Battery capacity estimation device and battery capacity estimation program

Abstract

Provided is a battery capacity estimation device capable of estimating battery capacity in consideration of the influence of a crack.　Provided is a battery capacity estimation device for estimating the battery capacity of a secondary battery having a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and an electrolyte. The battery capacity estimation device comprises: a deterioration state amount derivation unit (4) for deriving at least one of a deterioration state amount of the positive electrode active material due to a crack generated in the positive electrode active material as a result of a change in the volume of the positive electrode active material associated with charging and discharging of the secondary battery, and a deterioration state amount of an SEI coating film, formed on the surface of the negative electrode active material, due to a crack generated in the SEI coating film as a result of a change in the volume of the negative electrode active material associated with charging and discharging of the secondary battery; and a battery capacity estimation unit (5) for estimating the battery capacity after deterioration of the secondary battery on the basis of the deterioration state amount derived by the deterioration state amount derivation unit (4).

Description

Battery capacity estimation device and battery capacity estimation program

[0001] The present invention relates to a battery capacity estimation device and a battery capacity estimation program.

[0002] Depending on the application, secondary batteries may be used under different charge / discharge conditions, such as charge / discharge rate, upper and lower voltage limits, charging method (constant current charging, constant current-constant voltage charging, constant power-constant voltage charging, multi-stage charging, etc.), and storage time. Generally, deterioration progresses through several different mechanisms inside a battery, and the rate of progression of these changes changes in a complex manner when the charge / discharge conditions differ.

[0003] For example, Patent Document 1 (JP 2023-064746 A) points out the problem that when a rapid volume change occurs in the primary particles of the lithium composite oxide of the positive electrode active material during charge and discharge, or when stress accumulates due to repeated charge and discharge, cracks occur in the secondary particles, or the crystal structure collapses or changes (phase transition) occur in the crystal structure. Patent Document 1 also discloses a secondary battery in which the occurrence of particle cracks is suppressed by mixing positive electrode active materials with multiple particle sizes.

[0004] Furthermore, Patent Document 2 (WO 2021 / 020290) points out that when silicon oxide is used as the negative electrode active material, repeated expansion and contraction associated with charging and discharging tends to cause particle cracking and isolation, and therefore nonaqueous electrolyte energy storage elements using silicon oxide have a problem of low capacity retention during charge and discharge cycles. Patent Document 2 also discloses a battery design that suppresses particle cracking in the negative electrode active material by limiting the range of potential utilization of the negative electrode during charging and discharging.

[0005] JP 2023-064746 A International Publication No. 2021 / 020290

[0006] As described in Patent Documents 1 and 2, active material designs and battery designs have been developed to suppress deterioration caused by cracks, but it has not been possible to completely prevent cracks from occurring during long-term use of secondary batteries.

[0007] In particular, the decrease in discharge capacity caused by particle cracks due to expansion and contraction of the active material or cracks in the SEI (solid electrolyte interface) coating of the negative electrode is highly dependent on the SOC (State Of Charge) during charging and discharging, and a significant decrease in capacity may occur when charging and discharging in a specific SOC region.

[0008] Therefore, in order to operate secondary battery systems such as power storage systems and electric vehicles while taking into account the decline in battery capacity that occurs over long periods of use, it is necessary to accurately predict the decline in battery capacity due to cracks as described above. However, it has been difficult to accurately predict such deterioration that is highly dependent on the SOC using conventional simple prediction models based on the number of charge / discharge cycles and the total discharged amount of electricity. Therefore, although Patent Documents 1 and 2 describe the effects of cracks, they do not disclose a method for estimating battery capacity based on that information.

[0009] The present invention has been made in view of the above-mentioned problems, and its purpose is to provide a battery capacity estimation device and a battery capacity estimation program that can estimate battery capacity taking into account the influence of cracks.

[0010] A characteristic configuration of a battery capacity estimation device according to the present invention for achieving the above object is a battery capacity estimation device that estimates the battery capacity of a secondary battery having a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and an electrolyte, and includes: a degradation state quantity derivation unit that derives at least one of a degradation state quantity of the positive electrode active material due to cracks that occur in the positive electrode active material as a result of a volume change in the positive electrode active material occurring with charging and discharging of the secondary battery, and a degradation state quantity of an SEI coating that is formed on the surface of the negative electrode active material due to cracks that occur in the SEI coating as a result of a volume change in the negative electrode active material occurring with charging and discharging of the secondary battery; and a battery capacity estimation unit that estimates the battery capacity of the secondary battery after degradation based on the degradation state quantity derived by the degradation state quantity derivation unit.

[0011] On the positive electrode side, volume changes in the positive electrode active material occur as the secondary battery is charged and discharged, causing cracks to form in the positive electrode active material. These cracks cut the conductive paths in the positive electrode active material, reducing the amount of positive electrode active material connected to the surrounding area via conductive paths, which is thought to lead to a decrease in the battery capacity of the secondary battery. On the negative electrode side, volume changes in the negative electrode active material occur as the secondary battery is charged and discharged, causing cracks in the SEI coating formed on the surface of the negative electrode active material. The electrolyte decomposition reaction occurs on the surface of the negative electrode active material exposed by the cracks, resulting in the formation of a new SEI coating in the cracked area. Therefore, it is thought that the battery capacity of the secondary battery decreases as the cracks grow, forming a new SEI coating (i.e., lithium loss). In this manner, the present characteristic configuration derives at least one of a degradation state quantity indicating degradation of the positive electrode active material due to a volume change in the positive electrode active material and a degradation state quantity indicating degradation of the SEI coating due to a volume change in the negative electrode active material, and the battery capacity after degradation of the secondary battery can be estimated based on the degradation state quantity. Therefore, a battery capacity estimation device can be provided that can estimate the battery capacity taking into account the influence of cracks.

[0012] Another characteristic configuration of the battery capacity estimation device according to the present invention is that it includes: a positive electrode SOC determination unit that determines an SOC of the positive electrode active material; and a positive electrode stress derivation unit that derives stress applied to particles of the positive electrode active material at a predetermined timing based on the product of a volume change rate of the positive electrode active material corresponding to the SOC of the positive electrode active material at the predetermined timing determined by the positive electrode SOC determination unit, the rate being determined with reference to a positive electrode volume characteristic that indicates the relationship between the SOC of the positive electrode active material and the volume of the positive electrode active material, and a charge / discharge current at the predetermined timing, wherein the deterioration state quantity derivation unit derives the deterioration state quantity of the positive electrode active material due to cracks occurring in the positive electrode active material, which is derived based on a temporal change state of the stress applied to particles of the positive electrode active material derived at a plurality of timings by the positive electrode stress derivation unit.

