Battery capacity estimation device and battery capacity estimation program

Abstract

To provide a battery capacity estimation device capable of estimating battery capacity taking into account the effects of cracks.SOLUTION: A battery capacity estimation device 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, and includes a degradation state quantity derivation unit 4 that derives at least one of a degradation state quantity of the positive electrode active material caused by 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 caused by cracks that occur in the SEI coating formed on the surface of the negative electrode active material 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 5 that estimates the battery capacity after deterioration of the secondary battery on the basis of the degradation state quantity derived by the degradation state quantity derivation unit 4.SELECTED DRAWING: Figure 17

Description

[Technical field]

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

[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 deterioration 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 sudden volume change occurs in the primary particles of the lithium composite oxide of the positive electrode active material during charging and discharging, or when stress due to repeated charging and discharging accumulates, cracks occur in the secondary particles, or the crystal structure collapses or changes in the crystal structure (phase transition) occur. Patent Document 1 also discloses a secondary battery in which the occurrence of particle cracks is suppressed by mixing positive electrode active materials of multiple particle sizes.

[0004] Furthermore, Patent Document 2 (International Publication No. 2021 / 020290) points out that when silicon oxide is used as the negative electrode active material, the particles are prone to cracking and isolation due to repeated expansion and contraction accompanying charging and discharging, and therefore nonaqueous electrolyte storage elements using silicon oxide have a problem in that they have a low capacity retention rate during charge and discharge cycles. Patent Document 2 also discloses a battery design that suppresses particle cracking of the negative electrode active material by limiting the usable potential range of the negative electrode during charging and discharging. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2023-064746 A [Patent Document 2] International Publication No. 2021 / 020290 Summary of the Invention [Problem to be solved by the invention]

[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 during long-term use of secondary batteries.

[0007] In particular, the decrease in discharge capacity caused by particle cracks due to the 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 range.

[0008] Therefore, in order to operate a secondary battery system such as an electric power storage system or an electric vehicle, it is necessary to accurately predict the decrease in battery capacity caused by the above-mentioned cracks, but it has been difficult to accurately predict such deterioration that is highly SOC-dependent with a conventional simple prediction model based on the number of charge / discharge cycles and the total discharged amount of electricity, etc. In other words, although Patent Documents 1 and 2 describe the effects of cracks, they do not disclose a method for estimating battery capacity based on the effects.

[0009] The present invention has been made in consideration of the above problems, and has an object to provide a battery capacity estimation device and a battery capacity estimation program that can estimate a battery capacity taking into account the effects of cracks. [Means for solving the problem]

[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 a 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, the device comprising: A volume change occurs in the positive electrode active material as the secondary battery is charged and discharged.In front A deterioration state amount of the positive electrode active material due to cracks occurring in the positive electrode active material. based on a stress acting on particles of the positive electrode active material, the stress being derived with reference to a positive electrode volume characteristic indicating a relationship between an SOC of the positive electrode active material and a volume of the positive electrode active material; and a volume change occurs in the negative electrode active material as the secondary battery is charged and discharged. In front The deterioration state of the SEI film formed on the surface of the negative electrode active material due to cracks occurring in the SEI film. based on a stress applied in a planar direction of the SEI coating, the stress being derived with reference to a negative electrode volume characteristic indicating a relationship between an SOC of the negative electrode active material and a volume of the negative electrode active material; At least one of conduct A degradation state quantity derivation unit; The present invention is characterized in that it comprises a battery capacity estimation unit that estimates a battery capacity after deterioration of the secondary battery based on the amount of deterioration state derived by the amount of deterioration state derivation unit.

