Secondary battery degradation estimation device

Abstract

This invention provides a secondary battery degradation estimation device that can calculate the amount of SEI coating in a secondary battery by taking into account the SEI coating formed at cracks in the active material. [Solution] Based on the charge / discharge current Icd, PU42 periodically and repeatedly calculates the amount of SEI coating on exposed surfaces caused by cracking of the active material. PU42 periodically and repeatedly calculates the increase in the amount of SEI coating on newly exposed surfaces in the past. PU42 calculates the decrease in full charge capacity according to the sum of the newly created amount of SEI coating and the increase in the amount of SEI coating.

Description

Technical Field

[0001] The present invention relates to a secondary battery deterioration estimation device.

Background Art

[0002] For example, Patent Document 1 below describes a device that calculates the film thickness of the SEI film of a secondary battery on the assumption that the film thickness of the SEI film is proportional to the square root of time. In this device, the amount of the SEI film is grasped by multiplying the thus calculated film thickness by the surface area of the active material.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, the active material in a secondary battery can crack due to aging deterioration. And, an exposed surface, which is a surface not covered by the SEI film, occurs at the cracked portion. The SEI film is formed on this exposed surface. However, the above device does not consider the newly generated SEI film.

Means for Solving the Problems

[0005] Hereinafter, means for solving the above problems and their effects will be described. 1. A secondary battery degradation estimation device for estimating the degree of degradation of a secondary battery, configured to repeatedly perform an acquisition process, a new film amount calculation process, a partial increase amount calculation process, a film increase amount calculation process, and a capacity decrease amount calculation process, wherein the acquisition process is a process for acquiring the charge and discharge current of the secondary battery, the new film amount calculation process is a process for calculating the new film amount, which is the amount of SEI film newly formed on the cracked portion of the active material, which is the surface where SEI film has not been formed, based on the charge and discharge current as an input variable, and the partial increase amount calculation process is a process for calculating the partial increase amount and the timing of when the new film amount was calculated and the current timing A secondary battery degradation estimation device, comprising a process to change the partial increase amount according to the time difference, provided that the partial increase amount when the time difference with the time difference is long is less than or equal to the partial increase amount when the time difference is short, wherein the partial increase amount is the increase in the SEI coating at the cracked portion where the new coating amount was calculated at a past execution timing of the new coating amount calculation process, the coating increase amount calculation process is a process to calculate the increase in the SEI coating based on the new coating amount and the partial increase amount as input variables, and the capacity decrease amount calculation process is a process to calculate the decrease in the full charge capacity of the secondary battery based on the increase in the SEI coating as an input variable.

[0006] The ion concentration in the active material changes during charging and discharging of a secondary battery. This change in ion concentration causes a change in the volume of the active material, resulting in stress. When cracks occur in the active material due to this stress, exposed surfaces not covered by the SEI coating are created at the cracks, and the SEI coating is formed there. Therefore, in the above configuration, the amount of newly formed coating, which is the amount of SEI coating generated at newly formed cracks, is calculated based on the charging and discharging current.

[0007] The SEI film formed at the crack gradually increases in thickness. This rate of increase tends to decrease over time. Therefore, in the above configuration, the increase in the SEI film is repeatedly calculated, and the increase in film thickness is negatively correlated with the time difference between the timing of the calculation of the newly formed film and the current timing. This allows for highly accurate calculation of the amount of SEI film formed at the crack.

[0008] The SEI coating is generated by consuming electrolyte. Therefore, by accurately calculating the amount of SEI coating, the decrease in full charge capacity can be calculated with high accuracy. 2. The secondary battery degradation estimation device according to paragraph 1, wherein the new film amount calculation process includes a process to set the new film amount to zero when the magnitude of the charge / discharge current is less than or equal to a predetermined value, and the partial increase amount calculation process includes a process to calculate the partial increase amount for each different execution timing of the new film amount calculation process, and a process to set the partial increase amount corresponding to the execution timing in which the new film amount is set to zero to zero.

[0009] As described above, cracks occur in the active material due to volume changes caused by charging and discharging of the secondary battery. Therefore, in the above configuration, when the magnitude of the charge / discharge current is below a predetermined value, the generation of cracks is considered negligible, and the amount of newly formed coating is set to zero. Furthermore, the increase in SEI coating related to the cracks at that timing is always set to zero even when subsequent partial increase calculation processing is performed. As a result, the increase in SEI coating can be calculated with high accuracy.