[0013] According to the above-described characteristic configuration, the positive electrode stress deriving unit can derive the stress acting on the particles of the positive electrode active material at a predetermined timing based on the volume change rate of the positive electrode active material corresponding to the SOC of the positive electrode active material at the predetermined timing determined by the positive electrode SOC determining unit, and the degradation state quantity deriving unit can derive the degradation state quantity of the positive electrode active material due to cracks occurring in the positive electrode active material based on the temporal changes in the stress acting on the particles of the positive electrode active material derived at multiple timings by the positive electrode stress deriving unit (e.g., the fluctuation range of the stress on the particle surface, the number of cycles of stress fluctuation, etc.).

[0014] Another characteristic configuration of the battery capacity estimation device according to the present invention is that the positive electrode SOC determination unit determines the SOC of the positive electrode active material at the predetermined timing based on the SOC of the secondary battery at the predetermined timing, the battery capacity of the secondary battery at a past timing before the predetermined timing, and the amount of deviation between a capacity range of the positive electrode active material and a capacity range of the negative electrode active material, and the positive electrode stress derivation unit derives the stress applied to particles of the positive electrode active material at the predetermined timing based on the product of the volume change rate of the positive electrode active material, the charge / discharge current at the predetermined timing, and a ratio of an initial battery capacity of the secondary battery to the battery capacity of the secondary battery at the past timing.

[0015] According to the above-described characteristic configuration, the positive electrode SOC determination unit can more accurately determine the SOC of the positive electrode active material at a predetermined timing by taking into account the difference between the capacity range of the positive electrode active material and the capacity range of the negative electrode active material, i.e., by taking into account changes in the usable range of the capacity range of the positive electrode active material. The positive electrode stress derivation unit can accurately determine the stress applied to the positive electrode active material particles by taking into account the ratio of the initial battery capacity of the secondary battery to the battery capacity of the secondary battery at a past timing, i.e., by taking into account an apparent increase in current load due to a decrease in the battery capacity of the secondary battery.

[0016] Another characteristic configuration of the battery capacity estimation device according to the present invention is that it includes: a negative electrode SOC determination unit that determines an SOC of the negative electrode active material; and a negative electrode stress derivation unit that derives a stress applied in a plane direction of the SEI coating at a predetermined timing based on a volume of the negative electrode active material that corresponds to the SOC of the negative electrode active material at the predetermined timing determined by the negative electrode SOC determination unit, the volume being determined with reference to a negative electrode volume characteristic that indicates the relationship between the SOC of the negative electrode active material and the volume of the negative electrode active material, and the degradation state quantity derivation unit derives the degradation state quantity of the SEI coating due to cracks occurring in the SEI coating, which is derived based on a temporal change state of the stress applied in the plane direction of the SEI coating derived at a plurality of timings by the negative electrode stress derivation unit.

[0017] According to the above characteristic configuration, the negative electrode stress deriving unit can derive the stress applied in the in-plane direction of the SEI coating at a predetermined timing based on the volume of the negative electrode active material corresponding to the SOC of the negative electrode active material at the predetermined timing determined by the negative electrode SOC determining unit, and the degradation state quantity deriving unit can derive the degradation state quantity of the SEI coating due to cracks occurring in the SEI coating based on the temporal change in the stress applied in the in-plane direction of the SEI coating derived at multiple timings by the negative electrode stress deriving unit (e.g., the stress fluctuation width, the number of stress fluctuation cycles, etc.).

[0018] Another characteristic configuration of the battery capacity estimation device according to the present invention is that the negative electrode SOC determination unit determines the SOC of the negative electrode active material based on the SOC of the secondary battery at the predetermined timing, the battery capacity of the secondary battery at a past timing before the predetermined timing, and the capacity of the negative electrode active material.

[0019] According to the above characteristic configuration, the SOC of the negative electrode active material can be determined based on the SOC of the secondary battery at a predetermined timing, the battery capacity of the secondary battery at a past timing before the predetermined timing, and the capacity of the negative electrode active material.

[0020] A characteristic feature of the battery capacity estimation program according to the present invention for achieving the above object is that it causes a computer to function as each unit included in the battery capacity estimation device.

[0021] According to the above characteristic configuration, by making a computer function as each unit included in the battery capacity estimation device, it is possible to obtain the same effects as those of the battery capacity estimation device according to the present invention.

[0022] 1 is a diagram illustrating the configuration of a battery capacity estimation device according to a first embodiment; FIG. 2 is a graph illustrating the OCV of a secondary battery, the OCP of a positive electrode active material and a negative electrode active material, and the capacity ranges of the positive electrode active material and the negative electrode active material; FIG. 3 is a graph illustrating the transitions of current and SOC when charging and discharging are performed under condition 1; FIG. 4 is a graph illustrating the transitions of current and SOC when charging and discharging are performed under condition 2; FIG. 5 is a graph illustrating the transitions of current and SOC when charging and discharging are performed under condition 3; FIG. 6 is a graph illustrating the transitions of capacity (actual measured value), capacity (estimated value), and state of deterioration quantity when charging and discharging are performed under condition 1 in the first embodiment; FIG. 7 is a graph illustrating the transitions of capacity (actual measured value), capacity (estimated value), and state of deterioration quantity when charging and discharging are performed under condition 2 in the first embodiment; and FIG. 8 is a graph illustrating the transitions of capacity (actual measured value), capacity (estimated value), and state of deterioration quantity when charging and discharging are performed under condition 3 in the first embodiment. 10 is a graph showing changes in the capacity (actual measured value), the capacity (estimated value), and the state of deterioration quantity when charging and discharging are performed under condition 1 in the second embodiment. FIG. 11 is a graph showing changes in the capacity (actual measured value), the capacity (estimated value), and the state of deterioration quantity when charging and discharging are performed under condition 2 in the second embodiment. FIG. 12 is a graph showing changes in the capacity (actual measured value), the capacity (estimated value), and the state of deterioration quantity when charging and discharging are performed under condition 3 in the second embodiment. FIG. 13 is a diagram showing the configuration of a battery capacity estimation device of a third embodiment. FIG. 14 is a graph showing changes in the capacity (actual measured value), the capacity (estimated value), and the state of deterioration quantity when charging and discharging are performed under condition 1 in the third embodiment. FIG. 15 is a graph showing changes in the capacity (actual measured value), the capacity (estimated value), and the state of deterioration quantity when charging and discharging are performed under condition 2 in the third embodiment. FIG. 16 is a graph showing changes in the capacity (actual measured value), the capacity (estimated value), and the state of deterioration quantity when charging and discharging are performed under condition 3 in the third embodiment. FIG. 17 is a diagram showing the configuration of a battery capacity estimation device of a fourth embodiment. FIG. 18 is a graph showing changes in the capacity (actual measured value), the capacity (estimated value), and the state of deterioration quantity when charging and discharging are performed under condition 1 in the fourth embodiment. 10 is a graph showing changes in the capacity (actual measurement value), the capacity (estimated value), and the state amount of degradation when charging and discharging are performed under condition 2 in the fourth embodiment. 11 is a graph showing changes in the capacity (actual measurement value), the capacity (estimated value), and the state amount of degradation when charging and discharging are performed under condition 3 in the fourth embodiment.