[0011] On the positive electrode side, a volume change occurs in the positive electrode active material as the secondary battery is charged and discharged, causing cracks to occur in the positive electrode active material. It is believed that the cracks cut the conductive path in the positive electrode active material, and the amount of the positive electrode active material connected to the surroundings by the conductive path decreases, leading to a decrease in the battery capacity of the secondary battery. 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 occur in the SEI film 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 film in the cracked portion. Therefore, it is believed that the battery capacity of the secondary battery decreases as a new SEI film is formed (i.e., lithium loss occurs) due to the progression of the cracks. In this manner, in the present characteristic configuration, at least one of a degradation state amount indicating degradation of the positive electrode active material due to a volume change in the positive electrode active material and a degradation state amount indicating degradation of the SEI coating due to a volume change in the negative electrode active material is derived, and the battery capacity after degradation of the secondary battery can be estimated based on the degradation state amount. Therefore, it is possible to provide a battery capacity estimation device that can estimate battery capacity taking into account the effects of cracks.

[0012] Another characteristic configuration of the battery capacity estimation device according to the present invention is a positive electrode SOC determination unit that determines an SOC of the positive electrode active material, The abovea positive electrode stress derivation unit that derives a stress applied to particles of the positive electrode active material at a predetermined timing based on a product of a volume change rate of the positive electrode active material corresponding to an SOC of the positive electrode active material at the predetermined timing determined by the positive electrode SOC determination unit, the volume change rate being determined with reference to a positive electrode volume characteristic, and a charge / discharge current at the predetermined timing; 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, based on the temporal change state of the stress applied to the particles of the positive electrode active material derived by the positive electrode stress derivation unit at multiple timings.

[0013] According to the above characteristic configuration, the positive electrode stress derivation 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 determination unit. The deterioration state quantity derivation unit can derive 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 acting on the particles of the positive electrode active material derived at multiple timings by the positive electrode stress derivation unit (e.g., the fluctuation width 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 an SOC of the positive electrode active material at the predetermined timing based on an SOC of the secondary battery at the predetermined timing, a battery capacity of the secondary battery at a past timing before the predetermined timing, and a deviation amount between a capacity range of the positive electrode active material and a capacity range of the negative electrode active material; The positive electrode stress derivation unit derives the stress applied to the 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 the ratio of the initial battery capacity of the secondary battery to the battery capacity of the secondary battery at the past timing.

[0015] According to the above 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 considering the amount of deviation between the capacity range of the positive electrode active material and the capacity range of the negative electrode active material, i.e., by considering the change in the utilization range of the capacity range of the positive electrode active material, and the positive electrode stress derivation unit can accurately determine the stress applied to the positive electrode active material particles by considering 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 considering the apparent increase in current load due to the 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 a negative electrode SOC determination unit that determines an SOC of the negative electrode active material, The above a negative electrode stress derivation unit that derives a stress applied in a planar direction of the SEI coating at a predetermined timing based on a volume of the negative electrode active material corresponding to an SOC of the negative electrode active material at the predetermined timing determined by the negative electrode SOC determination unit, the SOC being determined with reference to a negative electrode volume characteristic, The deterioration state quantity derivation unit derives the deterioration state quantity of the SEI coating due to cracks occurring in the SEI coating, based on the temporal change state of the stress applied in the planar direction of the SEI coating derived at multiple timings by the negative electrode stress derivation unit.

[0017] According to the above characteristic configuration, the negative electrode stress derivation unit can derive the stress applied in the 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 determination unit. The degradation state quantity derivation unit can derive the degradation state quantity of the SEI coating due to cracks occurring in the SEI coating based on the temporal change state of the stress applied in the plane direction of the SEI coating derived at multiple timings by the negative electrode stress derivation unit (e.g., the stress fluctuation width, the number of cycles of stress fluctuation, etc.).

[0018] Another characteristic configuration of the battery capacity estimation device of 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 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.