[0010] 3. The secondary battery degradation estimation device according to 1 or 2 above, wherein the new film amount calculation process includes a process of calculating the surface area of ​​the crack based on the magnitude of the charge / discharge current as an input variable, and a process of substituting the value obtained by multiplying the surface area of ​​the crack by the initial film thickness into the new film amount, and the partial increase amount calculation process includes a process of substituting the value obtained by multiplying each of the surface areas of the crack calculated at different past execution timings of the new film amount calculation process by the film thickness increase amount into the partial increase amount, and a process of changing the film thickness increase amount according to the time difference, provided that the film thickness increase amount of the crack with a long time difference between the timing at which the new film amount was calculated and the current timing is less than or equal to the film thickness increase amount of the crack with a short time difference, and the film increase amount calculation process includes a process of calculating the increase amount of the SEI film by adding the new film amount and a plurality of partial increase amounts.

[0011] In the above configuration, the surface area of ​​the newly formed crack can be calculated based on the magnitude of the charge and discharge current, thereby appropriately calculating the surface area according to the magnitude of the stress applied to the active material. Furthermore, in the above configuration, the partial increase is calculated by multiplying the calculated surface area by the increase in film thickness. This allows for appropriate calculation of the partial increase at each crack.

[0012] 4. The secondary battery degradation estimation apparatus according to item 3 above, wherein the partial increase amount calculation process includes a process of calculating the sum of the partial increase amounts of multiple cracks where the time difference between the timing at which the amount of newly formed film was calculated and the current timing is greater than or equal to a predetermined value, by multiplying the sum of the surface areas of those cracks by the film thickness increase amount calculated by a common time difference.

[0013] The number of cracks targeted for calculating the increase in film thickness through the partial increase calculation process increases with the number of executions of the new film thickness calculation process. Therefore, when calculating the increase in film thickness for each crack individually, the computational load increases over time.

[0014] Incidentally, the increase in film thickness gradually decreases as the time elapsed since the crack occurred increases. Therefore, after a certain amount of time has passed since the crack occurred, the influence of the time elapsed since the crack occurred on the increase in film thickness decreases. Thus, in the above configuration, the increase in film thickness for each of the multiple cracks where the time difference between the timing at which the amount of new film was calculated and the current timing is greater than or equal to a predetermined value is considered to be the same. This makes it possible to strike a suitable compromise between reducing the computational load and calculating the partial increase with high accuracy.

[0015] 5. A secondary battery degradation estimation device according to 3 or 4 above, configured to perform a history storage process, wherein the history storage process is a process of storing the value of a history variable, the history variable is a variable indicating the charge and discharge history of the secondary battery, and the new film amount calculation process includes a process of changing the surface area based on the value of the history variable, even if the number of executions of the new film amount calculation process is the same, under the condition that the surface area of ​​the cracked portion when the period in which the magnitude of the charge and discharge current is less than or equal to a specified value is longer is less than or equal to the surface area when the period in which it is shorter.

[0016] According to Paris's law, the fatigue crack propagation rate is positively correlated with the number of times the load is applied. Therefore, the surface area at which a crack occurs tends to decrease as the period during which the charge / discharge current is below a specified value (such as when charge / discharge is stopped) lengthens. In the above configuration, the surface area is changed based on the value of the hysteresis variable. This allows for a more accurate calculation of the amount of new coating compared to when the value of the hysteresis variable is not considered.

[0017] 6. A secondary battery degradation estimation device according to any one of 1 to 5 above, which is configured to perform a notification process, wherein the notification process is a process of notifying that the secondary battery has deteriorated by operating a notification device when the amount of decrease in the full charge capacity exceeds a predetermined value.

[0018] In the above configuration, if the secondary battery deteriorates, it can be notified accordingly. [Brief explanation of the drawing]

[0019] [Figure 1] It is a system configuration diagram of a vehicle drive system according to an embodiment. [Figure 2] It is a flowchart showing the procedure of the process executed by the battery ECU shown in FIG. 1. [Figure 3] It is a flowchart showing the procedure of the process executed by the battery ECU shown in FIG. 1. [Figure 4] It is a flowchart showing the procedure of the process executed by the battery ECU shown in FIG. 1 in the second embodiment.

