree of deterioration of the secondary battery cannot be accurately estimated based on this growth degree.

[0011] The present invention has been completed in view of the above circumstances, and an object thereof is to accurately estimate the degree of deterioration of a secondary battery having a metallic lithium layer at the negative electrode.

[0012] [Technical means for solving the problem]

[0013] The present inventors found that the growth degree of the SEI film can be accurately estimated based on the internal impedance of the secondary battery immediately after the start of discharge, and thus completed the present invention. The present invention is a battery deterioration estimation device of the following (1) to (6) and a battery deterioration estimation method of the following (7).

[0014] (1) A battery deterioration estimation device for estimating the degree of deterioration of a secondary battery including a positive electrode, a negative electrode having a metallic lithium layer, and an electrolyte provided between the positive electrode and the negative electrode, and the battery deterioration estimation device includes:

[0015] A current measurement unit that measures the discharge current of the secondary battery at a specified time immediately after the start of discharge of the secondary battery;

[0016] A voltage measurement unit that measures the difference in voltage, i.e., the voltage drop, between the voltage of the secondary battery before the start of discharge and the voltage of the secondary battery at the specified time;

[0017] A calculation unit that calculates the internal impedance of the secondary battery at the specified time based on the measured discharge current and the measured voltage drop; and,

[0018] An estimation unit that estimates the degree of deterioration of the secondary battery based on the calculated internal impedance.

[0019] According to this structure, the internal impedance of the secondary battery immediately after the start of discharge is obtained by the current measurement unit, the voltage measurement unit, and the calculation unit. After the start of discharge, within the metallic lithium layer, the dissolution and precipitation of metallic lithium have not yet stabilized. Therefore, in the entire secondary battery, the decrease in the battery voltage caused by the diffusion resistance has not yet become severe. The estimation unit can accurately estimate the growth degree of the SEI film based on the internal impedance of the secondary battery in this state. As a result, the degree of deterioration of the secondary battery can be accurately estimated. As described above, according to this structure, the degree of deterioration of the secondary battery having a metallic lithium layer on the negative electrode can be accurately estimated.

[0020] (2) The battery deterioration estimation device according to the above (1), wherein the specified time is the time after a specified time of 0.001 seconds or more and 1.0 second or less has elapsed since the start of discharge of the secondary battery.

[0021] Although if the discharge time is short, the influence of the diffusion resistance and the like can be more effectively excluded, if the discharge time is too short, it is easily affected by the inductance of the wiring harness and the like, and accurate measurement cannot be performed. In this regard, according to this structure, the specified time as the time for measuring the internal impedance of the secondary battery is 1.0 second before the start of discharge, so the discharge time is short enough to more effectively exclude the influence of the diffusion resistance and the like. In addition, since this time is after 0.001 seconds or more since the start of discharge of the secondary battery, there will be no situation where the discharge time is too short, and it is not easily affected by the inductance of the wiring harness and the like. Based on the above, the growth degree of the SEI film can be estimated with higher accuracy.

[0022] (3) The battery deterioration estimation device according to the above (1) or (2), which includes:

[0023] A second current measurement unit that measures the discharge current of the secondary battery at a second specified time after the specified time, that is, the second discharge current;

[0024] A second voltage measurement unit that measures the difference between the voltage of the secondary battery before the start of discharge and the voltage of the secondary battery at the second specified time, that is, the second voltage drop; and,

[0025] A second calculation unit that calculates the internal impedance of the secondary battery at the second specified time based on the measured second discharge current and the measured second voltage drop;

[0026] The estimation unit comprehensively estimates the degree of deterioration of the secondary battery based on the internal impedance of the specified time calculated and the internal impedance of the second specified time calculated.

[0027] According to this structure, the internal impedance of the secondary battery at a second specified time after a specified time is obtained by the second current measurement unit, the second voltage measurement unit, and the second calculation unit. It has been confirmed that the internal impedance at the second specified time rises sharply at the time when the capacity of the secondary battery decreases sharply. Therefore, by also using the internal impedance at the second specified time, the degree of deterioration of the secondary battery can be estimated with higher accuracy.

[0028] (4) The battery deterioration estimation device according to (3) above, wherein the second specified time is a time at which a specified time of 3.0 seconds or more and 30 seconds or less has elapsed since the start of discharging of the secondary battery.