[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 timing prior to 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 of the battery capacity estimation device, it is possible to obtain the same effects as those obtained by the battery capacity estimation device according to the present invention. [Brief description of the drawings]

[0022] [Figure 1] 1 is a diagram illustrating a configuration of a battery capacity estimation device according to a first embodiment. [Diagram 2] 1 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. [Diagram 3] 1 is a graph showing changes in current and SOC when charging and discharging are performed under condition 1. [Figure 4] 13 is a graph showing changes in current and SOC when charging and discharging are performed under condition 2. [Diagram 5] 13 is a graph showing changes in current and SOC when charging and discharging are performed under condition 3. [Figure 6] 1 shows the transition of the capacity (actual measured value) of a secondary battery when charging and discharging are performed under conditions 1 to 3. [Figure 7]4 is a graph showing the transition of the capacity (actual value), the capacity (estimated value), and the amount of degradation when charging and discharging are performed under condition 1 in the first embodiment. [Figure 8] 11 is a graph showing the transition of the capacity (actual value), the capacity (estimated value), and the amount of degradation when charging and discharging are performed under condition 2 in the first embodiment. [Figure 9] 11 is a graph showing the transition of the capacity (actual value), the capacity (estimated value), and the amount of degradation when charging and discharging are performed under condition 3 in the first embodiment. [Figure 10] 11 is a graph showing the transition of the capacity (actual value), the capacity (estimated value), and the amount of degradation when charging and discharging are performed under condition 1 in the second embodiment. [Figure 11] 13 is a graph showing the transition of the capacity (actual value), the capacity (estimated value), and the amount of degradation when charging and discharging are performed under condition 2 in the second embodiment. [Figure 12] 13 is a graph showing the transition of the capacity (actual value), the capacity (estimated value), and the amount of degradation when charging and discharging are performed under condition 3 in the second embodiment. [Figure 13] FIG. 11 is a diagram illustrating a configuration of a battery capacity estimation device according to a third embodiment. [Figure 14] 13 is a graph showing the transition of the capacity (actual value), the capacity (estimated value), and the amount of degradation when charging and discharging are performed under condition 1 in the third embodiment. [Figure 15] 13 is a graph showing the transition of the capacity (actual value), the capacity (estimated value), and the amount of degradation when charging and discharging are performed under condition 2 in the third embodiment. [Figure 16] 13 is a graph showing the transition of the capacity (actual value), the capacity (estimated value), and the amount of degradation when charging and discharging are performed under condition 3 in the third embodiment. [Figure 17] FIG. 13 is a diagram illustrating a configuration of a battery capacity estimation device according to a fourth embodiment. [Figure 18] 13 is a graph showing the transition of the capacity (actual value), the capacity (estimated value), and the amount of degradation when charging and discharging are performed under condition 1 in the fourth embodiment. [Figure 19]13 is a graph showing the transition of the capacity (actual value), the capacity (estimated value), and the amount of degradation when charging and discharging are performed under condition 2 in the fourth embodiment. [Figure 20] 13 is a graph showing the transition of the capacity (actual value), the capacity (estimated value), and the amount of degradation when charging and discharging are performed under condition 3 in the fourth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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 in the case where a lithium nickel oxide (NCA)-based positive electrode active material is used as the positive electrode active material, and a graphite-based negative electrode active material is used as the negative electrode active material, but the materials of 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 including a positive electrode active material, a negative electrode including a negative electrode active material, and an electrolyte, the positive electrode active material and the negative electrode active material expand and contract repeatedly when the battery is repeatedly charged and discharged. It is presumed that the deterioration of the secondary battery, in which the battery capacity decreases, occurs due to cracks generated by the expansion and contraction.

[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 volume change occurs in the positive electrode active material due to 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 due to volume change occurs in the negative electrode active material as the secondary battery is charged and discharged, and a battery capacity estimation unit 5 that 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.