Mode for Carrying Out the Invention

[0020] <First Embodiment> Hereinafter, the first embodiment will be described with reference to the drawings. FIG. 1 shows the configuration of the vehicle drive system.

[0021] The in-vehicle battery 10 is a series connection body of battery cells 12(1), 12(2),... 12(n). The terminal voltage of the in-vehicle battery 10 may be, for example, several tens of volts to several hundreds of volts. The numbers in parentheses in the battery cells 12(1), 12(2),... 12(n) are numbers for identifying the individual units. Hereinafter, when summarizing the battery cells 12(1), 12(2),... 12(n), they will be described as battery cells 12. The battery cells 12 are lithium-ion secondary batteries.

[0022] The terminals of the in-vehicle battery 10 are connected to the power conversion circuit 22 via the system main relay 20. The power conversion circuit 22 is a circuit that supplies the power of the in-vehicle battery 10 to the motor generator 24. Also, the power conversion circuit 22 is a circuit that supplies the generated power of the motor generator 24 to the in-vehicle battery 10. The rotating shaft of the motor generator 24 is mechanically connected to the drive wheels of the vehicle.

[0023] The monitoring unit 30 is a circuit that monitors the states of the battery cells 12(1), 12(2),... 12(n) of the in-vehicle battery 10. The battery ECU 40 is a device that monitors the status of the onboard battery 10. The battery ECU 40 can communicate with the higher-level ECU 60 via the in-vehicle network 50. The higher-level ECU 60 is a device that manages the power of the vehicle's drive system. The higher-level ECU 60 controls the driving force of the motor generator 24 by outputting commands to the MGECU 70 via the in-vehicle network 50. The amount of power charged and discharged from the onboard battery 10 is also controlled by the control of the driving force. Therefore, the amount of power charged and discharged from the onboard battery 10 is controlled by the higher-level ECU 60 outputting commands to the MGECU 70 via the in-vehicle network 50.

[0024] The MGECU70 controls the motor generator 24. The MGECU70 operates the power conversion circuit 22 to control the torque and other parameters of the motor generator 24.

[0025] The battery ECU 40 refers to the charge / discharge current Icd of the vehicle battery 10 detected by the current sensor 80. The battery ECU 40 also refers to the cell temperature Tc of the battery cells 12(1), 12(2), ... 12(n), detected by the monitoring unit 30. Note that the cell temperature Tc may be detected separately for each of the battery cells 12(1), 12(2), ... 12(n).

[0026] The battery ECU 40 includes a PU 42 and a storage device 44. The PU 42 is a software processing unit such as a CPU. The storage device 44 may be an electrically rewritable non-volatile memory and a storage medium such as a disk medium.

[0027] "Determination of deterioration" The battery ECU 40 performs a process to determine whether or not the vehicle battery 10 has deteriorated based on the decrease in the vehicle battery 10's full charge capacity. This will be described in detail below.

[0028] Figures 2 and 3 show the procedure for the process related to the above determination. The process shown in Figures 2 and 3 is achieved by the PU 42 repeatedly executing the program stored in the memory device 44 at a predetermined period Δt. In the following, the step number of each process is represented by a number preceded by "S".

[0029] In the series of processes shown in Figures 2 and 3, PU42 first acquires the charge / discharge current Icd(k) and the cell temperature Tc(k) (S10). Here, the variable k in parentheses indicates the number of times the series of processes shown in Figures 2 and 3 are executed. The starting point for counting the number of executions may be, for example, when the system is completed as shown in Figure 1. Next, PU42 calculates the maximum stress σθcor based on the charge / discharge current Icd(k) as an input variable using the following equation (c1) (S12).

[0030] σθcor=E·Ω·rn·I(k) / {30·(1-ν)·F·D} …(c1) The maximum stress σθcor is the maximum stress generated by the diffusion of lithium ions in the active material. Equation (c1) above was derived using a model that considers the active material to be spherical. More specifically, it was derived by assuming that the lithium ion concentration in the active material is isotropic and follows a diffusion equation with a constant diffusion coefficient. Here, E is Young's modulus, ν is Poisson's ratio, Ω is the partial molar volume of the solute, F is Faraday's constant, rn is the radius of the active material, and D is the diffusion coefficient. The current density I(k) is the magnitude of the current density at the surface of the active material. The current density I(k) is calculated by PU42 by multiplying the absolute value of the charge / discharge current Icd(k) as an input variable by a predetermined coefficient. The predetermined coefficient is the reciprocal of the product of the surface area of ​​the electrode, the thickness of the electrode, and the surface area of ​​the active material per unit volume. In practice, however, the current density I(k) in equation (c1) may be replaced with the absolute value of the charge / discharge current Icd(k) by multiplying equation (c1) by a predetermined coefficient.