[0023] First Embodiment A battery capacity estimation device according to a first embodiment of the present invention will be described below with reference to the drawings. The battery capacity estimation device is a device that estimates the battery capacity of a secondary battery having a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and an electrolyte. The following embodiment will be described using a lithium nickel oxide (NCA)-based positive electrode active material as the positive electrode active material and a graphite-based negative electrode active material as the negative electrode active material, but the materials for the positive electrode active material and the negative electrode active material can be changed as appropriate.

[0024] In a secondary battery having a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and an electrolyte, repeated charge and discharge causes repeated expansion and contraction of the positive electrode active material and the negative electrode active material. It is presumed that cracks caused by the expansion and contraction cause deterioration in the secondary battery, resulting in a decrease in battery capacity.

[0025] Therefore, the battery capacity estimation device includes a degradation state quantity derivation unit 4 that derives at least one of the degradation state quantity of the positive electrode active material due to cracks that occur in the positive electrode active material as a result of volume changes in the positive electrode active material accompanying charging and discharging of the secondary battery, and the degradation state quantity of the SEI (solid electrolyte interface) coating formed on the surface of the negative electrode active material due to cracks that occur in the SEI coating as a result of volume changes in the negative electrode active material accompanying charging and discharging of the secondary battery, and a battery capacity estimation unit 5 that estimates the battery capacity after degradation of the secondary battery based on the degradation state quantity derived by the degradation state quantity derivation unit 4.

[0026] The deterioration state quantity derivation unit 4 provided in the battery capacity estimation device of the first embodiment derives the deterioration state quantity of the positive electrode active material due to cracks that occur in the positive electrode active material as a result of volume changes in the positive electrode active material accompanying charging and discharging of the secondary battery.

[0027] FIG. 1 is a diagram showing the configuration of a battery capacity estimation device according to a first embodiment. As shown in the figure, the battery capacity estimation device includes an operating state acquisition unit 1, an SOC determination unit 2, a stress derivation unit 3, a degradation state quantity derivation unit 4, and a battery capacity estimation unit 5. Additionally, the battery capacity estimation device according to this embodiment includes a memory unit 6 for storing information to be handled. Specifically, the battery capacity estimation device according to the first embodiment derives a degradation state of the positive electrode active material due to cracks that occur in the positive electrode active material as a result of volumetric changes in the positive electrode active material that occur during charging and discharging of the secondary battery, and estimates the battery capacity of the secondary battery after degradation based on the degradation state. Therefore, the SOC determination unit 2 includes a positive electrode SOC determination unit 2a, and the stress derivation unit 3 includes a positive electrode stress derivation unit 3a.

[0028] The battery capacity estimation device is realized using one or more computer devices equipped with information input / output functions, information communication functions, information processing functions, information storage functions, etc. In addition, in this embodiment, a battery capacity estimation program that causes the one or more computer devices described above to function as each unit of the battery capacity estimation device is installed in the storage medium of the one or more computer devices and executed, thereby realizing the battery capacity estimation device. In other words, the battery capacity estimation program is stored in a computer-readable storage medium (such as the storage unit 6 or another storage device, or a storage medium such as a CD, DVD, or Blu-ray (registered trademark)). In addition, a program product including the battery capacity estimation program realizes the functions of each unit of the battery capacity estimation device described below when the battery capacity estimation program is executed by the information processing function of the computer device.

[0029] For example, the operating state acquisition unit 1 can be realized using an information input / output function of a computer device. The SOC determination unit 2, stress derivation unit 3, degradation state quantity derivation unit 4, and battery capacity estimation unit 5 can be realized using an information processing function of a computer device. The storage unit 6 can be realized using an information storage function of a computer device.

[0030] 2 is a graph illustrating the OCV (open circuit voltage) of a secondary battery, the OCP (open circuit potential) of the positive electrode active material and the negative electrode active material, and the capacity range of the positive electrode active material and the negative electrode active material. The illustrated example shows a case where there is a difference in Δq between the capacity range of the positive electrode active material and the capacity range of the negative electrode active material, but the Δq shown in FIG. 2 is shown for illustrative purposes only, and its magnitude is not limited to that shown. Furthermore, while FIG. 2 shows a relationship where the negative electrode capacity is greater than the battery capacity, the magnitude of the negative electrode capacity is not limited to that shown.

[0031] The operating state acquisition unit 1 acquires information about the SOC of the secondary battery (hereinafter, sometimes referred to as "battery SOC") and information about the charge / discharge current of the secondary battery. Specifically, the operating state acquisition unit 1 acquires information about the SOC of the secondary battery and information about the charge / discharge current at a predetermined timing, such as every minute. For example, the SOC of the secondary battery can be derived by measuring the OCV of the secondary battery and based on the relationship between the measured OCV and the transition between the lower limit (SOC = 0%) and upper limit (SOC = 100%) of the battery capacity shown in FIG. 2 . Then, the information is stored in the storage unit 6 together with time information.

[0032] The positive electrode SOC determination unit 2a included in the SOC determination unit 2 determines the SOC of the positive electrode active material (hereinafter, may be referred to as "positive electrode SOC"). Specifically, the positive electrode SOC determination unit 2a determines the SOC of the positive electrode active material at a predetermined timing, such as every minute.

[0033] For example, the positive electrode SOC determination unit 2 a may determine the SOC of the positive electrode active material at a predetermined timing from the relationship between the battery SOC and the positive electrode SOC and the SOC of the secondary battery at the predetermined timing. In this embodiment, the relationship between the battery SOC and the positive electrode SOC is defined as "battery SOC = positive electrode SOC" as shown in the following equation 1.

[0034]

[0035] The positive electrode stress derivation unit 3a of the stress derivation unit 3 derives the stress (e.g., particle surface stress) applied to the particles of the positive electrode active material at a predetermined timing based on the product of the volume change rate of the positive electrode active material corresponding to the SOC of the positive electrode active material at a predetermined timing determined by the positive electrode SOC determination unit 2a, which is determined with reference to the positive electrode volume characteristic indicating the relationship between the SOC of the positive electrode active material and the volume of the positive electrode active material. In this embodiment, the stress is derived based on the following equation 2. Furthermore, the positive electrode volume characteristic defines the relationship between the positive electrode SOC, open circuit potential, active material volume (relative ratio), and volume change rate, as stored in the memory unit 6. Note that in FIG. 2, the SOC is shown in 10% increments for simplicity.