[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 volumetric 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 of the first embodiment. As shown in the figure, the battery capacity estimation device includes an operation state acquisition unit 1, an SOC determination unit 2, a stress derivation unit 3, a degradation state amount derivation unit 4, and a battery capacity estimation unit 5. In addition, the battery capacity estimation device of this embodiment includes a storage unit 6 that stores information to be handled. Specifically, the battery capacity estimation device of the first embodiment derives the degradation state of the positive electrode active material due to cracks that occur in the positive electrode active material caused by a volume change in the positive electrode active material accompanying charging and discharging of the secondary battery, and estimates the battery capacity after degradation of the secondary battery based on the degradation state. Therefore, the SOC determination unit 2 has a positive electrode SOC determination unit 2a, and the stress derivation unit 3 has a positive electrode stress derivation unit 3a.

[0028] The battery capacity estimation device is realized by using one or more computer devices having an information input / output function, an information communication function, an information processing function, an information storage function, etc. In this embodiment, the battery capacity estimation device is realized by installing and executing a battery capacity estimation program that causes the one or more computer devices described above to function as each part of the battery capacity estimation device.

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

[0030] FIG. 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 deviation amount of Δq between the capacity range of the positive electrode active material and the capacity range of the negative electrode active material, but Δq shown in FIG. 2 is described for illustrative purposes, and its magnitude is not limited to that shown. Also, FIG. 2 shows a relationship where the negative electrode capacity is greater than the battery capacity, but the magnitude of the negative electrode capacity is not limited to that shown.

[0031] The operating state acquisition unit 1 acquires information on the SOC of the secondary battery (hereinafter, may be referred to as "battery SOC") and information on the charge / discharge current of the secondary battery. Specifically, the operating state acquisition unit 1 acquires information on the SOC of the secondary battery and information on 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 transition between the lower limit (SOC=0%) and upper limit (SOC=100%) of the battery capacity shown in FIG. 2 and the measured OCV. 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 2a 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 formula 1.

[0034]

number

[0035] The positive electrode stress derivation unit 3a of the stress derivation unit 3 derives the stress (e.g., particle surface stress, etc.) 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, and the charge / discharge current at the predetermined timing. In this embodiment, the stress is derived based on the following formula 2. In addition, the positive electrode volume characteristic specifies the relationship between the positive electrode SOC, the open circuit potential, the active material volume (relative ratio), and the volume change rate, as stored in the memory unit 6. In FIG. 2, the SOC is described in 10% increments to simplify the drawing.

[0036]

number

[0037] When a secondary battery is repeatedly charged and discharged, the volume of the positive electrode active material repeatedly increases and decreases with the increase and decrease in the SOC of the positive electrode active material, which is thought to cause the stress on the particle surface of the positive electrode active material to increase and decrease, resulting in the generation of 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 derived by the positive electrode stress derivation unit 3a at multiple timings (e.g., the fluctuation range of the stress on the particle surface and the number of cycles of the stress fluctuation).

[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 the 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 iIn this embodiment, the crack density is calculated based on the following Equations 3 and 4.

[0040]

number

[0041] On the positive electrode side, a change in the volume of the positive electrode active material occurs with charging and discharging the secondary battery, causing cracks in the positive electrode active material, which then cuts off the conductive path in the positive electrode active material, reducing the amount of positive electrode active material connected to the surroundings by the conductive path, which is thought to lead to a decrease in the battery capacity of the secondary battery. Therefore, the degradation state amount derivation unit 4 derives the capacity loss (degradation state amount) 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 amount) in the positive electrode active material is derived based on the following formula 5.

[0042]

number

[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 the percolation theory, that 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 deterioration state quantity derived by the deterioration state quantity derivation unit 4. In this embodiment, the battery capacity is estimated based on the following formula 6.