[0031] PU42 calculates the newly formed surface area dA(k), which is the surface area of ​​the exposed surface where new cracks have formed in the active material at the current execution timing of the processes shown in Figures 2 and 3, based on the following formula (c2) (S14).

[0032]

number

[0033]

number

[0034] Solving equation (c3) above yields equation (c4).

[0035]

number

[0036] In this case, using the radius rn of the negative electrode active material and the number of active material cracks per unit area ρcr, the number of cracks in the negative electrode active material is "4·π·rn·rn·ρcr". Also, using the crack width lcr0, the total crack area Atotal of the negative electrode active material is "8·π·rn·rn·ρcr·a·lcr0".

[0037] Therefore, the newly formed surface area dA(k), which is the increase in the total surface area Atotal of the cracks in the negative electrode active material due to crack growth, is expressed by the following equation (c5).

[0038]

number

[0039] Next, PU42 substitutes the value obtained by multiplying the newly formed surface area dA(k) by the initial film thickness L0 into the new film amount ΔV1 (S16). The initial film thickness L0 is the thickness of the SEI film generated when the exposed surface of the active material that is not covered by the SEI film is exposed to the electrolyte. The new film amount ΔV1 is the volume of the SEI film generated when the exposed surface of the active material that is not covered by the SEI film is exposed to the electrolyte.

[0040] Next, PU42 calculates the amount of film increase ΔV2 at the cracks newly formed in the active material during the execution timings from the previous to N times prior in the series of processes shown in Figures 2 and 3, using the following formula (c6) (S18).

[0041]

number

[0042] PU42 calculates the surface area ΔA of the crack that occurred N+1 times prior to the series of processes shown in Figures 2 and 3 (S20). This process is the sum of the newly formed surface area dA calculated by process S14 in N+1 times prior to the current value obtained by PU42. Note that process S20 may also be a process of adding the newly formed surface area dA calculated N+1 times prior to the surface area ΔA calculated by the previous S20 process.

[0043] Then, PU42 calculates the increase in the SEI coating, ΔV3, which is the increase in the SEI coating at the crack that occurred N+1 times or earlier, using the following equation (c7) (S22).

[0044]

number

[0045] Next, PU42 substitutes the sum of the newly formed film amount ΔV1(k) and the film increase amounts ΔV2 and ΔV3 into the total increase amount of SEI film ΔVtotal(k) (S24 in Figure 3). Then, PU42 calculates the capacity decrease amount ΔC(k), which is the decrease in the fully charged capacity of the battery cell 12 relative to the total increase amount ΔVtotal (S26). This process may also include a process to calculate the decrease in lithium ions in the electrolyte from the total increase amount ΔVtotal using a coefficient that converts the volume of SEI film to the amount of lithium ions contained in the SEI film within the same volume.

[0046] PU42 substitutes the value obtained by subtracting the capacity reduction ΔC(k) from the full charge capacity C(k-1) into the full charge capacity C(k) (S28). The PU42 then determines whether the full charge capacity C(k) is below the threshold Cth (S30). This process determines whether the vehicle battery 10 has deteriorated. If the PU42 determines that it is below the threshold ΔCth (S30: YES), it notifies the user that the vehicle battery 10 has deteriorated by operating the output unit 82 shown in Figure 1 (S32). If the output unit 82 includes a display device, the process in S32 may be a process that outputs visual information indicating that deterioration has progressed.

[0047] PU42 updates the value of variable k (S34) when it completes the process in S32 or when it makes a negative determination in the process in S30. The process in S34 changes the value of variable k so that, for example, if the value of variable k in the current execution in Figures 2 and 3 was 1000, the value of variable k in the next execution in Figures 2 and 3 will be 1001.