[0036]

[0037] When a secondary battery is repeatedly charged and discharged, the volume of the positive electrode active material repeatedly increases and decreases as the SOC of the positive electrode active material increases and decreases, which is thought to cause stress on the particle surface of the positive electrode active material to increase and decrease, resulting in cracks in the positive electrode active material.

[0038] The deterioration state quantity derivation unit 4 derives the deterioration state quantity of the positive electrode active material due to cracks occurring in the positive electrode active material, based on the temporal change state of the stress applied to the particles of the positive electrode active material (e.g., the fluctuation range of the stress on the particle surface and the number of cycles of the stress fluctuation) derived at multiple times by the positive electrode stress derivation unit 3 a.

[0039] First, the degradation state quantity deriving unit 4 applies the rainflow method to the stress fluctuation pattern that occurs over time while the secondary battery is being charged and discharged, calculates the stress fluctuation range and the number of cycles of stress fluctuation, and derives the crack density in the positive electrode active material particles based on the stress fluctuation range and the number of cycles. For example, in the process of performing a simulation to estimate the battery capacity when charging and discharging are performed under conditions 1 to 3 described below, the stress fluctuation range Δσ ｉ and the number of cycles N ｉ In this embodiment, the crack density is calculated based on the following formulas 3 and 4.

[0040]

[0041] On the positive electrode side, volume changes in the positive electrode active material occur as the secondary battery is charged and discharged, causing cracks to form in the positive electrode active material. These cracks then cut the conductive paths in the positive electrode active material, reducing the amount of positive electrode active material connected to the surrounding area via conductive paths, which is thought to result in a decrease in the battery capacity of the secondary battery. Therefore, the degradation state quantity deriving unit 4 derives the capacity loss (degradation state quantity) in the positive electrode active material based on the amount of cracks that have occurred in the positive electrode active material particles over time. In this embodiment, the capacity loss (degradation state quantity) in the positive electrode active material is derived based on the following equation 5.

[0042]

[0043] The above formula 5 was determined based on the idea that when cracks occur between active material particles, some active material particles become isolated from the conductive paths and are unable to contribute to charging and discharging, and based on percolation theory, the amount of active material connected by conductive paths is proportional to the power of the amount of conductive paths.

[0044] The battery capacity estimation unit 5 estimates the battery capacity after deterioration of the secondary battery based on the degradation state quantity derived by the degradation state quantity derivation unit 4. In this embodiment, the battery capacity is estimated based on the following equation 6.

[0045]

[0046] In this embodiment, the transition (actual measured value) of the battery capacity was measured when charging and discharging were performed for a predetermined test period under three types of charging and discharging conditions (conditions 1 to 3).Then, the transition (estimated value) of the battery capacity estimated by the battery capacity estimation device of this embodiment was compared with the transition (estimated value) of the battery capacity estimated by the battery capacity estimation device to verify the validity of the transition (estimated value) of the battery capacity estimated by the battery capacity estimation device.

[0047] As shown in Table 1 below, under condition 1, charging is performed using the constant current-constant voltage (CCCV) method. The current during charging is 0.7 C and the voltage is 4.2 V. Under condition 2, charging is performed using the constant current (CC) method, and charging is completed at 4.2 V. The current is 0.7 C. Under condition 3, charging is performed using the constant current (CC) method, and charging is completed at 4.0 V. The current is 1.4 C. Figures 3 to 5 are graphs showing the changes in current, temperature, and SOC when charging and discharging are performed under each condition. Figure 6 shows the changes in discharge capacity (actual measured value) of the secondary battery when charging and discharging are performed under conditions 1 to 3.

[0048]

[0049] FIG. 7 is a graph showing the estimated battery capacity when charging and discharging were performed under Condition 1, and the transition of the actual measured value of the battery capacity when charging and discharging were performed under Condition 1. FIG. 7 also shows the transition of the estimated value of capacity loss (degradation state quantity) in the positive electrode active material due to cracks. Note that in the above-described Equations 2, 3, and 5, coef = 0.22, m = 3, and β = 0.6. As can be seen from FIG. 7, although the estimated value and the actual measured value diverge as the test period increases, the transition of the estimated value and the actual measured value is almost the same up to about 2000 hours of test period. Therefore, it can be said that the estimation result of the battery capacity by the battery capacity estimation device of this embodiment is relatively accurate.

[0050] FIG. 8 is a graph showing the estimated battery capacity when charging and discharging were performed under Condition 2, and the transition of the actual measured battery capacity when charging and discharging were performed under Condition 2. FIG. 8 also shows the transition of the estimated capacity loss (degradation state quantity) in the positive electrode active material due to cracks. Note that in the above-described Equations 2, 3, and 5, coef = 0.22, m = 3, and β = 0.6. As can be seen from FIG. 8, although the estimated values ​​and the actual measured values ​​diverge as the test period increases, the transition of the estimated values ​​and the actual measured values ​​is almost the same up to about 2000 hours of test. The characteristic of the battery capacity transition leveling off after the test period exceeds 2000 hours is similar for both the estimated values ​​and the actual measured values. Therefore, it can be said that the battery capacity estimation results obtained by the battery capacity estimation device of this embodiment are relatively accurate.

[0051] FIG. 9 is a graph showing the estimated battery capacity when charging and discharging are performed under condition 3, and the transition of the actual measured value of the battery capacity when charging and discharging are performed under condition 3. FIG. 9 also shows the transition of the estimated value of capacity loss (degradation state quantity) in the positive electrode active material due to cracks. Note that in the above-described Equations 2, 3, and 5, coef = 0.22, m = 3, and β = 0.6. As can be seen from FIG. 9, both the estimated and actual measured values ​​of the battery capacity decrease over time. Therefore, it can be said that the estimation result of the battery capacity by the battery capacity estimation device of this embodiment is relatively accurate.

[0052] As described above, the battery capacity estimation device of this embodiment can be said to be able to relatively accurately estimate the post-degradation battery capacity taking into account the effects of cracks, regardless of the type of charging and discharging performed.

[0053] Second Embodiment A battery capacity estimation device according to a second embodiment differs from the first embodiment in the method of determining the positive electrode SOC. The battery capacity estimation device according to the second embodiment will be described below, but a description of the same configuration as the first embodiment will be omitted.

[0054] The positive electrode SOC determination unit 2a determines the SOC of the positive electrode active material at a predetermined timing based on the relationship between the battery SOC and the positive electrode SOC and the SOC of the secondary battery at the predetermined timing. In this embodiment, the relationship between the battery SOC and the positive electrode SOC is defined as shown in the following equation 7. In other words, the positive electrode SOC determination unit 2a determines the SOC of the positive electrode active material at the predetermined timing based on the SOC of the secondary battery at the predetermined timing, the battery capacity of the secondary battery at a past timing before the predetermined timing, and the amount of deviation between the capacity range of the positive electrode active material and the capacity range of the negative electrode active material.