[0045]

number

[0046] In this embodiment, the transition (actual 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 a constant current-constant voltage charging (CCCV) method. The current during charging is 0.7C and the voltage is 4.2V. Under condition 2, charging is performed using a constant current (CC) method and charging ends at 4.2V. The current is 0.7C. Under condition 3, charging is performed using a constant current (CC) method and charging ends at 4.0V. The current is 1.4C. 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] [Table 1]

[0049] FIG. 7 is a graph showing the transition of the estimated battery capacity when charging and discharging under condition 1, and the actual measured value of the battery capacity when charging and discharging under condition 1. FIG. 7 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 addition, in the above-mentioned formulas 2, 3, and 5, coef=0.22, m=3, and β=0.6. As can be seen from FIG. 7, the estimated value and the actual measured value diverge as the test period becomes longer, but the estimated value and the actual measured value show almost the same transition until the test period reaches about 2000 hours. 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 transition of the estimated battery capacity when charging and discharging under condition 2, and the actual measured value of the battery capacity when charging and discharging under condition 2. FIG. 8 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 addition, in the above-mentioned formulas 2, 3, and 5, coef=0.22, m=3, and β=0.6. As can be seen from FIG. 8, although the estimated value and the actual measured value deviate from each other as the test period becomes longer, the estimated value and the actual measured value show almost the same transition until the test period reaches about 2000 hours. The characteristic that the transition of the battery capacity tends 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.

[0051] FIG. 9 is a graph showing the transition of the estimated battery capacity when charging and discharging are performed under condition 3, and 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 the capacity loss (degraded state amount) in the positive electrode active material due to cracks. In addition, in the above-mentioned formulas 2, 3, and 5, coef=0.22, m=3, and β=0.6. As can be seen from FIG. 9, both the estimated value and the actual measured value of the battery capacity decrease with the passage of 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 estimate the post-degradation battery capacity taking into account the effects of cracks relatively accurately regardless of the type of charging and discharging performed.

[0053] <Second embodiment> The battery capacity estimation device of the second embodiment is different from that of the first embodiment in the method of determining the positive electrode SOC. The battery capacity estimation device of the second embodiment will be described below, but the description of the same configuration as the above 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 formula 7. In other words, the positive electrode SOC determination unit 2a determines the SOC of the positive 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 amount of deviation between the capacity range of the positive electrode active material and the capacity range of the negative electrode active material.

[0055]

number

[0056] The positive electrode stress derivation unit 3a derives a stress (e.g., stress on the particle surface, etc.) acting on 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, 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 past timing. In this embodiment, the stress is derived based on the following formula 8.

[0057]

number

[0058] The above formula 8 aims 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 the decrease in the battery capacity of the secondary battery.

[0059] Then, similarly to the first embodiment, the degradation state quantity derivation unit 4 derives the degradation state quantity of the positive electrode active material due to cracks occurring in the positive electrode active material, which is derived based on the temporal change state of the stress applied to the particles of the positive electrode active material derived at multiple timings by the positive electrode stress derivation unit 3a (for example, the fluctuation width of the stress on the particle surface and the number of cycles of the stress fluctuation). For example, the degradation state quantity derivation unit 4 derives the crack density in the positive electrode active material particles based on the formulas 3 and 4 described in the first embodiment, and derives the capacity loss (degradation state quantity) in the positive electrode active material based on the formula 5 described in the first embodiment.

[0060] Then, similarly to the first embodiment described above, 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 described above.

[0061] In this embodiment, the transition (actual 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 actual value, and the validity of the transition (estimated value) of the battery capacity estimated by the battery capacity estimation device was verified. Conditions 1 to 3 are the same as those in the first embodiment, and the transition (actual measured value) of the battery capacity is also the same as that in the first embodiment.

[0062] FIG. 10 is a graph showing the transition of the estimated battery capacity when charging and discharging under condition 1, and the actual measured value of the battery capacity when charging and discharging under condition 1. FIG. 10 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 addition, in the above-mentioned formulas 3, 5, 7, and 8, coef=0.185, m=3, β=0.6, and Δq=0.14. As can be seen from FIG. 10, the estimated value and the actual measured value diverge as the test period becomes longer, but the estimated value and the actual measured value show almost the same transition until the test period reaches about 5000 hours. 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.