[0048] Furthermore, when PU42 completes the process in S34, it temporarily terminates the series of processes shown in Figures 2 and 3. "The operation and effects of this embodiment" PU42 assumes that cracks originally present on the active material surface gradually expand, and it repeatedly calculates the amount of newly formed SEI coating ΔV1, which is the amount of SEI coating newly formed in the cracked area due to crack expansion, based on the charge / discharge current Icd. This allows for the appropriate calculation of the amount of SEI coating formed on the newly exposed surface of the active material due to tensile stress caused by diffusion-induced stress.

[0049] Furthermore, PU42 repeatedly calculates the increase in the SEI coating amount ΔV2 and ΔV3, assuming that the growth rate of the already formed SEI coating is proportional to the elapsed time raised to the power of "-1 / 2". This allows for the accurate calculation of the increase in the already formed SEI coating.

[0050] Then, PU42 calculates the capacity reduction ΔC(k) of the battery cell 12 based on the amount of new film ΔV1 and the film increase amounts ΔV2 and ΔV3. This allows for highly accurate estimation of the degree of degradation of the vehicle battery 10. As a result, the vehicle battery 10 can be used sufficiently until it reaches the end of its lifespan. On the other hand, if the accuracy of the degradation estimation is low, there is a risk of fire and other problems from continuing to use a vehicle battery 10 that has reached the end of its lifespan, which could lead to the recall of a vehicle battery 10 that is not yet at the end of its lifespan.

[0051] <Second Embodiment> The second embodiment will be described below, focusing on the differences from the first embodiment, with reference to the drawings.

[0052] In the above embodiment, although the growth of the crack was modeled based on Paris's law, an approximation was made in which the value of the variable indicating the number of loads was considered to be "1" when calculating the new surface area dA. In contrast, in this embodiment, the new surface area is calculated taking into account the number of loads.

[0053] Figure 4 shows the part of the process for determining whether or not the vehicle battery 10 has deteriorated according to this embodiment that corresponds to Figure 2. For convenience, the same step numbers are assigned to the processes shown in Figure 2 in Figure 4.

[0054] In the series of processes shown in Figure 4, when the PU42 completes the process in S10, it determines whether one charge / discharge cycle of the on-board battery 10 has finished (S40). This process may determine that one cycle has finished when, for example, the sign of the charge / discharge current Icd has reversed twice. However, if the maximum value of the charge / discharge current Icd during the period between detecting a sign reversal of the charge / discharge current Icd and detecting another sign reversal is less than or equal to a specified value, the PU42 may not count the second sign reversal as a sign reversal.

[0055] If PU42 determines that one cycle has finished (S40:YES), it increases the cycle count Nc(k) by "1" (S42). On the other hand, if PU42 determines that one cycle has not finished (S40:NO), it maintains the value of the cycle count Nc(k) (S44).

[0056] If PU42 completes the processes in S42 and S44, it proceeds to the process in S12. If PU42 completes the process in S12, it calculates the new surface area dA(k) based on the above formula (c5) (S14a). If PU42 completes the process in S14a, it proceeds to the process in S16.

[0057] Thus, in this embodiment, the newly formed surface area dA(k) was calculated using the cycle count Nc, independently of the variable indicating the number of times the process for determining whether or not degradation has occurred. This allows for a more accurate calculation of the newly formed surface area dA(k) that reflects Paris's law. According to Paris's law, the more times the load is applied to the active material, the faster the crack growth rate. Conversely, this means that if the period during which the charge / discharge current Icd is negligibly small is long, the crack growth rate will be smaller than in the case of a shorter period. Therefore, the newly formed surface area dA(k) is calculated based on the cycle count Nc(k). As a result, even if the number of times the process for determining whether or not degradation has occurred is the same, if the period during which the onboard battery 10 is not charged or discharged is long, the newly formed surface area dA(k) can be calculated to a smaller value than in the case of a shorter period. Therefore, in this embodiment, the newly formed surface area dA(k) can be calculated with higher accuracy according to the history of stress applied to the active material.