[0029] According to this structure, the second specified time as the time for measuring the internal impedance of the secondary battery is after 3 seconds or more have elapsed since the start of discharging of the secondary battery, so that sufficient time can be ensured until the internal impedance of the secondary battery stabilizes. In addition, since the second specified time is 30 seconds before the start of discharging, a large amount of time can be avoided being consumed in obtaining the internal impedance.

[0030] (5) The battery deterioration estimation device according to (1) or (2) above, wherein the secondary battery and the battery deterioration estimation device are mounted on a vehicle.

[0031] According to this structure, the degree of deterioration of the secondary battery can be estimated inside the vehicle.

[0032] (6) The battery deterioration estimation device according to (5) above, which includes a notification device that notifies the driver of the vehicle that the secondary battery has deteriorated on the condition that the estimation unit determines that the secondary battery has deteriorated beyond a specified reference.

[0033] According to this structure, when the secondary battery deteriorates, the driver of the vehicle can quickly recognize this fact.

[0034] (7) A battery deterioration estimation method for estimating the deterioration of a secondary battery including a positive electrode, a negative electrode having a metallic lithium layer, and an electrolyte provided between the positive electrode and the negative electrode, and the battery deterioration estimation method is as follows:

[0035] Measure the discharge current of the secondary battery at a specified time immediately after the start of discharging of the secondary battery.

[0036] Measure the drop voltage, which is the difference between the voltage of the secondary battery before the start of discharging and the voltage of the secondary battery at the specified time.

[0037] Calculate the internal impedance of the secondary battery at the specified time based on the measured discharge current and the measured drop voltage.

[0038] Based on the calculated internal impedance described above, the degree of deterioration of the secondary battery is estimated.

[0039] According to this method, the same effect as that of the device in the above (1) can also be obtained.

[0040] (Advantages of the Invention)

[0041] As described above, based on the device in the above (1) and the method in the above (7), the growth degree of the SEI film of the secondary battery having a metallic lithium layer on the negative electrode can be estimated with high precision. Furthermore, according to the structures in the above (2) to (6) that cite the above (1), respective additional effects can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is a structural diagram showing a battery deterioration estimation device according to a first embodiment.

[0043] Figure 2 is a circuit diagram showing a circuit in a vehicle.

[0044] Figure 3 is a circuit diagram showing a situation during discharge.

[0045] Figure 4 is a circuit diagram showing a situation during charging.

[0046] Figure 5 is a circuit diagram showing a state in which an SEI film is formed.

[0047] Figure 6 is a circuit diagram showing the internal impedance of a secondary battery.

[0048] Figure 7 is a graph showing the relationship between the thickness of the SEI film and the impedance after 0.1 second.

[0049] Figure 8 is a graph showing the relationship between the discharge time of a secondary battery and the voltage between terminals.

[0050] Figure 9 is a graph showing the relationship between the number of charge-discharge cycles and the impedance after 10 seconds, and the relationship between the number of charge-discharge cycles and the capacity of the secondary battery.

[0051] Figure 10 is a graph showing the relationship between the number of charge-discharge cycles and the impedance after 0.1 second.

[0052] Figure 11 is a structural diagram showing a battery deterioration estimation device according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0053] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Note that the present invention is in no way limited to the following embodiments, and can be implemented with appropriate modifications without departing from the gist of the present invention.

[0054] [First Embodiment]

[0055] As Figure 2 shown, the battery degradation estimation device 50 of the present embodiment is mounted on the vehicle 100. An electrical device 70 and a secondary battery 30 are also mounted on the vehicle 100. The electrical device 70 includes a Power Control Unit (PCU) and the like. The secondary battery 30 supplies power to the electrical device 70. The battery degradation estimation device 50 estimates the degree of degradation of the secondary battery 30.

[0056] The secondary battery 30 is a semi-solid battery, and includes a positive electrode 38, a negative electrode 32, and an electrolyte 35. The positive electrode 38 includes a positive electrode current collector 38a and a positive electrode active material layer 38b. The positive electrode current collector 38a is made of a current collecting foil such as aluminum, for example. The positive electrode active material layer 38b is a layer such as lithium cobaltate, for example. The negative electrode 32 includes a negative electrode current collector 32a and a negative electrode active material layer 32b. The negative electrode current collector 32a is made of a current collecting foil such as copper, for example. The negative electrode active material layer 32b is a metallic lithium layer. The electrolyte 35 is a semi-solid electrolyte containing lithium ions Li+. The electrolyte 35 is separated into a positive electrode 38 side and a negative electrode 32 side by a separator 35s.