[0063] FIG. 11 is a graph showing the transition of the estimated battery capacity when charging and discharging are performed under condition 2, and the actual measured value of the battery capacity when charging and discharging are performed under condition 2. FIG. 11 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 addition, in the above-mentioned formulas 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 value and the actual measured value deviate as the test period becomes longer, the estimated value and the actual measured value show almost the same transition until the test period reaches about 2000 hours. The characteristic that the transition of the battery capacity tends 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.

[0064] FIG. 12 is a graph showing the transition of the estimated battery capacity when charging and discharging are performed under condition 3, and the actual measured value of the battery capacity when charging and discharging are performed under condition 3. FIG. 12 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 addition, in the above-mentioned formulas 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 value and the actual measured value of the battery capacity are reduced with the passage of 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 deterioration of the battery capacity is underestimated, and the estimation result of the battery capacity does not completely match the actual measured value. This is considered to be because the deterioration due to cracks in the positive electrode active material particles is small, while the deterioration due to cracks in the SEI coating of the negative electrode active material, which is not taken into account by the battery capacity estimation device of this embodiment, progresses.

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

[0066] <Third embodiment> The battery capacity estimation device of the third embodiment is different from the above-mentioned embodiments in the method of deriving the degradation state quantity by the degradation state quantity derivation unit 4. The battery capacity estimation device of the third embodiment will be described below, but a description of the same configuration as the above-mentioned embodiment will be omitted.

[0067] FIG. 13 is a diagram showing the configuration of a battery capacity estimation device of the third embodiment. As shown in the figure, the battery capacity estimation device includes an operation state acquisition unit 1, an SOC determination unit 2, a stress derivation unit 3, a degradation state amount derivation unit 4, and a battery capacity estimation unit 5. Specifically, the battery capacity estimation device of the third embodiment derives the degradation state amount of the SEI film formed on the surface of the negative electrode active material due to cracks that occur due to volume changes in the negative electrode active material accompanying charging and discharging of the secondary battery, and estimates the battery capacity after degradation of the secondary battery based on the degradation state. For this reason, the SOC determination unit 2 has a negative electrode SOC determination unit 2b, and the stress derivation unit 3 has a negative electrode stress derivation unit 3b.

[0068] As described later, a 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 as a result of volume changes in the negative electrode active material accompanying charging and discharging of the secondary battery.

[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 "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 formula 9.

[0071]

number

[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 formula 10. In addition, the negative electrode volume characteristic specifies the relationship between the negative electrode SOC, the open circuit potential, the active material volume (relative ratio), and the volume change rate, as stored in the memory unit 6. In addition, in FIG. 13, the SOC is shown in 10% increments to simplify the drawing.

[0073]

number

[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, based on the temporal change state of the stress applied in the surface direction of the SEI coating derived by the negative electrode stress derivation unit 3b at multiple timings (the stress fluctuation range and the number of cycles of stress fluctuation).

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

[0076]

number

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

[0078]

number

[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 film 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 film in the cracked portion. The above formula 12 was determined based on the idea that the battery capacity of the secondary battery decreases as a new SEI film is formed (i.e., lithium loss occurs) due to the progression of the cracks.

[0080] 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. In this embodiment, the battery capacity is estimated based on the following formula 13.

[0081]

number

[0082] In this embodiment, the transition (actual 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 actual value, and the validity of the transition (estimated value) of the battery capacity estimated by the battery capacity estimation device was verified. Conditions 1 to 3 are the same as those in the first embodiment, and the transition (actual measured value) of the 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 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. 14 also shows the transition of the estimated value of the capacity loss (degraded state amount) in the negative electrode active material due to cracks in the SEI coating. In addition, in the above-mentioned formulas 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 deviate from each other as the test period becomes longer, both the estimated value and the actual measured value show a tendency to decrease with the passage of 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 amount) in the negative electrode active material due to cracks in the SEI coating. In addition, in the above-mentioned formulas 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 are different, the estimated value and the actual measured value show a similar decreasing tendency with the passage of 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 the capacity loss (degraded state amount) in the negative electrode active material due to cracks in the SEI coating. In addition, in the above-mentioned formulas 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 estimated 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 estimate the post-degradation battery capacity taking into account the effects of cracks relatively accurately regardless of the type of charging and discharging performed.