[0058] <Correspondence> The correspondence between the matters in the above embodiment and the matters described in the "Means for Solving the Problems" section is as follows. Below, the correspondence is shown for each number of the solution means described in the "Means for Solving the Problems" section. [1] The degradation estimation device corresponds to the battery ECU40. The acquisition process corresponds to the process in S10. The new film amount calculation process corresponds to the processes in S12 to S16. The partial increase amount calculation process corresponds to the process in S18. The film increase amount calculation process corresponds to the process in S24. The capacity decrease amount calculation process corresponds to the process in S26. [2] The matters concerning Solution 2 correspond to the fact that when the charge / discharge current Icd(k) is zero, the maximum stress σθcor is set to zero. [3] The film thickness increase amount due to the partial increase amount calculation process corresponds to "(1 / 2)·Ksei0·exp{-Ea2 / (R / Tc)} / √{(ki)·Δt}". [4] "Sum of surface areas of cracks" corresponds to surface area ΔA. The common time difference corresponds to k·Δt. [5] The history storage process corresponds to the processes in S40 to S44. The history variable corresponds to the cycle count Nc. [6] The notification process corresponds to the process in S32. The notification device corresponds to the output unit 82.

[0059] <Other Embodiments> This embodiment can be implemented with the following modifications. This embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0060] "Regarding the calculation process for the amount of newly formed coating" It is not mandatory for the new film amount calculation process to include a process for calculating the maximum stress σθcor based on the above equation (c1). The new film amount calculation process may, for example, be a process that calculates the maximum stress σθcor based on an equation obtained by multiplying the above equation (c1) by a correction coefficient that takes into account boundary conditions due to contact between particles.

[0061] The method for calculating the amount of new coating, which calculates the new surface area dA(k) to zero when the magnitude of the charge / discharge current Icd is less than or equal to a predetermined value, is not limited to a method that uses a model in which the maximum stress σθcor is directly proportional to the current density I (charge / discharge current Icd). For example, the method for calculating the amount of new coating may include a process to determine whether the magnitude of the charge / discharge current Icd or the magnitude of the current density I is less than or equal to a predetermined value, and a process to substitute zero for the new surface area dA(k) if it is determined to be less than or equal to the predetermined value. Here, the predetermined value may be greater than zero.

[0062] The process for calculating the amount of new coating does not necessarily have to include a process of multiplying the new surface area dA(k) by the initial film thickness L0. The process for calculating the amount of new coating may also be a process of performing a map calculation on the new surface area dA(k) according to the map data. Here, the map data is data in which the input variable includes the charge / discharge current Icd, etc., and the output variable is the new surface area dA(k).

[0063] Map data is a set of data consisting of discrete values ​​of input variables and corresponding values ​​of output variables for each of the input variable values. Furthermore, the map operation may be a process in which, if the value of an input variable matches any of the input variable values ​​in the map data, the corresponding value of the output variable in the map data is the result of the operation. Alternatively, if the value of an input variable does not match any of the input variable values ​​in the map data, the result of the map operation may be a value obtained by interpolating the values ​​of multiple output variables included in the map data. Or, instead, if the value of an input variable does not match any of the input variable values ​​in the map data, the result of the map operation may be the value of the output variable in the map data corresponding to the closest value among the multiple input variable values ​​included in the map data.

[0064] "Regarding the calculation process for partial increase" It is not mandatory for the partial increase calculation process to include a process that calculates the partial increase in proportion to the -1 / 2 power of the time difference "(ki)·Δt" between the past execution timing and the current execution timing of the new film amount calculation process. For example, it may include a process that calculates the partial increase in proportion to the -1 / 2 power of the value obtained by multiplying the integer part when "ki" is divided by 10 by the period Δt.

[0065] The partial increment calculation process does not necessarily have to include a process to calculate the value of a function in which the dependent variable is the independent variable raised to the power of "-1 / 2". For example, the partial increment calculation process may be a process to calculate the partial increment using map data. Here, the map data may be, for example, data in which the input variable is "ki" and the partial increment is the output variable.

[0066] This map data should be such that, through map calculations, the partial increase amount is modified according to "ki" under the condition that the partial increase amount when "ki" is large is less than or equal to the partial increase amount when "ki" is small.

[0067] Furthermore, in statements such as "Change B according to A, provided that B is greater than or equal to B when A is small," "when A is large" and "when A is small" refer to the relative magnitude relationship when comparing the two. For example, "when A is large" corresponds to "when A is the first value," and "when A is small" corresponds to "when A is the second value, which is smaller than the first value." According to the above statement, depending on the settings of the first and second values, B when A is the first value may be larger than B when A is the second value. Also, the above statement means that B is changed according to A so that A when B is large is larger than A when B is small.