[0057] As Figure 3 shown, during discharge when the secondary battery 30 supplies power to the electrical device 70, lithium ions Li+ flow from the negative electrode active material layer 32b to the positive electrode 38 side through a path passing through the separator 35s. At the same time, electrons e flow from the negative electrode 32 to the positive electrode 38 side through a path passing through the circuit of the electrical device 70. Thus, in the vehicle 100, a current I flows from the positive electrode 38 side toward the negative electrode 32 side, causing the secondary battery 30 to discharge. With the discharge, metallic lithium gradually dissolves in the negative electrode active material layer 32b.

[0058] As Figure 4 shown, during charging when the secondary battery 30 is charged by a charging power source 200 outside the vehicle 100, lithium ions Li+ flow from the positive electrode active material layer 38b to the negative electrode 32 side through a path passing through the separator 35s. At the same time, electrons e flow from the positive electrode 38 to the negative electrode 32 side through a path passing through the charging power source 200. Thus, a current I flows from the negative electrode 32 side toward the positive electrode 38 side, charging the secondary battery 30. With the charging, metallic lithium gradually precipitates in the negative electrode active material layer 32b.

[0059] Moreover, by repeatedly performing such charge and discharge, Figure 5The SEI film 32a shown is formed on the negative electrode active material layer 32b and gradually grows. That is, the thickness Tg of the SEI film 32g gradually increases.

[0060] Hereinafter, the portion of the negative electrode active material layer 32b closer to the negative electrode current collector 32a than the SEI film 32g is referred to as the "remaining layer 32b1", and the portion of the negative electrode active material layer 32b closer to the positive electrode 38 than the SEI film 32g is referred to as the "precipitation layer 32b2".

[0061] Next, the principle of the battery deterioration estimation device 50 will be described. The battery deterioration estimation device 50 determines the degree of deterioration of the secondary battery 30 based on the growth degree of the SEI film 32g. This is because the growth of the SEI film 32g means a decrease in the activity of metallic lithium in the negative electrode active material layer 32b. Therefore, if the growth state of the SEI film 32g is known, the degree of decrease in the activity of metallic lithium can be estimated, and thus the degree of deterioration of the secondary battery 30 can be estimated.

[0062] Hereinafter, as Figure 6 shown, the resistance of the SEI film 32g is referred to as the "SEI film resistance R3,R4". The SEI film resistance R3,R4 gradually increases as the SEI film 32g grows. And, in a state where the SEI film 32g has grown to a certain extent or more, the resistance of the SEI film 32g accounts for a large proportion in the internal impedance Z of the entire secondary battery 30.

[0063] Specifically, the internal impedance Z of the secondary battery 30 is, for example, as Figure 6 shown, in addition to the SEI film resistance R3,R4, also includes the negative electrode interlayer resistance R1,R2, the separator resistance R5, the positive electrode internal resistance R6,R7, the positive electrode interlayer resistance R8,R9, etc.

[0064] The negative electrode interlayer resistance R1,R2 is the conduction resistance of electrons e between the negative electrode current collector 32a and the negative electrode active material layer 32b. The SEI film resistance R3,R4 is the conduction resistance of electrons e in the SEI film 32g. The separator resistance R5 is the conduction resistance of lithium ions Li+ in the separator 35s. The positive electrode internal resistance R6,R7 is the conduction resistance of lithium ions Li+ in the positive electrode active material layer 38b. The positive electrode interlayer resistance R8,R9 is the conduction resistance of electrons e between the positive electrode current collector 38a and the positive electrode active material layer 38b. If the SEI film 32g gradually grows, the proportion of the SEI film resistance R3,R4 in the internal impedance Z of the entire secondary battery 30 including these various elements also increases.

[0065] Therefore, the battery deterioration estimation device 50 predicts the deterioration state of the secondary battery 30 based on the internal impedance Z of the secondary battery 30.