[0087] <Fourth embodiment> The battery capacity estimation device of the fourth embodiment is different from the above-mentioned embodiments in the method of deriving the degradation state quantity by the degradation state quantity derivation unit 4. The battery capacity estimation device of the fourth embodiment will be described below, but a description of the same configuration as the above-mentioned embodiments will be omitted.

[0088] FIG. 17 is a diagram showing the configuration of a battery capacity estimation device of the fourth embodiment. As shown in the figure, the battery capacity estimation device includes an operation state acquisition unit 1, an SOC determination unit 2, a stress derivation unit 3, a degradation state amount derivation unit 4, and a battery capacity estimation unit 5. Specifically, the battery capacity estimation device of the fourth embodiment derives both the degradation state amount of the positive electrode active material caused by cracks generated in the positive electrode active material due to volume change of the positive electrode active material accompanying charge and discharge of the secondary battery, and the degradation state amount of the SEI coating caused by cracks generated in the SEI coating formed on the surface of the negative electrode active material due to volume change of the negative electrode active material accompanying charge and discharge of the secondary battery, and estimates the battery capacity after degradation of the secondary battery based on these degradation states. Therefore, the SOC determination unit 2 has a positive electrode SOC determination unit 2a and a negative electrode SOC determination unit 2b, and the stress derivation unit 3 has a positive electrode stress derivation unit 3a and a negative electrode stress derivation unit 3b.

[0089] [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 formula 14. t is derived based on Equation 20 described below.

[0090]

number

[0091] The positive electrode stress derivation unit 3a derives the stress (e.g., particle surface stress, etc.) 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, 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 past 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 formula 15. In addition, the positive electrode volume characteristic specifies the relationship between the positive electrode SOC, the open circuit potential, the active material volume (relative ratio), and the volume change rate, as stored in the memory unit 6. In FIG. 17, the SOC is described in 10% increments to simplify the drawing.

[0092]

number

[0093] Then, similarly to the first embodiment, the degradation state quantity derivation unit 4 derives the degradation state quantity of the positive electrode active material due to cracks occurring in the positive electrode active material, which is derived based on the temporal change state of the stress applied to the particles of the positive electrode active material derived at multiple timings by the positive electrode stress derivation unit 3a (for example, the fluctuation width of the stress on the particle surface and the number of cycles of the stress fluctuation). For example, the degradation state quantity derivation unit 4 derives the crack density in the positive electrode active material particles based on the formulas 3 and 4 described in the first embodiment, and derives the capacity loss (degradation state quantity) in the positive electrode active material based on the formula 5 described in the first embodiment.

[0094]

number

[0095] [Deterioration state quantity 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 formula 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]

number

[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 formula 17. In addition, the negative electrode volume characteristic specifies the relationship between the negative electrode SOC, the open circuit potential, the active material volume (relative ratio), and the volume change rate, as stored in the memory unit 6. In addition, in FIG. 17, the SOC is shown in 10% increments for the sake of simplicity.

[0099]

number

[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, based on the temporal change state of the stress applied in the surface direction of the SEI coating derived by the negative electrode stress derivation unit 3b at multiple timings (the stress fluctuation range and the number of cycles of stress fluctuation).

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

[0102]

number

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

[0104]

number

[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 formula 20.

[0106]

number

[0107] In the above formula 21, the shift amount Δq of the capacity range of the positive and negative electrodes at a given timing t In other words, the amount by which charging and discharging is no longer possible due to a shift in the capacity ranges of the positive and negative electrodes caused by side reactions such as the growth of the SEI film is calculated by adding the amount of SEI cracking to the initial shift.