[0068] It is not mandatory for the partial increase calculation process to include a process that calculates the partial increase in cracked areas where the time difference with the timing of the new film amount calculation process is greater than or equal to a predetermined value, in proportion to the power of "k·Δt" raised to the "-1 / 2" level. The partial increase calculation process may, for example, include a process that calculates the partial increase in cracked areas where the time difference is greater than or equal to a predetermined value, in proportion to the power of "{(2k-N) / 2}·Δt" raised to the "-1 / 2" level.

[0069] It is not mandatory for the partial increase calculation process to include a process that calculates the sum of the partial increases in cracks where the time difference from the current execution timing is greater than or equal to a predetermined value, by multiplying the sum of the surface areas of those cracks by the film thickness increase calculated based on a common time difference. For example, the partial increase calculation process may include a process that sets the partial increases in multiple cracks where the time difference is greater than or equal to a predetermined value to zero.

[0070] The partial increase calculation process does not necessarily have to be a process that calculates the increase in SEI coating in newly formed cracks from the previous execution timing to the current execution timing. For example, it may be a process that calculates the increase in SEI coating from the time when an SEI coating with an initial film thickness L0 was formed in the crack. This can be achieved by making the term multiplied by the newly formed surface area dA(k) in the above equation (c6) a term proportional to the power of "(ki)·Δt" raised to the "1 / 2" power.

[0071] "Regarding history storage processing" The history storage process does not necessarily have to be a process that stores the number of charge / discharge cycles Nc. For example, it may be a process that stores the integrated absolute value of the charge / discharge current Icd. In that case, the new coating amount calculation process may include a process that changes the surface area based on a value obtained by multiplying the integrated value by a predetermined coefficient.

[0072] "Regarding the execution timing of each process" In the above embodiment, the calculation process for the amount of new coating ΔV1 and the increase in coating amounts ΔV2 and ΔV3 was performed repeatedly and periodically with a period Δt, but this is not limited to this. For example, PU42 may periodically determine with a period Δt whether the absolute value of the charge / discharge current Icd is less than or equal to a predetermined value, and if it determines that it is less than or equal to the predetermined value, it may perform the process of substituting zero for the amount of new coating ΔV1(k) without performing the processes of S12 to S16. In that case, the variable k may indicate the number of times the process of determining whether the absolute value of the charge / discharge current Icd is less than or equal to a predetermined value has been performed. Also, for example, if PU42 determines that it is less than or equal to a predetermined value, it does not have to perform all of the calculation processes for the amount of new coating ΔV1 and the increase in coating amounts ΔV2 and ΔV3. However, in that case, the variable k shall indicate the number of times the process of determining whether the absolute value of the charge / discharge current Icd is less than or equal to a predetermined value has been performed.

[0073] For example, processes S12, S14a, and S16-S34 in the processes shown in Figures 2 and 4 may be executed if they are affirmed in process S40. In that case, the variable k may be a variable indicating the number of times process S40 is executed. Here, the current density for calculating the maximum stress σθcor may be the average value of the current density I described above in one cycle.

[0074] Regarding secondary batteries that are subject to calculation of the increase in SEI coating amount: The secondary battery used to calculate the increase in SEI coating is not limited to battery cell 12. The secondary battery may be, for example, an on-board battery 10. In that case, the cell temperature Tc used as an input variable for the calculation process of the increase in film thickness may be the average value of the individual cell temperatures Tc of the multiple battery cells 12 that make up the on-board battery 10.

[0075] "Regarding the use of the volume reduction calculation process" The capacity reduction calculation process is not limited to notifying users when the reduction in full charge capacity exceeds a predetermined value. For example, it may be used to update the full charge capacity for calculating the state of charge (SOC) each time.

[0076] "Regarding the Degradation Estimation Device" The degradation estimation device is not limited to one that performs various processes using a PU. The degradation estimation device may, for example, include a dedicated hardware circuit such as an ASIC that performs at least a part of the processes performed in the above embodiment. That is, the degradation estimation device may include any of the following processing circuits (a) to (c): (a) A processing circuit comprising a processing unit that performs all of the above processes according to a program and a program storage device such as a memory device that stores the program. (b) A processing circuit comprising a processing unit and a program storage device that perform a part of the above processes according to a program and a dedicated hardware circuit that performs the remaining processes. (c) A processing circuit comprising a dedicated hardware circuit that performs all of the above processes. Here, there may be multiple software execution devices comprising a processing unit and a program storage device, or multiple dedicated hardware circuits.