[0055]

[0056] The positive electrode stress derivation unit 3a derives stress (e.g., particle surface stress) acting on particles of the positive electrode active material at a predetermined timing based on the product of the volume change rate of the positive electrode active material corresponding to the SOC of the positive electrode active material at the predetermined timing determined by the positive electrode SOC determination unit 2a, the charge / discharge current at the predetermined timing, and the ratio of the initial battery capacity of the secondary battery to the battery capacity of the secondary battery at a previous timing, which is determined with reference to the positive electrode volume characteristic indicating the relationship between the SOC of the positive electrode active material and the volume of the positive electrode active material. In this embodiment, the stress is derived based on the following equation 8.

[0057]

[0058] The purpose of the above formula 8 is to accurately determine the stress applied to the positive electrode active material particles by taking into account the ratio of the initial battery capacity of the secondary battery to the battery capacity of the secondary battery at a past timing, that is, by taking into account the apparent increase in current load due to a decrease in the battery capacity of the secondary battery.

[0059] As in the first embodiment, the degradation state quantity deriving unit 4 derives the degradation state quantity of the positive electrode active material due to cracks occurring in the positive electrode active material, based on the temporal change in the stress applied to the particles of the positive electrode active material (e.g., the fluctuation range of the stress on the particle surface and the number of cycles of the stress fluctuation) derived at multiple times by the positive electrode stress deriving unit 3 a. For example, the degradation state quantity deriving unit 4 derives the crack density in the positive electrode active material particles based on Equation 3 and Equation 4 described in the first embodiment, and derives the capacity loss (degradation state quantity) in the positive electrode active material based on Equation 5 described in the first embodiment.

[0060] Then, as in the first embodiment, the battery capacity estimation unit 5 estimates the battery capacity after deterioration of the secondary battery based on the deterioration state quantity derived by the deterioration state quantity derivation unit 4 and equation 6 described in the first embodiment.

[0061] In this embodiment, the transition (actual measured value) of battery capacity was measured when charging and discharging were performed for a predetermined test period under three types of charging and discharging conditions (conditions 1 to 3).The transition (estimated value) of battery capacity estimated by the battery capacity estimation device of this embodiment was compared with the transition (estimated value) of battery capacity estimated by the battery capacity estimation device to verify the validity of the transition (estimated value).Conditions 1 to 3 are the same as those in the first embodiment, and the transition (actual measured value) of battery capacity is also the same as that in the first embodiment.

[0062] FIG. 10 is a graph showing the estimated battery capacity when charging and discharging were performed under Condition 1, and the transition of the actual measured value of the battery capacity when charging and discharging were performed under Condition 1. FIG. 10 also shows the transition of the estimated value of capacity loss (degradation state quantity) in the positive electrode active material due to cracks. Note that in the above-described Equations 3, 5, 7, and 8, coef = 0.185, m = 3, β = 0.6, and Δq = 0.14. As can be seen from FIG. 10, although the estimated value and the actual measured value diverge as the test period increases, the estimated value and the actual measured value show almost the same transition until the test period reaches about 5,000 hours. Therefore, it can be said that the battery capacity estimation result obtained by the battery capacity estimation device of this embodiment is relatively accurate.

[0063] FIG. 11 is a graph showing the estimated battery capacity when charging and discharging were performed under Condition 2, and the transition of the actual measured battery capacity when charging and discharging were performed under Condition 2. FIG. 11 also shows the transition of the estimated capacity loss (degradation state quantity) in the positive electrode active material due to cracks. Note that in the above-described Equations 3, 5, 7, and 8, coef = 0.185, m = 3, β = 0.6, and Δq = 0.14. As can be seen from FIG. 11, although the estimated values ​​and the actual measured values ​​diverge as the test period increases, the transition of the estimated values ​​and the actual measured values ​​is almost the same up to about 2000 hours of test. The characteristic of the battery capacity transition leveling off after the test period exceeds 2000 hours is similar for both the estimated values ​​and the actual measured values. Therefore, it can be said that the battery capacity estimation results obtained by the battery capacity estimation device of this embodiment are relatively accurate.

[0064] FIG. 12 is a graph showing the estimated battery capacity when charging and discharging were performed under condition 3, and the transition of the actual measured value of the battery capacity when charging and discharging were performed under condition 3. FIG. 12 also shows the transition of the estimated value of capacity loss (degradation state quantity) in the positive electrode active material due to cracking. Note that in the above-described Equations 3, 5, 7, and 8, coef = 0.185, m = 3, β = 0.6, and Δq = 0.14. As can be seen from FIG. 12, both the estimated and actual measured values ​​of the battery capacity decrease over time. Therefore, it can be said that the estimation result of the battery capacity by the battery capacity estimation device of this embodiment is relatively accurate. However, the degradation of the battery capacity is underestimated, and the estimated result of the battery capacity does not completely match the actual measured value. This is thought to be because while degradation due to cracking of the positive electrode active material particles is small, degradation due to cracking of the SEI coating of the negative electrode active material, which is not taken into account by the battery capacity estimation device of this embodiment, is progressing.

[0065] As described above, the battery capacity estimation device of this embodiment can be said to be able to relatively accurately estimate the post-degradation battery capacity taking into account the effects of cracks, regardless of the type of charging and discharging performed.

[0066] Third Embodiment A battery capacity estimation device according to a third embodiment differs from the above-described embodiments in the method for deriving the degradation state quantity by the degradation state quantity derivation unit 4. The battery capacity estimation device according to the third embodiment will be described below, but a description of the same configuration as in the above-described embodiments will be omitted.

[0067] 13 is a diagram showing the configuration of a battery capacity estimation device according to a third embodiment. As shown in the figure, the battery capacity estimation device includes an operating state acquisition unit 1, an SOC determination unit 2, a stress derivation unit 3, a degradation state quantity derivation unit 4, and a battery capacity estimation unit 5. Specifically, the battery capacity estimation device according to the third embodiment derives a degradation state quantity of an SEI film formed on the surface of a negative electrode active material due to cracks that occur as a result of volumetric changes in the negative electrode active material accompanying charge and discharge of the secondary battery, and estimates the battery capacity of the secondary battery after degradation based on the degradation state. Therefore, the SOC determination unit 2 includes a negative electrode SOC determination unit 2b, and the stress derivation unit 3 includes a negative electrode stress derivation unit 3b.

[0068] As will be described later, the degradation state quantity derivation unit 4 provided in the battery capacity estimation device of the third embodiment derives the degradation state quantity of the SEI coating formed on the surface of the negative electrode active material due to cracks that occur when volume changes occur in the negative electrode active material as the secondary battery is charged and discharged.