[0108] FIG. 18 is a graph showing the transition of the estimated battery capacity when charging and discharging are performed under condition 1, and 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 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, and Δq0=0.14. As can be seen from FIG. 18, the estimated value and the actual measured value diverge as the test period becomes longer, but the estimated value and the actual measured value show almost the same transition until the test period is about 2000 hours. 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.

[0109] FIG. 19 is a graph showing the transition of the estimated battery capacity when charging and discharging are performed under condition 2, and 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, and Δq0=0.14. As can be seen from FIG. 19, although the estimated value and the actual measured value deviate as the test period becomes longer, the estimated value and the actual measured value show almost the same transition until the test period reaches about 2000 hours. The characteristic that the transition of the battery capacity tends 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] FIG. 20 is a graph showing the transition of the estimated battery capacity when charging and discharging are performed under condition 3, and 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 addition, in the above-mentioned formulas 3, 5, and 15, coef=0.184, m=3, and β=0.6. In addition, in the above-mentioned formulas 17, 18, and 21, coef=0.126, m=2, and Δq0=0.14. As can be seen from FIG. 20, both the estimated value and the actual measured value of the battery capacity are decreasing with the passage of 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.

[0111] <Another embodiment> In the above embodiment, a specific example of the configuration of the battery capacity estimation device has been given, 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 the subject of battery capacity estimation is not particularly limited, and various types of secondary batteries can be subject to battery capacity estimation.

[0113] In the above embodiment, the method of determining the positive electrode SOC and the negative electrode SOC is specifically exemplified, 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, provided that no contradiction arises. Furthermore, the embodiments disclosed in this specification are illustrative, and the embodiments of the present invention are not limited thereto, and can be appropriately modified within the scope that does not deviate from the purpose of the present invention. [Industrial Applicability]

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

[0116] 1: Operation status acquisition section 2:SOC decision department 2a: Positive electrode SOC determination section 2b: Negative SOC determination section 3: Stress extraction section 3a: Positive electrode stress extraction section 3b: Negative electrode stress derivation part 4: Degradation state quantity derivation part 5:Battery capacity estimator

Claims

1. A battery capacity estimation device that estimates a 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 deterioration state quantity derivation unit that performs at least one of: deriving a deterioration state quantity of the positive electrode active material due to cracks occurring in the positive electrode active material as a result of a volume change in the positive electrode active material occurring during charging and discharging of the secondary battery, based on a stress applied to particles of the positive electrode active material derived with reference to a positive electrode volume characteristic that indicates a relationship between an SOC of the positive electrode active material and a volume of the positive electrode active material; and deriving a deterioration state quantity of the SEI coating due to cracks occurring in the SEI coating formed on a surface of the negative electrode active material as a result of a volume change in the negative electrode active material occurring during charging and discharging of the secondary battery, based on a stress applied in a planar direction of the SEI coating derived with reference to a negative electrode volume characteristic that indicates a relationship between an SOC of the negative electrode active material and a volume of the negative electrode active material; a battery capacity estimation unit that estimates a battery capacity after deterioration of the secondary battery based on the deterioration state amount derived by the deterioration state amount derivation unit.

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

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

4. a negative electrode SOC determination unit that determines an SOC of the negative electrode active material; a negative electrode stress derivation unit that derives a stress applied in a planar direction of the SEI coating at a predetermined timing based on a volume of the negative electrode active material corresponding to an 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 the negative electrode volume characteristic, The battery capacity estimation device according to any one of claims 1 to 3, wherein the deterioration state quantity derivation unit derives a deterioration state quantity of the SEI coating due to cracks occurring in the SEI coating, the deterioration state quantity being derived based on a temporal change state of the stress applied in the planar direction of the SEI coating derived by the negative electrode stress derivation unit at multiple timings.

5. 5. The battery capacity estimation device according to 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 predetermined timing, the battery capacity of the secondary battery at a past timing prior to the predetermined 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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