[0077] "Regarding rechargeable batteries" • It is not necessary for the secondary battery to be a battery installed in a vehicle. • The secondary battery is not limited to lithium-ion secondary batteries. The secondary battery may also be, for example, a nickel-metal hydride secondary battery. [Explanation of Symbols]

[0078] 10…Car battery 12…Battery cell 20... System Main Relay 22... Power conversion circuit 24…Motor Generator 40…Battery ECU 50…In-vehicle network 80...Current sensor

Claims

1. A secondary battery degradation estimation device for estimating the degree of degradation of a secondary battery, Acquisition process, new film amount calculation process, partial increase amount calculation process, film increase amount calculation process, and The system is configured to repeatedly execute the volume reduction calculation process. The aforementioned acquisition process is a process for acquiring the charge and discharge current of the secondary battery. The aforementioned new coating amount calculation process is a process that calculates the amount of new coating, which is the amount of SEI coating newly formed on the cracked portion of the active material, which is the surface on which the SEI coating has not been formed, based on the charge / discharge current as an input variable. The aforementioned partial increase amount calculation process is a process for calculating the partial increase amount, and includes a process for changing the partial increase amount according to the time difference, provided that the partial increase amount when the time difference between the timing when the amount of new film was calculated and the current timing is long is less than or equal to the partial increase amount when the time difference is short. The aforementioned partial increase is the increase in the SEI coating at the cracked portion where the amount of new coating was calculated at a past execution timing of the new coating amount calculation process. The aforementioned coating increase amount calculation process is a process that calculates the increase amount of the SEI coating based on the amount of newly formed coating and the partial increase amount as input variables. The capacity reduction calculation process is a secondary battery degradation estimation device that calculates the amount of decrease in the full charge capacity of the secondary battery based on the increase in the SEI coating as an input variable.

2. The process for calculating the amount of new coating includes setting the amount of new coating to zero if the magnitude of the charge / discharge current is less than or equal to a predetermined value. The secondary battery degradation estimation device according to claim 1, wherein the partial increase amount calculation process includes a process for calculating the partial increase amount for each different execution timing of the new film amount calculation process, and a process for setting the partial increase amount to zero corresponding to the execution timing in which the new film amount is set to zero.

3. The process for calculating the amount of new film includes a process for calculating the surface area of ​​the crack based on the magnitude of the charge / discharge current as an input variable, and a process for substituting the value obtained by multiplying the surface area of ​​the crack by the initial film thickness into the amount of new film. The partial increase calculation process includes a process of substituting the value obtained by multiplying the surface area of ​​the crack portion calculated at different past execution timings of the new film amount calculation process by the film thickness increase amount into the partial increase amount, and a process of changing the film thickness increase amount according to the time difference, provided that the film thickness increase amount of the crack portion with a long time difference between the timing at which the new film amount was calculated and the current timing is less than or equal to the film thickness increase amount of the crack portion with a short time difference. The secondary battery degradation estimation device according to claim 1, wherein the coating increase amount calculation process includes a process for calculating the increase amount of the SEI coating by adding the amount of the newly formed coating and a plurality of the partial increase amounts.

4. The secondary battery degradation estimation device according to claim 3, wherein the partial increase amount calculation process includes a process of calculating the sum of the partial increase amounts of a plurality of cracks where the time difference between the timing at which the amount of newly formed film was calculated and the current timing is greater than or equal to a predetermined value, by multiplying the sum of the surface areas of those cracks by the film thickness increase amount calculated by a common time difference.

5. It is configured to perform history storage processing, The aforementioned history storage process is a process for storing the values ​​of history variables, The aforementioned history variable is a variable that indicates the charge and discharge history of the secondary battery, The secondary battery degradation estimation device according to claim 3, wherein the new film amount calculation process includes a process to change the surface area based on the value of the history variable, even if the number of executions of the new film amount calculation process is the same, under the condition that the surface area of ​​the cracked portion when the period during which the magnitude of the charge / discharge current is less than or equal to a specified value is longer is less than or equal to the surface area when the period is shorter.

6. It is configured to perform notification processing, The secondary battery degradation estimation device according to claim 1, wherein the notification process is a process of notifying that the secondary battery has deteriorated by operating a notification device when the amount of decrease in the full charge capacity exceeds a predetermined value.

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