[0069] First, the negative electrode SOC determination unit 2b included in the SOC determination unit 2 determines the SOC of the negative electrode active material (hereinafter, may be referred to as the "negative electrode SOC"). Specifically, the negative electrode SOC determination unit 2b determines the SOC of the negative electrode active material at a predetermined timing, such as every minute.

[0070] For example, the negative electrode SOC determination unit 2b determines the SOC of the negative electrode active material at a predetermined timing from the relationship between the battery SOC and the negative electrode SOC and the SOC of the secondary battery at the predetermined timing. In this embodiment, the relationship between the battery SOC and the negative electrode SOC is defined as "battery SOC = negative electrode SOC" as shown in the following equation 9.

[0071]

[0072] The negative electrode stress derivation unit 3b of the stress derivation unit 3 derives the stress applied in the planar direction of the SEI coating at a predetermined timing based on the volume of the negative electrode active material corresponding to the SOC of the negative electrode active material at the predetermined timing determined by the negative electrode SOC determination unit 2b, which is determined with reference to the negative electrode volume characteristic indicating the relationship between the SOC of the negative electrode active material and the volume of the negative electrode active material. In this embodiment, the stress is derived based on the following equation 10. Furthermore, the negative electrode volume characteristic defines the relationship between the negative electrode SOC, open circuit potential, active material volume (relative ratio), and volume change rate, as stored in the memory unit 6. Note that in FIG. 13, the SOC is shown in 10% increments for simplicity.

[0073]

[0074] The deterioration state quantity derivation unit 4 derives the deterioration state quantity of the SEI coating due to cracks occurring in the SEI coating, which is derived based on the temporal change in the stress applied in the surface direction of the SEI coating (the stress fluctuation range and the number of cycles of stress fluctuation) derived at multiple times by the negative electrode stress derivation unit 3b.

[0075] First, the degradation state quantity deriving unit 4 derives the increment of crack density in the SEI coating of the negative electrode based on the fluctuation range of stress occurring over time and the number of cycles of stress fluctuation counted by the Rainflow method. In this embodiment, the increment of crack density is derived based on the following equation 11.

[0076]

[0077] Next, the degradation state quantity deriving unit 4 derives the degradation state quantity of the SEI coating due to cracks occurring in the SEI coating, based on the temporal changes in the stress applied in the plane direction of the SEI coating (the stress fluctuation range and the number of stress fluctuation cycles) derived at multiple times by the negative electrode stress deriving unit 3 b. In this embodiment, the degradation state quantity of the SEI coating of the negative electrode active material is derived based on the following equation 12.

[0078]

[0079] On the negative electrode side, a volume change occurs in the negative electrode active material as the secondary battery is charged and discharged, causing cracks to form in the SEI coating formed on the surface of the negative electrode active material, and a decomposition reaction of the electrolyte occurs on the surface of the negative electrode active material exposed by the cracks, resulting in the formation of a new SEI coating in the cracked area. The above formula 12 was determined based on the idea that the battery capacity of the secondary battery decreases as a new SEI coating is formed (i.e., lithium loss occurs) as the cracks grow.

[0080] The battery capacity estimation unit 5 estimates the battery capacity after deterioration of the secondary battery based on the degradation state quantity derived by the degradation state quantity derivation unit 4. In this embodiment, the battery capacity is estimated based on the following equation 13.

[0081]

[0082] In this embodiment, the transition (actual measured value) of battery capacity was measured when charging and discharging were performed for a predetermined test period under three types of charging and discharging conditions (conditions 1 to 3).The transition (estimated value) of battery capacity estimated by the battery capacity estimation device of this embodiment was compared with the transition (estimated value) of battery capacity estimated by the battery capacity estimation device to verify the validity of the transition (estimated value).Conditions 1 to 3 are the same as those in the first embodiment, and the transition (actual measured value) of battery capacity is also the same as that in the first embodiment.

[0083] FIG. 14 is a graph showing the estimated battery capacity when charging and discharging were performed under Condition 1, and the transition of the actual measured value of the battery capacity when charging and discharging were performed under Condition 1. FIG. 14 also shows the transition of the estimated value of capacity loss (degradation state quantity) in the negative electrode active material due to cracking of the SEI coating. Note that in the above-described Equations 10 and 11, coef = 0.17 and m = 2. As can be seen from FIG. 14 , although the estimated value and the actual measured value diverge as the test period increases, both the estimated value and the actual measured value tend to decrease over time. Therefore, it can be said that the estimation result of the battery capacity by the battery capacity estimation device of this embodiment is relatively accurate.

[0084] FIG. 15 is a graph showing the estimated battery capacity when charging and discharging are performed under condition 2, and the transition of the actual measured value of the battery capacity when charging and discharging are performed under condition 2. FIG. 15 also shows the transition of the estimated value of the capacity loss (degraded state quantity) in the negative electrode active material due to cracking of the SEI coating. Note that in the above-described Equations 10 and 11, coef = 0.17 and m = 2. As can be seen from FIG. 15, although the estimated value and the actual measured value deviate from each other, the estimated value and the actual measured value show a similar decreasing trend over time. Therefore, it can be said that the estimation result of the battery capacity by the battery capacity estimation device of this embodiment is relatively accurate.

[0085] FIG. 16 is a graph showing the estimated battery capacity when charging and discharging are performed under condition 3, and the transition of the actual measured value of the battery capacity when charging and discharging are performed under condition 3. FIG. 16 also shows the transition of the estimated value of capacity loss (degradation state quantity) in the negative electrode active material due to cracking of the SEI coating. Note that in the above-described Equations 10 and 11, coef = 0.17 and m = 2. As can be seen from FIG. 16, the estimated result of the battery capacity and the actual measured value are almost the same. Therefore, it can be said that the estimation result of the battery capacity by the battery capacity estimation device of this embodiment is relatively accurate.

[0086] As described above, the battery capacity estimation device of this embodiment can be said to be able to relatively accurately estimate the post-degradation battery capacity taking into account the effects of cracks, regardless of the type of charging and discharging performed.

[0087] Fourth Embodiment A battery capacity estimation device according to a fourth embodiment differs from the above-described embodiments in the method for deriving the degradation state quantity by the degradation state quantity derivation unit 4. The battery capacity estimation device according to the fourth embodiment will be described below, but a description of the same configuration as in the above-described embodiments will be omitted.