[0066] However, there are still problems as described below. When the secondary battery 30 discharges, the dissolution and precipitation of metallic lithium are stabilized in the negative electrode active material layer 32b. That is, the following situation is stabilized: in the negative electrode active material layer 32b as shown in Figure 5 the remaining metallic lithium in the remaining layer 32b1 in the negative electrode active material layer 32b temporarily dissolves, passes through the SEI film 32g, and then is inserted into the positive electrode active material layer 38b. In this process, the diffusion resistance accounts for a larger proportion in the internal impedance Z of the secondary battery 30. Therefore, the SEI film resistances R3 and R4 as shown in Figure 6 cannot be measured with high precision. Thus, the growth degree of the SEI film 32g as shown in Figure 5 cannot be estimated with high precision. As a result, the degree of deterioration of the secondary battery 30 cannot be estimated with high precision.

[0067] Therefore, Figure 5 the battery deterioration estimation device 50 as shown in estimates the degree of deterioration of the secondary battery 30 based on the internal impedance Z of the secondary battery 30 at a specified time immediately after the secondary battery 30 starts discharging. This is because the dissolution and precipitation of the aforementioned metallic lithium have not been stabilized immediately after the secondary battery 30 starts discharging. Specifically, the "specified time" here is the time after 0.1 seconds from the start of discharging of the secondary battery 30. Hereinafter, this time will be referred to as the "time after 0.1 seconds".

[0068] In addition, hereinafter, the discharge current of the secondary battery 30 at the time after 0.1 seconds will be referred to as the "current Ia after 0.1 seconds". In addition, as shown in Figure 8 the difference between the inter-terminal voltage Vo of the secondary battery 30 before the start of discharging and the inter-terminal voltage V of the secondary battery 30 at the time after 0.1 seconds is referred to as the "voltage drop ΔVa after 0.1 seconds". In addition, as shown in Figure 7 the internal impedance Z of the secondary battery 30 at the time after 0.1 seconds is referred to as the "impedance Za after 0.1 seconds". As shown in Figure 7 the impedance Za after 0.1 seconds gradually increases as the thickness Tg of the SEI film increases.

[0069] Next, the structure of the battery deterioration estimation device 50 as shown in Figure 3 will be described. The battery deterioration estimation device 50 includes a voltage detector 51, a current detector 52, an arithmetic device 57, and a notification device 59.

[0070] The voltage detector 51 detects the inter-terminal voltage V of the secondary battery 30. The current detector 52 detects the current I flowing from the positive electrode 38 side to the negative electrode 32 side of the secondary battery 30. Therefore, when the secondary battery 30 discharges, the discharge current of the secondary battery 30 is detected. The arithmetic device 57 estimates the growth degree of the SEI film 32g in the metallic lithium layer based on these discharge current and the inter-terminal voltage V, and thus estimates the degree of deterioration of the secondary battery 30.

[0071] Specifically, as shown in Figure 1 , the arithmetic unit 57 includes a voltage measurement unit 53, a current measurement unit 54, a calculation unit 55, and an estimation unit 56.

[0072] Based on the information from the current detector 52, the current measurement unit 54 measures the current Ia after 0.1 second. Based on the information from the voltage detector 51, the voltage measurement unit 53 measures the voltage drop ΔVa after 0.1 second.

[0073] Based on the voltage drop ΔVa after 0.1 second measured by the voltage measurement unit 53 and the current Ia after 0.1 second measured by the current measurement unit 54, the calculation unit 55 calculates the impedance Za after 0.1 second. That is, the value obtained by dividing the voltage drop ΔVa after 0.1 second by the current Ia after 0.1 second (ΔVa / Ia) is calculated as the impedance Za after 0.1 second.

[0074] Based on the impedance Za after 0.1 second calculated by the calculation unit 55, the estimation unit 56 estimates Figure 5 the growth degree of the SEI film 32g in the negative electrode active material layer 32b as shown. Specifically, for example, the estimation unit 56 has a table showing the relationship between the information based on the impedance Za after 0.1 second and the growth degree of the SEI film 32g. Based on the table, the growth degree of the SEI film 32g is estimated.

[0075] More specifically, as shown in Figure 10 , through the experiments of the present inventors, it was confirmed that as the number of charge-discharge cycles N increases, the impedance Za after 0.1 second gradually increases. Furthermore, it was confirmed that the increasing speed of the impedance Za after 0.1 second, that is, Figure 10 the slope of "Za" as shown, sharply increases after a specified number of cycles Nt. As shown in Figure 9 , after the specified number of cycles Nt, the capacity Sh of the secondary battery 30 sharply decreases.

[0076] Therefore, the estimation unit 56 determines that the growth degree of the SEI film 32g has reached a specified standard at the position where the slope of "Za" sharply becomes larger. Specifically, for example, the information based on the impedance Za after 0.1 second in the aforementioned table includes one or more of the "Za", the slope of the "Za", and the increasing speed of the slope of the "Za". The estimation unit 56 estimates the growth degree of the SEI film 32g based on the information based on the impedance Za after 0.1 second and the aforementioned table. Based on the growth degree, it is determined whether the SEI film 32g has grown more than the specified standard. And, the estimation unit 56 determines that the secondary battery 30 has deteriorated more than the specified standard on the condition that it is determined that the growth is more than the specified standard, and sends a notification signal to the notification device 59.

[0077] Figure 1 When the notification device 59 shown receives the said notification signal, it notifies the driver of the vehicle 100 shown that the secondary battery 30 has deteriorated. The said notification can be, for example, a visual notification such as using a lamp or a display, a voice-based notification such as using a warning sound or a broadcast, or a notification based on both of them. Figure 2 When the notification device 59 shown receives the said notification signal, it notifies the driver of the vehicle 100 shown that the secondary battery 30 has deteriorated. The said notification can be, for example, a visual notification such as using a lamp or a display, a voice-based notification such as using a warning sound or a broadcast, or a notification based on both of them.

[0078] Hereinafter, the structure and effects of the present embodiment will be summarized.

[0079] According to the present embodiment, as Figure 1 shown, the voltage detector 51, the current detector 52, the voltage measurement unit 53, the current measurement unit 54, and the calculation unit 55 cooperate to obtain the impedance Za after 0.1 second. At the acquisition time of the impedance Za after 0.1 second, that is, at the time after 0.1 second, in Figure 5 the negative electrode active material layer 32b shown, the dissolution and precipitation of the aforementioned metallic lithium have not been stabilized. Therefore, in the entire secondary battery 30, the decrease in the inter-terminal voltage V caused by the diffusion resistance has not become serious. The estimation unit 56 can accurately estimate Figure 5 the growth degree of the SEI film 32g shown according to the internal impedance Z of the secondary battery 30 in this state. As a result, the deterioration degree of the secondary battery 30 can be accurately estimated.

[0080] Moreover, these secondary batteries 30 and the battery deterioration estimation device 50 are mounted on the vehicle 100. Therefore, the deterioration degree of the secondary battery 30 can be estimated inside the vehicle 100.

[0081] Moreover, the notification device 59 notifies the driver of the vehicle 100 that the secondary battery 30 has deteriorated on the condition that the estimation unit 56 determines that the secondary battery 30 has deteriorated beyond a specified reference. Therefore, when the secondary battery 30 deteriorates, the driver of the vehicle can quickly recognize this fact.

[0082] In addition, the use of the battery deterioration estimation device 50 shown above is equivalent to the implementation of the battery deterioration estimation method.

[0083] [Second Embodiment]

[0084] Next, the second embodiment will be described with reference to Figure 11 For this embodiment, based on the first embodiment, the description will be centered on aspects different from it, and the description of aspects the same as or similar to the first embodiment will be omitted as appropriate.

[0085] The battery degradation estimation device 50 of the present embodiment also estimates the degradation degree of the secondary battery 30 based on the internal impedance Z of the secondary battery 30 at a second specified time after the 0.1-second time. Specifically, the "second specified time" here is the time when 10 seconds have elapsed since the secondary battery 30 started discharging. Hereinafter, this time will be referred to as the "time after 10 seconds".

[0086] In addition, hereinafter, the discharge current of the secondary battery 30 at the time after 10 seconds will be referred to as the "current Ib after 10 seconds". In addition, as Figure 8 shown, the difference between the inter-terminal voltage Vo of the secondary battery 30 before the start of discharge and the inter-terminal voltage V of the secondary battery 30 at the time after 10 seconds is referred to as the "voltage drop ΔVb after 10 seconds". In addition, the internal impedance Z of the secondary battery 30 at the time after 10 seconds is referred to as the "impedance Zb after 10 seconds". In addition, the "current Ib after 10 seconds" can also be renamed the "second discharge current". In addition, the "voltage drop ΔVb after 10 seconds" can also be renamed the "second voltage drop".