[0088] 17 is a diagram showing the configuration of a battery capacity estimation device according to a fourth embodiment. As shown in the figure, the battery capacity estimation device includes an operating state acquisition unit 1, an SOC determination unit 2, a stress derivation unit 3, a degradation state quantity derivation unit 4, and a battery capacity estimation unit 5. Specifically, the battery capacity estimation device according to the fourth embodiment derives both the degradation state quantity of the positive electrode active material due to cracks that occur in the positive electrode active material as a result of volumetric changes in the positive electrode active material during charging and discharging of the secondary battery, and the degradation state quantity of the SEI coating formed on the surface of the negative electrode active material due to cracks that occur in the negative electrode active material as a result of volumetric changes in the negative electrode active material during charging and discharging of the secondary battery. Based on these degradation states, the battery capacity after degradation of the secondary battery is estimated. Therefore, the SOC determination unit 2 includes a positive electrode SOC determination unit 2a and a negative electrode SOC determination unit 2b, and the stress derivation unit 3 includes a positive electrode stress derivation unit 3a and a negative electrode stress derivation unit 3b.

[0089] [Quantity of Deterioration State of Positive Electrode] In this embodiment, the positive electrode SOC determination unit 2a determines the positive electrode SOC at time t based on the following equation 14. ｔis derived based on Equation 20 described below.

[0090]

[0091] The positive electrode stress derivation unit 3a derives the stress (e.g., particle surface stress) applied to the particles of the positive electrode active material at a predetermined time based on the product of the volume change rate of the positive electrode active material corresponding to the SOC of the positive electrode active material at a predetermined time determined by the positive electrode SOC determination unit 2a, the charge / discharge current at the predetermined time, and the ratio of the initial battery capacity of the secondary battery to the battery capacity of the secondary battery at a previous time, which is determined with reference to the positive electrode volume characteristic indicating the relationship between the SOC of the positive electrode active material and the volume of the positive electrode active material. In this embodiment, the stress is derived based on the following equation 15. The positive electrode volume characteristic defines the relationship between the positive electrode SOC, open circuit potential, active material volume (relative ratio), and volume change rate, as stored in the memory unit 6. Note that in FIG. 17, the SOC is shown in 10% increments for simplicity.

[0092]

[0093] As in the first embodiment, the degradation state quantity deriving unit 4 derives the degradation state quantity of the positive electrode active material due to cracks occurring in the positive electrode active material, based on the state of temporal changes in the stress applied to the particles of the positive electrode active material (e.g., the fluctuation range of the stress on the particle surface and the number of cycles of stress fluctuation) derived at multiple times by the positive electrode stress deriving unit 3 a. For example, the degradation state quantity deriving unit 4 derives the crack density in the positive electrode active material particles based on Equation 3 and Equation 4 described in the first embodiment, and derives the capacity loss (degradation state quantity) in the positive electrode active material based on Equation 5 described in the first embodiment.

[0094]

[0095] [Quantity of Deterioration State of Negative Electrode] The negative electrode SOC determination unit 2b determines the SOC of the negative electrode active material at a predetermined timing based on the relationship between the battery SOC and the negative electrode SOC and the SOC of the secondary battery at the predetermined timing. In this embodiment, the relationship between the battery SOC and the negative electrode SOC is defined as shown in the following equation 16. In other words, the negative electrode SOC determination unit 2b determines the SOC of the negative electrode active material at a predetermined timing based on the SOC of the secondary battery at the predetermined timing, the battery capacity of the secondary battery at a past timing before the predetermined timing, and the capacity of the negative electrode active material.

[0096]

[0097] In the above formula 16, the change in the negative electrode utilization range due to deterioration can be accurately calculated by calculating the negative electrode SOC using the current battery capacity of the secondary battery and the negative electrode capacity.

[0098] The negative electrode stress derivation unit 3b of the stress derivation unit 3 derives the stress applied in the planar direction of the SEI coating at a predetermined timing based on the volume of the negative electrode active material corresponding to the SOC of the negative electrode active material at the predetermined timing determined by the negative electrode SOC determination unit 2b, which is determined with reference to the negative electrode volume characteristic indicating the relationship between the SOC of the negative electrode active material and the volume of the negative electrode active material. In this embodiment, the stress is derived based on the following equation 17. Furthermore, the negative electrode volume characteristic defines the relationship between the negative electrode SOC, open circuit potential, active material volume (relative ratio), and volume change rate, as stored in the memory unit 6. Note that in FIG. 17, the SOC is shown in 10% increments for simplicity.

[0099]

[0100] The deterioration state quantity derivation unit 4 derives the deterioration state quantity of the SEI coating due to cracks occurring in the SEI coating, which is derived based on the temporal change in the stress applied in the surface direction of the SEI coating (the stress fluctuation range and the number of cycles of stress fluctuation) derived at multiple times by the negative electrode stress derivation unit 3b.

[0101] First, the degradation state quantity deriving unit 4 derives the increment of crack density in the SEI coating of the negative electrode based on the fluctuation range of stress occurring over time and the number of cycles of stress fluctuation counted by the Rainflow method. In this embodiment, the increment of crack density is derived based on the following equation 18.

[0102]

[0103] Next, the degradation state quantity deriving unit 4 derives the degradation state quantity of the SEI coating due to cracks occurring in the SEI coating, based on the temporal changes in the stress applied in the plane direction of the SEI coating (the stress fluctuation range and the number of stress fluctuation cycles) derived at multiple times by the negative electrode stress deriving unit 3 b. In this embodiment, the degradation state quantity of the SEI coating of the negative electrode active material is derived based on the following equation 19.

[0104]

[0105] The battery capacity estimation unit 5 estimates the battery capacity after deterioration of the secondary battery based on the deterioration state quantities of the positive electrode side and the negative electrode side derived by the deterioration state quantity derivation unit 4. In this embodiment, the battery capacity is estimated based on the following equation 20.

[0106]

[0107] In the above formula 21, the deviation amount Δq of the capacity range of the positive and negative electrodes at a predetermined timing ｔ That is, the amount of charge / discharge that cannot be performed due to a shift in the capacity range of the positive and negative electrodes caused by side reactions such as the growth of an SEI film is calculated by adding the amount of SEI cracking to the initial shift.

[0108] FIG. 18 is a graph showing the estimated battery capacity when charging and discharging are performed under Condition 1, and the transition of the actual measured value of the battery capacity when charging and discharging are performed under Condition 1. FIG. 18 also shows the transition of the estimated value of the capacity loss (degradation state amount) in the positive electrode active material due to cracks. In the above-mentioned Equations 3, 5, and 15, coef = 0.184, m = 3, and β = 0.6. In the above-mentioned Equations 17, 18, and 21, coef = 0.126, m = 2, and Δq ０= 0.14. As can be seen from Figure 18, the estimated values ​​and the actual measured values ​​diverge as the test period increases, but the estimated values ​​and the actual measured values ​​show almost the same trends up to a test period of about 2000 hours. Therefore, it can be said that the estimation results of the battery capacity by the battery capacity estimation device of this embodiment are relatively accurate.