[0087] As Figure 11 shown, in addition to the state of the first embodiment, the arithmetic device 57 further includes a second voltage measurement unit 53b, a second current measurement unit 54b, and a second calculation unit 55b. The second voltage measurement unit 53b measures the voltage drop ΔVb after 10 seconds based on the information from the voltage detector 51. The second current measurement unit 54b measures the current Ib after 10 seconds based on the information from the current detector 52.

[0088] The second calculation unit 55b calculates the impedance Zb after 10 seconds based on the voltage drop ΔVb after 10 seconds measured by the second voltage measurement unit 53b and the current Ib after 10 seconds measured by the second current measurement unit 54b. That is, the value obtained by dividing the voltage drop ΔVb after 10 seconds by the current Ib after 10 seconds (ΔVa / Ib) is calculated as the impedance Zb after 10 seconds.

[0089] The estimation unit 56 comprehensively estimates the degradation degree of the secondary battery 30 based on the impedance Za after 0.1 second calculated by the calculation unit 55 and the impedance Zb after 10 seconds calculated by the second calculation unit 55b. Specifically, for example, the estimation unit 56 has a table showing the relationship between the multi-information and the growth degree of the SEI film 32g, and the multi-information includes information based on the impedance Za after 0.1 second and information based on the impedance Zb after 10 seconds. Based on the table, the growth degree of the SEI film 32g is estimated.

[0090] More specifically, as Figure 9As shown, through the experiments of the present inventor, it is confirmed that as the number of charge-discharge cycles N increases, the impedance Zb gradually increases after 10 seconds. Moreover, it is confirmed that the increasing rate of the impedance Zb after 10 seconds, that is, the slope of "Zb" in this Figure 9 sharply increases after a specified number of cycles Nt. In addition, as a reason, it may be that the remaining layer 32b1 shown in Figure 5 has been depleted at the specified number of cycles Nt. As Figure 9 shown, at the specified number of cycles Nt, the capacity Sh of the secondary battery 30 also sharply decreases.

[0091] Therefore, the estimation unit 56 also estimates the degree of deterioration of the secondary battery 30 based on the portion where the slope of this "Zb" sharply increases. Specifically, for example, the information based on the impedance Za after 10 seconds in the foregoing table includes one or more of this "Zb", the slope of this "Zb", and the increasing rate of the slope of this "Zb". The estimation unit 56 estimates the degree of deterioration of the secondary battery 30 according to the foregoing multi-information including the information based on the impedance Za after 10 seconds and the foregoing table. According to the degree of deterioration, it is determined whether the secondary battery 30 has deteriorated beyond a specified reference.

[0092] According to the present embodiment, as Figure 11 shown, the estimation unit 56 comprehensively estimates the degree of deterioration of the secondary battery 30 based on the impedance Za after 0.1 second and the impedance Zb after 10 seconds. Therefore, the degree of deterioration can be estimated with higher accuracy.

[0093] [Other Embodiments]

[0094] The embodiments shown above can be modified as follows, for example. Figure 2 The electrolyte 35 of the secondary battery 30 shown in

[0095] The aforementioned specified time may also be a time other than the time 0.1 second later. Among them, even in this case, the specified time is preferably a time at which a specified time of 0.001 second or more and 1.0 second or less has elapsed since the secondary battery 30 started discharging. This is because, although if the discharge time is short, the influence of diffusion resistance and the like can be more effectively eliminated, if the discharge time is too short, it is liable to be affected by the inductance of a wiring harness or the like, and accurate measurement cannot be performed. In this regard, if the specified time as the time for measuring the internal impedance Z of the secondary battery 30 is 1.0 second before the start of discharging, the discharge time is sufficiently short, so the influence of diffusion resistance and the like can be more effectively eliminated. In addition, this is because, if this time is 0.001 second or more after the secondary battery 30 starts discharging, there will be no situation where the discharge time is too short, and it is not liable to be affected by the inductance of a wiring harness or the like.

[0096] In terms of being able to more reliably perform measurement before this stabilization, the specified time is more preferably a time at which a specified time of 0.5 second or less has elapsed since the start of discharging, and further preferably a time at which a specified time of 0.2 second or less has elapsed since the start of discharging.