[0109] FIG. 19 is a graph showing the estimated battery capacity when charging and discharging are performed under condition 2, and the transition of the actual measured value of the battery capacity when charging and discharging are performed under condition 2. FIG. 19 also shows the transition of the estimated value of the capacity loss (degradation state amount) in the positive electrode active material due to cracks. In the above-mentioned formulas 3, 5, and 15, coef = 0.184, m = 3, and β = 0.6. In the above-mentioned formulas 17, 18, and 21, coef = 0.126, m = 2, Δq ０ = 0.14. As can be seen from Figure 19, although the estimated value and the actual measured value diverge as the test period increases, the estimated value and the actual measured value show almost the same trends up to about 2000 hours of test period. The characteristic that the battery capacity trends tend to level off after the test period exceeds 2000 hours is similar for both the estimated value and the actual measured value. Therefore, it can be said that the estimation result of the battery capacity by the battery capacity estimation device of this embodiment is relatively accurate.

[0110] 20 is a graph showing the estimated battery capacity when charging and discharging are performed under condition 3, and the transition of the actual measured value of the battery capacity when charging and discharging are performed under condition 3. FIG. 20 also shows the transition of the estimated value of the capacity loss (degradation state amount) in the positive electrode active material due to cracks. In the above-mentioned formulas 3, 5, and 15, coef = 0.184, m = 3, and β = 0.6. In the above-mentioned formulas 17, 18, and 21, coef = 0.126, m = 2, Δq ０ = 0.14. As can be seen from Fig. 20, both the estimated and measured battery capacities decrease over time. Therefore, it can be said that the battery capacity estimation results obtained by the battery capacity estimation device of this embodiment are relatively accurate.

[0111] <Other Embodiments> In the above embodiments, specific examples of the configuration of the battery capacity estimation device have been described, but the configuration can be modified as appropriate. Specifically, in each of the above embodiments, the battery capacity estimation device is not limited to being configured with the functional blocks shown in Figures 1, 13, and 17, and may be configured with any functional blocks. For example, each functional block of the battery capacity estimation device may be further subdivided, or conversely, some or all of the functional blocks may be combined.

[0112] In the above embodiment, the secondary battery to be subjected to battery capacity estimation is not particularly limited, and various types of secondary batteries can be subjected to battery capacity estimation.

[0113] In the above embodiment, a specific example of a method for determining the positive electrode SOC and the negative electrode SOC has been given, but the positive electrode SOC and the negative electrode SOC may be determined using other methods. For example, the determination method of Equation 16 described in the above fourth embodiment may be adopted in the above third embodiment.

[0114] The configurations disclosed in the above embodiments (including other embodiments, the same applies below) can be applied in combination with configurations disclosed in other embodiments, as long as no contradictions arise. Furthermore, the embodiments disclosed in this specification are examples, and the embodiments of the present invention are not limited to these, and can be modified as appropriate within the scope of not departing from the purpose of the present invention.

[0115] The present invention can be used in a battery capacity estimation device and a battery capacity estimation program that can estimate battery capacity taking into account the influence of cracks.

[0116] 1: Operation state acquisition unit 2: SOC determination unit 2a: Positive electrode SOC determination unit 2b: Negative electrode SOC determination unit 3: Stress derivation unit 3a: Positive electrode stress derivation unit 3b: Negative electrode stress derivation unit 4: Degradation state quantity derivation unit 5: Battery capacity estimation unit

Claims

1. A battery capacity estimation device that estimates the battery capacity of a secondary battery having a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and an electrolyte, comprising: a degradation state quantity derivation unit that derives at least one of a degradation state quantity of the positive electrode active material due to cracks that occur in the positive electrode active material as a volume change of the positive electrode active material occurs with charging and discharging of the secondary battery, and a degradation state quantity of the SEI coating due to cracks that occur in the SEI coating formed on the surface of the negative electrode active material as a volume change of the negative electrode active material occurs with charging and discharging of the secondary battery; and a battery capacity estimation unit that estimates the battery capacity of the secondary battery after degradation based on the degradation state quantity derived by the degradation state quantity derivation unit.

2. A battery capacity estimation device as described in claim 1, comprising: a positive electrode SOC determination unit that determines an SOC of the positive electrode active material; and a positive electrode stress derivation unit that derives a stress applied to particles of the positive electrode active material at a predetermined timing based on the product of a volume change rate of the positive electrode active material corresponding to the SOC of the positive electrode active material at the predetermined timing determined by the positive electrode SOC determination unit and a charge / discharge current at the predetermined timing, the rate being determined with reference to a positive electrode volume characteristic that indicates the relationship between the SOC of the positive electrode active material and the volume of the positive electrode active material, wherein the deterioration state quantity derivation unit derives the deterioration state quantity of the positive electrode active material due to cracks occurring in the positive electrode active material, which is derived based on a temporal change state of the stress applied to the particles of the positive electrode active material derived at a plurality of timings by the positive electrode stress derivation unit.

3. The battery capacity estimation device of claim 2, wherein the positive electrode SOC determination unit determines the SOC of the positive electrode active material at the specified timing based on the SOC of the secondary battery at the specified timing, the battery capacity of the secondary battery at a past timing prior to the specified timing, and the amount of deviation between the capacity range of the positive electrode active material and the capacity range of the negative electrode active material, and the positive electrode stress derivation unit derives the stress applied to particles of the positive electrode active material at the specified timing based on the product of the volume change rate of the positive electrode active material, the charge / discharge current at the specified timing, and a ratio of the initial battery capacity of the secondary battery to the battery capacity of the secondary battery at the past timing.

4. A battery capacity estimation device according to any one of claims 1 to 3, comprising: a negative electrode SOC determination unit that determines an SOC of the negative electrode active material; and a negative electrode stress derivation unit that derives a stress applied in a surface direction of the SEI coating at a predetermined timing based on a volume of the negative electrode active material corresponding to the SOC of the negative electrode active material at the predetermined timing determined by the negative electrode SOC determination unit, the volume being determined with reference to a negative electrode volume characteristic that indicates a relationship between the SOC of the negative electrode active material and the volume of the negative electrode active material, wherein the degradation state quantity derivation unit derives the degradation state quantity of the SEI coating due to cracks occurring in the SEI coating, which is derived based on a temporal change state of the stress applied in the surface direction of the SEI coating derived at a plurality of timings by the negative electrode stress derivation unit.

5. A battery capacity estimation device as described in claim 4, wherein the negative electrode SOC determination unit determines the SOC of the negative electrode active material based on the SOC of the secondary battery at the specified timing, the battery capacity of the secondary battery at a past timing prior to the specified timing, and the capacity of the negative electrode active material.

6. A battery capacity estimation program for causing a computer to function as each unit of the battery capacity estimation device according to any one of claims 1 to 3.

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