[0097] In the second embodiment, the aforementioned second specified time may also be a time other than the time 10 seconds later. Among them, even in this case, the second specified time is preferably a time at which a specified time of 3 seconds or more and 30 seconds or less has elapsed since the secondary battery 30 started discharging. This is because, if it is 3 seconds or more after the start of discharging, the time until the internal impedance Z of the secondary battery 30 stabilizes can be sufficiently ensured. In addition, it is because, if it is 30 seconds before the start of discharging, a large amount of time can be avoided being consumed in obtaining the internal impedance Z.

[0098] Reference numerals

[0099] 30 Secondary battery

[0100] 32 Negative electrode

[0101] 32b Negative electrode active material layer (lithium metal layer)

[0102] 35 Electrolyte

[0103] 38 Positive electrode

[0104] 50 Battery deterioration estimation device

[0105] 53 Voltage measurement unit

[0106] 53b Second voltage measurement unit

[0107] 54 Current measurement unit

[0108] 54b Second current measurement unit

[0109] 55 Calculation unit

[0110] 55b Second calculation unit

[0111] 56 Estimation unit

[0112] 59 Notification device

[0113] 100 Vehicle

[0114] Ia Current after 0.1 s (discharge current of secondary battery at specified time)

[0115] Ib Current after 10 s (second discharge current)

[0116] V Terminal voltage of secondary battery (voltage of secondary battery)

[0117] ΔVa Drop voltage after 0.1 s (drop voltage of secondary battery at specified time)

[0118] ΔVb Drop voltage after 10 s (second drop voltage)

[0119] Z Internal impedance

[0120] Za Impedance after 0.1 s (internal impedance at specified time)

[0121] Zb Impedance after 10 s (internal impedance at second specified time)

Claims

1. A battery degradation estimation device for estimating the degree of degradation of a secondary battery comprising a positive electrode, a negative electrode having a metal lithium layer, and an electrolyte disposed between the positive electrode and the negative electrode, and the battery degradation estimation device comprises: a current measuring unit for measuring a discharge current of the secondary battery at a predetermined time after the secondary battery starts to discharge; a voltage measuring unit for measuring a drop voltage which is a difference between a voltage of the secondary battery before the start of discharge and a voltage of the secondary battery at the predetermined time; a calculation unit that calculates the internal impedance of the secondary battery at the predetermined time based on the measured discharge current and the measured drop voltage; and The estimating unit estimates a degree of deterioration of the secondary battery based on the calculated internal impedance.

2. The battery degradation estimation device according to claim 1, wherein: The predetermined time is a time when a predetermined time of not less than 0.001 second and not more than 1.0 second has elapsed since the start of discharge of the secondary battery.

3. The battery degradation estimation device according to claim 1 or 2, wherein: have: a second current measuring unit for measuring a second discharge current of the secondary battery at a second predetermined time later than the predetermined time; A second voltage measuring unit measures a second drop voltage which is a difference between a voltage of the secondary battery before the start of discharge and a voltage of the secondary battery at the second predetermined time; and a second calculation unit for calculating the internal impedance of the secondary battery at the second predetermined time based on the measured second discharge current and the measured second drop voltage; The estimating unit comprehensively estimates a degree of deterioration of the secondary battery based on the calculated internal impedance at the predetermined time and the calculated internal impedance at the second predetermined time.

4. The battery degradation estimation device according to claim 3, wherein: The second predetermined time is a time when a predetermined time of 3.0 seconds to 30 seconds has elapsed since the secondary battery started discharging.

5. The battery degradation estimation device according to claim 1 or 2, wherein: The secondary battery and the battery degradation estimation device are mounted on a vehicle. 6 . The battery degradation estimation device according to claim 5 , further comprising a notification device for notifying a driver of the vehicle that the secondary battery has deteriorated, on the condition that the estimation unit determines that the secondary battery has deteriorated by a predetermined reference or more.

7. A battery degradation estimation method, for estimating the degradation of a secondary battery comprising a positive electrode, a negative electrode having a metal lithium layer, and an electrolyte disposed between the positive electrode and the negative electrode, wherein: measuring the discharge current of the secondary battery at a predetermined time after the secondary battery starts discharging, measuring the drop voltage, which is the difference between the voltage of the secondary battery before the start of discharge and the voltage of the secondary battery at the predetermined time, calculating the internal impedance of the secondary battery at the predetermined time based on the measured discharge current and the measured drop voltage, The degree of deterioration of the secondary battery is estimated based on the calculated internal impedance.

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